Abstract
Aqueous solutions of mixed CdS/ZnS semiconductor (SC) nanoparticle suspensions in phosphate buffers containing 10 mM [Fe(CN)6]4– were used for photochemical production of hydrogen via hydrated electron intermediates. CdS was doped with varying percentages of ZnS to expand the absorption range of the composite to the UV region. Results show that maximum generation of hydrated electrons by [Fe(CN)6]4– occurs at pH 6. Furthermore, native CdS amorphous nanoparticles give the greatest photocurrent. Studies also show that, in phosphate buffer, the steady state photocurrent was directly proportional to the CdS content in the mixture of CdS/ZnS. The aqueous nano-systems sustained their stability as indicated by the reproducibility of their photocatalytic activities. Solar radiated assemblies of CdS/ZnS/ [Fe(CN)6]4– sustained cyclic systems for continuous hydrogen production.
Highlights
Traditional chemical or electrochemical methods for production of hydrogen tend to be complicated and energy consuming process
The low band gap of CdS (2.3 eV) generated the greatest photochemical production of hydrogen compared with its mixtures with ZnS. This indicates that the addition of ZnS widened the band gap of the CdS/ZnS alloy, resulting in less absorption of the solar radiation
This widening of the band gap took place by a downward shift of the valence band, and asmall upward shift in the conduction band of the CdS/ZnS alloy.Studies show that the direct band gap of mixed CdS/ZnS materials varied monotonically with the percent of CdS in the mixture
Summary
Traditional chemical or electrochemical methods for production of hydrogen tend to be complicated and energy consuming process. Some of these methods are not even environmentally safe. The high band gap energy (3.2 eV) of TiO2 requires UV radiation for photoactivation, limiting its application in the visible light range, and charge carrier recombination (e−/h+) occurs within nanoseconds, limiting its photocatalytic activity [18]. The disadvantage of a homogeneous process for hydrated electron production is its irreversibility. Such a disadvantage can be overcome by the use of a semiconductor system which acts as an electron donor and reduces [Fe(CN)6]3– back to [Fe(CN)6]4–. Conditions that maximize the production of hydrated electrons were explored
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