Global warming, the most threatening problem to be solved by the scientists to meet the Kyoto Protocol of the United Nations Framework Convention on Climate Change, stimulated the researchers towards alternative fuel sources using artificial photosynthesis. From this standpoint, the development meth...
Global warming, the most threatening problem to be solved by the scientists to meet the Kyoto Protocol of the United Nations Framework Convention on Climate Change, stimulated the researchers towards alternative fuel sources using artificial photosynthesis. From this standpoint, the development method to convert carbon dioxide into more useful organic compounds inexpensively is highly desirable. TiO2, owing to its outstanding physico-chemical properties primarily because of its high stability towards photocorrosion and its relatively favourable band gap energy has been shown to be the most suitable semiconductor offering the highest light conversion efficiency. The introduction of transition metals on TiO2 has gained considerable attention over the years. Several studies have reported that incorporation of transition metal ions can effectively enhance the efficiency of TiO2-based catalytic systems. Furthermore, the noble metal dopants can change the distribution of electrons because of its own catalytic properties and effectively prevent the electron–hole recombinations, thereby enhance the photocatalytic efficiency of TiO2. However, there is considerable controversy on the effect of metal ions. Also, the loading level plays an important role as higher loading induces faster electron-hole recombination. Hence, it is utmost important to study the level of metal loading to exploit the maximum ability of noble metal-doped TiO2 towards photoreduction. One of the major drawbacks for the practical utilization of photocatalysis is the expensive liquid-solid separation, due to the formation of milky dispersions after mixing the catalyst in water. In order to minimize the above inconvenience, attempts have been made to immobilize the catalyst on rigid supports. The nature of the support is an important factor in the determination of performances of the active phase, notably for metals where metal-support interactions are involved. Silica has been selected as a unique support, since it has been used widely in industry and does not possess a charged framework, but a moderate hydrophobicity. The use of silica as a support for TiO2 has several advantages, since it possesses enhanced thermal/mechanical stability, high surface area and is economically attractive. From the catalytic scope, the deposition of TiO2 on SiO2 enables a better irradiation of the supported TiO2, as SiO2 is transparent to UV radiation. In addition, anatase phase is stabilized by interaction with SiO2 support and the performance of these catalysts is strongly depending upon the dispersion of TiO2 on SiO2. SiO2 supported TiO2 has been reported to exhibit different photocatalytic performance from that TiO2 itself does. As mentioned above, noble metal-doped TiO2 and TiO2/SiO2 show different properties according to their structural changes and metal-support interactions. Accordingly, it is certainly interesting to study the synergistic effect of both dopant and support effect on TiO2. However, no systematic studies have addressed the influence of metaldoped TiO2 on SiO2 support for photocatalytic reduction of carbon dioxide. In the present investigation, I carried out series of investigations on the effect of Ru dopant level, TiO2 loading on SiO2 and the support effect of SiO2 on Ru doped TiO2, paying particular attention to the role played by SiO2 support on Ru doped TiO2 as well as the metal-support interaction in the Ru-TiO2/SiO2 catalyst, which in turn is directly related to its performance in the target reaction. The study is also intended to give a picture of the influence of hole scavengers and catalyst loading on photocatalytic reduction of carbon dioxide, taking TiO2 as photocatalyst. Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0 wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10 wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5 wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10 wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of TiOSi bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties.
Global warming, the most threatening problem to be solved by the scientists to meet the Kyoto Protocol of the United Nations Framework Convention on Climate Change, stimulated the researchers towards alternative fuel sources using artificial photosynthesis. From this standpoint, the development method to convert carbon dioxide into more useful organic compounds inexpensively is highly desirable. TiO2, owing to its outstanding physico-chemical properties primarily because of its high stability towards photocorrosion and its relatively favourable band gap energy has been shown to be the most suitable semiconductor offering the highest light conversion efficiency. The introduction of transition metals on TiO2 has gained considerable attention over the years. Several studies have reported that incorporation of transition metal ions can effectively enhance the efficiency of TiO2-based catalytic systems. Furthermore, the noble metal dopants can change the distribution of electrons because of its own catalytic properties and effectively prevent the electron–hole recombinations, thereby enhance the photocatalytic efficiency of TiO2. However, there is considerable controversy on the effect of metal ions. Also, the loading level plays an important role as higher loading induces faster electron-hole recombination. Hence, it is utmost important to study the level of metal loading to exploit the maximum ability of noble metal-doped TiO2 towards photoreduction. One of the major drawbacks for the practical utilization of photocatalysis is the expensive liquid-solid separation, due to the formation of milky dispersions after mixing the catalyst in water. In order to minimize the above inconvenience, attempts have been made to immobilize the catalyst on rigid supports. The nature of the support is an important factor in the determination of performances of the active phase, notably for metals where metal-support interactions are involved. Silica has been selected as a unique support, since it has been used widely in industry and does not possess a charged framework, but a moderate hydrophobicity. The use of silica as a support for TiO2 has several advantages, since it possesses enhanced thermal/mechanical stability, high surface area and is economically attractive. From the catalytic scope, the deposition of TiO2 on SiO2 enables a better irradiation of the supported TiO2, as SiO2 is transparent to UV radiation. In addition, anatase phase is stabilized by interaction with SiO2 support and the performance of these catalysts is strongly depending upon the dispersion of TiO2 on SiO2. SiO2 supported TiO2 has been reported to exhibit different photocatalytic performance from that TiO2 itself does. As mentioned above, noble metal-doped TiO2 and TiO2/SiO2 show different properties according to their structural changes and metal-support interactions. Accordingly, it is certainly interesting to study the synergistic effect of both dopant and support effect on TiO2. However, no systematic studies have addressed the influence of metaldoped TiO2 on SiO2 support for photocatalytic reduction of carbon dioxide. In the present investigation, I carried out series of investigations on the effect of Ru dopant level, TiO2 loading on SiO2 and the support effect of SiO2 on Ru doped TiO2, paying particular attention to the role played by SiO2 support on Ru doped TiO2 as well as the metal-support interaction in the Ru-TiO2/SiO2 catalyst, which in turn is directly related to its performance in the target reaction. The study is also intended to give a picture of the influence of hole scavengers and catalyst loading on photocatalytic reduction of carbon dioxide, taking TiO2 as photocatalyst. Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0 wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10 wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5 wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10 wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of TiOSi bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties.
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