Pure NaNbO3 Research Articles

Cu-doped NaNbO3 nanorods: Enhanced photocatalytic activity for RhB dye removal and antibacterial activity against E. coli

Sodium niobate (NaNbO3) nanorods with Cu (0.00, 0.01, 0.02 and 0.04 mmol) insertion were prepared by the microwave-assisted hydrothermal method and the photocatalytic and antibacterial activity was explored for the first time. X-ray diffraction confirms the coexistence of two orthorhombic phases (P21ma and Pbma) for all samples, with the percentage of each phase being strongly influenced by doping. The micrographs reveal that doping did not alter the shape or size of the grains (nanorods, with a diameter of ∼200 nm and a length of tens micrometers). The samples of pure NaNbO3 and those with 0.01 and 0.02 mmol of Cu showed an average band gap value of 3.08 eV. However, the sample containing 0.04 mmol of Cu exhibited a slight redshift. The photocatalytic activity of the samples was assessed by the removal of Rhodamine B dye (RhB), under ultraviolet light. All doped samples exhibited superior performance, with the sample containing 0.02 mmol of Cu showing the best photocatalytic activity, achieving 100 % RhB removal in 50 min. This was attributed to a lower rate of recombination of photogenerated charges, as evaluated through photoluminescence analysis. Additionally, the photocatalyst demonstrated excellent recyclability over three cycles. Pure NaNbO3 nanorods showed no antibacterial activity, but doping with 0.04 mmol of Cu reduced the growth of Escherichia coli.

Revealing the role of B-site cations in the antiferroelectricity of NaNbO3-based perovskites

The promising prospects of antiferroelectric perovskite oxides in the realm of energy storage applications hinge on the unique field-induced phase transitions. Once the transition is triggered by the application of an electric field, characteristic double polarization loops appear. However, NaNbO3-based materials that exhibit a reversible phase transition are still rare, which hinders the practical applications of lead-free antiferroelectrics. Here, the impact of materials chemistry on the competition between antiferroelectric and ferroelectric states is demonstrated in a series of NaNbO3-based solid solutions with varying perovskite B-site cations, while the A-site is fixed as strontium. The crystal structure is analyzed on the basis of Rietveld refinement of high-energy X-ray diffraction data. The phase transition behavior as well as the antiferroelectric and ferroelectric properties are probed by a series of electrical measurements. The antiferroelectric phase is universally observed for all investigated materials in the virgin state. The SrTiO3-substituted system shows an irreversible phase transition similar to that of pure NaNbO3. In contrast, double polarization hysteresis loops are observed in the SrHfO3-, SrZrO3-, and SrSnO3-substituted systems. It is confirmed that compounds that can reduce the tolerance factor of the system contribute to the stabilization of the antiferroelectric order, while those that can reduce the electronegativity difference lead to more pronounced double loops. The competition between antiferroelectricity and ferroelectricity is linked to the competition between covalent and ionic bonding in perovskites.

Photocatalytic activity in graded off-valent cations substituted NaNbO3

This study investigates the impact of off-valent doping on the photocatalytic properties of NaNbO3 concerning the degradation of Methylene Blue. Compositions with x values of 0.00 (representing pure NaNbO3, denoted as NBO) and 0.05 within the material system Na1-xAxNbO3 (where A is K1+, Ba2+, La3+, abbreviated as K-NBO, Ba-NBO, and La-NBO respectively) were synthesized using the conventional solid-state reaction method. The UV–visible analysis revealed a decrease in the band gap for samples K-NBO and Ba-NBO, while an increase was observed for sample La-NBO. Raman modes of lower wave numbers merged and shifted towards the higher wave number side. The determination of valence band edge and conduction band edge involved computational analysis based on XPS survey scans, and the band gap energy values were derived from UV–Visible spectroscopy results. Examining the band diagram of the samples (NBO, K-NBO, Ba-NBO, and La-NBO) in conjunction with the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of MB dye provided insights into potential degradation mechanisms. Photocatalytic dye degradation experiments for Methylene Blue demonstrated that doping increased the degradation efficiency of samples K-NBO, Ba-NBO, and La-NBO compared to NBO. Among all NaNbO3 based prepared samples, Ba-NBO exhibited the highest degradation efficiency of 96%, however slightly less than the reference sample P25 TiO2.

