IIIIIIIIIII I IIIIIIIIIIIII - patentimages.storage.googleapis.com · US 9 , 919 , 927 B2 Page Doma 2 of the present disclosure further comprise a step of enhanc ing a quantum yield

IIIIIIIIIII I IIIIIIIIIIIII US009919927B2

( 12 ) United States Patent Tour et al .

( 10 ) Patent No . : US 9 , 919 , 927 B2 ( 45 ) Date of Patent : Mar . 20 , 2018

. ) ( 54 ) METHODS OF PRODUCING GRAPHENE QUANTUM DOTS FROM COAL AND COKE

( 71 ) Applicant : William Marsh Rice University , Houston , TX ( US )

U . S . CI . CPC . . . . . . . . COIB 31 / 0446 ( 2013 . 01 ) ; COIB 32 / 182

( 2017 . 08 ) ; COIB 32 / 184 ( 2017 . 08 ) ; ( Continued )

Field of Classification Search CPC . . . . . . . . . . . . CO1B 31 / 0446 ; CO1B 31 / 0484 ; C01B

31 / 0438 ; C01B 2204 / 02 ; C01B 2204 / 04 ; ( Continued )

( 58 )

( 72 ) Inventors : James M . Tour , Bellaire , TX ( US ) ; Ruquan Ye , Houston , TX ( US ) ; Changsheng Xiang , Houston , TX ( US ) ; Jian Lin , Houston , TX ( US ) ; Zhiwei Peng , Houston , TX ( US ) ; Gabriel Ceriotti , Montevideo ( UY )

( 56 ) References Cited U . S . PATENT DOCUMENTS

( 73 ) Assignee : WILLIAM MARSH RICE UNIVERSITY , Houston , TX ( US )

2004 / 0223901 A1 2006 / 0121279 A1 *

11 / 2004 Smalley et al . 6 / 2006 Petrik . . . . . . . . . . . . . . . . . . . . B82Y 30 / 00

428 / 403 ( Continued ) ( * ) Notice : Subject to any disclaimer , the term of this

patent is extended or adjusted under 35 U . S . C . 154 ( b ) by 0 days .

( 21 ) Appl . No . : 14 / 888 , 301 CN CN

FOREIGN PATENT DOCUMENTS 101973541 A 2 / 2011 102336404 A 2 / 2012

( Continued ) ( 22 ) PCT Filed : May 2 , 2014

PCT / US2014 / 036604 OTHER PUBLICATIONS ( 86 ) PCT No . : $ 371 ( c ) ( 1 ) , ( 2 ) Date : Oct . 30 , 2015

Wu , Yingpeng , et al . “ Efficient and Large Scale Synthesis of Graphene from Coal and Its Film Electrical Properties Studies . ” Journal of nanoscience and nanotechnology 13 . 2 ( 2013 ) : 929 - 932 . *

( Continued ) ( 87 ) PCT Pub . No . : W02014 / 179708 PCT Pub . Date : Nov . 6 , 2014 Primary Examiner — Richard M Rump

( 74 ) Attorney , Agent , or Firm — Winstead PC ( 65 ) Prior Publication Data US 2016 / 0060122 A1 Mar . 3 , 2016

Related U . S . Application Data ( 60 ) Provisional application No . 61 / 818 , 800 , filed on May

2 , 2013 .

( 57 ) ABSTRACT In some embodiments , the present disclosure pertains to methods of making graphene quantum dots from a carbon source ( e . g . , coal , coke , and combinations thereof ) by expos ing the carbon source to an oxidant . In some embodiments , the methods of the present disclosure further comprise a step of separating the formed graphene quantum dots from the oxidant . In some embodiments , the methods of the present disclosure further comprise a step of reducing the formed graphene quantum dots . In some embodiments , the methods

( Continued )

( 51 ) Int . CI . COIB 31 / 02 COIB 31 / 04

( 2006 . 01 ) ( 2006 . 01 )

( Continued )

- Select Carbon Source Select Carbon Source 10

Expose Carbon Source to Oxidant Epose Canton Source to onibara ] 2 | Form Graphene Quantum Dots |

Separate Graphene Quantum Dots from Oxidant

Enhance Quantum Yield of Graphene Quantum Dots

Reduce Graphene Quantum Dots

US 9 , 919 , 927 B2 Page 2 Doma

of the present disclosure further comprise a step of enhanc ing a quantum yield of the graphene quantum dots . In further embodiments , the methods of the present disclosure also include a step of controlling the diameter of the formed graphene quantum dots by selecting the carbon source . In some embodiments , the formed graphene quantum dots comprise oxygen addends or amorphous carbon addends on their edges .

40 Claims , 22 Drawing Sheets

( 51 )

( 52 )

Int . Cl . COIB 32 / 182 ( 2017 . 01 ) COIB 32 / 184 ( 2017 . 01 ) COIB 32 / 192 ( 2017 . 01 ) COIB 32 / 194 ( 2017 . 01 ) B82Y 40 / 00 ( 2011 . 01 ) U . S . CI . CPC . . . . . . . . . . COIB 32 / 192 ( 2017 . 08 ) ; COIB 32 / 194

( 2017 . 08 ) ; B82Y 40 / 00 ( 2013 . 01 ) ; COIB 2204 / 02 ( 2013 . 01 ) ; COIB 2204 / 04 ( 2013 . 01 ) ;

COIB 2204 / 32 ( 2013 . 01 ) ; YIOS 977 / 774 ( 2013 . 01 )

Field of Classification Search CPC . . C01B 2204 / 32 ; B82Y 40 / 00 ; Y10S 977 / 774 See application file for complete search history .

( 58 )

( 56 ) References Cited U . S . PATENT DOCUMENTS

Search Report and Written Opinion for Singapore Patent Applica tion No . 112015090115 , dated Jun . 20 , 2016 . International Search and Written Opinion for PCT / US2015 / 032209 , dated Mar . 3 , 2016 . International Search Report and Written Opinion for PCT / US2015 ) 036729 , dated Mar . 11 , 2016 . Ye R . et al . , Coal as an abundant source of graphene quantum dots . Nature Communications , Dec . 6 , 2013 , vol . 4 , 2943 . Pan et al . , “ Hydrothermal route for cutting graphene sheets Into blue - luminescent graphene 20 - 24 quantum dots ” , Advanced Mate rials [ online ] , Feb . 9 , 2010 ( Feb . 9 , 2010 ) [ Retrieved on Feb . 10 , 2016 ] , vol . 22 , issue 6 , pp . 734 - 738 ; Retrieved from internet : < DOI : 10 . 1002 / adrna . 200902825 > . Sasikala S . P . et al . , High Yield Synthesis of Aspect Ratio Controlled Graphenic Materials from Anthracite Coal in Supercritical Fluids , ACS Nano , 2016 , 10 ( 5 ) , pp . 5293 - 5303 . Zheng , X . T . , Ananthanarayanan , A . , Luo , K . Q . and Chen , P . ( 2015 ) , Glowing Graphene Quantum Dots and Carbon Dots : Prop erties , Syntheses , and Biological Applications . Small , 11 : 1620 1636 . doi : 10 . 1002 / smll . 201402648 . Cho H . et al . , Surface Engineering of Graphene Quantum Dots and Their Applications as Efficient Surfactants , ACS Applied Materials & Interfaces 2015 7 ( 16 ) , 8615 - 8621 . Wissler et al . , Graphite and carbon powders for electrochemical applications . J . Power Sources 156 , 142 - 150 ( 2006 ) . Marcano et al . , Improved synthesis of graphene oxide . ACS Nano 4 , 4806 - 4814 ( 2010 ) . Hong et al . Aggregation - induced emission : phenomenon , mecha nism and applications . Chem . Commun . 29 , 4332 - 4353 ( 2009 ) . Li et al . , Processable aqueous dispersions of graphene nanosheets . Nat . Nanotechnol . 3 , 101 - 105 ( 2008 ) . Zhu et al . , Strongly green - photoluminescent graphene quantum dots for bioimaging applications , Chem . Comm . 47 , 6858 - 6860 ( 2011 ) . Loh et al . , Graphene oxide as a chemically tunable platform for optical applications . Nature Chemistry 2 , 1015 - 1024 ( 2010 ) . Tapasztó et al . , Tailoring the atomic structure of graphene nanorib bons by scanning tunneling microscope lithography , Nature Nano technology 3 , 397 - 401 ( 2008 ) . Liu et al . , PEGylated nano - graphene oxide for delivery of water insoluble cancer drugs . J . Am . Chem . Soc . 130 , 10876 - 10877 ( 2008 ) . Guo et al . , Layered graphene quantum dots for photovoltaic devices . Angew . Che . Int . Ed . 49 , 3014 - 3017 ( 2010 ) . Cao et al . , A facile one - step method to produce graphene - CdS quantum dot nanocompsites as promising optoelectronic materials . Adv . Mater . 22 , 103 - 106 ( 2010 ) . Sternberg et al . , Solubilization of coals by reductive alkylation . Fuel 53 , 172 - 175 ( 1974 ) . Sun et al . , Functionalization by reductive alkylation and mapping of a subbituminous coal by energy dispersive X - ray spectroscopy . Energy and Fuels 25 , 1571 - 1577 ( 2011 ) . Lu et al . , Transforming C60 molecules into graphene quantum dots . Nat . Nanotechnol . 6 , 247 - 252 ( 2011 ) . Li et al . , Nitrogen - doped graphene quantum dots with oxygen - rich functional groups . J . Am . Chem . Soc 134 , 15 - 18 ( 2012 ) . Shen et al . , Facile preparation and upconversion luminescence of graphene quantum dots . Chem . Commun . 47 , 2580 - 2582 ( 2010 ) . Shinde et al . , Electrochemical preparation of luminescent graphene quantum dots from multiwalled carbon nanotubes . Chem . Eur . J . 18 , 12522 - 12528 ( 2012 ) . Peng et al . , Graphene Quantum Dots Derived from Carbon Fibers . Nano Lett . 12 , 844 - 849 ( 2012 ) . Hu et al . , One - Step Preparation of Nitrogen - Doped Graphene Quantum Dots from Oxidized Debris of Graphene Oxide . J . Mater . Chem . B 2013 , 1 , 39 . Kwon et al . , Electroluminescence from Graphene Quantum Dots Prepared by Amidative Cutting of Tattered Graphite . Nano Lett . 2014 , 14 , 1306 . Search Report for European Patent Application No . 14791674 . 6 , dated Nov . 24 , 2016 . Wu et al . , Efficient and large scale synthesis of graphene from caol and its film electrical property studies , Journal of Nanoscience and Nanotechnology , vol . 13 , No . 2 , Jan . 2013 , pp . 292 - 293 .

