Synthesis Of MoS₂-based Photocatalysts And Their Performance In Photocatalytic Degradation Of Antibiotics

With the continuous development of the pharmaceutical industry,the abuse of antibiotics and the consequent environmental problems have received much attention.It is important to develop effective degradation for antibiotics since all kinds of antibiotics enter the environments through various ways and harm to both the ecological environments and human health.Photocatalysis is considered to be an high-efficient,eco-friendly and sunlight-only technology for treating organic pollutants in environments,in which the development of new and high-efficient photocatalysts is one of the core issues.MoS₂has attracted much attention in the field of photocatalytic degradation due to its unique photoelectric properties.However,the photocatalytic activity of MoS₂seems to be inhibited due to the narrow response range of light and the trend of photogenerated electron-hole complexation.In this issue,the preparation of MoS₂-based composites to generate synergistic photocatalysis provides an effective solution.In view of this,MoS₂nanoflowers and two kinds of MoS₂-based composite photocatalysts including CdSe QDs@MoS₂and Ag₃PO₄@MoS₂were prepared and characterized in terms of their morphology,structure and composition.The performance of the as-prepared materials in photocatalytic degradation of fluoroquinolones and cephalosporin antibiotics were investigated.The present work aims to provide a useful experimental exploration for the effective removal of antibiotics in water.The thesis includes the following four parts:1.Firstly,the pollution and the treatments of antibiotic residues in water are introduced;secondly,the photocatalytic degradation and commonly used semiconductor photocatalytic materials are outlined;finally,the structure properties,preparation and modification methods of nano-MoS₂are reviewed.The aims and significance of this thesis are clarified as well.2.Flower-like nano-molybdenum disulfide（MoS₂）was prepared by a hydrothermal method and characterized.Then,the performance of the as-prepared nano MoS₂for the photocatalytic degradation of fluoroquinolones was studied in detail.With ciprofloxacin as the target,the effects of the amount of nano MoS₂,the p H value,the initial concentration of ciprofloxacin hydrochloride and the ionic strength on the degradation rate were investigated.The possible mechanism of the photocatalytic reaction was also briefly explored.The results showed that the degradation rate of 20mg·L^-1ciprofloxacin hydrochloride by 0.28 g·L^-1nano MoS₂was up to 83.72%under a neutral or weakly alkaline media.The presence of anions such as Cl^–,NO₃^–and SO₄^2–had inhibiting effect on the photodegradation.And·O₂^–was suggested to be the main active species produced during the photocatalytic reaction.Finally,the photodegradation of other fluoroquinolone antibiotics by nano MoS₂was briefly compared.3.A series of CdSe QDs@MoS₂nanocomposites（MCQs）were prepared by loading CdSe QDs onto MoS₂nanoflowers and characterized by XRD,SEM,TEM,HRTEM,BET,FI-IR,UV-vis DRS and PL spectroscopy.The photocatalytic degradation of ceftriaxone sodium by MCQs under the visible light irradiation was systematically studied.The results showed that the maximum degradation rate of ceftriaxone sodium could reach 85.47%and the total organic carbon removal rate was 71.81%within 180 min when MCQ-35 was used as the photocatalyst.The mechanisms related to the photogenerated charge transfer and transport at the composite interface as well as the enhanced photocatalytic performance were discussed in detail.In addition,it was revealed by the active species capture experiments that the contribution of the active species generated during the photocatalytic degradation was h⁺>·O₂^–>·OH.4.MoS₂@Ag₃PO₄nanocomposites with different ratios of the two components named as AM-30,AM-40,AM-50 and AM-60 were prepared by a chemical precipitation and characterized.The photocatalytic degradation of ceftiofur sodium（CFS）by the as-prepared materials was systematically studied.The results showed that the maximum degradation rate of CFS was as high as 91.40%within 120 min under the visible light irradiation with AM-50 as the photocatalyst.It was also found in cycle experiments that the degradation rate of CFS by AM-50 maintained at about85%when the photocatalyst was recycled for the 4th cycle.The radical capture experiments revealed that·O₂^–and h⁺were the main active species generated in the reaction,and consequently the possible photocatalysis mechanism was proposed.