Fabrication Of CNTs/Ag/TiO₂ Composite Catalysts And Their Photocatalytic Abilities

Compared to those traditional purification methods,photocatalysis becomes a research hot spot due to many advantages,such as high stability and degradation of pollutants under room temperature.In recent years,various photocatalysts were studied,among which TiO₂ is considered to be the most promising candidate due to its'non-toxicity,stable physical and chemical properties and low cost.However,the band gap of TiO₂ is 3.20 eV,indicating that TiO₂ can only respond to approximately 4%of the entire solar spectrum,which leads to the limited application of TiO₂.Moreover,the electron-hole pairs generated during the irradiation are so easy to recombine that further restricts the photocatalytic performance of TiO₂.Thus,design and synthesis of the novel catalysts with excellent photocatalytic activity is of great significance.The LSPR effect of noble metal nanoparticles and the photosensitizing effect of carbon nanotubes?CNTs?can develop the photocatalytic performance of TiO₂ under visible light dramatically.In this paper,TiO₂ is successfully composited with silver nanoparticles?AgNPs?and CNTs to obtain CNTs-Ag-TiO₂?CAT?composite with ternary structure during a facile procedure.The effects of the composite structure on the degradation of organic pollutant under visible light were studied.The details of this thesis are listed as follows:1.AgNPs coated CNTs?CA?was fabricated using in-situ chemical reduction method assisted by surface sensitization.The results showed that the pre-treatment of CNTs by acid washing?chemical oxidation?can improve the dispersion of CNTs and graft high density of functional groups on the surface.With the assistance of sensitizing agent,the functional groups can act as reduction points for reduction of Ag⁺.The size and the density of AgNPs can be successfully controlled by changing the amount of sensitizer.When the mass ratio of sensitizer v.s.CNTs was 2:1,a uniform coverage of AgNPs?the average radius is 3 nm?was obtained on the surface of CNTs?2.Carbon nanotube-silver-titanium dioxide composite?CAT?with a ternary structure was prepared by sol-gel method by controlling the reactant ratio and reaction rate.Using methylene blue as the organic pollutant,the photocatalytic properties of the mixture of CA and TiO₂?CA-T?were compared with CAT.Characterization methods such as UV-Vis absorption spectra,photoluminescence spectra,electrochemical impedance spectra and transient photocurrent response etc were used to study the effect of the sample's structure and the mass ratio of CA on photocatalytic performance was studied.The results showed that the degradation rate of MB by CA-T?the mass ratio of CA was 10%?under visible light reaches 42.9%in3 hours,while that of CAT?the mass ratio of CA was 15%?was increased to 80.8%under the same condition,indicating that the photocatalytic performance of TiO₂composites under visible was significantly improved.3.The formation of CA and CAT composite structure was speculated based on the morphology and structure analysis of the samples.By comparing the light response and luminescence properties of both CA-T and CAT structures,the mechanism of Ag as an intermediate layer and the detailed degradation process of CAT from the perspective of electron transfer and energy level change were proposed,which laid a foundation for the design and the construction of more TiO₂-based composite photocatalytic materials.