Xiaoman Li

Solar-Light-Driven Pure Water Splitting with Ultrathin BiOCl Nanosheets.

A suitable photocatalyst for overall water splitting has been produced by overcoming the disadvantage of the band structure in bulk BiOCl by reducing the thickness to the quantum scale. The ultrathin BiOCl nanosheets with surface/subsurface defects realized the solar-driven pure water splitting in the absence of any co-catalysts or sacrificial agent. These surface defects cannot only shift both the valence band and conduction band upwards for band-gap narrowing but also promote charge-carrier separation. The amount of defects in the outer layer surface of BiOCl results in an enhancement of carrier density and faster charge transport. First-principles calculations provide clear evidence that the formation of surface oxygen vacancies is easier for the ultrathin BiOCl nanosheets than for its thicker counterpart. These defects can serve as active sites to effectively adsorb and dissociate H2 O molecules, resulting in a significantly improved water-splitting performance.

Ultrathin mesoporous Co3O4 nanosheets with excellent photo-/thermo-catalytic activity

Ultrathin mesoporous Co3O4 nanosheets on a stainless steel mesh (SS–Co3O4) have been synthesized through an electrochemical deposition method. The SS–Co3O4 catalyst exhibits high photothermal performance, resulting in a considerable increase of temperature above the light-off temperature for VOC oxidation. Aerobic oxidations of propylene and propane under simulated sunlight were selected as probe reactions to explore the photo-/thermo-catalytic (PTC) activity. The results show that SS–Co3O4 with only 7 mg of Co3O4 grown on the substrate possesses superior PTC activity, which merely occurs around the directly grown SS–Co3O4 rather than the Co3O4 coated SS. The combined properties of SS–Co3O4 such as the ultrathin two-dimensional shape, foam-like porous inside architecture, and supported metal substrate could lead to the integrative advantages of the maximum utilization of photothermal conversion, more catalytically active sites, and enhanced amount and mobility of surface lattice oxygen species, resulting in excellent PTC activity of SS–Co3O4. This work provides insights into the rational design of monolith catalysts for the solar driven environmental purification and suggests new ideas toward the overall utilization of solar energy.

Surfactant-free hydrothermal fabrication of monoclinic BiVO4 photocatalyst with oxygen vacancies by copper doping

Poor electron transport leads to the high recombination of photogenerated charge carriers for photocatalysts, which limits the photocatalytic performance. In order to improve charge transport properties, Cu doped BiVO4(Cu–BiVO4) was prepared by a facile hydrothermal method. The doped material provided a maximal photocurrent of 10 μA cm−2 at +0.4 V vs. SCE, which was 5 times higher than the undoped one. The result implied much improvement for the separation of the carriers for Cu–BiVO4, which attributed to the suitable amount of oxygen vacancies as positive charge centers caused by doping. Oxygen vacancies trapped photogenerated electrons and thus inhibited the electrons–holes recombination. The photocatalytic degradation of rhodamine B (RhB) was used to evaluate the photoactivity of the materials. The results showed that the photocatalytic properties of the doped materials were evidently higher than the undoped BiVO4. The photocatalytic reaction mechanism is also discussed in this article, and the superoxide radical was confirmed to be the main active species for the photocatalytic degradation process.

Bi2WO6 quantum dot-intercalated ultrathin montmorillonite nanostructure and its enhanced photocatalytic performance

The kinetic competition between electron-hole recombination and water oxidation is a key limitation for the development of efficient solar water splitting materials. In this study, we present a solution for solving this challenge by constructing a quantum dot-intercalated nanostructure. For the first time, we show the interlayer charge of the intercalated nanostructure can significantly inhibit the electron-hole recombination in photocatalysis. For Bi2WO6 quantum dots (QDs) intercalated in a montmorillonite (MMT) nanostructure as an example, the average lifetime of the photogenerated charge carriers was increased from 3.06 μs to 18.8 μs by constructing the intercalated nanostructure. The increased lifetime markedly improved the photocatalytic performance of Bi2WO6 both in solar water oxidation and environmental purification. This work not only provides a method to produce QD-intercalated ultrathin nanostructures but also a general route to design efficient semiconductor-based photoconversion materials for solar fuel generation and environmental purification.

Efficient Solar-Driven Nitrogen Fixation over Carbon-Tungstic Acid Hybrids

Ammonia synthesis under mild conditions is of supreme interest. Photocatalytic nitrogen fixation with water at room temperature and atmospheric pressure is an intriguing strategy. However, the efficiency of this method has been far from satisfied for industrialization, mainly due to the sluggish cleavage of the N≡N bond. Herein, we report a carbon-tungstic-acid (WO3 ⋅H2 O) hybrid for the co-optimization of N2 activation as well as subsequent photoinduced protonation. Efficient ammonia evolution reached 205 μmol g-1  h-1 over this hybrid under simulated sunlight. Nitrogen temperature-programmed desorption revealed the decisive role of carbon in N2 adsorption. Photoactive WO3 ⋅H2 O guaranteed the supply of electrons and protons for subsequent protonation. The universality of carbon modification for enhancing the N2 reduction was further verified over various photocatalysts, shedding light on future materials design for ideal solar energy utilization.

Enhanced H2 evolution based on ultrasound-assisted piezo-catalysis of modified MoS2

Piezo-catalysis of H2 evolution from water has been realized from MoS2 nanosheets with few-layers using mechanical energy. The internal electric field along the [001] direction induced by ultrasonic compression has been proposed as the intrinsic driving force for the separation and transport of carriers in MoS2. In addition, we showed that the edge of MoS2 nanosheets provided active sites, which were beneficial for the HER (hydrogen evolution reaction) after acidification treatment; thus, the piezo-catalysis of H2 evolution reached 70 μmol g−1 h−1. Furthermore, surface-modified MoS2 using glutathione (GSH) achieved a high H2 evolution of ∼1250 μmol g−1 h−1. The decorated ligands of GSH played a key role in promoting the separation of carriers. Thus, we suggest that surface treatments, which bring enhanced piezo-electricity and catalytic coupling, lead to efficient carrier separation and a high possibility of energy transformation from mechanical energy to chemical energy.