Photoreductive synthesis of nanoscale zero-valent iron rod assisted by phosphotungstic acid over graphite carbon nitride and its enhanced removal of Cr(VI) from water

Abstract

Hexavalent chromium Cr(VI) as a virulent carcinogen has led to environmental pollution and health threats. Nanoscale zero-valent iron (NZVI) is considered one of the most effective environmental remediation materials in the field. NZVI/phosphotungstic acid/graphite carbon nitride (NZVI@HPW/g-C<inf>3</inf>N<inf>4</inf>) composites were facilely fabricated by photoreduction of ferrous irons on g-C<inf>3</inf>N<inf>4</inf> flakes with the assistance of phosphotungstic acid. The TEM, SEM-EDS, XRD, FTIR, BET, and XPS analyses were conducted to explore the surface morphology and mechanism of the composites. NZVI0.9@HPW/g-C<inf>3</inf>N<inf>4</inf> was chosen as the optimal composite for removing Cr(VI) from water. The kinetics and thermodynamics experiments showed that the adsorption of Cr(VI) fitted well with the pseudo-second-order kinetic model and the Langmuir isothermal model. The maximum adsorption capacity of the adsorbents was 164.81 mg/g. Results demonstrated that adsorption of Cr(VI) was a principal process via a redox reaction in which zero-valent iron was oxidized and Cr(VI) species was reduced to Cr(III). Furthermore, NZVI0.9@HPW/g-C<inf>3</inf>N<inf>4</inf> exhibited superior photocatalytic ability under visible light irradiation, which was 8.5 times higher than HPW/g-C<inf>3</inf>N<inf>4</inf> and 15 times higher than g-C<inf>3</inf>N<inf>4</inf>. This work will provide a promising prospect for the dual utilization of light in wastewater remediation.