Tailored Energy Funneling in Photocatalytic π-Conjugated Polymer Nanofibers for High-Performance Hydrogen Production.

The creation of artificial high-performance photosynthetic assemblies with a tailorable antenna system to deliver absorbed solar energy to a photosynthetic reaction center, thereby mimicking biological photosynthesis, remains a major challenge. We report the construction of recyclable, high-performance photosynthetic nanofibers with a crystalline π-conjugated polyfluorene core as an antenna system that funnels absorbed solar energy to spatially defined sensitized Co(II) porphyrin photocatalysts for the hydrogen evolution reaction. Highly effective energy funneling was achieved by tuning the dimensions of the nanofibers to exploit the very long exciton diffusion lengths (>200 nm) associated with the highly crystalline polyfluorene core formed using the living crystallization-driven self-assembly seeded growth method. This enabled efficient solar light-driven hydrogen production from water with a turnover number of over 450 for 8 h of irradiation, an H2 production rate of ca. 65 mmol h-1 g-1, and an overall quantum yield of 0.4% in the wavelength region (<405 nm) beyond the absorption of the molecular photocatalyst. The strategy of using a tailored antenna system based on π-conjugated polymers and maximizing exciton transport to a reaction center reported in this work opens up future opportunities for potential applications in other fields such as solar overall water splitting, CO2 reduction, and photocatalytic small molecule synthesis.

Seminaphthorhodafluor Derivatives Bridged Periodic Mesoporous Organosilicas for Detection of Cu2.

Seminaphthorhodafluor (SNARF) Schiff base (SNARF-SB) bridged periodic mesoporous organosilicas (SSPMOs) with "turn-on" fluorescence enhancement for sensing Cu2+ were synthesized via a template-directed co-condensation method. Small-angle x-ray scattering (SAXS) patterns, high resolution transmission electron microscope (HRTEM) images, and N2 adsorption-desorption isotherms indicated the presence of mesoporous structure in the SSPMOs. FT-IR spectra and 29Si MAS NMR data confirmed the successful incorporation of bridged organic groups in the framework of SSPMOs. The luminous properties that SSPMOs had a selective response to Cu2+ were investigated by UV-Vis absorption spectroscopy and fluorescence spectroscopy. The limit of detection (LOD) was 5.1 × 10-7 M and binding stoichiometry was determined 1:1 between SNARF-SB and Cu2+. The fluorescence enhancement of SSPMOs towards Cu2+ was induced by ring-opening of the spirolactam in SNARF-SB in framework of SSPMOs, which was confirmed by FT-IR spectra of SNARF-SB with Cu2+. Moreover, SSPMOs have improved fluorescence lifetimes compared with that of SNARF-SB. Therefore, SSPMOs can be a progressive chemical sensor for Cu2+ due to its high selectivity, recyclability, and stability.

Development of Binary Coassemblies for Sensitively and Selectively Detecting Gaseous Sarin.

The low sensitivity and poor selectivity of fluorescence sensors for real gaseous sarin detection greatly hinder their real-world applications. In this work, we report the development of a novel fluorophore with an active N-H vibration in the benzimidazole group for the sensitive detection of gaseous sarin. We demonstrate that the interactions between the nucleophilic fluorine atom in sarin and the electrophilic hydrogen atom in the benzimidazole group of the fluorophore can restrict the N-H vibration to yield sensitive fluorescence-enhancing responses. On the basis of this mechanism, the experimental and theoretical limits of detection for gaseous sarin can reach as low as 50 and 4.8 ppb, respectively. We further coassemble this fluorophore with another two D-A fluorophores containing different acceptor groups and use the resulting coassemblies as sensor array members to obtain access to differential combined responses to gaseous sarin compared with various interferents, including diethylchlorophosphate and acids. This two-member sensor array proves to be capable of detecting trace sarin in complex environments, demonstrating its potential applications in the real world.

High-Efficient Ultrathin PdCuMo Porous Nanosheets with Abundant Defects for Oxygen Reduction Reaction.

