ABSTRACT
In this study, the flexoelectric characteristics of 2D TiO2 nanosheets are examined. The theoretical calculations and experimental results reveal an excellent strain-induced flexoelectric potential (flexopotential) by an effective defect engineering strategy, which suppresses the recombination of electron-hole pairs, thus substantially improving the catalytic activity of the TiO2 nanosheets in the degradation of Rhodamine B dye and the hydrogen evolution reaction in a dark environment. The results indicate that strain-induced bandgap reduction enhances the catalytic activity of the TiO2 nanosheets. In addition, the TiO2 nanosheets degraded Rhodamine B, with kobs being ≈1.5 × 10-2 min-1 in dark, while TiO2 nanoparticles show only an adsorption effect. 2D TiO2 nanosheets achieve a hydrogen production rate of 137.9 µmol g-1 h-1 under a dark environment, 197% higher than those of TiO2 nanoparticles (70.1 µmol g-1 h-1). The flexopotential of the TiO2 nanosheets is enhanced by increasing the bending moment, with excellent flexopotential along the y-axis. Density functional theory is used to identify the stress-induced bandgap reduction and oxygen vacancy formation, which results in the self-dissociation of H2O on the surface of the TiO in the dark. The present findings provide novel insights into the role of TiO2 flexocatalysis in electrochemical reactions.
ABSTRACT
Multi-walled carbon-nanotube (MWCNT)-decorated WTe2 nanostars (WTe2@CNT nanocomposites) are to be employed for the first time as anode candidates in the development of lithium-ion (Li-ion) batteries. WTe2@CNT nanocomposites deliver a high discharge capacity of 1097, 475, 439, 408, 395 and 381 mA h g-1 with an increasing current density of 100, 200, 400, 600, 800 and 1000 mA g-1, respectively, while WTe2 nanostars exhibit a reversible capacity of 655, 402, 400, 362, 290 and 197 mA h g-1 with the aforementioned current densities. Furthermore, WTe2@CNT nanocomposites exhibit a superior reversible capacity of 592 mA h g-1 at 500 mA g-1 with a capacity retention of 100% achieved over 500 cycles, while bare WTe2 nanostars deliver â¼85 mA h g-1 over 350 cycles. This remarkable Li cycling performance is attributed to MWCNTs interconnected with WTe2 nanostars. In addition, the exposed active interlayers of the WTe2 nanostars, which are responsible for maintaining the structural integrity of the electrodes, buffer the large volume expansion within the WTe2 nanostars, avoiding the agglomeration of the particles. The layered WTe2 nanostars were synthesized via the solution-phase method, and present extremely good possibilities for the scaling-up of Li-ion battery storage systems.
ABSTRACT
The synthesis of LiNbO3-type R3C ZnSnO3 is still a challenging task under an extremely high-pressure condition. In this work, we have not only successfully synthesized R3C ZnSnO3 nanowires (NWs) through a hydrothermal process, but ZnSnO3 NWs with a high concentration of oxygen vacancies (referred to as [Formula: see text] NWs), exhibiting a highly efficient hydrogen evolution reaction compared to unannealed ZnSnO3 and ZnO NWs. The x-ray diffraction pattern and Raman spectra both confirm that the as-synthesized ZnSnO3 NWs mainly belong to the R3C space group with a second phase of ZnSn(OH)6. The conversion efficiency of the solar-to-hydrogen [Formula: see text] NWs and the unannealed ZnSnO3 NWs is 4.8% and 1.5%, respectively. The enhancement factor of the [Formula: see text] NWs is up to 320%. The photocurrent of the ZnSnO3 NWs and the [Formula: see text] NW photoelectrodes is even 5.39 and 16.23 times higher than that of the ZnO NWs, demonstrating that the high concentration of oxygen vacancies is regarded as a useful approach to enhance the photoelectrochemical response. To the best of our knowledge, this is the first report to reveal the performance of hydrogen evolution reaction by LiNbO3-type R3C ZnSnO3 NWs, which could offer a promising way of energy harvesting when using ferroelectric materials.
