Phosphorous graphitic carbon nitride nanosheets integrated cellulose nanofiber membranes via electrospinning for efficiently selective sorption and photoreduction of U(VI)

Abstract

Since photoreduction of U(VI) is a promising strategy to extract aquatic U(VI), the application scalability can be improved by integrating powdered photocatalyst with membranes. Herein, phosphorous graphitic carbon nitride nanosheets (PCNNSs) with improved porosity (78.6–183.1 m²/g) and abundant P-containing groups (12.7–7.4 wt% of P) were synthesized via co-thermolysis of guanidine phosphonate and melamine. PCNNSs exhibited narrowed band gaps (2.63–2.69 eV), decreased valence bands (1.71–1.79 eV) and improved absorption of visible light. By dispersing powdered PCNNSs in spinning solvent of cellulose, they were successfully integrated together as cellulose/PCNNS (CL/PCNNS) membranes via electrospinning technique. CL/PCNNS membranes presented quick capture equilibrium (5.0 h), high q_max (153.8–243.3 mg/g) and excellent selectivity from simulate nuclide wastewater and seawater. Moreover, CL/PCNNS membranes showed an enhanced photoreduction rate of U(VI) (0.018–0.078 min⁻¹) and favorable reusability (82 % remained rate after six cycles). It was proven that high production of reductive radicals (•O₂^-) and low generation of oxidation radicals (•OH) by CL/PCNNS membranes, promoting the photoreduction of U(VI) to U(IV). Our work pave a way for the modification of carbon nitride materials and their integration with electrospinning membranes in the nuclide remediation.