One-step synthesis of lychnophora residue-derived porous carbon sheets for highly efficient removal of copper(Ⅱ)

Abstract

In this study, the lychnophora residue-derived porous carbon sheets (LRPCSs) were synthesized using a facile one-step pyrolysis method, and the physicochemical properties of LRPCSs were analyzed via various characterization apparatus, its adsorption behaviors and mechanism for copper(Ⅱ) (Cu(II)) were also investigated. The LRPCSs possessed three-dimensional honeycomb sheet structure, a specific surface area of 14.6 m2·g−1, abundant mineral elements (K, Ca, and Mg), and the oxygen- and sulfur-containing functional groups, which would offer more active sites for the fast adsorption of Cu(II). Batch experiments demonstrated that the adsorption properties of Cu(II) by LRPCSs raised with the raising of biochar dose, pH value (2−6), Cu(II) concentration, and temperature. The isotherms and kinetics studies showed that the adsorption data conformed very well to Langmuir isotherm (R2 ≥0.9975) and pseudo-second-order kinetic models (R2 ≥0.9941). The maximum Cu(II) adsorption capacities of LRPCSs were respectively 103.09, 120.48, and 153.85 mg·g−1 at 298, 308, and 318 K, which were superior to previously reported biochar adsorbents. The thermodynamic studies indicated that the Cu(II) adsorption with LRPCSs was an automatic, endothermal, and entropy-raising process (ΔG° = −6.82∼−8.47 kJ·mol−1, ΔH° = 17.89 kJ·mol−1, ΔS° = 83.07 J·(mol·K)−1). The adsorption capacity of Cu(II) with LRPCSs still remained 85% after four adsorption-desorption cycles. Furthermore, the ion exchange and surface complexation were the predominant mechanism for the Cu(Ⅱ) adsorption by LRPCSs, with cation-π interaction and pore capture playing a secondary role. This study showed that LRPCSs could be an effective, low-cost, and reusable adsorbent with great potential for application in remediating the Cu(II)-containing wastewater pollution.