Doping vs Functionalization—Strategies for Enhancing the Sonophotocatalytic Degradation of Contaminants of Emerging Concern with 2D-Materials-Based Composites

The presence of contaminants of emerging concern (CECs) in wastewater poses significant risks to both human health and ecosystem biodiversity due to their persistence, bioaccumulation, and potential to disrupt biological processes [1]. Consequently, there is an urgent need for advanced materials and technologies with enhanced properties to face these resilient contaminants.<br/>Bismuth sulfur iodide (BiSI) is a promising sonocatalyst due to its unique properties [2]. However, its narrow bandgap leads to rapid electron-hole recombination, hindering its effectiveness as a photocatalyst. To overcome this, doping and functionalization of BiSI with 2D materials may significantly enhance its catalytic performance by improving visible light absorption, increasing surface area, and promoting efficient electron-hole separation. Such improvements make 2D@BiSI composites highly effective for CECs degradation, offering sustainable and efficient solutions for water purification through combined sonophotocatalytic technologies [3].<br/>In this study, we explored four different modification strategies of BiSI: (i) surface doping with silver (Ag) ions, improving visible light absorption; (ii) structural doping with oxygen to introduce sulfur vacancies and enhance carrier separation and transfer; (iii) functionalization with carbon nitride (C₃N₄), aiming to boost the photocatalytic activity; and (iv) functionalization with graphene oxide (GO), aiming to increase the surface area for contaminant adsorption.<br/>All composites were fully characterized for their structural, physical-chemical, and optical properties, and applied to the degradation of carbamazepine (CBZ) through photocatalysis, sonocatalysis, and combined sonophotocatalysis. All modifications allowed to improve the degradation efficiencies. The combined sonophotocatalytic approach under ultrasound and visible light irradiation achieved degradation efficiencies higher than 90% for the modified Ag@BiSI, O-BiSI, C₃N₄@BiSI, and GO@BiSI catalysts. Remarkably, the 2D-based composites functionalized with C₃N₄ and GO achieved nearly complete degradation of CBZ, showing a synergistic effect in sonophotocatalysis with efficiency improvements of 145% and 157% for C₃N₄@BiSI and GO@BiSI, respectively. These achieved efficiencies were far superior to the sum of the efficiencies of each individual technique for both 2D-materials-based composites. Proposed degradation mechanisms highlight the impact of each modification on generating reactive oxygen species and specific degradation pathways.<br/>These findings underscore the critical role of tailored modifications in significantly enhancing the sonophotocatalytic activity of BiSI-based catalysts. The integration of 2D materials, such as C₃N₄ and GO, not only allows for boosting the adsorption and photocatalytic capacity but also offers a sustainable and effective approach for the degradation of persistent contaminants in water. This study demonstrates the potential of advanced material design in developing robust and high-performance catalysts for environmental remediation, paving the way for more efficient solutions to address the challenges posed by contaminants of emerging concern.<br/><br/><i><b>References</b><br/>1. You, Q. et al. Defects controlling, elements doping, and crystallinity improving triple-strategy modified carbon nitride for efficient photocatalytic diclofenac degradation and H₂O₂ production. Applied Catalysis B: Environmental 321, 121941 (2023);<br/>2. Zarandona, A et al. Sonophotocatalytic removal of organic dyes in real water environments using reusable BiSI@PVDF-HFP nanocomposite membranes. Chemosphere 357, 142069 (2024);<br/>3. Iqbal, M. A. et al. Advanced photocatalysis as a viable and sustainable wastewater treatment process: A comprehensive review. Environmental Research 253, 118947 (2024).</i>