Charge self-regulation over in-plane two-dimensional/two-dimensional hetero-cocatalyst for robust photocatalytic hydrogen generation.

The rationally designing and constructing atomic-level heterointerface of two-dimensional (2D) chalcogenides is highly desirable to overcome the sluggish H2O-activation process toward efficient solar-driven hydrogen evolution. Herein, a novel in-plane 2D/2D molybdenum disulfide-rhenium disulfide (ReS2-MoS2) heterostructure is well-designed to induce the charge self-regulation of active site by forming electron-enriched Re(4-δ)+ and electron-deficient S(2-δ)- sites, thus collectively facilitating the activation of adsorbed H2O molecules and its subsequent H2 evolution. Furthermore, the obtained in-plane heterogenous ReS2-MoS2 nanosheet can powerfully transfer photoexcited electrons to inhibit photocarrier recombination as observed by advanced Kelvin probe measurement (KPFM), in-situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient absorption spectroscopy (fs-TAS). As expected, the obtained ReS2-MoS2/TiO2 photocatalyst achieves an outperformed H2-generation rate of 6878.3 µmol h-1 g-1 with visualizing H2 bubbles in alkaline/neutral conditions. This work about in-plane 2D/2D heterostructure with strong free-electron interaction provides a promising strategy for designing novel and efficient catalysts for various applications.

Single Mn atom modulated molecular oxygen activation over TiO2 for photocatalytic formaldehyde oxidation.

In single-atom catalysts, the atomically dispersed metal sites are pivotal for oxygen molecule activation. We hypothesize that dispersing single Mn atoms on TiO2 nanosheets may improve the photocatalytic oxidation of formaldehyde (HCHO) in the gas phase under ambient conditions. Density function theory (DFT) and experimental experiments were carried out to single Mn atoms not only improved the transfer of localized electrons and photogenerated electrons but also enhanced the activation/dissociation of O2 to generate monoatomic oxygen ions (O-) as the final reactive oxygen species (ROS). In photocatalytic experiments, Mn/TiO2 photocatalyst removed 100 % of HCHO at a low concentration of 7.6 ppm, and reaching excellent mineralization efficiency of over 99.6 %. According to the proposed reaction mechanism, O2 spontaneously adsorbs onto the Mn/TiO2 surface, forming two adsorbed O- after electron donation into the π2p* antibonding orbitals of O2. The adsorbed O- then reacts with gaseous HCHO to produce the key intermediate dioxymethylene (DOM), finally fulfilling a more favorable oxidation process on the Mn/TiO2 surface. This research illustrates the key role of O- in HCHO oxidation and paves the way for practical HCHO removal using TiO2-based photocatalysts.

High-yield and crystalline graphitic carbon nitride photocatalyst: One-step sodium acetate-mediated synthesis and improved hydrogen-evolution performance.

To avoid the drawbacks (such as multi-step operations and causing big quality loss) of currently reported molten salt-assisted strategy for the preparation of crystalline graphitic carbon nitride (g-C3N4) photocatalysts, in this study, an innovative and one-step sodium acetate (CH3COONa)-mediated synthesis strategy has been designed to synthesize a high-yield and crystalline g-C3N4 photocatalyst. It is found that CH3COONa can strongly combine with dicyandiamide (DCDA) to availably prevent the massive sublimation of DCDA and the following intermediates, causing the high-efficiency transformation of DCDA into g-C3N4 with a high yield (52.2 wt%). In addition to the promoted denitrification and quick polymerization of DCDA via CH3COONa, the produced Na2CO3 from CH3COONa decomposition at a higher temperature can further accelerate the polymerization reaction of 3-s-triazine units, leading to the final production of highly ordered and crystalline g-C3N4. Consequently, the resultant high-yield and crystalline g-C3N4 shows an obviously strengthened hydrogen (H2)-evolution rate, about 2.4 times higher than that of bulk g-C3N4, which is due to the synergetic function of highly crystalline structure, reduced band gap and cyano-groups. The current one-step CH3COONa-mediated synthesis strategy may open a novel horizon for the facile preparations and various applications of crystalline g-C3N4 materials.

