Hydrochar Derived from Invasive Pontederia crassipes: In Situ Modification and Application for Methylene Blue Adsorption

In this study, hydrochar was prepared from the invasive aquatic plant Pontederia crassipes through hydrothermal carbonization and modified in situ using zirconium oxychloride (ZrOCl2), poly(acrylic acid) (PAAC), sulphuric acid (H2SO4) and phosphoric acid (H2PO4). The synthesized materials were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Their adsorption performance was evaluated for the removal of methylene blue (MB) from aqueous solutions using batch experiments and the adsorption data were analyzed using isotherm and kinetic models. The experimental adsorption capacity of the unmodified hydrochar was 30.96 mg g–1. Modification with ZrOCl2, PAAC, H2SO4 and H3PO4 resulted in adsorption capacities of 39.21, 30.31, 42.20 and 42.31 mg g–1, respectively. The H2SO4- and H3PO4-modified hydrochars exhibited the highest adsorption capacities among the prepared materials. The adsorption data were reported to follow the Langmuir isotherm and pseudo-second-order kinetic models.