2011 / 0186789 A1 *

2011 / 0217721 AL 2012 / 0068152 A1 2012 / 0201738 A1 *

8 / 2011 Samulski . . . . . . . . . . . . . B82Y 30 / 00 252 / 514

9 / 2011 Allam et al . 3 / 2012 Hwang et al . 8 / 2012 Kwon . . . . . . . . . . . . . . . . . . B01J 6 / 004

423 / 415 . 1 11 / 2012 Li et al . 8 / 2013 Lee

10 / 2015 Tour et al .

2012 / 0279570 AL 2013 / 0202866 AL 2015 / 0280248 A1

FOREIGN PATENT DOCUMENTS CN CN CN CN CN WO WO WO WO WO WO

101973541 B 102849724 A * 102849724 A 102336404 B * 102336404 B

WO 2011 / 019095 A1 WO - 2011019184 A2 WO - 2014 / 037484 A1 WO - 2014 / 064298 A1 WO - 2016 / 025051 A2 WO - 2016 / 053411 A1

9 / 2012 1 / 2013 1 / 2013 4 / 2013 4 / 2013 2 / 2011 2 / 2011 3 / 2014 5 / 2014 2 / 2016 4 / 2016

OTHER PUBLICATIONS Pan , Dengyu , et al . “ Hydrothermal route for cutting graphene sheets into blue - luminescent graphene quantum dots . ” Advanced Materials 22 . 6 ( 2010 ) : 734 - 738 . * Zhou , Quan , et al . “ Graphene sheets from graphitized anthracite coal : preparation , decoration , and application . ” Energy & Fuels 26 . 8 ( 2012 ) : 5186 - 5192 . * International Search Report and Written Opinion for PCT / US2014 / 036604 , dated Sep . 2 , 2014 . International Preliminary Report on Patentability for PCT / US2014 / 036604 , dated Nov . 12 , 2015 .

US 9 , 919 , 927 B2 Page 3

( 56 ) References Cited

OTHER PUBLICATIONS

Zhou et al . , graphene sheets from graphitized anthracite coal : preparation , decoration , and application , Energy and Fuels , vol . 26 , No . 8 , Aug . 16 , 2012 , pp . 5186 - 5192 . Li et al . , Synthesis of graphene nanosheets from petroleum asphalt by pulsed arc discharge in water , Chemical Engineering Journal , vol . 215 - 216 , Nov . 10 , 2012 , pp . 45 - 49 . First Office Action for Chinese Application No . 201480036235 . 4 , dated Oct . 28 , 2016 .

* cited by examiner

U . S . Patent Mar . 20 , 2018 Sheet 1 of 22 US 9 , 919 , 927 B2

10 Select Carbon Source

12 Expose Carbon Source to Oxidant

14 Form Graphene Quantum Dots |

16 Separate Graphene Quantum Dots from Oxidant

Enhance Quantum Yield of Graphene Quantum Dots

Reduce Graphene Quantum Dots |

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US 9 , 919 , 927 B2 Sheet 22 of 22 Mar . 20 , 2018 atent

US 9 , 919 , 927 B2

30

METHODS OF PRODUCING GRAPHENE one or more bases ( e . g . , sodium hydroxide ) , treatment of the QUANTUM DOTS FROM COAL AND COKE graphene quantum dots with one or more dopants ( e . g . ,

NaHz , NaHSe , NaH PO3 ) , and combinations of such treat CROSS - REFERENCE TO RELATED ments .

APPLICATIONS 5 In further embodiments , the methods of the present dis closure also include a step of controlling the diameter of the

This application claims priority to U . S . Provisional Patent formed graphene quantum dots . In some embodiments , the Application No . 61 / 818 , 800 , filed on May 2 , 2013 . The controlling comprises selecting the carbon source . For entirety of the aforementioned application is incorporated instance , in some embodiments , the selected carbon source herein by reference . 10 is bituminous coal , and the formed graphene quantum dots

have diameters ranging from about 1 nm to about 5 nm . In STATEMENT REGARDING FEDERALLY some embodiments , the selected carbon source is anthracite ,

SPONSORED RESEARCH and the formed graphene quantum dots have diameters ranging from about 10 nm to about 50 nm . In some embodi

This invention was made with government support under 15 ments , the selected carbon source is coke , and the formed Grant No . FA9550 - 09 - 1 - 0581 , awarded by the U . S . Depart - graphene quantum dots have diameters ranging from about ment of Defense ; Grant No . FA9550 - 12 - 1 - 0035 , awarded by 2 nm to about 10 nm . the U . S . Department of Defense ; and Grant No . N00014 - In some embodiments , the formed graphene quantum dots 09 - 1 - 1066 , awarded by the U . S . Department of Defense . have a crystalline hexagonal structure . In some embodi The government has certain rights in the invention . 20 ments , the formed graphene quantum dots have a single

layer . In some embodiments , the formed graphene quantum BACKGROUND dots have multiple layers , such as from about two layers to

about four layers . In some embodiments , the formed gra Graphene quantum dots ( GQDs ) find applications in phene quantum dots are functionalized with a plurality of

many fields . However , current methods of making graphene 25 functional groups , such as amorphous carbons , oxygen quantum dots suffer from various limitations , including groups , carbonyl groups , carboxyl groups , esters , amines , quality , yield , and efficiency . The present disclosure amides , and combinations thereof . In some embodiments , addresses these limitations . the formed graphene quantum dots comprise oxygen

addends or amorphous carbon addends on their edges . SUMMARY

DESCRIPTION OF THE FIGURES In some embodiments , the present disclosure pertains to

methods of making graphene quantum dots from a carbon FIG . 1 provides a scheme of a method of preparing source . In some embodiments , the carbon source is selected graphene quantum dots ( GQDs ) from a carbon source . from the group consisting of coal , coke and combinations 35 FIG . 2 provides schemes and data relating to the synthesis thereof . In some embodiments , the methods comprise expos - and characterization of GQDs produced from bituminous ing the carbon source to an oxidant . The exposing results in coal ( b - GQDs ) . FIG . 2A provides macro - scale image and the formation of the graphene quantum dots . simplified illustrative nanostructures of bituminous coal .

In some embodiments , the carbon source includes at least FIG . 2B provides a scanning electron microscopy ( SEM ) one of coke , bituminous coal , anthracite , and combinations 40 image of ground bituminous coal with sizes ranging from 1 thereof . In some embodiments , the oxidant is a mixture of micron to hundreds of microns in diameter . FIG . 2C pro sulfuric acid and nitric acid . vides a schematic illustration of the synthesis of b - GQDs .

In some embodiments , a carbon source is exposed to an Oxygenated sites are shown in red . FIG . 2D provides a oxidant by sonicating the carbon source in the presence of transmission electron microscopy ( TEM ) image of b - GQDs the oxidant . In some embodiments , the exposing comprises 45 showing a regular size and shape distribution . FIG . 2E heating the carbon source in the presence of the oxidant . shows a high resolution TEM ( HRTEM ) image of represen

In some embodiments , the methods of the present disclo - tative b - GODs from FIG . 2D . The inset is the two - dimen sure further comprise a step of separating the formed gra - sional fast Fourier transform ( 2D FFT ) image that shows the phene quantum dots from the oxidant . In some embodi - crystalline hexagonal structure of these quantum dots . FIG . ments , the separating occurs by neutralizing a solution 50 2F is an atomic force microscopy ( AFM ) image of b - GQDs , comprising the formed graphene quantum dots , filtering the showing heights between 1 . 5 nm to 3 nm . solution , and dialyzing the solution . In some embodiments , FIG . 3 provides SEM images of various carbon sources . the separating occurs by cross - flow filtration , washing with FIG . 3A provides an SEM image of anthracite showing the a sodium hydroxide solution , hydrothermal treatment , and irregular size and shape distribution ranging from 1 micron combinations of such steps . 55 to hundreds of microns in diameter . The scale bar is 1 um .

