Visible light promoted photocatalytic degradation of benzidine-based anionic diazo dye and its mechanistic studies using copper carbon dots incorporated biochar

Abstract

The increase in anthropogenic activities has an incremental effect on the contamination of water. Apart from all types of pollutants present in water, dyes contribute a major part to water pollution. In the current research, there is more emphasis on the synthesis of copper carbon dots doped biochar (Cu-CD-BC) and its application in the removal of benzidine-based anionic diazo dye i.e., Congo red (CR) dye from water samples under visible light irradiation in quick period. The novel copper doped carbon dots (Cu-CDs) prepared from the hydrothermal route were impregnated on the surface of biochar synthesized from pyrolytic carbonization to trigger the photocatalytic properties. The morphological structure and surface functionalities of the synthesized materials were characterized using HRTEM, UV, FESEM, XRD, and FTIR techniques. The Cu-CD-BC showed 99 % removal of CR dye at 20 mg L^–1 in the shortest 12 mins of reaction time reported to date. Batch studies were conducted to evaluate the effect of different parameters like catalyst dosage, pH, contact time, and initial dye concentration. Radical trapping studies were conducted to determine the effect of radicals on the degradation activity. From the trapping experiments, it was evaluated that the ∙O₂⁻ and ∙OH radicals facilitate the degradation mechanism. To compare the effectiveness of the catalyst, we also conducted experiments using Cu-CDs, pristine biochar, and Cu-CD-BC for the removal studies. The findings indicated that the biochar and Cu-CDs showed poor photocatalytic properties which are enhanced when the Cu-CDs are impregnated on the surface of biochar. The mechanistic pathway was also framed based on trapping and GCMS results. Cycle studies were done to determine the efficiency and reusability of the catalyst.