Cu-Co Bimetallic Heterogeneous Fenton-like Catalysts With The Investigation In Structure-Activity Relationship

The wastewater discharge has greatly increased with the development of industry in recent years.However,some refractory organics ingredients,especially for aromatic compounds,are difficult to be treated by traditional methods and their residues in the environment would pose a serious threat to ecological balance and human health.Fenton reaction,as one of advanced oxidation processes,is an efficient treatment method which could completely oxidize resistant organics into small non-toxic molecules such as CO2 and H2O by ·OH.Thus,the development of economic heterogeneous Fenton or alike catalysts is of great significance.Cu and Co,as nonnoble metal materials with low cost and high stability,have exhibited excellent Fenton catalytic activity.Herein,the controlled synthesis of high-efficiency Cu-Co-based catalysts with the establishment of structure-performance relationship for further rational design of catalysts in this kind is of great value for this practical process.This dissertation has synthesized a series of non-supported and supported Cu-Co catalysts by control of low-dimension morphology,exposed crystal facet and size effect with strong Cu-Co bimetallic interaction.The fabricated material as Cu-Co LDH,exposed {112} plane Cu-Co3O4 and CoCu/γ-Al2O3 exhibited outstanding catalytic performance for both industrial and simulated wastewater.Meanwhile,this study provided a comprehensive study for the structure-activity relationship of different catalysts which focusing on the discussion of active sites,the crystal growth mechanism and the process of H2O2 activation.The primary findings are given as follows:1.The Cu-Co LDH was prepared by a facile co-precipitation method.It exhibited great degradation performance for the treatment of anthraquinone containing H2O2 production wastewater(AHE).The variation of synthesis pH value has found to significantly influence the catalyst structure and resulted performances.The gradual oxidation of Co2+to Co3+with the increase of pH made the structure met the certain M2+/M3+ratio requirement in the LDH framework,therefore the Cu-Co LDH was obtained under a synthesis surrounding of pH=12.0 with COD and TOC indexed of AHE reduced to 33.0 mg/L and 15.1 mg/L after treatment with good stability.It was found that the performance of catalyst is directly related to the concentration of surface oxygen vacancies.Thus,LDH structure with highest concentration of oxygen vacancies exhibited best performance.Further investigation declared that the LDH structure is conducive to the generation of the Co-O-Cu oxo-bridge.It greatly facilitated electron transfer with weakder M-O bond energy,promoting generation of surface oxygen vacancies which strengthened the H2O2 adsorption and H2O2 dissociation with improved electron transfer.2.Modification strategy of lattice defects in Cu-Co catalysts.The surface defect density was controlled by the modification of Cu-Co LDH structure via changing Cu/Co molar ratio based on the previous preparation method.Cu has found to inhibit the formation of β-Co(OH)2 while promoting the oxidation of Co2+to Co3+with the generation of octahedral coordination(MO6)structure in hydrotalcite-like α-Co(OH)2,which satisfied the necessary requirements for LDH formation.The Cu-Co interaction and MO6-rich structure benefited the generation of Co-O-Cu oxo-bridge structure,and the distortion in crystal structure further elongated M-O bond with reduced bond energy,which promoted the generation of surface oxygen vacancies.Moreover,structureperformance analysis proved the surface oxygen vacancies was the main active sites and mainly promoted the production of surface hydroxyl groups,the adsorption of H2O2 and the elongation of its O-O bonds during the reaction with greatly improved electron transfer under bimetallic interaction.Co4Cu1 LDH with a molar ratio of Co/Cu=4:1 had the strongest relectrions for LDH structure and shown the best performance with 99%removal of RhB within 10 minutes.3.Control strategy of electronic structure in Cu-Co catalysts.The Cu-Co bimetallic catalyst was prepared by one-step co-precipitation method based on previous study with modification of Co/Cu ratio and addition of high concentration of NH4F in ambient condition.It was found that more Cu-Co3O4 with {112} exposed facet was obtained under condition of Co/Cu=1:2.Different from above previous conclusion,it was found that the surface oxygen vancancies were no longer the key to the improvement of catalytic performance in this work,which resulted from the different electronic structure on the surface of the catalysts.Meanwhile,the addition of Cu has facilitated the oxidation of Co2+to Co3+and promoted the generation of Cu-CoOOH,which decomposed into Cu-Co3O4 with {112} exposed facet for its structural instability.Also,Cu doping on the {112} facet of Co3O4 would adjust the adsorption energy of H2O2 on active sites to a suitable range and benefit for the stretching of O-O bond in adsorbed H2O2.Also,Cu+ site on the {112} facet of Co3O4 provided stronger electron donation with accelerated reduction process,which is beneficial to the dissociation and activation of H2O2.The highest MNZ removal by this Co1Cu2 was 99.9%with good stability.4.The influence of size effect on the catalytic performance of Cu-Co catalysts.The Al2O3 supported Cu-Co bimetallic catalyst was fabricated via a sol-gel way.A series of mesoporous CoxCuy/γ-Al2O3 catalysts was obtained and the paricle size decreased with an increase in Co content.For Co-Cu bimetallic catalysts,the size effect contributed for the exposure of active site and reduction process.In particular,a small amount of Cu doping increased the amount of CoO6 structure of the surface CoAl2O4 lattice for Co7.5Cu2.5/Al2O3,where the reduction ability of Cu has greatly increased,greatly promoting the catalytic performance.The highest degradation removal of 95.5%CAP was achieved when the loading of Co and Cu is modified to Co7.5Cu2.5/Al2O3.In all,it was summarized that the Cu-Co interaction,defect density,size effect with octahedral coordination environment and the facet control of Cu-Co3O4 would greatly influence the electronic structure of the active sites on the surface for the improvement of catalytic activity.The future work will put more focus on the rational design of the robust Cu-Co catalysts as well as the reaction mechanism.