Hydrothermal synthesis and piezoelectricity of p-SnO nanoparticle/n-ZnSnO3 nanorod array heterojunction films

We investigated the hydrothermal fabrication of n-ZnSnO₃ nanorod array films decorated with various ratios of p-SnO nanoparticles on fluorine-doped tin oxide substrates and their synergistic piezoelectricity-induced applications. We used Mott–Schottky measurements and an energy band diagram to determine the materials’ conductivity type. The associated current–voltage characteristics and charge transport behavior were elucidated by investigating Schottky barriers, Schottky emissions, tunneling, depletion regions, and piezopotential-induced energy band bending. The piezoelectric coefficients (d₃₃) of the ZnSnO₃ nanorod array and the Composite II film were measured to be approximately 15.4 and 17.3 p.m.·V⁻¹, respectively. Theoretical simulation of piezopotential distributions revealed that compressive deformation was predominant for samples under stress. The Composite II film exhibited reliable piezophotodegradation activity for rhodamine B (RhB) solutions, with a degradation rate constant of approximately 1.2 × 10⁻² min⁻¹ under visible-light irradiation, approximately 2.5 times that of the individual ZnSnO₃ film, partially due to intimate contact between the two constitutive components, high electrochemical surface areas, and facilitated charge carrier transport resulting from piezopotential-induced energy band bending. This study revealed the positive effect of piezoelectricity on photodegradation and established a paradigm to allow wide-bandgap materials to function in the visible-light range through a p–n junction.     

Piezopotential‐Induced Schottky Behavior of Zn1−xSnO3 Nanowire Arrays and Piezophotocatalytic Applications

This article presents the piezotronic‐ and piezophototronic effect‐enhanced photocatalysis (piezophotocatalysis) of Zn_1?xSnO₃ (ZTO) nanowires fabricated through a two‐step hydrothermal reaction. The highlights of this research include (1) tailoring hydrothermal synthesis parameters to obtain well‐aligned LN‐type single‐crystalline ZTO nanowire arrays; (2) exploring the piezopotential‐driven piezotronic and piezophototronic effects of ZTO nanowires; (3) identifying Schottky barrier height variations; and (4) exploiting synergistic piezophotocatalysis for decomposing methylene blue (MB). Transmission electron microscopy, electron probe energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy analyses reveal highly crystalline Zn‐deficient ZTO nanowires. The band gap is estimated to be approximately 3.8 eV. The ZTO nanowires exhibit piezopotential‐modulated piezotronic and piezophototronic effects. The corresponding Schottky barrier height variation is calculated using thermionic emission‐diffusion theory. The calculated photodegradation rate constant k of the sample, under pressure from ultrasonic vibration and a piece of glass, is approximately 1.5 × 10^?2 min^?1, approximately four times higher than that of ZTO nanowires in the absence of stress. The observed synergistic piezophotocatalysis is attributed to (1) band bending of ZTO nanowires; (2) application of alternating ultrasonic vibration; (3) MB mass transfer enhancement; and (4) abundant active reaction sites generated from ZTO nanowire surface sweeping.     

Strongly enhanced piezoelectric-catalysis of ZnSnO3/graphite hybrid materials for dye wastewater decomposition

In this study, the strongly-enhanced piezoelectric catalytic performance for dye decomposition was exhibited by sol-gel-synthesized ZnSnO₃ with the addition of a certain proportion of graphite. With increasing graphite content from 0 to 5%, decomposition ratio of RhB dyes first increases and then decreases, reaching maximum value of ∼100% for the ZnSnO₃ with 3% graphite addition. Reaction rate constant reached a maximum of ∼0.098 min⁻¹ at 3% graphite content, while that of the pristine ZnSnO₃ is only ∼0.02 min⁻¹. Graphite particles can transfer piezoelectrically-negative charges, which helps to reduce the recombination of charges, thereby improving piezoelectric catalytic performance. Strong piezoelectric catalytic activity makes novel ZnSnO₃/graphite hybrid materials potential for dye decomposition from wastewater.     

Synthesis,Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays

Preferred oriented ZnFe₂O₄ nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe₂ nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe₂O₄ nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe₂O₄ nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.     

