Presentation on theme: "Perspectives on photocatalysis to the water and wastewater treatment"— Presentation transcript:
1 Perspectives on photocatalysis to the water and wastewater treatment Prof Regina de F P M MoreiraDepartamento de Engenharia Química e Engenharia de AlimentosUniversidade Federal de Santa CatarinaFlorianópolis - SC
2 Number of patents in photocatalysis Number of papers in Photocatalysis:1975–1980: 2492000–2010:TiO2 - the most used photocatalyst (non-toxic, stable and not expensive)Air treatmentWater and wastewater treatmentSelf cleaning surfacesNumber of papers/year (www.sciencedirect.com)Number of patents in photocatalysisPublications about “nanoparticle photocatalysts”Balkus Jr, K., New and Future Developments in Catalysis -Catalysis by Nanoparticles, 2013, Pages 213–244
3 Photocatalysis(1975–1985)semiconductor/solution interface under UV irradiation several semiconductorsPolycristalline materials were the most suitable.Photocatalysts in aqueous suspensions.( )Thin films;Doping of semiconductors to explore visible light;Dye sensitization (photocatalysts in aqueous suspension).Industrial activities.(2006–2010):Nanophotocatalysts
4 Photocatalytic activity and semiconductor properties PhotocatalystsSemiconductorsConduction Band (CB) electrons have a chemical potential of to -1.5 V vs NHE hence they can act as reductants.Valence Band (VB) holes exhibit a strong oxidative potential to V vs NHEPhotocatalytic activity and semiconductor propertiesEnergy band configuration determinates the absorption of incident photons, photoexcitation of electron-hole pairs, migration of carriers, and redox capabilities of excited-state electrons and holes.Band-edge positions of semiconductor photocatalysts relative to the energy levels of various redox couples in water.Energy bands engineeringH Tong, S Ouyang, Y Bi, N Umezawa, M Oshikiri, J Ye, Nanophotocatalytic materials: possibilities and challenges, Adv Mater 2012, 24,
5 Photocatalysts ENERGY BAND ENGINEERING Some important aspects: Optical absorption: direct and narrow bandgap semiconductors are more likely to exhibit high absorbance suitable for the efficient harvesting of low energy photons.Disadvantages:recombination electron/holeBand-edge positions are frequently incompatible with the electrochemical potential necessary to trigger specific redox reactionsModulate the band gap and band-edge positions in a precise manner different strategiesImprovement of light sensitization by the inclusion of quantum dots, plasmon-exciton coupling between anchored noble metal nanoparticle co-catalysts and the host semiconductor, and photon coupling in semiconductor photonic crystals.
6 Energy Band Engineering Modiulation of VBAdjustment of the CBContinuous modulation of the VB and/or CBPhotocatalytic degradation of pollutants in water or wastewater oxygen as electron acceptorVB Redox potential should be sufficiently positive in order to the holes act as electron acceptor ; oxidation reactionCB: Redox potential should be sufficiently negative in order to the oxygen act as electron acceptor reduction reactionA. Millis and S. L. Hunte J. Photochem. Photobiol. A: Chem 180 (1997) 1
7 Energy Band Engineering CB slightly negative ;VB significantly positive with respect to the oxidization of H2O (vs NHE).Oxide semiconductors ThereforeFor the consideration of stability of materials, raising to top of the VB to narrow the bandgap takes precedence over all other methods of energy-band modulation.To adjust the level of the VB: the most effective strategies:Doping with 3d transition elementsCations with d10 our d10s2 configurationsNon-metal elements
8 Energy band engineering A) TiO2 Doping N, S, C, metals strategies to raise the VB maximumB) TiO2 Dye surface sensitizationC) Surface modification to increase stabilityD) Coupled semiconductorsE) Novel semiconductor containing 3d metals.Miao Zhang et al, Angew. Chem. Int. Ed. 2008, 47, 9730 –9733
9 A) Doping with non-metal: C, N, P, B, S A.1.1 Doping with sulfurA.1.2 Doping with nitrogenSuccessful example of band-edge control for the utilization of visible light mechanism under debate.Hybridization of the N-related states with the host VB;N-doping in TiO2 is accompanied by formatin of Ti3+ via donor-type deffectsMechanism of photocatalytic activity of TiO2 doped with SS.X. Liu, X.Y. Chen, J. Hazard. Mater. 152, 48–55 (2008)K. HASHIMOTO et al. Jpn. J. Appl. Phys., Vol. 44, No. 12 (2005)Doping with N, C, S narrows the bandgap by less than 0.3 V.Significant extension of visible light absorption via anion doping remains a big challenge.
