1、Applied Catalysis B: Environmental 166167 (2015) 366373Contents lists available at ScienceDirectApplied Catalysis B: Environmentaljournal homepage: light photoactivity enhancement viag-C3N4nanocompositeDaimei , RuilongYongfaaNationalSchoolbarticleArticleReceivedReceived21AcceptedAvailableKeyword:Ph
2、otocatalysisg-CSensitizationPorphyrinsynthesizedassemble3N4withtransfer 2014 Elsevier B.V. All rights reserved.1.semiconductor,applicationcatalysis,etordiation,forusinghigh5,6withtheofblocksmethodsformance(Y.http:/dx.doi.org/10.1016/j.apcatb.2014.11.0500926-3373/IntroductionGraphite-like carbon nitr
3、ide (g-C3N4), a metal-free polymerhas attracted plenty of attention due to its potentialin solar energy conversion, photosynthesis, electro-bioimaging and biomedical application 14. Since Wangal. firstly reported that the polymeric g-C3N4shows superior H2O2evolution activities via water splitting un
4、der visible light irra-it is considered as an especially promising photocatalysthydrogen gas production and organic pollutants degradationsolar energy due to its simple fabrication, low-cost andstability under light irradiation in solution with pH = 014. However, the bandgap of g-C3N4is still as lar
5、ge as 2.7 eVan absorption edge just at 450 nm, which largely restrictsvisible-light utilization efficiency. In addition, the high degreerecombination between photoinduced electrons and holes alsoits practical application. To overcome these problems, manyhave been proposed to improve the photocatalyt
6、ic per-of g-C3N4, for example, by doping nonmetallic elementCorresponding authors. Tel.: +86 10 82332274; fax: +86 10 82322974.E-mail addresses: (D. Chen), Zhu).7, and coupling g-C3N4with metals 8, organic semiconductors9,10, graphene 11,12, activated by organic dyes 13.Among the various strategies
7、 for visible-light harvesting, dyesensitization is an efficient and widely used route to extendthe spectral response region of wide-band-gap semiconductors1416. Many dye sensitized photocatalysts have been developedfor H2production, such as sensitized semiconductors 17,18, sen-sitized multiwall carb
8、on nanotubes 19 and sensitized reducedgraphene oxide 20. Obviously, dye sensitization of g-C3N4canalso be an efficient way to enhance the utilization efficiency of vis-ible light. Until now, several dyes such as Erythrosin B (ErB), EosinY (EY), poly(3-hexylthiophene) (P3HT) and zinc phthalocyanines(
9、ZnPc) were used as sensitizers of g-C3N4to enhance the pho-tocatalytic H2production activity with considerable visible lightutilization efficiency 13,2123.Porphyrins as light harvesting materials play an important rolein photosynthesis. As they possess good chromophore activitiesover the solar spect
10、rum and good electron donating propertiesdue to their large p-electron systems, porphyrin compounds havebeen widely regarded as excellent photosensitizers for photocata-lysts. For example, the metalloporphyrin-modified TiO2systemhas been reported for the photocatalytic degradation of variouskinds of
11、 organic pollutants in water under visible light irradiation2426. In generally, metalloporphyrin modified photocatalysts2014 Elsevier B.V. All rights reserved.Chena, Kewei Wanga,b, Wangzhi Honga,bZhub,Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes,of Materia
12、ls Sciences and Technology, China University of Geosciences, Beijing 100083,Department of Chemistry, Tsinghua University, Beijing, 100084, PR Chinainfohistory:5 October 2014in revised formNovember 201424 November 2014online 29 November 20143N4abstractCu (II) meso-Tetra (4-carboxyphenyl)posites have
