NH4Cl-induced low-temperature formation of nitrogen-rich g-C3N4 nanosheets with improved photocatalytic hydrogen evolution

The high-temperature secondary calcination (>500 °C) of bulk g-C3N4 usually suffers from a very low yield of g-C3N4 nanosheets owing to its serious and massive depolymerization. In this study, a NH4Cl-induced low-temperature second-calcination approach has been used to synthesize nitrogen-rich g-C3N4 nanosheets with a high yield (ca. 32 wt%), which includes the initial intercalation of NH4Cl into the interlayers of bulk g-C3N4 and the following direct low-temperature calcination at 400 °C. It is found that during the calcination process, the thermal gas flow (HCl and NH3) from NH4Cl decomposition not only can efficiently facilitate the delamination and depolymerization of the g-C3N4 structure, but also can introduce many amino groups on the g-C3N4 surface, resulting in the successful synthesis of nitrogen-rich g-C3N4 nanosheets at such a low temperature. Experimental data suggests that the resulting nitrogen-rich g-C3N4 nanosheets show a distinct enhancement for the H2-evolution performance mainly owing to the introduction of amino groups, which can efficiently enrich H+ from water to facilitate the rapid generation of H2. This study may open up a fire-new insight for the preparation of high-efficiency nanometer materials.