Novel nitrogen self-doped hydrochar from Siam weed (Chromolaena odorata L.) leaves for highly efficient removal of crystal violet from water

Abstract

Indonesia possesses abundant biomass resources with great potential for value-added applications. Siam weed (Chromolaena odorata L.), an invasive plant species, is widely distributed and underutilized. In this study, nitrogen self-doped hydrochar (NSD-HC) was synthesized from Siam weed leaves via hydrothermal carbonization, followed by KOH treatment, producing a pore-like structure with abundant surface functionalities. The NSD-HC was analyzed using FTIR, SEM, EDS, XRD, Raman, XPS, and UV-vis spectrometry to elucidate its characteristics. Its adsorption performance was evaluated against various synthetic dyes, including crystal violet (CV), under different adsorption conditions (contact time, CV concentration, and NSD-HC weight). The data indicated that the adsorption kinetics fitted with the PSO model, while the equilibrium data followed the Langmuir isotherm model. The NSD-HC exhibited rapid adsorption kinetics with a maximum adsorption capacity of 37.47 mg g⁻¹. The adsorption efficiency was associated with electrostatic interactions, hydrogen bonding, and π–π interactions between NSD-HC's active sites and CV molecules. This study demonstrates a sustainable and cost-effective method for valorizing invasive biomass into a good adsorbent, enabling efficient treatment of dye-laden wastewater while mitigating the ecological impact of invasive species.