Comparative study of doped and co-doped TiO2 for photocatalytic degradation of organic pollutant: A review

Titanium dioxide is the most widely used photocatalyst because of its properties. Despite the excellent properties, its application is restricted to the ultraviolet light region because of its large bandgap, high recombination rate and low quantum efficiency for visible light activities. Different research techniques, such as dye sensitization, heterojunction, doping, and co-doping of TiO2, have been adopted to address this issue. Dye sensitization suffers from poor photostability, and heterojunctions are hindered by high interface resistance. Hence, doping which modifies the intrinsic electronic structure, creates intermediate energy levels, and enables low-cost production is strategic. Although doped TiO2 systems have many merits, they suffer from low quantum efficiency and, fast recombination of photogenerated charge-carriers. Additionally, excessive dopants act as recombination sites, which affects the photocatalytic performance. Recent increase in co-doping TiO2 research allows for lattice stability and more precise tuning of TiO2 for better efficiency. Many studies conducted on doping and co-doping of TiO2 are mostly focused on the catalyst’s photodegradation performance. However, there exists no comparative analysis of single-doped and co-doped TiO2 presently. This review focuses on a comparative analysis of the band structure, charge-carrier separation, mechanism, and photocatalytic performance of single-doped and co-doped TiO2 in degradation performance of organic pollutant. The results of the findings suggest that under optimized conditions, co-doping with metals and non-metals can be used as an efficient strategy for wastewater treatment and environmental remediation. Additionally, it highlights the opportunities and challenges in this domain, aiming for further studies and experimentation for new innovations in environmental remediation.