| Summary: | Benzene is a typical volatile organic compound (VOC) and is found widely in industrial waste gases. In this study, trimesoyl chloride-melamine copolymer (TMP)-TiO<sub>2</sub> nanocomposites with excellent photocatalytic efficiency in visible-light degradation of gas-phase benzene were synthesized via an in situ hydrothermal synthesis. The optimal conditions for TMP-TiO<sub>2</sub> nanocomposite synthesis were determined by orthogonal experiments. The structural, physiochemical, and optoelectronic properties of the samples were studied by various analytical techniques. Ultraviolet-visible diffuse reflectance spectroscopy and surface photovoltage spectra showed that the positions of the light-absorbance edges of the TMP-TiO<sub>2</sub> nanocomposites were sharply red-shifted to the visible region relative to those of unmodified TiO<sub>2</sub>. The most efficient TMP-TiO<sub>2</sub> nanocomposite was used for photocatalytic oxidative degradation of gas-phase benzene (initial concentration 230 mg m<sup>−3</sup>) under visible-light irradiation (380–800 nm); the degradation rate was 100% within 180 min. Under the same reaction conditions, the degradation rates of unmodified TiO<sub>2</sub> (hydrothermally synthesized TiO<sub>2</sub>) and commercial material Degussa P25 were 19% and 23.6%, respectively. This is because the Ti–O–N and Ti–O–C bonds in TMP-modified TiO<sub>2</sub> reduce the band gap of TMP-TiO<sub>2</sub>. The amide bonds in the TMP decrease the TiO<sub>2</sub> nanoparticle size and thus increased the specific surface area. The conjugated structures in the TMP provide abundant active sites for trapping photogenerated electrons and promote the separation and transfer of photogenerated electrons and holes.
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