Controllable Synthesis of g-C3N4 Inverse Opal Photocatalysts for Superior Hydrogen Evolution

The growing frustration from facing energy shortages and unbalanced environmental issues has obstructed the long-term development of human society. Semiconductor-based photocatalysis, such as water splitting, transfers solar energy to storable chemical energy and is widely considered an economic and clean solution. Although regarded as a promising photocatalyst, the low specific surface area of g-C3N4 crucially restrains its photocatalytic performance. The macro-mesoporous architecture provides effective channels for mass transfer and full-light utilization and improved the efficiency of the photocatalytic reaction. Herein, g-C3N4 with an inverse opal (IO) structure was rationally fabricated using a well-packed SiO2 template, which displayed an ultrahigh surface area (450.2 m(2).g(-1)) and exhibited a higher photocatalytic H-2 evolution rate (21.22 mu mol.h(-1)), almost six times higher than that of bulk g-C3N4 (3.65 mu mol.h(-1)). The IO g-C3N4 demonstrates better light absorption capacity than bulk g-C3N4, primarily in the visible spectra range, owing to the multiple light scattering effect of the three-dimensional (3D) porous structure. Meanwhile, a lower PL intensity, longer emission lifetime, smaller Nyquist semicircle, and stronger photocurrent response (which synergistically give rise to the suppressed recombination of charge carriers) decrease the interfacial charge transfer resistance and boost the formation of photogenerated electron-hole pairs. Moreover, the existing N vacancies intensify the local electron density, helping increase the number of photoexcitons. The N-2 adsorption-desorption test revealed the existence of ample mesopores and macropores and high specific surface area in IO g-C3N4, which exposes more active edges and catalytic sites. Optical behavior, electron paramagnetic resonance, and electrochemical characterization results revealed positive factors, including enhanced light utilization, improved photogenerated charge separation, prolonged lifetime, and fortified IO g-C3N4 with excellent photocatalytic performance. This work provides an important contribution to the structural design and property modulation of photocatalysts.