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

The high-temperature secondary calcination (>500 degrees 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 degrees 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 H-2-evolution performance mainly owing to the introduction of amino groups, which can efficiently enrich H+ from water to facilitate the rapid generation of H-2. This study may open up a fire-new insight for the preparation of high-efficiency nanometer materials. (C) 2019 Elsevier Ltd. All rights reserved.