Research On Photocatalytic Reduction Of Carbon Dioxide And Water Decomposition By La₂CuO₄

The flourishing development of modern society relies on the large-scale use of fossil energy such as oil,coal and natural gas,but it also causes very serious environmental problems.The carbon accumulated in the earth's crust for thousands of years is released into the atmosphere by human beings in the form of carbon dioxide in a very short time,which greatly exceeds the self-regulating ability of the natural environment and causes a series of climate anomalies.Therefore,the proportion of non-fossil energy in primary energy will continue to increase,especially solar energy,which is an inexhaustible source of energy.More and more researchers are turning to the field of photocatalytic energy conversion,such as photocatalytic carbon dioxide reduction and photocatalytic decomposition of water.Most of the solar spectrum is in the visible range,so the best choice for energy conversion using solar energy is to use a visible-light-responsive material as a catalyst to make more efficient use of sunlight.Therefore,materials with narrow optical band gaps generally have superior catalytic performance in the field of photocatalysis,while satisfying other conditions.In this thesis,the narrow bandgap material La₂CuO₄ was used as the research object,and the performance and analysis of the solar energy to chemical energy conversion process of carbon dioxide reduction and water decomposition were studied.The main research contents are as follows:Research on photocatalytic reduction of carbon dioxide by La₂CuO₄ powder.In this thesis,the preparation method of La₂CuO₄ powder was improved.The pure phase La₂CuO₄powder photocatalyst was prepared by sol-gel method and applied to photocatalytic reduction of carbon dioxide.Compared with the conventional solid phase sintering method,the CO yield of the sample prepared by the sol-gel method reached 2.97 ?mol·g-1·h-1 in the 8-hour reaction process,and the CH4 yield reached 0.82 ?mol·g-1·h-1,which was 4 times and 5 times higher than the former.This is mainly due to the fact that the sol-gel method reduces the particle size and increases the surface active sites.Comparing the phase components before and after the reaction,it was found that the La2O3 heterophase was produced,and it was accompanied by the formation of elemental Cu near the active site,indicating that the photochemical stability of the La₂CuO₄ powder photocatalyst was not good.By supporting Ag,Co metal promoter,not only the activity of photocatalytic reduction of carbon dioxide is enhanced,but also the light stability of the catalyst itself is improved.Preparation of La₂CuO₄ thin film photocathode by spray pyrolysis and its properties.In this thesis,a pure phase La₂CuO₄ thin film photocathode was successfully prepared by spray pyrolysis on FTO substrate.Compared with the film prepared by traditional electrophoretic deposition method,the electrode prepared by this process has obviously superior photocurrent performance and dark state.In the 1 M Na2SO4 solution at pH=7,the film prepared by spray pyrolysis had a saturated photocurrent density of about 0.3 mA·cm-2,which was nearly 10 times higher than that of the former.However,the light stability of the La₂CuO₄ thin film photocathode is not good,and it is reduced by about 70%in 300 seconds.The metal catalyst is subsequently deposited by magnetron sputtering to protect the matrix catalyst.