In some embodiments , the methods of the present disclo - FIG . 3B provides an SEM image of coke , showing normal sure further comprise a step of reducing the formed gra - spherical shapes with approximately 110 um in diameter . phene quantum dots . In some embodiments , the reducing The scale bar is 300 um . comprises exposure of the formed graphene quantum dots to FIG . 4 provides data relating to the characterization of a reducing agent , such as hydrazine , sodium borohydride , 60 various carbon sources . FIG . 4A provides X - ray photoelec heat , light , sulfur , sodium sulfide , sodium hydrogen sulfide , tron spectroscopy ( XPS ) survey of carbon sources . The and combinations thereof . analysis indicates that anthracite has more Al and Si content

In some embodiments , the methods of the present disclo - than bituminous coal and coke . FIG . 4B shows high reso sure also comprise a step of enhancing the quantum yield of lution Cis XPS spectra of carbon sources where the 284 . 4 the graphene quantum dots . In some embodiments , the 65 eV peak is assigned to C = C is double bond . FIG . 4C shows enhancing occurs by hydrothermal treatment of the graphene solid state Fourier transform infrared ray ( ssFTIR ) spectra of quantum dots , treatment of the graphene quantum dots with bituminous coal showing C _ 0 , C = C , C = 0 , H - Csp3 and

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0 H vibration modes at 1000 , 1600 , 1700 , 2922 and 3360 ( b - GQDs * ) . The concentration of these GQDs solutions was cm - 1 as labeled , respectively . Weak C = C and C – O vibra 80 mg / L and the pH was ~ 6 . FIG . 13B shows the PL tion modes for coke and anthracite are shown . FIG . 4D emission wavelength vs . the size of the GQDs , smaller shows Raman spectra of carbon sources . D , G , 2D and 2G GQDs lead to blue shift . FIG . 13C shows PL emission peaks are labeled at 1337 , 1596 , 2659 and 2913 cm - 1 , 5 spectrum of b - GQDs excited at 345 nm from pH 3 to 10 . The respectively . red arrow shows the red shift of emission with change of pH

FIG . 5 provides data relating to the characterization of from 6 to 3 and the blue arrow shows the blue shift of b - GQDs . FIG . 5A shows the size distribution of b - GQDs at emission from pH 7 to 10 . FIG . 13D shows excitation and 2 . 96 + 0 . 96 nm . FIG . 5B shows a TEM image of a non - fully emission contour map of b - GODs at pH 3 ( top ) , pH 7 cut larger size b - GQD showing different nanometer - sized 10 ( middle ) and pH 11 ( bottom ) .

FIG . 14 provides additional data relating to the photo crystalline domains as highlighted by the circles . The inset physical characterizations of GQDs . FIG . 14A provides UV is an FFT pattern that shows the crystalline hexagonal absorptions of three types of GQDs , showing absorbance of structure of the highlighted domains . The scale bar is 10 nm . 0 . 13 at 345 nm . FIG . 14B provides a Jablonski diagram FIG . 5C shows the AFM height profile of b - GQDs . obtained from FIG . 13C . A denotes absorption . GS is ground FIG . 6 provides data relating to the characterization of 15 state . PL is photoluminescence . ES is excited state . IC is

b - GQDs . FIG . 6A provides a Raman spectrum of the internal conversion . Nonag is non - aggregated state . Ag is the b - GQDs . FIG . 6B provides a high resolution C1s XPS . A aggregated state . A , n , b signify acidic , neutral and basic , new peak corresponding to COOH appears at 288 . 3 eV . FIG . respectively . FIG . 14C provides the PL intensity of b - GQDs 6C provides an ssFTIR spectrum showing different vibration at different concentrations . 1 is the starting solution with a modes as labeled . 20 concentration of 3 mg / mL . 2 signifies that the concentration

FIG . 7 provides data relating to the TEM characterization of the starting solution has been diluted 2 times , to make the of b - GQDs . FIG . 7A shows the TEM image . The size is concentration 1 . 5 mg / mL . The remaining concentrations approximately 2 to 3 nm . A few outliers , which were not follow in the same manner . The pH of the solutions was 6 . fully cut , have sizes larger than 4 . 5 nm . The scale bar is 10 FIG . 14D is a summary of peak intensity and relative nm . FIG . 7B shows the size distribution histogram of the 25 quantum yield with respect to the dilution factors . The peak b - GODs . intensity was fitted to y = 1 / ( 0 . 68 + 0 . 28x ) ; R2 = 0 . 97 . The

FIG . 8 provides comparative images of GQDs prepared normalized quantum yield was fitted to y = ( 1 . 33 - X ) / ( 1 - x ) ; from coal and graphite . The left beaker in FIG . 8A contains R2 = 0 . 90 .

FIG . 15 provides time - resolved photoluminescence decay bituminous coal oxidized at 100° C . with sulfuric and nitric in profiles of b - GODs at pH 3 ( FIG . 15A ) , PH 7 ( FIG . 15B ) , acids for 24 h . The right beaker in FIG . 8A is graphite treated 30 and pH 11 ( FIG . 15C ) . FIG . 15D shows the photobleaching under the same conditions . FIG . 8B provides an SEM image properties of a - GQDs , C - GQDs , b - GQDs , and fluorescein . of the treated graphite from FIG . 8A . The scale bar is 2 mm . FIG . 16 shows a photo of 5 g of graphene quantum dots FIG . 8C provides a high resolution SEM image of FIG . 8B . produced from anthracite ( a - GQDs ) in a glass vial . The total The scale bar is 100 um . FIG . 8D provides a TEM image of yield of graphene quantum dots produced from the oxidation GQDs synthesized by treating bituminous coal with KMnad 35 of 30 g of anthracite with sulfuric acid and nitric acid was H2SO4 / H3PO4 . The scale bar is 50 nm . 5 . 3 g .

FIG . 9 provides TEM images of GQDs produced from FIG . 17 shows additional data relating to the character coke ( c - GQDs ) and anthracite ( a - GQDs ) . FIG . 9A provides ization of a - GQDs . FIG . 17A shows TEM images of a TEM image of c - GODs showing the consistent round a - GODs . FIG . 17B shows high resolution TEM image of shape and size distribution of 5 . 8 + 1 . 7 nm . FIG . 9B provides 40 a - GQDs . The inset FFT pattern shows graphitic structure . a TEM image of a - GQDs showing stacking layer structures . FIG . 17C shows the size distribution of a - GQDs . FIG . 9C provides an HRTEM image of c - GQD . Insets are FIG . 18 shows the spectrum of a - GQDs with 514 nm laser FFT patterns of the highlighted areas . FIG . 9D provides an excitation . G and D Raman peaks of a typical oxidized HRTEM image of a - GOD . Insets are the FFT patterns of graphitic structure were observed . high and low layered structure . They both show crystalline 45 FIG . 19 shows XPS spectra of a - GQDs . FIG . 19A shows hexagonal patterns . a survey profile . Sodium is likely due to some carboxylates

FIG . 10 provides data relating to the characterization of at the edges of the GODs . This can be removed through C - GQDs and a - GQDs . FIG . 10A provides the size distribu - acidification . FIG . 19B is a high resolution C1s XPS spec tion of c - GQDs . FIG . 10B provides an AFM image of trum of a - GQDs , where the 284 . 4 eV peak is assigned to a - GODs . The scale bar is 100 nm . FIG . 10C provides the 50 C = C is double bonds . height profile from FIG . 10B . FIG . 10D provides the size FIG . 20 shows the FTIR spectrum of a - GQDs . distribution of a - GQDs . FIG . 21 provides data relating to the photophysical char

FIG . 11 provides data relating to the further characteriza - acterizations of a - GQDs . FIG . 21A is a UV - Vis absorbance tion of c - GQDs and a - GQDs . FIG . 11A provides Raman of a - GQDs . FIG . 21B is a photoluminescent ( PL ) emission spectra showing that the 2D and 2G peaks disappeared due 55 of a - GQDs excited at 345 nm . The inset is a photograph to the oxidation . FIG . 11B provides high resolution Cis XPS showing fluorescence of a - GQDs in DI water at 0 . 1 mg of c - GODs and a - GODs that show new shoulders at 288 . 3 mL - 1 . eV corresponding to the carboxyl groups . FIG . 11C shows FIG . 22 provides PL emission ( FIG . 22A ) and absorbance SsFTIR spectra of c - GQDs and a - GQDs showing C - O , spectra ( FIG . 22B ) of graphene quantum dots before and C = 0 and 0 - H vibration modes . 60 after hydrothermal treatment . The spectra show that hydro

FIG . 12 provides the TGA characterizations of GQDs in thermal treatment increased the quantum yield of graphene air and argon ( Ar ) , including a - GQDs ( FIG . 12A ) , b - GQDs quantum dots . ( FIG . 12B ) , and c - GQDs ( FIG . 12C ) .

FIG . 13 provides data relating to the photophysical char DETAILED DESCRIPTION acterizations of GQDs . FIG . 13A shows PL emission of 65 GQDs excited at 345 nm . Inset is the photograph showing It is to be understood that both the foregoing general fluorescence of yellow ( a - GQDs ) , green ( c - GQDs ) and blue description and the following detailed description are illus

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600 . 0

64 . 10

trative and explanatory , and are not restrictive of the subject oxidants , quantum yield enhancers , and reducing agents to matter , as claimed . In this application , the use of the singular form various types and sizes of graphene quantum dots in a includes the plural , the word “ a ” or “ an ” means “ at least controllable manner . one ” , and the use of “ or ” means “ and / or ” , unless specifically Carbon Sources stated otherwise . Furthermore , the use of the term “ includ - 5 Various types of carbon sources may be utilized to form ing ” , as well as other forms , such as " includes ” and graphene quantum dots . In some embodiments , the carbon " included ” , is not limiting . Also , terms such as " element ” or source is coal . “ component ” encompass both elements or components com As summarized in Tables 1 and 2 , coal is the most prising one unit and elements or components that comprise affordable , abundant , and readily combustible energy more than one unit unless specifically stated otherwise . unit unless specifically stated otherwise . 10 10 resource being used worldwide .

