Preparations Of High-effective Semiconductor Photocatalytic Materials And Their Photocatalytic Performances

ABSTRACT:With the rapid development of economy, people are facing the problem of energy shortage and environment pollution. Although the government invested a large amount of money and energy to respair the damaged environment, the outcome was not optimistic. Therefore, air and water pollution are major facing challenges in the21th century. Semiconductor photocatalysis has been extensively investigated in the organic pollutant degradation due to its outstanding catalytic performance, mild reaction conditions, abundance and no secondary pollution.The n-type titanium dioxide (TiO2) has been considered as the most promising photocatalyst in the control of environment pollution, but the direct bandgap of3.2eV restricts its application in visible-light region. The p-type semiconductor cuprous oxide (Cu2O) with a direct bandgap of2.0eV and monoclinic scheelite bismuth vanadate (BiVO4) with a direct bandgap of2.4eV have attracted considerable attention recently owing to its good visible-light absorption property, but they suffers from the problem of low quantum efficiency which results from the easy recombination of photo-generated electron-hole pairs. Coupling one semiconductor with another semiconductor to form heterojunctions and expand the light response range are considered to be two important ways to improve the photocatalytic properties of semiconductor materials.In this paper, we adopted a facile and effective method to synthesize photocatalyst material Cu2O, TiO2and a composite semiconductor with p-n heterojunctions. Properties of the prepared materials for methyl orange (MO) and Rhodamine B (RhB) photocatalytic degradation were also investigated. The research conclusions are presented as follows:(1) Hollow core like Cu2O with a diameter of400-1000nm was synthesized by a solvothermal method using ammonium nitrate as the directing agent and glucose as the reducing agent, and without adding any surfactant. Photocatalytic tests showed that after1h dark adsorption and with the irradiation of an ordinary9W energy-saving fluorescent lamp for2h, the MO degradation ratio with Cu2O as the photocatalyst reaches99%and the main effect is adsorption. The RhB photocatalytic degradation ratio for Cu2O reaches60%under the condition of1h dark adsorption and with the irradiation of the9W energy-saving fluorescent lamp for5h, and the main effect is photocatalytic degradation.(2) Anatase TiO2with high energy (001) and (100) facets was synthesised by a hydrothermal method using NaF and HCl as additives. The obtained product consisted of TiO2nanoparticles (50-100nm) and microcrystalline (0.5-1.0μ.m) with smooth and flat crystal surface. The truncated triangular prism morphology of TiO2was observed for the first time to our best knowledge. After1h dark adsorption and with a300W xenon lamp irradiation for3h, the RhB photocatalytic degradation and removal ratio of TiO2are90.0%and92.7%, respectively, better than that of TiO2prepared under other conditions and commercial TiO2(P25).(3) A novel visible-light-responding BiVO4-Cu2O-TiO2ternary heterostructure composite was successfully fabricated by wet chemical processes, showing better photocatalytic properities compared to Cu2O and Cu2O-TiO2. After1h dark adsorption and with the irradiation of the9W energy-saving fluorescent lamp for8h, the removal and photocatalytic degradation ratios of RhB for5%BiVO4-40%Cu2O-TiO2reach98.3%and97.8%, respectively. The excellent catalyst mechanism of BiVO4-Cu2O-TiO2ternary heterostructure composite was explained by experimental methods of UV-Visible diffuse reflectance spectroscopy, fluorescence spectroscopy, capture experiment, AC impedance analysis and energy band structure. This work provides a new direction for the design and preparation of new type of visible-response catalysts.