Optimization of thermal exfoliation of graphitic carbon nitride for methylparaben photocatalytic degradation under simulated solar radiation

Abstract

Previous studies have shown that the exfoliation of graphitic carbon nitride (g-C₃N₄) is essential to obtain materials with good photocatalytic properties. However, in most studies the influence of exfoliation variables was investigated in an unsystematic way by changing the levels of one factor at a time. In this work, a full factorial design 3² was employed to evaluate the influence of temperature and time used in the thermal exfoliation of bulk g-C₃N₄ obtained from urea (bulk-U), on the photocatalytic performance for 5 mg L⁻¹ methylparaben degradation under simulated solar radiation. Based on the thermal stability of the starting bulk-U, the levels of the design were set in the range of 400 to 450 °C for temperature and 2 to 6 h for time. The results showed an enhancement in the photocatalytic activity with an increase in both factors, obtaining the maximum response at T = 450 °C and t = 6 h. An economic evaluation at the laboratory scale including the main costs derived from the synthesis stage and the photocatalytic degradation procedure was also performed, comparing all the exfoliated materials. The total expenses could be minimized without compromising good photocatalytic activity with the material obtained by exfoliation of bulk-U at 450 °C for 2 h. Detailed characterization of the materials was carried out by XRD, FT-IR, adsorption–desorption of N₂, TEM, SEM, UV-Vis DR, and PL spectroscopy. It was inferred that the enhancement of the photocatalytic performance induced by the exfoliation was mainly related to the consequent increase in the surface area and the improvement in the separation of photogenerated charge pairs derived from the unpacking of the stacked layers.