Adsorption-desorption behavior perspective deciphers the photo-detoxification of high-concentration Cr(VI) by...

Most studies on crystalline/amorphous hetero-junction photocatalysts for pollutant treatment focus on enhancing charge carrier separation and transport, while largely overlooking the critical role of adsorption-desorption behavior in determining actual photocatalytic performance, particularly for high-concentration Cr(VI) reduction. Herein, we adopt an adsorption-desorption behavior perspective to decipher the structure-activity relationship of a novel crystalline Bi₄O₅I₂/amorphous Fe₂O₃ hetero-junction (BOI/a-FO) rather than pursuing conventional optoelectronic optimization. Specifically, an amorphous Fe₂O₃ phase is intentionally introduced to endow the hetero-junction with excellent adsorption-desorption properties. Experimental results show that, compared with the hetero-junction containing 0.7 g amorphous Fe₂O₃ (BOI/a-FO-d), the hetero-junction with 0.1 g amorphous Fe₂O₃ (BOI/a-FO-a) exhibits weaker light absorption, lower charge carrier signals, etc., yet demonstrates higher photocatalytic activity. This anomalous phenomenon is attributed to the excellent adsorption-desorption behavior imparted by the amorphous Fe₂O₃. Systematic characterization reveals that the strong adsorption originates from oxygen vacancies synergistically induced by OH^- and Fe²⁺, while the surface positive charge brought by the amorphous phase further enhances pollutant adsorption and product desorption. DFT calculations further confirm that the introduction of amorphous Fe₂O₃ significantly increases the adsorption energy for Cr(VI) and promotes the desorption of Cr(III). Additionally, the hetero-junction exhibited efficient charge carrier separation. Therefore, the optimized photocatalyst achieved efficient photo-reduction of 0.26 g·L^-1 Cr(VI) within 180 min and maintained stable activity over five consecutive cycles. Soybean seed germination assays and cytotoxicity tests demonstrated a significant reduction in the biotoxicity of the treated wastewater, providing important references for the application of interface engineering in photocatalysis.