Highly Efficient Removal of Cr(VI) from Wastewater by Nitrogen-Rich Graphene Oxide/Polyvinyl Alcohol Composites

Nitrogen-rich graphene oxide/polyvinyl alcohol (PGOPA) composites were synthesized through the coupling and Schiff base reactions of graphene oxide (GO) with polyvinyl alcohol (PVA) and polyethyleneimine (PEI). Fourier-transform infrared spectroscopy (FTIR), Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed the successful preparation of PGOPA. The maximum adsorption capacities were 680.3 mg/g at 298 K, 694.4 mg/g at 308 K, and 704.2 mg/g at 318 K, exceeding those of most previously reported GO-based materials. PGOPA exhibited excellent cycling stability, retaining 87.2% of its initial adsorption capacity after six consecutive adsorption-desorption cycles. In the absence of competing anions (SO42- and PO43-), PGOPA showed remarkable selectivity for Cr(VI). Adsorption experiments showed the adsorption isotherm of PGOPA for Cr(VI) followed the Langmuir model. The pseudo-second-order model fitted this adsorption process well, indicating chemisorption characteristics. XPS revealed that the adsorption mechanism primarily involved electrostatic interactions and the reduction of Cr(VI) to Cr(III). This work provides valuable technical support for the structural design of highly selective adsorbents for Cr(VI) removal from wastewater.