Controlled Synthesis、The AgCl Surface Modification Of La（OH）₃ Nanorods And Mechanism For Photocatalytic Removal Of NO

Air pollution has become the most significant issue in the environmental problem.Low concentration of NO is considered as one of the primary air pollutants, it is responsible for atmospheric environmental problems like photochemical smog, acid rain and dust-haze. There are some problems exist in the traditional treatment methods. For example, the low use ratio, high energy consumption and produce secondary pollution.This paper study the new La（OH）₃ photocatalyst, and applied to efficiently remove of NO. By means of chemical precipitation and hydrothermal method to synthesize the La（OH）₃ nanorods, and achieved the control of microstructure. In order to enhance the use ratios of the visible light, we modified the samples and compose the Ag/AgCl/La（OH）₃ ternary heterostructures. The as-prepared samples were structural characterized and active free radicals captured by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray Photoelectron Spectroscopy, N2adsorption-desorption isotherms, UV-vis diffuse reflectance spectroscopy,Photoluminescence, Electron spin resonance and Electron paramagnetic resonance generation. The results as follows:（1） Chemical precipitation method synthesize of La（OH）₃ nanorods: La（OH）₃nanorods have been successfully prepared by a facile precipitation method using La（NO3）₃·6H2O and ammonia solution as precursors. The synthesis procedure is very simple and can be finished within a short time. The La（OH）₃ nanorods exhibit high photocatalytic activity for NO removal. The high photocatalytic activity of La（OH）₃nanorods is attributed to the presence of oxygen-vacancy and one dimensional nanostructure. The role of oxygen-vacancy in formation of new impurity level below conduction band, which endow the defective La（OH）₃ with extended UV light absorption; One dimensional nanostructure effectively preventing the recombination of electron-hole pairs, thus in promoting photocatalysis efficiency.（2） Hydrothermal method synthesize of La（OH）₃ nanorods: La（OH）₃ nanorods have been synthesized by a hydrothermal method using La（NO3）₃·6H2O and ammonia solution as precursors. The hydrothermal temperature has a great influence on the photocatalytic activity of La（OH）₃ nanorods. The highest photocatalytic performance can be achieved when the temperature is controlled at 180°C. The ESR capture experiments show that hydroxyl radicals are the dominant reactive species during photocatalysis. The signal of ?OH radical for La-180 is strongest. So the photocatalytic activity of La-180 is highest. The generation of more ?OH radicals by La-180 is associated with the enhanced UV-light absorption lead to the band gap decreases. The morphology of La-180 which are uniformly dispersed and regular, thus photogenerated electron-hole pairs separation efficiency.（3） Ag/AgCl@La（OH）₃ heterostructures: Ag/AgCl@La（OH）₃ composites was constructed through a two-step synthesis route. AgCl was produced by a facile anion exchange reaction and accompanied with the formation of metallic Ag by photoreduction of Ag+ ions under natural solar irradiation. The Ag/AgCl/La composites exhibit an enhanced activity for NO removal in comparison with Ag/AgCl and La（OH）₃.The remarkable improvement of NO removal capability can be ascribed to the enhanced visible-light harvesting which was related to the surface plasmon resonance effects of Ag metal, and decreased recombination of photogenerated electron–hole pairs owing to the interaction of Ag/AgCl and La（OH）₃. The effect of Ag/AgCl content on the photocatalytic performance was evaluated. The highest photocatalytic performance can be achieved when the mass ratio of Ag/AgCl to La（OH）₃ is controlled at 1:2. On the basic of capture active radical, the photocatalytic mechanism for NO removal was proposed.This study provides methods which show simple, low cost, non-toxic side effect properties to synthesize La based photocatalysts, modification of brondband based catalyst and its photocatalytic mechanism also establishes and technological base for its practical application.