Nano Ca–Mg–Zn ferrites as tuneable photocatalyst for UV light-induced degradation of rhodamine B dye and antimicrobial behavior for water purification

We report the synthesis of Ca-doped Mg–Zn ferrite Mg_0.4Zn_(0.6-x)Ca_xFe₂O₄ nanomaterials with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 through citrate precursor approach and their structural, morphological, optical, photocatalytic, and antimicrobial properties were systematically studied. The prepared nanoferrites's cubic spinel structure with an average crystallite size of 15–38 nm was evaluated by the XRD examination. The spherical morphology of these ferrite nanoparticles was seen from scanning electron microscopy (SEM). The observed bands at 560 cm⁻¹ and 406 cm⁻¹ in the FTIR spectra confirmed the spinel structure of the synthesized nanoferrite. The optical study confirmed an optical band gap of 1.60 eV–1.86 eV. The photocatalysis was done for the degradation of rhodamine B dye solution under UV light. All the synthesized nano ferrites displayed a promising antimicrobial potential upon Candida albicans fungi. Mg_0.4Zn_0.1Ca_0.5Fe₂O₄ nanoparticles have a better photocatalytic response (99.5%) for the degradation of rhodamine B dye and show superior antimicrobial activity (96.1%) for the inhibition of Candida albicans fungi.     

Direct Growth and Photoluminescence of SiO<Subscript>x</Subscript> Nanowires and Aligned Nanocakes by Simple Carbothermal Evaporation

The growth of SiO_x nanowires and nanocakes on an Au-coated n-type-Silicon (100) substrate was achieved via carbothermal evaporation. The effects of the Au layer thickness and the rapid heating rate on the morphology of obtained SiO_x nanowires were investigated. A broad emission band from 290 to 600 nm was observed in the photoluminescence (PL) spectrum of these nanowires. There are four PL peaks: one blue emission peak 485 nm (2.56 eV) two green bands centered at 502 nm (2.47 eV) and 524 nm (2.37 eV) for nanocakes and one ultraviolet emission peak at 350 nm (3.54 eV) and a hemisphere curve over the bluish green area taken for SiO_x nanowires. These emissions may be related to the various oxygen defects and twofold coordinated silicon lone pair centers.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

Effect of Fe3+ substitution on the structural modification and band structure modulated UV absorption of hydroxyapatite

The effect of Fe³⁺ ionic substitution in hydroxyapatite (Ca_10-xFe_x(PO₄)₆(OH)₂) was studied using structural modifications, resulting in an improvement in UV absorption through a tailored optical band structure. Ca²⁺ of HA being larger compared to Fe³⁺ contributes to the shrinkage of the lattice. Undoped HA has a peak at 1085 cm⁻¹ (ʋ₃ PO₄³⁻) which is shifted to 1033 cm⁻¹ for Fe-HA, because of the perturbation in HA structure. An improvement of UV absorption in the entire UVA and UVB range with an increase in Fe content because of a decrease in bandgap from 5.9 eV to 2.1 eV with undoped and doped HA. Theoretically obtained band gap and optical behaviour of the systems are well correlated with the experimental findings. Moreover, the use of marine biowaste from cuttlefish bone, as the source of HA; low cost and promising UV absorption can have a potential application as UV protective sunscreen filters.     

Synthesis and Characterization of Tin Disulfide (SnS2) Nanowires

The ordered tin disulfide (SnS₂) nanowire arrays were first fabricated by sulfurizing the Sn nanowires, which are embedded in the nanochannels of anodic aluminum oxide (AAO) template. SnS₂ nanowire arrays are highly ordered and highly dense. X-ray diffraction (XRD) and corresponding selected area electron diffraction (SAED) patterns demonstrate the SnS₂ nanowire is hexagonal polycrystalline. The study of UV/Visible/NIR absorption shows the SnS₂ nanowire is a wide-band semiconductor with three band gap energies (3.3, 4.4, and 5.8 eV).     

Hollow ZnSnO3 cubes@carbon/reduced graphene oxide ternary composite as anode of lithium ion batteries with enhanced electrochemical performance

The ternary composite, carbon coated hollow ZnSnO₃ (ZS@C) cubes encapsulated in reduced graphene oxide sheets (ZS@C/rGO), was synthesized via low-temperature coprecipitation and colloid electrostatic self-assembly. The uniform carbon-coating layer not only plays a role in buffering the volume change of ZnSnO₃ cubes in the charging/discharging processes, but also forms three-dimensional network with the cooperation of graphene to maintain the structural integrity and improve the electrical conductivity. The results show that the reduced graphene oxide sheets encapsulated ZS@C microcubes with a typical core-shell structure of ~700 nm in size exhibit an improved electrochemical performance compared with bare ZS@C microcubes. The ZS@C/rGO electrode delivered an initial discharge capacity of 1984 mA h g⁻¹ at a current density of 0.1 A g⁻¹ and maintained a capacity of 1040 mA h g⁻¹ after 45 cycles. High specific capacity and superior cycle stability indicate that the ZS@C/rGO composite has a great potential for the application of lithium-ion anode material.     

