Zhaoyang Fan

Highly Efficient Photocatalyst Based on a CdS Quantum Dots/ZnO Nanosheets 0D/2D Heterojunction for Hydrogen Evolution from Water Splitting

A novel CdS/ZnO heterojunction constructed of zero-dimensional (0D) CdS quantum dots (QDs) and two-dimensional (2D) ZnO nanosheets (NSs) was rationally designed for the first time. The 2D ZnO NSs were assembled into ZnO microflowers (MFs) via an ultrasonic-assisted hydrothermal procedure (100 °C, 12 h) in the presence of a NaOH solution (0.06 M), and CdS QDs were deposited on both sides of every ZnO NS in situ by using the successive ionic-layer absorption and reaction method. It was found that the ultrasonic treatment played an important role in the generation of ZnO NSs, while NaOH was responsible to the assembly of a flower-like structure. The obtained CdS/ZnO 0D/2D heterostructures exhibited remarkably enhanced photocatalytic activity for hydrogen evolution from water splitting in comparison with other CdS/ZnO heterostructures with different dimensional combinations such as 2D/2D, 0D/three-dimensional (3D), and 3D/0D. Among them, CdS/ZnO-12 (12 deposition cycles of CdS QDs) exhibited the highest hydrogen evolution rate of 22.12 mmol/g/h, which was 13 and 138 times higher than those of single CdS (1.68 mmol/g/h) and ZnO (0.16 mmol/g/h), respectively. The enhanced photocatalytic activity can be attributed to several positive factors, such as the formation of a Z-scheme photocatalytic system, the tiny size effect of 0D CdS QDs and 2D ZnO NSs, and the intimate contact between CdS QDs and ZnO NSs. The formation of a Z-scheme photocatalytic system remarkably promoted the separation and migration of photogenerated electron-hole pairs. The tiny size effect effectively decreased the recombination probability of electrons and holes. The intimate contact between the two semiconductors efficiently reduced the migration resistance of photogenerated carriers. Furthermore, CdS/ZnO-12 also presented excellent stability for photocatalytic hydrogen evolution without any decay within five cycles in 25 h.

Rationally Designed Porous MnOx–FeOx Nanoneedles for Low-Temperature Selective Catalytic Reduction of NOx by NH3

In this work, a novel porous nanoneedlelike MnOx-FeOx catalyst (MnOx-FeOx nanoneedles) was developed for the first time by rationally heat-treating metal-organic frameworks including MnFe precursor synthesized by hydrothermal method. A counterpart catalyst (MnOx-FeOx nanoparticles) without porous nanoneedle structure was also prepared by a similar procedure for comparison. The two catalysts were systematically characterized by scanning and transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and their catalytic activities were evaluated by selective catalytic reduction (SCR) of NOx by NH3. The results showed that the rationally designed MnOx-FeOx nanoneedles presented outstanding low-temperature NH3-SCR activity (100% NOx conversion in a wide temperature window from 120 to 240 °C), high selectivity for N2 (nearly 100% N2 selectivity from 60 to 240 °C), and excellent water resistance and stability in comparison with the counterpart MnOx-FeOx nanoparticles. The reasons can be attributed not only to the unique porous nanoneedle structure but also to the uniform distribution of MnOx and FeOx. More importantly, the desired Mn4+/Mnn+ and Oα/(Oα + Oβ) ratios, as well as rich redox sites and abundant strong acid sites on the surface of the porous MnOx-FeOx nanoneedles, also contribute to these excellent performances. In situ DRIFT suggested that the NH3-SCR of NO over MnOx-FeOx nanoneedles follows both Eley-Rideal and Langmuir-Hinshelwood mechanisms.

Fabrication of g-C3N4/Au/C-TiO2 hollow structures as visible-light-driven Z-scheme photocatalysts with enhanced photocatalytic H2 evolution

The Z‐scheme photocatalytic system for water splitting based on semiconductors has exhibited great potential for H2 fuel production from renewable resources. In this work, we constructed g‐C3N4/Au/C‐TiO2 hollow spheres as an all‐solid‐state Z‐scheme photocatalytic system with Au nanoparticles as the electron mediator. The as‐synthesized g‐C3N4/Au/C‐TiO2 photocatalyst showed a remarkably enhanced photocatalytic H2 evolution rate under visible‐light irradiation (λ>420 nm), which was 86 and 42 times higher than those of pure C‐TiO2 and g‐C3N4, respectively. The enhancement of photocatalytic performance can be mainly attributed to the intentionally designed Z‐scheme system, which not only promoted the efficient transfer and separation of photogenerated electron–hole pairs, but also retained the strong redox ability of the charge carriers. In addition, the Z‐scheme system also achieved high visible‐light absorption and utilization owing to the surface plasmon resonance (SPR) effect of Au nanoparticles and hollow structures of C‐TiO2. All the factors synergistically promote the photocatalytic activity of the g‐C3N4/Au/C‐TiO2 hollow nanospheres, providing a promising method for the rational design of highly efficient visible‐light‐driven photocatalysts.

