Preparation, Photocatalytic Activity And Machenism Of Plasmonic Photocatalysts

The growing concerns about environmental and energy crises have stimulated intense research on solar energy utilization. In the field of the elimination of organic pollutants, solar photocatalysis by semiconductors has emerged as one of the most promising technologies.The most common photocatalyst is Ti O2, and some non Ti O2-based photocatalysts, such as carbon nitride and bismuth-based Oxides, have recently attracted a great deal of interest in photocatalytic application. However, the practical applications of these photocatalysts are severely limited of its poor solar energy harvesting ability and fast recombination of photogenerated electrons and holes.Herein, a series of plasmonic photocatalysts, Pt-Ti O2/Si O2, Ag/g-C3N4 and Ag@Ag Br/g-C3N4, with efficient visible-light photocatalytic activity and charge separation ability were prepared based on Ti O2 and g-C3N4 substrates. Much attention has been focused on the porous properties and energy band matching. The chemistry composition, crystal structures, porosity, morphologies, and photophysical properties of the products were well-characterized by X-ray diffraction(XRD), Fourier Transform infrared spectrometer(FT-IR), N2 adsorption/desorption, X - ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), field emission scanning electron microscopy(FESEM), UV-Vis diffuse reflectance spectra(UV-Vis/DRS).Their photocatalytic ability, mineralization ability and reusability were evaluated by degradation of aqueous PNP, BPA, MO or RB under the simulated-sunlight or visible-light irradiation. Moreover, photoelectrochemical experiments,free radical and hole scavenging experiments and analysis of intermediates were applied to find out the photocatalytic mechanism and photocatalytic degradation pathway of plasmonic photocatalysts toward organic pollutions.The main results was concluded as follows:1 Preparation, characterization and photocatalytic activity of Pt-Ti O2/Si O2Pt-Ti O2/Si O2 with ordered or dis ordered mesoporous structure were controllably fabricated in bi-Ti source system(TTIP and Ti Cl4) and single-Ti source system(TTIP) by using P123 as the soft template and TEOS as Si source. The characterized result showed that ordered mesoporous material possessed 2D hexagonal p6 mm structure and disordered mesoporous material possessed 3D interconnected structure. Both of them exhibited anatase and rutile biphase with large pore size(13.2, 13.4 nm) and high surface area(231, 268 m2g-1).The absorption of them appeared in the whole range of visible-light.The photocatalytic activity of ordered mesoporous Pt-Ti O2/Si O2 is higher than dis-ordered mesoporous Pt-Ti O2/Si O2 with similar Pt loading. Ordered mesoporous Pt-Ti O2/Si O2 with 0.4%Pt loading exhibited highest photocatalytic activity toward PNP and BPA.PNP was completely decomposited after 60 min under simulated sunlight irraditation and reached to 64%decomposition after 240 min under visible-light irradiation,while BPA was fastly decomposited after 10 min under visible-light irraditation.2 Preparation, characterization, photocatalytic activity and mechanism of Ag/g-C3N4A series of silver deposited g-C3N4 plasmonic photocatalysts with Ag loading from 0.1to 5 wt% were prepared by thermal polymerization of urea precursor combined with the photodeposition method. The characterized result showed that Ag/g-C3N4 displays the platelet-like morphology with micro-meso pores structure and possessed larger BET surface area(64-68 m2 g-1), meanwhile, sphere-like silver particles homogeneously dispersed on the surface of g-C3N4 platelets. The absorption of them appeared in the whole range of visible-light.Ag/g-C3N4 with Ag loading of 2% showed the highest visible-light photcatalytic activity.The decomposition of MO reached to 91% within 60 min, which is 2 and 1.6 times faster than Ti O2(P25) and g-C3N4; the decomposition of PNP reached to 98% within 120 min, which is10 and 1.2 times faster than Ti O2(P25) and g-C3N4. As-prepared Ag/g-C3N4 heterostructures show excellent catalytic stability after 5 consecutive photocatalytic degradation of MO.Based on the photoelectrochemical experiments and free radical and hole scavenging experiments, it showes that the separation of photogenerated electrons and holes is not satisfied. Only two kind of active species(h VB+ and·O2-) were detected in the g-C3N4 system.After Ag modified, the photogenerated electrons can transfer to the Ag, making the separation of electrons and holes easier. And the electrons accumulated on the surface of Ag can participate in the multiple-electron reduction of oxygen, leading to the generation of·OH,which improved the photocatalytic of Ag/g-C3N4.3 Preparation, characterization, photocatalytic activity and mechanism of Ag@ABr/g-C3N4On the base of Ag/g-C3N4, a series of Ag@Ag Br grafted graphitic carbon nitride plasmonic photocatalysts were fabricated through photoreducing Ag Br/g-C3N4 bybrids prepared by deposition-precipitation method. The characterized result showed that sphere-like Ag@Ag Br particles had two kind of size(200 nm and 1000nm), which contacted with g-C3N4 closely. The absorption of them appeared in the whole range of visible-light.Ag@Ag Br/g-C3N4 with Ag@Ag Br content of 50% showed the highest visible-light photcatalytic activity. After 10 min, the photocatalytic degradation of MO and RB reaches94% and 95%, which is 5 and 1.6 times faster than g-C3N4. As-prepared Ag@Ag Br/g-C3N4 heterostructures remains 70% photocatalytic activity after 4 consecutive photocatalytic degradation of MO.Based on the photoelectrochemical experiments and free radical and hole scavenging experiments, it showes that Z-scheme structure has been constructed within the Ag@Ag Br/g-C3N4, which keeps the e CB-with high reduction capability in CB of g-C3N4 and h VB+ with high oxidation capability in VB of Ag Br. Therefore, three kind of active species(h VB+,·O2-and Br0) were detected in the Ag@Ag Br/g-C3N4 system, which improved the photocatalytic of Ag/g-C3N4.Based on the intermediates indentified in the Ag@Ag Br/g-C3N4 system, the photcatalytic degradation pathway of MO is put forward. With the help of active species(h VB+,·O2-and Br0), the cleavage of C-N bond within MO and ring-opening reaction occurred,resulting in a series of organic acids including oxalic acid, lactic acid and formic acid. The final products were SO42-, NO3-, CO2 and H2 O.