ABSTRACT
We demonstrate highly antibacterial activities for killing off Staphylococcus aureus and Escherichia coli using ZnO nanowires decorated with ZnO quantum dots (so-called ZnO QDs/NWs) under visible-light irradiation and dark conditions. The average size of the ZnO QDs is in the range of 3-5 nm; these were uniformly dispersed on the ZnO nanowires' surface to form the ZnO QDs/NWs. A significant blue-shift effect was observed using photoluminescence (PL) spectra. The size of the ZnO QDs is strongly dependent on the material's synthesis time. The ZnO QDs/NWs exhibited an excellent photocatalytic activity under visible-light irradiation. The ZnO QDs' active sites (i.e. the O-H bond and Zn(2+)) accelerate the photogenerated-carrier migration from the QDs to the NWs. As a consequence, the electrons reacted with the dissolved oxygen to form oxygen ions and produced hydroperoxyl radicals to enhance photocatalytic activity. The antibacterial activities (as indicated by R-factor-inhibiting activity) of the ZnO QDs/NWs for killing off Staphylococcus aureus and Escherichia coli is around 4.9 and 5.5 under visible-light irradiation and dark conditions, respectively. The hydroxyl radicals served as an efficient oxidized agent for decomposing the organic dye and microorganism species. The antibacterial activities of the ZnO QDs/NWs in the dark may be attributed to the Zn(2+) ions that were released from the ZnO QDs and infused into the microbial solution against the growth of bacteria thus disrupting the microorganism. The highly antibacterial and photocatalytic activity of the ZnO QDs/NWs can be well implanted on a screen window, thus offering a promising solution to inhibit the spread of germs under visible-light and dark conditions.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Nanowires/chemistry , Photochemical Processes , Quantum Dots/chemistry , Zinc Oxide/chemistry , Anti-Bacterial Agents/administration & dosage , Escherichia coli/drug effects , Escherichia coli/ultrastructure , Nanowires/microbiology , Particle Size , Quantum Dots/microbiology , Staphylococcus aureus/drug effects , Staphylococcus aureus/ultrastructure , Zinc Oxide/administration & dosageABSTRACT
Core-shell InSb-SiO(2) nanoballs/microballs were synthesized on a Si substrate by carbonthermal reactions at a temperature of 900 °C. High-resolution transmission microscopy (HRTEM) images revealed that the surfaces of the InSb nanoballs/microballs were covered by amorphous SiO(2) layers. On the basis of our theoretical calculation, the thermal expansion coefficient (TEC) of the InSb crystals is ten times higher than that of the SiO(2) shell. Therefore, the SiO(2) serves as a constraining shell for the InSb core so that the compressive stress of â¼-94 MPa can accumulate in the InSb core while a tensile stress of 196 MPa forms in the SiO(2) shell. The thermal excitation accumulated compressive stress in the InSb core, causing a partial structural phase transition from a cubic zinc-blende structure to a hexagonal wurtzite structure. Many lattice defects, such as stacking faults and Moiré fringes, have been observed on the surface of the InSb core. In situ temperature-dependent XRD patterns showed that a reversible InSb hexagonal (002) peak appeared and disappeared as the temperature increased and decreased at a transit point of 200 °C, respectively. As the temperature increased, the XRD diffraction peaks of the InSb wurtzite phase shifted significantly to lower angles because of the formation of compressive stress in the InSb nanoballs. The pressure-induced partial structural phase transitions of the nanostructured InSb occurred at -94 MPa of the compressive stress. This is the first report of this value, which is the lowest value in the pressure-induced phase transition of the nanostructure InSb from the cubic zinc-blende structure to the hexagonal wurtzite structure.
