PHOTOCATALYSIS OFCO2 REDUCTION USINGCOBALT-BASED METALORGANICFRAMEWORKSMok Hui MinU1421075KChemical and Biomolecular EngineeringCN Yang Scholar !rogramme Undergradua"e #eearch E$%erience&CY1400' #e%or" 2015Men"ored B()*ocia"e !ro+eor ,imo"h( ,an ,ha"" Yang-r Boon Ng1 | P a g eAbstrat--------------------------------------------------------------------------------------------!I"tr#$%t"--------------------------------------------------------------------------------------! C%rre"t te'"#(#g&es &" CO2 a)t%re-----------------------------------------------! C%rre"t te'"#(#g&es &" CO2 se)arat"-------------------------------------------* MOFs a"$ CO2 a)t%re----------------------------------------------------------------+ Cata(,t& )r#)ert&es #- MOFs--------------------------------------------------------. A&/s---------------------------------------------------------------------------------------.Met'#$#(#g,-------------------------------------------------------------------------------------0 S,"t'es&s #- MOFs--------------------------------------------------------------------0 Ge"erat" #- #- CO2 Is#t'er/s---------------------------------------------------1 P'#t#ata(,s&s #- CO2 re$%t" %s&"g 2&s&b(e (&g't---------------------------3Res%(ts a"$ D&s%ss"------------------------------------------------------------------------3 S#(2#t'er/a( reat"s-------------------------------------------------------------3 C'arater&sat" #- 4C#5b),65b$67----------------------------------------------892 | P a g eC#"te"t Page P#:$er ;-Ra, D&enerallytheycontainsilicon, aluminiumandoxygen in their framework. Theycontaincations, water and4or othermolecules within their pores. :defining feature of 9eolites is that their frameworks are made up of a tetrahedron geometrywith the metal atoms surrounded by ) oxygen atoms *-2+ This framework creates cavities ofvarious si9es.&embranes%embranes, made of polymers or ceramics, are used to separate CO2 from other gases andto allow CO2 to be absorbed from a gas stream into a solvent *-2+.CO2is separated fromother gaseous molecules according to their relative solubility and diffusivity in the polymerand their si9e, which then determines their permeability across the membrane *-5+. owever,theuseof membranesforCO2capturestill doesnot allowfor ahighdegreeofCO2separation due to similarity in si9e between CO2 and 72. 7ew materials are required for moreeffective separation of CO2 using membranes.III MOFs and CO2 Capture#nrecent years, anewclassof crystallineporousmaterials, metal!organicframeworks'%O&s(, have been discovered to hold much potential for CO2 capture. %O&s can be usedas a solid sorbent, or used to synthesise %O&s!based membranes. %O&s are constructedusing metal ions such as Ti, =n or Co which are coordinated to organic linkers *-)+.Thechoice of the metal and linker has significant effects on the properties of the particular %O&. %O&s have extremely large internal surface!areas which create many adsorption sites thatallowforhigh!densitystorage.Theirstructurescanalsobeeasilyvariedandtailoredforvarious functions by using different metals and linkers to allow for variation in pore si9e andporesurfaceproperties. #naddition, theyarealsoveryrobust, withhighmechanical andthermal stabilities. *-)+*-/+ 6 | P a g e:s such, the structural tunability and stability of %O&1 allows them to be optimised for CO2capture. Theopennessof the%O&structuresalsoallowfor quickuptakeofCO2andremoval of CO2. *-8+ %O&sareconstructedbyaself!assemblyreactionbetweenthemetal ionsandorganiclinkers in polar solutions to form an extended structure under mild conditions.MOROME ICatal!tic"roperties o# MOFs Catalyticproperties can be conferredto%O&sbyimmobili9ingphotocatalyticsites into aporous %O& matrix. ?ifferent type of catalytic sites can be introduced into %O&s by varyingthetypeof metal ionororganicligandusedtoconstruct the%O&matrix. &orexample,porphyrinsusedasbuildingblocksfor%O&sallowsforvisiblelight photocatalysisof thegeneration of hydrogen from water *-;+. #n this case the %O& uses :l as the metal ion andthe linker consists of four ben9oate groups around a central porphyrin core *-;+.