Thermally-assisted photodegradation of lignin by TiO2/H2O2 under visible/near-infrared light irradiation

Abstract

As a bio-recalcitrant organic pollutant in paper mill effluent, lignin is generally removed by an advanced oxidation process, such as a TiO2/H2O2 photocatalytic technique under irradiation with ultraviolet light, which only accounts for less than 5% of sunlight. Herein, we reported a TiO2/H2O2-based thermally-assisted photocatalytic process that allows lignin to be efficiently degraded under visible/near-infrared light at an elevated temperature. Adsorption of H2O2 on TiO2 nanoparticles and an increase of temperature facilitate the production and separation of charge carriers under near-infrared and visible light irradiation, accelerate carrier transfer at the TiO2-electrolyte interface and promote the production of hydroxyl radicals. A higher level of H2O2 addition results in an increased degradation rate of lignin, while the optimal temperature for the thermally-assisted photodegradation of lignin is 70°C. A charge carrier excitation and transfer process was proposed for the TiO2/H2O2 thermally-assisted photocatalytic process. This work describes a new method for the photodegradation of organic pollutants, such as residual lignin in paper mill effluent, using wide band gap semiconductors under visible and near-infrared light irradiation.