Surface Modification Of Copper Oxide And Their Photocatalytic Properties

Since the industrial revolution,with the rapid development of technology and industries,great changes have taken place in people’s way of life and living standards.But at the same time,various environmental and resource problems are also becoming more and more serious,of which water pollution and shortage of chemical energy are the most serious problems.The photocatalytic technology with semiconductor metal oxides as catalyst developed in the late 20th century can be used to degrade organic pollutants and splite water to produce hydrogen,which provides us with a way to solve environmental pollution and energy shortage.At present,the most widely used photocatalyst is TiO₂,but because its wide band gap can only make use of ultraviolet light which accounts for a small proportion of sunlight,so the study of narrow band gap semiconductor photocatalyst is the focus of the current research.Copper oxides are common P-type narrowband semiconductors,which have been widely studied in recent years because of their low price and strong visible light response.However,the photocatalytic efficiency of copper oxides is not very high due to the easy recombination of electron and holes in copper oxides.The purpose of this paper is to enhance the photocatalytic performance of copper oxides by modifying them,and the mechanism of the improvement of photocatalytic activity is discussed.The main research contents and results are as follows:1.We used ethanol quenching to modify the CuO nanocrystal surface.The CuO is heated to a high temperature（800℃）and immediately quenched by submersion in absolute ethanol.The photocatalytic decomposition of rhodamine B demonstrated that,under ultraviolet light irradiation,better photocatalytic performance was achieved with our modified CuO than with CuO.The characterization such as X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy indicated that by rapid absolute ethanol quenching,the interaction between hot CuO and absolute ethanol led to the introduction of a high concentration of oxygen vacancies on the surface of the CuO.The results of X-ray diffraction and X-ray photoelectron spectroscopy showed that CuO nanoparticles were partially reduced to Cu₂O and Cu after being quenched with ethanol,so the CuO-Cu₂O heterogeneous junctions and Schottky heterogeneous junctions of Cu and CuO may also be formed,thus facilitating electron-hole separation and enhancing their photocatalytic activity.2.The surface of nano-CuO crystals were directly modified by mixed grinding with TiO₂.The modified CuO（M-CuO）showed significantly improved photocatalytic in splitting water to produce hydrogen under simulated sunlight irradiation,which was 4.35 times than that of TiO₂under the same conditions.This method of modifying nano-CuO is simple,efficient and environmentally friendly.The characterization results of XPS and EPR confirmed that this method could generate oxygen vacancy in the M-CuO composite structure.The analysis of UV-vis absorption spectrum shows that M-CuO still has strong light absorption in the visible range,but its band gap has widened from 1.59 e V to 2.7 e V,which can produce photo-generated carriers with stronger redox capacity,and reach the conditions for photocatalytic hydrogen production.For these reasons,M-CuO showed excellent photocatalytic hydrogen production efficiency under simulated sunlight.3.The energy band structure and density of states（DOS）of copper oxides（CuO and Cu₂O）and copper oxides with oxygen vacancies were calculated by the first-principle theory.The band structure and density of states are analyzed to theoretically explore the electronic structure changes of copper oxides（CuO and Cu₂O）in the presence of oxygen vacancy defects.The results show that the valence bands of both CuO and Cu₂O are mainly composed of Cu’s 3d electron and O’s 2p electron,while the conduction band is mainly composed of Cu’s 3p electron and O’s 2p electron,and the electron composition of the valence band and the conduction band don’t changed after adding the oxygen vacancy,but the band gap is slightly larger.Oxygen vacancies can also lead to a defect energy level between the valence and conduction bands of CuO crystals,which is mainly composed by 4s,3p electrons of Cu and 2p electrons of O.Due to the existence of the defect energy level,electrons can leap from the top of the valence band to the defect energy level,and then from the defect energy level to the bottom of the conduction band,thereby improving the charge-hole separation efficiency and enhancing the photocatalytic activity of CuO.