Adsorption And Degradation Of Antibiotic Under Visible Light By Novel Composite Hydrogel

The mass production and abuse of antibiotics caused a serious threat to human health and ecological environment,and the most frequently detected antibiotics in surface water of China were mainly sulfonamides and fluoroquinolones.Therefore,sulfamethoxazole and norfloxacin were selected(as the representative substances of sulfonamides and fluoroquinolones,respectively)in this thesis to study how to effectively remove them from the aquatic environment.In view of the characteristics of environmental friendly and simple operation,photocatalysis has gradually become a research hotspot in the treatment of antibiotics in water.However,there were still a lot of shortcomings in the technology,such as low photocatalytic efficiency,low utilization of visible light and poor separation effect,etc.A novel composite hydrogel loaded with nano-photocatalyst was synthesized in this thesis to adsorb and enrich antibiotics from water,meanwhile,the photocatalytic degradation of antibiotics under visible light was carried out.This method overcame the shortcomings of the photocatalytic technology mentioned above,perfectly.In this thesis,N-methyl maleic acid(N-Methylmaleamic acid,NMMA)and 2-hydroxyethyl acrylate(2-hydroxyethyl acrylate,HEA)were used as monomers to prepare the hydrogel carrier p(HEA/NMMA)by low temperature irradiation polymerization.The novel composite hydrogels with adsorption and photocatalytic properties were obtained by loading the nanoparticles of zinc oxide and copper sulfide on hydrogel carrier using in situ precipitation method,they could be called as zinc oxide composite hydrogel(p(HEA/NMMA)-ZnO)and copper sulfide composite hydrogel(p(HEA/NMMA)-CuS).The swelling properties,Zeta potential,surface morphology,structure characteristics,thermal stability and optical properties of the hydrogel carrier and the novel composite hydrogels(p(HEA/NMMA)-ZnO)and p(HEA/NMMA)-CuS)were analyzed by corresponding characterization methods.Combined with the above characteristics,the adsorption effect,adsorption behavior,influencing factors and adsorption mechanism of the novel composite hydrogels toward antibiotics were disscussed.Meanwhile,the efficiencies,kinetics and influencing factors of antibiotic degradation by the novel composite hydrogels under visible light were systematically investigated,and the corresponding degradation mechanism was obtained through the analysis of the antibiotic degradation products and molecular theoretical calculation.Finally,the acute toxicity of the antibiotic degradation products under the action of the composite hydrogels was evaluated,and the treatment efficiency of the simulated wastewater was discussed.Through the above researches,the main conclusions were as follows:1.Characterization of the p(HEA/NMMA)and two novel composite hydrogelsThe results of the corresponding characterization showed that the surface of the p(HEA/NMMA)contains carboxyl,hydroxyl and amide groups,and the amide groups on the hydrogel monomer played a major role in the loading of copper sulfide and zinc oxide nanoparticles.Two novel composite hydrogels contained 10 wt%CuS nanoparticles and 15 wt%ZnO nanoparticles,respectively.The visible light absorption of p(HEA/NMMA)-ZnO or p(HEA/NMMA)-CuS was significantly stronger than that of pure ZnO or CuS nanoparticles,respectively.Under visible light,the electrons and holes produced by ZnO nanoparticles and two novel composite hydrogels could be effectively separated.However,the electrons and holes produced by pure CuS nanoparticles could not be effectively separated.2.The adsorption efficiency and mechanism of the two novel composite hydrogels toward antibioticsThe equilibrium adsorption capacity of the novel composite hydrogels toward antibiotics increased with the rise of initial antibiotic concentration.When the initial concentration of NOR was 0.64 mmol/L,the maximum theoretical adsorption capacity of NOR by p(HEA/NMMA)-ZnO was 52.6 mg/g,and the maximum theoretical adsorption capacity of NOR by p(HEA/NMMA)-CuS was 31.0 mg/g with the initial concentration of SMX at 2.0 mmol/L.The adsorption of NOR and SMX on two novel composite hydrogels had a good agreement with Langmuir isotherm model.The adsorption of NOR and SMX by p(HEA/NMMA)was mainly due to the action of amides in polymer monomers.The adsorption of NOR on p(HEA/NMMA)-ZnO was mainly owing to the role of zinc oxide nanoparticles,and the amide groups in the monomers only played auxiliary role.The adsorption of SMX on p(HEA/NMMA)-CuS was attributed to the interaction of copper sulfide nanoparticles and amide groups on hydrogel monomers.3.The degradation efficiency and mechanism of the two novel composite hydrogels toward antibioticsUnder 500 w visible light,the degradation efficiency of 0.16 mmol/L NOR by 2.0 g/L p(HEA/NMMA)-ZnO reached to 89.5%within 60 min,and the degradation efficiency of 0.20 mmol/L SMX by 2.0 g/L p(HEA/NMMA)-CuS was 90.9%within 12 h.The effect of visible light intensity on the degradation efficiency of NOR by p(HEA/NMMA)-ZnO was not obvious,but the degradation efficiency of SMX by p(HEA/NMMA)-CuS decreased with the reduce of visible light intensity.Under visible light,the degradation of NOR by p(HEA/NMMA)-ZnO mainly attributed to the role of holes and superoxide radicals(·O2-)in the oxidation process,the hydroxyl radicals(·OH)only played auxiliary role.During the degradation of SMX by p(HEA/NMMA)-CuS,the holes play an important role,·OH only played auxiliary role.The mineralization ratio of NOR by p(HEA/NMMA)-ZnO was 77.2%,and the mineralization ratio of SMX by p(HEA/NMMA)-CuS was 43.6%.The results of repeated experiments showed that the two novel composite hydrogels had a good reutilization.4.The acute toxicity evaluation of the products and the treatment effect of the simulated antibiotic wastewater in laboratory of antibiotics degraded by the novel composite hydrogelsThe Photobacterium phosphorem T3 was used to evaluate the acute toxicity before and after degradation.After photocatalytic degradation of different concentrations of NOR and SMX by the two novel composite hydrogels,the inhibitory effect on luminescence of Photobacterium phosphorem T3 decreased in different degrees,indicating that the acute toxicity of NOR and SMX was decreased after degradation,respectively.Compared with the control group in pure antibiotics water,the final degradation efficiency of NOR by p(HEA/NMMA)-ZnO was unaffected in two kinds of simulated marine aquaculture wastewater and medium hardness synthetic water.While the degradation efficiency of NOR in simulated synthetic wastewater was inhibited about 10%.The final degradation efficiency of SMX by p(HEA/NMMA)-CuS in two kinds of simulated marine aquaculture wastewater was slightly reduced,and the degradation efficiency of SMX by p(HEA/NMMA)-CuS in the medium hardness synthetic water and the simulated synthetic sewage was decreased about 15%and 20%,respectively.