Facile Sol-gel Route Research Articles

Synthesis and electrochemical performance of Ni doped Na3V2(PO4)3/C cathode materials for sodium ion batteries

To improve the electrochemical performances of Na3V2(PO4) cathode materials in sodium ion batteries, Na3V2-xNix(PO4)3/C (x = 0, 0.01, 0.03 and 0.05) materials were designed and prepared through a facile sol-gel route. The effect of Ni doping on the composition and crystal structure of Ni doped Na3V2(PO4)/C samples was investigated. The results confirmed that Ni atoms were successfully doped into Na3V2(PO4) crystal and substituted the V sites. It is shown that a carbon layer of about 2 nm was covered on the particle surface of the sample, which is beneficial for enhancing the electronic conductivity. The discharge capacities of all Ni doped samples were improved at high rates (2, 5 and 10 C). When Ni doping content was 3%, the sample exhibited the best rate performance and cycling capability. Na3V1.97Ni0.03(PO4)3/C sample delivered the specific capacity of 98.1 mAh·g−1 at 5 C, which is much higher than that of pristine sample, 64.3 mAh·g−1. The capacity retentions of Na3V1.97Ni0.03(PO4)3/C and pristine samples were 93.5% and 60.2%, after 50 cycles at 5 C, respectively. Electrochemical impedance spectroscopy and cyclic voltammetry performance analyses revealed that the polarization of the electrodes decreased and the diffusion coefficient of sodium ions increased by Ni doping.

Controllable synthesis of Fe2O3-carbon fiber composites via a facile sol-gel route as anode materials for lithium ion batteries

The Fe2O3-carbon fiber composites were prepared by a facile sol-gel method. The uniform distribution of Fe2O3 grains on the surface of carbon fibers was confirmed by field emission scanning electron microscopy and transmission electron microscopy. The impact of the Fe2O3 content in composite materials on electrochemical performance was also investigated in this study. The results show that the capacity degradation during cycling is associated with the content of Fe2O3 in composite materials. Comparative study of three composite samples with different Fe2O3 contents revealed that the best electrochemical performance with good cycling stability, high reversible capacity and improved rate capability was exhibited by the Fe2O3@carbon fiber sample. Even after 150 cycles at a constant current density of 50mAg−1, a high reversible discharge capacity of 634mAhg−1 can be achieved, which is comparable to its theoretical value (607mAhg−1). More importantly, the one-dimensional nanofibrous structure can be well preserved even after a long-time charge/discharge process over to 50 cycles, which demonstrates the structural robustness of the composite materials. The morphological robustness and excellent electrochemical performance of the Fe2O3@carbon fiber hybrid show its promise as an anode material for high-performance lithium-ion batteries (LIBs).

Elevated electrochemical property of LiMn2O4 originated from nano-sized Mn3O4

By employment of nano-sized pre-prepared Mn3O4 as precursor, LiMn2O4 particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn3O4 is studied. The structure, morphology, and element distribution of the as-synthesized LiMn2O4 samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn2O4 synthesized by facile solid state method (SS-LMO), LiMn2O4 synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10−11 cm2 s−1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g−1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li+ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.

Marangoni effect induced macro porous surface films prepared through a facile sol-gel route

Based on TiO2 as a model system, the sol-gel one step facile method is established to fabricate the macro-porous morphology films on the basis of Marangoni effect. In this proposed mechanism, the binary mixture of hydrophilic CuCl2 and lipophilic Ti-O network is used in sol to produce phase separation. A suitable evaporation rate in the gel film process leads to the macro-porous film due to Marangoni effect. It is observed that the macro-porous morphology of the film sustains during the annealing process, which suggests the creation of porous surface morphology in gel film stage rather than due to annealing. To analyze the preparation mechanism, the sol-gel process and microstructure of films are examined using TG-DTA, SEM, TEM, XRD, Raman, UV-Vis, XPS and FTIR. Furthermore, the optical-thermal properties are studied for the potential applications of such porous surface films as solar selective absorber.

Nano-sheet-like KNiPO4 as a positive electrode material for aqueous hybrid supercapacitors

A facile sol-gel thermolysis route was adopted to synthesize KNiPO4 nano-sheets for the design of hybrid supercapacitors. The phase purity, homogeneity, and functional groups present in the synthesized KNiPO4 were characterized through X-ray diffraction and FTIR measurements. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed that the nano-sheet-like particles were loosely stacked. The electrochemical properties of the KNiPO4 electrode were studied in various aqueous-based electrolytes such as 1M LiOH, 1M NaOH, and 1M KOH to explore their superior performances. Among these electrolytes, the KNiPO4 electrode provided a maximum specific capacity of 278 Cg−1 in 1M KOH at 5mVs−1. A hybrid supercapacitor was fabricated using the synthesized KNiPO4 as the positive electrode and activated carbon as the negative electrode in a 1M KOH aqueous electrolyte. The supercapacitor exhibited a specific capacitance of 48Fg−1 in 1M KOH at 0.6mAcm−2 and energy density of 13Whkg−1 at a power density of 59Wkg−1. In addition, the hybrid system retained 93% of its initial specific capacitance even after 2000 cycles. A KNiPO4-based hybrid system thus exhibits superior characteristics and hence is a promising candidate for high-performance electrochemical energy storage devices.