Effect of heat treatment on the structure and photocatalytic properties of BiYO3 and BiY0.995Ni0.005O3 ceramic powders

BiYO₃ powders were synthesized by the Pechini method under low-temperature conditions. When the heat treatment was performed at T < 600 °C, a mixture of tetragonal and cubic phases was obtained, while for T ≥ 600 °C, only the fluorite-like cubic phase was observed. Based on the Rietveld refinement, approximately 2% and 1% of the tetragonal phase remained in samples calcined at 400 °C and 500 °C for 1 h, respectively. The crystal size calculated for these samples was 4.4–48.1 nm, depending on the calcination temperature. The specific surface area of the samples diminished with heat treatment and reached a minimum at 800 °C. The band gap of samples with mixed phases was close to 2.16 eV and was ~2 eV for samples with a cubic phase. Photocatalytic tests demonstrate that BiY_0.995Ni_0.005O₃ calcined at 800 °C had the best performance: it degraded more than 80% of the antibiotic oxytetracycline when irradiated with visible light. The Ni-doped BiYO₃ material could degrade the antibiotic in tap water at an environmentally relevant concentration (μg L⁻¹ levels) and showed steady activity throughout four reaction cycles.     

Hydrothermal fabrication of p-Cu2O−n-ZnO films and their properties for photodegradation and ultraviolet sensors

This article reports spin coating and hydrothermal approaches to the synthesis of Cu₂O seed layer−ZnO and Cu₂O film−ZnO heterojunction films on fluorine-doped tin oxide substrates. Cu₂O seed layers and an ethylene glycol (EG) reducing agent were employed to obtain pure, uniform, and adhesive Cu₂O films on the substrate. Transmission electron microscopy validated the heterojunctions with clear interfaces between each component on the p-Cu₂O film−n-ZnO (with EG) sample, the conductive types of which were determined through Mott−Schottky measurements. Constructed energy band diagrams supported the Mott−Schottky result, manifesting favorable conduction band positions for the generation of •O₂⁻ radicals for all constituent materials and indicating smooth charge carrier transport for the p-Cu₂O film−n-ZnO (with EG) sample. Furthermore, abundant p−n junction interfaces synergistically enabled the sample to exhibit the most satisfactory photodegradation capability (rate constant ≈ 8.9 × 10⁻³ min⁻¹), which was attributable to the predominance of •OH radicals. The sample's rectifying (diode) behavior with a ratio of the current density (J) at +3 V (forward bias) to that at −3 V (reverse bias) of approximately 27 was observed without ultraviolet illumination. Moreover, the J at −3 V is under illumination approximately 80 times that without illumination, implying the suitability of the sample for UV detectability.     

Synthesis of Yb and Sc stabilized zirconia electrolyte (Yb0.12Sc0.08Zr0.8O2–δ) for intermediate temperature SOFCs: Microstructural and electrical properties

Ceramic electrolytes based on Yb and Sc stabilized zirconia enable efficient heat transfer and effective ionic conductivity. Here, the design and synthesis of Yb and Sc stabilized zirconia electrolyte is presented for intermediate temperature solid oxide fuel cells (SOFCs). Yb_0.12Sc_0.08Zr_0.8O_2–δ was synthesized using the sol-gel method, and a thorough characterization of the electrolyte properties was conducted including structural and electrical properties. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) confirmed the composition of the electrolyte. A single-phase cubic structure with a density of 6.7041 ± 0.0008 g cm⁻³ was obtained. The thermal expansion coefficient in the temperature range from 25 °C to 800 °C is equal to 1.17 × 10⁻⁶ K⁻¹. The activation energy of 1.06 eV and 1.15 eV was obtained for the bulk and grain boundary conductivity, respectively. The ionic conductivity of approx. 2.10 S m⁻¹ was achieved at 667 °C, thus it is suitable for efficient ionic conduction at intermediate temperatures.     

