Application Of Gold/Silver Doped Semiconductors In Photocatalytic Hydrogen Production

Hydrogen(H2)is regarded as an important clean energy source in this century because of its high energy density and environmental protection.However,the traditional industrial H2 production method has the disadvantages of high cost,harsh reaction conditions,many by-products and so on.Photocatalytic H2 production technology is a carbon-free and pollution-free process with the characteristics of economy and simple operation,it is one of the most promising methods for H2 production.Up to now,photocatalytic semiconductors have been extensively studied,including graphite phase carbon nitride(g-C3N4),cadmium sulfide(CdS),titanium dioxide(TiO2)and so on.However,most semiconductors have the disadvantages of easy recombination of photogenerated carriers and low utilization of sunlight.Therefore,it is necessary to modify them and prepare a low-cost,efficient and stable photocatalyst.In this paper,g-C3N4,CdS and TiO2 semiconductor materials were modified by gold and silver doped semiconductors,and their photocatalytic activity and stability were studied.The main contents are as follows:(1)AuNPs/g-C3N4 hybrids were by in-situ doping technique.Firstly,gold-cyanoguanidine microspheres(GCMs)were synthesized by complexing cyanoguanidine with chloroauric acid.Then GCMs were mixed with cyanoguanidine solution evenly.After freezing-drying,they were calcined at 550? in Ar atmosphere,and then binary size AuNPs/g-C3N4 hybrids were prepared.Compared with pure g-C3N4,AuNPs/g-C3N4 hybirds exhibited enhanced visible photocatalytic activity and stability for H2 production,its activity of visible photocatalytic H2 production was approximately 348 times and 25 times higher than that of pure g-C3N4 and 25 times state-of-the-art 3 wt%-Pt/g-C3N4.The key function of binary size AuNPs in improving the photocatalytic activity of g-C3N4 lies in two aspects:(?)AuNPs as an electron sink,it inhibits the recombination of photogenerated electrons and holes in g-C3N4 matrix;(?)plentiful hot electrons generated from the SPR effect of larger AuNPs can be injected into g-C3N4 due to the formation of a Schottky barrier between AuNPs and g-C3N4.(2)AgNPs/CdS heterostructure photocatalysts were synthesized by photodeposition.Firstly,CdS nanofibers were synthesized by microwave-assisted synthesis using thiourea and cadmium chloride as raw materials and ethylenediamine as solvent.Then silver nitrate and CdS powders were added into 20%methanol solution,and AgNPs/CdS photocatalyst was obtained by irradiation with 300 W xenon lamp for 1 h.Under the same conditions,the photocatalytic activity of AgNPs/CdS hybrids photocatalysts for the H2 generation from pure ethanol under visible light irradiation is 40 times higher than that of pure CdS,which can be attributed to the SPR effect of AgNPs and the formation of Mott-Schottky heterojunction at the interface between CdS and AgNPs.In this work,visible light-driven COx-free splitting of ethanol into H2 and acetaldehyde catalyzed by fibrous AgNPs/CdS hybrids,which provided a non-emission and easy-to-achieve approach for the development of H2 energy,the progress of green organic chemistry and the sustainable development of low-carbon society.(3)AuNPs/TiO2 heterostructure photocatalyst was synthesized by photodeposition.Firstly,TiO2 nanosheets were synthesized by one-step solvothermal method using titanium tetrachloride as raw material and ethylene glycol as solvent.Next,chloroauric acid and TiO2 powder were added to ethanol solvent,followed by stirring in vacuum for 1 h,then irradiated by 300 W xenon lamp for 1.5 h,AuNPs/TiO2 photocatalyst was finally obtained.Compared with pure TiO2,the photocatalytic activity of AuNPs/TiO2 hybrids for decomposition of ethanol to H2 was enhanced,and its photocatalytic activity for H2 production is 153 times higher than that of pure T1O2.The enhanced photocatalytic activity of T1O2 by AuNPs can be attributed to:(i)AuNPs as an sink,can capture electrons easily,which not only promotes electron transfer to the catalyst surface,but also inhibits the rapid recombination of photogenerated charges;(li)schottky barrier is formed between AuNPs and TiO2,which increases the rate of charge generation and electron transfer.