Preparation Of Multi-layered Double(Hydrogen) Oxides And Their Activation For Pms Degradation Of Phenol Wastewater

Phenol wastewater is a typical hard-to-degrade industrial wastewater,which can adversely affect human body,flora and fauna,and even the whole ecological environment if not treated properly.In recent years,Advanced Oxidation Processes（AOPs）have stood out due to their fast degradation efficiency,high mineralization and mild reaction conditions.Compared with hydroxyl radicals（HO·）,AOPs based on sulfate radicals(SO₄^·-)are widely used because of their longer half-life,higher redox potential,wider pH range and higher mineralization of SO₄^·-produced during the reaction.Layered double hydroxides（LDHs）have great activation performance for peroxynitrite（PMS）,and have better degradation effect for most of the refractory pollutants with higher stability.LDHs are roasted at a certain temperature to remove interlayer crystalline water and interlayer anions to form highly dispersed layered double metal oxides（LDOs）,which retain the unique layered structure of LDHs and have the advantages of larger specific surface area,more uniform distribution of active sites and better stability,and are also gradually applied in the field of wastewater treatment.In this study,cobalt-iron-copper elements were used as the base materials to successfully prepare layered double（hydrogen）oxides,and Co₂Fe₃Cu₄-LDHs/PMS and Co₂Fe₃Cu₄-LDOs/PMS systems were constructed and applied to the degradation of phenol wastewater,respectively.The specific studies and results are as follows:（1）Co₂Fe₃Cu₄-LDHs catalysts were prepared by co-precipitation method.The microstructures of the crystalline structure and the composition of the phases were analyzed by such characterization techniques as scanning electron microscope（SEM）,X-ray diffraction（XRD）,Fourier Transform Infrared Spectrometer（FT-IR）,the specific surface and porosity analyzer（Brunauer-Emmett-Teller,BET）and thermogravimetric analysis（TG-DTG）.After that,the Co₂Fe₃Cu₄-LDHs/PMS system was constructed and a series of degradation experiments were carried out to investigate the degradation ability of the whole system and the optimum reaction conditions for phenol as the target pollutant.Finally,the catalytic mechanism of the reaction was initially investigated by combining free radical quenching experiments and X-ray photoelectron spectroscopy（XPS）characterization.The characterization results exhibited that the Co₂Fe₃Cu₄-LDHs catalysts with regular shape and high purity were successfully prepared in this study.The degradation experiments indicated that the oxidation system has a great degradation capacity for phenol.At room temperature,pH=7.0,PMS concentration of 1.50 mmol/L,and Co₂Fe₃Cu₄-LDHs dosage of 0.20 g/L,the phenol was completely degraded（100.00%）by the reaction for 40 min.At the same time,it demonstrated good stability and reusability.The radical quenching experiments illustrated that both HO·and SO₄^·-radicals were generated during the reaction,with SO₄^·-as the main active radical,while the existence of a synergistic mechanism in the catalytic mechanism was confirmed by XPS analysis.（2）The effects of transition metal ratio,alkali ratio in precipitant,pH of the preparation system,aging time,aging temperature and roasting temperature on the microstructure and catalytic activity of the catalyst were investigated,and then the preparation conditions of Co_xFe_yCu_z-LDOs were optimized.The results revealed that the optimum conditions for the preparation of Co_xFe_yCu_z-LDOs were Co:Fe:Cu=2:3:4;Na OH:Na₂CO₃=1:3;the pH of the preparation system was 10.0;the aging temperature was 60℃;the aging time was 24 h;and the roasting temperature was 500℃.（3）Co₂Fe₃Cu₄-LDOs magnetic non-homogeneous catalysts were prepared by the"co-precipitation+roasting"method.The morphological characteristics,magnetic properties and other physical and chemical properties were analyzed.The Co₂Fe₃Cu₄-LDOs/PMS system was constructed for the degradation of phenol wastewater.It was shown that the magnetic non-homogeneous catalyst with a large specific surface area was successfully prepared in this experiment.The system showed a strong degradation effect on phenol.At room temperature,pH=7.0,the concentration of PMS was 2.50 mmol/L and the amount of Co₂Fe₃Cu₄-LDOs was0.20 g/L,the removal rate of phenol was 97.50%within 60 min.Meanwhile,the cycle experiments and ion-dissolution tests confirmed that Co₂Fe₃Cu₄-LDOs have good reusability and stability,and the metal ions dissolution was also inhibited to a certain extent.The radical quenching experiments and XPS characterization results suggested that there was a Co/Fe/Cu synergistic mechanism in the catalytic mechanism,and both HO·and SO₄^·-radicals were generated during the reaction,with SO₄^·-being the main active radical.