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View Article OnlineView Journal | View Issue

Enhanced electro

aDepartment of Materials Science and Eng

Republic of Korea. E-mail: dslim@korea.a

3290-3272bSchool of Civil, Environmental and Architec

02841, Republic of Korea. E-mail: heedeung

+82-2-3290-4861

Cite this: RSC Adv., 2017, 7, 6229

Received 4th November 2016Accepted 3rd January 2017

DOI: 10.1039/c6ra26287b

www.rsc.org/advances

This journal is © The Royal Society of C

chemical oxidation of phenol byboron-doped diamond nanowire electrode

Choong-Hyun Lee,a Eung-Seok Lee,a Young-Kyun Lim,a Kang-Hee Park,b

Hee-Deung Parkb and Dae-Soon Lim*a

We fabricated a boron-doped diamond nanowire (BDDNW) electrode via metal-assisted chemical etching

(MACE) of Si and electrostatic self-assembly of nanodiamond (ESAND) seeding to provide a large surface

area during the electrochemical oxidation process. The effect of nanostructuring of the BDD surface on

the electrochemical oxidation performance and the current efficiency of the electrode in phenol were

examined. Uniformly covered BDD on nanotextured Si substantially enhanced the electrochemical

activity of the electrode. The effective surface area calculated from cyclic voltammetry (CV) was

enhanced several times compared to that of a conventional planar BDD electrode. The BDDNW

electrode also exhibited greatly enhanced chemical oxygen demand (COD), total organic carbon (TOC)

removal behavior, and current efficiency. Furthermore, because of its excellent oxidation performance,

the BDDNW electrode also exhibited much lower energy consumption in the phenol oxidation process.

1. Introduction

Large amounts of industrial wastewater containing toxic andnondegradable organic compounds have recently been dis-charged into the aquatic environment. For effective remedia-tion of these effluents, some researchers have suggested the useof advanced oxidation processes (AOPs) that mainly utilizehydroxyl radicals (cOH), which are highly oxidative agents.1

Exploiting the powerful oxidation ability of cOH (E0 ¼ 2.80 V),AOPs can nonselectively react and mineralize organiccompounds such as phenols, dyes, pharmaceuticals, herbicidesand surfactants.2–5 Various AOP methods such as the Fentonprocess, ozonation, photocatalysis, ultrasound and electro-chemical oxidation treatments are available for producingcOH.6–10 Electrochemical oxidation process are considered themost promising treatment method because of their high effi-ciency, wide applicability and environmental compatibility.11,12

In an electrochemical oxidation process, various factors suchas the applied current density, electrolytes, pH, operatingtemperature, initial organic concentration and electrode mate-rial can affect oxidation performance.13,14 The oxidation effi-ciency of an organic pollutant during treatment shows anespecially strong dependence on the anode material becausecOH are directly produced on the surfaces of the anode asa consequence of electrochemical water electrolysis.11 Several

ineering, Korea University, Seoul 02841,

c.kr; Fax: +82-2-928-3584; Tel: +82-2-

tural Engineering, Korea University, Seoul

@korea.ac.kr; Fax: +82-2-928-7656; Tel:

hemistry 2017

candidates for the anode material, including Pt, IrO2, SnO2,PbO2, glassy carbon (GC) and boron-doped diamond (BDD),have been investigated.15–18 Among these, BDD has been widelyaccepted as the most powerful anode material because of to itsextremely high overpotential for the oxygen evolution reaction(OER).11,19,20 Additionally, BDD exhibits weak adsorption char-acteristics and tends to be chemically inert; consequently,numerous electrochemical wastewater treatment studies havebeen conducted on various organic oxidation mechanismsinvolving BDD anodes.21–23

