Controllable Fabrication And Photocatalytic Properties Of Novel Molybdate Crystals

With the industrialization of the increasingly serious environmental pollution caused by more and more toxic and harmful substances through the atmosphere, water and soil into the food and thus endanger human health. Environmental factors have become important factors threatening food security, one of the semiconductor photocatalyst in solving environmental pollution has a great prospect. As photocatalyst crystalline phase, specific surface area, morphology and surface structure are directly related to the nature and properties. Thus, by changing the preparation methods and conditions to achieve the crystalline phase, size, morphology and surface structure of local control of micro/nano materials, to explore the formation mechanism of its photocatalytic properties, which has important theoretical and practical significance. Hence, in the present paper, NiMoO4 nanorods, PbMoO4 microcrystals with preferentially exposed (001) facets, hierarchical PbMoO4 microspheres and Bi2MoO6 microcrystals with preferentially exposed (010) facets were prepared. Moreover, the effects of reaction conditions on crystalline phase, morphology, exposed crystal facets, light absorption and photocatalytic performance of the obtained samples were also primarily discussed, which is initially revealed their formation mechanism, and speculated the underlying factors on the photocatalytic material with high photocatalytic activity. The photocatalysis degradation of two antibiotics widely used in both human and veterinary medicine:oxytetracycline (OTC) and oetracycline (TC) in aqueous were investigated by Bi2MoO6 nanoplates with preferentially exposed (010) facets under visible light irradiation. The detail researches and the conclusions are summarized as follows:1. One dimensional NiMoO4·0.91H2O nanorods has been synthesized by a facile hydrothermal method. The effect of different synthetic conditions on the morphologies of the final products was investigated. NiMoO4·0.91H2O nanorods can be further converted to monoclinic a-NiMoO4 nanorods by calcinating at 500-900℃for 5 h without significant alteration of the nanorod structure. The photocatalytic property of the obtained a-NiMoO4 nanorods and Ag-loaded a-NiMoO4 nanorods has been tested by degradation of Rhodamine B (RhB) under UV light irradiation.2. Lead molybdate (PbMoO4) microcrystals with preferentially exposed (001) facets have been synthesized by a facile surfactant-assisted hydrothermal process in the presence of cetyltrimethylammonium bromide (CTAB). The effects of the CTAB addition amount, hydrothermal temperature on the morphologies and the crystal facets of PbMoO4 were investigated in detail. Experimental results indicate that the diffraction peak intensity ratio of (112) to (001) crystal facets for the product can be delicately controlled by simply adjusting the addition amount of CTAB and hydrothermal temperature. And the products derived from hydrothermal treatment at 180℃for 24 h in the presence of 0.05 mol/L CTAB exhibit an obvious exposed (001) facets with minimum peak intensity ratio (I112/004=0.08) of the (112) and (004) crystal facets. Moreover, the obtained PbMoO4 with preferentially exposed (001) facets exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under UV light irradiation in comparison with the PbMoO4 obtained in absence of CTAB and the commercial phototcatalyst (P25).3. Hierarchical PbMoO4 microcrystals were synthesized via a simple nitric acid-assisted hydrothermal process without addition of template or organic directing reagent. The scheelite-type tetragonal PbMoO4 with various hierarchical microstructures can be controllably fabricated by adjusting the experimental conditions such as hydrothermal temperature, time and nitric acid concentration. Experimental results indicate that hierarchical PbMoO4 microspheres with a size of 5-10μm, which are assembled by slablike microcrystals with an average thickness of～230 nm, can be obtained from a hydrothermal treatment at 160℃for 24 h in the presence of HNO3 solution, whereas only irregular particles and aggregations are obtained without HNO3 solution. The hierarchical PbMoO4 microspheres show more excellent photocatalytic activity than the irregular PbMoO4 particles for the degradation of rhodamine B (RhB) under UV light irradiation. Furthermore, a possible nitric acid-assisted formation mechanism for the hierarchical PbMoO4 microspheres is proposed, which might represent a new fabrication strategy for other nano/microstructures with desired morphology.4. Bismuth molybdate (Bi2MoO6) nanoplates with preferentially exposed (010) facets have been synthesized by a facile hydrothermal process. The effects of pH, hydrothermal temperature and the CTAB addition amount on the morphologies and the crystal facets of Bi2MoO6 were investigated in detail. Experimental results indicate that the diffraction peak intensity ratio of (131) to (010) crystal facets for the product can be delicately controlled by simply adjusting the pH value of the reactant. And the products derived from pH=10 at 140℃for 72 h in the presence of 0.03 mol/L CTAB exhibit an obvious exposed (131) facets with minimum peak intensity ratio (I131/I010=0.54) of the (131) and (010) crystal facets. Moreover, the obtained Bi2MoO6 nanoplates with, preferentially exposed (010) facets exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light irradiation.5. The aim of this study is the evaluation of photocatalysis to degrade two antibiotics widely used in both human and veterinary medicine:oxytetracycline (OTC) and oetracycline (TC), in Bi2MoO6 aqueous suspension under visible light irradiation. The effects of catalyst amount, initial pH value, and initial concentration of each substrate on the photocatalytic degradation rates were investigated in detail. Experimental results indicate that pH has a significant effect on OTC and TC degradation. The optimal values of the operation parameters under the related constraint conditions were found at pH= 11.0, BilMoO6 concentration of 1.4 g/L and initial concentration of 20 mg/L. Under this condition,42.1% of OTC and 58.8% of TC were degraded under visible light irradiation for 60 min, respectively. The disappearance of these two compounds follows a pseudo-first-order kinetics according to the Langmuir-Hinshelwood (L-H) model and the rate constants were 0.00664 and 0.00845 min-1 for OTC and TC, respectively. It was observed that the surface reaction on BiiMoO6 played a important role in the degradation of OTC and TC, and the further study of reactive oxygen species (ROSs) indicated that the photohole (h+) was responsible for the major degradation of OTC and TC.