WS2/Graphitic Carbon Nitride Heterojunction Nanosheets Decorated with CdS Quantum Dots for Photocatalytic Hydrogen Production

Two-dimensional/two-dimensional (2D/2D) stacking heterostructures are highly desirable in fabricating efficient photocatalysts because face-to-face contact can provide a maximized interfacial region between the two semiconductors; this largely facilitates the migration of charge carriers. Herein, a WS2 /graphitic carbon nitride (CN) 2D/2D nanosheet heterostructure decorated with CdS quantum dots (QDs) has been designed, for the first time. Optimized CdS/WS2 /CN without another cocatalyst exhibits a significantly enhanced photocatalytic H2 evolution rate of 1174.5 μmol h-1  g-1 under visible-light irradiation (λ>420 nm), which is nearly 67 times higher than that of the pure CN nanosheets. The improved photocatalytic activity can be primarily attributed to the highly efficient charge-transfer pathways built among the three components, which effectively accelerate the separation and transfer of photogenerated electrons and holes, and thus, inhibit their recombination. Moreover, the extended light-absorption range also contributes to excellent photocatalytic efficiency. In addition, the CdS/WS2 /CN photocatalyst shows excellent stability and reusability without apparent decay in the photocatalytic H2 evolution within 4 cycles in 20 h. It is believed that this work may shed light on specifically designed 2D/2D nanosheet heterostructures for more efficient visible-light-driven photocatalysts.

Ultrathin Al 2 O 3 -coated reduced graphene oxide membrane for stable lithium metal anode

Lithium (Li) metal has been considered as the most attractive anode materials for Li-ion batteries (LIBs) due to its high theoretic specific capacity. The formation of unstable solid electrolyte interphase (SEI) and dendritic Li on the metal anode, however, hindered its practical application. Herein, to address the issues, a Li-free electrode with ultrathin Al2O3 coated on reduced graphene oxide (rGO) membrane that covers a Cu foil current collector was developed. The composite electrode exhibits excellent interfacial protection of lithium metal deposited between Cu foil and rGO electrochemically. Firstly, it affords good Li+ permeability from the electrolyte. Secondly, the ultrathin Al2O3 has sufficient mechanical strength to inhibit the penetration of Li dendrite. Li metal was observed uniformly deposited between rGO membrane and Cu collector, and stable cycle performance of Li plating/stripping with Coulombic efficiency of ~ 91.75% at the 100th cycle is achieved in organic carbonate electrolyte without any additives.Graphical Abstract

Mn−Co Mixed Oxide Nanosheets Vertically Anchored on H2Ti3O7 Nanowires: Full Exposure of Active Components Results in Significantly Enhanced Catalytic Performance

The full exposure of active ingredients plays an important role in the enhancement of catalytic performance. In this work, a series of novel catalysts, Mn−Co mixed oxide nanosheets with ultrathin thickness (about 3.5 nm) and different Mn/Co ratios (0.52, 0.69, and 1.52) vertically anchored on a support (H2Ti3O7 nanowires), are rationally developed. This unique structure not only fully exposes the active ingredients of the Mn−Co mixed oxides, but also is very favorable for the diffusion and transfer of gas molecules through the space between these standing nanosheets. As expected, the developed catalysts (MnOx‐CoOy/H2Ti3O7, MnCoTi), especially MnCoTi‐2 with the Mn/Co molar ratio of 0.69, present excellent low‐temperature selective catalytic reduction (SCR) performance, high N2 selectivity, superior water tolerance and stability. The relative turnover frequency (TOF) value over MnCoTi‐2 at 100 °C is as high as 9.25×10−4 s−1 under the gas hourly space velocity (GHSV) of 200 000 h−1, which is rarely reported among Mn‐Ti, Mn−Co, and Mn−Co‐Ti mixed oxide catalysts. The results of in situ diffuse reflectance infrared Fourier transform spectroscopy suggest that the coordinated NH3, NH4+ ions, adsorbed NO2, and bidentate nitrate are the reactive species and the Eley–Rideal and Langmuir–Hinshelwood mechanisms can be simultaneously involved on the surface of the MnCoTi‐2 at a relatively low temperature (90 °C).

Efficient spatial charge separation and transfer in ultrathin g-C3N4 nanosheets modified with Cu2MoS4 as a noble metal-free co-catalyst for superior visible light-driven photocatalytic water splitting

Developing photocatalysts with efficient spatial charge separation and transfer as well as a high light-harvesting ability remains a key challenge. Here, we report a facile in situ process to decorate ultrathin g-C3N4 nanosheets (NSs) with a co-catalyst, Cu2MoS4, for photocatalytic water splitting. The as-obtained Cu2MoS4/g-C3N4 exhibits a superior photocatalytic H2 evolution rate of 2170.5 μmol h−1 g−1 under visible light irradiation, which is nearly 677 and 34 times higher than that of bulk g-C3N4 and g-C3N4 NSs, respectively, and far exceeds that of most g-C3N4 catalysts modified with other sulphide co-catalysts reported in the literature, demonstrating that Cu2MoS4 can serve as a promising non-noble metal co-catalyst to couple with g-C3N4 for highly efficient photocatalysts. Structural characterization confirms the well-defined morphology of Cu2MoS4/g-C3N4 in which Cu2MoS4 hollow spheres are uniformly attached on the ultrathin g-C3N4 NSs with numerous micropores and vacancies. The optical properties indicate that Cu2MoS4/g-C3N4 possesses a superb visible light absorption ability. The photoluminescence spectra, photocurrent response, and electrochemical impedance spectra combine to prove the highly efficient separation and migration of photogenerated electrons and holes. All these factors synergistically enhance the photocatalytic activity of Cu2MoS4/g-C3N4 for photocatalytic water splitting, providing new insights into the rational design of high-performance visible light-driven photocatalysts based on earth-abundant elements.