ABSTRACT
This study develops a single-atom Pt-loaded graphitic carbon nitride (SA-Pt/CN) and evaluates its piezo-flexocatalytic properties by conducting a hydrogen evolution reaction (HER) and Rhodamine B (RB) dye degradation test under ultrasonic vibration in the dark. SA-Pt/CN has a hydrogen gas yield of 1283.8 µmol g-1 h-1 , which is 23.3 times higher than that of pristine g-C3 N4 . Moreover, SA-Pt/CN enhances the dye degradation reaction rate by ≈2.3 times compared with the pristine sample. SA-Pt/CN exhibits lattice distortion and strain gradient enlargement caused by the single atom Pt at the N sites of g-C3 N4 , which disrupts the symmetric structure and contributes to the enhancement of piezoelectric and flexoelectric polarization. As far as it is known, this is the first study to investigate the piezo-flexocatalytic reaction of SA-Pt/CN without light irradiation and provides new insights into single-atom piezocatalysts.
ABSTRACT
A high-entropy oxide nanocomposite with Ag(CuZn)(AlCr)2O4 and CuO phases is fabricated to form an abundantly hierarchical wrinkled surface. Application of a mechanical force to the nanocomposite resulted in a nonhomogeneous strain gradient at the interface between the Ag(CuZn)(AlCr)2O4 and CuO phases, changing the local charge distribution and creating flexoelectric polarization that delayed electron/hole recombination. Transmission electron microscopy energy-dispersive X-ray spectroscopy mapping revealed that the Ag, Cu, Zn, Al, Cr, and O elements were highly distributed throughout the nanocomposite. The nanocomposite produced 2116 µmol·g-1 h-1 of H2 without external light irradiation, which is 980% higher than the H2 produced by the same nanocomposite under the photocatalytic process. A strong electrical field is observed at the interface between the Ag(CuZn)(AlCr)2O4 and CuO phases, demonstrating that a flexoelectric potential (flexopotential) is established at the structural boundaries because the strain gradient is localized at these interfaces. The nanocomposite is a promising approach for environmentally friendly energy production.
ABSTRACT
Sn-doped rutile TiO2 nanowires were synthesized by a thermal reactive evaporation route. Field emission scanning electron microscopy (FESEM) imaging reveals that the Sn-doped TiO2 nanowires exhibited diameters of 80-150 nm and 2-3 microns in length. High-resolution transmission electron microscopy (HRTEM) imaging makes it possible to observe that Sn-doped TiO2 nanowires show a certain lattices fringe of approximately 0.32 nm, which demonstrates that the nanowires are single crystalline with rutile structure and grow along the [110] axis. Cathodoluminescence (CL) reflected that on the surface of Sn-doped TiO2 nanowires, many oxygen vacancies and defect states were formed during the crystal growth. These defect states raised a broad emission peak around the red-orange band. The ethanol sensing properties of Sn-doped rutile TiO2 nanowires at a temperature of 190 degrees C for the ethanol concentrations of 50, 100, 150, 200, 400, 500, and 600 ppm, correspond to the sensor' sensitivity of 7, 12, 18, 19, 23, and 26%, respectively. The sensitivity increased with an increase in the ethanol concentration. As-synthesized TiO2 nanowires revealed a turn-on field, approximately 5.1 V/microm, at a current density of 1 microAcm(-2).
ABSTRACT
An heterologous expression of Vitreoscilla hemoglobin (VHb) for improving cell growth and recombinant protein production has been successfully demonstrated in various hosts, including Pichia pastoris. Lower temperature cultures can enhance target protein production in some studies of P. pastoris. In this study, the strategy of combining heterologous VHb expression and lower temperature cultures in P. pastoris showed that final cell density and viability of VHb+ strain at 23 °C were higher than that at 30 °C. In addition, the effects of VHb expression on recombinant β-galactosidase production and oxygen uptake rate were also higher at 23 °C than at 30 °C. Consequently, lower temperature cultures can enlarge VHb effectiveness on cell performance of P. pastoris. This is because VHb activity obtained at 23 °C cultures was twofold higher than that at 30 °C cultures, due to a different heme production. This strategy makes P. pastoris an excellent expression host particularly suitable for increasing the yields of the low-stability and aggregation-prone recombinant proteins.
