Study On Catalytic Degradation Of Organic Pollutants In Industrial Wastewater By Transition Metal-based Perovskites

With the deterioration of water source in China,versatile types of aqueous organic pollutants have been emerged in wastewater and imposed intensive impacts on both human beings and natural lives.They are characterized by high ammonia nitrogen,complicated structures and with high concentrations.Moreover,most of the aqueous organics are toxic and difficult to biodegrade.Among the aqueous organics,heterocyclic organic pollutants are highly toxic and difficult to degrade,and their treatment processes have received widespread attention.The traditional water treatment technologies such as the adsorption,distillation/extraction and biodegradation are unable to treat this kind of pollutants.The emerging advanced oxidation processes（AOPs）utilizing the generated reactive oxygen species（ROS）with strong oxidation potentials have become the crucial methods to efficiently degradation these recalcitrant organic pollutants.Among AOPs,catalytic ozonation and catalytic persulfate technologies with the merits of fast reaction rate,and strong oxidation ability and wide application range can efficiently destruct the heterocyclic organics.Transition metal oxides as catalysts can efficiently catalyze ozone and peroxymonosulfate（PMS）,generating a large number of free radicals and resulting a complete mineralization.In this study,transition metal perovskite-based catalytic materials（LMO and LBCM）with different structures and morphologies were synthesized,and their physical and chemical properties were explored by advanced characterization techniques,and their performance in catalytic ozone oxidation and catalytic peroxymonosulfate oxidation were investigated accordingly.Moreover,the in-depth mechanistic insights of catalytic active sites and the type of free radicals generated during the catalytic oxidation process and its contribution to the degradation of organic pollutants were elucidated.In the work of LMO catalyzing ozonation to degrade aqueous organic pollutants,different LMO catalysts with hierarchical structures were synthesized by adjusting the precursor ratios of Mn and La.The synthesized catalysts obtained an excellent catalytic activity for ozone activation and resulted in a degradation of 50 mg/L of oxalic acid（OA）in 45 minutes and 50 mg/L of benzotriazole（BTA）in 30 minutes,respectively.The surface hydroxyl group,Mn³⁺/Mn⁴⁺redox cycle and oxygen vacancies were suggested as the active sites.It was found that he spontaneous dissociation of ozone molecules on these active sites resulted in the formation of ROS.In-situ EPR and free radical quenching experiments further confirmed that hydroxyl radicals（·OH）and singlet oxygen（¹O₂）were the dominant ROS for destruction of organics.This work probed the active sites on LMO catalysts and the mechanism of ROS generation.In the work of LBCM catalyzing PMS for the degradation of organic pollutants,LBCM materials with different morphologies were synthesized by adjusting the ratio of Co and Mn in the B-sites of the perovskites.LBCM material with a cubic structure can efficiently activated PMS,resulting in the degradation of 25 mg/L of phenol in 25 minutes and degradation of 25mg/L of p-chlorophenol,p-nitrophenol,and p-hydroxybenzene in 60 minutes.Lewis acid sites such as surface hydroxyl groups,redox cycles of Mn³⁺/Mn⁴⁺and Co³⁺/Co⁴⁺and oxygen vacancies were suggested as the active sites for PMS activation.In situ EPR and quenching tests confirmed that the·OH,sulfate radical(SO₄^·-)were the main ROS for organics destruction.This work also explored the effects of different reaction parameters such as reaction temperatures,initial p H of the solution,pollutant concentrations,oxidant dosages,anions in the water,and humic acid on phenol degradation.This work achieved the control of the perovskite morphology by adjusting the proportion of coordination metals.Moreover,the mechanisms of transition metal-based perovskites in PMS activation have been elucidated.