Novel wet pyrolysis providing simultaneous conversion and activation to produce surface-functionalized biochars for cadmium remediation

The enhancement of surface functional groups of biochar is essential to improving the biochar contaminant adsorption. Current pyrolysis methods that are accompanied by activation are energy consuming and costly. Herein, a novel wet-pyrolysis system that was carried out in open air, with simultaneous conversion and modification to produce an effective biochar adsorbent, is described. Within this system, the surface of the biochar was oxidized partially to produce sufficient functional groups at the surface, whereas carbonization of the biomass (miscanthus sacchariflora) occurs under an acidic catalyst. The characteristic results confirmed the attachment of abundant surface functional groups, including hydroxyl and carboxyl groups, which increased in content with the ongoing reaction time. Neutralization with sodium carbonate removed the hydrogen bonds and enhanced the adsorption properties. The biochar that was obtained by using this technique exhibited an excellent cadmium adsorption capacity of 197 mg .g−1 and a high removal efficiency of 99%. Analysis of the Cd-loaded biochar indicated that adsorption occurred via ion exchange, and formed cadmium complexes. It could be concluded that this novel wet-pyrolysis system is a promising approach to produce biochar efficiently and cost-effectively for heavy-metal remediation.