Heterogeneous Catalytic Ozonation By LaCoO₃ Based Perovskite Type Oxides In Reclaimed Water:benzotriazole Removal Efficiency And Mechanism

Ozone is widely used in water and wastewater treatment due to its high oxidation capacity.However,ozonation cannot completely removal some organic contaminants and may lead to the formation of toxic by-products,such as bromate(BrO₃^-).Therefore,it is a challenge to enhance organic pollutants degradation and toxic by-products inhibition simultaneously in ozonation.Heterogeneous catalytic ozonation with solid catalysts has been considered as a practical and efficient alternative technique to overcome these drawbacks.Therefore,it is necessary to study the new efficient solid catalyst,interface reaction mechanism and the performance on the removal micro-pollutants and the elimination of toxic by-products,in catalytic ozonation.Based on above,this study focused on catalytic ozonation with perovskites based catalysts,to analysis the structure-activity relationship of interface structure and catalytic activity,to reveal the interaction mechanism of catalytic ozonation by perovskites based catalysts,micro-pollutants degradation pathway,and the elimination mechanism of toxic by-products.The obtained conclusion can promote the understanding and application of heterogeneous catalytic ozonation.Firstly,typical perovskite type oxides including LaFeO₃(LFO)and LaCoO₃(LCO)were selected as heterogeneous catalysts in catalytic ozonation.Results suggested that LFO could not accelerate ozone decomposition to form hydroxyl radicals.Therefore,LFO showed no catalytic activity for benzotriazole(BZA)degradation.The complex[Fe-H₂O₂]_s generated on the surface of LFO,resulting in the reduction of BrO₃^-to HOBr/OBr^-.Compared with the sole ozonation,the presence of LCO could accelerate BZA degradation and BZA removal efficiency achieved 100%at 15 min.The cyclic of Co³⁺/Co²⁺on LCO surface promoted H₂O₂ formation,which could inhibit BrO₃^-generation simultaneously.Secondly,the important factors were investigated to enhance BZA degradation and BrO₃^–elimination synchronously.Result suggested that the optimum LCO dose and BZA concentration were0.25 g/L and 1.0-5.0 g/L,respectively.In LCO catalytic ozonation,the optimal solution pH was 7.22.A much lower[NH₄⁺-N]([NH₄⁺-N]/[Br^-]<15)was able to decrease BrO₃^-generation,compared with that used in the sole ozonation.LCO catalytic ozonation was more effective for enhancing BZA degradation and eliminating BrO₃^-under lower[HCO₃^-/CO₃^2-](<100 mg/L(as Ca CO₃)).Moreover,a practical strategy for BZA degradation and BrO₃^–elimination with and without Br^–was developed.Thirdly,BZA degradation and toxic by-products inhibition efficiency were also evaluated in effluent organic matter(Ef OM)removal in LCO catalytic ozonation.Results showed that BZA degradation ability increased significantly in LCO catalytic ozonation at the first 10 min.Moreover,the presence of LCO accelerated the degradation of tryptophan,fluvic-like and humic-like substances.In addition,better reduction performance of aldehydes was achieved at lower ozone dose(1.0 mg/L).In LCO catalytic ozonation,total halogenated by-products decreased significantly when O₃ dose was 2.0 mg/L compared with sole ozonation.The introduction of LCO could removal DBPs precursors,such as trichloromethane,bromochloroacetonitrile,trichloroacetonitrile,dichloroacetamide and trichloronitromethane;however,the precursor of dichloroacetonitrile was promoted.Finally,the combination of g-C₃N₄(CN)and LCO was studied to enhance the electron transfer and catalytic ozonation ability,based on above obtained interaction mechanism of LCO catalytic ozonation.The formation of-C-O-Cobond indicated the chemical bonding between CN and LCO.Bond-C-O-Coand nitrogen vacancy could promote the delocalized electrons transfer and ozone decomposition.Therefore,BZA degradation efficiency was promoted.In addition,the fast charge transfer facilitated the cyclic reaction of Co³⁺/Co²⁺,which further enhanced BrO₃^–elimination efficiency.At that time,BrO₃^–inhibition efficiency achieved 77.4%.In summary,LaCoO₃ based perovskite type oxides were applied to the catalytic ozonation in this study,accelerating benzotriazole degradation and toxic by-products reduction synchronously.Additionally,the cyclic reaction between Co³⁺/Co²⁺accelerated ozone decomposition and H₂O₂ formation,which promoted BrO₃^-elimination.Additionally,the novel BrO₃^-reduction pathway was proposed,which contributed for the basic chemical principle of catalytic ozonation technology.