Although BDD exhibits outstanding electro-oxidationperformance, its utilization has thus far been limited tolaboratory-scale experiments; its high cost makes it impracticalin real wastewater treatment applications. To increase BDDelectrode productivity and to overcome the drawback of its highcost, extensive effort has been directed toward achievingimproved performance through modication of the conven-tional BDD electrode. The effect of the boron doping concen-tration of BDD on the oxidation of an aromatic compound hasbeen studied by Bogdanowicz et al.24 A higher boron dopinglevel of BDD was observed to lead to changes in diamondcrystallites and in the density of the active sites on the surface,resulting in better oxidation performance. The inuence ofsurface termination of BDD electrodes on organic oxidation hasbeen investigated in several studies.25,26 The O-terminated BDDsurface obtained via anodic polarization exhibits increasedhydrophilicity, resulting in enhanced oxidation power of theanode. Souza et al. investigated the mineralization efficiency of2,4-dichlorophenoxyacetic acid with respect to the sp3/sp2 ratioin BDD electrodes.27 They demonstrated that a higher content ofsp3 diamond leads to more rapid oxidation.

RSC Adv., 2017, 7, 6229–6235 | 6229

Fig. 1 Schematic of the fabrication process for a BDDNW electrode.

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Because the quantity of the produced cOH and its mobilitymainly depend on the anode material, the surface area of theelectrode is a critical factor in determining its oxidationperformance. Although many reviews and research articlesemphasize the effects of a large surface area of electrodes, onlya few studies have focused on the BDD electrode surfacearea.28–30 He et al. fabricated a porous BDD electrode usinga porous Ti substrate and demonstrated its electrochemicaloxidation treatment performance. BDD pores with dimensionson the order of several tens of micrometers provided a largeeffective surface area and promoted current efficiency in thedecomposition of various organic compounds. Nevertheless,fabrication of BDD on a Ti substrate requires long cooling timeat the end of the CVD process because of the large thermalexpansion gap and because of the problem of poorer long-termstability compared to that of Si-based BDDs, which results indelamination of the diamond lm from the substrate due toresidual stress.7,31 Moreover, the porous BDD of He et al. islimited to microsized structures, leaving the correspondingnanostructures, which are expected to exhibit substantiallygreater surface areas, unexplored.

To date, Si-based BDD nanostructures have been fabricatedusing various methods, including reactive-ion etching (RIE) ofdiamond, metal-assisted chemical etching (MACE) of Si, fabri-cation of carbon nanotube (CNT)–diamond hybrid structuresand carbon dioxide activation.32–37 However, even though manytechniques related to the nanostructuring of the BDD surfacehave been reported, these structures have only been applied inelectrochemical sensor applications, not in electrochemicalwastewater treatment processes.

In previous work, we examined the effect of micro-scaledtexturing of BDD surface on dye (methyl orange) oxidation.38

In this work, we demonstrate the electrochemical phenoloxidation performance of nanostructured BDD electrodesfabricated by a simple etching treatment of Si substrates. Weachieved a substantially greater surface area of BDD using theMACE process and electrostatic self-assembly of nanodiamond(ESAND) seeding. Nanocrystalline BDDs were deposited ontoa substrate with a nanotextured Si surface morphology. BDDnanowires (BDDNWs) were thereby formed, providing a muchlarger surface area than the microstructure electrode examinedin our previous work.38 We compared the electrochemicaloxidation performance of the BDD nanowire and of theconventional planar BDD by examining the cyclic voltammetry(CV), chemical oxygen demand (COD), total organic carbon(TOC) and energy consumption of these two electrode materialsin the oxidation of phenol.

