Study On The Selective Adsorption And Degradation Of Antibiotic Residues In Wastewater And Its Mechanism

The abuse of antibiotics has led to the long-term presence of antibiotics in environmental waters. It was persistent pollutant which cause serious harm to the environment and human body, therefore, it is urgent to remove the environmental antibiotic residues. Adsorption has the advantages of easy operation, low cost, high efficiency and no toxic byproducts, and has been widely used in the treatment of antibiotic wastewater. Among the many kinds of adsorbent materials, biomass materials are cheap, non-toxic, biocompatible and biodegradable, but their mechanical strength stability is poor and difficult to recycle. The above problems can be solved by chemical modification of the biomass material and the introduction of the magnetic material which can be easily separated and recovered. Although the adsorption can achieve the purpose of removal of antibiotic residues, only from one phase to another phase, can not be completely mineralized and achieve the depth removal of antibiotic effluent. The photocatalytic technology has the advantages of low running cost,environmental friendly and low secondary pollution, has been widely used in the deep treatment of environmental antibiotic wastewater. Among the many photocatalytic materials, TiO₂, ZnFe₂O₄ and other inorganic materials have the advantages of simple preparation and good stability. However, these single photocatalytic materials have been severely limit their application because of low photocatalytic activity. These problems can be solved by load and recombination method. Therefore, the preparation of magnetic composite adsorbents with good stability and the composite photocatalytic material with high photocatalytic activity has become the key to remove the antibiotic residues in the environment.Accordingly, in this paper, a variety of composite adsorbent materials with magnetic separation capability and high adsorption capacity were prepared by modifying the biomass materials. By doping, loading and recombination, the composite photocatalysts with high photocatalytic activity and stability were prepared to realize the high efficiency removal of antibiotics in the water environment. The physicochemical properties, adsorption behavior and photocatalytic degradationmechanism of composite materials and composite photocatalysts were elucidated by a series of characterization analysis, performance testing and mechanism discussion experiments.This work mainly includes four aspects as following:1.Preparation of magnetic chitosan based composite microspheres and behavior research on the removal of antibiotics?1?A magnetically separable adsorbent, named CTS/HNTs-Fe₃O₄ microspheres are prepared by emulsion crosslinking method and characterized by FT-IR, VSM,XRD, SEM and TEM. The adsorption performance was investigated by removal of tetracycline from the solution. The effects of the initial concentration of TC solution?C0?, temperature, initial pH value?pH0? of TC solution and the adsorption dose on the adsorption capacity of the microspheres are investigated. The optimum pH value for TC adsorption is found at pH = 5.0, and the adsorption capacity increased with the increase in adsorption temperature. Adsorption equilibrium and kinetic characteristics of adsorption process were analysed by the Langmuir model and pseudo-second order equation. CTS/HNTs-Fe₃O₄ microspheres could be easily separated from the aqueous solution in a magnetic field, it show good magnetic separation characteristics. The adsorption-desorption experiments implied that CTS/HNTs-Fe₃O₄ microspheres can be used as promising adsorbents for the removal of TC from wastewater and has good stability.?2? A magnetically separable adsorbent, named CTS/kaolin/Fe₃O₄ magnetic microspheres were prepared by emulsion crosslinking method. Its physical and chemical properties were analysed by FT-IR, VSM, XRD, SEM, TEM, EDS and TGA.The microspheres were used as adsorbents for the removal of CIP from aqueous solution. Adsorption of CIP from aqueous solution was investigated in terms of adsorbent dose, initial pH?pH0? and initial concentration. The optimum pH value for ciprofloxacin adsorption is found at pH0=6, and the adsorption capacity is highest as adsorbent dose is 15 mg. Adsorption equilibrium and kinetic process follow the Langmuir model and pseudo-second order equation. The reusability experiments of chitosan/kaolin/Fe₃O₄ magnetic microspheres showed adsorption capacity has noobviously deterioration by four repeated cycles in performance and were reused in the magnetic field.2.Design and performance study of surface molecular imprinted polymer based biomass magnetic composite materials?1?With chloramphenicol as the template molecule, core-shell magnetic CTS imprinted polymers were prepared via situ precipitation polymerization. The