Improving CO2 Photoconversion by Layered Materials: Boosted Optoelectronic Performance and Catalytic Activity of g-C3N4 by Ultrasound Exfoliation

Exfoliation of graphitic carbon nitride g-C3N4 by means of ultrasound (US) treatment at varying input power is investigated. Exfoliation of g-C3N4 displays a strong dependence of US input power, with a slightly enhanced bandgap (2.8 eV), but most of all increased lifetime of photogenerated electrons, as observed through diffuse reflectance spectroscopy (DRS) and spectrofluorimetry data. Among all applied power (varied between 30 and 120 W), 120 W sufficiently exfoliated and tuned physicochemical properties of g-C3N4. Compared to bulk as prepared sample, exfoliated g-C3N4 exhibited improvement in photo-induced charge carrier transfer and separation, resulting in higher photocatalytic efficiencies. FE-SEM and TEM images of both bulk and exfoliated g-C3N4 show the effect of the exfoliation power on the nanosheet, pseudo-lamellar structure. A change in US input power correlates well with amonotonous variation of the bandgap, of the charges lifetime of the materials and, most importantly, of the catalytic performance determined through an innovative high-pressure reactor in solid–liquid–gas phase. The catalytic results demonstrate this material as an efficient photocatalyst to obtain high yield of formic acid with net productivities ranging from ∼5100 to ∼8200 mmol/kgcat h at 80 °C in water, which is among the highest reported in the literature.