2. Experimental procedure

A p-type Si (100) wafer with 0.005 U cm resistivity was used asthe substrate. The Si substrate was cleaned ultrasonically withethanol and deionized water and subsequently immersed in 1%HF solution for 30 min. For Si surface nanotexturing, the MACEprocess was conducted in a solution of 4.5 M HF and 0.01 MAgNO3.39 Prior to chemical etching, the Si substrate wasimmersed in Piranha solution for 1 h to provide a hydrophilic

6230 | RSC Adv., 2017, 7, 6229–6235

surface. The surface-treated Si substrate was dipped into anetching solution for 5 min at 50 �C and then into a 30% HNO3

solution to remove residual silver dendrites.To provide a diamond nucleation site, we seeded nano-

diamonds onto the Si substrate using the ESAND seedingtechnique. The conventional planar Si and nanotextured Sisubstrate were coated with poly(diallyldimethylammoniumchloride) (PDDA) to provide a positively charged surface. Thenegatively charged nanodiamond particles in a poly(sodium 4-styrene sulfonate) (PSS) and nanodiamonds conjugate solutionwere electrostatically attached to the Si surfaces. Furtherinformation on the ESAND seeding method is provided in ourprevious report.40 Aer nanodiamond seeding, the planar BDDand BDDNW electrodes were synthesized by using hot-lamentchemical vapor deposition (HFCVD) at a substrate temperatureof 800 �C for 4 h. As the carbon source, 1 vol% of CH4 in H2 wasfed at a total ow rate of 100 sccm; the diluted B2H6 gasconcentration was maintained at [B]/[C] ratio of 5000 ppm inboth electrodes. The total chamber pressure was maintained atless than 10 kPa. The BDDNW fabrication processes, includingthe nanodiamond seeding process, are depicted in Fig. 1.

Aer deposition, the microstructures and electrochemicalproperties of the BDD nanowire electrode were analyzed. Field-emission scanning electron microscopy (FESEM, Hitachi S-4300) was used to examine the surface morphology. ForRaman spectra analysis, Raman spectroscopy with a 514.5 nmAr-ion laser was used A potentiostat (Princeton AppliedResearch, VersaSTAT3) with a three-electrode cell of platinum,Ag/AgCl and a BDD nanowire electrode, representing thecounter, reference and working electrodes, respectively, wasused for electrochemical analyses.

cOH produced by electrodes was determined by DNPH (2,4-dinitrophenylhydrazine) probe.41 Constant current density of 30mA cm2 was applied in 0.5 M Na2SO4 solution with 5 mMmethanol for 10 min. Formaldehyde was produced by reactingwith methanol and transformed to a formaldehyde derivative by20 mM DNPH (200 mL) with 1 M HCl (50 mL). Formaldehydederivative was measured by Agilent 1260 high-performanceliquid chromatography (HPLC) with UV absorbance at 360 nm.

To evaluate the bulk oxidation performance of the electrode,we constructed a single-compartment electrolytic circulationcell that operates in galvanostatic mode. The BDD nanowireelectrode and a stainless steel plate were used as the anode andthe cathode, respectively; the area of both electrodes was 4 � 4

This journal is © The Royal Society of Chemistry 2017

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cm2. The target organic compound was 1.0 mM phenol in 0.5 MNa2SO4 electrolyte (500 mL). The current density was xed at 30mA cm�2, and the total ow rate was 1 L min�1. During the 5hours electrolysis, 2 mL of samples were extracted. Aer elec-trolysis, the COD (Hach DR-5000), the TOC (Shimadzu TOC-VCPH) and the phenol concentration (HPLC) were determined.

3. Results and discussion

We fabricated conventional planar BDD and BDDNW electrodesvia the ESAND seeding and HFCVD techniques. Fig. 2(a)–(d)shows the surface and cross-sectional microstructures of theelectrodes. Diamond crystals with a size of a few hundrednanometers were formed on planar Si, without formingpinholes. The thickness of the diamond layer in the planar BDDwas approximately 200 nm. In the case of the BDDNW electrode,nanocrystalline BDDs grew well along the etched Si surfaces; theaverage length and thickness of the BDD nanowires were200 nm and 750 nm, respectively. The ESAND method has beenpreviously demonstrated to enable dense nanodiamond seed-ing on a complex nanotextured Si substrate without physicaldamage.36,38 Even though the planar BDD and BDDNW sampleswere fabricated under the same growth conditions, BDDNWexhibited a relatively lower growth rate, as indicated by itssmaller crystal size and smaller lm thickness. In Ramanspectroscopy, both of planar BDD and BDDNW showed intenseand clear nanocrystalline diamond peaks around 1130 cm�1.42

