A review on the synthesis, characterization, and recent advancements of visible light-activated C-TiO2 nanomaterials for environmental remediation

The prevalence of TiO₂ nanomaterials in the field of photocatalysis have been eminent but its extensive implementation has been hindered due its wide bandgap that requires UV light for excitation and frequent recombination of photogenerated electron and hole pairs. The potential of carbon doping in enhancing the photocatalytic activity of TiO₂ is attributed to its ability to act as a trapping center and transport channel for electrons which promotes efficient separation of photo-induced electron and hole pairs, ability to act as a sensitizer, and capability to promote an electron coupling effect and create a localized occupied state of TiO₂ in order to narrow the bandgap of the photocatalyst. The efficiency of carbon-doped TiO₂ (C-TiO₂) photocatalysts can be controlled by several parameters such as surface area of photocatalyst, particle size, catalyst concentration, amount of target pollutant and irradiation time. Hence, the synthesis methodology and the characterization of these nanoparticles are critical in producing highly efficient visible light activated photocatalysts. These photocatalysts have been utilized in the degradation of organic and inorganic pollutants existing in wastewater systems. In addition, the photocatalytic activity of C-TiO₂ has been tested for microbial inactivation as an alternative solution to the costly traditional disinfection techniques. This review reports and summarizes various characterization techniques and methods for the synthesis of C-TiO₂ nanomaterials applied in the recent years. Moreover, the photocatalytic efficiency of C-TiO₂ for environmental remediation is discussed while noting the limitations and challenges for the continuous progress and development of C-TiO₂ photocatalysts.