13、been facilelya sensitizer could easilying interaction. The CuTCPP/g-Cdegradation than pure g-CCuTCPP/g-C3N4compositespure g-C3N4under the visiblefrom the efficient electronsefficiently visible-light harvestingoxidative species of CuTCPP/g-Cpossible charge transfer mechanismCuTCPP hybridizedZongb, We
14、nqing Yaob,Laboratory of Mineral Materials,Chinaporphyrin (CuTCPP) hybridized g-C3N4(CuTCPP/g-C3N4) com-through the ethanol dispersion method. CuTCPP molecules ason the surface of g-C3N4nanosheets mainly through H9266H9266 stack-3N4composites show much higher photocatalytic activity for phenolunder
15、visible light irradiation. The optimum photocatatlytic activity of theweight ratio of CuTCPP at 0.75% is almost 2.2 times as high as that oflight. The enhancement of the visible light photocatalytic activity comesfrom photoexcited CuTCPP molecules to g-C3N4sheets and moredue to the CuTCPP sensitizat
16、ion. Both the holes and O2are main3N4for phenol degradation under visible light irradiation. Finally, theof enhanced visible light photocatalytic activity was proposed.D. Chen et al. / Applied Catalysis B: Environmental 166167 (2015) 366373 367were prepared by covalent interaction between the differ
17、entfunctional groups ( COOH, OH, etc.) in the periphery of the por-phyrin ring and the surface of photocatalysts. It is widely acceptedthat the covalent bands can form channels, which can enhancethe electron transfer between porphyrins and photocatalysts, andfurther lead to the delocalization of p*
18、orbits of porphyrins 25.However, the amount of porphyrins absorbed on the surface of thephotocatlayststophyrinnanocompositeH9266actspositeUVvisphotoexcitederingwithwithorareespeciallytainmentsensitizedg-Cphotocatalysissensitizercaninteractions,structure,ityoflengthwithitytheferapplicationdegradation
19、2.2.1.Chemicalcarboxyphenyl)byanalytically2.2.2.2.1.Cputreaction.into2.2.2.ultrasonicethanolto(0.1an hour. Then the resulting suspension was continually stirred ina fume hood at 60C for a night. After completely volatilizationof the ethanol, the samples were dried at 100C for 8 h. A seriesof CuTCPP/
20、g-C3N4photocatalysts with the different mass ratios ofCuTCPP were prepared by this method, which were denoted asX%CuTCPP/g-C3N4, where X represents the weight ratios of CuTCPPin total (X% = 0.1%, 0.25%, 0.5%, 0.75%, 0.8%, 0.9%, 1%, 2%).is limited because most of porphyrins are difficultcovalently in
21、teract with photocatlaysts. Zhu et al. prepared por-uncovalently functionalized reduced graphene oxide (RGO)by immobilizing porphyrin on RGO nanosheets viaH9266stacking interactions. Porphyrin moiety in the nanocompositeas a photosensitizer and harvesting irradiation light. This com-shows remarkable
22、 enhanced photocatalytic activity underlight irradiation due to the fast electrons transfer fromporphyrin molecules to RGO sheets 27,28. Consid-the g-C3N4has analogue structure with RGO (planar layersH9266 electron conjugation), it is expected to interact stronglyporphyrins through electrostatic int
23、eraction, H9266H9266 stacking,hydrogen bonding. However, to the best our knowledge, thereno studies about the sensitization of g-C3N4with porphyrin,the using the dye sensitized g-C3N4for the organic con-degradation. Therefore, a systemic investigation of dyeg-C3N4and the oxidation mechanic of the dy
24、e sensitized3N4for the photodegradation needs further studied.In our paper, we reported the preparation, characterization, andofCuTCPP/g-C3N4composites.ChoosingCuTCPPasatohybridizewithg-C3N4isnotonlyduetothatporphyrineasily hybridize with g-C3N4through strong H9266H9266 stackingbut also due to its n
25、ice locally conjugated aromaticas well as its remarkable chemical and thermal stabil-benefitting for photocatalytic reactions. The optical absorptiong-C3N4( 420 nm); (b) over g-C3N4and 0.75%CuTCPP/g-C3N4photocatalysts underdifferent wavelength light irradiation.370 D. Chen et al. / Applied Catalysis