Core–shell engineered g-C3N4 @ NaNbO3 for enhancing photocatalytic reduction of CO2

Photocatalytic reduction of carbon dioxide is a technology that effectively utilizes CO2 and solar energy. Sodium niobate (NaNbO3) has received much attention in the field of photocatalysis due to its excellent photocatalytic properties. However, the application of NaNbO3 in the field of photocatalysis is still limited by poor reaction to visible light and easy recombination of photo-generated carriers. Heterojunction with g-C3N4 to construct core–shell structure can effectively improve the above problems. Combining the two can design a core–shell composite material that is beneficial for photocatalytic reduction of CO2. Herein, we prepared a core–shell heterojunction g-C3N4/NaNbO3 by uniformly impregnating urea on the surface of NaNbO3 chromium nanofibers with NaNbO3 nanofibers prepared by electrospinning as a catalyst carrier, and urea as a precursor of g-C3N4. The core–shell structure of g-C3N4/NaNbO3 was verified by a series of characterization methods such as XPS, XRD, and TEM. It was found that under the same conditions, the methanol yield of core–shell g-C3N4/NaNbO3 was 12.86 μmol·g−1·h−1, which is twice that of pure NaNbO3 (6.67 μmol·g−1·h−1). This article highlights an impregnation method to build core–shell structures for improved photocatalytic reduction of CO2.

Studies on structural, optical and electrical behavior of La and Cr modified NaNbO3 (x ≤ 0.15)

Samples with compositions x ≤ 0.15 in the material system Na1-xLaxNb1-xCrxO3 have been prepared by conventional solid-state reaction method. Rietveld refined XRD patterns show the formation of single phase with orthorhombic (Pbcm) structural symmetry. FTIR spectra show the shifting of bands towards higher wavenumber side with dopant concentration x. UV–visible spectra show the red shift of absorption edge resulting in decrease of the band gap with x. SEM images show the decrease in the average grain size with La and Cr doping. X-Ray photoelectron spectra of a few samples have been recorded to analyze the oxidation states of various elements and oxygen vacancies estimation. Dielectric plots exhibited two anomalies, one at 404K and the other one at 610K for pure NaNbO3 over the temperature range from 300K to 773K. The high temperature dielectric anomaly at 610K for x = 0 has disappeared for higher x and dispersion above 500K becomes more prominent. Tanδ with temperature plots show almost two anomalies for x = 0 which seems to be disappeared with increasing x. The conductivity is found to increase with increasing dopant concentration.

Construction of [NbO]6-x -xS Structure to Change Charge Density and Regulate Spontaneous Polarization to Achieve Efficient Pyro-Photo-Electric Water Splitting System of NaNbO3.

Pyroelectric materials in the field of photoelectrochemical (PEC) water splitting still face the problems of difficult low spontaneous polarization intensity and excessive carrier recombination. Based on the above problems, we altered the interaction between S-Nb-S in the [NbO]6-x -xS structure, and the constructed [NbO]6-x -xS structure achieved the regulation of charge density change and spontaneous polarization. The results show that under the stimulation of light and temperature fluctuations, the current density of the NS-4 photoanode is as high as 0.574 mA/cm2 at 1.23 VRHE , which is about 1.59 times higher than the pure NaNbO3 current density value, and the NS -4 photoanode achieves IPCE value of 16.08 %. The first-principles density-functional theory calculations (DFT) reveal the principle of the [NbO]6-x -xS structure for the suppression function of the carrier recombination and the improvement function of the pyroelectric effect. The analysis shows that the S-doping leads to the weakening of S-Nb-S interactions in the [NbO]6-x -xS structure, which improves the pyroelectric effect and suppresses the photo/pyro-generated carrier recombination, and effectively enhances the performance of the pyro-photo-electric synergistic water splitting system. This work promotes the development of pyroelectric materials in the field of photoelectrochemical water splitting.