BDDNW showed slightly lower 1332 cm�1 band which

Fig. 2 (a) SEM image of top view of planar BDD, (b) side view of planarBDD, (c) top view of BDDNW, (d) side view of BDDNW and (e) Ramanspectras of electrodes.

This journal is © The Royal Society of Chemistry 2017

attributed to the sp3 crystalline diamond phase and larger Gpeak (1550 cm�1) which attributed to the sp2 amorphouscarbon.43,44 The peaks at 1430 and 1470 cm�1 are related withtranspolyacetylene at grain boundaries which are typicallyobserved in synthetic diamond lm.45 Even though crystallinesp3 diamond phase portion was decreased, a larger crystalpopulation and additional grain boundaries via surface nano-structuring of BDD would enhance its electrochemical proper-ties, as measured on the basis of its electro-oxidationperformance.

Fig. 3 shows the electrochemical properties of the planarBDD and BDDNW electrodes. Cyclic voltammograms obtainedat a scan rate of 50 mV s�1 in 0.5 MH2SO4 are shown in Fig. 3(a).Both planar and BDDNW electrodes exhibit the wide workingpotentials (�2.3 V) and high OER potentials typically observedfor BDD electrodes. The OER potential is important in theelectro-oxidation process because the cOH evolution reactionand the OER are competitive reactions. A higher OER potentialrestrains the oxygen evolution from water electrolysis andproduces more cOH on the surface of the anode. Therefore, BDDexhibits a substantially higher electro-oxidation power thanother electrodes.46,47 The current density of the BDDNW elec-trode is greater than that of the planar BDD electrode because of

Fig. 3 Cyclic voltammograms of planar BDD and BDDNW electrodesin a (a) 0.5 M H2SO4 and (b) 3 M KCl solution containing 10 mMFe(CN)6

3�/4�; the voltammograms were collected using a scan rate of50 mV s�1.

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the BDDNWs' greater surface area; consequently, the BDDNWelectrode should exhibit excellent electrochemical activitytoward organic compounds. Increased surface area is alsoobserved in the cyclic voltammograms for the Fe(CN)6

3�/4�

redox couple, as shown in Fig. 3(b). In the case of the planarBDD, the anodic peak current (Ip,a) and the cathodic peakcurrent (Ip,c) were 1.28 mA and �1.27 mA, respectively. Thepeak-to-peak separation potential (DEp) was 0.62 V. However,the BDDNW electrode shows signicantly enhanced Ip,a (2.63mA) and Ip,c (�2.38 mA) values and a signicantly reduced DEpvalue (0.22 V). The lower DEp suggests that the electron transferkinetics and the electrochemical activity of BDDNW are muchbetter than those of the planar BDD electrode.48 Additionally,higher peak currents (Ip) indicate a larger effective surface areabecause the increase of Ip is proportional to the effective surfacearea. Fig. 4(a) shows variation of Ip with respect to the squareroot of the scan rate (v1/2) for the electrodes. Both peak currentsshow linear relationships, implying quasi-reversible behavior.Under this condition, the effective surface area is proportionalto Ip/v

1/2, as shown in the following equation:

Ip ¼�2:69� 105

�n3=2AD0

1=2C*0v

1=2

where n is the number of electrons in the redox reaction, A is theelectrode's surface area (cm2), D is the diffusion coefficient for

Fig. 4 (a) Peak current versus the square root of the scan rate and (b)formaldehyde produced by reacting cOH with methanol.