properties of obtained MMIPs were characterized by SEM, TEM, XRD, TGA and so on. Adsorption experiments show that Adsorption equilibrium and kinetic process follow the Langmuir model and pseudo-second order equation. Selective adsorption experiments show that the obtained magnetic CTS MIPs showed specific recognition and selectivity for CAP. The obtained MMIPs showed the good stability and regeneration property.?2?A novel thermalresponsive and mag-yeast molecularly imprinted polymers?TMMIPs? were prepared via in situ precipitation polymerization method. The properties of obtained TMMIPs were characterized by SEM, TEM, XRD, TGA and so on. Equilibrium and kinetic characteristics of adsorption processes were analysed by the Langmuir model and pseudo-second order equation. TMMIPs exhibited magnetic sensitivity, magnetic stability and thermal stability. Reversible recognition and release of template molecule were realized by changing environmental temperatures.Selective adsorption experiments show that TMMIPs have good selectivity.3.Construction of carbon-based carrier Ferrite composite photocatalyst and behavior research on antibiotic degradation?1?Ni_xZn_1-xFe₂O₄/CNTs composite photocatalysts were prepared by hydrothermal method. The physical and chemical properties of the samples were characterized by XRD, Raman, TGA, FT-IR, UV-vis, VSM, SEM, PL and TEM. The effect of hydrothermal reaction time on the formation of ferrite crystal was discussed. The effects of different Ni doping amount on the photocatalytic activity of Ni_xZn_1-xFe₂O₄ photocatalyst and the photocatalyst of Ni0.5Zn0.5Fe₂O₄/CNTs with different CNTs content on the degradation of tetracycline wastewater were investigated. The results show that the photocatalytic activity of Ni0.5Zn0.5Fe₂O₄/CNTs?5 % CNTs?photocatalyst is high, and the degradation rate of tetracycline is 96 %. After four photocatalytic degradation experiments, the composite photocatalyst remained high photocatalytic activity, and the stability of the composite catalyst was better.?2?Visible-light-driven g-C₃N₄/ZnFe₂O₄ heterostructured photocatalysts were prepared by a simple hydrothermal synthesis method.The composition, structure,morphology, and optical absorption properties of the as-prepared g-C₃N₄/ZnFe₂O₄ composites were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL, BET and FTIR. The result shows that we have found a phenomenon of different proportions of the g-C₃N₄/ZnFe₂O₄ composition, 1:2 fraction has the highest rate of the degradation of spiramycin under visible light irradiation, and the degradation rate of tetracycline is 95 %. After five photocatalytic degradation experiments, The composite catalyst has better photocatalytic activity. These results further show that the g-C₃N₄/ZnFe₂O₄ heterostructured photocatalysts have the characteristics of good stability and easy recycling.4.Consruction of composite photocatalyst based on TiO₂ and research on photodegradation performance for antibiotics?1?Firstly, B-Ni-TiO₂ and g-C₃N₄ were respectively prepared by sol-gel method and calcination method. Secondly, B-Ni-TiO₂/g-C₃N₄ composite photocatalysts were prepared by heating reflux method. The physical and chemical properties of the composite photocatalyst were characterized by XRD, UV-vis, FT-TR, SEM, PL and TEM. The effects of different photocatalysts on the degradation of chloramphenicol were investigated. After the combination of g-C₃N₄ and B-Ni-TiO₂, the separation efficiency of photo-generated electrons and holes can be accelerated and the photocatalytic activity can be improved. When the composite ratio was 50 %, the degradation rate of chloramphenicol to the composite catalyst is up to 95 %. After five cycles of photocatalytic degradation, the photocatalytic activity of the composite catalyst remained high, and the composite catalyst had better stability and regeneration performance.?2?A petaloid nanostructure anatase TiO₂/BiOCl was successfully prepared by a facile hydrothermal method. The obtained the phase structures, morphologies, surfaceareas, optical properties, and electronic state of samples were systematically characterized by XRD, SEM, BET, UV-vis DRS, FTIR, and PL. Photocatalytic degradation performance of the composite photocatalyst was studied by using the aqueous solution of tetracycline as the target pollutant, and the photocatalytic degradation kinetics and the process of the degradation of tetracycline were analyzed.The results showed that the formation of the heterogeneous structure promoted the separation of the electron and the hole, and enhanced the photolysis activity. The optimal experimental conditions of photocatalytic degradation of tetracycline activity up to 99.1 %, photolysis kinetics followed pseudo-first order kinetics equation, the photolysis process showed that ·O₂- active species play a major role in the photocatalytic degradation process.