| The biggest challenge facing humanity in the 21st century is energy shortages and the environmental contamination caused by industrialization and population growth. Thus, the development of renewable technologies for environmental remediation and energy production is highly desired. Semiconductor photocatalysis as an emerging technique, which considerably meets the requirements for the current issues on environment and energy, has been widely regarded as a great potential technique in the future. Semiconductor based photocatalysts have received great attention due to their applications in environmental pollution mediation and solar energy conversion. An ideal photocatalyst should have both a wide photoabsorption range and a low recombination rate of the photogenerated charge carriers.The n-type titanium dioxide (TiO2) and stannic dioxide (SnO2) have been extensively studied as the most promising photocatalysts due to their exceptional photocatalytic performance, long-term stability, abundance and nontoxicity. However, due to their wide band gap (-3.2 eV for TiO2 and 3.6 eV for SnO2), they only absorb ultraviolet (UV) light which contributes less than 4% of the total energy of the solar spectrum. Moreover, the fast recombination of the photo-generated electron-hole pairs dissipates the input energy in the form of heat or emitted light, which is one of the main reasons for the low efficiency in photocatalysis application.This article begin with a review of the recent progress in the rational design and fabrication of advanced photocatalytic materials in the framework of nanotechnology, such as constructing heterojunctions and introducing dopants. Then we demonstrated an effective way to fabricate SnO2 based heterojunction photocatalysts, as well as a facile microwave-assisted method to prepare N-doped TiO2 nanocrystals, to improve the light absorption ability, photo-generated carriers separation efficiency and photocatalytic properties.. The main contents were summarized as follows:1. Oxygen vacancies modified SO2/graphene quantum dots (GQDs) compoundsWe employ a two-step reaction process to realize the integration of SnO2 and GQDs, and oxygen vacancies modification from the reduction of SnO2 by GQDs in the high temperature annealing process. The synergistic effect of SnO2/GQDs heterojunctions and oxygen vacancies significantly improved the light absorption ability and photocatalytic properties. The photocatalytic degradation of methylene blue (MB) experiments under Xe arc lamp irradiation shows that oxygen vacancies modified SnO2/GQDs compouds exhibit enhanced photocatalytic activity than bareSnO2 nanords (～8 times in kinetic constants). The concentration of oxygen vacancies doping and quantity of GQDs could be tuned to improve the photocatalytic activity by changing the annealing temperature. The results showed that oxygen vacancies modified SnO2/GQDs compouds exhibit the highest photocatalytic activity with an annealing temperature at 450℃.2. N-doped TiO2 nanocrystalsWe report a facile preparation of N-doped TiO2 nanocrystals (N-TiO2) via a microwave-assisted method using TiCl3 and excessive ammonia solution, followed by freeze drying and annealing process. The prepared N-TiO2 nanocrystals possess as small as ca.10 nm in average particle size, the nitrogen content of sample of about 4.6% and specific surface area of-172.3 m2/g. N doped TiO2 nanocrystals exhibit much higher photocatalytic activity than pure TiO2 nanocrystals and commercial P25, which should be attributed to the improved light absorption ability, enhanced photo-generated carriers separation efficiency and enlarged surface area due to N doping and ultra-small particle size. The concentration of N doping and specific surface area could be tuned by changing the annealing temperature. |
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