Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2 S4 -based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy.

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single-side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2 C3 Tx MXene quantum dots (MQDs) and α-Fe2 O3 nanodots (FO) are anchored on the surface of ZnIn2 S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S-O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high-performance composite electrodes.

Photogenerated charge separation at BiVO4 photoanodes enhanced by a Ag-modified porphyrin polymer skeleton.

Bismuth vanadate (BiVO4) has been considered a promising photoactive material in photoelectrochemical (PEC) water-splitting systems. However, the performance of BiVO4-based photoanodes is currently unsatisfactory, indicating the need for new architectural designs to improve their efficiency. In this paper, a porphyrin-phosphazene polymer (THPP-HCCP) was synthesized with a sizeable conjugated structure, and Ag particles were deposited on its surface as an organic-inorganic composite interface improvement layer. The deposition of the composite polymer film on BiVO4 resulted in a significant increase in photocurrent density, reaching up to 2.2 mA cm-2 (1.23 V vs. RHE), almost three times higher than pristine BiVO4, which benefits from the synergistic effect of Ag nanoparticles and porphyrin-phosphazene. Furthermore, photophysical and intensity-modulated photocurrent analysis demonstrated that the Ag-THPP-HCCP heterostructures could broaden the light-absorbing range and facilitate hole transfer to the semiconductor surface, resulting in an improved water oxidation process. The dynamic charge transport behavior of Ag-THPP-HCCP/BiVO4 was investigated using scanning photoelectrochemical microscopy, which showed that the rate constant (Keff) exhibits an almost 4-fold increase compared to pristine BiVO4, indicating a significant improvement in the transport of photogenerated holes. This experiment presents a novel strategy for designing high-efficiency polymer-based photoanodes.

Achieving Ultrasensitive Point-of-Care Assay for Mercury Ions with a Triple-Mode Strategy Based on the Mercury-Triggered Dual-Enzyme Mimetic Activities of Au/WO3 Hierarchical Hollow Nanoflowers.

The exploration of new strategies for portable detection of mercury ions with high sensitivity and selectivity is of great value for biochemical and environmental analyses. Herein, a straightforward, convenient, label-free, and portable sensing platform based on a Au nanoparticle (NP)-decorated WO3 hollow nanoflower was constructed for the sensitive and selective detection of Hg(II) with a pressure, temperature, and colorimetric triple-signal readout. The resulting Au/WO3 hollow nanoflowers (Au/WO3 HNFs) could efficaciously impede the aggregation of Au NPs, thus significantly improving their catalytic activity and stability. The sensing mechanism of this new strategy using pressure as a signal readout was based on the mercury-triggered catalase mimetic activity of Au/WO3 HNFs. In the presence of the model analyte Hg(II), H2O2 in the detection system was decomposed to O2 fleetly, resulting in a detectable pressure signal. Accordingly, the quantification of Hg(II) was facilely realized based on the pressure changes, and the detection limit could reach as low as 0.224 nM. In addition, colorimetric and photothermal detection of Hg(II) using the Au/WO3 HNFs based on their mercury-stimulated peroxidase mimetic activity was also investigated, and the detection limits were calculated to be 78 nM and 0.22 µM for colorimetric and photothermal methods, respectively. Hence, this nanosensor can even achieve multimode determination of Hg(II) with the concept of point-of-care testing (POCT). Furthermore, the proposed multimode sensing platform also displayed satisfactory sensing performance for the Hg(II) assay in actual water samples. This promising strategy may provide novel insights on the fabrication of a multimode POCT platform for sensitive, selective, and accurate detection of heavy metal ions.

Controlled growth of AgI nanoparticles on hollow WO3 hierarchical structures to act as Z-scheme photocatalyst for visible-light photocatalysis.

Controllable fabrication of nanomaterials with hierarchical architecture have received much attention in the field of photocatalysis due to their enhanced light-harvesting efficiency. Moreover, fabricating direct Z-scheme heterojunctions havebeenproven to be effective way to enhance the photocatalytic performance of photocatalysts. Herein, hierarchically hollow WO3 nanoflower was successfully synthesized by a simple hydrothermal treatment of tungsten chloride (WCl6) in ethanol solution. Decoration of the obtained WO3 with AgI nanoparticles in situ can form the Z-scheme AgI/WO3 hollow hierarchical nanoflowers (AgI/WO3 HHNFs). The AgI/WO3 HHNFs exhibited excellent photocatalytic activity and remarkable stability for the degradation of tetracycline hydrochloride (TC-HCl) and Eosin B (EB) under the irradiation of a low energy consume light (LED lamp, 5 W). Interestingly, compared to pure AgI nanoparticles, 3D hollow WO3 nanoflowers and AgI/WO3 nanosheets, the AgI/WO3 HHNFs revealed conspicuously enhanced photocatalytic activity. Thisphenomenon could be associated to three aspects, namely the high light-harvesting efficiency, increased light trapping and scattering capability and strongly coupled Z-scheme heterointerface, which effectively improved the photoelectron-hole sepreation efficiency. Our work therefore provide a novel insight for the fabrication of 3D hollow hierarchical structures.

Enhanced strength of nano-polycrystalline diamond by introducing boron carbide interlayers at the grain boundaries.

Polycrystalline diamond with high mechanical properties and excellent thermal stability plays an important role in industry and materials science. However, the increased inherent brittle strength with the increase of hardness has severely limited its further widespread application. In this work, we produced well-sintered nano-polycrystalline (np) diamond by directly sintering fine diamond powders with the boron carbide (B4C) additive at high pressure and high temperatures. The highest hardness value of up to ∼90 GPa was observed in the np-diamond (consisting of fine grains with a size of 16 nm) by adding 5 wt% B4C at 18 GPa and 2237 K. Moreover, our results reveal that the produced samples have shown noticeably enhanced strength and toughness (18.37 MPa m0.5) with the assistance of the soft phase at the grain boundaries, higher than that of the hardest known nano-twined diamond by ∼24% and a little greater than that of the toughest CVD diamond (18 MPa m0.5). This study offers a novel functional approach in improving and controlling the hardness and stiffness of polycrystalline diamond.