High energy storage properties of NaNbO3-based relaxor antiferroelectric ceramics for capacitor applications

A new generation of environmentally benign NaNbO3 (NN)-based antiferroelectric ceramics have gained great interest in energy storage capacitors. Nevertheless, the low breakdown electric field (Eb) and high energy density loss in pure NN ceramic restrict the improvement of the energy storage property. A combined optimization strategy was implemented in this work, and ceramics of (1-x)NaNbO3-x(Bi1/2Li1/2)HfO3 (abbreviated as NN-xBLH, x = 0.00–0.18) were developed. BLH was initially introduced to stablize the AFE state and achieve the relaxor enhancement effect. Then, a viscous polymer rolling process (VPRP) was empolyed to obtain highly dense and ultra-thin ceramic disks with a thickness of ∼100 μm. Ultimately, at 560 kV/cm, a high Wrec of 7.1 J/cm3 and η of 85.9% were concurrently attained in the NN-0.18BLH ceramic. Meanwhile, the NN-0.18BLH ceramic displays improved thermal stability (25–120 °C). All of these findings show that the NN-0.18BLH ceramic is anticipated to be utilized in future energy storage applications.

High-Pressure Vibrational and Structural Studies of the Chemically Engineered Ferroelectric Phase of Sodium Niobate

Pure NaNbO3 has an antiferroelectric phase at ambient pressure. The structural behaviour of the chemically engineered ferroelectric phase of sodium niobate, NNBT05: [(0.95) NaNbO3-(0.05) BaTiO3], under high-pressure has been studied using Raman scattering and angle-dispersive synchrotron X-ray diffraction techniques. At pressure > 1 GPa, noticeable changes in the Raman spectra can be seen in the low wavenumber modes (150–300 cm−1). Large changes in the positions and intensities of the Raman bands as a function of pressure provide evidence for structural phase transition. The results indicate significant changes in the bond-lengths and the orientation of the NbO6 octahedra at ~1 GPa, and a transition to the paraelectric phase at ~5 GPa, which are at lower pressures than previously found in pure NaNbO3. The powder X-ray diffraction pattern shows an appreciable change in the peak profile in terms of position and width on increasing pressure. The pressure dependences of the structural parameters show that the response of the lattice parameters to pressure is strongly anisotropic. By fitting the pressure–volume data using the Birch–Murnaghan equation of state, the isothermal bulk modulus was estimated. The experimental results suggest that on doping BaTiO3 in NaNbO3, the bulk modulus increases. The bulk modulus of NNBT05 has been estimated to be 164.5 GPa, which is fairly close to 157.5 GPa, as previously observed in NaNbO3.

Synthesis and dielectric behaviour of La and Cr modified NaNbO3 (x ≤ 0.06)

Compositions with x = 0 and x = 0.06 in the material system Na1-xLaxNb1-xCrxO3 are prepared by conventional solid-state reaction method. XRD results show that all the prepared samples exist in single phase having orthorhombic structure with Pbcm space group symmetry. UV results show a decrease in band gap with x = 0.06. FTIR results show the shifts of bands towards higher wavenumber side for x = 0.06. Dielectric plots from room temperature to 773 K show two anomalies one at 404 K and other at 610 K for pure NaNbO3. For La and Cr doped sample with x = 0.06, the anomaly appearing at 404 K for pure sample is suppressed and a new anomaly starts appearing at 490 K. Also, the anomaly appearing at 610 K in NaNbO3 has disappeared and the signature of anomaly at 695 K is seen in modified NaNbO3 with x = 0.06.

Preparation of BaTiO3/NaNbO3 composite ceramics based on the [101]-oriented NaNbO3 crystals and their dielectric properties

NaNbO3 (NN) crystals with preferential growth of the [101] crystal axis were prepared by the molten salt method. Based on use of the prepared [101]-oriented NN powder as the raw material, BT/NN composite ceramics were prepared by the conventional solid-state reaction method. The effects of the amount of NN and sintering temperature on the microstructure and dielectric properties of the BT/NN composite ceramics were systematically studied. The optimal component ratio for the preparation of composite ceramics was explored by adjusting the contents of BT and NN. When BT: NN is 5 : 5, the dielectric constant of the BT/NN composite is 1112, which is higher than the dielectric constant of the single-component BT of 658 and NN of 550. Simultaneously, the phase transition temperature of composite ceramics is approximately 416 °C, which is significantly higher than the phase transition temperature of pure NN of 338 °C, further improving the phase stability of the NN structure. The preparation of BT/NN composite ceramics provides important guidance for the design of the ferroelectric-antiferroelectric composites and improvement of lead-free piezoelectric ceramics.