6232 | RSC Adv., 2017, 7, 6229–6235

the molecules in the solution (cm2 s�1), C* is the concentra-tion of molecules in the bulk solution (mol cm�3), v is the scanrate (V s�1) and Ip is the peak current (A).49 The calculatedeffective surface areas of the planar BDD and BDDNW elec-trodes were 1.61 and 4.78 cm2, respectively. Generally,a nanostructured surface exhibits a geometric area enhancedby a factor of thousands compared to that of its 2-dimensionalplanar surface counterpart; however, the BDDNW electrodeexhibits an increase in the electrochemical effective area thatis several orders of magnitude lower. Because surface regionsthat are not fully activated are also present, a large gapbetween the geometric area and the effective surface area ispossible.50 Even though nanostructuring of BDD leads to onlya threefold greater effective surface area, this greater surfacearea provides a substantially greater number of electro-chemical reaction sites and generates cOH in substantiallygreater quantities, resulting in greater electro-oxidation effi-ciency. These results are reected in the formaldehyde deriv-ative concentration (Fig. 4(b)), which has positive relation withthe amount of generation cOH.41 cOH generation rate ofBDDNW is always higher than planar BDD for the entireelectrolysis time.

To evaluate the electro-oxidation performance, we conductedbulk electrolysis of 1 mM phenol using a single-compartmentelectrolytic cell with parallel electrodes. Fig. 5 showsa decrease of the COD and the instantaneous current efficiency(ICE) as a function of specic charge amount on the planar BDD

Fig. 5 (a) COD and (b) ICE curves for phenol oxidation on differentelectrodes.

This journal is © The Royal Society of Chemistry 2017

Fig. 6 (a) TOC, phenol removal (inset) and (b) MCE curves for phenoloxidation on different electrodes.

Fig. 7 Specific energy consumption with respect to phenol mineral-ization on different electrodes.

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and BDDNW electrodes. The ICE for the anodic oxidation ofphenol was calculated using the following equation:

ICE ð%Þ ¼ FV

�ðCODÞt � ðCODÞtþDt

�

8IDt� 100

where F is the Faraday constant (C mol�1); V is the total volumeof bulk electrolyte; (COD)t and (COD)t+Dt are the COD at times tand t + Dt (g L�1), respectively; I is the current (A), and 8 is theequivalent mass of oxygen.51 Final COD removal in the planarBDD and BDDNW was 94.4% and 98.9%, respectively. The CODvalue in the BDDNW at 2.5 A h L�1 was not recorded because ofthe detection limit (>2 mg L�1). COD removal occurred muchmore rapidly in BDDNW; thus, the COD removal rate in theBDDNW electrode was substantially increased by the nano-structuring of the BDD surface. In the general case, the ICE wasmaintained at 100% at a high concentration of the organiccompound and then exponentially decreased with decreasingconcentration because of the depletion of organic compoundsnear the electrode surface, i.e., mass transfer limitation.52 Heet al. reported that the increased fraction of current efficiency ofa microporous Ti/BDD electrode was smaller than they expectedbecause the electrode's surface could not be exploitedcompletely in a mass transport control situation.53 In our case,the initial ICE values were�40% and�60% for planar BDD andBDDNW, respectively, indicating that a quite low concentrationof the organic compound was used in the system. However, theICE values until a specic charge of 1.5 A h L�1 in BDDNWelectrode were signicantly higher than in the case of the planarBDD. In particular, COD removal was completed in only 2.5 A hL�1, which is earlier than in the case of phenol oxidation on themicrostructured Ti/BDD electrode; thus, BDDNW could removeCOD more efficiently even though it operated under mass-transfer-limiting conditions.53

Fig. 6 shows the TOC, phenol removal and the mineraliza-tion efficiency (MCE). The MCE was calculated according to theequation:

