Structural Regulation Of Co/Fe-LDH On The Efficiency Of Activated Persulfate Degradation Of Aniline

Rational design and development of high efficiency and stable catalyst is principal to promote the development of catalytic industry.In order to achieve the goal,it’s necessary to fully understand and accurately describe the structure-performance relationship of catalysts.Layered double hydroxides（LDH）has become a hot research topic in catalyst field especially AOP catalysis because of the unique layered structure and interlayer ion exchangeability.The types of metal cations and interlayer anions in LDH lamellar structure can be changed and adjusted in a certain range,which makes LDH a highly active catalyst.In this study,aniline wastewater common in the organic chemical industry is taken as the representative pollutant.First of all,the influence of alkaline environment on the structure of Co/Fe-LDH was further analyzed based on the previous research.Secondly,Co/Fe-LDH prepared under the optimal alkaline environment is taken as the research object to explore a series of structural changes in the thermal environment.Then,combined with the thermodynamic analysis,the whole heat treatment process was calculated and analyzed to achieve the thermodynamic model of Co/Fe-LDH sintering process.Finally,the catalytic degradation of aniline by potassium persulfate catalyzed by Co/Fe-LDH/LDO was studied.Specific research contents and conclusions are as follows:The structure regulation of Co/Fe-LDH catalyst under different preparation and treatment environment was investigated.The morphology and crystal type of Co/Fe-LDH catalyst prepared under the condition of strong and weak alkali medium were analyzed.The results showed that the environment with ammonia and ammonium chloride as weak alkali medium was more favorable for the formation of the structure of Co/Fe-LDH catalyst.The catalyst prepared under the condition of weak alkali medium was heat treated,and the characterization test was carried out between the catalyst and the calcined product Co/Fe-LDO.The morphology changes,crystal changes,elemental distribution and valence changes,molecular structure and functional group distribution changes of a series of reactions occurred within the temperature range of heat treatment were systematically studied.The results show that the increase of calcination temperature leads to the mutual compression of Co/Fe-LDH,which destroys the layered structure and leads to its deformation and collapse.The structural changes are caused by the dehydration reaction and crystallization reaction,and the Co₃O₄ crystal is formed during the transformation of Co/Fe-LDH to Co/Fe-LDO.A thermodynamic model of the transformation of Co/Fe-LDH into Co/Fe-LDO during heat treatment was established and the reaction mechanism of the change of catalyst structure was further explained.The measured TG/DTG/DSC curves were analyzed,and the three stages of LDH calcination process were demonstrated by the changes of weight and energy.Using four deconvolution fitting methods（Gauss,Lorentz,Bigaussian and Weibull）,mathematical deconvolution analysis（MDA）was applied to the Co/Fe-LDH heat treatment process,and the kinetic parameter values of each fitting peak were calculated using KAS and other conversion methods.The kinetics parameters obtained were defined as the initial values of the reaction kinetics model.Sestak-Berggren model was successfully used to describe the reaction process of Co/Fe-LDH in calcination,and the pyrolysis mechanism of Co/Fe-LDH was further explained.The effect of Co/Fe-LDH prepared in weak base medium and its calcined product Co/Fe-LDO on the degradation of aniline catalyzed by potassium persulfate was investigated.The 3D-EEM test and GC test showed that the catalytic activity of Co/Fe-LDO was significantly higher than that of Co/Fe-LDH,in which Co/Fe-LDH could also catalyze persulfate to achieve a good removal effect on aniline.However,the metal in the catalyst without heat treatment mainly exists in the form of hydroxide,and the stability is not good.The reason is that the calcination process makes the hydroxide gradually change into a more stable oxide,and the increase of specific surface area leads to higher catalytic activity.