Study On Photocatalytic Degradation Of Methylene Blue By Fe-Mn-Ni/Fe-Mn-Co Ternary Metal Oxides

Semiconductor photocatalytic technology is one of the most promising advanced oxidation technologies.However,there are still some problems to be solved in the application of photocatalytic technology,such as the development of new semiconductor,the improvement of the catalytic activity and the reduction of pollutant degradation time.The calcined oxides of hydrotalcite are often used as semiconductor photocatalysts because of their large surface area,strong adsorption of pollution and simple synthesis.In this paper,the catalytic activities of two kinds of Hydrotalcite calcined oxide?FeMnNi-LDO and FeMnCo-LDO?in photocatalytic system with the addition of sodium bisulfite?NaHSO₃?were investigated in an aim to increase the discoloration and mineralization efficiency of methylene blue?MB?.The structure and composition of as-synthesized oxides were characterized by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,Brunauer,Emmett,and Teller?BET?,UV-Vis diffuse reflectance spectroscopy,X-ray fluorescence?XRF?,Inductively coupled plasma-opticalemission spectroscopy?ICP-OES?andX-ray Photoelectron spectrometry?XPS?.The photocatalytic mechanism of MB degradation for FeMnNi-LDO and FeMnCo-LDO with NaHSO₃ was discussed.The obtained conclusions are showen as follows.?1?NiFe-MnO₄^--LDH was obtained by inserting the excess permanganate ions into the interlayer of NiFe-CO₃^--LDH under the protection of N₂ which was synthesized by hydrothermal method.According to the results of XRD?FTIR?XRF,the permanganate ions had been inserted into the interlayer.After calcined at 450?,the FeMnNi-LDO was obtained.The results of BET?UV-Vis indicated that FeMnNi-LDO possessed higher specific area and stronger visible light absorption capacity compared with NiFe-LDO.The FeMnNi-LDO showed faster and higher photocatalytic activity for MB than NiFe-LDO with the addition of NaHSO₃.Moreover,the ternary complex oxide exhibited satisfactory reusability after three cycles.?2?A series of ternary FeMnCo-LDO complex metal oxide were synthesized through the thermal decomposition of the precursor FeMnCo-LDH.When NaHSO₃ is added under visible light irradiation,the photocatalytic degradation effect of the catalyst on MB is greatly improved.Under the same conditions,all the manganese containing samples showed much better photocatalytic degradation of MB than manganese free oxide and the photocatalytic activity increased as the content of Mn in the molar range of Mn³⁺/Fe³⁺in 0.5⁸.[8]FeMnCo-LDO whose Mn³⁺/Fe³⁺is 8 possessed the best photocatalytic activity of 92%for MB with the NaHSO₃.In addition to determining the role of Mn and the Mn/Fe ratio of the complex oxide catalysts on the decomposition of MB,the stability and reusability of[1]FeMnCo-LDO catalyst were also tested and found to be good.?3?Four different chemicals were used to carry out the radical-trapping experiments using to find out the predominant reactive oxygen species.The existence of hydroxyl scavenger tert-butanol,holy scavenger disodium ethylenediaminetetraacetate,superoxide scavenger benzoquinone and Mn???scavenger sodium pyrophosphate inhibited the course of reaction in some degree and the degradation rate decreased about 1%,10%,50%and 30%,repectively.The results showed that the high efficient of developments were attribute to the superoxide and Mn???,rather than hydroxyl and holy.