Presentation on theme: "Perspectives on photocatalysis to the water and wastewater treatment Prof Regina de F P M Moreira Departamento de Engenharia Química e Engenharia de Alimentos."— Presentation transcript:
Perspectives on photocatalysis to the water and wastewater treatment Prof Regina de F P M Moreira Departamento de Engenharia Química e Engenharia de Alimentos Universidade Federal de Santa Catarina Florianópolis - SC
Photocatalysis Number of papers/year (www.sciencedirect.com) Number of papers in Photocatalysis: 1975–1980: –2010: Number of patents in photocatalysis Air treatment Self cleaning surfaces Water and wastewater treatment TiO 2 - the most used photocatalyst (non-toxic, stable and not expensive) Balkus Jr, K., New and Future Developments in Catalysis - Catalysis by Nanoparticles, 2013, Pages 213–244 Publications about “nanoparticle photocatalysts”
Photocatalysis (1975–1985)semiconductor/solution interface under UV irradiation several semiconductors Polycristalline 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
Photocatalysts Semiconductors Conduction 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 NHE Band-edge positions of semiconductor photocatalysts relative to the energy levels of various redox couples in water. H Tong, S Ouyang, Y Bi, N Umezawa, M Oshikiri, J Ye, Nanophotocatalytic materials: possibilities and challenges, Adv Mater 2012, 24, Photocatalytic activity and semiconductor properties Energy 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. Energy bands engineering
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/hole -Band-edge positions are frequently incompatible with the electrochemical potential necessary to trigger specific redox reactions -Modulate the band gap and band-edge positions in a precise manner different strategies -Improvement 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.
Energy Band Engineering I.Modiulation of VB II.Adjustment of the CB III.Continuous modulation of the VB and/or CB A. Millis and S. L. Hunte J. Photochem. Photobiol. A: Chem 180 (1997) 1 VB Redox potential should be sufficiently positive in order to the holes act as electron acceptor ; oxidation reaction CB: Redox potential should be sufficiently negative in order to the oxygen act as electron acceptor reduction reaction Photocatalytic degradation of pollutants in water or wastewater oxygen as electron acceptor
Energy Band Engineering Oxide semiconductors CB slightly negative ; VB significantly positive with respect to the oxidization of H 2 O (vs NHE). Therefore For 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: I.Doping with 3d transition elements II.Cations with d 10 our d 10 s 2 configurations III.Non-metal elements
A) TiO 2 Doping N, S, C, metals strategies to raise the VB maximum B) TiO 2 Dye surface sensitization C) Surface modification to increase stability D) Coupled semiconductors E) Novel semiconductor containing 3d metals. Energy band engineering Miao Zhang et al, Angew. Chem. Int. Ed. 2008, 47, 9730 –9733
A) Doping with non-metal: C, N, P, B, S Mechanism of photocatalytic activity of TiO 2 doped with S S.X. Liu, X.Y. Chen, J. Hazard. Mater. 152, 48–55 (2008) A.1.1 Doping with sulfur K. HASHIMOTO et al. Jpn. J. Appl. Phys., Vol. 44, No. 12 (2005) A.1.2 Doping with nitrogen 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. 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. Successful 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 TiO 2 is accompanied by formatin of Ti 3+ via donor-type deffects
Nanofio dopado com nitrogênio Nanofio Photocatalytic degradation of Phenol in aqueous solution using nanowires of N- doping TiO 2 Ilha, José, Moreira, Degradação fotocatalítica de fenol utilizando nanofios de dióxido de titânio modificados com nitrogênio). UFSC, 2012 PhotocatalystBandgap (eV) TiO 2 P253,05 Nanowire TiO 2 2,62 N-doped TiO 2 nanowired2,53 Catalisadork' (10 -3 min -1 ) P252,6 nanowireTiO 2 0,6 N doped TiO 2 nanowired1,1 Pseudo first order kinetic constant for the phenol minearlization using different photocatalysts Phenol initial concentration: 100 mg/ L; Photocatalyst dosage 1g/L.
Effect of nitrogen content Decomposition of rhodamine B after 1 h using TiO 2 or N- TiO 2 (different N/Ti ratio) under visible light. Ye Cong et al., J. Phys. Chem. C, Vol. 111, No. 19, 2007, N doped TiO 2 Theoretical studies: only 1% atomic% N (0.53 % w/w) on TiO 2 is necessary to activate photocatalytic reactions under visible light. Fu, Zhang, Zhang, Zu, J Phys Chem B 2006, 110, 3061.