Novel wide band-gap polymer utilizing fused hetero-aromatic unit for efficient polymer solar cells and field-effect transistors

Novel wide band-gap polymer of PBTFT containing dibenzosexithiophene-alt-bithiophene backbone was designed and synthesized via the Stille cross-coupling reaction. This polymer exhibited good thermal stability, well coplanar backbone and a broad absorption band from 350 nm to 610 nm with a wide optical band-gap of 2.02 eV. The polymer solar cells (PSCs) based on the PBTFT:PC₇₁BM active layer showed the power conversion efficiency of 3.0% with an open circuit voltage of 0.70 V, a short-circuit current of 7.94 mA cm⁻² and a fill factor of 53.98% under the illumination of AM.1.5, 100 mW cm⁻². Holes mobility up to 0.028 cm² V⁻¹ s⁻¹ with an on-off ratio of 1.0 × 10⁶ was obtained in the PBTFT-based organic field-effect transistors (OFETs). Our work indicates that the dibenzosexithiophene-alt-bithiophene based copolymer can be efficiently applied in PSCs and OFETs.     

Piezo-assisted photoelectric catalysis degradation for dyes and antibiotics by Ag dots-modified NaNbO3 powders

NaNbO₃ is explored as a potential candidate for catalysis due to its excellent piezoelectricity. However, its photocatalysis is significantly limited for the inherent characteristics of wide band gap. In this work, NaNbO₃ and Ag dots-modified NaNbO₃ micron-sized powders are prepared and applied in piezo-photocatalysis to explore the coupling effects. The results show that the piezocatalysis degradation efficiency of RhB solution (the initial concentration C₀ = 5 mg/L) reaches 92.3% within 30 min, and the rate constant k is 0.0889 min^?1. The efficiency of piezo-photocatalysis degradation reaches 92.7% in 25 min, and the rate constant k is 0.11 min^?1 for NaNbO₃. The rate constant k of Ag dots-modified NaNbO₃ for piezo-photocatalytic degradation of RhB (C₀ = 5 mg/L) is increased to 0.16314 min^?1. The optical and electrochemical activities of NaNbO₃-0.75hAg are studied to reveal the role of Ag nanoparticles. The band gap of NaNbO₃ is 3.59 eV, which is decreased to 3.36 eV after the modification with Ag dots. The lower band gap means that e^? in the valence band is more easily excited to shift the conduction band, which is beneficial to the photocatalytic reaction process. In addition, NaNbO₃-0.75hAg has a higher photogenerated carrier density, a faster electron-hole pair separation and transfer rate, which are beneficial to the catalytic oxidation process. The work provides a useful means to decease the band gap of NaNbO₃ and achieve outstanding piezo-photocatalysis for degradation of hazardous organic dyes in contaminated water.     

Characterization and Optical Properties of the Single Crystalline SnS Nanowire Arrays

The SnS nanowire arrays have been successfully synthesized by the template-assisted pulsed electrochemical deposition in the porous anodized aluminum oxide template. The investigation results showed that the as-synthesized nanowires are single crystalline structures and they have a highly preferential orientation. The ordered SnS nanowire arrays are uniform with a diameter of 50 nm and a length up to several tens of micrometers. The synthesized SnS nanowires exhibit strong absorption in visible and near-infrared spectral region and the direct energy gap E _g of SnS nanowires is 1.59 eV.     

Mn-modified HfO2 nanoparticles with enhanced photocatalytic activity

Round shaped Mn-modified HfO₂ nanoparticles were prepared by the Pechini type sol-gel method. The effects of Mn ions on the structure, particle growth, composition, optical properties and photocatalytic performance of HfO₂ particles were investigated. The structure analysis revealed that the insertion of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions inhibited the complete stabilization of tetragonal HfO₂. Also, the decrease of particle size to values lower than 5 nm and the shift of optical band gap from 5.7 to 2.1 eV was obtained as effect of increasing the Mn content. HfO₂ nanoparticles modified with 10 w% Mn exhibited the highest photocatalytic performance, reaching an efficiency of 91.93% in the decomposition of methylene blue, after 120 min of sunlight irradiation. The efficient trapping of photogenerated electrons on the surface of these nanoparticles generated •O₂⁻ radicals, which were the main oxidative species involved in the degradation of the dye. The improved photocatalytic performance of these nanoparticles is then attributable to their increased surface area, suitable photoactivation, and effective transport of photoexcited charge carriers. Based in studies of band gap, valence band position and active species, a mechanism of photodegradation for this photocatalyst was also proposed and discussed.     

