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Bi5O7I nanosheets and Bi5O7I nanorods photocatalysts were successfully fabricated by calcination and hydrothermal methods respectively. The different morphologies of Bi5O7I were characterized by XRD, SEM, HRTEM, UV–vis DRS and PL. The as-prepared samples were used to photocatalytic removal of Hg0 under visible-light irradiation. The results indicated that the photocatalytic activity of Bi5O7I nanorods is better than that of Bi5O7I nanosheets. It can be attributed to the synergistic and internal electric field effects of the (0 0 1) and (1 0 0) facets of Bi5O7I nanorods, which improves the photogenerated charge transfer and separation efficiency.

The flower-like BiOI/Bi5O7I heterojunction photocatalysts were prepared by a pH adjustment method, and the photocatalytic oxidation activity of the as-prepared samples was investigated by gas-phase Hg0 removal. XRD, SEM, TEM, UV-vis, and PL characterization analysis method were adopted to evaluate the physicochemical property of samples. It was found that the sample showed an excellent photocatalytic performance for mercury removal when the pH of the sample fabrication arrived at 10.0. It can be attributed to the formation of an interfacial heterojunction between BiOI and Bi5O7I, which inhibits the recombination of electrons and holes. A possible photocatalytic reaction mechanism for the oxidation of Hg0 has also been proposed.

A series of BiOIO3 were prepared via in-situ crystallization method with different calcining temperatures. All samples were characterized by XRD, SEM, UV–vis, PL to explore the effect of internal electric field (IEF) among different dimensions. B-200 (calcinated under 200 °C) with the optimized IEF attained the most superior photocatalytic oxidation capacity in removing gas-phase Hg0. Also, the formed 2D mixed 3D dimension changes the inter-atomic spacing to make the band bend upward, then moves the electrons and holes in the horizontally opposite direction. In combination with the above factors, the optimized IEF and dimension effectively intensify the separation of charge carriers and make the photocatalytic performance greatly improved.

To explore the effect of pH on the photocatalytic oxidation activities of BiOCl catalysts, the BiOCl catalysts under different pH values were prepared via a facile hydrothermal method. The as-prepared catalysts were characterized by BET, XRD, HRSEM, SEM and UV–vis to find out the impact of pH values. Photocatalytic ability of BiOCl catalysts were evaluated by oxidation of gaseous elemental mercury under UV light irradiation. It was found that BiOCl catalysts prepared under alkaline condition exhibited the best photocatalytic oxidation activities. The difference of photocatalytic activity among the as-prepared catalysts can be attribute to the growth orientation of the crystal BiOCl catalyst and the adsorption capacity of elemental mercury.

Fe-doped TiO2 hollow microspheres were prepared by the hydrothermal method and characterized by the X-ray diffraction (XRD), the Scanning Electronic Microscopy (SEM), the Energy Dispersive X-Ray (EDX), the Brunauer-Emmett-Teller (BET), and the UV–visible diffuse-reflectance spectrum (UV–Vis). The as-prepared samples were evaluated for photocatalytic removal of Hg0 under ultraviolet light irradiation. The results showed that the sample had a good photocatalytic performance. When M* (the molar ratio of Fe/Ti) was 0.05, the mercury removal efficiency reached up to 100%. It was found that the incorporation of iron narrowed the energy band gap of TiO2 (from 3.11 eV to 2.58 eV) and the absorbing boundary increased from 398 nm to 480 nm. While too much Fe3+ may occupy the capture sites of electrons and holes, which leads to a decrease of photocatalytic efficiency.

An amorphous phase TiO2 was fabricated via a fast and simple hydrolysis method and it was characterized with XRD, TEM, BET, UV–Vis, XPS and EPR. The as-prepared amorphous TiO2 has a specific surface area record-breaking 100 times that of crystal TiO2. The results show that the as-samples had better photocatalytic property, which was evaluated for gas-phase Hg0 oxidation under LED light, and photocatalytic efficiency reached up to 40%, which is 1.4 times that of commercial P25. It can be mainly attributed to the large specific surface area of amorphous TiO2 providing more reactive sites and its surface oxygen vacancies as carriers transport channels.