CB e - e - e - e - e - e - VB h + h + h + h + h + Recombination e - /h + e - (M) M+e - EgEg B – Metal doping Metal promoter: attracts the electrons to the CB recombination is inhibited.
ionic radius of the metal similar to the Ti 4+, Exhibit 2 or more oxidation states. Energy levels M n+ /M (n+1) similar to Ti 3+ /Ti 4+, Electronegativity: higher than Ti incomplete/parcial electronic configuration Ionic radius B – Metal Doping
Effect of Pt-metal content in Pt/TiO 2 (P25) catalysts on CH 4 yield for photocatalytic reduction of CO 2 after 7 h UV irradiation at 323 K, H 2 O/CO 2 = Fotoactivity of TiO 2 doped with Pt effect of the metal concentration on the production of methane by the photoreaction: CO 2 + H 2 O CH 4 + O 2 Q.-H. Zhang et al. / Catalysis Today 148 (2009) 335–340 B – Noble metals doping
Capítulo 6 Copper, zinc and Chromium De Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44 Photocatalyst synthesis: photodeposition by controllingl of precursor metals solubility B – Non noble metal doping
Photocatalytic denitrification: – Photoreduction of NO 3 - to produce N 2 – Hole scavanger: Formic acid (electron donor) – Nitrate electron acceptor Theoretical molar ratio to reduce nitrate to nitrogen CHOOH:NO 3 - = 8:1 Capítulo 6 De Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44 B - Non-noble metals doping Copper, zinc and Chromium De Bem Luiz et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44
Kinetics of photocatalytic degradation of nitrate and formic acid (measured as TOC), and formation of products (ammonia and nitrite) pH 2.5. TiO 2, Zn-TiO 2, Cr-TiO 2 e Cu-TiO 2 = 1g L -1. NO 3 - = 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 B – Non-noble metal doped TiO 2 Time, min No N-byproducts NH 4 + main byproduct
Capítulo 6 Copper, zinc or chromium: –Zn-TiO 2 : 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 B – Non noble metal doping
Effect of dissolved oxygen on the photocatalytic activity of Zn-TiO 2 – O 2 competes with NO 3 - ions, acting as electron acceptor Selectivity [%] Nitrate conversion after 2 h[%] Activity [µmol NO3- (min g catalisador ) -1 ] Presence of O 2 (air) By purging argon (without O Photocatalytic nitrate reduction using 4.4% Zn–TiO 2 as photocatalyst Moreira et al., Journal of Photochemistry and Photobiology A: Chemistry 246 (2012) 36– 44 B – Doping with non noble metals
C) Coupling semiconductors 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. 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.
The electron transference from CdS to TiO 2 increase the charge separation and the photocatalytic efficiency. Sclafani, A.; Mozzanega, M.-N.; Pichat, P. J. Photochem. Photobiol. A: Chem. 1991, 59, 81. 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 extending The potential of VB or CB of coupled semiconductors should be more negative or less positive, respectively, than pure TiO 2 Hole produced in the VB remains in the CdS particle Electron it is transferred to the CB of TiO 2 particle.
Hybrid seminconductors– TiO 2 /graphene 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 structure - High range of light absorption -TiO 2 /graphene composites Strong interaction aromatic rings of graphene and organic molecules Bond Ti-O-C graphene acts as co-catalyst (Lv et al., Procedia Engineering 27 (2012) TiO 2 (P25)-graphene photocatalytic activity is higher than pure TiO 2 P25 (Zhang et al., 4 (2010) 380) is promising to simultaneously possess excellent adsorptivity, transparency, conductivity, and controllability, which could facilitate effective photodegradation of pollutants.
Kinetic of photocatalytic degradation of Rhodamine B High activity results from: Strong coupling between TiO 2 on graphene oxide facilitate interfacial change transfer; (GO ) acts as electron acceptor and inhibits the e/h recombation. Liang et al, Nano Res,2010. Huimin et al., Chinese Journal of Catalysis, 33 (2012) TiO 2 /Graphene Scheme of the Photocatalytic Degradation of methylene blue (a) TiO 2 (b) TiO 2 /Graphene E. Lee et al. / Journal of Hazardous Materials 219– 220 (2012) 13– 18 Kinetic constant for the photocatalytic degradation of Rhodamine B
ZnFe 2 O 4 /Magnetic graphene Nanosheets of graphene and ZnFe 2 O 4 nanocrystals Comparing ZnFe 2 O 4 and ZnFe 2 O 4 /grafeno Composite ZnFe 2 O 4 /grafeno catalyst for photodegradation Generation of HO* radicals via photochemical reactions of H 2 O 2 under visible light ZnFe 2 O 4 – with (a) and without (b) magnetic field The photogenerated electrons of excited ZnFe 2 O 4 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 activity Spinel ZnFe 2 O 4 (Eg= 1.90 eV) Fu e Wang, Ind Eng Chem Res 50 (2011) Magnetic semiconductor material
Lanthanide modified semiconductor photocatalystss General enhancement in the photocatalytic activity: -Enhanced adsorption of the organics; -Effective separation of e/h -High intrinsic absorptivity under UV irradiation due to the ability of RE metal ions to trap electrons and minimize e/h recombination The biggest difference between the transition metal ion and the lanthanide ions nature of the 4f orbitals Lanthanide excellent optical properties Incorporation of Rare-Earths metal ions leads to the formation of multi energy levels below the conduction band edge of TiO 2 Lanthanide 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 Ln 3+ /TiO 2 Weber, Grady and Kookdali, Cat Sci & Tech 2012, 2, 683.