10 Nanofio dopado com nitrogênio Nanofio Photocatalytic degradation of Phenol in aqueous solution using nanowires of N-doping TiO2Ilha, José, Moreira, Degradação fotocatalítica de fenol utilizando nanofios de dióxido de titânio modificados com nitrogênio). UFSC, 2012Nanofio dopado com nitrogênioNanofioPhotocatalystBandgap (eV)TiO2 P253,05Nanowire TiO22,62N-doped TiO2 nanowired2,53Pseudo first order kinetic constant for the phenol minearlization using different photocatalystsCatalisadork' (10-3min-1)P252,6nanowireTiO20,6N doped TiO2 nanowired1,1Phenol initial concentration: 100 mg/ L; Photocatalyst dosage 1g/L.
11 N doped TiO2 Effect of nitrogen content Theoretical studies: only 1% atomic% N (0.53 % w/w) on TiO2 is necessary to activate photocatalytic reactions under visible light.Fu, Zhang, Zhang, Zu, J Phys Chem B 2006, 110, 3061.Decomposition of rhodamine B after 1 h using TiO2 or N- TiO2 (different N/Ti ratio) under visible light.Ye Cong et al., J. Phys. Chem. C, Vol. 111, No. 19, 2007,
12 B – Metal doping CB e- e- e- e- e- e- e- e- e- e- e- e- VB h+ h+ h+ h+ h+ h+ h+ h+ h+ h+Recombinatione-/h+e-(M) M+e-EgMetal promoter: attracts the electrons to the CB recombination is inhibited.
13 B – Metal Doping ionic radius of the metal similar to the Ti4+ , Exhibit 2 or more oxidation states.Energy levels Mn+ /M(n+1) similar to Ti3+ /Ti4+ ,Electronegativity: higher than Tiincomplete/parcial electronic configurationIonic radius
14 B – Noble metals dopingFotoactivity of TiO2 doped with Pt effect of the metal concentration on the production of methane by the photoreaction: CO2 + H2O CH4 + O2Effect of Pt-metal content in Pt/TiO2 (P25) catalysts on CH4 yield for photocatalytic reduction of CO2 after 7 h UV irradiation at 323 K, H2O/CO2 = 0.02.Q.-H. Zhang et al. / Catalysis Today 148 (2009) 335–340
15 B – Non noble metal doping Capítulo 6Copper, zinc and ChromiumDe Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44Photocatalyst synthesis: photodeposition by controllingl of precursor metals solubility“síndrome do bebê azul” que pode ser fatal em recém-nascidosExcesso de NO3- em águas superficiais e subterrâneas:
16 B - Non-noble metals doping Capítulo 6Copper, zinc and ChromiumDe Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44Photocatalytic denitrification:Photoreduction of NO3- to produce N2Hole scavanger: Formic acid (electron donor)Nitrate electron acceptorTheoretical molar ratio to reduce nitrate to nitrogen CHOOH:NO3- = 8:1Mudanças na seletividade (SN), na atividade (A) e na porcentagem de conversão de nitrato (C%). A seletividade por nitrogênio é definida como a razão entre a concentração de nitrato reduzida para formar nitrogênio considerando que nenhum outro sub-produto seja formado além de nitrito (NO3-) e amônia (NH3). A conversão de nitrato é a porcentagem de nitrato reduzida. A atividade para redução de nitrato equivale à massa molar de nitrato reduzida em determinado tempo por massa de catalisador usada (mol NO3-/min.g catalisador).De Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44
17 B – Non-noble metal doped TiO2 NH4+ main byproductNoN-byproductsTime, minKinetics of photocatalytic degradation of nitrate and formic acid (measured as TOC), and formation of products (ammonia and nitrite)pH 2.5. TiO2, Zn-TiO2, Cr-TiO2 e Cu-TiO2 = 1g L-1. NO3- = 0.6 mM (9 mg N L-1); CHOOH = 9.8 mM (117.4 mg COT L-1).Moreira., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44
18 B – Non noble metal doping Capítulo 6Copper, zinc or chromium:Zn-TiO2: higher photocatalytic activity than Cr-TiO2 or Cu-TiO2, and lower byproducts formation.Zn action To promote efficient charge separation (e-/h+)Moreira et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44
19 B – Doping with non noble metals Effect of dissolved oxygen on the photocatalytic activity of Zn-TiO2O2 competes with NO3- ions, acting as electron acceptorPhotocatalytic nitrate reduction using 4.4% Zn–TiO2 as photocatalystSelectivity [%]Nitrate conversion after 2 h[%]Activity [µmolNO3- (min gcatalisador) -1]Presence of O2 (air)77.287.54.11By purging argon (without O295.491.714.24Moreira et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44
20 C) Coupling semiconductors Ensemble of nanoparticles may exhibit new collective properties resulting from the inter-particle coupling of surface electrons (excitons), plasmons or magnetic moments.induce a substantial alteration of the electronic structures of the nanoparticle ensemble bonding and anti-bonding levels are formed, yielding a new electronic structure.Illustration of an electronic bond formed between (A) two atoms and (B) two nanocrystals.Tong, Ouyang, Bi, Umezawa, Oshikiri, Ye, Adv Mater 2012, 24, 229.
