Efficient Degradation Of Tetracycline With N-rGO/CuO(NGC)catalysts Via Persulfate Activation Under High Salinity Condition

The rapid development of social industrialization is often accompanied by numerous environmental problems.With the gradual enhancement of people’s environmental awareness,many countries have increasingly higher requirements for pollutant discharge.At present,many industries produce a large amount of wastewater in the production and manufacturing process.However,due to the existence of refractory organic pollutants,this kind of wastewater is easy to lead to poor salt product quality and low recovery efficiency in the secondary recovery of salt.As a promising advanced oxidation technology,activated persulfate method has the advantages of simple operation,fast reaction rate and low toxicity.The hydroxyl radicals（HO·）and sulfate radicals(SO₄^·-)generated by this technology have the advantages of high redox potential and non-selectivity,which are commonly used to treat various hard-to-degrade organic pollutants.However,SO₄^·-and HO·are often quenched in high salt environments to produce radicals with low oxidation activity(e.g.,Cl^·-),resulting in greatly reduced catalytic efficiency.In order to overcome the above bottleneck problem of low efficiency in the treatment of high salt wastewater by activated persulfate method,N-r GO/CuO loaded catalyst（NGC）was prepared with nitrogen-doped graphene as the carrier and CuO as the loading in this paper.The catalysts were used to investigate the removal efficiency of organic matter in salt-free and high-salt environments with tetracycline as the target pollutant,respectively,and to study its free radical pathway and non-free radical pathway in the activated persulfate method.The main research contents and results are as follows:（1）The composite NGC was prepared by hydrothermal method.The crystal structure,surface morphology,elemental composition and chemical structure of the catalyst were explored by various analytical methods.The results showed that the composite catalyst NGC was successfully prepared.（2）The degradation efficiencies of PS,r GO/PS,NG/PS,CuO/PS,GC/PS and NGC/PS systems for tetracycline were investigated under salt-free and high-salt environments,respectively.The experimental results showed that the composite catalyst NGC maintained the best catalytic performance in both salt-free and high-salt environments.The optimum reaction conditions of the catalytic reaction were further investigated with NGC as the object.Under the optimum reaction conditions of p H=7,catalyst concentration of 0.2 g/L,initial tetracycline concentration of 20 mg/L and PS concentration of 1 m M,the removal rate of tetracycline by NGC/PS system could reach 97.76%within 90 min,and other anions such as Cl^-,SO₄^2-and HCO₃^-had no significant effect on the NGC/PS system.In addition,it was found that the catalyst NGC showed well stability and reusability in the degradation of tetracycline in high salt environment.（3）The free radical and non-free radical pathways in the NGC active persulfate process were studied using active species capture experiments,electron paramagnetic resonance spectroscopy（EPR）,electrochemical tests,Fourier infrared spectroscopy（FTIR）analysis,zeta potential testing and X-ray photoelectron spectroscopy（XPS）.Finally,the intermediate products in the degradation process of tetracycline were detected by gas chromatography-mass spectrometry（GC-MS）and the possible structure of the intermediate products was deduced.The toxicity of the intermediate products was analyzed by ECOSAR procedure,which provided a theoretical basis for achieving the harmless degradation of tetracycline.