The section headings used herein are for organizational purposes and are not to be construed as limiting the subject TABLE 1 matter described . All documents , or portions of documents , The world ' s three major regions for coal production and consumption . cited in this application , including , but not limited to , 15 patents , patent applications , articles , books , and treatises , are Production Consumption

Region ( Million Tons ) ( Million Tons ) hereby expressly incorporated herein by reference in their entirety for any purpose . In the event that one or more of the Asia Pacific 2686 . 3 2553 . 2

North America 533 . 7 incorporated literature and similar materials defines a term Europe and Eurasia 457 . 1 499 . 2 in a manner that contradicts the definition of that term in this 20 application , this application controls . Graphene quantum dots ( GQDs ) generally refer to disc

shaped graphene compositions , such as disc - shaped gra TABLE 2 phene oxides . Graphene quantum dots have found numerous Recent coal prices in North America . applications . For instance , graphene quantum dots can be 25 used as fluorophores for medical imaging . Graphene quan Price

tum dots have been synthesized or fabricated from various Region ( US dollars per ton )

carbon - based materials , including fullerenes , glucose , Central Appalachia 12 , 500 Btu 67 . 27

graphite , graphene oxides , carbon nanotubes ( CNTs ) , and Northern Appalachia 13 , 000 Btu , Illinois Basin 11 , 800 Btu , 45 . 15 carbon fibers . Physical approaches such as lithography have 30 Powder River Basin 8 , 800 Btu , 10 . 55

also been used to fabricate graphene quantum dots from Uinta Basin 11 , 700 Btu 35 . 85 various carbon sources . For instance , lithography has been - used to etch graphene quantum dots from graphene . The structure of coal is complex . The simplified compo However , current methods for the fabrication of graphene 25 de 35 sition contains angstrom or nanometer - sized crystalline car quantum dots suffer from numerous limitations . For bon domains with defects that are linked by aliphatic amor instance , lithography techniques are expensive and imprac phous carbon . Although research on the chemistry of coal tical for the production of bulk quantities of graphene has been reported , the angstrom - and nano - scale crystalline quantum dots . Likewise , current carbon - based materials that domains of coal are implied to impede their further use in are utilized for the production of graphene quantum dots can 40 electrical , mechanical and optical applications . Conse be expensive in bulk quantities . Moreover , current methods quently , coal is still mainly used as an energy source . of growing graphene quantum dots may not be able to Thus , coal ' s structural characteristics create a perception control the size of the formed graphene quantum dots . that coal is only useful for producing energy through burn Therefore , new methods are required for the bulk production ing . By contrast , Applicants have utilized coal for the first of graphene quantum dots in a controllable manner . Various 45 time to produce graphene quantum dots . embodiments of the present disclosure address these needs . Various types of coals may be utilized as carbon sources

In some embodiments , the present disclosure pertains to to form graphene quantum dots . In some embodiments , the methods of making graphene quantum dots from a carbon coal includes , without limitation , anthracite , bituminous source , such as coal , coke and combinations thereof . In some coal , sub - bituminous coal , metamorphically altered bitumi embodiments , such methods involve exposing the carbon 50 nous coal , asphaltenes , asphalt , peat , lignite , steam coal , source to an oxidant . In some embodiments , such exposure petrified oil , and combinations thereof . In some embodi results in the formation of graphene quantum dots . In some ments , the carbon source is bituminous coal . In some embodiments illustrated in FIG . 1 , the methods of the embodiments , the carbon source is anthracite . present disclosure involve : selecting a carbon source ( step The use of additional carbon sources can also be envi 10 ) and exposing the carbon source to an oxidant ( step 12 ) 55 sioned . For instance , in some embodiments , the carbon to form graphene quantum dots ( step 14 ) . In some embodi - source is coke . In some embodiments the coke is made from ments , the methods of the present disclosure can also include pitch . In some embodiments , the coke is made from bitu a step of separating the formed graphene quantum dots from minous coals . In some embodiments , the coke is made from the oxidant ( step 16 ) . In some embodiments , the methods of pitch and bituminous coals . In some embodiments , the the present disclosure also include a step of enhancing the 60 carbon source is a combination of coke and coal . quantum yield of the graphene quantum dots , such as Oxidants through hydrothermal treatment , washing with a sodium In some embodiments , graphene quantum dots form by hydroxide solution , or both ( step 18 ) . In some embodiments , exposing the carbon source to a an oxidant . Various oxidants the methods of the present disclosure can also include a step may be utilized to form graphene quantum dots . In some of reducing the formed graphene quantum dots ( step 20 ) . As 65 embodiments , the oxidant includes an acid . In some embodi set forth in more detail herein , the methods of the present m ents , the acid includes , without limitation , sulfuric acid , disclosure may utilize various types of carbon sources , nitric acid , phosphoric acid , hypophosphorous acid , fuming

US 9 , 919 , 927 B2

sulfuric acid , hydrochloric acid , oleum ( i . e . , sulfuric acid sulfuric acid and the second oxidant is nitric acid . Additional with dissolved sulfur trioxide ) , chlorosulfonic acid , and methods of exposing carbon sources to oxidants can also be combinations thereof . envisioned .

In some embodiments , the oxidant utilized to form gra The exposure of carbon sources to oxidants can lead to the phene quantum dots is a mixture of sulfuric acid and nitric 5 formation of graphene quantum dots . Without being bound acid . In some embodiments , the oxidant includes , without by theory , Applicants envision that , upon the exposure of limitation , potassium permanganate , sodium permanganate , coal or coke to oxidants , graphene quantum dots form by hypophosphorous acid , nitric acid , sulfuric acid , hydrogen exfoliation of the carbon source by the oxidants . In particu peroxide , and combinations thereof . In some embodiments , lar , Applicants envision that the crystalline carbon within the the oxidant is a mixture of potassium permanganate , sulfuric 10 coal structure is oxidatively displaced to form graphene

quantum dots . acid , and hypophosphorous acid . Separation of Graphene Quantum Dots from Oxidants In some embodiments , the oxidant is in the form of a In some embodiments , the methods of the present disclo liquid medium , such as a liquid solution . In some embodi sure also include a step of separating the formed graphene

ments , the oxidant includes an anion . In some embodiments , 15 quantum dots from oxidants . In some embodiments , the the oxidant includes , without limitation , permanganates separating includes neutralizing a solution that contains the ( e . g . , potassium permanganate , sodium permanganate , and formed graphene quantum dots , filtering the solution , and ammonium permanganate ) , chlorates ( e . g . , sodium chlorates dialyzing the solution . In some embodiments , the separating and potassium chlorates ) , perchlorates , hypochlorites ( e . g . , step includes dialyzing a solution that contains the formed potassium hypochlorites and sodium hypochlorites ) , hypo - 20 graphene quantum dots . Additional methods of separating bromites , hypoiodites , chromates , dichromates , nitrates , graphene quantum dots from oxidants can also be envi nitric acid , sulfuric acid , chlorosulfonic acid , oleum , and sioned . combinations thereof . In more specific embodiments , the Enhancing the Quantum Yield of Graphene Quantum oxidant includes , without limitation , potassium permangan - Dots ate , potassium chlorate , hydrogen peroxide , ozone , nitric 25 In some embodiments , the methods of the present disclo acid , sulfuric acid , oleum , chorosulfonic acid , and combi - sure also include a step of enhancing the quantum yield of nations thereof . the graphene quantum dots . In some embodiments , the

In more specific embodiments , the oxidant includes a enhancing occurs by hydrothermal treatment of the graphene compound that is dissolved in an acid . In some embodi quantum dots , treatment of the graphene quantum dots with ments , the compound includes , without limitation perman - 30 one or more bases ( e . g . , sodium hydroxide ) , treatment of the

graphene quantum dots with one or more hydroxides , treat ganates ( e . g . , potassium permanganate , sodium permangan ment of the graphene quantum dots with one or more ate , and ammonium permanganate ) , chlorates ( e . g . , sodium dopants ( e . g . , NaH3 , NaHSe , NaH PO3 ) , and combinations chlorates and potassium chlorates ) , perchlorates , hypochlo of such treatments . rites , hypobromites , hypoiodites , chromates , dichromates , 35 In more specific embodiments , the quantum vield of the nitrates , nitric acid , peroxides ( e . g . , hydrogen peroxide ) , graphene quantum dots can be enhanced by treating the ozone , and combinations of thereof . In some embodiments , graphene quantum dots with hydroxide in water to increase the acid includes , without limitation , sulfuric acid , nitric their quantum yield . In further embodiments , the quantum acid , oleum , chorosulfonic acid , and combinations thereof . yield of the graphene quantum dots can be enhanced by

In more specific embodiments , the compound includes at 40 hydrothermal treatment of the graphene quantum dots . In least one of potassium permanganate , sodium hypochlorite , some embodiments , the hydrothermal treatment of the gra potassium hypochlorite , potassium chlorate , nitric acid , and phene quantum dots involves treating the graphene quantum combinations thereof . In additional embodiments , the com dots with water under pressure in a container ( e . g . , a sealed pound is dissolved in sulfuric acid . vessel ) at temperatures above 100° C . ( e . g . , temperatures of

In further embodiments , the oxidant is potassium perman - 45 about 180 to 200° C . ) . In further embodiments , the quantum ganate dissolved in sulfuric acid ( also referred to as KMnO4 yield of the graphene quantum dots can be enhanced by a H , SO2 ) . In some embodiments , the oxidant is nitric acid combined hydrothermal treatment and hydroxide treatment dissolved in sulfuric acid ( also referred to as HNOZ / H , SO . ) . of the graphene quantum dots . Additional methods of The utilization of additional oxidants can also be envisioned . enhancing the quantum yield of graphene quantum dots can Exposure of Carbon Sources to Oxidants 50 also be envisioned . Various methods may be utilized to expose carbon sources In some embodiments , the enhancement step enhances the

to oxidants . In some embodiments , the exposing occurs quantum yield of the graphene quantum dots by at least while the carbon source and the oxidant are in a liquid about 50 % , at least about 100 % , at least about 200 % , at least solution . In some embodiments , the exposing includes soni - about 1 , 500 % , at least about 1 , 700 % , or at least about cating the carbon source in the presence of the oxidant . In 55 2 , 000 % . In some embodiments , the enhancement step some embodiments , the exposing includes stirring the car - enhances the quantum yield of the graphene quantum dots bon source in the presence of the oxidant . In some embodi - by at least about 2 , 000 % . ments , the exposing includes heating the carbon source in Reduction of Formed Graphene Quantum Dots the presence of the oxidant . In some embodiments , the In some embodiments , the methods of the present disclo heating occurs at temperatures of at least about 100° C . In 60 sure also include a step of reducing the formed graphene some embodiments , the heating occurs at temperatures rang - quantum dots . In some embodiments , the reducing includes ing from about 100° C . to about 150° C . exposure of the formed graphene quantum dots to a reducing

In some embodiments , two or more oxidants may be agent . In some embodiments , the reducing agent includes , exposed to the carbon source in a sequential manner . For without limitation , hydrazine , sodium borohydride , heat , instance , in some embodiments , a first oxidant is mixed with 65 light , sulfur , sodium sulfide , sodium hydrogen sulfide , and a carbon source . Thereafter , a second oxidant is mixed with combinations thereof . Additional methods by which to the carbon source . In some embodiments , the first oxidant is reduce graphene quantum dots can also be envisioned .

