Construction of MXene/Bi2WO6 Schottky Junction for Highly Efficient Piezocatalytic Hydrogen Evolution and Unraveling Mechanism.

For the first time, a series of MXene (Ti3C2Tx)/Bi2WO6 Schottky junction piezocatalysts were constructed, and the piezocatalytic hydrogen evolution activity was explored. Optimal Ti3C2Tx/Bi2WO6 exhibits the highest piezocatalytic hydrogen evolution rate of 764.4 µmol g-1 h-1, which is nearly 8 times higher than that of pure Ti3C2Tx and twice as high as that of Bi2WO6. This value also surpasses that of most recently reported typical piezocatalysts. Moreover, related experimental results and density functional theory calculations reveal that Ti3C2Tx/Bi2WO6 can provide unique channels for efficient electron transfer, enhance piezoelectric properties, optimize the adsorption Gibbs free energy of water, reduce activation energy for hydrogen atoms, endow robust separation capacity of charge carrier, and restrict the electron-hole recombination rate, thus significantly promoting the efficiency of hydrogen evolution reaction. Ultimately, we have unraveled an innovative piezocatalytic mechanism. This work broadens the scope of MXene materials in a sustainable energy piezocatalysis application.

Construction of an Advanced NiFe-LDH/MoS2-Ni3S2/NF Heterostructure Catalyst toward Efficient Electrocatalytic Overall Water Splitting.

Developing high-efficiency, low-cost, and earth-abundant electrocatalysts toward the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is highly desirable for boosting the energy efficiency of water splitting. Herein, we adopted an interfacial engineering strategy to enhance the overall water splitting (OWS) activity via constructing a bifunctional OER/HER electrocatalyst combining MoS2-Ni3S2 with NiFe layered double hydroxide (NiFe-LDH) on a nickel foam substrate. The NiFe-LDH/MoS2-Ni3S2/NF electrocatalyst delivers superior OER/HER activity and stability, such as low overpotentials (220 and 79 mV for OER and HER at current densities of 50 and 10 mA cm-2, respectively) and a low Tafel slope. This excellent electrocatalytic performance mainly benefits from the electronic structure modulation and synergistic effects between NiFe-LDH and MoS2-Ni3S2, which provides a high electrochemical activity area, more active sites, and strong electron interaction. Furthermore, the assembly of NiFe-LDH/MoS2-Ni3S2/NF into a two-electrode system only requires an ultra-low cell voltage of 1.50 V at a current density of 10 mA cm-2 and exhibits outstanding stability with a decay of current density of only 2.11% @50 mA cm-2 after 50 h, which is far superior to numerous other reported transition metal NiFe-LDH and MoS2-Ni3S2-based as well as RuO2||Pt-C electrocatalysts. This research highlights the rational design of heterostructures to efficiently advance electrocatalysis for water splitting applications.

Ce-regulating defect and morphology engineering for efficiently enhancing the piezocatalytic performances of BiOBr.

Cerium-doped bismuth oxybromide (1%, 5% and 10% Ce-BiOBr) piezocatalysts were synthesized. The piezocatalytic activity was efficiently regulated by defect and morphology engineering. Among them, the 5% Ce-BiOBr exhibits the highest piezocatalytic hydrogen production property with an evolution rate of 1147.6 µmol g-1 h-1, nearly twice that of the original BiOBr. Additionally, the MO dye degradation efficiency of 5% Ce-BiOBr reaches 91.9% within 60 min, with a higher reaction kinetic constant (0.0376 min-1) that was 6.1 times larger than that of pure BiOBr. These outstanding performances of 5% Ce-BiOBr surpass those of most other piezocatalytic material systems.

Rational design of CdS/BiOCl S-scheme heterojunction for effective boosting piezocatalytic H2 evolution and pollutants degradation performances.

