The effects of the nanostructure of mesoporous TiO2 on optical band gap energy
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Mesoporous TiO2 is prepared by sol–gel process with a triblock copolymer as an organic template and aqueous TiOCl2 solution as inorganic precursor. The XRD patterns reveal that only the anatase phase can be observed in mesoporous TiO2, regardless of the different calcining temperatures, and with increasing calcining temperature the grain size gradually increases. The grain sizes of TiO2 increased from 4.7 to 11.9 nm with calcining temperature increasing from 300 to 400 °C. The pore size and the surface area evaluated from the Barrett–Joyner–Halenda model and Brunauer–Emmett–Teller method indicated that the average pore sizes increased from 87 to 153 Å and specific surface areas decreased from 179.71 to 74.31 m2/g for 300–400 °C calcination. The relationship between the optical band gap (E g) and microstructure of anatase has been determined and discussed. The quantum confinement effect is observed at grain sizes lower than 10 nm, and the estimated E g shifts from 3.32 to 3.46 eV. These results suggest that there are potential applications of mesostructured TiO2 with nanocrystals in the design of optical devices and photocatalysts.
KeywordsMesoporous TiO2 Optical band gap Sol–gel
This work was financially supported by the National Science Council of Taiwan, the Republic of China, grant No. NSC 97-2221-E-020-024 and NSC 98-2221-E-020-020, which are gratefully acknowledged.