Biochar derived from waste newspapers for removing copper ions from aqueous solution

Abstract

Objective A series kinds of biochar were produced from waste newspapers by pyrolysis at different temperatures (400, 500 and 600℃). The ability of removing copper ions from an aqueous solution of these biochar will be testified and the corresponding adsorbing mechanism also will be discussed. Method The following techniques have been utilized to characterize the structure and properties of biochar, which are elemental analysis, Brunauer-Emmett-Teller method (BET), Fourier transform-infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic absorption spectroscopy (AAS). Result The fabricated biochar (WBC-600) exhibits a typical porous structure and its specific surface area is high as 211 m2·g-1. This structure will be beneficial for removing Cu2+ from aqueous solution. Furthermore, physical and chemical properties of biochar varied significantly based on the pyrolysis temperatures. It is revealed that the aromaticity, specific surface area, pH, and ash content of the biochar increased gradually with the increasing pyrolysis temperature, while the hydrogen, nitrogen and oxygen contents decreased. Batch adsorption experiments were performed to examine the effects of initial pH, contact time, Cu2+ concentration, and temperature on the adsorption capacity of Cu2+. The maximum adsorption capacities of waste newspapers biochar, WBC-400, WBC-500, and WBC-600 were 107, 115 and 138 mg·g-1 at 30℃ (pH 5.0), respectively. The pseudo-second-order kinetics model and Langmuir adsorption isotherm model were suitable for describing the adsorption process, indicating that chemical sorption was a rate-limiting step and adsorption took place at specific homogeneous sites within the adsorbent (monolayer adsorption). The calculated ΔHo values indicated that the adsorption process was endothermic. Furthermore, the adsorption mechanism for WBC was attributed to precipitation, ion exchange, π-π interactions, and complexation. Conclusion The biochar fabricated from waste newspapers by the process suggested in our study meets the criterion of being an effective adsorbent for removing Cu2+ from an aqueous solution. Moreover, since the original material, waste newspaper, is a typical solid waste disposal, the manufacturing of the biochar will have benefits both to reduce cost and protect environment.