Selective removal of Cr(VI) from solution by polyethyleneimine modified hydrochar loaded nanoscale zero-valent iron with high adsorption capacity

In this paper, a novel polyethyleneimine (PEI) surface-modified hydrochar (HTC) loaded nanoscale zero-valent iron (nZVI) adsorbent (HTCTSIP-5) was developed. HTCTSIP-5 showed excellent adsorption of Cr(VI) with a low cost of preparation and easy separation. A comparison of the electrochemical properties showed that HTCTSIP-5 had a stronger electron transfer capacity than nZVI, which was beneficial for the Cr(VI) reduction to Cr(III). The zero charge point of HTCTSIP-5 was 8.32, indicating its strong adsorption capacity for Cr(VI) within a wide pH range. The Langmuir model was found to accurately depict the adsorption of Cr(VI) by HTCTSIP-5, exhibiting a remarkable maximum adsorption capacity of 532.35 mg/g at the temperature of 318 K, surpassing that of the majority of comparable adsorbents. HTCTSIP-5 showed excellent selectivity and anti-interference when co-existing ion tests were performed. It still had a strong adsorption capacity after several cycles. HTCTSIP-5 had been shown by XPS analysis to primarily remove Cr(VI) from solution by reduction and adsorption, with the removal of Cr(VI) by reduction representing 78.72% of the total Cr(VI) removed. HTCTSIP-5′s ultra-high stability and Cr(VI) removal capability proved its viability for applications in treating wastewater containing Cr(VI).