Subject(s)
Bacterial Proteins/metabolism , Truncated Hemoglobins/metabolism , Bacterial Proteins/genetics , Biomass , Cell Proliferation/drug effects , Hemin/pharmacology , Oxygen/metabolism , Pichia , Recombinant Proteins/biosynthesis , Recombinant Proteins/genetics , Temperature , Truncated Hemoglobins/genetics , beta-Galactosidase/biosynthesis , beta-Galactosidase/geneticsABSTRACT
Eco-friendly energy harvesting from the surrounding environment has been triggered extensive researching enthusiasm due to the threat of global energy crisis and environmental pollutions. By the conversion of mechanical energy that is omnipresent in our environment into electrical energy, triboelectric nanogenerator (TENG) can potentially power up small electronic devices, serves as a self-powered detectors and predominantly, it can minimize the energy crisis by credibly saving the traditional non-renewable energy. In this study, we present a novel bio-based TENG comprising PDMS/α-Fe2O3 nanocomposite film and a processed human hair-based film, that harvests the vibrating energy and solar energy simultaneously by the integration of triboelectric technology and photoelectric conversion techniques. Upon illumination, the output voltage and current signals rapidly increased by 1.4 times approximately, compared to the dark state. Experimental results reveal that the photo-induced enhancement appears due to the effective charge separation depending on the photosensitivity of the hematite nanoparticles (α-Fe2O3 nanoparticles) over the near ultraviolet (UV), visible and near infrared (IR) regions. Our work provides a new approach towards the self-powered photo-detection, while developing a propitious green energy resource for the circular bio-economy.
ABSTRACT
In this work, we discover a piezoelectrocatalytic system composed of a ferroelectric heterostructure of BaTiO3 (BTO)@MoSe2 nanosheets, which exhibit piezoelectric potential (piezopotential) coupling with electrocatalyzed effects by a strain-induced piezopotential to provide an internal bias to the catalysts' surface; subsequently, the catalytic properties are substantially altered to enable the formation of activity states. The H2 production rate of BTO@MoSe2 for the piezoelectrocatalytic H2 generation is 4533 µmol h-1 g-1, which is 206% that of TiO2@MoSe2 for piezophototronic (referred to as piezophotocatalytic process) H2 generation (â¼2195.6 µmol h-1 g-1). BTO@MoSe2 presents a long-term H2 production rate of 21.2 mmol g-1 within 8 h, which is the highest recorded value under piezocatalytic conditions. The theoretical and experimental results indicate that the ferroelectric BTO acts as a strain-induced electric field generator while the few-layered MoSe2 is facilitating piezocatalytic redox reactions on its active sites. This is a promising method for environmental remediation and clean energy development.
ABSTRACT
The continuous quest to enhance the output performance of triboelectric nanogenerators (TENGs) based on the surface charge density of the tribolayer has motivated researchers to harvest mechanical energy efficiently. Most of the previous work focused on the enhancement of negative triboelectric charges. The enhancement of charge density over positive tribolayer has been less investigated. In this work, we developed a layer-by-layer assembled multilayer graphene-based TENG to enhance the charge density by creatively introducing a charge trapping layer (CTL) Al2O3 in between the positive triboelectric layer and conducting electrode to construct an attractive flexible TENG. Based on the experimental results, the optimized three layers of graphene TENG (3L-Gr-TENG) with CTL showed a 30-fold enhancement in output power compared to its counterpart, 3L-Gr-TENG without CTL. This remarkably enhanced performance can be ascribed to the synergistic effect between the optimized graphene layers with high dielectric CTL. Moreover, the device exhibited outstanding stability after continuous operation of >2000 cycles. Additionally, the device was capable of powering 20 green LEDs and sufficient to power an electronic timer with rectifying circuits. This research provides a new insight to improve the charge density of Gr-TENGs as energy harvesters for next-generation flexible electronics.