Band gap tunning to enhance photovoltaic response in NaNbO3-based bulk ferroelectrics

The observation of anomalous photovoltaic effect and switchable photocurrent in ferroelectrics receive extensive attention for its great advantages in next-generation high-performance photovoltaic devices, but the key factor, the wide band gap results in low photocurrent output and photoelectric conversion efficiency. Focusing on narrowing band gap to improve photovoltaic performance in NaNbO3, in this work, we fabricated the NaNbO3 and 0.8NaNbO3-0.2La(Mn0.5Ni0.5)O3 (abbreviated as 0.2NLMNO) ferroelectric ceramics through a solid state method. The optical absorption spectra reveal the band gap of ceramics reduce from 3.42 eV to 2.11 eV and the light absorption in visible region is significantly enhanced. A higher symmetry of crystal structure and great reduced resistance of grain and grain boundary induced by introducing La(Mn0.5Ni0.5)O3. What's more, the photocurrent density of 0.2NLMNO improves approximately 10 times larger than that of pure ferroelectric NaNbO3, it is expected to explore a new ferroelectric material with photovoltaic effect.

Surfactant-bridged forming of core-shell NaNbO3@g-C3N4 microcuboid: An approach to produce semiconductor heterojunction

The separation of photoexcited carriers affects critically the photoelectric properties of semiconductor materials. Heterostructure forming between suitable semiconductors can drive effectively the carriers towards different directions at the interface thus promote the separation. In this research, various surfactants, including anionic sodium dodecyl sulphate, cationic polyethylenediamine and hexadecyltrimethylammonium bromide (CTAB), were applied to fabricate perovskite NaNbO3@graphitic carbon nitride (g-C3N4) heterostructures and the resulting photoelectric performances were compared. In the presence of CTAB, a core-shell microstructure with uniform g-C3N4 coating on NaNbO3 microcuboid was obtained and exhibited the highest photocatalytic, which is 33 times higher than that of pure NaNbO3, as well as the highest photoresponse properties among all the synthesized structures. The formation mechanism of core-shell NaNbO3@g-C3N4 composite and reasons for the photoelectric property enhancement were discussed based on the heterostructure model. Our results propose that surfactant-assisted method can provide a feasible approach to fabricate the semiconductor heterojunction by bridging the constructing components.

Domain morphology of newly designed lead‐free antiferroelectric NaNbO3‐SrSnO3 ceramics

AbstractReversible antiferroelectric‐ferroelectric phase transitions were recently observed in a series of SrSnO3‐modified NaNbO3 lead‐free antiferroelectric materials, exhibiting well‐defined double polarization hysteresis loops at ambient conditions. Here, transmission electron microscopy was employed to investigate the crystallography and domain configuration of this newly designed system via electron diffraction and centered dark‐field imaging. It was confirmed that antiferroelectricity is maintained in all compositions, manifested by the characteristic ¼ superlattice reflections in the electron‐diffraction patterns. By investigating the antiferroelectric domains and domain boundaries in NaNbO3, we demonstrate that antiphase boundaries are present and their irregular periodicity is responsible for the streaking features along the ¼ superlattice reflections in the electron‐diffraction patterns. The signature domain blocks observed in pure NaNbO3 are maintained in the SrSnO3‐modified ceramics, but disappear when the amount of SrSnO3 reaches 7 mol.%. In particular, a well‐defined and distinct domain configuration is observed in the NaNbO3 sample modified with 5 mol.% SrSnO3, which presents a parallelogram domain morphology.

In Situ Corrosion Fabrication of NaNbO3 /Nb3 O7 F Heterojunctions with Optimized Band Realignment for Enhanced Photocatalytic Hydrogen Evolution.