Piezocatalysis as an emerging technology is broadly applied in hydrogen evolution and organic pollutants degradation aspects. However, the dissatisfactory piezocatalytic activity is a severe bottleneck for its practical applications. In this work, CdS/BiOCl S-scheme heterojunction piezocatalysts were constructed and explored the performances of piezocatalytic hydrogen (H2) evolution and organic pollutants degradation (methylene orange, rhodamine B and tetracycline hydrochloride) under strain by ultrasonic vibration. Interestingly, CdS/BiOCl presents a volcano-type relationship between catalytic activity and CdS contents, namely firstly increases and then decreases with the increase of CdS content. Optimal 20 % CdS/BiOCl endows superior piezocatalytic H2 generation rate of 1048.2 µmol g-1h-1 in methanol solution, which is 2.3 and 3.4 times higher than that of pure BiOCl and CdS, respectively. This value is also much higher than the recently reported Bi-based and most of other typical piezocatalysts. Meanwhile, 5 % CdS/BiOCl delivers the highest reaction kinetics rate constant and degradation rate toward various pollutants compared with other catalysts, which also exceeds that of the previously numerous results. Improved catalytic capacity of CdS/BiOCl is mainly ascribed to the construction of S-scheme heterojunction for enhancing the redox capacity as well as inducing more effective charge carriers separation and transfer. Moreover, S-scheme charge transfer mechanism is demonstrated via electron paramagnetic resonance and Quasi-In-situ X-ray photoelectron spectroscopy measurements. Eventually, a novel piezocatalytic mechanism of CdS/BiOCl S-scheme heterojunction has been proposed. This research develops a novel pathway for designing highly efficient piezocatalysts and provides a deeper understanding in construction of Bi-based S-scheme heterojunction catalysts for energy conservation and wastewater disposal applications.

Effect of Gd-Doping on Structural, Optical, and Magnetic Properties of NiFe2O4 As-prepared Thin Films via Facile Sol-Gel Approach.

In the present research work, gadolinium-doped nickel ferrite (NiFe2-x Gd x O4, x = 0-0.1) thin films have been synthesized by a facile sol-gel approach. The structural, optical, and magnetic performances of Gd-doping on nickel ferrite films have been investigated. The X-ray diffraction pattern indicated a cubic spinel ferrite structure and that the lattice parameter increased, while the crystalline size decreased with increasing the Gd concentration. Scanning electron microscopy analysis indicated that Gd-doped thin films were dense and smooth. The optical band gap value of the as-prepared thin films increased with increasing the Gd concentration. It showed that Gd-doping endowed nickel ferrite thin films with much better saturation magnetization (278.53 emu/cc) and remnant magnetization (67.83 emu/cc) at an appropriate 0.05 Gd-doping concentration. In addition, our results also revealed that the saturation magnetization remarkably increased, then sharply decreased with increasing of Gd doping content, which is attributed to effects of Gd-doping, exchange interaction, and redistribution of cations. Moreover, X-ray photoelectron spectroscopy analysis exhibited the effect of Gd-doping substitution on exchange interaction and redistribution of cations at the octahedral site and tetrahedral site.

Effective promoting piezocatalytic property of zinc oxide for degradation of organic pollutants and insight into piezocatalytic mechanism.

The piezoelectric zinc oxides with different morphology (ZnO nanoparticles and nanorods, hereafter abbreviated as ZnO NPs and NRs) are successfully synthesized using facile, green and harmless solid-state chemistry method at room temperature. The piezocatalytic activity of zinc oxide towards methylene blue (MB) of organic pollutants degradation has been explored under ultrasonic vibration. The ZnO NRs exhibit effectively enhanced piezocatalytic performance towards degradation dye compared with the ZnO NPs. In particular, the piezocatalytic decolorization ratio of MB solution is up to ~38% in ZnO NRs under 120 min, ~ 99% under 5.5 h and show good recycling utilization characteristics, indicating great potential for dye wastewater decolorization treatment. The main oxidizing hydroxyl radical (OH) and superoxide radicals (O2-) of the piezocatalytic reactions are confirmed and the production of piezocatalytic degradation process induced polarization electric charges. Moreover, we investigate the relationship between morphology and piezoelectric potential based on the finite element method for ZnO NPs and NRs, which further clarify the enhanced piezocatalytic activity and insight into piezocatalytic mechanism. This work offers a novel strategy towards wastewater decontamination applications and further understanding the relationship between piezocatalysis, morphology, and piezocatalytic mechanism in piezoelectric materials.