Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye

TiO_2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating Mg Al hydrotalcite(Ti–Mg Al–LDH) was prepared by chemical vapor deposition(CVD) method.Response surface method(RSM) was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N2 flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti–Mg Al–LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process.According to the results from X-ray diffraction, scanning electron microscopy, Brunner–Emmet–Teller and Barrett–Joyner–Hallender, thermogravimetric and differential thermal analysis, UV–vis diffuse reflectance spectra analyses, the Ti species(TiO_2or/and Ti~(4+)) were successfully coated on the Mg Al–LDH matrix. The Ti species on the surface of the Ti–Mg Al–LDH lead to a higher photocatalytic performance than commercial TiO_2-P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating Mg Al–LDH material with good photocatalytic performances.     

Hydrotalcites and organo‐hydrotalcites as sorbents for removing pesticides from water

Abstract

This paper reports on the adsorption of different organic pesticides by hydrotalcite, hydrotalcite heated to 500°C and organo‐hydrotalcite in aqueous medium by employing adsorption isotherms, and using X‐ray diffraction and infrared spectroscopy techniques. The results suggest that the adsorption capacity of the different materials depends on their nature as well as on the structure, polarity and hydrophobic or anionic nature of the pesticides. The results also show that hydrotalcite, both natural and after calcination at 500°C, is not a good sorbent of hydrophobic pesticides. The data demonstrated that both types of hydrotalcite, however, are very good sorbents of glyphosphate. Furthermore, the organo‐hydrotalcites may be as good sorbents as organo‐montmorillonites for hydrophobic pesticides.     

水滑石类材料的合成及其在污染控制中的应用

水滑石类材料具有独特的性能,作为催化及吸附材料应用广泛.本文就水滑石类材料的合成现状进行了概述,并就水滑石类材料的碱性,阳离子的可搭配性,层间阴离子的可交换性等几个方面以及在污染控制中应用进行论述.     

N-doped CoAl oxides from hydrotalcites with enhanced oxygen vacancies for excellent low-temperature propane oxidation

A series of nitrogen-doped CoAlO (N-CoAlO) were constructed by a hydrothermal route combined with a controllable NH₃ treatment strategy. The effects of NH₃ treatment on the physico-chemical properties and oxidation activities of N-CoAlO catalysts were investigated. In comparison to CoAlO, a smallest content decrease in surface Co³⁺ (serving as active sites) while a largest increased amount of surface Co²⁺ (contributing to oxygen species) are obtained over N-CoAlO/4h among the N-CoAlO catalysts. Meanwhile, a maximum N doping is found over N-CoAlO/4h. As a result, N-CoAlO/4h (under NH₃ treatment at 400°C for 4 hr) with rich oxygen vacancies shows optimal catalytic activity, with a T₉₀ (the temperature required to reach a 90% conversion of propane) at 266°C. The more oxygen vacancies are caused by the co-operative effects of N doping and suitable reduction of Co³⁺ for N-CoAlO/4h, leading to an enhanced oxygen mobility, which in turn promotes C₃H₈ total oxidation activity dominated by Langmuir-Hinshelwood mechanism. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analysis shows that N doping facilities the decomposition of intermediate species (propylene and formate) into CO₂ over the catalyst surface of N-CoAlO/4h more easily. Our reported design in this work will provide a promising way to develop abundant oxygen vacancies of Co-based catalysts derived from hydrotalcites by a simple NH₃ treatment.