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Carbon Based Nanosemiconductor Hybrid Materials: Synthesis, Characterization and Their Photocatalytic Activity

Author: TianLiHong
Tutor: ZuoLing
School: Wuhan University
Course: Inorganic Chemistry
Keywords: CNT-TiO2 CNT-WO3 RGO-WO3 RGO-BiOCl ethoxy groups modified TiO2nanocrystals Photocatalytic
CLC: O643.3
Type: PhD thesis
Year: 2012
Downloads: 93
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In recent years, as the increasing of industry and agricultural, environmentalpollution especially water contamination is paid more attention. Somenon-biodegradable substrates such as dyes and dye intermediates are harmful to notoly human but also animals and plants. Photocatalytic decomposition of organicpollutants with metal oxide semiconductor is fascinating due to involving theconversion of solar energy. However, some inorganic semiconductors have lowquantum efficiency. For example TiO2, it has wide binding energy and only absorbsultraviolet light. WO3has high conductive energy and electrons on conduct band cannot react with O2, so there are a few reports on the degradation of organic pollutantson WO3catalysts. In this paper, we take note of the excellent properties of carbonmaterials such as carbon nanotubes and graphene and synthesize the carbonmaterials/semiconductors hybrids to enhance the photocataytic activity ofsemiconductors. The main investigations are as follows:(1) MWCNT/TiO2hybrid nanostructures were prepared via solvothermal synthesisand sol–gel method with benzyl alcohol as a surfactant. As-prepared hybrid materialswere characterized by X-ray diffraction, transmission electron microscopy, UV–visdiffuse reflectance spectra and X-ray photoelec-tron spectroscopy.The resultsshowed that MWCNTs were uniformly decorated with anatase nanocrystals insolvothermal condition, but MWCNTs were embedded in a majority of TiO2nanoparticles by sol–gel method.When the weight ratio of MWCNTs to TiO2was20%, MWCNT/TiO2hybrid nanostructures prepared by solvothermal synthesisexhibited higher visible-light-driven photocatalytic activity than that prepared bysol–gel method. Post-annealing of MWCNT/TiO2nanostructures at400℃resulted inthe formation of the carbonaceous Ti–C bonds on the interface between TiO2andMWCNTs, which enhanced the photoabsorbance of the hybrid materials in the visiblelight region and improved the visible-light degradation efficiency of methylene blue.(2) The CNTs-WO3hybrid nanostructures were fabricated by a facile solvothermalsynthesis and found to existing high photocatalytic activity for degradation of methylblue under visible light irradiation. The materials were investigated by TEM, XRD,UV-vis and XPS respectively. The results demonstrated that monoclinic WO3nanosheets aligned on CNTs and a strong interaction existed between CNTs and WO3.It is interesting that the content of CNTs played the important role on controlling the dispersion of WO3on CNTs surface. When the content of CNTs was15%, small andthin WO3nanosheets laid on CNTs uniformly. PL results of CNTs-WO3indicated thatthe enhanced photocatalytic activity was attributed to the effective separation ofelectrons and holes on hybrid materials under visible light irradiation. In addition, thepresence of radical scavengers such as KI、Fe3+and methanol demonstrated thathydroxyl radicals were responsible for the photocatalytic degradation of organic dyeon CNTs-WO3, which were mainly originated from the photoreduction of oxygen.(3) A series of reduced graphene oxide-WO3nanobelt hybrids were fabricated via insitu hydrothermal method. The morphology and structure of hybrids werecharacterized by scanning electron micrograph and high-resolution transmissionelectron micrograph. It is found that graphene oxide restrains the growth oforthorhombic WO3along (002) orientation and results in the shorter WO3nanobeltscompared with pure WO3. WO3nanobelts well-decorate on graphene oxide surface.RGO-WO3nanobelt hybrids show an enhanced visible light photocatalytic activity ondegradation of methylene blue. The optimum hybrid is that one with1.0wt%graphene oxide and its pseudo-first-order rate constant (k) is up to2-foldimprovement compared to the pure WO3nanobelts. The enhancement ofphotocatalytic activity is ascribed to the synergistic effects between WO3and reducedgraphene oxide, which efficiently separate the photogenerated electrons and holes.Accordingly, the photocatalytic mechanism of RGO-WO3nanobelt hybrids is alsoproposed and confirmed by transient photocurrent response.(4) Reduced graphene oxide-BiOCl hydrid materials were fabricated bysolvothermal method with benzyl alcohol as solvent. Condensation steps led to theformation of [Bi2O2]nbonds in nonaqueous solvothermal processes such as alkylhalide elimination and ester elimination. Therefore,(001) planes dominated BiOClmicrosheets were obtained. UV-vis diffuse reflection results showed the band gap ofBiOCl microsheets was about3.25eV. However, for RGO-BiOCl hybrid materials, theaddition of GO resulted in the formation of BiOCl nanoplates on the edge of reducedgraphene oxide, which was ascribed to selective growth of (001) and (110) planefamily of BiOCl. RGO-BiOCl hybrid materials showed enhanced photocatalyticactivity under visible light irradiation compared with BiOCl-ref. The band gap ofRGO-BiOCl narrowed and RGO prohibited the combination of electrons and holes,which ehanced the photocatalytic activity of RGO-BiOCl.(5) TiO2nanocrystals modified by ethoxy groups were prepared by a facilenonhydrolytic solvothermal method and characterized by XRD, TEM, TG-DTA and XPS, which showed an enhanced visible-light photocatalytic activity on thedegradation of Rhodamine B compared with TiO2modified by benzyloxy groups andthe“naked”TiO2. The adsorption and degradation pathway of Rhodamine B on TiO2modified by ethoxy groups were also investigated. The zeta-potential (ζ) resultsshowed that the TiO2modified by ethoxy groups had high negative surface charge,which incited the positive-N(Et)2group of RhB absorbing on the TiO2surface andpreferably led the N-dealkylation pathway under visible light irradiation.

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