US 9 , 919 , 927 B2 10

In some embodiments , the non - reduced versions of gra In some embodiments , the carbon source used to form phene quantum dots are water soluble . In some embodi graphene quantum dots is coke , and the formed graphene ments , the reduced versions of graphene quantum dots are quantum dots have diameters ranging from about 2 nm to soluble in organic solvents . about 10 nm , from about 4 nm to 8 nm , or from about 4 nm

Control of Graphene Quantum Dot Formation 5 to about 7 . 5 nm . In some embodiments , the carbon source In some embodiments , the methods of the present disclo - used to form graphene quantum dots is coke , and the formed

sure also include one or more steps of controlling the shape graphene quantum dots have diameters of about 6 nm . In or size of the formed graphene quantum dots . For instance , some embodiments , the carbon source used to form gra in some embodiments , the methods of the present disclosure phene quantum dots is coke , and the formed graphene may include a step of controlling the diameter of the formed 10 quantum dots have diameters of about 7 . 5 nm . graphene quantum dots . In some embodiments , the step of The formed graphene dots of the present disclosure can controlling the diameter of the formed graphene quantum also have various structures . For instance , in some embodi dots includes selecting the carbon source . For instance , in ments , the formed graphene quantum dots have a crystalline some embodiments , the selected carbon source is bitumi - hexagonal structure . In some embodiments , the formed nous coal , and the formed graphene quantum dots have 15 graphene quantum dots have a single layer . In some embodi diameters ranging from about 1 nm to about 5 nm . In some ments , the formed graphene quantum dots have multiple embodiments , the selected carbon source is anthracite , and layers . In some embodiments , the formed graphene quantum the formed graphene quantum dots have diameters ranging dots have from about two layers to about four layers . In from about 10 nm to about 50 nm . In some embodiments , the some embodiments , the formed graphene quantum dots have selected carbon source is coke , and the formed graphene 20 heights ranging from about 1 nm to about 5 nm . quantum dots have diameters ranging from about 2 nm to In some embodiments , the formed graphene quantum dots about 10 nm . are functionalized with a plurality of functional groups . In

Formed Graphene Quantum Dots some embodiments , the functional groups include , without The methods of the present disclosure may be utilized to limitation , amorphous carbon addends , oxygen groups , car

form various types of graphene quantum dots with various 25 bonyl groups , carboxyl groups , esters , amines , amides , and sizes . For instance , in some embodiments , the formed gra - combinations thereof . In some embodiments , the formed phene quantum dots have diameters ranging from about 1 graphene quantum dots are edge functionalized . In some nm to about 50 nm . In some embodiments , the formed embodiments , the formed graphene quantum dots include graphene quantum dots have diameters ranging from about oxygen addends on their edges . In some embodiments , the 18 nm to about 40 nm . In some embodiments , the formed 30 formed graphene quantum dots include amorphous carbon graphene quantum dots have diameters ranging from about addends on their edges . In some embodiments , the addends 1 nm to about 20 nm . In some embodiments , the formed can be appended to graphene quantum dots by amide or ester graphene quantum dots have diameters ranging from about bonds . 1 nm to about 10 nm . In some embodiments , the formed In some embodiments , the functional groups on the gra graphene quantum dots have diameters ranging from about 35 phene quantum dots can be converted to other functional 1 nm to about 20 nm . In some embodiments , the formed groups . For instance , in some embodiments , the graphene graphene quantum dots have diameters ranging from about quantum dots can be heated with an alcohol or phenol to 1 nm to about 7 . 5 nm . In some embodiments , the formed convert the graphene quantum dots ' carboxyl groups to graphene quantum dots have diameters ranging from about esters . In some embodiments , the graphene quantum dots 4 nm to about 7 . 5 nm . In some embodiments , the formed 40 can be heated with an alkylamine or aniline to convert the graphene quantum dots have diameters ranging from about graphene quantum dots ' carboxyl groups to amides . In some 1 nm to about 5 nm . In some embodiments , the formed embodiments , the graphene quantum dots can be treated graphene quantum dots have diameters ranging from about with thionyl chloride or oxalyl chloride to convert the 1 . 5 nm to about 3 nm . In some embodiments , the formed graphene quantum dots ' carboxyl groups to acid chlorides , graphene quantum dots have diameters ranging from about 45 and then treated with alcohols or amines to form esters or 2 nm to about 4 nm . In some embodiments , the formed amides , respectively . Depending on the length of the alco graphene quantum dots have diameters of about 3 nm . In hols or amines used , such steps could render different some embodiments , the formed graphene quantum dots have solubility properties to the graphene quantum dots . For diameters of about 2 nm . instance , the more aliphatic or aromatic the addends , the less

In more specific embodiments , the carbon source used to 50 water soluble and the more organic soluble would be the form graphene quantum dots is bituminous coal , and the graphene quantum dot . formed graphene quantum dots have diameters ranging from The methods of the present disclosure may be utilized to about 1 nm to about 5 nm , from about 2 nm to 4 nm , or from form various amounts of graphene quantum dots from about 1 . 5 nm to about 3 nm . In some embodiments , the carbon sources . In some embodiments , the yields of isolated carbon source used to form graphene quantum dots is 55 graphene quantum dots from carbon sources range from bituminous coal , and the formed graphene quantum dots about 10 % by weight to about 50 % by weight . In some have diameters of about 3 nm . In some embodiments , the embodiments , the yields of isolated graphene quantum dots carbon source used to form graphene quantum dots is from carbon sources range from about 10 % by weight to bituminous coal , and the formed graphene quantum dots about 20 % by weight . have diameters of about 2 nm . 60 In some embodiments , the methods of the present disclo

In some embodiments , the carbon source used to form sure may be utilized to produce bulk amounts of graphene graphene quantum dots is anthracite , and the formed gra - quantum dots . In some embodiments , the bulk amounts of phene quantum dots have diameters ranging from about 10 produced graphene quantum dots range from about 10 kg to nm to about 50 nm . In some embodiments , the carbon source one or more tons . In some embodiments , the bulk amounts used to form graphene quantum dots is anthracite , and the 65 of produced graphene quantum dots range from about 1 g to formed graphene quantum dots have diameters ranging from about 10 kg . In some embodiments , the bulk amounts of about 18 nm to about 40 nm . produced graphene quantum dots range from about 1 g to

US 9 , 919 , 927 B2 12

about 1 kg . In some embodiments , the bulk amounts of The chemical compositions of the carbon sources were produced graphene quantum dots range from about 1 g to investigated by X - ray photoelectron spectroscopy ( XPS ) about 500 g . and are summarized in FIGS . 4A - B and Table 3 .

The graphene quantum dots of the present disclosure may also have various quantum yields . For instance , in some 5 TABLE 3 embodiments , the quantum yields of the graphene quantum Summary of atomic concentrations of carbon sources . dots are less than 1 % and greater than 0 . 1 % . In some embodiments , the quantum yields of the graphene quantum Elements ( % ) dots are between 1 % and 10 % . In some embodiments , the Carbon C O AL Si quantum yields of the graphene quantum dots can be as high 10 50 % . In some embodiments , the quantum yields of the Anthracite 72 . 94 17 . 29 3 . 15 4 . 62

84 . 48 Bituminous coal 14 . 86 graphene quantum dots may be near 100 % . 0 . 65 Coke 93 . 69 5 . 51 0 . 8 Advantages

As set forth in more detail herein , Applicants have estab - 15 lished that the unique coal and coke structures have an The Cls high resolution XPS reveals that bituminous coal advantage over their pure spa carbon allotropes for produc - has more carbon oxidation than anthracite and coke . The ing graphene quantum dots . Without being bound by theory , solid state Fourier transform infrared ( ssFTIR ) spectra ( FIG . it is envisioned that the amorphous carbon within the coal 4C ) are consistent with the XPS results , showing the pres and coke structures is easier to displace under the oxidation 20 ence of C — 0 , C = O , H - Cmz and O H vibration modes conditions typically used when compared with reaction on for bituminous coal . ACO vibration mode was apparent pure spa carbon structures . As such , the methods of the for anthracite but not for coke , which is obtained from present disclosure provide new and effective methods of devolatilization and carbonization of tars and pitches . The producing bulk quantities of graphene quantum dots in a Raman spectra ( FIG . 4D ) of anthracite and coke show D , G , controllable manner from various types of coals and cokes . 25 2D and 2G peaks , while no apparent 2D and 2G peak is Moreover , Applicants envision that the graphene quantum observed for bituminous coal . It is therefore seen that

dots of the present disclosure can find numerous applica - anthracite and coke contain certain amounts of graphite - like tions . For instance , the graphene quantum dots of the present stacking domains , while bituminous coal has a higher pro disclosure can find applications in road stickers , road signs , portion of aliphatic carbon and smaller polyaromatic coatings , clothing , paints , photographic processing materi - 30 domains . als , and combinations thereof . As depicted in FIG . 2C , the GQDs derived from bitumi

nous coal were obtained by sonicating the bituminous coal Additional Embodiments in concentrated sulfuric acid and nitric acid , followed by

heat treatment at 100 or 120° C . for 24 h . The microstructure Reference will now be made to more specific embodi - 35 of 100° C . - derived bituminous coal GQDs ( b - GQDs ) was

ments of the present disclosure and experimental results that investigated by transmission electron microscopy ( TEM ) . provide support for such embodiments . However , Appli FIG . 2D shows the b - GQDs with uniformly distributed sizes cants note that the disclosure below is for illustrative pur - and shapes that are 2 . 96 + 0 . 96 nm in diameter ( FIG . 5A ) . The poses only and is not intended to limit the scope of the fast Fourier transform ( FFT ) pattern of representative claimed subject matter in any way . 40 b - GQDs is inset in the corresponding high resolution TEM

