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Tannin-based carbon xerogel as a promising co-catalyst for photodegradation processes based on solar light: a case study using the tin (IV) oxide/carbon xerogel composite

Abstract This work aimed to evidence the potential use of tannin-based carbon xerogel as a co-catalyst in photocatalytic processes based on solar light. Specifically, the tin (IV) oxide/carbon xerogel photocatalyst (SnO2/XC) was developed with the objective of improving the photoactivity of tin (IV) oxide (SnO2) under simulated solar light. The photocatalytic efficiency was determined by the degradation of the 4-chlorophenol molecule. The synthesis proposed in this work is based on a simple one-pot precipitation reaction, using black wattle tannin and tin chloride as precursors. The materials synthesized were characterized by X-ray diffractometry, diffuse reflectance spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, scanning electron microscopy, adsorption isotherms, and chronoamperometry. Results showed the presence of tetragonal SnO2 in the samples synthesized. Carbon xerogel addition led to an increased specific surface area (55% higher) and lower bandgap energy (from 3.64 eV to 3.58 eV). The photocatalytic evaluation shows that the SnO2/XC composite has superior photocatalytic efficiency (44% removal vs 20% for the SnO2), obtaining a reaction rate constant (kapp = 0.00172 min−1) which is nearly double the one obtained by the pure SnO2 (kapp = 0.00096 min−1). The chronoamperometric results indicated that the proposed modification enhanced the photocurrent generation and charge separation in the SnO2/XC, facilitating the formation of active radicals during the process and further degrading the reaction intermediates formed during the photodegradation process.