Sustainable Photodegradation of Pharmaceuticals: KOH-Impregnated Palm Oil Mill Effluent Sludge Biochar-BiOBr Nanocomposite for Wastewater Treatment

Abstract

In the search for a cost-effective and environmentally friendly photocatalyst for the efficient degradation of CIP antibiotic pollutants, biochar (BC) produced from palm oil mill sludge was used as a base to fabricate biochar-based BiOBr composites by varying the mass ratio of biochar and BiOBr via a hydrothermal route. The prepared BBC (BiOBr-biochar) composites exhibited the features of a crystal plane that could be assigned to tetragonal BiOBr with a high specific surface of 267 m2/g (BBC-1:1) when different mass ratios of BC were incorporated with BiOBr. This composite facilitates the reduction of the band gap of BiOBr from 2.87eV to 2.42eV (BBC-1:1) and is consistent with the reduction of recombination rate of electron-hole pairs as suggested by UV-Vis DRS and photoluminescence (PL), respectively. Consequently, the synergistic effect of biochar (BC) and pure BiOBr leads to a higher degradation efficiency of CIP on the BBC composite, with the BBC-1:1 composite showing the highest efficiency (97.49%) and that of pure BiOBr being 55.66% under optimized conditions. The degradation rate of the BBC-1:1 composite was 0.0156min-1 which is 3.25 times that of BiOBr (0.0048min-1). Furthermore, the scavenging experiments confirmed the significant contribution of the active radicals h+ and O2- as the main photoactive species in the photocatalytic degradation process, while the •OH- effect is insignificant in the degradation of CIP. Consequently, the photocatalytic degradation mechanism was discussed and the regeneration test confirmed the high stability of the BBC composites up to 77% for the seven cycles. These results show that the BBC composite is suitable for large-scale practical applications as a green photocatalyst.