Phosphorus-doped pistachio shell hydrochar for sustainable copper(II) ion adsorption: A circular bioeconomy approach

Abstract

The development of phosphorus-doped hydrochar adsorbents from biomass waste via hydrothermal carbonisation (HTC), a process that mimics natural carbonisation under controlled conditions, offers a sustainable solution for waste management and environmental protection applications. In this work, biomass waste from the pistachio processing factories, specifically the soft outer shells of Pistacia vera pistachios (PHHC), was used as a precursor for designing efficient adsorbents for copper ions (Cu2+) removal from aqueous solutions. This research investigates the development of hydrochar-based engineered adsorbents with surface modifications using hydrochloric acid, sodium hydroxide, and phosphoric acid to boost adsorption efficiency. Among the various modifications, the use of H3PO4 was found to be optimal for Cu2* removal. The adsorbents were characterised for their surface morphology and chemical composition using scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive spectroscopy, and thermogravimetric analysis. The maximum Cu2* adsorption capacity onto PHHC-H3PO4 hydrochar was 312.50 mg/g at 298 K. Furthermore, the adsorption isotherms indicated a monolayer adsorption process following the Langmuir model, confirming the high affinity and efficiency of PHHC-H3PO4 hydrochar for Cu2* removal. This study offers a scalable and efficient strategy for the removal of heavy metals, offering a significant advancement over existing strategies in literature and paving the way for future studies on regeneration and real wastewater applications.