Enhancement Mechanism Of Catalytic Degradation Of PPCPs By CuMgFe LDH Materials

The massive input of new pollutants into the environment brings potential risks to human health and eco-environmental safety.The 14th five year plan for national economic and social development of the people’s Republic of China and the outline of long-term objectives for 2035 emphasize"paying attention to the treatment of new pollutants"in the chapter of in-depth pollution prevention and control action.Therefore,higher requirements are put forward for the treatment of wastewater containing new pollutants.Advanced oxidation technology has been widely used in the advanced treatment of wastewater containing new pollutants.As a catalytic material,hydrotalcite like（LDH）has some scientific problems,such as low atomic utilization rate and slow electron transfer rate.Therefore,taking drugs and skin care compounds（PPCPs）as the representative of typical new pollutants,starting from the intrinsic activity of LDH materials,this paper prepared LDH of metal ions in different layers,clarified the relationship between metal ions in different layers of LDH and intrinsic catalytic activity,regulated the lattice change of LDH surface by Ni,clarified the strengthening mechanism of lattice effect in catalytic degradation of PPCPs,and regulated the electronic properties between layers by ch3ncs,The enhancement mechanism of electronic interlayer effect on catalytic degradation of PPCPs was clarified.The main research contents and conclusions are as follows:（1）The coprecipitation method was used to prepare CuFe LDH,MgFe LDH and CuMgFe LDH materials.Taking benzotriazole（BTA）as the representative of typical skin care compounds,the effects of the BTA degradation by three LDH materials were studied,and the structure-activity relationship between different laminate metal combinations and catalytic intrinsic activity was clarified.On this basis,the contributions of Cu,Mg and Fe sites to intrinsic catalytic activity were explored from reactive oxygen species（ROS）quenching experiment and molecular dynamics simulation.The results showed that the addition of ROS quencher had no effect on the degradation of BTA by CuFe LDH,indicating that the Cu site is mainly contributed to adsorption effect of BTA.In contrast,the BTA degradation performance of CuMgFe LDH with N₂aeration is only 20.4%,while the degradation performance of cumgfe LDH with air aeration is increased by 60.8%,up to 81.2%.Therefore,N₂molecule is selected to explore the adsorption behavior of Mg and Fe sites on LDH based materials and the energy required for activation by Mg and Fe sites.The catalyst poisoning experiment showed that the Fe site showed a key contribution（3.9%）,and the Mg site only showed a weak contribution（0.7%）.When the temperature reaches400℃,the total adsorption energy of effective adsorption molecular weight increases from-0.100 e V to-1.270 e V,indicating that the catalytic degradation reaction of Mg and Fe metal sites still needs higher reaction activation energy.（2）The degradation mechanism of BTA is strengthened by doping Ni into the LDH surface interface to regulate its crystal surface effect for reducing the activation energy required for the catalytic reaction.The results show that CuFe LDH is difficult to combine Ni on its surface interface because of its stable structure.Besides,Ni/MgFe LDH are mainly bridged in the form of M-O,while Ni/CuMgFe LDH are combined on the surface interface in the form of M-O and lattice replacement.The lattice expansion and surface defects of LDH caused by Ni doping,where the a-axis and b-axis extend from 3.12（?）to 5.26（?）and 5.78（?）,respectively,and the lattice strain increases from 0.15%to 0.43%,which is mainly caused by Ni replacing Fe.The lattice distortion of Ni/CuMgFe LDH forms more oxygen vacancy,up to 30.7%,which is conducive to the formation of Cu⁺（8.8%）surface chemical environment and improves its electron transfer ability,up to 2 times than that of CuMgFe LDH.Taking BTA as the model pollutant,when process conditions suitable(dosage=0.1 g/L,p H=7,c（BTA）=10 mg/L,the BTA degradation efficiency of Ni/CuMgFe LDH reaches92.7%,which is 30.3%higher than that of CuMgFe LDH,and it has better tolerance and buffer capacity in the actual wastewater environment.Free radical quenching experiment,electron paramagnetic spectroscopy and electrochemical active area analysis confirmed that·O₂^-,·H and·OH were the main active species in the catalytic reaction.A two-way mechanism of BTA degradation of BTA by Ni/CuMgFe LDH under different aeration conditions was proposed.With N₂aeration,it is the nucleophilic reaction dominated by·O₂^-and·H,where the main degradation product is aniline.With air condition,it is mainly the electrophilic degradation reaction mediated by·OH,where the main degradation product is small molecular acid.（3）Ni/CuMgFe LDH and sodium stearate（SA）were compounded in one step on Ni foam membrane by hydrothermal method.A hydrophobic membrane material CuMgFe LDH/Ni foam+SA with high efficiency for water oil separation and simultaneous removal of BTA was developed.Its application potential in the removal of BTA in oily wastewater was studied.CuMgFe LDH/Ni foam+SA not only has simultaneous high separation efficiency and BTA removal ability,but also has excellent stability.The results show that the composite CuMgFe LDH/Ni foam+SA has a rough surface to provide more contact area,and the surface hydrophobicity changes from hydrophilicity（34.2°）to hydrophobicity（127.8°）.The separation efficiency of CuMgFe LDH/Ni foam+SA for petroleum ether/water,soybean oil/water and oil/water mixtures is more than 92.2%.Besides,the separation efficiency of CuMgFe LDH/Ni foam+SA for petroleum ether/water mixture remained above 92%in five cycles,indicating its long-term availability.Finally,BTA degradation performance of BTA by CuMgFe LDH/Ni foam+SA can reach 65.31%in the separation process of petroleum ether/water mixture.（4）A series of CuMgFe-CH₃NCS LDH materials with different CH₃NCS content were prepared by impregnation method,and their catalytic properties for typical pharmaceutical compounds of ciprofloxacin（CIP）were studied.X-ray absorption spectroscopy（XAS）and Fourier transform infrared spectroscopy（FT-IR）confirmed that CH₃NCS successfully anchored the Cu site in CuMgFe LDH into the interlayer to form an electron channel,which promoted the formation of Cu⁺（53.67%）and Fe²⁺（65.2%）,and improved its electron transfer ability up to nearly 10 times.The interlayer electron channel constructed by CuMgFe-CH₃NCS LDH is that its degradation performance of CIP is improved from 19.2%to 82.7%.Through ROS quenching experiment and EPR analyze,¹O₂,H₂O₂and·OH is confirmed that the main reactive oxygen species in the degradation process.Meanwhile,comparing the types of ROS generated before and after anchoring,it shows that the electron channel constructed by CH₃NCS enhances the generation of ¹O₂.Finally,based on the combined ecotoxicity of intermediates in different pathways,it is proposed that the degradation pathway dominated by ¹O₂has the lowest ecotoxicity,which realizes the efficient and safe degradation of CIP.