Preparation And Properties Of Non-stoichiometric Cu₂S And CuAlO₂ Photocatalytic Materials

With the developing of science and technology and the expanding of people's demand for energy,the problems of environmental pollution and energy crisis are emerging day by day.Among the many solutions,semiconductor photocatalysis technology has attracted much attention because of its ability of degrading organic pollutants and decompose aquatic hydrogen at room temperature.Copper-based oxygen group compounds have been considered as excellent photocatalytic semiconductor materials because of their non-toxic,cheap and suitable spectral response range.In the previous research,it has been proved that it has great potential for the application of hydrogen decomposition,CO₂ reduction and pollutant degradation.However,some defects will inevitably be caused in the process of experimental preparation.For example,the volatility of S often leads to the loss of S atoms in Cu_2-xS,and the existence of defects will have a serious impact on the photocatalytic performance of semiconductor.Therefore,the aim at improving photocatalytic ability can be achieved by studying and utilizing its non-stoichiometric ratio.So Cu_2-xS and Cu Al O₂as two typical copper based oxygen compounds are selected.To ensure the preparation of non-stoichiometric samples without introducing other impurities,and to study and utilize the non-stoichiometric ratio by combining calculation and experiment.The LSPR effect of Cu_2-xS in the literature is explained on the atomic level by first principles calculation.The reason is that the Fermi level passes through the valence band makes Cu_2-xS become degenerate semiconductor.Combining simulation and experiment,the influence of size of Cu_2-xS changes into LSPR effect and photocatalytic performance was studied.It is found that as the size gradually decreases,the absorption peak of LSPR has a red shift.Cu_7.2S₄ powder was synthesized by hydrothermal method,and the size of Cu_7.2S₄powder was changed by adjusting the amount of PVP.The absorption curve of Cu_7.2S₄ powder was obtained by measuring the absorption spectrum,which was consistent with the simulation results.Cu_7.2S₄ can degrade 30%of 40 mg/L Methyl Orange solutions in 2 hours.Moreover,the absorption of LSPR effect in the near infrared region can also be used in the photocatalytic reaction,which broadens the spectral response range.The non-stoichiometric defect of interstitial oxygen in Cu Al O₂ was screened out by first-principle calculations,which is beneficial to the photocatalytic reaction and is easier to prepare.Under the guidance of results of calculation,the preparation process of Cu Al O₂ solid-phase synthesis was optimized,and the non-stoichiometric ratio Cu Al O_2+?with different excess oxygen content was successfully obtained.Through the electrochemical characterization and photocatalytic performance characterization,it is found that the introduction to excess oxygen is beneficial to increase the carrier concentration from 1.2×10²⁰cm^-3to 1.9×10²⁰cm^-3,and the photocurrent can gradually increase from 5.03?A to 11.75?A.However,with the introduction of excess oxygen,its hydrogen production activity increased from 1.69?mol/h to 1.96?mol/h and then decreased to 1.25?mol/h.The reason may be that the size of micro-crystals prepared in air atmosphere is too large,the specific surface area is obviously reduced,and the interface resistance is increased,which hinders the charge transfer process of photo-generated electron holes,resulting in the decrease of hydrogen production rate.In this thesis the microstructure of non-stoichiometric Cu_2-xS semiconductors was studied at atomic level by first principle calculation and simulation.The reason of LSPR effected in Cu_2-xS and its effect on photocatalytic performance was explained.Different sizes of Cu_2-xS were obtained by using the experimental preparation,which verified the accuracy of the calculation results.In the study of ternary non stoichiometric Cu Al O_2+?,non-stoichiometric Cu Al O_2+?and pure Cu Al O₂ were obtained by adjusting the change of atmosphere during the solid phase synthesis.Using photo-electrochemical test,it is found that the introduction of excess oxygen can improve the photocurrent and carrier concentration,and enhance the photocatalytic performance.These results provide some new ideas and research cases for the development and exploration of non-stoichiometry in copper based oxy compounds.