Spent-coffee grounds-derived biochar-supported heterogeneous photocatalyst: a performance evaluation and mechanistic approach for the degradation of pentachlorophenol

The study presents a facile and green approach to synthesizing crystalline TiO2 nanoparticles on a surface of biochar derived from abundantly available biomass waste, i.e., spent-coffee grounds (SCGs), via a simple sol–gel route. The biochar–TiO2 nanocomposite was used as an effective heterogeneous photocatalyst for the degradation and mineralization of priority pollutants, i.e., pentachlorophenol (PCP) in the aqueous phase. The physiochemical assessment of nanocomposite supports the efficient attachment of TiO2 to biochar, lowers the bandgap energy and particle size, and increases light absorption and durability for easy material separation after use. The radical scavenging experiments results revealed the dominance of superoxide radical anions (O2˙−) followed by hydroxyl radicals (HO˙) and photogenerated holes (h+) for the PCP degradation. Possible degradation mechanism and degradation pathways of PCP was also proposed. Besides, the nanocomposite material exhibited high stability for up to five cycles with negligible activity loss, further confirmed by the FT-IR analysis. Thus, biochar–TiO2 hybrid nanocomposite shows excellent photocatalytic activity for the degradation of organic pollutants in terms of performance metrics, which was far superior to the reported biomass-derived biochar/TiO2 materials and photocatalysts for PCP removal.