Synthesis and Characterization of Ferric Vanadate Nanorods for Efficient Electrochemical Detection of Ascorbic Acid.

This study reports the synthesis of ferric vanadate (FeVO4) via a facile hydrothermal method, focusing on demonstrating its exceptional electrochemical (EC) properties on detecting low-density ascorbic acid (AA). The phase purity, crystallinity, structure, morphology, and chemical compositional properties were characterized by employing X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy techniques. EC impedance spectroscopy and cyclic voltammetry techniques were also adopted in order to assess the EC response of a FeVO4-modified glassy carbon electrode for sensing AA at room temperature. The AA concentration range adopted in this experiment is 0.1-0.3 mM at a working electric potential of -0.13 V. The result showed functional excellence of this material for the EC determination of AA with good stability and reproducibility, promising its potentiality in connection with relevant sensing applications.

Construction of 1T-MoS2 quantum dots-interspersed (Bi1-x Fe x )VO4 heterostructures for electron transport and photocatalytic properties.

The present study reports trigonal phase molybdenum disulfide quantum dots (MoS2/QDs)-decorated (Bi1-x Fe x )VO4 composite heterostructures. Initially, (Bi1-x Fe x )VO4 heterostructure nanophotocatalysts were synthesized through the hydrothermal method decorated with 1T-MoS2 via a sonication process. 1T-MoS2@(Bi1-x Fe x )VO4 heterostructures were characterized in detail for phase purity and crystallinity using XRD and Raman spectroscopy. The Raman mode evaluation indicated monoclinic, mixed monoclinic-tetragonal and tetragonal structure development with increasing Fe concentration. For physiochemical properties, SEM, EDX, XPS, PL, EPR, UV-visible and BET techniques were applied. The optical energy band gaps of 1T-MoS2@(Bi1-x Fe x )VO4 heterostructures were calculated using the Tauc plot method. It shows a blue shift initially within a monoclinic structure then a red shift with an increase of Fe concentration. 1T-MoS2@(Bi40Fe60)VO4 with 2 wt% of 1T-MoS2-QDs carrying a mixed phase exhibited higher photocatalytic activity. The enhanced photocatalytic activity is attributed to the higher electron transportation from (Bi1-x Fe x )VO4 surface onto 1T-MoS2 surface, consequently blocking the fast electron-hole recombination within (Bi1-x Fe x )VO4. 1T-MoS2 co-catalyst interaction with (Bi1-x Fe x )VO4 enhanced the light absorption in the visible region. The close contact of small 1T-MoS2-QDs with (Bi1-x Fe x )VO4 develops a high degree of crystallinity, with fewer defects showing mesoporous/nanoporous structures within the heterostructures which allows more active sites. Herein, the mechanism involved in the synthesis of heterostructures and optimum conditions for photocatalytic degradation of crystal violet dye are explored and discussed thoroughly.

Bismuth vanadate/MXene (BiVO4/Ti3C2) heterojunction composite: enhanced interfacial control charge transfer for highly efficient visible light photocatalytic activity.

We have synthesized BiVO4/Ti3C2 nanocomposite via a low-cost hydrothermal method and investigate its photocatalytic degradation activity against monoazo (methyl orange) and diazo dye (Congo red) in an aqueous solution under visible light. The physiochemical characterization exhibited that the addition of MXene in pristine BiVO4 nanocomposite led to an increase in specific surface area and reduction in optical band gap energy. MXene also helps in enhancing visible light response via a higher electron-hole pair generation rate and long lifetime. The synthesized BiVO4/Ti3C2 heterojunction composite exhibited 99.5 % degradation efficiency within 60 min for Congo red and 99.1 % for methyl orange solution in 130 min owed to a large specific surface area (1.79 m2/g), reduced band gap (1.99 eV), and low recombination rate of charge carriers. The chemical mechanism for BiVO4/Ti3C2 nanocomposite proposes that Ti3C2 role-plays as electron capture because of the higher potential of MXenes, tuning band gap energy which paves the way to excellent photocatalytic action. This work opens a new basis for developing Ti3C2 based promising and inexpensive co-catalyst for efficient solar utilization in photocatalytic-related applications in the future.

An efficient and stable inverted perovskite solar cell involving inorganic charge transport layers without a high temperature procedure.