To reduce the over-dependence on Pt, Pd-based catalysts have become one of the most effective candidates for oxygen reduction reaction (ORR). In order to further accelerate the ORR kinetics and strengthen the catalytic performance of Pd catalysts, component optimization and morphology design have been adopted. Although great progress has been made, it is still difficult to obtain porous ultrathin nanosheets with excellent performance by a simple method. Here, ultrathin PdCuMo porous nanosheets (PdCuMo NSs) were successfully prepared. This structure possessed a large specific surface area with rich cavities and structural defects, significantly enhancing its ORR performance. In special, the mass activity of PdCuMo NSs was 1.46 A mg-1 at 0.90 V, which was 12.2, 8.6, and 2.7 times as high as that of Pd/C, Pt/C, and PdCuMo nanoparticles (PdCuMo NPs), respectively. In addition, it had an excellent ability to resist CO poisoning and exhibited remarkable long-term stability.

0D/1D organic ferroelectrics/multiferroics for ultrahigh density integration: Helical hydrogen-bonded chains, multi-mode switching, and proton synaptic transistors.

In recent years, room-temperature ferroelectricity has been experimentally confirmed in a series of two-dimensional (2D) materials. Theoretically, for isolated ferroelectricity in even lower dimensions such as 1D or 0D, the switching barriers may still ensure the room-temperature robustness for ultrahigh-density non-volatile memories, which has yet been scarcely explored. Here, we show ab initio designs of 0D/1D ferroelectrics/multiferroics based on functionalized transition-metal molecular sandwich nanowires (SNWs) with intriguing properties. Some functional groups such as -COOH will spontaneously form into robust threefold helical hydrogen-bonded chains around SNWs with considerable polarizations. Two modes of ferroelectric switching are revealed: when the ends of SNWs are not hydrogen-bonded, the polarizations can be reversed via ligand reorientation that will reform the hydrogen-bonded chains and alter their helicity; when both ends are hydrogen-bonded, the polarizations can be reversed via proton transfer without changing the helicity of chains. The combination of those two modes makes the system the smallest proton conductor with a moderate migration barrier, which is lower compared with many prevalent proton-conductors for higher mobility while still ensuring the robustness at ambient conditions. This desirable feature can be utilized for constructing nanoscale artificial ionic synapses that may enable neuromorphic computing. In such a design of synaptic transistors, the migration of protons through those chains can be controlled and continuously change the conductance of MXene-based post-neuron for nonvolatile multilevel resistance. The success of mimicking synaptic functions will make such designs promising in future high-density artificial neutral systems.

Photoelectrochemical Cytosensing of RAW264.7 Macrophage Cells Based on a TiO2 Nanoneedls@MoO3 Array.

We have developed a photoelectrochemical (PEC) cytosensor for ultrasensitive detection of RAW264.7 cells by the signal change of a TiO2 nanoneedles (NNs)@MoO3 array. For the first time, a TiO2 NNs@MoO3 array was adopted for the fabrication of the cytosensor for the signal output. The well-matched alignment of TiO2 NNs and MoO3 efficiently suppresses the recombination of photogenerated electron and hole (e-/h+) pairs for improved photon-to-current conversion efficiency. The RAW264.7 cell and F4/80 antibody could form the biocomplexes because of the specific recognition between each other. The constructed PEC cytosensor based on the TiO2 NNs@MoO3 array displayed good PEC property for detection of RAW264.7 cells. The numbers of RAW264.7 cells are directly detected through the decrement of photocurrent intensity, due to the increased steric hindrance when RAW264.7 cells are captured. The PEC cytosensor showed an ultrasensitive response to RAW264.7 cells with a linear range of 50-15 000 cells/mL and a detection limit of 50 cells/mL. The designed cytosensor based on a TiO2 NNs@MoO3 array offers an ideal platform to detect RAW264.7 cells with excellent stability, reproducibility, and selectivity and served as a model for the fabrication of cytosensors for other cells.

Actively Q-switched ytterbium-doped fiber laser by an all-optical Q-switcher based on graphene saturable absorber.