Ultra-small molybdenum sulfide nanodot-coupled graphitic carbon nitride nanosheets: Trifunctional ammonium tetrathiomolybdate-assisted synthesis and high photocatalytic hydrogen evolution.

The preparation of nanoscale molybdenum sulfide (MoS2)-modified graphitic carbon nitride (g-C3N4) nanosheets usually contains complex and multiple-step operations, including the separate synthesis of nanoscale MoS2 and g-C3N4 nanosheet, and their subsequent composite process. To effectively overcome the above drawbacks, herein, a facile one-step trifunctional ammonium tetrathiomolybdate ((NH4)2MoS4)-assisted approach has been designed to produce ultra-small MoSx nanodot-coupled g-C3N4 nanosheet photocatalyst, including the first addition of ammonium chloride (NH4Cl) and (NH4)2MoS4 into melamine precursors and their following one-step calcination. During high-temperature calcination, except for the promoting generation of the g-C3N4 nanosheets by produced ammonia (NH3) and hydrogen sulfide (H2S) gases, the above (NH4)2MoS4 decomposition not only can efficiently clip the s-heptazine framework to produce more terminal amino groups and cyano groups, but also can produce ultra-small MoSx nanodots on the resultant g-C3N4 nanosheet surface, resulting in the final production of ultra-small MoSx nanodot-coupled g-C3N4 nanosheets. The resultant MoSx nanodot-coupled g-C3N4 nanosheets evidently exhibit increased photocatalytic hydrogen (H2)-generation rate, about 8-fold increase to the traditional MoS2-modified g-C3N4 photocatalyst. The increased H2-generation rate can be mainly attributed to the synergism of MoSx nanodots and cyano group on the g-C3N4 nanosheet surface. The current facile technology could open the sights for the preparation of other high-efficiency photocatalysts.

High-yield lactic acid-mediated route for a g-C3N4 nanosheet photocatalyst with enhanced H2-evolution performance.

Facile and novel strategies to prepare g-C3N4 nanosheets are required to greatly improve their photocatalytic H2-production activity. In this study, a lactic acid-mediated synthesis route has been developed to prepare g-C3N4 nanosheets, which includes the preassembled formation of lactic acid-melamine co-monomers, followed by direct high-temperature calcination. In this case, it is found that during high-temperature calcination, the lactic acid molecules can greatly prevent the serious polymerization of melamine molecules, resulting in the formation of g-C3N4 nanosheets. Moreover, owing to the strong coupling with melamine molecules, lactic acid can also significantly increase the production rate (ca. 35.16 wt%) of g-C3N4 nanosheets from the melamine precursor via preventing the rapid sublimation of melamine and its intermediates during the calcination progress compared with the well-known two-step calcination method. Photocatalytic experimental data reveal that the resultant g-C3N4 nanosheet photocatalysts show a greatly improved H2-production rate, and the g-C3N4 (500 µL) sample exhibits the best photocatalytic performance, which is obviously two times higher than that of the conventional bulk g-C3N4. In addition to lactic acid, it is very interesting to find that acetic acid can also be used to prepare g-C3N4 nanosheets via a similar formation mechanism, strongly suggesting the universality and versatility of the present lactic acid-mediated synthesis route. The present synthesis strategy may broaden the horizons for the synthesis of high-efficiency photocatalysts.

New general sulfinylating process for asymmetric synthesis of enantiopure sulfinates and sulfoxides.

[reaction: see text] A general process for the efficient synthesis of sulfinyl transfer agents has been developed using cinchona alkaloids quinine and quinidine as chiral auxiliaries. The importance of these new and unique sulfinyl transfer agents is exemplified by the expedient synthesis of several sulfoxides in excellent enantiopurities and high yields.