Performance and mechanism study of g-C3N4/rGO heterojunction enhanced NO3− reduction by nZVI under visible light irradiation.

Zero valent iron (ZVI) is a low-cost, earth-abundant reactive metal, and it has a strong reducing ability with a standard redox potential of − 0.44 V. Therefore, it is an effective and widely used reducing agent for pollutant degradation. Since nanoscale zero valent iron (nZVI) shows a larger specific surface area which leads to the faster reaction rate and higher conversion efficiency, it has been widely used in NO 3 − nitrogen reduction reaction, however, it shows disadvantages of poor chemical stability, narrow applicable pH, and low total nitrogen (TN) removal efficiency. To solve these problems, in this paper, the nZVI nanoparticles were deposited on the g-C 3 N 4 /rGO composite, and its NO 3 − removal efficiency under visible light irradiation was investigated. The effects of nZVI loading, initial pH of solution, catalyst dosage and initial NO 3 − concentration on NO 3 − reduction performance were studied. The results showed that the g-C 3 N 4 /rGO/nZVI material achieved 100% of NO 3 − reduction efficiency in 60 min. And the TN removal efficiency of g-C 3 N 4 /rGO/nZVI was 82.8%, superior to nZVI and g-C 3 N 4 /nZVI (13.3% and 38.2%, respectively). Finally, the denitrification mechanism of g-C 3 N 4 /rGO/nZVI was proposed as follows: Under light irradiation, the photogenerated electrons on g-C 3 N 4 transferred via rGO to the nZVI surface, thus improving the reactivity and stability of nZVI. The photogenerated electrons and active electrons on the surface of nZVI reduced NO 3 − to N 2 , NH 4 +, and other products, while the photogenerated holes further oxidized part of NH 4 + to N 2 and other gaseous products. During this process, the rGO material could inhibit the oxidation of nZVI by the photogenerated holes from g-C 3 N 4. [Display omitted] • g-C 3 N 4 /rGO serves as a support for nZVI to enhance its stability and activity. • The rGO in g-C 3 N 4 /rGO hindered the oxidation of nZVI by photogenerated holes. • The NO 3 − reduction mechanism was explored and the reduction products were analyzed. • NO 3 − was completely removed and the selectivity of gaseous products were 82.8%. [ABSTRACT FROM AUTHOR]