@y initiating desirable photocatalytic properties into a %O&structure, %O&s could bespecifically designed for the reduction of CO2 in addition to carbon capture. ,ith the ease intailoring and synthesising the %O& structure, combined with the plethora of combinations ofligand and metal ion, %O&s show much prospect in CO2reduction. Aeduction ofCO2intocarbon!based organic products such as C), which can act as energy sources, directly uponcapture also reduces the need for storage of CO2. $ | P a g eF&g%re 2> C#/b&"at" #- #rga"& (&"=ers a"$ /eta( "s t# -#r/ a" e@te"$e$ MOF str%t%re 42*7 %i&s?espitethewidearrayof existing%O&sfor effectiveCO2capture, thestudyof %O&BsapplicationstophotocatalyticreductionofCO2isstill widelyunexplored. #nfact, manyconventional photocatalystsofCO2reduction, suchas TiO2and=n2>eO)areactiveonlyunder CD light. *-;+*-.+ #t is pertinent to develop photocatalysts which can reduce CO2 evenunder visible light for more efficient reduction of CO2. This pro$ect aimed to explore the field of photocatalytic reduction of CO2using visible lightthrough the synthesis of a %O& which could effectively serve the purpose of CO2captureand photocatalytic reduction of CO2 under visible light. The scope of work for this pro$ect wassegmented into 5 main phases" &irstly, the experimentation on various combinations of metalions and ligands to synthesis colored %O&s which shows potential for photocatalytic activityunder visiblelight. 1econdly, efficiencyofCO2uptakeof the%O&swas assessedbymeasuring the CO2 isotherms. Thirdly, the photocatalytic properties of the %O& under visiblelight was investigated by irradiating the %O& with Ee light source. &'T(ODO#O)*I '!nthesis o# MOFs Syntesis of cru%e pro%uctFanthanides with an oxidation state of5 were postulated to form %O&s with one organicligand and transition metals with an oxidation state of 2 were postulated to form %O&s withtwo organic ligands. ,hile products from a variety of both combinations were created in anattempt tosynthesise%O&structures, onlyCo!based%O&swerefoundtobecolored.6hotocatalytic activity requires for a %O& to be colored, thus we narrow down our focus toonly Co! based %O&s.&or this pro$ect, the general synthesis procedure for the Cobalt %O&s was to add Co'xmmol(, to organic linkers : 'ymmol, y=0, x or 0.5 x(, @ 'zmmol, z=0, x or0.5 x( to yield *Co':(y'@(9+, where : and @ represented either aibn, bpy, or 2bdc. Cp to( | P a g eF&g%re !> F(#:'art s'#:&"g 2ar%s stages #- )r#Aettwo linkers were used to synthesise Co!based %O&s. @y varying :, @,x, y and z,different combinations were created in an attempt to synthesise different Co!based %O&s.The mixture was then added into a solution containing ?imethylformamide '?%&( '-2ml(. :llchemicals were purchased from commercial suppliers and used without further purification. The above mixture was stirredat roomtemperature for -/minutes,sealed in a 25!mFTeflon!lined stainless steelautoclave and heated at -82GCfor three days underautogenouspressure. :ll aciddigestion bombs werepurchased from Fatech1cientific 1upplies 6te Ftdwherethe25mF Tefloncupswere soaked in an acid bath containing /% HCl for two days prior to each synthesis. Thereaction system was subsequently cooled to room temperature over 8 hours.Purification of cru%e pro%uct:fter the reaction, the resultant suspension was filtered using vacuum filtration. ?uring thefiltration, the suspension was rinsed with a small amount of ethanol to ensure that there wereno impurities left behind. The 25mF Teflon flask was also rinsed with ethanol a few times toensure that there were no crystals left behind.Crystallo!rapic analysis6owder E!ray diffraction patterns of all samples were recorded on a @ruker 6owder E!ray?iffraction1ystem'%6?( intherangeof /o to/2o. Cnit!cell crystallographicdataof allsamples were acquired at -/2 H on a @ruker kappa :63E##!CC? area detector instrumentwith %o HI monochromated radiation 'JK2.;-2;5 L( the M!N scan technique.II)eneration o# CO2 Isother&s* | P a g eF&g%re *> 2!