ABSTRACT
Water pollution is one of the leading causes of death and disease worldwide, yet mitigating it remains a challenge. This paper presents an efficient new strategy for the processing of wastewater utilizing an accessible redox reaction with MoSe2 nanoflowers, which shows a strong oxidizing ability and permits the decomposition of dye molecules in dark environments without the need for an external power source. This reaction can treat wastewater at a decomposition rate above 0.077 min-1 , even when interacting with organic pollutants at concentrations up to 1500 ppm. Theoretical calculations by Dmol3 simulation elucidates that the reactions proceed spontaneously, and the kinetic constant (kobs ) for this redox reaction with 10 ppm RhB dye is 0.53 min-1 , which is 65 times faster than the titanium dioxide photocatalytic wastewater treatment. More importantly, the residual waste solution can be further utilized as a precursor to reconstruct the MoSe2 nanoflowers. To demonstrate the effectiveness and reusability, the treated effluent is directly used as the sole source of irrigated water for plants with no adverse effect. This method offers an eco-friendly and more accessible way to treat industrial wastewater with zero-discharge.
ABSTRACT
This work reports a new approach to amending polydimethylsiloxane (PDMS) by supporting α-Fe2O3 nanoparticles (NPs), thereby generating a material suitable for use as a negative triboelectric material. Additionally, human hair exhibits a profound triboelectrification effect and is a natural regenerative substance, and it was processed into a film to be used as a positive triboelectric material. Spatial distribution of α-Fe2O3 NPs, the special surface morphologies of a negative tribological layer containing nano-clefts with controlled sizes and a valley featuring a positive tribolayer based on human hair made it possible to demonstrate facile and scalable fabrication of a triboelectric nanogenerator (TENG) presenting enhanced performance; this nanogenerator produced a mean peak-to-peak voltage of 370.8 V and a mean output power density of 247.2 µW cm-2 in the vertical contact-separation mode. This study elucidates the fundamental charge transfer mechanism governing the triboelectrification efficiency and its use in harvesting electricity for the further development of powerful TENGs suitable for integration into wearable electronics and self-charging power cells, and the work also illustrates a recycling bioeconomy featuring systematic utilization of human hair waste as a regenerative resource for nature and society.
Subject(s)
Electric Power Supplies , Nanoparticles , Electricity , Electronics , Humans , NanotechnologyABSTRACT
Single crystal wafers, such as silicon, are the fundamental carriers of advanced electronic devices. However, these wafers exhibit rigidity without mechanical flexibility, limiting their applications in flexible electronics. Here, we propose a new approach to fabricate 1.5 in. flexible functional zinc oxide (ZnO) single crystal wafers with high electron mobility (>100 cm2 V-1 s-1) and optical transparency (>80%) by a combination of thin-film deposition, a chemical solution method, and surficial treatment. The uniformity of the flexible single crystal wafers is examined by an advanced scanning X-ray diffraction technique and photoluminescence spectroscopy. The transport properties of ZnO flexible single crystal wafers retain their pristine states under various bending conditions, including cyclability and endurability. This approach demonstrates a breakthrough in the fabrication of the flexible single crystal wafers for future flexible optoelectronic applications.
ABSTRACT
A p-type ethanol sensor with a response time of approximately 8.3 s at room temperature was produced by SnO(2):Sb nanowires. The electrical properties of p-type SnO(2) nanowires are stable with a hole concentration of 1.544 x 10(17) cm(-3) and a field-effect mobility of 22 cm(2) V(-2) S(-1). X-ray photoelectron spectroscopy (XPS) and Hall measurement revealed that as-synthesized nanowires exhibit p-type behavior. A comprehensive investigation of the p-type sensing mechanism is reported.