26、 B: Environmental 166167 (2015) 366373Fig.0.25%CuTCPP/g-Con/offchromatogramstionbeoxidizedacidtionpeaksintensityCisdegradeddationenhancedinofphotocatalystiousFig.andwavelength.nolwholeenhancementCuTCPPphotocatalyticitywavelengthsdecreaseCthewavelengths,extendof0.25%CuTCPP/g-Celectrodestransientcorre
27、latecarriersover0.75%CuTCPP/g-Casoverthe4. The transient photocurrent density responses of pure g-C3N4,3N4and 0.75%CuTCPP/g-C3N4samples electrodes with lightcycles under visible light irradiation (NAK 420 nm).The phenol photodegradation intermediates are investigated byof phenol before and after pho
28、tocatalytic degrada-for 10 h monitored at 275 nm (Fig. S3). The peak at 5.3 min canidentified as that of phenol. The peak at 3.2, 2.8 and 2.1 min areintermediates, which might be hydroquinol (HQ), maleic(MA) and the lower fatty acid, respectively 34,35. As the reac-proceeded, the peak of phenol beca
29、me lower, whereas theof the intermediate species increased gradually. The higherof intermediates by 0.75%CuTCPP/g-C3N4than pure g-3N4indicates that the degradation ability of 0.75%CuTCPP/g-C3N4remarkably enhanced and the intermediates could be furtherby ring cleavage and finally subjected to complet
30、e degra-to CO2and H2O.In order to clearly elucidate the extended photoresponse andphotocatalytic activity of CuTCPP/g-C3N4photocatalystlonger wavelength visible regions, the wavelength dependencephotocatalytic activity for phenol degradation over sensitizationinvestigated in the range of 420550 nm u
31、sing var-band pass filters (NAK = 420, 450, 470, 490, 510 and 550 nm).3b compared the value of rate constants k of pure g-C3N40.75%CuTCPP/g-C3N4composite under different ranges of theThe overall enhanced photocatalytic activity for phe-degradation is observed on 0.75%CuTCPP/g-C3N4across theof its ab
32、sorption spectrum. This wavelength-independentindicates there may be some interactions betweenand g-C3N4that plays an important role in improving theactivity. It can be seen that the photocatalytic activ-decrease with increasing wavelengths. With the increase thefrom 420 nm to 550 nm, the rate const
33、ants of g-C3N4from0.01098to0.00045 h1,andthoseof0.75%CuTCPP/g-3N4decrease from 0.02368 to 0.00128 h1. This fact is ascribed todecrease of the available photon energy with the increase ofand further confirms that CuTCPP as sensitizer canphotoresponse of g-C3N4and improve utilization efficiencyvisible
34、 light.The photocurrent responses of 0.75%CuTCPP/g-C3N4,3N4and pure g-C3N4after deposition on ITOunder visible light (NAK 420 nm), are shown in Fig. 4. Thephotocurrent responses of a photocatalysis may directlywith the recombination efficiency of the photogenerated3638. It is obvious to observe that
35、 the photocurrentCuTCPP/g-C3N4is greatly improved, and the optimum3N4sample electrode is about 3.5 times as highthat of the pure g-C3N4electrode. The enhanced photocurrentCuTCPP/g-C3N4sample implies more efficient separation ofphotoinduced electron-hole pairs and longer lifetime of theFig. 5. UVvis
36、diffuse reflection spectra of g-C3N4, CuTCPP and CuTCPP/g-C3N4photocatalysts.photogenerated charge carriers than that of pure g-C3N4, which isbeneficial for its enhanced photocatalytic activity.3.3. Mechanism of photocatalytic activity enhancementThe absorption range of light plays an important role
37、 in thephotocatalysis, especially for the visible light photodegradation ofcontaminants. Fig. 5 shows the UVvis diffuse reflectance spec-troscopy (DRS) of CuTCPP/g-C3N4composites, as well as pureg-C3N4and CuTCPP. The pure g-C3N4exhibits a fundamentalabsorption edge at 450 nm, corresponding to the ba
