Self-cleaning vegetable-tanned leather: photocatalytic activity of ZnO and BiOI nanoparticles immobilized by succinic acid

Abstract

In this work, succinic acid was evaluated for the first time as a chemical binder to immobilize ZnO and BiOI nanoparticles on a vegetable-tanned crust leather surface to confer self-cleaning properties through photocatalytic activity. In a previous work, a new methodology for collagen esterification using polycarboxylic acids was developed. The effects of ZnO concentration and curing temperature on photocatalytic performance were systematically evaluated using a factorial design and Minitab 18 software. The optimal conditions were obtained at a concentration of 0.5 (wt%) and a curing temperature of 30 °C. These parameters were used in the BiOI immobilization methodology. Photocatalytic activity was assessed using methylene blue photocatalytic activity indicator ink (PAII) under simulated solar radiation. Statistical analysis revealed that ZnO concentration was the most significant parameter affecting photocatalytic efficiency. However, higher concentrations (0.75 wt%) promoted nanoparticle agglomeration, reducing the availability of active sites, as evidenced by SEM analysis. Comparatively, BiOI showed lower photocatalytic performance, attributed to its lower specific surface area (6.65 m² g^-1) relative to ZnO (10–25 m² g^-1) and TiO₂ (35–65 m² g^-1). Additionally, contact angle analysis revealed that immobilization of photocatalysts significantly increased the hydrophobicity of the leather surface, with contact angles rising from 53° for untreated leather to 137° for BiOI-modified samples. These changes in surface wettability contribute to improved self-cleaning functionality. Overall, these findings validate the effectiveness of this novel succinic acid-mediated immobilization strategy for producing self-cleaning leather materials and highlight the critical role of optimizing nanoparticle concentration to maximize performance.