Preparation Of CdS And Influence Of Cocatalyst On Its Photolysis Of Water Hydrogen Production

Hydrogen, as a kind of renewable energy, has attracted more and more attentiondue to its pollution-free and efficiency and other advantages. Making full use of solarenergy to produce hydrogen is regarded as one of the“dream”techniques. In1972,Fujishima and Honda successfully split water into hydrogen by photoelectrolysisusing TiO2as electrode. Since then, semiconductors are widely used as catalyst forphotocatalytic hydrogen production. The conventional photocatalysts,(such as TiO2,ZnO and ZnS), only absorb the UV light, which accounts for only4%of the totalsunlight, and thus greatly restricts their practical applications. On the contrary, visiblelight accounts for a large fraction (46%) of the solar spectrum, so it is highly desirableto develop photocatalysts with high activities under visible-light illumination.CdS is an important II-VI semiconductor with relatively narrow bulk band gap(2.42eV), which makes CdS a competitive candidate as photocatalyst.Disadvantageously, the rapid recombination of the excited electron-hole pairs andlimited available sun energy spectrum limit the applications in photocatalysis. Noblemetals, such as Pt, Pd, Rh etc. are usually loaded on CdS as cocatalysts to enhance thehydrogen evolution performance. But the noblemetals are costly and also theirutilization rate is low. Based on the above analysis, we have successfully preparedwool-Pd/CdS photocatalysts, Cd/CdS photocatalysts and flower-like CdS.A kind of recyclable cocatalyst that the wool supported palladium cocatalyst wassynthetized. Wool-Pd as a recycled cocatalyst was loaded on CdS to form thephotocatalysts wool-Pd/CdS. The results indicated that the efficiency ofphotocatalytic hydrogen production was improved under visible light irradiation. Itshowed that the recycled cocatalyst wood-Pd could improve the efficiency ofphotocatalytic activity because of introducing oxidation cocatalyst PdS and reductioncocatalyst Pd. They could effectively prohibit the recombination of photogeneratedelectrons and holes.A certain amount of Na2S2O3·5H2O solution added to the solution containingcadmium ion to form Cd/CdS photocatalysts in the presence of simulated solarirradiation. Cd as cocatalyst introduced in the preparation of CdS was demonstrated as an effcient visible light responsive photocatalyst for hydrogen evolution inphotocatalytic water splitting reaction. The experimental results showed that most ofCd/CdS photocatalysts had higher photocatalytic activity because of effectivephotoexcited electron hole pair separation.A novel flower-like CdS nanoarchitectures were synthesized via a faciletemplate-free hydrothermal process only using Cd(NO3)24H2O and thiourea asprecursors and L-Histidine as a chelating agent. The activity of CdS with L-Histidineis markedly enhanced to376.7μmol/h, nearly13times than pure CdS, and theH2-production rate is signifcantly improved. Furthermore, the photocatalytic activityexperiment illustrated that flower-like CdS with L-Histidine was more stable thanpure CdS in the hydrogen generation. In addition, a growth mechanism of flower-likeCdS nanoarchitectures was proposed. The imidazole ring of L-Histidine captured theCd ions from the solution, and prevented the growth of the CdS nanoparticles.