38、nd gap of 2.7 eV.The pure CuTCPP sample has strong absorption in visible region(400700 nm) and a strongest absorption intensity peak at 538 nm,which identified as the Q band of porphyrin. As increasing theloading amount of CuTCPP in the CuTCPP/g-C3N4composites, theabsorption intensities of the compo
39、sites are enhanced and theabsorption edges also show a slight red shift. The CuTCPP/g-C3N4composite samples show hybrid absorption features of g-C3N4andCuTCPP, which allows for more efficient utilization of the solarspectrum to create photogenerated electrons and holes. Fig. S2 (seethe Supporting In
40、formation) shows that the Q bands centered at545 nm attributed to the Q band of CuTCPP adsorbed on the g-C3N4nanosheet is founded to have a slight red shift of 7 nm ascompared to its absorption in methanol at 538 nm, suggesting thatH9266H9266 stacking interactions between the individual components i
41、nthe CuTCPP/g-C3N4nanocomposite 39,40. A significant broaden-ing of the Soret band peak can also be observed in the absorptionof CuTCPP solid and CuTCPP absorbed on the g-C3N4as comparedto the absorption spectra of in methanol. This phenomenon is dueto the dye aggregations on the solid substrates 41
42、.It is well known that phase structure, BET surface area,and separation efficiency of photogenerated charges are thekey factor to influent the photocatalytic activity. As can beseen from the XRD spectra, the crystal phase structure of g-C3N4does not changed after the hybridization of the g-C3N4.The
43、BET surface area of g-C3N4is 8.2 m2/g, and those of0.1%CuTCPP/g-C3N4, 0.25%CuTCPP/g-C3N4, 0.75%CuTCPP/g-C3N4,0.9%CuTCPP/g-C3N4, 1.0%CuTCPP/g-C3N4, and 2.0%CuTCPP/g-C3N4are 10.1 m2/g, 9.8 m2/g, 7.3 m2/g, 7.2 m2/g, 7.0 m2/g, 6.3 m2/g,respectively. This fact shows that the hybridization with CuTCPPhas
44、a little effect in BET surface area of g-C3N4. Furthermore,the adsorption experiment shows that adsorption abilities of theg-C3N4and CuTCPP/g-C3N4nanocomposites toward phenol arealmost same. Therefore, the important reason for the enhance-ment of photocatalytic activity on CuTCPP/g-C3N4nanocomposite
45、is due to the effective separation of the photogeneratedD. Chen et al. / Applied Catalysis B: Environmental 166167 (2015) 366373 371Fig. 6. Photoluminescence spectra of pure g-C3N4, pure CuTCPP, 0.25%CuTCPP/g-C3N4and 0.75%CuTCPP/g-C3N4photocatalysts.electron-hole pairs induced by the energy level ma
46、tch betweeng-C3N4and CuTCPP.Photoluminescence (PL) technique can be also employed toinvestigate the migration, transfer and recombination processesof photogenerated electronhole pairs in semiconductors 42.Fig. 6 presents the photoluminescence spectra for pure g-C3N4,0.75%CuTCPP/g-C3N4, 0.25%CuTCPP/g
47、-C3N4and pure CuTCPP at anexcitation wavelength of 375 nm. Pure g-C N shows a strong,wideresponseCg-ChinderedintensityansomeconcludedCreasoncomposites.chargechemicalshows0.75%CuTCPP/g-CtrodesarconmoreFig.C(samples electrode are smaller than that of pure g-C3N4electrode,suggesting that CuTCPP/g-C3N4c
48、omposite structure can make theseparation and immigration of photogenerated electron-hole pairsmore efficient, which is in good accordance with the result of thephotocurrent measurement.It is important to detect main oxidative species in the pho-tocatalytic process for elucidating the photocatalytic
49、 mechanism.The main oxidative species in photocatalytic process are detectedthrough the trapping experiments of radicals using IPA as hydroxylradical scavenger 44 and CH2O2as holes radical scavenger 45,and purging N2as O2scavenger46, respectively. As shownin Fig. 8a, the photocatalytic degradation of phenol with g-C3N4hardly has any change by the addition of IPA in the reaction sys-tem, while has a remarkably decrease by the addit
