Fabrication of trimodal porous silica/g-C[formula omitted]N[formula omitted] nanotubes for efficient visible light photocatalytic reduction of CO[formula omitted] to ethanol

Abstract

The novel composite photocatalyst of trimodal porous silica (TPS)/g-C3N4 nanotubes was fabricated via a two-step hydrothermal synthesis method with intermediate pretreatment. The TPS was extracted from rice husk, which is agricultural waste, to further reduce the cost of photocatalyst preparation. A series of characterization results, including X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, N2 adsorption–desorption, and pore size analysis, illustrated the properties of crystal, pore structure, and morphology of the composite photocatalyst. The TPS/g-C3N4 presented a hollow tubular shape with a large surface area and CO2 adsorption capacity, so there were more catalytic active reaction sites. The photocatalytic activity measurement was operated, and only ethanol was detected when g-C3N4 NT and composite TGNT were used as photocatalysts. In particular, the ethanol yield of TGNT2 was 196μm/g, and after 10 cycles of running, the photocatalytic activity decreased by less than 5%. UV–Vis diffuse reflectance spectra, photoluminescence spectra, and photoelectrochemical analysis revealed the mechanism of the photocatalytic activity enhancement from the aspects of visible light absorption, photo-generated electron–hole pair separation and transfer, and charges recombination. It theoretically explained the prospect of this fabrication strategy. It demonstrated that TGNT is a low-cost, stable, efficient, and promising photocatalyst to reduce CO2 to ethanol under visible light.