Hydrothermal conversion of Cu-laden biomass to one-step doped hydrochar used as a potential adsorbent for 2-nitrophenol removal

Moving towards a circular economy offers a viable path to mitigating stress on natural resources. This study revealed that hydrothermal carbonization can effectively valorize Cu-loaded spent biomass into a Cu-enriched hydrochar to be used as sorbent of organic pollutants. The structural properties and surface analysis of the obtained hydrochars were assessed using various techniques, and its adsorption capacity was evaluated through the removal of 2-nitrophenol from artificially contaminated aqueous solutions in batch adsorption tests. Central Composite Design and the Response Surface Methodology were utilized to optimize the hydrothermal carbonization process. The study was aimed at examining the individual and combined effects of hydrothermal temperature and residence time on hydrochars yield and their specific surface area. The N2 adsorption/desorption showed that Cu-SG biomass-derived hydrochar exhibited a higher specific surface area compared with raw biomass-derived hydrochar. The results obtained indicate that the hydrochar produced at 210 °C with a 5 h reaction time (HC-210-5) is a highly efficient adsorbent for 2-nitrophenol, exhibiting a capacity ranging from 1.3 mg/g to 7.7 mg/g at low concentrations (ranging from 5 to 50 ppm). The kinetic study reveals that the adsorption process onto HC-210-5 follows pseudo-second-order kinetics, while the equilibrium isotherms were determined using the Freundlich isotherm model. These findings endorse the viability of a one-step synthesis of Cu-doped hydrochars from Cu-contaminated biomass as a promising and efficient adsorbent for the removal of micropollutants from wastewater.