Despite the successful enhancement in the high-power conversion efficiency (PCE) of perovskite solar cells (PSCs), the poor stability of PSCs is one of the major issues preventing their commercialization. The attenuation of PSCs may be due to the lower heat resistance of the organic charge transport layer and the tendency to aggregate at high temperatures. Here we report cerium oxide (CeO x ) as an electron transport layer (ETL) prepared through a simple solution processed at a low temperature (∼100 °C) to replace the organic charge transport layer on top of the inverted planar PSCs. The CeO x layer has excellent charge selectivity and can provide the perovskite film with protection against moisture and metal reactions with the electrode. The solar cell with CeO x as the electron transport layer has a power conversion efficiency of 17.47%. These results may prove a prospect for practical applications.

All-Inorganic Perovskite Solar Cells Based on CsPbIBr2 and Metal Oxide Transport Layers with Improved Stability.

Despite the successful improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs), the issue of instability is still a serious challenge for their commercial application. The issue of the PSCs mainly originates from the decomposition of the organic-inorganic hybrid perovskite materials, which will degrade upon humidity and suffer from the thermal environment. In addition, the charge transport layers also influence the stability of the whole devices. In this study, inorganic transport layers are utilized in an inverted structure of PSCs employing CsPbIBr2 as light absorbent layer, in which nickel oxide (NiOx) and cerium oxide (CeOx) films are applied as the hole transport layer (HTL) and the electron transport layer (ETL), respectively. The inorganic transport layers are expected to protect the CsPbIBr2 film from the contact of moisture and react with the metal electrode, thus preventing degradation. The PSC with all inorganic components, inorganic perovskite and inorganic transport layers demonstrates an initial PCE of 5.60% and retains 5.56% after 600 s in ambient air at maximum power point tracking.

Hydrothermal synthesis of In2O3 nanoparticles hybrid twins hexagonal disk ZnO heterostructures for enhanced photocatalytic activities and stability.

In2O3 nanoparticles hybrid twins hexagonal disk (THD) ZnO with different ratios were fabricated by a hydrothermal method. The as-obtained ZnO/In2O3 composites are constituted by hexagonal disks ZnO with diameters of about 1 µm and In2O3 nanoparticles with sizes of about 20-50 nm. With the increase of In2O3 content in ZnO/In2O3 composites, the absorption band edges of samples shifted from UV to visible light region. Compared with pure ZnO, the ZnO/In2O3 composites show enhanced photocatalytic activities for degradation of methyl orange (MO) and 4-nitrophenol (4-NP) under solar light irradiation. Due to suitable alignment of their energy band-gap structure of the In2O3 and ZnO, the formation of type п heterostructure can enhance efficient separation of photo-generate electro-hole pairs and provides convenient carrier transfer paths.

Hydrothermal-Assisted Sintering Strategy Towards Porous- and Hollow-Structured LiNb3O8 Anode Material.

Porous- and hollow-structured LiNb3O8 anode material was prepared by a hydrothermal-assisted sintering strategy for the first time. The phase evolution was studied, and the formation mechanism of the porous and hollow structure was proposed. The formation of the unique structure can be attributed to the local existence of liquid phase because of the volatilization of Li element. As the anode material, the initial discharge capacity is 285.1 mAhg-1 at 0.1 C, the largest discharge capacity reported so far for LiNb3O8. Even after 50 cycles, the reversible capacity can still maintain 77.6 mAhg-1 at 0.1 C, about 2.5 times of that of LiNb3O8 samples prepared by traditional solid-state methods. The significant improvement of Li storage capacity can be attributed to the special porous and hollow structure, which provides a high density of active sites and short parallel channels for fast intercalation of Li+ ions through the surface.

Preparation and Photocatalytic Performance of Hollow Structure LiNb3O8 Photocatalysts.

Hollow structure LiNb3O8 photocatalysts were prepared by a hydrothermal method assisting sintering process. The particles' aggregation to form hollow structures with obvious cavities can be attributed to the Li element volatilization during calcination process. All the LiNb3O8 powders show high photocatalytic efficiency of degradation of methylene blue (MB), especially for the sample calcined at 700 °C (LNO700), with only 3 h to completely decompose MB. The photo-degradation of MB follows the pseudo-first-order kinetics, and the obtained first-order rate is 0.97/h. The larger degradation rate of LNO700 can be attributed to its hollow structure which provides a larger specific surface area and more active sites to degrade the MB molecules. The cycling test of photo-degradation and adsorption of MB over LNO700 powder indicates that the hollow structure of the LiNb3O8 photocatalyst is stable and the LiNb3O8 photocatalyst is an efficient photocatalyst with good reusability, confirmed by the XRD and X-ray photoelectron spectroscopy tests before and after photo-degradation of MB.