/L TeB#"-(&"e$ sta&"(ess stee( a%t#(a2eF&g%re +> 5a6 Mag"et& S%s)e"s" Ba(a"e5b6 Me'a"&s/ #- a Mag"et& S%s)e"s" Ba(a"e&orthisstep,themainapparatususedwasamagnetic suspension balance '%1@(, which allowed for the contactless weighing of sampleshightemperature'2)5O5 F(#:'art s'#:&"g a )#s&t&2e test res%(t -#r )'#t#ata(,s&s #- CO2 re$%t"*Co'bpy('bdc(+%O&, usingtheexperimental procedures describedin themethodologysection. Sample Cobalt0III2 Clori%e(exay%rate /it Res%(ts #- test -#r )'#t#ata(,t& )r#)ert&es #- 4C#5b),65b$67:sobservedfromfigure-5, *Co'bpy('bdc(+ remainedpurpleuponirradiationwithvisiblelight. indicating that no reaction occurred between the %O& and TO3:. #t is thus unable toact as a photocatalyst for the reduction of CO2 using T3O:4alcohols as electron donors.CONC#USIONI '7A#UATION O. R'SU#TSTwo reported Cobalt based %O&s,*Co'aibn('bdc(+ and *Co'bpy('bdc(+ ,were synthesisedwhere *Co'aibn('bdc(+ quickly lost its crystalinity after removal of maiden solvent. ?ue to theinstability of *Co'aibn('bdc(+ in air, it is unsuitable for CO2capture. Thus, the focus of thispro$ect was to focus on further characterisation on *Co'bpy('bdc(+. TheCO2isothermfor*Co'bpy('bdc(+showedthat it effectivelycapturedCO2at ambientcondition. #t was speculated that Co would have light absorption in the visible light spectrumwhich can be used to create electron hole pair system for T3O:, where the electrons can beused for photocatalysis. owever, it displayed a negative result when tested for itsphotocatalytic properties despite having colored crystals.*Co'bpy('bdc(+ is thus unsuitablefor use as a photocatalyst for the reduction of CO2 to C) under visible light.#nconclusion, thetwoCobalt!based%O&ssynthesi9edinthispro$ect wereshowntobeunsuitable for photocatalysis of CO2 reduction. *Co'aibn('bdc(+is unsuitable for CO2 capture,and thus CO2reductiondue to the instability of the %O&s formed with the organic linkersused. *Co'bpy('bdc(+ is unsuitable due to its lack of photocatalytic activity under visible light.They could however, form stable %O&s with other organic ligands. ,hile *Co'bpy('bdc(+ isshowntobeunresponsivetovisiblelight, it couldstill adsorblight intheCDregion. #naddition, sinceonlytwocombinationsof Co!based%O&sweresynthesi9ed, thelackofsuccess in generating a suitable Co!based %O& may not be due to the use of unsuitableligands, but due to the wrong ratio of the metal ions and organic ligands used. 1table andphotocatalytic%O&scouldalsohavebeengeneratedwiththeuseof morethan-or 2organic ligands.II .UTUR' @ORA1$ | P a g eTheuseof %O&s for thephoto!catalysis of CO2reductionstill holds muchuntappedpotential. Three possible ways of expanding on this pro$ect are listed below.&irstly,theisothermmeasurementsconductedinthispro$ect canberepeatedtoensureconsistent results and further analysed for the CO2 capturing efficiency. 1econdly,agreater varietyof metalsandorganiclinkerscouldhavebeenused. #nthispro$ect, only two organic linkers were used and this greatly limited the number ofcombinationsof metalsandorganiclinkersthat couldbeusedtogenerate%O&s. Othergood candidates such as 2!aminoterephathalic acid or ),)Ba9opyridine can be used.Thirdly, only two combinations of Co!based %O&s are synthesised in this pro$ect. : greaternumber of combinations with different proportions of Cobalt to organic ligands could havebeen used to generate %O&s.Fastly, accurate photocatalytic efficiency of a %O& can be measured using a photocatalyticset up in which the amount of C)produced per sample can be evaluated with the use ofgas chromatography.ACANO@#'D)'&'NTS# wouldliketothankmymentor, :ssociate6rofessor TimothyTanfor theopportunitytoembark on this pro$ect.#n addition, # greatly appreciate the efforts of our collaborating supervisor, ?r @oon 7g, inguiding and supervising me throughout the pro$ect.&inally, # would also like to thank the C7T16 director, :ssociate 6rofessor Tan Choon ongwho has provided much encouragement and support for my research pursuits.R'.'R'NC'S-( 1. Eiang, T. e, =. =hang, . ,u, ,. =hou, A. Hrishna and @. Chen. Nat. Commun., '22-2(, 5, -larborg, 6., V Uensen, :. ?. '22-2(. Oxy!fuel combustion of solid fuels. %rogress in Energ& and Combustion 'cience, #('/(, /.-!82/eO) nanoribbons toward improved photocatalytic reduction of CO2 into renewable hydrocarbon fuel.Journal of the American Chemical 'ociet&, 2#)')-(, -)5./!-)5.;.25( Aetrieved from http"44www.integral!health!guide.com4powdered!9eolite42)( Aetrieved from http"44theconversation.com4mof!the!chart!why!a!record!breaking!surface!area!matters!