( HRTEM ) image ( FIG . 2E ) . The observed hexagonal lattice Example 1 . Preparation of Graphene Quantum Dots in the FFT images reveals that the b - GQDs are crystalline

from Coal and Coke hexagonal structures . Applicants also observed a few larger dots ( > 20 nm ) that were not fully cut . In addition , Applicants

In this Example , Applicants report a facile approach to 45 saw many crystalline domains within the dots that are linked synthesize tunable graphene quantum dots from various by amorphous carbon ( FIG . 5B ) . This supports the proposed types of coal and coke . Applicants also establish that the micro - structure of coal . An atomic force microscopy ( AFM ) unique coal and coke structures have advantages over pure image of the b - GQDs reveals that their heights are 1 . 5 to 3 spé - carbon allotropes for producing graphene quantum dots . nm ( FIGS . 2F and 5C ) , suggesting that there are 2 to 4 layers For instance , the crystalline carbon within the coal structure 50 of graphene oxide - like structures . is easier to oxidatively displace than when pure spé - carbon As expected , the integrated intensity ratios of amorphous structures are used , resulting in nanometer - sized graphene D bands to crystalline G bands ( IJI , ) for bituminous coal quantum dots with amorphous carbon addends on the edges . is 1 . 06 + 0 . 12 , which increased to 1 . 55 + 0 . 19 after oxidative The synthesized graphene quantum dots , produced in up to cutting into b - GQDs ( FIG . 6A ) , owing to the introduction of 20 % isolated yield from coal and coke in a cost effective 55 defects to the basal planes and the edges . The b - GODs show manner , are soluble and fluorescent in aqueous solution . high solubility in water ( > 15 mg / mL ) , which is attributed to

In this Example , Applicants used an inexpensive facile the introduction of hydrophilic functionalities . This is veri one - step wet - chemistry route to fabricate GQDs from three fied by the high resolution Cis XPS ( FIG . 6B ) where a new types of carbon sources : anthracite ( " a " ) , bituminous coal shoulder at 288 . 3 eV is present , corresponding to the car ( “ b ” ) and coke ( “ c ” ) . FIG . 2A illustrates the macro - scale 60 boxyl groups . The functionalization is also confirmed by the image and simplified nanostructure of coal before any heat increased intensity of C — O , C = 0 and 0 - H vibration treatment . The crystalline domains are connected by ali - modes in the ssFTIR spectrum ( FIG . 6C ) . phatic amorphous carbon chains . Scanning electron micros - The size of b - GQDs can be tuned by varying the oxidation copy ( SEM ) shows that ground bituminous coal ( FIG . 2B ) cutting temperature . GODs from bituminous coal produced and anthracite ( FIG . 3A ) have irregular size and shape 65 at 120° C . ( b - GQDs * ) were characterized by TEM ( FIG . distributions , but coke ( FIG . 3B ) has a regular spherical 7A ) . The size and shape of b - GQDs * are normally distrib shape . uted with an average diameter of 2 . 30 + 0 . 78 nm ( FIG . 7B ) .

13 US 9 , 919 , 927 B2

14 To show the advantage of coal and coke over pure TABLE 5

spé - carbon large flake graphite structures for synthesizing Water content in GODs samples . GQDs , Applicants treated graphite ( Sigma - Aldrich , ca . 150

um flakes ) under the same oxidative reaction conditions Type of GQDs Water content ( wt % ) used for bituminous coal . The solution of bituminous coal 5

a - GODS 13 . 8 + 1 . 3 after the oxidation reaction was clear with little sediment at b - GODs 12 . 5 + 1 . 1 the bottom of the beaker , while the graphite reaction product C - GQDs 11 . 3 + 1 . 3 contained large amounts of black graphite flakes ( FIG . 8A ) . After filtration and washing of the graphite - derived mixture 10 In terms of size and shape , b - GQDs are smaller and more with aqueous and organic solvents , the collected dried uniform than c - GQDs and a - GQDs , which likely originate graphite flakes represent 95 % w / w of starting material . The from the different intrinsic morphologies of the starting SEM images of these treated graphite flakes ( FIGS . 8B - C ) coals . The yields of isolated GQDs from these three carbon show that they retain their original size and structure with sources are 10 to 20 wt . % ( noting that oxidation has makes 100 um . This is because me large graphite structure 15 increased the weight of the final structures ) . flakes > 100 um . This is because the large graphite structure usually requires stronger oxidative reaction conditions , such The photophysical properties of the GQDs were investi as KMnO4 with H3PO4 and H2SO4 that were used for gated by ultraviolet - visible ( UV ) spectroscopy , photolumi synthesizing graphene oxide . The disordered configuration nescence ( PL ) spectroscopy and time - correlated single - pho and small crystalline domains that appear in coal confer ton counting spectroscopy . FIG . 13A shows the PL emission advantages over graphite , such as easy dispersion , exfolia - 20 spectra of a - GQDs , b - GQDs * and C - GQDs excited at 345 tion , functionalization and chemical cutting . Indeed , the nm . The corresponding UV absorption is depicted in FIG . stronger KMnO4 / H3PO4 / H2SO4 conditions can afford 14A . The emission maxima of a - GQDs , c - GQDs and GQDs from coal , as shown in FIG . 8D . However , the b - GQDs * solutions are at 530 nm , 480 nm and 450 nm , workup is more laborious for the removal of the manganese corresponding to the orange - yellow , green and blue fluores salts . When using fuming sulfuric acid and fuming nitric 25 cence , respectively , shown in the inset photograph of FIG . acid , higher degrees of exfoliation and oxidation of the final 13A . The PL mechanism of GQDs is affected by their size , GODs were attained . zigzag edge sites and the defects effect . Applicants note that

the PL intensities follows the trend of a - GQDs > c - GQDs > b GQDs were also synthesized from coke and anthracite GQDs * , the same trend as their sizes and Raman I , IG using the same method that was used for bituminous coal . 30 values . This is consistent with other work showing that GQDs from coke ( c - GQDs ) and anthracite ( a - GQDs ) were larger GQDs with higher defects usually give enhanced PL characterized using the same analytical techniques as used intensity with b - GQDs . The TEM image of c - GQDs ( FIG . 9A ) shows The quantum confinement effect is a major property of a uniform size of 5 . 8 - 1 . 7 nm ( FIG . 10A ) . The a - GQDs were quantum dots that has a size dependent effect on their PL in a stacked structure with a small round layer atop a larger 35 properties . Smaller quantum dots usually lead to a blue thinner layer ( FIG . 9B ) . The stacked structure was further shifted emission . To confirm the quantum confinement confirmed by AFM ( FIGS . 10B - C ) . The height profile shows effect , Applicants plotted the PL emission wavelength vs . the several areas with two adjacent peaks in which the higher size of the dots , as shown in FIG . 13B . When the size of the peak is 1 to 2 layers higher than the base layer . The average dots changed from 2 . 96 nm ( b - GODs ) to 2 . 30 nm diameter of the larger stacks of a - GODs is 29 + 11 nm ( FIG . 40 ( b - GQDs * ) , the emission wavelength blue shifted from 500 10D ) . HRTEM images of c - GOD and a - GOD with the nm to 460 nm . This suggests that these carbon dots are corresponding FFT pattern inset both show crystalline hex - quantum dots . agonal structures ( FIGS . 9C - D ) . Both c - GQDs and a - GQDs PL emission was found to be pH - dependent . A gradient show high solubility in water . In addition , their Raman , PL intensity change of b - GQDs with pH is shown in FIG . XPS , and ssFTIR spectra ( FIGS . 11A - C ) are similar to those 45 13C . The intensity maximizes at pH 6 and 7 . A red shift from

500 nm to 550 nm with decreasing intensity was observed as of b - GQD . The Id ratios of the coal and corresponding the pH changed from 6 to 3 . When the pH increased from 7 GQDs are summarized in Table 4 . to 10 , the PL intensity decreased and blue shifted to 450 nm . FIG . 13D reveals the excitation - emission contour maps of TABLE 4 50 b - GQDs in buffered solutions of NaOAc / HOAC ( pH 3 ) ,

Summary of I , / Ig for carbon sources and corresponding GQDs . NaH PO / NaOH ( PH 7 ) and NaHCOz / NaOH ( pH 11 ) . The Stokes shift obtained from excitation / emission peaks in the

Materials IDIG contour map was ca . 110 nm , attributed to the regular distribution of GQDs . In acid and neutral pH environments , Anthracite 1 . 50 + 0 . 11

a - GQDs 1 . 90 + 0 . 22 the excitation wavelength maximizes at 380 to 400 nm , Bituminous coal 1 . 06 = 0 . 12 while in alkaline solution , a new peak of PL excitation ( PLE ) b - GODs 1 . 55 + 0 . 19 appears at 310 to 345 nm . It is suspected that the excitation Coke 1 . 02 + 0 . 15 C - GODs 1 . 28 0 . 18 band from 380 to 400 nm corresponds to the excitation of an

aggregated state and the band at 310 to 345 nm corresponds 60 to the non - aggregated state . The deprotonation of carboxyl

