MXene-Functionalized Polyethyleneimine Gel and Its Adsorption-Assisted Photocatalysis Behavior for Efficient CR(VI) Removal from Water

The high-performance removal of highly toxic Cr(VI), along with its efficient conversion into less toxic Cr(III), will hold promise for water treatment. Herein, a novel transition metal carbide (MXene)-functionalized polyethyleneimine (PEI) gel has been designed for efficient Cr(VI) removal from water. The titanium dioxide (TiO₂) generated by self-oxidation of MXene acts as a photocatalytic species, while MXene serves as a medium for charge separation and transfer. The PEI networks provide numerous adsorption-active sites (i.e., amine groups), stabilize the photocatalytic species (i.e., TiO₂), and medium (i.e., MXene), thereby endowing the composite gel with both adsorption and photocatalysis ability. Its adsorption behavior conforms to pseudo-second-order kinetics and the Langmuir adsorption model, with a maximum adsorption capacity of up to ∼431 mg·g⁻¹. Importantly, this composite gel can convert about 90% of highly toxic Cr(VI) into less toxic Cr(III) through adsorption-assisted photocatalysis way. This work presents foundational findings for developing multi-functional gels aimed at wastewater treatment.