Conversion of spent coffee grounds to biochar as promising TiO 2 support for effective degradation of diclofenac in water

A novel composite, biochar derived from spent coffee grounds with immobilized TiO 2 (biochar–TiO 2 ) was prepared, characterized, and applied as an alternative, effective, and sustainable photocatalyst for degrading diclofenac from aqueous solution. Composites with different mass ratios between TiO 2 and biochar were prepared by mechanical mixing and subsequent pyrolysis in an inert atmosphere of N 2 at 650°C. The sample with biochar–TiO 2 ratio of 1:1 presented a degradation efficiency of 90% at just 120 min versus 40% for TiO 2 used as reference. This fact is associated with a set of intrinsic characteristics obtained during the formation of the composite, such as superior pore size, avoiding the recombination of the ē / h + pair, bandgap reduction, and promotion of reactive oxygen species due to phenolic groups present on the biochar surface. The dominant reactive species involved during the photocatalytic degradation of diclofenac were h + and • OH. The diclofenac degradation pathways were determined based on the identification of intermediates and nonpurgeable organic carbon (NPOC) analysis. The novel biochar–TiO 2 composite prepared in this work showed high physical–chemical stability and efficiency over five consecutive cycles of reuse, proving to be a highly promising photocatalyst for degrading diclofenac in water.