Subject(s)
Antimony/chemistry , Chemistry Techniques, Analytical/methods , Ethanol/analysis , Nanowires/chemistry , Tin Compounds/chemistry , Nanowires/ultrastructure , Photoelectron Spectroscopy , Sensitivity and Specificity , TemperatureABSTRACT
High density Sb-doped SnO2 nanobelts and beak-like nanorods were synthesized on alumina substrates using thermal evaporation. X-ray diffraction (XRD) pattern shows that both the nanobelts and beak-like nanorods are single crystals with the tetragonal rutile structure. Transmission electron microscopy (TEM) images show that the nanobelts grow along the [110] direction, but the nanorods grow with an abrupt change from the [101] direction to the [301] direction. X-ray photoelectron spectroscopy (XPS) analysis shows that the Sb 3d 3/2 peak of not fully oxidized beak-like nanorods shifts from 540.5 eV to 535.4 eV, and the Sn 3d 3/2 peak also shifts from 496.3 eV to 492.8 eV. Room temperature cathodoluminescence (CL) measurements show that both the nanobelts and beak-like nanorods exhibit blue and orange emissions that are related to the interstitial defects and oxygen deficiencies. The comparative study of CL measurements between nanobelts and beak-like nanorods demonstrate that the optical properties can be modified by altering the oxygen deficiencies.
ABSTRACT
Intense light attenuation in water/wastewater results in photocatalysts exhibiting a low quantum efficiency. This study develops a novel piezoelectrocatalysis system, which involves quartz microrods (MRs) abundantly decorated with active-edge-site MoS2 nanosheets to form a quartz microrods@few-layered MoS2 hierarchical heterostructure (QMSH). Through theoretical calculations, it is found that the quartz MRs serve as a parallel-plate capacitor, which is self-powered to provide an internal electric field to the few-layered MoS2 nanosheets surrounding the quartz MR surfaces, and the piezoelectric potential (piezopotential) effectively facilitates redox reactions with the free carriers in MoS2 . The self-powered quartz MRs in the QMSH present an internal bias to the MoS2 nanosheets, thus yielding a piezoelectrocatalysis system. An efficient piezoelectrocatalytic hydrogen evolution reaction and decomposition of wastewater without light irradiation can be achieved simultaneously. The second-order rate constant of the QMSH is ≈0.631 L mg-1 min-1 , which is 650-fold that of quartz MRs, indicating that the piezoelectric heterostructural catalysts display exceptionally high efficiency on piezoelectrocatalytic redox reactions rather than in the piezocatalytic process. The H2 -production rate of QMSH catalysts approaches ≈6456 µmo1 g-1 h-1 and peaks at ≈16.8 mmol g-1 in 8 h. The piezoelectrocatalytic process may be a promising method for treating industrial wastewater and producing clean energy.
ABSTRACT
In the era of Internet of Things, the demand for flexible and transparent electronic devices has shifted to the forefront of materials science research. However, the radiation damage to key performance of transparent devices under radiative environment remains as a critical issue. Here, we present a promising technology for nonvolatile transparent electronic devices based on flexible oxide heteroepitaxy. A direct fabrication of epitaxial lead lanthanum zirconate titanate on transparent flexible mica substrate with indium tin oxide electrodes is presented. The transparent flexible ferroelectric heterostructures not only retain their superior performance, thermal stability, reliability, and mechanical durability, but also exhibit remarkably robust properties against to a strong radiation exposure. Our study demonstrates an extraordinary concept to realize transparent flexible nonvolatile electronic devices for the design and development of next-generation smart devices with potential application in electronics, automotive, aerospace, and nuclear systems.
ABSTRACT
Single- and few-layer MoS2 nanoflowers are first discovered to have a piezo-catalyst effect, exhibiting an ultra-high degradation activity in the dark by introducing external mechanical strains. The degradation ratio of the Rhodamine-B dye solution reaches 93% within 60 s under ultrasonic-wave assistance in the dark.