A comparative study of different activation methods for hydrochar: surface properties and removal of pharmaceutical pollutant in water.

Contaminants of emerging concerns, such as sulfonamides, have been frequently discovered in surface water, and the design of biomass-based adsorbents is a promising research direction to remove them from water. In this study, hydrothermal carbonization was utilized to prepare hydrochar (HC) from orange peels along with various activations, including hydrogen peroxide (H₂O₂) and HCl. The main goals of the present study are (i) to prepare hydrochars that were activated by different chemical methods and (ii) to provide insights into the adsorption mechanism of pollutant removal using sulfamethoxazole (SMX) as a model pharmaceutical pollutant. The H₂O₂ activated hydrochar (ACHC) exhibited the best adsorption capacity for removal of 40 μM SMX from water, i.e., 1.971 mg g^-1 using 0.2 g L^-1 ACHC. Scanning electron microscopy (SEM) studies revealed that the ACHC exhibited a coral-like structure and the highest amount of mesopores (74.6 m² g^-1) and BET area of 79.5 m² g^-1. The effects of pH, adsorbent dosage, initial concentration, and adsorption temperature were investigated, and a substantial relationship between porosity and adsorption suggests that mesoporosity played a crucial role in the adsorption process for all the activated hydrochars. The mechanism of SMX adsorption involves reversible chemisorption and retention in the pores of the adsorbent surface. The use of ACHC was also tested in different water matrices to highlight its potential applications in wastewater treatment, and it exhibited an adsorption capacity of 0.598 and 0.429 mg g^-1 in tap water and wastewater effluents, respectively.