Photocatalytic Hydrogen Evolution by MoO₃@<i>g</i>-C₃N₄ and MoO₃@<i>f</i>-MWCNT Nanocomposites in Deionized and Natural Seawater under Visible Light

Visible-light-driven photocatalysts are predominantly useful for converting solar to hydrogen energy via photocatalytic water-splitting reactions. The heterojunction composite materials have exhibited remarkable advantages for visible-light photocatalytic H2 evolution. We have successfully synthesized MoO3@f-MWCNT and MoO3@g-C3N4 nanocomposites and characterized them using PXRD, UV-DRS, Raman spectroscopy, XPS, PL, TRPL, FE-SEM, HR-TEM, BET, and photocurrent. The photocatalytic water-splitting efficiency of MoO3@f-MWCNT and MoO3@g-C3N4 was measured under visible light (λ ≥ 420 nm) irradiation using TEOA as a sacrificial reagent in DI water and natural seawater. The H2 evolution rate in DI water for MoO3@f-MWCNT is 2313.56 μmol g–1 h–1, and for MoO3@g-C3N4 is 2530.35 μmol g–1 h–1 with an apparent quantum efficiency (AQE) of 6.38 and 6.93%, respectively. In natural seawater, the H2 evolution rate is 2632.20 and 2845.06 μmol g–1 h–1, with an AQE of 7.21 and 7.77%, respectively. The rate of H2 evolution slightly increased in natural seawater than DI water. The Tafel slope values for MoO3@g-C3N4 and MoO3@f-MWCNT are 59 and 92 mV dec–1, respectively. The lowest Tafel value of MoO3@g-C3N4 exhibited a faster rate of reaction. Thus, the surface interaction between the MoO3 and the porous g-C3N4 materials may create synergistic effects, which facilitate electron transport at the interface and significantly boost the photocatalytic activity. Thus, MoO3@g-C3N4 is a promising photocatalyst for renewable energy production.