| With the acceleration of economic development and urbanization,the types and quantities of organic pollutants in water environment are increasing,so efficient,low-cost and environment-friendly water treatment technologies are highly desired to meet the national demand of environmental protection.The peroxymonosulfate(PMS)-based heterogeneous catalytic oxidation processes can remove water pollutants with high efficiency,wide applicable range of pH and strong anti-interference ability.However,this technology still faces three major problems before practical application,namely,the activity and stability of transition metal-based catalytic materials are weak,the powder catalyst is difficult to be separated and recycled,and there is lack of effective methods for determination of the low-concentration PMS residual in water.In this dissertation,multiple strategies,including morphological control,bimetallic combination,interfacial structure regulation,mechanochemical synthesis,and immobilization on millimeter-scale support,to improve the catalytic performance of metallic catalysts.These strategies were found to be feasible and effective for high-efficiency removal of various organic pollutants and enabled the establishment and stable operation of fixed bed reactor.The physicochemical properties of the as-prepared catalysts are characterized and the reaction mechanisms were elucidated in depth.Moreover,a molecular fluorescence method was developed to implement ultrasensitive detection of PMS in water.Therefore,this dissertation provides new ideas and scientific basis for the application of PMS-based heterogeneous catalytic oxidation technologies in water treatment.The main contents and achievements of this dissertation are summarized as follows:1.Non-classical crystallization strategy to regulate the internal and external structure of Co-Fe PBA for improving the PMS activation performance.Structure regulation can effectively improve the catalytic performance of nanomaterials.To address the challenge of controlling the internal structure of metallic nanomaterials,a citrate-guided non-classical crystallization strategy was developed,the effect and mechanism of the internal and external structure regulation of Co-Fe PBA were studied,and the performance of the prepared PBA materials to activate PMS for organic pollutant removal was investigated.The results show that by changing the concentration of citrate and metal precursors in the non-classical crystallization process,the internal structure,opening degree and growth direction of Co-Fe PBA can be adjusted to prepare PBA nanomaterials with various structures.Citrate played a key role in the formation and assembly of PBA primary particles,and it also regulated the subsequent evolution of the assembly into a solid or hollow structure.The prepared Co-Fe PBA material had excellent performance of activating PMS to remove bisphenol A(BPA).Compared with the hollow cube and solid cube structure,the catalytic reaction rate of the cubic frame structure was increased by 4 and 14 times,proving the effectiveness of structure control on the improvement of catalytic performance.2.Bimetallic synergism for efficient activation of PMS.To improve the performance of Mn/Fe-based materials for PMS activation,Mni.8Fe1.2O4 nanosphere catalyst was synthesized.The performance of the catalyst for PMS activation to degrade BPA was comprehensively evaluated,and the synergistic effect between Mn and Fe was explored.The results showed that the catalytic activity of Mn1.8Fe1.2O4 nanospheres was substantially higher than that of the corresponding monometallic oxides and remained efficient in the pH range from 4 to 10.The synergistic catalytic effect between solid Mn and Fe was proven through a series of control experiments.Mn was inferred as the main catalytic active site on the catalyst surface,while Fe(?)was the main adsorption site for the reaction substrate.The effective combination of the two functions led to the bimetallic synergism.3.Regulation of interface structure to enhance the catalytic activity.To further improve the catalytic activity of Mn/Fe oxides and realize the continuous flow reaction mode,the interface structures between Mn/Fe oxide nanoparticles was constructed,and their efficiency for PMS activation and removal of different organic pollutants was studied.Firstly,effective interfacial structures between commercial Mn oxides and Fe2O3 nanoparticles were constructed through physical grinding/ball-milling.The existence of Mn/Fe interfacial effect and its universality for Mn oxides with different valences and for different organic pollutants were proven by control experiments.To further optimize the Mn/Fe-oxide interface structure and implement it in the continuous flow mode,Fe2O3 nanoparticles with smaller size were used as support to load MnOx with impregnation-calcination method.As a result,the interfacial atomic ratio and the catalytic activity of the catalyst were further enhanced.Lastly,millimeter-scale porous Fe-Ti oxide pellets were used as support and the Mn/Fe-oxide interface was constructed in the pellets via loading MnOx with the impregnation-calcination method.The obtained Mn-Fe-Ti oxide pellets were filled into a fixed bed and achieved the stable and efficient treatment of simulated BPA-containing wastewater in continuous flow mode.4.Mechanochemical synthesis of supported MnOx/Fe2O3 catalyst.Compared with the wet chemical synthesis methods that are complex and difficult to control,developing a greener,simpler and more economical mechanochemical method to prepare supported catalysts is of great significance.With inert Fe2O3 nanoparticles as the support and steel ball mill tank and beads themselves as the Mn precursor,supported MnOx/Fe2O3 catalyst was prepared through mechanical ball milling.The physicochemical properties and catalytic performance of the catalyst were investigated.The results showed that the Mn loading in the catalyst was 1.4 wt%.When applied to the activation of PMS,the catalyst achieved complete oxidation of BPA and 80%removal of TOC within 5 min,and it showed good recycling stability.The used steel tank and beads could be self-cleaned by no-load ball milling,showing good sustainability for utilization.5.Coupling of hollow Mn-Fe oxide nanocubes with PMS to remove organic arsenic.p-Arsanilic acid(p-ASA)is widely used as an organoarsenic feed additive in worldwide breeding industry.Effective removal of p-ASA from water is required for avoidance of serious arsenic pollution to the environment.Thus,hollow Mn-Fe-mixed oxide(MnFeO)nanocubes were prepared for catalytic oxidation and removal ofp-ASA and the total arsenic.The performance and reaction mechanism of the PMS/MnFeO heterogeneous oxidation system were studied.The results revealed that PMS alone could effectively oxidize p-ASA and partially convert it into inorganic arsenic,while the presence of MnFeO nanocubes led to adsorption of p-ASA and formation of the ligand-metal oxide interface.The interface significantly promoted the oxidation of adsorbed p-ASA by PMS and ultimately improve the removal ratio of total arsenic.No formation of reactive oxygen species like SO4·-,·OH or 1O2 was involved in the PMS/MnFeO oxidation system.As a result,the selective oxidation of p-ASA could be realized,and the interference of common constituents in actual water samples on the removal of total arsenic could be weakened.The used MnFeO catalyst could be regenerated by simply elution with alkaline solution,and the regenerated catalyst showed good recycling stability.6.Molecular fluorescence method for ultrasensitive detection of PMS in water.With the rapid development of PMS related technologies and their applications in the field of water treatment,a simple,rapid and sensitive method is urgently needed for the accurate measurement of residual PMS concentration during the oxidation processes and its trace detection after releasing to natural water bodies.Therefore,a fluorescence method for PMS determination was established based on the SO4·--induced aromatic hydroxylation by using benzoic acid(BA)as a chemical probe and Co2+ as the PMS activator.The comprehensive evaluation showed that the BA fluorescence method has rapid reaction equilibrium(<1 min),ultrahigh sensitivity(LOD=10 nM;LOQ=33 nM),excellent selectivity,good stability,and a wide detection range(0-100 ?M).Moreover,this method worked well in the presence of possible interfering substances,including two other peroxides(i.e.,peroxydisulfate and hydrogen peroxide),some common ions and organics.The test results for real water samples further validated the practical utility of the developed fluorescence method. |
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