Enhanced hydrogen and 5-hydroxymethylfurfural (5-HMF) production via photoreforming of cotton cellulose: role of cellulose allomorphs in Pt–g-C3N4–Bi3TiNbO9 catalysis

Photoreforming cellulose to simultaneously produce 5-hydroxymethylfurfural (5-HMF) and hydrogen represents a promising strategy for harnessing solar energy. However, the development of highly efficient photocatalysts for this reaction remains a challenge, and the influence of cellulose’s crystalline structure on conversion efficiency is not well understood. In this study, a Pt-modified g-C₃N₄–Bi₃TiNbO₉ heterojunction photocatalyst was synthesized to explore the photocatalytic reforming of four crystalline forms of cellulose. The results demonstrate that the crystalline structure of cellulose significantly affects hydrogen and 5-HMF production, with the order of activity being cellulose III > IV > II > I. Among the cellulose types tested, cellulose III exhibited the highest performance, achieving 51.8 μmol g⁻¹ h⁻¹ of hydrogen and 113.4 μmol g⁻¹ h⁻¹ of 5-HMF, surpassing the yields from cellulose I, II, and IV when using the Pt_1.0–g-C₃N₄–Bi₃TiNbO₉(2:1) heterojunction. Additionally, a lower degree of polymerization of cellulose was found to favor the coproduction of hydrogen and 5-HMF, as it enhances the breakdown of cellulose via reactive species. Factors such as cellulose powder size, solution pH, and catalyst-cellulose interactions were also shown to influence the yields. Density functional theory (DFT) calculations revealed an electron migration of 0.019684e between the O 2p and Bi 6p orbitals of Bi₃TiNbO₉(220) and the C 2p and N 2p orbitals of g-C₃N₄, confirming interfacial electron transfer. The calculated adsorption energies followed the trend: cellulose IV (− 1.72 eV) > I (− 1.73 eV) > II (− 1.94 eV) > III (− 2.07 eV), consistent with experimental results, except for cellulose IV.

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