Oxidative ( in air ) and non - oxidative ( in argon ) thermal groups of GQDs in alkaline solution increases the electro gravimetric analysis ( TGA ) were performed on the GODs static repulsions between them , overcoming the trend of ( FIG . 12 ) . GQDs tested in air tended to have higher weight aggregation through layer - layer stacking . The aggregation in loss and were less stable than those tested in argon using the acid / neutral solution , however , reduces the band gap and same temperature program . The difference in weight loss of 65 consequently a red - shift excitation is observed . the GQDs is attributed to their different oxidation levels . The T he corresponding Jablonski diagram based on the con water content of GQDs is summarized in Table 5 . tour map is depicted in FIG . 14B . A 0 . 66 eV difference in

15

10

US 9 , 919 , 927 B2 16

absorption is observed between the non - aggregated and In a scale - up procedure , 30 g of coal ( e . g . , anthracite ) or aggregated states , which leads to different emission energy coke was first suspended in 600 mL of concentrated sulfuric gaps . A photon screening effect is also seen in the contour acid . The reaction was then stirred and 200 mL of nitric acid maps showing that the emission wavelength of b - GQDs is was slowly added into the solution in 10 portions . Each excitation - independent . At the same pH environment , no 5 portion was added in every other 10 min ( explosion can apparent PL emission peak shift is observed when b - GODs happen if more nitric acid is added for each time ) . The are excited from 300 to 400 nm , which is different from mixture was then stirred and heated in an oil bath at 120° C . other reported GQDs . Without being bound by theory , this is for 48 h . The solution was cooled to room temperature and thought to be due to the more uniform size of the synthesized poured into a beaker containing 2 L ice , followed by adding b - GQDs . NaOH until the pH was 7 . The beaker was in a bucket full

The PL intensity of GQDs decreased while the quantum of ice while adding NaOH to balance the generated heat . The yield ( QY ) increased as the solution was gradually diluted neutral mixture was then filtered through a filter paper ( Cat . with DI water from a concentration of 3 mg / mL while No . 1002150 ) and the filtrate was purified using a tangential keeping the pH constant at 6 ( FIG . 14C ) . A slight blue shift 15 flow filtration system ( Krosflo Research Iii , molecular of the PL intensity maximum was observed when the weight cutoff is 3 kD ) for 5 days . After purification , the solutions were diluted , attributed to the lower aggregation of solution was concentrated using rotary evaporation to obtain GODs within the diluted solutions , thus affording higher solid GODs . band gaps . The relative QYs of different concentrations are summarized in FIG . 14D . The lower QY at higher GQDs 30 Example 1 . 2 . Materials concentration may be attributed to the aggregation quench ing effect from stacking of polyaromatic structures . Anthracite ( Fisher Scientific , Cat . No . 898806 ) , bitumi

The time - resolved photoluminescence decay profiles of nous coal ( Fisher Scientific , Cat . No . 998809 ) , coke ( M - I b - GOD at pH 3 , 7 and 11 are shown in FIGS . 15A - C . The SWACO , Product Name : C - SEAL ) , graphite ( Sigma - Al corresponding lifetimes , calculated by fitting to exponential 25 drich , Cat . No . 332461 , ca . 150 um flakes ) , H . SO . ( 95 % functions using iterative reconvolution , are summarized in 98 % , Sigma - Aldrich ) , HNO3 ( 70 % , Sigma - Aldrich ) , H3PO4 Table 6 . ( 285 % , Sigma - Aldrich ) , and KMnO4 ( Sigma - Aldrich ) were

used as received unless otherwise noted . Polytetrafluoroeth TABLE 6 lyene ( PTFE ) membranes ( Sartorius , Lot No . 11806 - 47 - N ) Lifetime calculations from the time - resolved decay profiles of b - GODs .

Percent a ge age ( % )

12

uct No . 1 - 0150 - 45 ) were used to purify the graphene quan tum dots ( GQDs ) . Mica discs ( product # 50 ) were purchased from Ted Pella , Inc . Ti

( ns )

Percent age age ( % )

T2 ( ns )

Percent - Ave . age age ? I ( % ) ( ns )

T3 ( ns ) pH pH

3 0 . 26 0 . 02 18 1 . 01 + 0 . 03 40 3 . 83 + 0 . 05 42 2 . 06 35 Example 1 . 3 . Sample Characterizations 7 0 . 49 + 0 . 0522 1 . 31 + 0 . 08 38 4 . 54 + 0 . 0940 2 . 42 11 0 . 89 + 0 . 01 51 3 . 75 + 0 . 04 49 2 . 29

Scanning electron microscopy ( SEM ) was performed on a FEI Quanta 400 high resolution field emission SEM , 5 nm The observed Ti ( < 0 . 5 ns ) at pH 3 and 7 is thought to be Au was sputtered ( Denton Desk V Sputter system ) on the due to the photoluminescence decay of the aggregated state , 40 coal or coke surface before imaging . The high - resolution which is not present in alkaline solution . For pH 7 , the

lifetime of tz ( > 3 ns ) is longer , which accounts for the higher transmission electron microscope ( TEM ) images were taken using a 2100F field emission gun TEM with GODs directly PL emission at neutral pH as shown in FIG . 13B . The

photostability of the GQDs was tested and is shown in FIG . transferred onto a C - flat TEM grid . The atomic force micro 151 . No rapid photobleaching was observed from any of the 45 scope ( AFM ) image was obtained on a Digital Instrument three GQDs within 2 h . This is far more stable than in the Nanoscope IIIA AFM . The GQDs aqueous solution was comparison experiment using fluorescein . spin - coated ( 3000 rpm ) on a freshly cleaved mica substrate

In sum , Applicants have developed a facile approach to and dried at room temperature before imaging . X - ray pho prepare different nanometer - sized graphene quantum dots toelectron spectroscopy ( XPS ) spectra were measured on a from various coals and coke and established that the unique 50 PHI Quantera SXM scanning X - ray microprobe with 45° structure of coal is advantageous for making GODs . The takeoff angle and 100 um beam size . The pass energy for specific methodologies used are summarized herein . surveys was 140 eV and 26 eV for high resolution scans .

Raman microscopy was performed with Renishaw Raman Example 1 . 1 . Fabrication of GQDs from Coal and microscope using 514 - nm laser excitation at room tempera

Coke 55 ture . UV - Visible spectra were recorded on a Shimadzu UV - 2450 UV - Vis spectrophotometer . Steady state photolu

In a typical procedure , 300 mg of coal or coke was minescence spectra were obtained in a HORIBA Jovin Yvon suspended in concentrated sulfuric acid ( 60 mL ) and nitric Fluorolog 3 , with excitation at 370 nm . Time - resolved acid ( 20 mL ) . This was followed by cup sonication ( Cole studies was performed using an Edinburgh Instruments Parmer , model 08849 - 00 ) for 2 h . The reaction was then 60 OD470 single - photon counting spectrometer with a high stirred and heated in an oil bath at 100° C . or 120° C . for 24 speed red detector , and using a 370 nm picosecond pulse h . Next , the solution was cooled to room temperature and diode laser . poured into a beaker containing 100 mL ice , followed by adding NaOH until the pH was 7 . The neutral mixture was Example 1 . 4 . Relative Quantum Yield Calculation then filtered through a 0 . 45 um polytetrafluoroethylene 65 ( PTFE ) membrane and the filtrate was dialyzed in 1000 - Da The quantum yields of the graphene quantum dots were dialysis bag for 5 d . calculated with the following formula :

0 ; = 7 , 1 - 10 - Ai nos

US 9 , 919 , 927 B2 17 18

cated in 0 . 2 M NaOH for 2 h . Next , the GQDs were hydrothermally treated in Teflon - sealed autoclave for 10 h at 200° C . After that , the solution was dialyzed for 1 day . The resulting pH is 7 after dialysis .

The spectra in FIG . 22 and the comparative chart in Table In this formula , 0 , = 1 is the normalized quantum yield of 7 show that the quantum yield of GQDs improved signifi

reference . In this work , 0 . 125 mg / mL b - GQDs aqueous cantly after hydrothermal treatment . solution was used as the reference . 0 , is the relative quantum yield with respect to the reference . The integrated intensities TABLE 7 . ( area ) of sample and reference are I , and I , , respectively . A , 10 – and A , are the absorbance . n ; and n , are the refractive indices Comparison of GODs Ouantum Yield after Hydrothermal Treatment .

of the samples and reference solution , respectively . OY at 300 nm OY at 345 nm

Example 1 . 4 . Energy Gap Calculation Samples Qya Qyo ya Qyo 15

10 cu Oy 0 . 267 As - prepared 0 . 188 0 . 274 0 . 193 The energy gaps of the graphene quantum dots were Improved QY 5 . 33 5 . 33 3 . 77 3 . 77 4 . 73 4 . 73 3 . 34 3 . 34 calculated with the following formula :

Rhodamine B ;

E = hca bFluorescein

In this formula , h is the Planck constant , c is the speed of 20 In this Example , Applicants improved the quantum yield light , and à is the wavelength of absorption or emission . of coal - derived graphene quantum dots ( GQDs ) by hydro

thermal treatment . Hydrothermal treatment of nanoparticles Example 2 . Preparation of Graphene Quantum Dots in concentrated NaOH solution has been shown to be an

from Anthracite ( a - GQDs ) effective approach to remove the surface impurities of 25 nanoparticles . Chem . Mater . 21 , 3917 - 3923 ( 2009 ) . As

