Xue Lu Wang

Fluorine‐Doped Porous Single‐Crystal Rutile TiO2 Nanorods for Enhancing Photoelectrochemical Water Splitting

Fluorine-doped hierarchical porous single-crystal rutile TiO(2) nanorods have been synthesized through a silica template method, in which F(-) ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at -0.33 V vs. Ag/AgCl) under 100 mW cm(-2) of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO(2) single crystals.

Manipulating solar absorption and electron transport properties of rutile TiO2 photocatalysts via highly n-type F-doping

In this work, we report a facile and nontoxic one-pot hydrothermal method for synthesizing F-doped rutile single crystalline TiO2 with tuneable solar absorption. The optical band gap of the catalyst can be easily manipulated from 3.05 to 2.58 eV via altering the initial F : Ti molar ratio of reaction precursors. The photoanodes made of rutile TiO2 single crystals with appropriate F-doping concentration show excellent photoelectrocatalytic activity towards water oxidation under ultraviolet and visible light illumination. The best photoelectrocatalytic performance under UV irradiation can be obtained by F-doped TiO2 with an initial F : Ti molar ratio of 0.1, which is almost 15 times higher than that of un-doped TiO2. Further, the F-doped TiO2 photoanodes also exhibit superior photoelectrocatalytic activity under visible irradiation, and the best performance can be achieved by F-doped TiO2 photoanode with an initial F : Ti molar ratio of 0.05. The superior photoelectrocatalytic activity could be attributed to the highly n-type dopant introduced by fluorine, which significantly tunes the electrical conductivities and band structures of the resulting TiO2 photoanodes, and thus the photoelectrocatalytic activities under both UV and visible irradiation. Different techniques have been employed to characterize the electrical conductivity, charge carrier density and band structures of the F-doped rutile TiO2 films, such as photoelectrochemical method, electrical impedance spectroscopy (EIS) measurements, Mott–Schottky plots and XPS valence band spectra.

Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions

Proton transfer (PT) processes in solid–liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid–liquid phases.

Structure disorder of graphitic carbon nitride induced by liquid-assisted grinding for enhanced photocatalytic conversion

Graphitic-C3N4 with a disordered structure was processed for the first time by a liquid-assisted planetary ball milling approach. Through this simple and effective mechanochemistry method, the milled samples displayed outstanding visible-light photoactivity and the optimized one showed 7-fold higher H2 evolution rate than the bulk one.

Switching the photocatalytic activity of g-C3N4 by homogenous surface chemical modification with nitrogen residues and vacancies

A facile two-step homogenous approach is established to produce and control the nitrogen vacancies on g-C3N4 photocatalysts. The g-C3N4 undergoes a solvothermal N2H4·H2O reduction inactivation and subsequent thermal reduction process to reactivate and achieve an enhanced photocatalytic activity toward hydrogen evolution.

Controllable Synthesis of Hexagonal WO3 Nanoplates for Efficient Visible‐light‐driven Photocatalytic Oxygen Production

Facilitating charge-carrier separation and transfer is fundamentally important to improve the photocatalytic performance of semiconductor materials. Herein, two-dimensional hexagonal WO3 nanoplates were synthesized by a two-step route: rapid evaporation and solid-phase sintering. The as-prepared WO3 exhibits an enhanced activity of photocatalytic water oxidation compared to bulk monoclinic WO3 . The electron dynamics analysis reveals that a more efficient charge-carrier separation in the former can be obtained, the origin of which can be attributed to an increased number of surface defects in hexagonal WO3 nanoplates. This work not only presents a novel and simple method to produce two-dimensional hexagonal WO3 nanoplates, but also demonstrates that surface defects and two-dimensional geometric structures can promote the charge separation, which may be extended to the design of other efficient photocatalysts.

Black Tungsten Nitride as a Metallic Photocatalyst for Overall Water Splitting Operable at up to 765 nm

Semiconductor photocatalysts are hardly employed for overall water splitting beyond 700 nm, which is due to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs; however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Black tungsten nitride is now employed as a metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization.

Brønsted base site engineering of graphitic carbon nitride for enhanced photocatalytic activity

Graphitic carbon nitride (g-C3N4) is a promising two-dimensional polymeric photocatalyst in the field of solar energy conversion. In the past few years many modifications of g-C3N4 have been studied extensively; however, the difficulty in obtaining detailed structural information both on its intrinsic covalent interactions and surrounding bonding environments largely restricts the rational design and development of inherent structure-controlled g-C3N4 based photocatalysts and fundamental understanding of their mechanistic operations. Herein, we demonstrate a high-pressure hydrogenation treatment method for g-C3N4 and introduce 1D 13C and 15N and 2D 15N Radio Frequency-driven Dipolar Recoupling (RFDR) solid-state nuclear magnetic resonance spectroscopy for identifying the structural information and surrounding hydrogen-bonding environment of treated g-C3N4 samples. The surface Bronsted base sites of g-C3N4 samples can be tuned systematically through changing the treatment conditions. We find that the terminal isolated –NH2 and the hydrogenated nitrogen species in treated g-C3N4 samples seem to be the origin of their improved activities for photocatalytic hydrogen evolution and favor the enhancement of light harvesting and carrier transport. The as-prepared HCN400-4-2 sample treated at a pressure of 4 MPa and a temperature of 400 °C for 2 h in a hydrogen atmosphere displays the highest H2 evolution reaction (HER) activity, which is over 26 times higher than that of pristine g-C3N4.

Bottom-Up Enhancement of g-C3N4 Photocatalytic H2 Evolution Utilising Disordering Intermolecular Interactions of Precursor

Disordered intermolecular interaction carbon nitride precursor prepared by water-assisted grinding of dicyandiamide was used for synthesis of g-C3N4. The final sample possesses much looser structure and provides a broadening optical window for effective light harvesting and charge separation efficiency, which exhibits significantly improved H2 evolution by photocatalytic water splitting. The bottom-up mechanochemistry method opens new vistas towards the potential applications of weak interactions in the photocatalysis field and may also stimulate novel ideas completely different from traditional ones for the design and optimization of photocatalysts.

Metallic Ni3P/Ni Co‐catalyst to Boost Photocatalytic Hydrogen Evolution

Metallic Ni3 P/Ni can be used as a co-catalyst to replace noble metal Pt for efficient photocatalytic hydrogen evolution, due to its excellent trapping-electron ability. The applications of metallic Ni3 P/Ni co-catalyst on CdS, Zn0.5 Cd0.5 S, TiO2 (Degussa P25) and g-C3 N4 are further confirmed, indicating its versatile applicability nature like Pt.