Eupatorium adenophorum derived adsorbent by hydrothermal-assisted HNO3 modification and application to Pb2+ adsorption

Abstract Eupatorium adenophorum (EA), a kind of invasive plant, was utilized as feedstock to prepare the adsorbent using HNO3 impregnation (2.0 mol·L-1) before or after hydrothermal carbonization (HTC) for Pb2+ adsorption in wastewater. A series of batch adsorption experiments including the solution pH, adsorbent dose and contact time showed prominent Pb2+ adsorption performance of HNO3-HTC-EA prepared by HNO3 modification first and then HTC treatment (e.g., equilibrium adsorption amount, 164.68 mg·g-1). The kinetic and isotherm analysis demonstrated that a physico-chemical complex adsorption was the main controlled step for two kinds of HNO3-modified hydrochars adsorption, and Pb2+ adsorption process of HNO3-HTC-EA was multi-molecular layer adsorption. According to the physicochemical structure of HNO3-modified hydrochars comparison before and after Pb2+ adsorption, the surface complexation, electrostatic attraction, cation-π bond interactions and physical adsorption were main adsorption mechanisms. In addition, the developed mesopores of adsorbent could ensure the full binding of functional groups in the pores/channel with Pb2+, improving the Pb2+ adsorption capacity. Hydrothermal-assisted HNO3 modification provided a method to make use of Eupatorium adenophorum and other global exotic plants.