In this study, pure ZnCo₂O₄ and SnO₂/ZnCo₂O₄ mix photocatalysts have been synthesized by the sol-gel process with three different SnO₂ loading percentages (10, 20, and 30 wt %). Their photocatalytic activities were assessed on the degradation of organic pollutants in water under visible illumination. The structural, morphological, and optical properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR), nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), and UV–Visible diffuse reflectance measurements. The results have shown that the materials are composed of a crystalline ZnCo₂O₄ matrix with a decrease in crystallite size with the amount of SnO₂. Weakly crystalline SnO₂ is also observed for loaded samples. The specific surface area is modified with the loading ratio. The evaluation of the photoactivity of the samples under visible light for the degradation of p-nitrophenol has highlighted that all materials are highly photoactive under visible light thanks to heterojunction between the two oxides. An application test has been conducted on a dye, congo red, showing the same tendencies. An optimal amount of SnO₂ loading is observed for the sample containing 20 wt % of SnO₂. A comparison with commercial Evonik P25 showed that the materials developed in this work have five to six times better efficiency under visible light, leading to a promising photocatalyst material.

This work is part of the valuation of biomaterials abundant in nature; lichens (Xanthoria parietina) are part of this family. The lichens were heat-treated at different temperatures (60.80, 100, and 120°C) and characterised by different techniques (FTIR, SEM, and BET). These biomaterials have been used as biosorbents for two cationic dyes which are methylene blue and gentian violet. After optimisation of the parameters, the biosorption of these dyes was carried out at an adsorbent dose of 1 g/L, pH = 6, and a contact time at the equilibrium of 1 h. The adsorption kinetics perfectly follows the pseudo-second-order model as well as that of intraparticle diffusion. The adsorption isotherms of these two cationic dyes were carried out at 25, 40 and 60°C. The isotherms are of type L, they are well described by the Redlich Peterson model (R² > 0.99) and a low mean error (E% ≤ 10%). The physisorption of methylene blue is generally non-spontaneous (∆G° > 0), exothermic (∆H° < 0), and ordered (∆S° > 0). On the other hand, the physisorption of gentian violet is generally spontaneous (∆G° < 0), endothermic (∆H° > 0), and disordered (∆S° < 0). After adsorption of methylene blue or gentian violet by the heat-treated lichens, a decrease in the intensities of the infrared bands characteristic of our materials was observed. The attenuation of these bands could be attributed to the coverage of our materials by the cationic dyes.