Carbon Vacancy-Modified Carbon Nitride Allotropic Composite for Solar Hydrogen Generation Coupled with Selective Oxidation of 5-Hydroxymethylfurfural

Abstract

A melon-poly­(heptazine imide) (PHI) carbon nitride allotropic composite is constructed by partial phase conversion of melon-based carbon nitride through hydrothermal treatment using pure water. Solid-state nuclear magnetic resonance characterization reveals the existence of the intrinsic defects of carbon vacancies in the melon-PHI carbon nitride allotropic composite. In the presence of the Pt nanoparticle cocatalyst and the hole scavenger of triethanolamine, the carbon vacancy-modified melon-PHI allotropic composite exhibits superior photocatalytic performance for hydrogen production compared to the pristine melon-based carbon nitride. Moreover, the simultaneous H2 evolution from water splitting coupled with selective oxidation of 5-(hydroxymethyl) furfural to 2,5-diformylfuran is achieved over the carbon vacancy-modified melon-PHI allotropic composite photocatalyst with activities of 41 and 49 μmol g–1 h–1 under AM 1.5G (100 mW cm–2) illumination with a UV filter. Density functional theory calculations suggest that the defective heptazine rings with carbon vacancies locate in the PHI portion and contribute to the major charge density of the highest occupied molecular orbital in the PHI portion of the the allotropic composite. This intrinsic defect allows the improvement of photocharge separation and the creation of additional active sites in the carbon nitride photocatalyst to boost the performances of photocatalytic redox reactions.

Defective Potassium Poly(Heptazine Imide) Preventing Spin Delocalization and Hole Transfer Deactivation for Efficient Solar Energy Conversion and Storage

“…The Mott-Schottky plot of KPHIs was constructed following the procedure described in the previous works. [23,33] Examinations of Photocatalytic and Dark Photocatalytic Properties: Photocatalytic hydrogen evolution over KHPI was conducted under AM 1.5G simulated sunlight at 100 mW cm −2 (100 W, Model 94011A, Oriel). 5 mg of KPHI photocatalyst was suspended in 30 mL aqueous solution with 10 vol% TEOA and 3 wt% Pt (H 2 PtCl 6 ⋅6H 2 O).…”

“…The chemical shifts of 13 C signal acquired from KHPI were referenced to adamantane with respect to TMS. [23,33] The chemical states of C and N in KPHI were examined by X-ray photoelectron spectroscopy (XPS, Thermo Scientific Thermo K-Alpha) equipped with a charge neutralizer. The XPS valence band (VB) spectrum for KPHI was also measured using this apparatus.…”

“…Compared to KMACN with a band gap of 2.56 eV, BKCN and BKM exhibit smaller band gaps of 2.42 and 2.49 eV, respectively, with stronger absorption band tails at long wavelengths. The conduction and valence band edge positions of BKM, BKCN, and KMACN are illustrated in Figure 4c, which are established by combining the results of the Mott-Schottky plots, XPS-valence band (VB) spectra, and Tauc plots [23,33] shown in Figure S6, Supporting Information and Figure 4b, respectively. The band gaps of KMACN, BKCN, and BKM straddle the reduction potential of water as well as the oxidation potential of triethanolamine (TEOA).…”