MCE ð%Þ ¼ DðTOCÞexpDðTOCÞtheor

� 100

where D(TOC)exp is the experimental TOC variation andD(TOC)theor is the TOC variation theoretically calculated underthe assumption that the applied electrical charge is only usedfor the mineralization reaction.21 The removal of TOC is typi-cally slower than that of COD because electro-oxidation doesnot correspond to a direct combustion reaction. As wasobserved in the case of COD removal, the removal of TOC andphenol were faster in BDDNW. The total removal rates of TOCwere 80% and 96.9% for the planar BDD and BDDNW, respec-tively. The total removal rates of phenol were 79% and 97% forthe planar BDD and BDDNW, respectively, meaning thatBDDNW produced muchmore cOH than the planar BDD, whichled to a higher derived rate for the complete combustion ofphenol into CO2. These results are reected in the MCE results(Fig. 6(b)), which show higher values for the entire electrolysistime, implying that the BDDNW electrode generated largeramounts of cOH during the electrochemical oxidation process.Because electrochemical phenol oxidation performance is

This journal is © The Royal Society of Chemistry 2017

affected by various electrolysis conditions such as initialconcentration, electrolyte, pH, temperature and current density,the efficiency of BDDNW electrode may be further increasedwith optimizing process variables in future works.54,55

Fig. 7 shows specic energy consumption plotted withrespect to phenol mineralization. The difference in the requiredspecic energy increases dramatically with increasing thedesired phenol mineralization. According to an extrapolation ofthe data, 27.5 kW h m�3 is required for 80% mineralization of

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phenol using the planar BDD electrode, whereas only 12.1 kW hm�3 is required using the BDDNW electrode. These resultssuggest that electrochemical oxidation of phenol using theBDDNW electrode is much more efficient from the standpointof the economics of the oxidation process.

4. Conclusions

By using a metal-catalyzed silicon etching process and electro-static nanodiamond seedingmethod, we successfully fabricateda BDDNW electrode for electrochemical oxidation processes.The BDDNW electrode exhibited an effective surface area thatwas three times greater than that of the planar-type BDD elec-trode; it also exhibitedmuch faster electro-oxidation kinetics. Inbulk electrolysis of phenol-containing water, the BDDNW elec-trode showed much higher COD and TOC removal rates as wellas a higher current efficiency. Because of the large effectivesurface area of the nanowires, the BDDNW electrode generatedlarge amounts of cOH. Despite the mass transfer limitation, theBDDNW electrode exhibited highly improved electrochemicaloxidation performance compared to the microtextured BDDelectrode investigated in our previous study as well as comparedto other microstructured BDD electrodes. Additionally, nano-structuring of the BDD electrode reduced specic energyconsumption for 80% mineralization of phenol by a factor ofmore than 2 compared to the conventional planar BDD elec-trode. These results indicate that because of the larger surfacearea of nanostructured BDD, nanostructuring of the BDD elec-trode may solve the problem associated with the high produc-tion cost per unit area of BDD electrodes and can potentially beapplied in applications involving real wastewater.

Acknowledgements

This work was supported by Korea Ministry of Environment(MOE) as “Public Technology Program based on EnvironmentalPolicy” (No. E416-00070-0604-0).

References

1 M. Cheng, G. M. Zeng, D. L. Huang, C. Lai, P. Xu, C. Zhangand Y. Liu, Chem. Eng. J., 2016, 284, 582–598.

2 J. Hoigne, Water Sci. Technol., 1997, 35, 1–8.3 M. Pera-Titus, V. Garcia-Molina, M. A. Banos, J. Gimenez andS. Esplugas, Appl. Catal., B, 2004, 47, 219–256.

