Conversion of spent coffee grounds to biochar as promising TiO2 support for effective degradation of diclofenac in water

Abstract

A novel composite, biochar derived from spent coffee grounds with immobilized TiO2 (biochar–TiO2) was prepared, characterized, and applied as an alternative, effective, and sustainable photocatalyst for degrading diclofenac from aqueous solution. Composites with different mass ratios between TiO2 and biochar were prepared by mechanical mixing and subsequent pyrolysis in an inert atmosphere of N2 at 650°C. The sample with biochar–TiO2 ratio of 1:1 presented a degradation efficiency of 90% at just 120 min versus 40% for TiO2 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–TiO2 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.