Adsorption–photocatalytic synergistic removal of MB by peanut shell biochar-supported TiO2/Ce–C3N4 heterojunctions

Based on the excellent adsorption and electron transfer ability of biochar, the combination of a photocatalyst and biochar is an effective strategy to enhance overall photocatalytic activity. Hence, a series of peanut shell biochar-loaded TiO₂/Ce–C₃N₄ heterojunctions were prepared by adjusting the mass ratio of TiO₂ and Ce–C₃N₄, and their structure and properties were intensively characterized by applying various advanced techniques. In addition, their photocatalytic degradation activity was investigated using methylene blue solution (MB) as an organic pollutant model under visible light irradiation. Results showed that the photocatalytic activity of BC/TiO₂/Ce–C₃N₄ was significantly improved by adsorption–photocatalytic synergic effects. After 30 min of adsorption and 7 min of visible light irradiation, the removal rate for MB reached 100%. The adsorption and photocatalytic degradation processes followed the pseudo-second-order kinetic model and first-order kinetic model, respectively. The rate constant of photocatalytic degradation was 0.3325 min⁻¹, which was 19 times and 16 times that of Ce–C₃N₄ and TiO₂, respectively. The introduction of BC and the construction of heterojunctions led to a decrease in the band gap energy of BC/TiO₂/Ce–C₃N₄, which accelerated the separation and migration of photogenerated carriers and effectively inhibited the recombination of photogenerated electron holes. In addition, capture experiments showed that the main active groups for the degradation of MB by BC/TiO₂/Ce–C₃N₄ were ˙O₂⁻ and h⁺, and a possible photodegradation mechanism was proposed for the prepared composites. The significantly strengthened photocatalytic activity and excellent stability make BC/TiO₂/Ce–C₃N₄ a promising dual-function composite for affordable, fast and efficient decontamination of MB from wastewater.