We demonstrate an all-optical Q-switcher based on graphene saturable absorber (GSA). Due to the cross absorption modulation (XAM) effect in graphene, we can change the transmittance of signal light periodically by introducing a train of laser pulses into graphene. This allows controlling the Q-factor of the cavity. This Q-switcher has many advantages such as all-fiber structure, all-optical modulation, broadband applications. With this Q-switcher, we have successfully fabricated an actively Q-switched ytterbium-doped fiber laser. The pulse repetition rate can be tuned from 30.32 kHz to 101.29 kHz. What's more, synchronization of the Q-switched laser pulses and modulation laser pulses can be realized, which has many potential applications such as nonlinear frequency conversion, multi-color pump probe spectroscopy and Raman scattering spectroscopy.

1,2,4-triazole-assisted metal-organic framework-derived nitrogen-doped carbon nanotubes with encapsulated Co4N particles as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries.

The design of high-performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) dual-functional catalysts is not only important for the further applications of zinc-air batteries (ZABs) but also a major challenge in the field of energy conversion. The cheap 1,2,4-triazole (1,2,4-TZ) can be decomposed easily by heat, making it a high research value in carbon catalysts derived from metal-organic frameworks (MOFs). Here, Co4N particles encapsulated at the top of N-doped carbon nanotubes (Co4N@NCNTs) were conveniently prepared by 1,2,4-TZ-assisted pyrolysis of Co-MOF-74 for the first time. Owing to the excellent activity of Co4N particles and the highly graphitized N-doped carbon nanotubes (NCNTs), Co4N@NCNTs obtained at 900 °C (Co4N@NCNT-900) exhibited astonishing catalytic performance in both ORR and OER, and high reversible oxygen bifunctional activity (ΔE = 0.685 V). Moreover, Co4N@NCNT-900 displayed a larger discharge power density (122 mW cm-2), a better specific capacity (811.8 mAh g-1), and more excellent durability during the ZAB test, implying that Co4N@NCNT-900 can act as a bifunctional high active catalyst in ZABs.

Structurally-supported PtCuCo nanoframes as efficient bifunctional catalysts for oxygen reduction and methanol oxidation reactions.

Developing highly durable and active catalysts with the morphology of structurally robust nanoframes toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acidic environment is crucial but still a great challenge to completely achieve in a single material. Herein, PtCuCo nanoframes (PtCuCo NFs) with internal support structures as enhanced bifunctional electrocatalysts were prepared by a facile one-pot approach. PtCuCo NFs exhibited remarkable activity and durability for ORR and MOR owing to the ternary compositions and the structure-fortifying frame structures. Impressively, the specific/mass activity of PtCuCo NFs were 12.8/7.5 times as large as that of commercial Pt/C for ORR in perchloric acid solution. For MOR in sulfuric acid solution, the mass/specific activity of PtCuCo NFs was 1.66 A mgPt-1/4.24 mA cm-2, which was 5.4/9.4 times as large as that of Pt/C. This work may provide a promising nanoframe material to develop dual catalysts for fuel cells.

Unconventional Ferroelectricity with Quantized Polarizations in Ionic Conductors: High-Throughput Screening.

Ferroelectricity is generally a displacive phenomenon within a unit cell in which ions are placed asymmetrically. In ionic conductors, ions can also be electrically displaced but by much longer distances. They are mostly nonpolar with symmetrical lattices due to the nondirectional character of ionic bondings. Here we propose that the combination of two such displacive modes may give rise to unconventional ferroelectricity with quantized polarizations, where even one local vacancy may induce giant polarization in ubiquitous ionic conductors. Such systems should be insulating with ion vacancies inclined to aggregate at one side. Our high-throughput screening combined with ab initio calculations provided 35 candidates, from which we select KSnS4 and Na4SnS4 to show the existence of such long ion displacement ferroelectricity with a change in integer quantum number in polarizations during switching. The polarizations can be unprecedentedly large with a moderate density of ion vacancies that can be experimentally achieved via ion deintercalation.

Ultra-high piezoelectric coefficients and strain-sensitive Curie temperature in hydrogen-bonded systems.

