Synthesis Of Cadmium Sulfide-based Nanomaterials For Photocatalytic H₂ Evolution

As an emerging strategy for solar energy conversion,photocatalysis has been widely studied by researchers around the globe due to its energy-saving and environmental properties,therefore designing and fabrication of photocatalysts with superior activities have been a heated topic in current photocatalysis research.Owing to its abundance on earth and non-toxicity to human,metal oxides such as TiO₂ are considered to be a kind of ideal material for photocatalysis.However,the bandgap energies of most metal oxides are too large to for them to make good use of sunlight,which severely limited their applications on photocatalytic energy conversion.In order to address the aforementioned issues,and to design wide solar spectrum responsible photocatalysts with efficient charge separation capabilities for photocatalytic energy conversion applications,this article would be focusing on the following aspects:1)Within the theoretical knowledge framework of tuning the migration rate of photogenerated charge carriers in photocatalysts,we would choose proper co-catalysts to load on visible-light active metal sulfides to experimentally verify the ideas,and finally the results are targeted on improving the photocatalytic activities.2)Synthesis a series of metal-glycerol microspheres using quasi-emulsion templated methods,and then hollowing the interiors of the microspheres by Ostwald Ripening to achieve higher specific surface areas.The hollow structure would provide more active sites for photocatalytic reactions and therefore enhancing the photoactivities.All the contents could be listed as follows:In the first chapter,a brief summary with a global view on the advancement of photocatalysis is made,which includes the history of photocatalysis and the basic mechanism of how photocatalysts work.We have summarized the commonly used strategies used to design high-efficiency photocatalysts,and have theoretically explained how to choose a proper cocatalyst to load on a semiconductor to form a efficient photocatalytic system,thus providing a theoretical view of photocatalysts designing.Besides,we have also summarized the recent progress on morphology modulation for semiconducting nanomaterials used in photocatalysis,which offers a new way for researchers to optimize the activities of the photocatalysts.In the second chapter,we established an efficient photocatalytic system by crafting hole capturing CoO_x cocatalyst onto semiconducting CdS nanorods which resulted in intimately contacted interfaces.Specifically,the negatively charged surface of CdS nanorods acts as a matrix for adsorbing Co²⁺ions through electrostatic interaction,leading to the in situ grown of CoO and Co₃O₄ on the surface.Due to the hole capture effect of CoO_x and the intimately contacted CoO_x/CdS interfaces,photogenerated electrons and holes were directionally transported to CdS nanorods and the CoO_x,respectively,thereby the charge separation efficiency was greatly improved.As a consequence,the illustrational CdS/CoO_x core-shell NRs possessed more superior photostability under visible light illumination??>420 nm?,and correspondingly exhibits ca.43-folds faster of H₂ evolution rate than the pristine CdS nanorods.The feasibility and reproducibility of this strategy offers a new way of designing photocatalysts with optimized charge separation and enhanced stability,and is expected to design other solar energy conversion systems.In the third chapter,we synthesized Cd-glycerate microsphere precursors using a quasi-emulsion templated method.The microsphere precursors were then etched by S2-under solvothermal conditions,the final product exhibited different hollow structures by varying the time of solvothermal etching,which is mainly caused by Ostwald Ripening.We investigated the transformation and the morphology-dependent relationships between the different hollow structures.It turned out that the double-shelled cadmium sulfide hollow microspheres possessed better charge transfer capabilities,therefore exhibiting more superior activities regarding photocatalytic hydrogen evolution.In the final chapter,we summarized the conclusions we had drawn in our experiments and analyzed the current status of research on photocatalysis.Moreover,we also made some predictions of the on-going trend of photocatalysis from our own point of view.