Benzene is a typical volatile organic compound (VOC) and is found widely in industrial waste gases. In this study, trimesoyl chloride-melamine copolymer (TMP)-TiO₂ 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-TiO₂ 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-TiO₂ nanocomposites were sharply red-shifted to the visible region relative to those of unmodified TiO₂. The most efficient TMP-TiO₂ nanocomposite was used for photocatalytic oxidative degradation of gas-phase benzene (initial concentration 230 mg m⁻³) 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 TiO₂ (hydrothermally synthesized TiO₂) 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 TiO₂ reduce the band gap of TMP-TiO₂. The amide bonds in the TMP decrease the TiO₂ 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.

The photocatalytic activity of titanium dioxide (TiO₂) is largely hindered by its low photoresponse and quantum efficiency. TiO₂ modified by conjugated polymers (CPs) is considered a promising approach to enhance the visible light responsiveness of TiO₂. In this work, in order to investigate the effect of CP structural changes on the photocatalytic performance of TiO₂ under visible light, trimesoyl chloride–melamine polymers (TMPs) with different structural characteristics were created by varying the parameters of the polymerisation process of tricarbonyl chloride (TMC) and melamine (M). The TMPs were subsequently composited with TiO₂ to form complex materials (TMP–TiO₂) using an in situ hydrothermal technique. The photocatalytic activity of TMP–TiO₂ was evaluated by the degradation of rhodamine B (RhB). The results showed that the trend of the structure of the TMP with the reaction conditions was consistent with the visible light responsiveness of TMP–TiO₂, and TMP (1:1)–TiO₂ had the best photocatalytic activity and could degrade 96.1% of the RhB. In conclusion, our study provided new insights into the influence of the structural changes of TMPs on the photocatalytic activity of TMP–TiO₂ under visible light, and it improves our understanding of how conjugated polymers affect the photocatalytic activity of TiO₂ under visible light.