A green catalyst and sensor: band engineering of Bi2Fe4O9-based S-scheme p–n/n homo-heterojunction for detection and degradation of cytotoxic drug

Abstract

With the aim of targeting two major and widespread global environmental concerns, solid waste and contaminated water, a novel and sustainable p–n/n homo-heterojunction was designed via the assimilation of Bi₂Fe₄O₉ (BF) and amine-functionalized calcium-packed rGO extracted from Tamarindus indica shell (AFTS). In situ formation of highly crystalline calcium carbonate within AFTS led to the creation of a p–n homojunction. Consequently, n-type defect states were introduced within the fabricated homo-heterojunction (BF 50AFTS), resulting in excellent conducting attributes. For the very first time, the designed homo-heterojunction was tested for two potential applications, i.e., electrochemical detection and adsorptive degradation of pharmaceutical drugs (doxorubicin and levofloxacin). The highly enhanced photocatalytic activity offered by the fabricated p–n/n homo-heterojunction was attributed to the enhanced surface area and S-scheme charge transfer mechanism. Feasible interactions, possible intermediates under different reaction conditions, unique degradation pathways, the interference of coexisting anions and the leaching of metal ions were also explored in detail. Ecotoxicity assessment of intermediates and by-products (for green algae and fish) showcased a significant decrease in the toxicity of the recycled water. The synthesized homo-heterojunction exhibited appreciable efficacy towards the detoxification of collected real pharmaceutical wastewater in the presence of the catalyst and light only. The great enhancement in the surface area and the presence of surface functionalities resulted in ultra-trace level detection of the drug doxorubicin in tap water, river water, urine and whole-blood samples. The successful mineralization of industrial water and its reduced phytotoxicity demonstrated the outstanding practical applicability of the designed homo-heterojunction for the annihilation of pharmaceutical waste.