Oxygen Vacancies Trigger Rapid Charge Transport Channels at the Engineered Interface of S-Scheme Heterojunction for Boosting Photocatalytic Performance.

Although oxygen vacancies (Ovs) have been intensively studied in single semiconductor photocatalysts, exploration of intrinsic mechanisms and in-depth understanding of Ovs in S-scheme heterojunction photocatalysts are still limited. Herein, a novel S-scheme photocatalyst made from WO3-Ov/In2S3 with Ovs at the heterointerface is rationally designed. The microscopic environment and local electronic structure of the S-scheme heterointerface are well optimized by Ovs. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that Ovs trigger additional charge movement routes and therefore increase charge separation efficiency. In addition, Ovs have a synergistic effect on the thermodynamic and kinetic parameters of S-scheme photocatalysts. As a result, the optimal photocatalytic performance is significantly improved, surpassing that of single component WO3-Ov and In2S3 (by 35.5 and 3.9 times, respectively), as well as WO3/In2S3 heterojunction. This work provides new insight into regulating the photogenerated carrier dynamics at the heterointerface and also helps design highly efficient S-scheme photocatalysts.

A Flexible, Robust, and Gel-Free Electroencephalogram Electrode for Noninvasive Brain-Computer Interfaces.

Brain-computer interfaces (BCIs) enable direct and near-instant communication between the brain and electronic devices. One of the biggest remaining challenges is to develop an effective noninvasive BCI that allows the recording electrodes to avoid hair on human skin without the inconveniences and complications of using a conductive gel. In this study, we developed a cost-effective, easily manufacturable, flexible, robust, and gel-free silver nanowire/polyvinyl butyral (PVB)/melamine sponge (AgPMS) electroencephalogram (EEG) electrode that circumvents problems with hair. Because of surface metallization by the silver nanowires (AgNWs), the sponge has a high conductivity of 917 S/m while its weight remains the same. The flexible sponge framework and self-locking AgNWs combine to give the new electrode remarkable mechanical stability (the conductivity remains unchanged after 10 000 cycles at 10% compression) and the ability to bypass hair. A BCI application based on steady-state visual evoked potential (SSVEP) measurements on hairless skin shows that the BCI accuracy of the new electrode (86%) is approximately the same as that of conventional electrodes supported by a conductive gel (88%). Most importantly, the performance of the AgPMS on hairy skin is not significantly reduced, which indicates that the new electrode can replace conventional electrodes for both hairless and hairy skin BCIs and other EEG applications.

Digital quantification of DNA by mapping polarization degree related with coding gold nanorods.

The development of highly sensitive and low-cost methods for detecting DNA is of critical importance. Here, we describe a strategy for the highly sensitive and low-cost digital detection of target DNA. Individual DNA molecules were encoded with a single gold nanorod (Au NR), which was then separated and enriched using the magnetic immune-separation process, followed by dehybridization and dispersion into a buffer solution and immobilization on glass slides for polarized dark-field microscopic imaging. With the imaging we can get the first three data sets of the Stokes vector, and the experimental degree of the linear polarization of the light scattered by the Au NR was obtained. Using the Monte Carlo simulation program, the Muller matrix of the Au NRs was simulated and the simulated degree of the linear polarization was calculated to be 0.58. Based on the experimental and simulated degree of the linear polarization, the Au NRs were identified and quantified with an in-house Matlab program, and the concentration of the target DNA at the femtomolar level was therefore achieved.

Phase intensity nanoscope (PINE) opens long-time investigation windows of living matter.

Fundamental to all living organisms and living soft matter are emergent processes in which the reorganization of individual constituents at the nanoscale drives group-level movements and shape changes at the macroscale over time. However, light-induced degradation of fluorophores, photobleaching, is a significant problem in extended bioimaging in life science. Here, we report opening a long-time investigation window by nonbleaching phase intensity nanoscope: PINE. We accomplish phase-intensity separation such that nanoprobe distributions are distinguished by an integrated phase-intensity multilayer thin film (polyvinyl alcohol/liquid crystal). We overcame a physical limit to resolve sub-10 nm cellular architectures, and achieve the first dynamic imaging of nanoscopic reorganization over 250 h using PINE. We discover nanoscopic rearrangements synchronized with the emergence of group-level movements and shape changes at the macroscale according to a set of interaction rules with importance in cellular and soft matter reorganization, self-organization, and pattern formation.