We propose a new approach to obtain ultra-high piezoelectric coefficients that can be infinitely large theoretically, where ferroelectrics with strain-sensitive Curie temperature are necessary. We show the first-principles plus Monte Carlo simulation evidence that many hydrogen-bonded ferroelectrics (e.g. organic PhMDA) can be ideal candidates, which are also flexible and lead-free. Owing to the specific features of hydrogen bonding, their proton hopping barrier will drastically increase with prolonged proton transfer distance, while their hydrogen-bonded network can be easily compressed or stretched due to softness of hydrogen bonds. Their barriers as well as the Curie temperature can be approximately doubled upon a tensile strain as low as 2%. Their Curie temperature can be tuned exactly to room temperature by fixing a strain in one direction, and in another direction, an unprecedented ultra-high piezoelectric coefficient of 2058 pC/N can be obtained. This value is even underestimated and can be greatly enhanced when applying a smaller strain. Aside from sensors, they can also be utilized for converting either mechanical or thermal energies into electrical energies due to high pyroelectric coefficients.

Room-Temperature Ferroelectricity in 2D Metal-Tellurium-Oxyhalide Cd7Te7Cl8O17 via Selenium-Induced Selective-Bonding Growth.

Two-dimensional (2D) ferroelectric materials have attracted increasing interest due to meeting the requirements of integration, miniaturization, and multifunction of devices. However, the exploration of intrinsic 2D ferroelectric materials is still in the early stage, for which the related reports are still limited, especially fewer ones prepared by chemical vapor deposition (CVD). Here, the ultrathin metal-tellurium-oxyhalide Cd7Te7Cl8O17 (CTCO) flakes as thin as 3.8 nm are realized via the selenium-induced selective-bonding CVD method. The growth mechanism has been confirmed by experiments and theoretical calculations, which can be ascribed to the induction of selective bonding of a hydrogen atom in H2O molecules by the introduction of selenium, leading to the generation of strong oxidants. Excitingly, switchable out-of-plane ferroelectric polarization was observed in CTCO flakes down to 6 nm at room temperature, which may be caused by mobile Cl vacancies. This work has implications for the synthesis and applications of 2D ferroelectric materials.

Strain-induced phase transition and giant piezoelectricity in monolayer tellurene.

We report the transition of a strain-induced centrosymmetric ß-phase to a non-centrosymmetric α-phase for monolayer tellurene based on density functional theory calculations. The phase transition is represented by the displacement of the middle-layer Te atoms from the center of the unit cell in the y-direction. The critical point for the phase transition is found to be at 0.5% biaxial tensile strain. By analyzing the bond variation and the phonon spectra, we attribute the phase transition to the decrease of the bonding strength at the tensile strain and the atom migration corresponding to the phonon vibration mode along the distorted direction. The transition to the α-phase under strain is further confirmed from the calculated electronic band structure where the spin-orbit coupling (SOC) induces a large Rashba splitting due to symmetry breaking, which may enable the control of spin via the electric field. Two-dimensional ferroelectrics can be formed upon transition of the strain-induced ß-phase to the α-phase, and a high polarization of about 90 µC cm-2 can be achieved via a tensile strain, giving rise to a giant piezoelectric coefficient that is two orders of magnitude higher than that of the MoS2 monolayer.

Unusual Ferroelectricity of Trans-Unitcell Ion-Displacement and Multiferroic Soliton in Sodium and Potassium Hydroxides.

We show the first-principles evidence of a hitherto unreported type of ferroelectricity with ultralong ion-displacement in sodium and potassium hydroxides. Even a small number of proton vacancies can completely change the mode of proton-transfer from intra-unitcell to trans-unitcell, giving rise to multiferroic soliton with "mobile" magnetism and a tremendous polarization that can be orders of magnitude higher compared with most perovskite ferroelectrics. Their vertical polarizations of thin-film are robust against a depolarizing field, rendering various designs of two-dimensional ferroelectric field-transistors with nondestructive readout and ultrahigh on/off ratio via sensing the switchable metallic/insulating state.

The Association between Vitamin D Deficiency and Sleep Disorders: A Systematic Review and Meta-Analysis.

