Preparation and Enhanced Visible-Light Photocatalytic H₂-Production Activity of Graphene/C₃N₄Composites

TLDR

Graphene/g‑C3N4 composites were fabricated by impregnating graphene oxide with polymerized melamine and reducing with hydrazine, then calcining at 550 °C, and characterized by XRD, TEM, UV‑vis, BET, XPS, FT‑IR, Raman, PL, and transient photocurrent measurements to assess charge dynamics. The composites exhibit up to a 3.07‑fold increase in visible‑light photocatalytic H₂ production at ~1.0 wt % graphene, owing to graphene’s conductive pathways that enhance charge separation, as confirmed by PL and photocurrent studies, and show promise for water treatment and dye‑sensitized solar cells.

Abstract

Graphene and graphitic carbon nitride (g-C3N4) composite photocatalysts were prepared by a combined impregnation−chemical reduction strategy involving polymerization of melamine in the presence of graphene oxide (precursors) and hydrazine hydrate (reducing agent), followed by thermal treatment at 550 °C under flowing nitrogen. The resulting graphene/g-C3N4 composite photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, UV−visible spectrophotometry, nitrogen adsorption, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The transient photocurrent response was measured for several on−off cycles of intermittent irradiation. The effect of graphene content on the rate of visible-light photocatalytic hydrogen production was studied for a series of graphene−graphitic carbon nitride composite samples containing Pt as a cocatalyst in methanol aqueous solutions. This study shows that graphene sheets act as electronic conductive channels to efficiently separate the photogenerated charge carriers and, consequently, to enhance the visible-light photocatalytic H2-production activity of g-C3N4. The optimal graphene content was determined to be ∼1.0 wt %, and the corresponding H2-production rate was 451 μmol h−1 g−1, which exceeded that of pure g-C3N4 by more than 3.07 times. The proposed mechanism for the enhanced visible-light photocatalytic activity of g-C3N4 modified by a small amount of graphene was further confirmed by photoluminescence spectroscopy and transient photocurrent response. The metal-free graphene/g-C3N4 composites showed high visible-light photocatalytic activity, which makes them promising nanomaterials for further applications in water treatment and dye-sensitized solar cells.