Study On The Synthesis Of Quantum Dots (CdSe,CdS) Decorated Composite Materials And Their Photocatalytic Properties

Photocatalytic technique has become one of the effective ways to solve the problems of environmental pollution and energy crisis,and it has also received considerable attention in the field of organic synthesis.However,the low utilization of sunlight and quantum efficiency greatly limit the practical application of traditional photocatalyst represented by TiO2.As a kind of novel nano-materials,quantum dots(QDs)have many unique properties such as quantum size effect,surface effect and tunable band gap.So synthesizing QDs decorated composite materials promises to be a new way to develop the photocatalysts with wide spectral response and high quantum efficiency.In this paper,the synthesis of water soluble CdSe QDs was first exploited.Then linker assisted assembly method was employed to synthesis CdSe QDs decorated TiO2(denoted as CS-T)and CdSe QDs decorated anatase TiO2 with exposed {101}facets(denoted as CS-T101).Finally photodeposition method was adopted to prepare CdS QDs decorated InOOH(denoted as CdS-In).The degradation of organic pollutants such as malachite green and reduction of nitro aromatics represented by 4-nitroaniline were chosen as model reactions to evaluate the photocatalytic properties of our as-prepared QDs decorated composite materials.The photocatalytic mechanism was investigated extensively.The main conclusions are as follows:(1)The as-prepared water soluble CdSe QDs have an excitonic absorption peak at wavelength of about 500 nm,exhibiting obvious quantum size effect.(2)For photocatalytic degradation towards MG under visible light irradiation,the apparent rate constants k value of CS-T is 52.5,4.5,4.6 and 7.2 times larger than those of pure TiO2,CdSe QDs,TiO2-xNx and bulk CdSe modified TiO2,respectively.Due to quantum size effect,the conduction band potentials of CdSe QDs(-0.79 V)is more negative than that of bulk CdSe(-0.58 V).More quantities of active species(O2·-,H2O2,·OH)are produced in CS-T system.(3)For 5%CS-T001,the photocatalytic conversion ratio of 4-nitroaniline(4-NA)reaches up to 98.9%under visible light irradiation for 30 min.The high activity of CS-T001 is ascribed to the synergy between the decoration of CdSe QDs and exposure of TiO2 {001} facets.(4)CdS-In-120 exhibits much higher photocatalytic activity than both InOOH and commercial CdS for reduction of 4-NA under visible light irradiation.It could not only realize the visiblization of InOOH,but also disperse quantum-sized CdS evenly with the aid of substrate material InOOH,enhancing the activity of CdS.The features and innovations of this thesis are as follows:(1)An aqueous phase method that is easy-operated,environmentally benign and moderate is utilized to prepare water soluble CdSe QDs,avoiding the complicated operation,high toxic and rigorous reaction conditions of the traditional organic phase method.(2)Facile and green methods are provided to synthesize QDs decorated composite materials:linker assisted assembly method for CS-T and CS-T001,photodeposition method for CdS-In.Therefore,visible light responsive photocatalysts with superior activity are obtained.(3)The important roles of QDs(CdSe,CdS)and substrate materials(TiO2,T001 and InOOH)in photocatalytic process are illuminated extensively and systematically for the first time,and the mechanism of the enhanced photocatalytic activity are proposed.