Boosting the Electrocatalytic Water Oxidation Performance of CoFe2O4 Nanoparticles by Surface Defect Engineering.

Spinel oxides have attracted widespread interest for electrocatalytic applications owing to their unique crystal structure and properties. The surface structure of spinel oxides significantly influences the electrocatalytic performance of spinel oxides. Herein, we report a Li reduction strategy that can quickly tune the surface structure of CoFe2O4 (CFO) nanoparticles and optimize its electrocatalytic oxygen evolution reaction (OER) performance. Results show that a large number of defective domains have been successfully introduced at the surface of CFO nanopowders after Li reduction treatment. The defective CFO nanoparticles demonstrate significantly improved electrocatalytic OER activity. The OER potential observed a negative shift from 1.605 to 1.513 V at 10 mA cm-2, whereas the Tafel slope is greatly decreased to 42.1 mV dec-1 after 4 wt % Li reduction treatment. This efficient Li reduction strategy can also be applied to engineer the surface defect structure of other material systems and broaden their applications.

Ultralow-temperature photochemical synthesis of atomically dispersed Pt catalysts for the hydrogen evolution reaction.

Efficient control of nucleation is a prerequisite for the solution-phase synthesis of nanocrystals. Although the thermodynamics and kinetics of the formation of metal nanoparticles have been largely investigated, fully suppressing the nucleation in solution synthesis remains a major challenge due to the high surface free energy of isolated atoms. In this article, we largely decreased the reaction temperature for ultraviolet (UV) photochemical reduction of H2PtCl6 solution to -60 °C and demonstrated such a method as a fast and convenient process for the synthesis of atomically dispersed Pt. We showed that the ultralow-temperature reaction efficiently inhibited the nucleation process by controlling its thermodynamics and kinetics. Compared with commercial platinum/carbon, the synthesized atomically dispersed Pt catalyst, as a superior HER catalyst, exhibited a lower overpotential of approximately 55 mV at a current density of 100 mA cm-2 and a lower Tafel slope of 26 mV dec-1 and had higher stability in 0.5 M H2SO4.

Room temperature Mg reduction of TiO2: formation mechanism and application in photocatalysis.

Defects in metal oxides can significantly improve their physical and chemical properties. However, the conventional methods to generate defects often require complex procedures and harsh conditions. In this study, we design a simple and room-temperature preparation route to prepare defective metal oxide nanoparticles with high yield. The formation of defects is attributed to the generation of oxygen vacancies (VO) and hydrogenation caused by charge transfer at a Mg-metal oxide junction structure. Defective TiO2 exhibits excellent performance toward wastewater cleaning and water splitting. The proposed route is promising in terms of convenience, low cost, and large-scale production.

Tuning defects in oxides at room temperature by lithium reduction.

Defects can greatly influence the properties of oxide materials; however, facile defect engineering of oxides at room temperature remains challenging. The generation of defects in oxides is difficult to control by conventional chemical reduction methods that usually require high temperatures and are time consuming. Here, we develop a facile room-temperature lithium reduction strategy to implant defects into a series of oxide nanoparticles including titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2), and cerium dioxide (CeO2). Our lithium reduction strategy shows advantages including all-room-temperature processing, controllability, time efficiency, versatility and scalability. As a potential application, the photocatalytic hydrogen evolution performance of defective TiO2 is examined. The hydrogen evolution rate increases up to 41.8 mmol g-1 h-1 under one solar light irradiation, which is ~3 times higher than that of the pristine nanoparticles. The strategy of tuning defect oxides used in this work may be beneficial for many other related applications.

Microscopic Differentiation of Plasmonic Nanoparticles for the Ratiometric Read-out of Target DNA.

The development of highly sensitive and rapid methods for detecting DNA is of critical importance. Here, we describe a strategy for the digital detection of target DNA at the femto-molar level. Individual DNA molecules were encoded with a single gold nanorod (AuNR), separated and enriched by magnetic immune-separation. The coding gold nanorods were then de-hybridized and dispersed into a gold nanosphere (AuNS) solution at a certain concentration, and both gold nanoparticles were immobilized on glass slides for dark-field microscopic imaging. Using an in-house Matlab program, the concentration of the target DNA was calculated based on the ratio of the coding gold nanorods to gold nanospheres. By combining the coding of individual biomolecules with a single gold nanorod and the use of gold nanospheres as an internal standard, a method for the rapid and accurate digital detection of target DNA to the femto-molar level was developed.