A Metal-Free Oxygenated Covalent Triazine 2-D Photocatalyst Works Effectively from the Ultraviolet to Near-Infrared Spectrum for Water Oxidation Apart from Water Reduction.

Solar-driven water splitting is highly desirable for hydrogen fuel production, particularly if water oxidation is effectively sustained in a complete cycle and/or by means of stable and efficient photocatalysts of main group elements, for example, carbon and nitrogen. Despite extensive success on H2 production on polymer photocatalysts, polymers have met with very limited success for the rate-determining step of the water splitting-water oxidation reaction due to the extremely slow "four-hole" chemistry. Here, the synthesized metal-free oxygenated covalent triazine (OCT) is remarkably active for oxygen production in a wide operation window from UV to visible and even to NIR (up to 800 nm), neatly matching the solar spectrum with an unprecedented external quantum efficiency (even 1% at 600 nm) apart from excellent activity for H2 production under full arc irradiation, a big step moving toward full solar spectrum water splitting. Experimental results and DFT calculations show that the oxygen incorporation not only narrows the band gap but also causes appropriate band-edge shifts. In the end, a controlled small amount of oxygen in the ionothermal reaction is found to be a promising and facile way of achieving such oxygen incorporation. This discovery is a significant step toward both scientific understanding and practical development of metal-free photocatalysts for cost-effective water oxidation and hydrogen generation over a large spectral window.

Unique hole-accepting carbon-dots promoting selective carbon dioxide reduction nearly 100% to methanol by pure water.

Solar-driven CO2 reduction by abundant water to alcohols can supply sustainable liquid fuels and alleviate global warming. However, the sluggish water oxidation reaction has been hardly reported to be efficient and selective in CO2 conversion due to fast charge recombination. Here, using transient absorption spectroscopy, we demonstrate that microwave-synthesised carbon-dots (mCD) possess unique hole-accepting nature, prolonging the electron lifetime (t50%) of carbon nitride (CN) by six folds, favouring a six-electron product. mCD-decorated CN stably produces stoichiometric oxygen and methanol from water and CO2 with nearly 100% selectivity to methanol and internal quantum efficiency of 2.1% in the visible region, further confirmed by isotopic labelling. Such mCD rapidly extracts holes from CN and prevents the surface adsorption of methanol, favourably oxidising water over methanol and enhancing the selective CO2 reduction to alcohols. This work provides a unique strategy for efficient and highly selective CO2 reduction by water to high-value chemicals.

Nitrogen-Mediated Graphene Oxide Enables Highly Efficient Proton Transfer.

Two-dimensional (2D) graphene and graphene oxide (GO) offer great potential as a new type of cost-efficient proton-exchange membranes (PEM) for electrochemical devices. However, fundamental issues of proton transfer mechanism via 2D membranes are unclear and the transfer barrier for perfect graphene are too high for practical application. Using ab initio molecular dynamic simulations, we screened the proton transfer barrier for different un-doped and nitrogen doped GO membranes, and clarified the corresponding transfer mechanisms. More significantly, we further identify that N-mediated GO can be built into a highly efficient PEM with a proton transfer rate of seven orders of magnitude higher than an un-doped case via. a proton relay mechanism between a ketone-like oxygen and a pyridine-like nitrogen across the vacancy site. The N-doped 2D GO is also impermeable to small molecules, and hence a highly efficient PEM for practical applications.

Compressive straining of bilayer phosphorene leads to extraordinary electron mobility at a new conduction band edge.

By means of hybrid DFT calculations and the deformation potential approximation, we show that bilayer phosphorene under slight compression perpendicular to its surface exhibits extraordinary room temperature electron mobility of order 7 × 10(4) cm(2) V(-1) s(-1). This is approximately 2 orders of magnitude higher than is widely reported for ground state phosphorenes and is the result of the emergence of a new conduction band minimum that is decoupled from the in-plane acoustic phonons that dominate carrier scattering.

Fe2 O3 -TiO2 nanocomposites for enhanced charge separation and photocatalytic activity.

Photocatalysis provides a cost effective method for both renewable energy synthesis and environmental purification. Photocatalytic activity is dominated by the material design strategy and synthesis methods. Here, for the first time, we report very mild and effective photo-deposition procedures for the synthesis of novel Fe2 O3 -TiO2 nanocomposites. Their photocatalytic activities have been found to be dramatically enhanced for both contaminant decomposition and photoelectrochemical water splitting. When used to decompose a model contaminant herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), monitored by both UV/Vis and total organic carbon (TOC) analysis, 10% Fe-TiO2 -H2 O displayed a remarkable enhancement of more than 200 % in the kinetics of complete mineralisation in comparison to the commercial material P25 TiO2 photocatalyst. Furthermore, the photocurrent is nearly double that of P25. The mechanism for this improvement in activity was determined using density functional theory (DFT) and photoluminescence. These approaches ultimately reveal that the photoelectron transfer is from TiO2 to Fe2 O3 . This favours O2 reduction which is the rate-determining step in photocatalytic environmental purification. This in situ charge separation also allows for facile migration of holes from the valence band of TiO2 to the surface for the expected oxidation reactions, leading to higher photocurrent and better photocatalytic activity.

Highly efficient photocatalytic H2 evolution from water using visible light and structure-controlled graphitic carbon nitride.

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported. The g-C3N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20,000 µmol h(-1) g(-1) under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5% under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.