Heterostructured photocatalysis is a significant issue owing to the unique band alignment, improved spectrum absorption, and enhanced photocatalytic activity. However, the construction of uniform, controllable, and effective heterojunctions is still a huge challenge. Herein, NaNbO3 /Nb3 O7 F heterojunctions are fabricated through an in situ corrosion technique for the first time. The influence of phase transformation on the hydrogen evolution reaction (HER) activity is investigated systematically in terms of photocatalytic water splitting for H2 production. Interestingly, the band realignment and good interfacial contact endow the NaNbO3 /Nb3 O7 F heterojunctions with a high HER activity (43.3 mmol g-1 h-1 ), which is about 2.4 times that of pure Nb3 O7 F and 1.36 times that of pure NaNbO3 . The results may provide some new insights into the corrosion technique and HER activity of novel heterostructured catalysts.

Synthesis, characterization, and visible light–induced photocatalytic evaluation of WO3/NaNbO3 composites for the degradation of 2,4-D herbicide

In this research study, WO3/NaNbO3-coupled photocatalysts were synthesized at three WO3 mass ratios (15, 85, and 95 wt%) and characterized. These composites were characterized via X-ray powder diffraction, N2 physisorption, UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and photoluminescence techniques. For comparison, bare WO3 and NaNbO3 were also synthesized and characterized. 2,4-Dichlorophenoxyacetic acid (2,4-D) was degraded under visible light to evaluate its photocatalytic performance. The WO3 (95 wt%)/NaNbO3 composite showed higher photocatalytic activity than pure WO3 and NaNbO3 and even than the 15 and 85 wt% coupled materials; thus, the combination with the highest ratio of WO3 with respect to NaNbO3 showed increased photocatalytic activity compared with the bare materials.

Construction of dual ion (Fe3+/Fe2+ and Nb5+/Nb4+) synergy and full spectrum 1D nanorod Fe2O3/NaNbO3 photo-Fenton catalyst for the degradation of antibiotic: Effects of H2O2, S2O82− and toxicity

Designing a green and efficient catalyst to effectively degrade antibiotics is still one of the hot topics of research. Firstly, 1D nanorod Fe2O3/NaNbO3 composite was successfully prepared by the two steps strategy through hydrothermal combined calcination method. In addition, the photocatalytic activity of the samples was evaluated by the degradation of tetracycline (TC) under visible light irradiation. The test results show that the 5% Fe2O3/NaNbO3 nanorod material exhibits superior degradation rate of TC (89.4% removal efficiency in 90 min), and shows 5.62 times than that of NaNbO3 nanorods. Under UV–visible light irradiation, 5% Fe2O3/NaNbO3 nanorod composite with H2O2 solution can degrade 97.4% of TC in 60 min, which is 12.1 times greater to that of the pure NaNbO3 nanorods. The outstanding degradation performance may be attributed to the introduction of Fe2O3 nanoparticles, which can activate H2O2 more efficiently and produce more free radicals to degrade pollutants. At the same time, the 5% Fe2O3/NaNbO3 nanorod composite can also act as an activate persulfate (PS) and generate SO4− to efficiently degrade TC. In addition, the catalyst also showed good performance in degrading TC in the presence of different anions and cations. Plant growth experiment (mung bean seeds) results showed that the degradation products have obvious lower toxicity. This study provides new domain about the designing of a photo-Fenton catalyst having dual ion synergy (Fe3+/Fe2+ and Nb5+/Nb4+) and full spectrum response.

Enhanced photocatalytic performance of NaNbO3 nanorods by loading Al2O3 nanoparticles

Herein, we report the fabrication of UV-active NaNbO3/Al2O3 (30 wt.%) ferroelectric heterojunction photocatalyst with enhanced photoelectrochemical activity to Methylene Blue (MB). Pure NaNbO3 nanorods (NRs) were synthesized by a facile hydrothermal process and NaNbO3/Al2O3 composite was prepared by an ultrasonic vibration method. The heterostructures showed a remarkable increase in photocurrent density and the MB degradation ratio reached 88% in the initial 15 min and eventually reached 98.6% in 75 min. The high photocatalytic efficiency is attributed to the ferroelectric polarization of NaNbO3 with the forming of heterojunction electric fields assisted by Al2O3. These properties demonstrate that NaNbO3/Al2O3 ferroelectric heterojunction photocatalyst shows promising photoactivity and provides an effective method to improve the photocatalytic properties of other ferroelectrics.

