Design of p-n homojunctions in metal-free carbon nitride photocatalyst for overall water splitting

Two-dimensional (2D) carbon nitride (CN) photocatalysts are attracting extensive attention owing to their excellent photocatalytic properties. In this study, we successfully prepared CN materials with heterogeneous structures via hydrothermal treatment, high-temperature roasting, ball milling, sintering, and other processes. Benefitting from interface interactions in hybrid architectures, the CN photocatalysts exhibited high photocatalytic activity. The rate of hydrogen production using these CN photocatalysts reached 17028.82 μmol h−1 g−1, and the apparent quantum efficiency was 11.2% at 420 nm. The ns-level time-resolved photoluminescence (PL) spectra provided information about the time-averaged lifetime of fluorescence charge carriers; the lifetime of the charge carriers causing the fluorescence of CN reached 9.99 ns. Significantly, the CN photocatalysts displayed satisfactory results in overall water splitting without the addition of sacrificial agents. The average hydrogen and oxygen production rates were 270.95 μmol h−1 g−1 and 115.21 μmol h−1 g−1 in 7 h, respectively, which were promising results for the applications of the catalysts in overall water splitting processes. We investigated the high efficiency of the prepared CN photocatalysts via a series of tests (UV-vis diffuse reflectance spectroscopy, photocurrent response measurements, PL emission spectroscopy, time-resolved PL spectroscopy, and Brunauer-Emmett-Teller analysis). Furthermore, the Mott-Schottky plot and current-voltage curve were acquired via electrochemical tests. The fabricated CN photocatalyst had a small p-n junction in its heterogeneous structure, which further enhanced its photocatalytic efficiency. Therefore, this work can promote the development of CN photocatalysts.