Investigation On The Design And Synthesis Of Environmental-Friendly Nanomaterials Based On Zinc And Their Energy Conversion And Application

As the energy crisis and environmental pollution become more and more serious,the development of environment-friendly energy materials and the management of the polluted environment have become the focus of scholars'researches.Solar energy is one of the most promising clean energy,but the instability and discontinuity limit its application.Developing stable photovoltaic conversion system is an effective way to store solar energy.However,most of the traditional photovoltaic conversion materials involve the use of precious metal or high toxic organic solvents,while the low toxicity and low cost materials are usually less active.Therefore,it is of great significance to design low toxicity,low cost and high efficiency energy materials to make full use of solar energy and reduce environmental pollution during the process of energy conversion.In this dissertation,a series of environment-friendly zinc-based energy materials were synthesized and the properties and mechanism of their photoelectric conversion were systematically studied,mainly including the following four parts:?1?The preparation of 2-aminoethanethiol hydrochloride?MA?-Cd_xZn_1-xTe Nanocrtystals?NCs?and their application in aqueous processed solar cells.MA capped Cd_xZn_1-xTe NCs with excellent solubility and film-forming properties were successfully prepared and applied to aqueous-processed NCs solar cells.The highest power conversion efficiency?5.96%?and photocurrent(21.2 mA cm^-2)based on aqueous-processed NCs solar cells were achieved.The mechanism for the improvement of power conversion efficiency was systematically studied.The experimental results showed that the introduction of zinc ions not only reduced the toxicity of CdTe active layer to some extent,but also widened the Fermi level offset between active layer and electron transport layer,increased the open circuit voltage by 12%,and lengthened the depletion region from 130 to 137 nm.Especially,the depletion region was further successfully tuned from 137 to 171 nm,and even lengthened to a record thickness of 200 nm by introducing a bulk heterojunction layer and further optimizing the annealing temperature.As a result,a champion thickness ratio?74%?of depletion region to active layer was achieved.More efficient transport and extraction efficiency as well as prolonged lifetime of carriers were realized.This work provides a simple way to prepare polynary NCs and highlights a prospective method to develop more efficient,cost-effective and easily operated solution-processed environment-friendly solar cells applied in the field of energy storage and conversion.?2?The preparation of three-dimensional?3D?ZnO-SnS porous composite materials and their application in photocatalysis.A novel solution approach was put forward to design environmentally friendly three dimensional ZnO-SnS porous photocatalysts,which degraded organic dyes?such as rhodamine B?within 80 min.A systematic study of catalytic mechanism showed that the introduction of SnS photosensitizer increased the sunlight absorption range of ZnO.Besides,the construction of quasi-type II p-n heterojunction improved the separation rate of carriers and inhibited the photocorrosion of ZnO.In addition,the design of three-dimensional porous structure ensured a high specific surface area of catalyst.This work lays a theoretical foundation for the design of environment-friendly ZnO and SnS based photocatalysts.?3?The preparation of two-dimensional?2D?ZnS-SnS₂ porous nanosheets and their application in photocatalytic water splitting.The 2D ZnS-SnS₂ porous nano-sheet was prepared by a simple two-step method.An optimized photocatalytic H₂ generation rate of 536?mol h^-1g^-1 was achieved without any surfactant or co-catalyst,which was much higher than that of ZnS and SnS₂ based photocatalysts under the same conditions.Moreover,the porous nanosheets had fairly good photocatalytic stability.A systematic study of catalytic mechanism showed that ZnS-SnS₂ successfully combined the high reduction potential of ZnS and wide sunlight absorption range of SnS₂.In addition,the unique 2D porous nano-structure maintained a high specific surface area(246.7 m² g^-1)and a large number of reactive sites.Besides,the construction of type I heterojunction between ZnS and SnS₂ greatly promoted the separation ability of carriers.This work demonstrates the great potential of ZnS-SnS2 porous nanosheets as a low toxicity,low cost and high efficiency photocatalysts in energy conversion.?4?Design and synthesis of zero-dimensional/three-dimensional?0D/3D?g-C₃N₄/ZnS composite photocatalysts and their application in photocatalytic water splitting.The hydroxyl modified zero-dimensional g-C3N4 NPs were prepared by a simple one-step hydrothermal method.While reducing the dimension,improving the hydrophily and specific surface area,the narrowed band gap was realized.When combined with ZnS,the obtained g-C₃N₄/ZnS photocatalysts possessed a catalytic activity of 5.6 mmol h^-1g^-1 under visible light,which was obviously higher than most of ZnS and g-C3N4 based catalysts.A systematic study of catalytic mechanism by the combination of experiment and theoretical calculation showed that the catalyst had the advantages of wide absorption range,high specific surface area,high hydrophily and efficient carrier separation ability.This work sets a reference for the preparation of 0D g-C3N4 nanoparticles and provides theoretical guidance for the design of zinc-based composite photocatalysts and their application in energy conversion.