CeO 2 /TiO 2 J. Xie et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 372 (2010) 107–114 (a) UV vis absorption spectra fo undoped and Ce-doped TiO 2 microspheres (b) Photographs of Ce-doped TiO 2 samples TOC removal efficiencies (Methylene blue) during visible light irradiation (t=180 min) Effect of cerium doping the photocatalytic activity to degrade methylene blue: From 1 – 5% cerium excess Ce 4+ dopants may introduce the indirect recombination of electrons and holes to reduce the photocatalytic activity. Effect of cerium doping the photocatalytic activity to degrade methylene blue: From 1 – 5% cerium excess Ce 4+ dopants may introduce the indirect recombination of electrons and holes to reduce the photocatalytic activity.
Photocatalytic degradation of methylene blue – different catalysts and P25 J. Xie et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 372 (2010) 107–114 CeO 2 /TiO 2 Photocatalytic degradation of Rhodamine B– different catalysts and P25
Compósitos de TiO 2 dopados com Er 3+ :YAlO 3 /Fe- e Co Fe and Co ions doped into TiO 2 powder to restrain the recombination Er 3+ :YAlO 3 upconversion luminescence agent can transform the visible light into UV light more efficiently Degradation of organic compounds in the presence of Er 3+ :YAlO 3 /(Co or Fe)/TiO 2 under visible light Visible light is converted luz UV pelo Er 3+ :YAlO 3. UV light can excite TiO 2 -> electrons transfer from VB to CB e/h pairs no recombination due to presence of Fe or Co ions Visible light is converted luz UV pelo Er 3+ :YAlO 3. UV light can excite TiO 2 -> electrons transfer from VB to CB e/h pairs no recombination due to presence of Fe or Co ions R. Xu et al. / Solar Energy Materials & Solar Cells 94 (2010) 1157–1165
TiO 2 composites doped with Er 3+ :YAlO 3 /Fe- or Co Photocatalytic degradation of azo fuchsine int the presence of photocatalysts Fe or Co/TiO 2 and different amouns of Er 3+ :YAlO 3 Fe/TiO 2 Co/TiO 2 5% Er 3+ YAlO 3 /Fe/TiO 2 10% Er 3+ YAlO 3 /Co/TiO 2 25% Er 3+ YAlO 3 /Co/TiO 2 25% Er 3+ YAlO 3 /Fe/TiO 2 R. Xu et al. / Solar Energy Materials & Solar Cells 94 (2010) 1157–1165
Bismutum Spinels BiWO 6, Bi 4 Ti 3 O 12, BIOX (X=Cl, Br, I), Bi 2 O 3 photocatalytic activity under UV and visible light Eg = 2,9 a 3,5 eV, depending on the preparation method (Chen et al., 2012). Bi 2 S 3 Eg= 1,3 a 1,7 eV (Mesquita e Silva, 34ª Reunião SBQ, 2011). * Bi 2 O 2 CO 3 High activity: morphology, low band gap energy. (Chen et al., 2012) * CdBiYO 4 ( Du and Juan, Solid State Sciences, 14 (2012) ) spinel
Copper nanowires Yu 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 Nanowires CuO e Cu(OH) 2 CuO Eg ~1.2 eV UV absorption spectra of CuO nanowires Photocatalytic degradation of Rhodamine B using different photocatalysts under UV light Nanowires of CuO Efficient charge separation and increase of photocatalytic activity FESEM images of sample
Tungstenium oxides WO 3 + co-catalyst(Pt, Cu, or Pd): high photocatocalytic efficency to degrade organics WO 3 --> Conduction Band ( +0.5 V vs NHE) is more positive than that for O 2 reduction O 2 + e = O 2 *- (aq) V vs NHE; O 2 + H + + e = HO 2 * (aq), V vs NHE WO 3 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 compounds S. Nishimoto et al. / Chemical Physics Letters 500 (2010) 86–89 WO 3 Eg = 2,5 ev
Photocatalytic degradation of Phenol TOC initial = 130 ppm S. Nishimoto et al. / Chemical Physics Letters 500 (2010) 86–89 Photocatalytic degradation of Phenol TOC initial = 130 ppm
d 0 e d 10 Óxidos metálicos d 0 Ti 4+ : TiO 2, SrTiO 3, K 2 La 2 Ti 3 O 10 Zr 4+ : ZrO 2 Nb 5+ : K 4 Nb 6 O 17, Sr 2 Nb 2 O 7 Ta 5+ : ATaO 3 (A=Li, Na, K), BaTa 2 O 6 W 6+ : AMWO 6 (A=Rb, Cs; M=Nb, Ta) d 10 Ga 3+ : ZnGa 2 O 4 In 3+ : AInO 2 (A=Li, Na) Ge 4+ : Zn 2 GeO 4 Sn 4+ : Sr 2 SnO 4 Sb 5+ : NaSbO 7 Domen et al. New Non-Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem E) Photocatalysts Photocatalytic activity of oxides and nitrides d 10 metals it is associated with the CB of the hybridized sp-orbitals, that are able to produce photoexcited eletrons with high mobility. Generally, the band gap energy is high
Final Remarks The 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 activity Promissor materials Graphene Rare earths Composites and doped co-catalyts Reactor design is still a big challenge