Ultra-efficient removal of aqueous hexavalent chromium by activated biochar nanoparticles derived from squid ink

Biochar have been recognized as efficient and renewable carbon sorbents, which attracted much attention on Cr contamination remediation in wastewater. In this study, we propose a cost-effective one-step strategy to synthesize activated biochar nanoparticles derived from squid ink (AS-BC) for aqueous Cr(VI) removal. The results demonstrated that AS-BC achieved a removal rate of 24.29 h^-1 at 700 °C (400-times higher than the unmodified one). This was also a state-of-the-art removal performance for aqueous Cr(VI) compared to other reported materials. AS-BC possessed an enormous specific surface (2408 m²/g at 700 °C) with abundant O- and N-containing groups, condensed aromatic structures, and high electron transfer capacity (3.64 and 2.13 mmol e^-/g for EAC and EDC at 700 °C), contributing to the ultra-efficient removal of Cr(VI) by synergistic adsorption and reduction. AS-BC absorbed Cr(VI) in the form of HCrO₄^- by electrostatic attraction with protonated amine-N and hydroxy (-NH₃⁺ and -OH₂⁺) groups and Cr(III) in the form of Cr³⁺ by complexation with amine-N and hydroxy groups. With a hydroxy-quinone and conjugated π-electron system, AS-BC served as mediator and shuttle to accelerate electron transfer in Cr(VI) reduction with an electron donor. Therefore, our findings highlight the immense potential of AS-BC biochar nanoparticles represent a potential alternative for high-performance Cr(VI) remediation in wastewater.