Abstract
Nitrogen doping in combination with the brookite phase or a mixture of TiO2 polymorphs nanomaterials can enhance photocatalytic activity under visible light. Generally, nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and with long time heating treatment. Furthermore, the surface areas of them are low (<125 m2/g). There is hardly a report on the simple and direct preparation of N-doped anatase/brookite mixed phase TiO2 nanostructures using sol-gel method at low heating temperature. In this paper, the nitrogen-doped anatase/brookite biphasic nanoparticles with large surface area (240 m2/g) were successfully prepared using sol-gel method at low temperature (165 °C), and with short heating time (4 h) under autogenous pressure. The obtained sample without subsequent annealing at elevated temperatures showed enhanced photocatalytic efficiency for the degradation of methyl orange (MO) with 4.2-, 9.6-, and 7.5-fold visible light activities compared to P25 and the amorphous samples heated in muffle furnace with air or in tube furnace with a flow of nitrogen at 165 °C, respectively. This result was attributed to the synergistic effects of nitrogen doping, mixed crystalline phases, and high surface area.
Highlights
Heterogeneous photocatalytic processes involving TiO2 semiconductor particles have been shown to be a promising process for the treatment of dye effluents [1]
The synthesis process of this work was modified from a typical sol-gel method by using
A supercritical drying process was often used in the conventional sol-gel method [28]
Summary
Heterogeneous photocatalytic processes involving TiO2 semiconductor particles have been shown to be a promising process for the treatment of dye effluents [1]. Large band gap energy (3.2 eV) for anatase TiO2 limits its practical application for natural solar applications [2]. To develop more light-efficient catalysts, there is an urgent need to develop photocatalytic systems which are able to operate effectively under visible light irradiation. A number of systems have been reported to improve the visible-light activity of TiO2. Selecting the reasonable substrate and activity test are helpful to systematically and comprehensively assess the photocatalytic efficiency of the catalysts [3]. Nitrogen-doped (N-doped) TiO2 is one of the most typical examples of the visible-light photocatalysts, which is due to nitrogen doping can decrease the band gap energy and enhance the Catalysts 2017, 7, 376; doi:10.3390/catal7120376 www.mdpi.com/journal/catalysts
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