Enhanced antiferroelectricity and double hysteresis loop observed in lead-free (1−x)NaNbO3-xCaSnO3 ceramics

Well-defined polarization-electric field double hysteresis loops are rarely observed in pure NaNbO3 (NN) ceramics due to the metastability of the field-induced ferroelectric phase. In order to stabilize the antiferroelectric phase, various ABO3-type binary oxides were incorporated into a NaNbO3 ceramic, where the B-site is occupied with transition elements. In this work, CaSnO3 was chosen to construct the NaNbO3-based solid solution by reducing the Goldschmidt tolerance factor and ionic polarizability. X-ray diffraction patterns, transmission electron microscopy images, and Raman spectra indicate enhanced antiferroelectricity. Typical double hysteresis loops were also observed from polarization-electric field measurements in ambient conditions with slightly weakened maximum polarization as the content of CaSnO3 increased. Our results reveal the generality of this strategy and pave the way for various applications involving high-power energy for NaNbO3-based ceramics.

An urchin-like SnO2/NaNbO3 nanocomposite with stable humidity-sensing properties at room temperature

An urchin-like nano-composite of SnO2/NaNbO3 was fabricated by the hydrothermal method and the influence of the Sn/Nb ratio in the samples on their humidity-sensing properties was investigated. The phases and morphologies of these composites and their elemental distributions were analyzed by X-ray diffraction scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The sensor based on the optimum Sn/Nb ratio of 1:0.4 exhibited remarkable humidity-sensing properties, including a good response (S = 4823.8) that was 8.72 times higher than that of the pure SnO2 sensor (S = 553.01). The composites showed rapid response and recovery times (3/9 s), as well as good stability, linearity, and excellent selectivity. The fabrication and humidity-sensing mechanisms were systematically analyzed using analog computations and Nyquist diagrams, respectively. Compared with pure NaNbO3 and SnO2 sensors, our easily prepared SnO2/NaNbO3 sensor demonstrates good sensing properties and holds great promise for use in humidity-sensing applications.

A new insight into the enhanced visible light-induced photocatalytic activity of NaNbO3/Bi2WO6 type-II heterostructure photocatalysts

In this study, a series novel NaNbO3/Bi2WO6 heterojunction composites with a type-II alignment were fabricated via a facile wet impregnation method. The as-prepared photocatalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy (DRS), photocurrent (PC) and electrochemical impedance spectroscopy (EIS) analyses. The 30 wt% NaNbO3/Bi2WO6 composite exhibited the best performance in the case of degrading rhodamine B (RhB) aqueous solution under visible light irradiation (λ > 410 nm), which was ∼2.5 times and ∼40 times that of pure Bi2WO6 and NaNbO3, respectively. The improved photocatalytic performance was further demonstrated by 2-chlorophenol under the same reaction conditions. This may be attributed to the enhanced electron-hole separation efficiency in Bi2WO6 with the assistance of NaNbO3, as well as the dye-sensitization effect of RhB dye itself. Intermediates produced during the reaction and RhB degradation pathway were investigated as well. Radical quenching experiments revealed h+ played the predominant role; O2·- functioned as well to some degree. Based on experimental results, the potential functioning mechanism was proposed, which is different from previously reported type-II heterostructure systems when Bi2WO6 works as the electron reservoir and O2·- is one of the dominant active species. The as-prepared photocatalyst composite exhibited excellent stability after repetitively running five times. Effects of several operating parameters on the catalyst performance including initial RhB concentration, catalyst dosage, reaction temperature and initial pH were also discussed. This study provides solid evidence for NaNbO3 to be a promising candidate for photocatalysis and gives out a novel photocatalytic mechanism of Bi2WO6-based heterostructures.