Preparation Of High-entropy Oxides By Solution Combustion Method And Study Of Catalytic Performance

With the rapid development of the pharmaceutical industry,antibiotics are frequently used in daily life,which brings more and more serious water pollution problems and seriously endangers human health.Due to the complexity of antibiotic composition and the difficulty of degrading,it is urgent to find a technology for antibiotic wastewater treatment that removes it thoroughly.Advanced oxidation technology（AOPs）based on persulfate,due to its advantages of high efficiency,environmental protection and stability,has good application prospect in refractory wastewater treatment in recent years.There are many activation ways of persulfate and each has its own advantages.However,the activation of peroxymonosulfate（PMS）by transition metal oxides has gradually attracted the attention of researchers because of its advantages such as fast catalytic rate,mild reaction condition and reusable.In this paper,tetracycline hydrochloride（TC-HCl）was used as the target degradant.By synthesizing different types of heterogeneous catalysts of multiple transition metals-high entropy oxides,and exploring the performance of different types of high entropy oxides to activate peroxymonosulfate（PMS）to degrade pollutants.The main findings were as follows:（1）The spinel-type high entropy oxide was prepared by the solution combustion method-(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)₃O₄.Their structure,morphology,composition and specific surface area were characterized by XRD,SEM,EDS,XPS and BET.The results showed that(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)₃O₄,as a heterogeneous catalyst,has strong ability to activate PMS.The influence of preparation parameters and reaction conditions during the reaction process was further explored.The results showed that when glycine was used as fuel,the synthesis temperature was 550℃,the combustion ratioφ（the ratio of fuel to oxidizer）was 1,the dosage of catalyst and PMS was 100 mg/L,p H was 5,and the reaction temperature was 20℃,the prepared catalyst showed good performance of activating PMS to degrade TC-HCl.The degradation rate of TC-HCl at reaction temperature conforms to Arrhenius equation.The radical quenching experiment showed that the active free radicals produced during the degradation process were SO₄^·-and^·OH,in which SO₄^·-was the main active free radical.The XRD results of the cyclic experiment showed that the structure of the catalyst had no obvious change and had good stability.（2）The rock salt type high entropy oxide(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O was prepared by solution combustion method.The properties of the catalyst were characterized by XRD,SEM,EDS,XPS and BET.The catalysts synthesized at different calcination temperatures were analyzed.The results showed that when the calcination temperature was 800℃,the synthesized catalyst had the best catalytic activity.The main factors affecting the degradation rate of TC-HCl were studied,including catalyst dosage,PMS dosage,initial TC-HCl concentration,p H value,reaction temperature,etc.The free radical trapping experiments with tert-butanol and methanol showed that the main active group was SO₄^·-.After five cycles,the degradation efficiency of the catalyst was still above 90%.Combined with the XRD before and after the cycle,the catalyst had excellent cyclic stability.（3）High dispersion rock salt type high entropy oxide powders were prepared by salt-assisted solution combustion.Their structure,morphology and specific surface area were characterized by XRD,SEM,TEM,and BET,etc.The effect of sodium chloride addition on catalyst preparation was studied.The results showed that the addition of Na Cl could effectively improve the agglomeration of powders,increase the specific surface area of the catalyst,and further improve the degradation efficiency of TC-HCl.When the ratio of Na Cl to all metal cations was 1:10,the synthesized catalyst had high purity and good crystallinity.The specific surface area of the catalyst was more than two times higher than that of the catalyst without Na Cl added.The degradation rate was 96%within 16 min.The effects of some common anions Cl^-,NO₃^-,SO₄^2-and HCO₃^-on the degradation of the system were studied.Free radical capture experiments showed that SO₄^·-was the main active species in the degradation process.The catalyst was easy to be separated from water.The cyclic stability of the catalyst was verified by cyclic experiments,which indicated that the catalyst had excellent cyclic stability performance.