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The characteristics and diclofenac adsorption properties of a carbon adsorbent prepared from palm kernel shells were studied. The adsorbent prepared via hydrothermal carbonization followed by an activation in nitrogen flow had a mesoporous structure with homogenous pore distribution and the specific surface area of 131 m2g−1. The Raman spectra showed a formation of graphene or graphite structures in the material during activation with small number of defects based on its ID/IG ratio of about 0.5. The FTIR analysis showed both a qualitative and quantitative decrease in the functional groups of the raw material after activation. The developed adsorbent was found to be effective in the removal of diclofenac with 95% maximum removal at pH 2, adsorbent dose of 15 gL−1 and adsorbate dose of 50 mgL−1. Diclofenac adsorption followed the Langmuir isotherm model with correlation coefficient R2 > 0.98. The adsorption kinetics was explained by the second-order kinetic model with rate constant (K2) 0.869 min−1. The interaction via aromatic π–π stacking and hydrogen bonding between -OH groups of phenol and carboxylic acid groups of DCF are leading to a good adsorption efficiency despite of the low surface area of the adsorbent. Graphic abstract

This paper presents results related to the development of a carbon composite intended for water purification. The aim was to develop an adsorbent that could be regenerated using light leading to complete degradation of pollutants and avoiding the secondary pollution caused by regeneration. The composites were prepared by hydrothermal carbonization of palm kernel shells, TiO2, and W followed by activation at 400 °C under N2 flow. To evaluate the regeneration using light, photocatalytic experiments were carried out under UV-A, UV-B, and visible lights. The materials were thoroughly characterized, and their performance was evaluated for diclofenac removal. A maximum of 74% removal was observed with the composite containing TiO2, carbon, and W (HCP25W) under UV-B irradiation and non-adjusted pH (~5). Almost similar results were observed for the material that did not contain tungsten. The best results using visible light were achieved with HCP25W providing 24% removal of diclofenac, demonstrating the effect of W in the composite. Both the composites had significant amounts of oxygen-containing functional groups. The specific surface area of HCP25W was about 3 m2g−1, while for HCP25, it was 160 m2g−1. Increasing the specific surface area using a higher activation temperature (600 °C) adversely affected diclofenac removal due to the loss of the surface functional groups. Regeneration of the composite under UV-B light led to a complete recovery of the adsorption capacity. These results show that TiO2- and W-containing carbon composites are interesting materials for water treatment and they could be regenerated using photocatalysis.

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