4 S. W. da Silva, C. R. Klauck, M. A. Siqueira andA. M. Bernardes, J. Hazard. Mater., 2015, 282, 241–248.

5 A. R. F. Pipi, I. Sires, A. R. De Andrade and E. Brillas,Chemosphere, 2014, 109, 49–55.

6 K. Ikehata, N. J. Naghashkar and M. G. Ei-Din, Ozone: Sci.Eng., 2006, 28, 353–414.

7 Y. Tian, X. M. Chen, C. Shang and G. H. Chen, J. Electrochem.Soc., 2006, 153, J80–J85.

8 E. Brillas, I. Sires and M. A. Oturan, Chem. Rev., 2009, 109,6570–6631.

9 Y. G. Adewuyi, Environ. Sci. Technol., 2005, 39, 8557–8570.

6234 | RSC Adv., 2017, 7, 6229–6235

10 S. G. Kumar and K. S. R. K. Rao, RSC Adv., 2015, 5, 3306–3351.

11 A. Kra, M. Stadelmann and M. Blaschke, J. Hazard. Mater.,2003, 103, 247–261.

12 A. Sakalis, K. Fytianos, U. Nickel and A. Voulgaropoulos,Chem. Eng. J., 2006, 119, 127–133.

13 T. Bechtold, A. Turcanu and W. Schrott, Diamond Relat.Mater., 2006, 15, 1513–1519.

14 R. E. Palma-Goyes, F. L. Guzman-Duque, G. Penuela,I. Gonzalez, J. L. Nava and R. A. Torres-Palma,Chemosphere, 2010, 81, 26–32.

15 J. T. Xing, D. H. Chen, W. Zhao, X. L. Peng, Z. L. Bai,W. W. Zhang and X. X. Zhao, RSC Adv., 2015, 5, 53504–53513.

16 S. P. Li, Y. H. Li, X. Y. Zeng, W. R. Wang, R. X. Shi andL. N. Ma, RSC Adv., 2015, 5, 68700–68713.

17 Y. Wang, C. C. Shen, L. F. Li, H. Y. Li and M. M. Zhang, RSCAdv., 2016, 6, 30598–30610.

18 A. Urtiaga, P. Fernandez-Castro, P. Gomez and I. Ortiz,Chem. Eng. J., 2014, 239, 341–350.

19 J. H. T. Luong, K. B. Male and J. D. Glennon, Analyst, 2009,134, 1965–1979.

20 W. Zhang, S. Y. Zhu, R. Luque, S. Han, L. Z. Hu and G. B. Xu,Chem. Soc. Rev., 2016, 45, 715–752.

21 E. Brillas, B. Boye, I. Sires, J. A. Garrido, R. M. Rodriguez,C. Arias, P. L. Cabot and C. Comninellis, Electrochim. Acta,2004, 49, 4487–4496.

22 F. Montilla, P. A. Michaud, E. Morallon, J. L. Vazquez andC. Comninellis, Electrochim. Acta, 2002, 47, 3509–3513.

23 P. Canizares, C. Saez, J. Lobato and M. A. Rodrigo, Ind. Eng.Chem. Res., 2004, 43, 6629–6637.

24 R. Bogdanowicz, A. Fabianska, L. Golunski, M. Sobaszek,M. Gnyba, J. Ryl, K. Darowicki, T. Ossowski, S. D. Janssens,K. Haenen and E. M. Siedlecka, Diamond Relat. Mater.,2013, 39, 82–88.

25 C. Chen, E. Nurhayati, Y. Juang and C. Huang, J. Environ.Sci., 2016, 45, 100–107.

26 D. A. Tryk, H. Tachibana, H. Inoue and A. Fujishima,Diamond Relat. Mater., 2007, 16, 881–887.

27 F. L. Souz, C. Saez, M. R. V. Lanza, P. Canizares andM. A. Rodrigo, Electrochim. Acta, 2016, 187, 119–124.

28 B. P. Chaplin, Environ. Sci.: Processes Impacts, 2014, 16, 1182–1203.

29 A. Kra, Int. J. Electrochem. Sci., 2007, 2, 355–385.30 M. Panizza, P. A. Michaud, G. Cerisola and C. Comninellis,

Electrochem. Commun., 2001, 3, 336–339.31 P. Y. Lim, F. Y. Lin, H. C. Shih, V. G. Ralchenko, V. P. Varnin,

Y. V. Pleskov, S. F. Hsu, S. S. Chou and P. L. Hsu, Thin SolidFilms, 2008, 516, 6125–6132.

32 Y. S. Zou, Y. Yang, Y. L. Zhou, Z. X. Li, H. Yang, B. He, I. Belloand W. J. Zhang, J. Nanosci. Nanotechnol., 2011, 11, 7914–7919.