In this Example , graphene quantum dots were prepared shown in the PL emission in FIG . 22A , the PL intensity of from anthracite . 30 g of anthracite ( Fisher Scientific , Cat . GQDs increased dramatically after the hydrothermal treat No . 898806 ) was suspended in 600 mL of concentrated ment . In addition , as summarized in Table 7 , the quantum sulfuric acid ( 95 - 98 % , Sigma Aldrich ) . The reaction was yield ( QY ) after hydrothermal treatment increased 20 times . then mechanically stirred . Next , 200 mL of nitric acid ( 70 % , 30 Such observations were similar to the quantum yield of Sigma Aldrich ) was slowly added into the slurry in 10 PEGylated GQDs made from graphite ( 6 % ) . portions over 100 min ( caution : the rate of nitric acid Without being bound by theory , it is envisioned that the addition to sulfuric acid should be controlled to minimize improved quantum yield is attributed to the removal of uncontrollable exothermic events ) . The mixture was then surface impurities , which increases the non - radiative relax mechanically stirred and heated in an oil bath at 120° C . for 35 ation of GQDs . However , the removal process can also be 48 h . The solution was cooled to room temperature and due to the hydrothermal treatment , including treatment with slowly poured into a beaker containing 2 L of crushed ice . aqueous NaOH . The beaker was then placed in a bucket of ice for cooling , Carbon - nanoparticles with hetero - element doping have followed by adding NaOH solid until the pH was 7 . The also been shown to increase the QY . Kang et al . , J . Mater . neutralized mixture was then filtered through filter paper 40 Chem . A . ( 2014 ) ( DOI : 10 . 1039 / C4TA00860J ) . The doping ( Cat . No . 1002150 ) and the filtrate was purified using process can be achieved by hydrothermally treating the tangential flow filtration system ( Krosflo Research lii , GQDs with NaHS , NaHSe or NaH2PO3 , which act as molecular weight cutoff is 3 KD ) for 5 days . After purifica - reducing dopants . By using the hydrazine reduction reaction tion , the solution was concentrated using rotary evaporation ( Carbon 49 , 3019 - 3023 ( 2011 ) ) , the GQDs can also be ( 50° C . under vacuum ) to obtain 5 . 3 g of solid a - GQDs . 45 doped with nitrogen . These approaches can increase the QYs FIGS . 16 - 21 provide data relating to the characterization through introduction of heteroatoms .

of the formed a - GODs on the 5 g scale ( i . e . , a yield of 5 . 3 Without further elaboration , it is believed that one skilled g ) . In particular , FIG . 16 shows a photo of the produced in the art can , using the description herein , utilize the present a - GODs . TEM images in FIGS . 17B - C show that the pro - disclosure to its fullest extent . The embodiments described duced a - GQDs have a graphitic structure . In addition , the 50 herein are to be construed as illustrative and not as con size distribution in FIG . 17C shows that the a - GQDs have straining the remainder of the disclosure in any way what sizes that range from about 1 nm to about 6 nm . Likewise , soever . While the embodiments have been shown and the Raman , XPS and FTIR spectra in FIGS . 18 - 20 show that described , many variations and modifications thereof can be the produced GODs are oxidized . In addition , the photo made by one skilled in the art without departing from the physical characterizations in FIG . 21 show that the produced 55 spirit and teachings of the invention . Accordingly , the scope a - GQDs are fluorescent . of protection is not limited by the description set out above ,

but is only limited by the claims , including all equivalents of Example 3 . Improving the Quantum Yield of the subject matter of the claims . The disclosures of all

Coal - Derived Graphene Quantum Dots patents , patent applications and publications cited herein are hereby incorporated herein by reference , to the extent that In this Example , Applicants improved the quantum yield they provide procedural or other details consistent with and

of coal - derived graphene quantum dots ( GQDs ) by hydro - supplementary to those set forth herein . thermal treatment .

Graphene quantum dots were synthesized by sonicating What is claimed is : 3 . 0 g of anthracite in 60 mL of 95 % sulfuric acid and 20 mL 65 1 . A method of making graphene quantum dots from a of 70 % nitric acid . Next , the solution was heated to 80° C . carbon source , wherein the method comprises : for one day . Thereafter , the as - prepared GQDs were soni exposing the carbon source to an oxidant ,

20 US 9 , 919 , 927 B2

19 wherein the carbon source is selected from the group 20 . The method of claim 19 , wherein the reducing com

consisting of coal , coke and combinations thereof , prises exposure of the formed graphene quantum dots to a wherein the exposing comprises stirring and heating the reducing agent .

carbon source in the presence of the oxidant , and 21 . The method of claim 19 , wherein the reducing agent wherein the exposing provides oxidative reaction con - 5 on 5 is selected from the group consisting of hydrazine , sodium

borohydride , heat , light , sulfur , sodium sulfide , sodium ditions sufficient to result in formation of the gra hydrogen sulfide , and combinations thereof . phene quantum dots from the carbon source . 22 . The method of claim 1 , wherein the formed graphene 2 . The method of claim 1 , wherein the carbon source quantum dots have diameters ranging from about 1 nm to comprises coal , wherein the coal is selected from the group about 50 nm . consisting of anthracite , bituminous coal , sub - bituminous 10 23 . The method of claim 1 , wherein the carbon source is coal , metamorphically altered bituminous coal , asphaltenes , bituminous coal , and wherein the formed graphene quantum asphalt , peat , lignite , steam coal , petrified oil , and combi dots have diameters ranging from about 1 nm to about 5 nm . nations thereof . 24 . The method of claim 1 , wherein the carbon source is

3 . The method of claim 1 , wherein the carbon source anthracite , and wherein the formed graphene quantum dots 15 have diameters ranging from about 10 nm to about 50 nm . comprises coke .

4 . The method of claim 1 , wherein the carbon source 25 . The method of claim 1 , wherein the carbon source is comprises bituminous coal . coke , and wherein the formed graphene quantum dots have

5 . The method of claim 1 , wherein the carbon source diameters ranging from about 2 nm to about 10 nm . comprises anthracite . 26 . The method of claim 1 , further comprising a step of

6 . The method of claim 1 , wherein the oxidant comprises 20 controlling the diameter of the formed graphene quantum an acid . dots .

7 . The method of claim 6 , wherein the acid is selected 27 . The method of claim 26 , wherein the controlling from the group consisting of sulfuric acid , nitric acid , comprises selecting the carbon source . CO 28 . The method of claim 27 , wherein the selected carbon phosphoric acid , hypophosphorous acid , fuming sulfuric acid , hydrochloric acid , oleum , chloro sulfonic acid , and 25 source is bituminous coal , and wherein the formed graphene combinations thereof . quantum dots have diameters ranging from about 1 nm to

8 . The method of claim 1 , wherein the oxidant is a mixture about 5 nm .

of sulfuric acid and nitric acid . 29 . The method of claim 27 , wherein the selected carbon 9 . The method of claim 1 , wherein the oxidant is selected 30 source is anthracite , and wherein the formed graphene

from the group consisting of potassium permanganate , 30 quantum dots have diameters ranging from about 30 nm to sodium permanganate , hypophosphorous acid , nitric acid , about 50 nm . sulfuric acid , hydrogen peroxide , and combinations thereof . 30 . The method of claim 27 , wherein the selected carbon

10 . The method of claim 1 , wherein the oxidant is a source is coke , and wherein the formed graphene quantum mixture of potassium permanganate , sulfuric acid , and hypo - 35 dots have diameters ranging from about 2 nm to about 10 phosphorous acid .

11 . The method of claim 1 , wherein the exposing com 31 . The method of claim 1 , wherein the formed graphene prises sonicating the carbon source in presence of the quantum dots have a crystalline hexagonal structure . oxidant . 32 . The method of claim 1 , wherein the formed graphene

12 . The method of claim 1 , wherein the heating occurs at 20 quantum dots have a single layer . temperatures of at least about 100° C . 0 33 . The method of claim 1 , wherein the formed graphene

13 . The method of claim 1 , wherein the heating occurs at quantum dots have multiple layers . temperatures ranging from about 100° C . to about 150° C . 34 . The method of claim 33 , wherein the formed graphene

14 . The method of claim 1 , further comprising a step of quantum dots have from about two layers to about four separating the formed graphene quantum dots from the 45 layers . oxidant . 45 35 . The method of claim 1 , wherein the formed graphene

15 . The method of claim 14 , wherein the separating quantum dots are functionalized with a plurality of func ? comprises : tional groups .

neutralizing a solution comprising the formed graphene 36 . The method of claim 35 , wherein the functional quantum dots , groups are selected from the group consisting of amorphous

50 filtering the solution , and carbon , oxygen groups , carbonyl groups , carboxyl groups , dialyzing the solution . esters , amines , amides , and combinations thereof . 16 . The method of claim 1 , further comprising a step of 37 . The method of claim 35 , wherein the formed graphene

enhancing a quantum yield of the graphene quantum dots . quantum dots are edge functionalized with a plurality of functional groups . 17 . The method of claim 16 , wherein the enhancing 55

occurs by hydro thermal treatment of the graphene quantum 55 38 . The method of claim 37 , wherein the formed graphene quantum dots comprise oxygen addends on their edges . dots , treatment of the graphene quantum dots with one or 39 . The method of claim 37 , wherein the formed graphene more bases , treatment of the graphene quantum dots with

one or more hydroxides , treatment of the graphene quantum quantum dots comprise amorphous carbon addends on their dots with one or more dopants , and combinations thereof . edges .

18 . The method of claim 16 , wherein the enhancing 60 40 . The method of claim 1 , wherein the formed graphene occurs by hydro thermal treatment of the graphene quantum quantum dots are utilized in road stickers , road signs , dots . coatings , clothing , paints , photographic processing materi

19 . The method of claim 1 , further comprising a step of als , and combinations thereof . reducing the formed graphene quantum dots . * * * * *

a hypo - 35 nm .

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IIIIIIIIIII I IIIIIIIIIIIII - patentimages.storage.googleapis.com · US 9 , 919 , 927 B2 Page Doma 2 of the present disclosure further comprise a step of enhanc ing a quantum yield