Synthesis and electronic behaviors of TiO2/carbon clusters/Cr2O3 composite materials
Introduction
Multi-electron transfer by photo-irradiation has been attracting the attention of chemists in viewpoint of electronic and/or magnetic devices production, oxidation–reduction, artificial photosynthesis, solar cell production, and so on. So far various photochemical effects have been reported with the use of TiO2 and modified inorganic metal compounds, however, only under the irradiation of limited wavelength [1], [2], [3], [4], [5], [6], [7], [8], [9]. We considered that such a function could be achieved by the combination of carbon clusters and photosensitive semiconductors, where carbon clusters are expected to act as a visible-light absorptive site and an electron transport bed and semiconductors to act as an electron excitation site.
We recently reported the synthesis of metal–organic moiety hybrid copolymers [10], [11], [12], [13] and the calcinations of such copolymers under a reducing atmosphere produce new types of composite materials involving nano-sized inorganic metal compounds and carbon clusters. The resultant new composite materials show photo-responsive oxidation–reduction function with an electron transfer between the metal compounds and carbon clusters [14], [15], [16], [17]. Especially, it was found that CeO2/carbon clusters/Ho2O3 composite loaded with Pt particles showed an electron transfer process of CeO2 → carbon clusters → Ho2O3 → Pt which could decompose water to H2 and O2 with an H2/O2 molar ratio of 2 under whole visible-light irradiation, while no water photodecomposition was observed for both CeO2/carbon clusters and Ho2O3/carbon clusters systems [18]. These findings strongly indicate that the combination of two metal oxides with carbon clusters is important to develop an efficient photocatalyst. The authors have thus been examining to clarify the electron transfer features and/or photocatalytic activities of the combinations of various metal oxides/carbon clusters composite materials.
On the other hand, we considered that such composite materials could also be obtained by the microwave treatment instead of thermal heating of aggregated complexes composed with inorganic metal compounds and organic polymers. The band gap of TiO2 (B.G. = 3.2 eV) is rather close to that of Cr2O3 (B.G. = 3.5 eV) with similar band structure, and thus a smooth electron transfer feature between two metal oxides could be attained. Thus, TiO(acac)2- and/or Cr(acac)3-contained epoxy resin complexes I, II and/or III were subjected to microwave irradiation to obtain calcined materials Ic, IIc and/or IIIc (Scheme 1) and further their electronic features were also examined. In this communication, we report the electronic features of TiO2/Cr2O3/carbon clusters composite material obtained by the microwave treatment of TiO(acac)2- and/or Cr(acac)3-contained epoxy resin complexes.
Section snippets
Reagents
Commercially available titanyl acetylacetonate TiO(acac)2, tris(2,4-pentanedionate)chromium Cr(acac)3, bisphenol A diglycidyl ether (DGEBA), phthalic anhydride (PA), graphite, 1,4-hydroquinone, 1,4-benzoquinone, citric acid, and methylene blue were used.
Synthesis of complexes
A mixture of TiO(acac)2 and/or Cr(acac)3, DGEBA and PA in 500 mL of acetone was stirred at room temperature for 1 h. Additionally, graphite was added into the above solution and then the resulting mixture was stirred for 1 h. After the solvent was
Characterization of the materials
In order to investigate the dispersion states of metal compounds in the epoxy resins, the SEM–EDX spectra of complex III were measured (Fig. 1) indicating that Ti and Cr atoms were uniformly dispersed in the resin. The elemental analysis of complexes I, II, and III (Table 2) showed the presence of each metal atom.
The microwave irradiation on complexes I, II and III gave black-colored materials Ic's, IIc's and IIIc's, respectively. The results of the elemental analysis of the calcined materials
Conclusions
Microwave treatment of TiO(acac)2- and Cr(acac)3-contained epoxy resin III gave nano-sized TiO2/carbon clusters/Cr2O3 composite material IIIc which showed an electron transfer in the process of TiO2 → carbon clusters → Cr2O3. The surface characterizations of the resulting composites indicate that they are composed of nano-sized particles of TiO2, carbon clusters and Cr2O3. The decomposition of methylene blue in the presence of IIIc has been successfully achieved under visible-light irradiation.
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2013, Ceramics InternationalCitation Excerpt :We have recently reported the synthesis of such composite materials by the calcination of either metal–organic moiety hybrid copolymers or inorganic metal compound/organic polymer complexes. An efficient visible light-responsive electron transfer between carbon phases and metal compounds was observed for those novel composite materials [10–23]. We have also shown that MnO2–loaded ZrO2/carbon clusters composite material could decompose water to H2 and O2 under visible light irradiation, however the photo-catalytic activity of the material was rather low [21].