33 N. J. Yang, H. Uetsuka and C. E. Nebel, Adv. Funct. Mater.,2009, 19, 887–893.

34 D. B. Luo, L. Z. Wu and J. F. Zhi, ACS Nano, 2009, 3, 2121–2128.

This journal is © The Royal Society of Chemistry 2017

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35 H. Zanin, P. W. May, D. J. Fermin, D. Plana, S. M. C. Vieira,W. I. Milne and E. J. Corat, ACS Appl. Mater. Interfaces, 2014,6, 990–995.

36 S. K. Lee, M. J. Song, J. H. Kim, T. S. Kan, Y. K. Lim, J. P. Ahnand D. S. Lim, NPG Asia Mater., 2014, 6, e115.

37 J. F. Zhang, T. Nakai, M. Uno, Y. Nishiki and W. Sugimoto,Carbon, 2014, 70, 207–214.

38 J. Y. Bak, C. H. Lee, J. D. Kim and D. S. Lim, J. Korean Phys.Soc., 2016, 68, 109–114.

39 K. Q. Peng, Z. P. Huang and J. Zhu, Adv. Mater., 2004, 16, 73–76.

40 J. H. Kim, S. K. Lee, O. M. Kwon and D. S. Lim, J. Nanosci.Nanotechnol., 2009, 9, 4121–4127.

41 C. Tai, J. F. Peng, J. F. Liu, G. B. Jiang and H. Zou, Anal. Chim.Acta, 2004, 527, 73–80.

42 K. Siuzdak, R. Bogdanowicz, M. Sawczak and M. Sobaszek,Nanoscale, 2015, 7, 551–558.

43 J. V. Macpherson, Phys. Chem. Chem. Phys., 2015, 17, 2935–2949.

44 P. W. May, W. J. Ludlow, M. Hannaway, P. J. Heard,J. A. Smith and K. N. Rosser, Chem. Phys. Lett., 2007, 446,103–108.

This journal is © The Royal Society of Chemistry 2017

45 S. Prawer and R. J. Nemanich, Philos. Trans. R. Soc., A, 2004,362, 2537–2565.

46 M. Panizza and G. Cerisola, Electrochim. Acta, 2003, 48, 3491–3497.

47 M. Panizza and G. Cerisola, Electrochim. Acta, 2004, 49, 3221–3226.

48 X. H. Kang, J. Wang, H. Wu, I. A. Aksay, J. Liu and Y. H. Lin,Biosens. Bioelectron., 2009, 25, 901–905.

49 A. J. Bard and L. R. Faulkner, Electrochemical Methods:Fundamentals and Applications, Wiley, New York, 2000.

50 S. Trasatti and O. A. Petrii, J. Electroanal. Chem., 1992, 327,353–376.

51 C. Comninellis and C. Pulgarin, J. Appl. Electrochem., 1991,21, 703–708.

52 C. A. Martinez-Huitle and S. Ferro, Chem. Soc. Rev., 2006, 35,1324–1340.

53 Y. P. He, W. M. Huang, R. L. Chen, W. L. Zhang andH. B. Lin, Sep. Purif. Technol., 2015, 149, 124–131.

54 P. Canizares, J. Lobato, R. Paz, M. A. Rodrigo and C. Saez,Water Res., 2005, 39, 2687–2703.

55 C. Comninellis and A. Nerini, J. Appl. Electrochem., 1995, 25,23–28.

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