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Ordered mesoporous carbon/g-C3N4 (OMC/g-C3N4) composites with efficient photocatalytic activity under visible light irradiation were prepared by a facile heating method. The as-prepared OMC/g-C3N4 composites were thoroughly characterized by X-ray diffraction, Fourier transform infrared spectroscopy, elemental analyses, transmission electron microscopy with energy dispersion X-ray spectroscopy, N2 adsorption-desorption analysis, UV-vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. The photocatalytic activities were evaluated by degrading Rhodamine B dye, and OMC/g-C3N4 composites exhibited much higher photocatalytic activities than pristine g-C3N4. Moreover, the catalysts retained good stability and the photodegradation efficiency hardly changed after five cycles. The degradation rate of the OMC/g-C3N4 photocatalyst was almost 10 times as high as that of the pristine g-C3N4, which indicated that OMC played an important role in the remarkable improvement of photocatalytic activity. The significant enhancement in photodegradation activity over the OMC/g-C3N4 catalyst could be ascribed to the combined effects coming from the enhanced visible light adsorption, enriched adsorption of the dye on the catalyst and subsequent efficient separation of photogenerated electrons and holes. In addition, a possible mechanism for the photodegradation process was proposed on the basis of active species scavenging experiments.

g-C3N4 prepared from guanidine hydrochloride exhibited a large surface area and a reduced recombination rate of electrons and holes, leading to improved photocatalytic activity for degrading RhB under visible light.

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Catalytic coupling of carbon dioxide with epoxides to obtain cyclic carbonates is an important reaction that has been receiving renewed interest. In this contribution, the cycloaddition reaction in the presence of various hydrogen bond donors (HBDs) catalyzed by hydroxyl/carboxyl task-specific ionic liquids (ILs) is studied in detail. It was found that the activity of ILs could be significantly enhanced in the presence of ethylene glycol (EG), and EG/HEBimBr were the most efficient catalysts for the CO2 cycloaddition to propylene oxide. Moreover, the binary catalysts were also efficiently versatile for the CO2 cycloaddition to less active epoxides such as styrene oxide and cyclohexene oxide. Besides, the minimum energy paths for this hydrogen bond-promoted catalytic reaction were calculated using the density functional theory (DFT) method. The DFT results suggested that the ring-closing reaction was the rate-determining step in the HEBimBr-catalyzed cycloaddition reaction but the EG addition could remarkably reduce its energy barrier as the formation of a hydrogen bond between EG and the oxygen atom of epoxides led this process along the standard SN2 mechanism. As a result, the ring-opening reaction became the rate-determining step in the EG/HEBimBr-catalyzed cycloaddition reaction. The work reported herein helped the understanding and design of catalysts for efficient fixation of CO2 to epoxides via hydrogen bond activation.

A series of mesoporous graphitic carbon nitride (mg-C3N4) materials have been prepared with urea and tetraethylorthosilicate (TEOS) as the precursors, which were thermally polycondensed to obtain the g-C3N4/silica composites, after silica was removed, mg-C3N4 with large surface area (170 m2 g–1) was successfully prepared. Excitingly, TEOS did not only act as a mesoporous-directing agent but also as the promoter for the urea polycondensation to g-C3N4, which made the urea polycondensation proceed at relatively low temperature. Thus, volatilization or/and decomposition of urea in the process of thermal treatment were reduced, resulting in the product yield of g-C3N4 from 0.3 to 0.4 g/10 g urea remarkably increasing to 1.2 g/10 g urea. Moreover, superior photocatalytic activities were observed for degrading methyl orange (MO) and H2 generation from water splitting over the mg-C3N4 photocatalyst. The facilely developed method for high-yield mesoporous g-C3N4 from cost-effective urea was more attractive for its wide applications in environmental treatment and energy development fields.

A periodic mesoporous organosilica with a basic urea-derived framework (PMO-UDF) was prepared and characterized thoroughly. The PMO-UDF showed an enhanced CO capture capacity at low pressure (≤1 atm) and an exceptional catalytic activity in CO coupling reactions with various epoxides to yield the corresponding cyclic carbonates under mild conditions because of the presence of a high surface area, basic pyridine units, and multiple hydrogen-bond donors. The highly stable catalyst could be reused at least six successive times without a significant decrease of the catalytic efficiency or structural deterioration, thus the PMO-UDF composite is considered as a promising material for CO capture and conversion.

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