In situ polarization and dielectric property measurements of Pb(Zr0.52Ti0.48)O3 ferroelectric nanocrystals.

Pb(Zr0.52Ti0.48)O3/polycarbonate (PZT/PC) composite films with different concentration of PZT ferroelectric nanocrystals are prepared. The polarization and dielectric relaxation behavior of PZT ferroelectric nanocrystals are characterized using in situ transmittance and X-ray diffraction (XRD) measurements for the first time. It's found that 10% PZT/PC composite film has the largest orientation change and negligible dielectric relaxation after poling (the φ value of 13.8% is almost constant with time even for 168 h). Based on the XRD results, we consider that the preferential orientation of PZT nanocrystals to align in PC matrix after poling is [001] direction.

The Effects of Li/Nb Ratio on the Preparation and Photocatalytic Performance of Li-Nb-O Compounds.

The effects of Li/Nb ratio on the preparation of Li-Nb-O compounds by a hydrothermal method were studied deeply. Li/Nb ratio has a great impact on the formation of LiNbO3; the ratio smaller than 3:1 is beneficial to the formation of LiNbO3, while larger than 3:1, forms no LiNbO3 at all and the morphology and chemical bond of Nb2O5 raw material are totally modified by Li ions. The reason can be attributed to the large content of LiOH, which is beneficial to form Li3NbO4 not LiNbO3, and also, even if LiNbO3 particle locally forms, it is easily dissolved in LiOH solution with strong alkalinity. Pure LiNb3O8 powders are obtained with two absolutely opposite Li/Nb ratios: 8:1 and 1:3; the former shows a unique porous and hollow structure, quite different from the particle aggregation (the latter shows). Compared with Li/Nb = 1:3, the 4.2 times higher photocatalytic performance of LiNb3O8 (Li/Nb = 8:1) are observed and it can be attributed to the unique porous and hollow structure, which provides a high density of active sites for the degradation of MB. Compared to LiNbO3, the improved photocatalytic performance of LiNb3O8 can be attributed to its layered structure type with the reduced symmetry enhancing the separation of electrons and holes.

Visible Light-Driven Photocatalytic Performance of N-Doped ZnO/g-C3N4 Nanocomposites.

N-doped ZnO/g-C3N4 composites have been successfully prepared via a facile and cost-effective sol-gel method. The nanocomposites were systematically characterized by XRD, FE-SEM, HRTEM, FT-IR, XPS, and UV-vis DRS. The results indicated that compared with the pure N-doped ZnO, the absorption edge of binary N-doped ZnO/g-C3N4 shifted to a lower energy with increasing the visible-light absorption and improving the charge separation efficiency, which would enhance its photocatalytic activity. Compared with the pure g-C3N4, ZnO, N-doped ZnO and the composite ZnO/g-C3N4, the as-prepared N-doped ZnO/g-C3N4 exhibits a greatly enhanced photocatalytic degradation of methylene blue and phenol under visible-light irradiation. Meanwhile, N-doped ZnO/g-C3N4 possesses a high stability. Finally, a proposed mechanism for N-doped ZnO/g-C3N4 is also discussed. The improved photocatalysis can be attributed to the synergistic effect between N-doped ZnO and g-C3N4, including the energy band structure and enhanced charge separation efficiency.

Efficient Visible-Light Photocatalytic Properties in Low-Temperature Bi-Nb-O System Photocatalysts.