Evolution of TiOx-SiOx nano-composite during annealing of ultrathin titanium oxide films on Si substrate

This paper discusses the formation of the TiO_x-SiO_x nano-composite phase during annealing of ultrathin titanium oxide films (~27 nm). The amorphous titanium oxide films are deposited on silicon substrates by sputtering. These films are important for high-k dielectrics and sensing applications. Annealing of these films at 750 °C in the O₂ environment (for 15–60 min) resulted in the polycrystalline rutile phase. The films exhibit Raman peaks at 150 cm⁻¹ (B_1g), 435 cm⁻¹ (E_g), and 615 cm⁻¹ (A_1g) confirming the rutile phase. The signature TO (1078 cm⁻¹) and LO (1259 cm⁻¹) infrared active vibrational modes of Si–O–Si bond confirms the presence of silicon-oxide. The X-ray photoelectron spectra of the TiO_x films show multiple peaks corresponding to Ti metal (453.8 eV); Ti⁴⁺ state (458.3 eV (Ti 2p_3/2) and 464 eV (Ti 2p_1/2)); and Ti³⁺ state (456.4 eV (Ti 2p_3/2) and 460.8 eV (Ti 2p_1/2)). The O1s XPS spectra peaks at 530–533 eV can be attributed to Ti–O and Si–O bonds of the TiO_x-SiO_x nano-composite phase in the annealed films. The depth profiling XPS study shows that the top surface of the annealed film is mainly TiO_x and the amount of SiO_x increases with the depth.     

La-doped WO3@gCN Nanocomposite for Efficient degradation of cationic dyes

In present investigation, gCN supported carbon coated Lanthanum doped tungsten oxide (C@LWO/gCN) composite were synthesized via hydrothermal approach. The photodegradation of different cationic dyes like malachite green (MG), crystal violet (CV) and methylene blue (MB) has been carried out under prepared C@LWO/gCN composite. Furthermore, the comparative photodegradation was also performed using pristine LWO and C@LWO nanowires. The synthesized samples were characterized via physiochemical techniques such as XRD, FESEM, EDX, FTIR, BET and UV/Vis spectroscopy. The results proved incorporation of La ions into WO₃ lattice and reduced band gap of doped sample which significantly boost up the capability of the material towards photodegradation. The maximum degradation was found out at pH = 6, 5 mg catalyst dose, 5 ppm dye concentration and 35 °C temperature. The achieved results proved that the trapping agents compete with prepared composite specie for the h⁺, e⁻, HO^● and O₂^●- radicals. The obtained experimental records of photodegradation of cationic dyes using C@LWO/gCN composite has correlation with pseudo first order kinetics, Langmuir-Hinshelwood model and t_1/2. The simplest facile synthetic approach, remarkable photodegradation performance against colored and colorless effluents suggest that C@LWO/gCN composite exhibit great potential for large-scale wastewater treatment.     

Nanowires embedded porous TiO2@C nanocomposite anodes for enhanced stable lithium and sodium ion battery performance

A porous carbon nanocomposite with embedded TiO₂ nanowires (NWs) was synthesized using a two-step synthetic method in which carbon matrix was obtained by carbonizing a vacuum dried gel. This unique structure in which TiO₂ nanowires uniformly distributed in and tightly bonded to the carbon matrix shortened the electron transport path and reduced the transmission resistance. Nanoporous structure ensured continuous transfer of Li⁺/Na⁺ and supplied a large specific surface area of 280.82 m² g⁻¹ to provide more active sites. Different from other existing works on TiO₂@C anode materials with TiO₂ loading higher than 60 wt%, the obtained very small amount of TiO₂ (~12 wt%) improved the electrochemical and long-cycle performance of carbon substrate with TiO₂ NWs embedded significantly, due to uniformly distributed TiO₂ NWs throughout the carbon matrix. These TiO₂@C composite anodes could deliver a specific capacity of 286 mA h g⁻¹ at 0.3 C, 197 mA h g⁻¹ at 0.15 C for lithium and sodium ion batteries, respectively. It maintained remarkably stable reversible capacities of 128 and 125 mA h g⁻¹ for lithium and sodium ion batteries at 3 C during 2500 cycles, respectively. Smaller fluctuations and smoother curves demonstrated that sodium ion storage was more stable than lithium ion storage for the TiO₂@C composite anode. In addition, the capacitive contributions of TiO₂@C in both systems are quantified by kinetics analysis.