21 C) Coupling semiconductors Interesting way to increase the efficiency of a photocatalytic process:- by increasing the charge separation- by extending the energy range of photoexcitation for the system- by extendingThe potential of VB or CB of coupled semiconductors should be more negative or less positive, respectively, than pure TiO2Hole produced in the VB remains in the CdS particleElectron it is transferred to the CB of TiO2 particle.The electron transference from CdS to TiO2 increase the charge separation and the photocatalytic efficiency.Sclafani, A.; Mozzanega, M.-N.; Pichat, P. J. Photochem. Photobiol. A: Chem. 1991, 59, 81.
22 Hybrid seminconductors– TiO2/graphene is promising to simultaneously possess excellent adsorptivity, transparency, conductivity, and controllability, which could facilitate effective photodegradation of pollutants.Graphene increase the electric conductivity, charge transfer and chemical stability- Decrease recombination electron/hole due to the high electronic conductivity of graphene;High active site concentration, due to the high ratio area:volume, and bidimensional structureHigh range of light absorptionTiO2/graphene composites Strong interaction aromatic rings of graphene and organic moleculesBond Ti-O-C graphene acts as co-catalyst (Lv et al., Procedia Engineering 27 (2012)TiO2 (P25)-graphene photocatalytic activity is higher than pure TiO2 P25 (Zhang et al., 4 (2010) 380)
23 Kinetic of photocatalytic degradation of Rhodamine B TiO2/GrapheneScheme of the Photocatalytic Degradation of methylene blue (a) TiO2 (b) TiO2/GrapheneE. Lee et al. / Journal of Hazardous Materials 219– 220 (2012) 13– 18High activity results from:Strong coupling between TiO2 on graphene oxide facilitate interfacial change transfer;(GO ) acts as electron acceptor and inhibits the e/h recombation.Kinetic of photocatalytic degradation of Rhodamine BKinetic constant for the photocatalytic degradation of Rhodamine BLiang et al, Nano Res,2010.Huimin et al., Chinese Journal of Catalysis, 33 (2012)
24 ZnFe2O4/Magnetic graphene Nanosheets of graphene and ZnFe2O4 nanocrystalsComparing ZnFe2O4 and ZnFe2O4/grafenoComposite ZnFe2O4/grafeno catalyst for photodegradationGeneration of HO* radicals via photochemical reactions of H2O2 under visible lightSpinel ZnFe2O4 (Eg= 1.90 eV) Magnetic semiconductor materialZnFe2O4 – with (a) and without (b) magnetic fieldThe photogenerated electrons of excited ZnFe2O4 were transferred instanteously from the conduction band of ZnFe2O4 to graphene at the site of generation via a percolation mechanism, resulting in a minimized charge recombination enhanced photocatalytic activityFu e Wang, Ind Eng Chem Res 50 (2011)
25 Lanthanide modified semiconductor photocatalystss The biggest difference between the transition metal ion and the lanthanide ions nature of the 4f orbitalsLanthanide excellent optical propertiesIncorporation of Rare-Earths metal ions leads to the formation of multi energy levels below the conduction band edge of TiO2Lanthanide ions may act as electron scavenger and suppress e/h recombination;Lanthanite ions also can faciliate the adsorption of organics or act as electron acceptors (minimizing e/h recombination)Photocatalytic activity of Ln3+/TiO2Weber, Grady and Kookdali, Cat Sci & Tech 2012, 2, 683.General enhancement in the photocatalytic activity:Enhanced adsorption of the organics;Effective separation of e/hHigh intrinsic absorptivity under UV irradiation due to the ability of RE metal ions to trap electrons and minimize e/h recombination
26 (b) Photographs of Ce-doped TiO2 samples CeO2/TiO2TOC removal efficiencies (Methylene blue) during visible light irradiation (t=180 min)(a) UV vis absorption spectra fo undoped and Ce-doped TiO2 microspheres(b) Photographs of Ce-doped TiO2 samplesEffect of cerium doping the photocatalytic activity to degrade methylene blue:From 1 – 5% cerium excess Ce4+ dopants may introduce the indirect recombination of electrons and holes to reduce the photocatalytic activity.J. Xie et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 372 (2010) 107–114
