Study On Biomimetic Photocatalytic Degradation Of Organic Pollutants

Water pollution has serious negative effects on human survival and development.Biological methods have high treatment efficiency and good ecological integration compared to physical and chemical methods.However,due to the presence of considerable amounts of toxic and hazardous pollutants in industrial wastewater,as well as when the pollutants are present at low levels in the water,the efficiency of the biological treatment method is significantly reduced.Considering that self-purification process of natural water could be regarded as a combination of physical,chemical and biological processes.Therefore,the trend is directed to simulate the self-purification process and develop ecological methods to minimize the secondary pollution or pollution transfer in wastewater treatment.In this work,we select clean energy-solar energy as the energy source,some transition metal ions（Fe,Mn,Co,Cu）which are widely found in nature as catalysts,and air as the oxidant,to focus on the biomimetic degradation of two typical organic pollutants-organic ligands and aromatic compounds.Firstly,the biomimetic homogeneous photocatalytic system,in which water-soluble compounds containing Fe,Mn,Co or Cu were used as catalysts,was designed for the removal of organic pollutants with coordination properties.The results showed that the organic ligands were easily removed under acidic conditions,for the organic ligands promoted the redox cycle of the transition metal ion pairs,thus a synergistic effect improving the removal of organic ligands.Based on this result,the biomimetic photocatalytic system was applied to the degradation of EDTA with strong coordination properties,and an excellent removal of Cd²⁺ion from EDTA solution,with a residual concentration as low as 0.01 mg L^-1,demonstrated that EDTA was almost completely degraded.solving the problem of difficult removal of heavy metal ions in the presence of strong coordination agents.Secondly,a bio-mimetic heterogeneous photocatalytic system,in which water-insoluble oxides containing Fe,Mn,Co and Cu were used as catalysts,was designed for the removal of organic pollutants without coordination properties,and anoxic operation mode was adopted to reduce the secondary pollution to the environment caused by complete mineralization.The results showed that:under alkaline conditions and with cobalt-manganese oxides composite as the catalyst,alkylbenzenes was degraded with more than 80%removal percentages,especially a removal percentage as high as 96.47%for o-or p-xylene.The photodegradation products are small molecules such as citric acid,formic acid salt and acetic acid salt.Similarly,under alkaline conditions,an obvious photodegradation of quinoline and pyridine was observed with manganese-containing oxides/phosphates as catalyst,especially a removal percentage as high as 92.36%for pyridine.Under near-neutral conditions,the manganese oxide-containing catalyst was effective for degrading indole,pyrrole,imidazole and pyrimidine,among which pyrrole showed the best degradation in terms of 59.60%of change in total organic carbon after treatment.To investigate whether harmful substances are produced during the biomimetic anoxic photodegradation,the biodegradability of the aromatic compounds after the biomimetic degradation was measured.The results showed that the aromatic compounds were decomposed into small molecules and thus biodegradability were all significantly improved.Among them,the BOD₅/COD of the wastewater containing alkylbenzenes was higher than 0.3,changed from refractory wastewater to easily biodegradable wastewater.Nitrogen-containing aromatic compound wastewater is generated without harmful components during the degradation process,in which the BOD₅/COD was higher than 0.3 of imidazole-containing wastewater is converted from a hard-to-biodegrade wastewater to a biodegradable one.