The Photocatalytic Activity Of Montmorillonite-TiO₂ Nanocomposites With Core-shell Structure And Its Effection

has wide range applications in the fields of semiconductor nanomaterials because of its advantages of high chemical stability, excellent photocatalytic properties and lower cost. But there are some problems need to solve about cost and recycle. The nano-titania composite with other materials as a feasible technology to solve these problems. Therefore, the study of its photocatalytic properties of composite materials have great significance.In this work, we studied the effection of montmorillonite on the photocatalytic activity of TiO2 nanoparticles (P25) photoctatlytic degradation of methyl orange. On this basis, we synthesised the TiO2-montmorillonite nanocomposites with core-shell structure by hedrothermal method, and take a series characterization. Also, we studied its activity of photocatalytic reduction water for hydrogen production, photodegradation methyl orange and the effection of pH and other factors. The main results are as follows.(1) The degradation of methyl orange in water was used to examine the effect of montmorillonite on the photocatalytic activity of TiO2 nanoparticles (P25) photocatalytic degradation of methyl orange. It is found that montmorillonite can inhibit the photocatalytic decomposition of methyl orange, but the photocatalytic activity of P25 will be enhanced obviously when there are certain concentrations of montmorillonite in reaction solution. The enhanced photocatalytic activity might be ascribed to the light scattering induced by montmorillonite particles. Additionally, the effect of montmorillonite on the photocatalytic activity of P25 was studied as a function of pH of the solution, initial methyl orange concentration, and reaction atmosphere. The results are as follows:a) The degradation ratio of MO is almost constant with increasing pH from 4 to 7, and then decreases gradually from 7 to 9 in both the presence and absence of montmorillonite. One possible explanation is that the surface of P25 is negatively charged when the pH of the solution is in the range of 7 to 9. As a result, the adsorption of anionic MO species is hindered and the degradation of MO is restrained, b) The degradation ratio of MO is almost changed with the initial concentration of MO in both the presence and absence of montmorillonite. It is unfavorable to photocatalytic degradation of methyl orange when the initial concentration of MO is very low or high. The photocatalytic activity of P25 is optimal When the initial concentration of MO is 10 mg-L-1. Because higher concentration of the substrate will cause that the light absorption of the solution increases, the light absorption of the solution leads to a decrease of effective light absorption of the photocatalyst. c) The photocatalytic activity of P25 in the N2 atmosphere is almost same as that in air. This phenomenon implies that the oxidation of dyes caused by the holes is the major reaction pathway. Montmorillonite does not influence the reaction pathway of MO degradation.(2) We synthesised the Montmorillonite-TiO2 nanocomposites with core-shell structure by hedrothermal method, and loaded 5% CuO on the nanocomposites. We studied its photocatalytic performance of reduction water for hydrogen production in the presence of methanol sacrifice agent, we found that the nanocomposites have a good photocatalytic performance of reduction water for hydrogen production under the irradiation of UV light. The hydrogen production rate of the nanocomposites is 237.6μmol/g-h. it enhanced 16% compare with 5% CuO-TiO2 (204.12μmol/g-h). That may be due to the TiO2 nanoparticals have a highly disperse on the montmorillonite, the agglomeration of the TiO2 nanoparticals has been decreased, the effective interface between TiO2 nanoparticals and methanol solution has been increased. Thereby, the photocatalytic properties of the nanocomposites has been improved. In addition, the light-induced carriers are easy migrate to the surface of nanocomposites because of the shell of TiO2 is very thin. This may be a possibale reason for enhanced the photocatalytic properties. We believe the reation mechanism is that the electron transfers from the valence band to the conduction band when the TiO2 nanoparticals are excited by UV light. Then electrons move to CuO, reduced water have hydrogen. In this proess, copper oxide plays an important role because it is the reactive sites of the photocatalytic reduction reaction. The pure nanocomposites have lower photocatalytic activity compare with the nanocomposites loaded by copper oxide, and its rate of hydrogen production is 108μmol/g-h. Also, we studied the effect of the pH, concentration of catalyst and sacrifice agent on the photocatalytic hydrogen production. From the studied we can see, a) The photocatalytic hydrogen production rate of nanocomposites are increased with the increasing of pH, because the redox potential of H+/H2 will decreased with the the increasing of pH, that beneficial to the photoccatalytic hydrogen production, b) The photocatalytic activity of nanocomposites will be increased with the increasing of sacrifice agent. Because the hole consumption increased gradually with the increasing of sacrifice agent, the separetion of electronic-hole will be enhanced with the increasing of hole consumption, c) The best photocatalytic activity has been found when there have an appropriate catalyst concertration (0.4 g/L), because it has maximum utilization of light in the appropriate catalyst concertration.(3) The degradation of methyl orange in water was used to examine the photocatalyst activity of Montmorillonite-TiO2 nanocomposites with core-shell structure, we found that the nanocomposites have a good photocatalyst activity like TiO2, the photodegradation ratio are exceed 90%. The utilization of TiO2 in Montmorillonite-TiO2 nanocomposites with core-shell structure has been greatly improved, decreased the cost. Also, we studied the effect of pH, concentration of methyl orange and catalyst on the photocatalytic degradation of methyl orange, and stability of catalyst. The results show that, a) The degradation ratio of methyl orange is decrease with increasing pH, the photocatalytic activity in acidity environment is better than alkaline environment, b) It is unfavorable to photocatalytic degradation of methyl orange when the initial concentration of methyl orange is high. The photocatalytic activity of nanocomposites is optimal when the initial concentration of methyl orange is low. c) The lower concertation of catalyst have a great photocatlytic activity, It can be used in the concertation of catalyst is 0.25 mg/mL. d) The Montmorillonite-TiO2 nanocomposites have a good stability, it have a good photocatlytic activity after several cycles.