Porous carbon-doped g-C₃N₄/polyniline heterosturctures for efficient photocatalytic solar-driven hydrogen peroxide production

Abstract

Graphitic carbon nitride (g-C3N4) has emerged as an innovative photocatalyst with a band gap of 2.7 eV and active under visible light. However, its commercialisation is hindered by limitations such as insufficient light absorption, low surface area, low charge transfer rate and fast recombination of electron-hole pairs. Therefore, this study aims to improve the optical and electronic properties of g-C3N4 through carbon doping, morphological design, and heterojunction formation, leading to improvements in photocatalytic performance. In this study, kapok fibre, a polysaccharide material, was used as a bio-template for the microtubular structure and carbon doping source, while silica acted as a hard template for introducing porosity via the chemical vapour deposition method. The impact of different silica precursor amounts (5–15%) was explored to optimise porosity. Moreover, heterostructure formation between C-doped g-C3N4 (CCN) and polyaniline (PANI) was prepared through an in-situ oxidative polymerisation reaction. A comprehensive examination of the material's structural and textural characteristics, along with its crystallinity, chemical composition, optical properties, and charge carrier mobility, was conducted using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), nitrogen adsorption/desorption, X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis-Differential Thermogravimetry (TGA-DTG), Ultraviolet-Visible (UV-VIS) and Photoluminescence (PL) spectroscopy, and photoelectrochemical measurements. The results indicate that a 15% silica precursor is optimal for synthesising highly ordered porous CCN, facilitating the growth of PANI in the heterostructure. The PANI/CCN heterojunction photocatalyst showed the highest hydrogen peroxide production, 3922 μM g-1 h-1, which is 2.0, 4.2, and 5.6-fold over the CCN, PANI, and g-C3N4, respectively. This enhanced photocatalytic activity is attributed to its broadened visible light absorption, narrowed band gap of 2.09 eV, and improved charge separation and transfer, as evidenced by reduced PL intensity and a smaller Nyquist radius in EIS analysis. Moreover, the photocatalyst retained over 97 % of its activity after five consecutive cycles, demonstrating its excellent photostability. In conclusion, an essential aspect of designing highly efficient photocatalysts for the future involves the creation of interconnected heterojunctions characterised by CCN porosity and optimal concentrations of PANI within the heterojunction nanoarchitecture. The CCN/PANI structure, which forms a highly ordered photocatalyst, offers significant potential for practical photocatalytic applications.