Low-temperature Bi-Nb-O system photocatalysts were prepared by a citrate method using homemade water-soluble niobium precursors. The structures, morphologies, and optical properties of Bi-Nb-O system photocatalysts with different compositions were investigated deeply. All the Bi-Nb-O powders exhibit appreciably much higher photocatalytic efficiency of photo-degradation of methyl violet (MV), especially for Bi-Nb-O photocatalysts sintered at 750 °C (BNO750), only 1.5 h to completely decompose MV, and the obtained first-order rate constant (k) is 1.94/h. A larger degradation rate of Bi-Nb-O photocatalysts sintered at 550 °C (BNO550) can be attributed to the synergistic effect between ß-BiNbO4 and Bi5Nb3O15. Bi5Nb3O15 with small particle size on ß-BiNbO4 surface can effectively short the diffuse length of electron. BNO750 exhibits the best photocatalytic properties under visible-light irradiation, which can be attributed to its better crystallinity and the synergistic effect between ß-BiNbO4 and α-BiNbO4. The small amount of α-BiNbO4 loading on surface of ß-BiNbO4 can effectively improve the electron and hole segregation and migration. Holes are the main active species of Bi-Nb-O system photocatalysts in aqueous solution under visible-light irradiation.

The Polymerization Effect on Synthesis and Visible-Light Photocatalytic Properties of Low-Temperature ß-BiNbO4 Using Nb-Citrate Precursor.

Low-temperature ß-BiNbO4 powders (denoted as Low-ß) were prepared by citrate and Pechini methods using homemade water-soluble niobium precursors. The addition of ethylene glycol and the resultant polymerization effect on the synthesis and visible-light photocatalytic performance of ß-BiNbO4 powders were fully investigated. The polymerization effect is beneficial to lower the phase formation temperature and obtain smaller particle catalysts. Both methods can synthesize catalysts with excellent performance of visible-light degradation of methyl violet (MV). The Low-ß BiNbO4 powder prepared by citrate method shows better degradation rate of about 1 h to decompose 80 % of MV and also displays good photocatalytic stability. The photodegradation of MV under the visible-light irradiation followed the pseudo-first-order kinetics according to the Langmuir-Hinshelwood model, and the obtained first-order rate constant and half-time are 2.85 × 10(-2) min(-1) and 24.3 min, respectively. The better photocatalytic performance of BiNbO4 powders prepared by citrate method can be attributed to its smaller band gap and better crystallinity.

The Antibacterial Activity of Ta-doped ZnO Nanoparticles.

A novel photocatalyst of Ta-doped ZnO nanoparticles was prepared by a modified Pechini-type method. The antimicrobial study of Ta-doped ZnO nanoparticles on several bacteria of Gram-positive Bacillus subtilis (B. subtilis) and Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) were performed using a standard microbial method. The Ta-doping concentration effect on the minimum inhibitory concentration (MIC) of various bacteria under dark ambient has been evaluated. The photocatalytical inactivation of Ta-doped ZnO nanoparticles under visible light irradiation was examined. The MIC results indicate that the incorporation of Ta(5+) ions into ZnO significantly improve the bacteriostasis effect of ZnO nanoparticles on E. coli, S. aureus, and B. subtilis in the absence of light. Compared to MIC results without light irradiation, Ta-doped ZnO and pure ZnO nanoparticles show much stronger bactericidal efficacy on P. aeruginosa, E. coli, and S. aureus under visible light illumination. The possible antimicrobial mechanisms in Ta-doped ZnO systems under visible light and dark conditions were also proposed. Ta-doped ZnO nanoparticles exhibit more effective bactericidal efficacy than pure ZnO in dark ambient, which can be attributed to the synergistic effect of enhanced surface bioactivity and increased electrostatic force due to the incorporation of Ta(5+) ions into ZnO. Based on the antibacterial tests, 5 % Ta-doped ZnO is a more effective antimicrobial agent than pure ZnO.

Preparation, characterization and photocatalytic properties of ZnTiO3 powders.

A novel photocatalyst ZnTiO(3) powder was prepared by a modified alcoholysis method, using ethylene glycol as reagent/solvent and acetylacetone as stabilizer. A series of analytical techniques were used to characterize the crystallinity, composition, bandgap, morphology, specific surface area and grain size of ZnTiO(3) powders. The relationship between the physicochemical property and the photocatalytic activity was deeply investigated, too. It is found that the photocatalytic activity is dependent on the phase of catalysts. The product of ZnTiO(3) with pure hexagonal-phase calcined at 800 degrees C for 3h exhibits the maximum photocatalytic performance in the photochemical degradation of the azo dye methyl violet under solar light irradiation. The processing parameters such as the concentration of catalysts and the pH value also play an important role in tuning the photocatalytic activity. The optimal concentration and pH value of the pure hexagonal-phase ZnTiO(3) is around 4g/L and 8 in a 10mg/L dye-aqueous solution, respectively.