Removal of organic compounds in wastewater using cocoa shell‑based activated carbon–SiO2 nanoparticles

This work aimed to use low-cost residual cocoa shell biomass for the preparation of activated carbon with different amounts of SiO2 nanoparticles using the coprecipitation method. The use of residual plant biomass seeks to strengthen the challenges of the bioeconomy in the generation of value-added products for the agro-industry. Subsequently, the adsorption capacity of phenol and 3,4-dimethoxybenzyl alcohol as representative species of persistent organic pollutants was quantified. The chemical activation of the carbon was carried out at 480 °C during 30 min with a 1.5 phosphoric acid (H3PO4) impregnation ratio. The activated carbons were characterized by Fourier transform infrared spectroscopy (FTIR), showing the presence of functional groups associated with substances such as phenols, carboxylic acids, aromatic rings, and SiO2. Also, activated carbons were structurally characterized with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), finding that the granules had structured surfaces but with irregular size and disordered channels, which facilitates the impregnation of SiO2 nanoparticles onto the activated carbon surface. The adsorption study of the organic compounds was carried out using UV–Vis spectroscopy. The adsorption isotherms, which were adjusted to the Langmuir, Freundlich and Temkin models, were determined with correlation coefficients of 0.9835, 0.9885 and 0.987. On the other hand, the adsorbent materials achieved removal percentages around 97.9% and 97.8% for phenol and 3,4-dimethoxybenzyl alcohol, respectively. The results showed that activated carbons with SiO2 nanoparticles increased the specific surface area by up to 20%. Therefore, this property allows a greater interaction of contaminants at the time of adsorption. Graphical abstract