Epidemiology studies have investigated the association between vitamin D and the risk of sleep disorders, but the results remain controversial. Therefore, we conducted this meta-analysis with the goal of clarifying the association between vitamin D and sleep disorders risk. All relevant studies were searched using PubMed, EMBASE, and Web of Science from inception to January 2018. Pooled odds ratios (ORs) and 95% confidence interval (CIs) were calculated using a fixed-effect model A total of nine studies (6 cross-sectional, 2 case-control, and 1 cohort studies) involving 9397 participants were included. By comparing the lowest verse highest levels of serum vitamin D, we found that participants with vitamin D deficiency (VDD) had a significantly increased risk of sleep disorders (OR: 1.50, 95% CI: 1.31, 1.72). Subgroup analysis showed that VDD also was associated with poor sleep quality (OR: 1.59, 95% CI: 1.23, 2.05), short sleep duration (OR: 1.74, 95% CI: 1.30, 2.32), and sleepiness (OR: 1.36, 95% CI: 1.12, 1.65). Subgroup analyses further indicated that serum 25(OH)D <20 ng/mL could significantly increase the risk of unhealthy sleep. This meta-analysis suggest that vitamin D deficiency is associated with a higher risk of sleep disorders. More high-quality cohort studies and randomized controlled trials (RCTs) are needed to verify this association.

Combination of Carrier Concentration Regulation and High Band Degeneracy for Enhanced Thermoelectric Performance of Cu3SbSe4.

The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu3SbSe4 has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu3SbSe4. Compared to the samples at the same Al/In doping level, the slightly Ga-doped sample presents better TE performance over the wide temperature range, and the Cu3Sb0.995Ga0.005Se4 sample presents a record high ZT value of 0.9 among single-doped Cu3SbSe4 at 623 K, which is about 80% higher than that of pristine Cu3SbSe4. This work offers an alternative approach to boost the TE properties of Cu3SbSe4 by selecting efficient dopant to weaken the coupling between electrical conductivity and Seebeck coefficient.

A new method for simultaneous measurement of Seebeck coefficient and resistivity.

A new method has been proposed and verified to measure the Seebeck coefficient and electrical resistivity of a sample in the paper. Different from the conventional method for Seebeck coefficient and resistivity measurement, the new method adopts a four-point configuration to measure both the Seebeck coefficient and resistivity. It can well identify the inhomogeneity of the sample by simply comparing the four Seebeck coefficients of different probe combinations, and it is more accurate and appropriate to take the average value of the four Seebeck coefficients as the measured result of the Seebeck coefficient of the sample than that measured by the two-point method. Furthermore, the four-point configuration makes it also very convenient to measure the resistivity by using the Van der Pauw method. The validity of this method has been verified with both the constantan alloy and p-type Bi2Te3 semiconductor samples, and the measurement results are in good agreement with those obtained by commercial available equipment.

Ultrasensitive photoelectrochemical aptasensing of miR-155 using efficient and stable CH3NH3PbI3 quantum dots sensitized ZnO nanosheets as light harvester.

An ultrasensitive photoelectrochemical (PEC) aptasensor based on a novel signal amplification strategy was developed for the quantitative determination of microRNA (miR)-155. CH3NH3PbI3 quantum dots (QDs) functionalized ZnO nanosheets (NSs) were employed as the light harvester. Owing to the synergetic effect between CH3NH3PbI3 QDs and ZnO NSs, ZnO@CH3NH3PbI3 can provide an obviously increasing PEC signal by forming the heterojunction. Due to the larger steric hindrance, the sensitive decrease of the PEC signal can be achieved by the specific recognition between the primers and ssDNA of miR-155. In this sense, this developed aptasensor can achieve a high sensitivity (especially in the presence of the low concentrations of miR-155) and a wide detection range (0.01fmol/L to 20,000pmol/L). Under the optimal conditions, the proposed aptasensor offered an ultrasensitive and specific determination of miR-155 down to 0.005fmol/L. This aptassay method would open up a new promising platform at ultralow levels for early diagnose of different miRNA.