27 CeO2/TiO2Photocatalytic degradation of methylene blue – different catalysts and P25Photocatalytic degradation of Rhodamine B– different catalysts and P25J. Xie et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 372 (2010) 107–114
28 Compósitos de TiO2 dopados com Er3+:YAlO3/Fe- e Co Fe and Co ions doped into TiO2 powder to restrain the recombinationEr3+:YAlO3 upconversion luminescence agent can transform the visible light into UV light more efficientlyDegradation of organic compounds in the presence of Er3+:YAlO3/(Co or Fe)/TiO2 under visible lightVisible light is converted luz UV pelo Er3+:YAlO3.UV light can excite TiO2 -> electrons transfer from VB to CBe/h pairs no recombination due to presence of Fe or Co ionsR. Xu et al. / Solar Energy Materials & Solar Cells 94 (2010) 1157–1165
29 TiO2 composites doped with Er3+:YAlO3/Fe- or Co 25% Er3+YAlO3/Fe/TiO225% Er3+YAlO3/Co/TiO210% Er3+YAlO3/Co/TiO25% Er3+YAlO3/Fe/TiO2Fe/TiO2Co/TiO2Photocatalytic degradation of azo fuchsine int the presence of photocatalysts Fe or Co/TiO2 and different amouns of Er3+:YAlO3R. Xu et al. / Solar Energy Materials & Solar Cells 94 (2010) 1157–1165
30 Bismutum SpinelsBiWO6, Bi4Ti3O12, BIOX (X=Cl, Br, I), Bi2O3 photocatalytic activity under UV and visible lightEg = 2,9 a 3,5 eV, depending on the preparation method (Chen et al., 2012).Bi2S3 Eg= 1,3 a 1,7 eV (Mesquita e Silva, 34ª Reunião SBQ, 2011).* Bi2O2CO3 High activity: morphology, low band gap energy. (Chen et al., 2012)* CdBiYO4 (Du and Juan, Solid State Sciences, 14 (2012) ) spinel
31 Copper nanowires CuO Eg ~1.2 eV Nanowires CuO e Cu(OH)2 FESEM images of sampleNanowires of CuOEfficient charge separation and increase of photocatalytic activityUV absorption spectra of CuO nanowiresPhotocatalytic degradation of Rhodamine B using different photocatalysts under UV lightYu Li, Xiao-Yu Yang, Joanna Rooke, Guastaaf Van Tendeloo, Bao-Lian Su. Ultralong Cu(OH)2 and CuO nanowire bundles: PEG200-directed crystal growth for enhanced photocatalytic performance, Journal of Colloid and Interface Science 348 (2010) 303–312
32 O2 + H+ + e = HO2* (aq), 0.046 V vs NHE Tungstenium oxidesWO3 + co-catalyst(Pt, Cu, or Pd): high photocatocalytic efficency to degrade organicsWO3 --> Conduction Band ( +0.5 V vs NHE) is more positive than that for O2 reductionO2 + e = O2*- (aq) V vs NHE;O2 + H+ + e = HO2* (aq), V vs NHEWO3 can act as photocatalyst sensible to visible light in the presence of an electron acceptor (ozônio V vs NHE).Ozone reacts with the photoexcited electrons oxidation of organic compoundsWO3 Eg = 2,5 evS. Nishimoto et al. / Chemical Physics Letters 500 (2010) 86–89
33 Photocatalytic degradation of Phenol TOC initial = 130 ppm S. Nishimoto et al. / Chemical Physics Letters 500 (2010) 86–89Photocatalytic degradation of PhenolTOC initial = 130 ppm
34 d0 e d10 Óxidos metálicos E) Photocatalysts d10 d0 Ga3+: ZnGa2O4 Domen et al. New Non-Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem. 2007d10Ga3+: ZnGa2O4In3+: AInO2 (A=Li, Na)Ge4+: Zn2GeO4Sn4+: Sr2SnO4Sb5+: NaSbO7d0Ti4+: TiO2, SrTiO3, K2La2Ti3O10Zr4+: ZrO2Nb5+: K4Nb6O17, Sr2Nb2O7Ta5+: ATaO3(A=Li, Na, K), BaTa2O6W6+: AMWO6 (A=Rb, Cs; M=Nb, Ta)TiO2 1967, published 1972Generally, the band gap energy is high Photocatalytic activity of oxides and nitrides d10 metals it is associated with the CB of the hybridized sp-orbitals, that are able to produce photoexcited eletrons with high mobility.
35 Final RemarksThe function and engineering of co-catalysts is one of the most important subjects in photocatalysis.Challenge and perspectives photocatalysts sensible to visible light and high activityPromissor materialsGrapheneRare earthsComposites and doped co-catalytsReactor design is still a big challenge