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L-cystine-assisted Hydrothermal Synthesis Of Mn-Cd-S Solid Solution For Efficient Photocatalytic Hydrogen Evolution Under Visible Light Irradiation

Posted on:2015-11-06Degree:MasterType:Thesis
Country:ChinaCandidate:L Q ZhangFull Text:PDF
GTID:2181330431490170Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Photocatalytic water splitting into H2using solar energy is considered to be one of themost ideal approaches to address energy and environmental problems. The bottleneck forphotocatalytic H2production using solar energy towards practical applications is to developvisible-light-driven photocatalysts that are higly efficient, stable and inexpensive. Manytransition metal chalcogenides exhibit strong absorption in the visible region due to the higherorbital of S3p than that of O2p, with the potential for photocatalytic H2production undervisible light irradiation. L-cystine contains-SH,-NH2,-COOH functional groups, which has astrong affinity to metal cations to form metal-ligand complexes and is now attracting intenseresearch interest to be an alternative sulfur source to generate binary or ternary metal sulfidenanostructures. This thesis focuses on the synthesis of nanostructured Mn-Cd-S solid solution,CdS as well as ZnS by a facile, environmental-friendly, cost-effective and low-temperaturehydrothermal method adopting L-cystine as the sulfur source and the coordinating molecule.In addition, the photocatalytic activity and stability of Mn-Cd-S solid solutions for waterdecomposition to H2under visible light irradition are also investigated. The obtained mainresults are follows:(1) A series of Mn1-xCdxS solid solutions with hexagonal wurtzite structure have beenfabricated with the assistance of L-cystine as the S source and cheating reagent via a facilehydrothermal route at a lower temperature (130°C). The band gaps of the solid solutions canbe adjusted by changing the ratio of γ-MnS to h-CdS. Efficient hydrogen production from theaqueous solution containing S2-/SO32-as sacrificial reagents is observed over thesephotocatalysts under visible light irradiation. Among all samples, the highest photocatalyticactivity is observed on Mn0.24Cd0.76S photocatalyst, with the rate of H2-production10.9mmolh-1g-1, corresponding to an apparent quantum yield as high as9.5%at420nm even in theabsence of co-catalysts, which far exceeds that of CdS. The excellent photoactivity of thiscomposition is mainly related to the energy band structure as well as large specific surfacearea and high crystallinity. Moreover, Mn0.24Cd0.76S solid solution also displays good stabilityand anti-photocorrosion capability during the photocatalytic reducing water to hydrogen undervisible light. (2) Spherical and rod-like CdS have been synthesized solvothermally in a mixed solventof water/ethylenediamine by adopting L-cystine as the sulfur source and the coordinatingagent. The phase and morphology of CdS nanocrystals could be effectively controlled byadjusting the molar concentration and molar ratio of Cd(CH3COO)2·4H2O and L-cystine, thevolume ratio of water/ethylenediamine, reaction temperature as well as the reaction time.(3) ZnS nanoparticles with cubic and hexagonal phase have been fabricated by a facile,environmental-friendly, cost-effective and low-temperature hydrothermal method adoptingL-cystine as the sulfur source and the coordinating molecule. The crystalline phase,morphology and size of ZnS nanoparticles could be adjusted by changing the molar ratio ofZn(CH3COO)2·4H2O and L-cystine, the reaction temperature as well as the reaction time.
Keywords/Search Tags:Mn-Cd-S solid solution, CdS, ZnS, L-cystine, hydrothermal, H2, visible light
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