Low-temperature synthesis of δ-Bi2O3 hierarchical nanostructures composed of ultrathin nanosheets for efficient photocatalysis

Due to its highest conductivity of any oxide material, the delta phase of Bi2O3 (δ-Bi2O3) is recognized as one of the most technologically important materials for various applications, including photocatalysis. Nevertheless, the δ-Bi2O3 phase is not stable at room temperature. Herein, we demonstrate that δ-Bi2O3 can be synthesized at low temperature through a facile sol-gel route in the presence of metavanadate oxyanion (VO3−). The chemical state and local structure of V are investigated by synchrotron-based techniques, such as X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Our findings demonstrate the critical role of VO3− in stabilizing the δ-Bi2O3 phase. The crystallinity of δ-Bi2O3 is dramatically increased by the addition of VO3−. In the absence of VO3−, amorphous product is obtained. The as-synthesized δ-Bi2O3 possesses 3D hierarchical nanostructures constructed by ultrathin nanosheets with a few nanometers thick (~5nm). The nanosheets are composed of ultrasmall nanoparticles in the range of 1–2nm in size. Such a unique hierarchitecture of δ-Bi2O3 allows efficient light utilization due to multiple reflections and scattering, indicated by its excellent photocatalytic activity for the degradation and mineralization of atrazine in aqueous solution.

One-pot sol-gel synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon

A single pot sol-gel method was adopted for the synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon for the first time. The catalysts were successfully synthesized via a facile sol-gel route without the assistance of any surfactants. The as-synthesized catalysts were completely characterized for their structural, textural and redox properties using several analytical techniques. The X-Ray diffraction analysis confirmed the formation of NiMgO solid solution and magnesioferrites as the active phases in the fresh catalysts. The inter-aggregation of nanoparticles in the catalyst generated pores, and a mesoporous texture resulted. The hydrogen chemisorption analysis indicated that the NiMgO solid solution was very difficult to reduce compared to the magnesioferrites. The thermocatalytic decomposition of methane at 700°C, 800°C and 900°C fully validated their enhanced catalytic activity and stability for the reaction. The initial hydrogen yield and total carbon yield were found to be significantly increased, when the reaction temperature was increased. However, the highest catalytic performance was shown by the Fe/MgO catalyst. Moreover, no catalyst deactivation was observed for both of the catalysts for a period of 360min of time on stream. This could be ascribed to their enhanced catalytic stability due to the presence of metal nanoparticles dispersed on the surface of the support, with proper metal-support interaction rather than their specific surface area. Multiwalled carbon nanotubes with metal encapsulated carbon particles and few layered graphene sheets were deposited over Ni/MgO and Fe/MgO catalysts, respectively. The studies of the effect of reaction temperature on the crystalline properties of the deposited nanocarbon indicated that the crystallinity and graphitization degree were increased with increasing reaction temperatures.

Facile synthesis of large-sized monolithic methyltrimethoxysilane-based silica aerogel via ambient pressure drying

In this study, large-sized monolithic methyltrimethoxysilane-based silica aerogels were prepared via a facile sol–gel route using ambient pressure drying. The structural, morphological, and hydrophobic properties of the aerogels were characterized by scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method, and contact angle. Thermal conductivity, thermal stability, and mechanical properties of the samples were also evaluated. The ambient pressure dried aerogels showed macro-pore structure and low density (as low as 75 kg m−3). The Young’s modulus of the aerogels was observed to increase from 0.043 to 1.102 MPa with an increase in the density of the aerogels from 75 to 141 kg m−3. Simultaneously, the aerogels exhibited superhydrophobicity (>150°), low thermal conductivity (0.036 W m−1 K−1), and good thermal stability in air atmosphere. Both the simple fabricating process and the superior performance of the monolithic silica aerogel make it as a promising candidate for energy-saving sector. Large-sized monolithic methyltrimethoxysilane-based silica aerogel with superhydrophobicity was successfully prepared by a one-step sol–gel method via ambient pressure drying using methyltrimethoxysilane as precursor, distilled water as solvent, and ammonia as alkali catalyst.

Mesoporous nano-bioglass designed for the release of imatinib and in vitro inhibitory effects on cancer cells

For treating bone cancer, controlled drug delivery is an important strategy. Bioactive scaffolds are widely used biomaterials due to their usefulness in localized drug delivery. The aim of this study was to develop mesoporous bioglass (MBG) with improved bioactivity and controllable drug delivery rate. By using pluronic 123 (P123) as a template, a facile sol-gel route was employed for the synthesis of MBG nanoparticles (NPs). The composition of the prepared sample was estimated by using energy dispersive X-ray spectroscopy (EDX). These nanoparticles demonstrated the specific surface area of 310m2/g and pore size of 13nm as measured by brunauer-emmett-teller (BET) and barrett-joyner-halenda (BJH) method, respectively. The spherical shape of NPs was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Imatinib (IMT); an anti-cancer drug was loaded with the efficiency of 77.59%. The drug release kinetics were precisely controlled by changing the pH (4.4 to 10.4) as well as drug loading concentration (0.2–1.0mg/mL). The maximum cumulative drug release of 81% was observed over a time period of 250h at pH of 4.4. Importantly, significant inhibitory effects on the viability of the MG-63 osteocarcinoma cancer cells at 12.19μg/mL of IMT-MBG were observed. Furthermore, MBG demonstrated ionic dissolution with the release of Ca, K, Si, Na, and P ions upon immersion in simulated body fluid (SBF), which support the formation of hydroxycarbonate apatite (HCA), as confirmed by wide-angle X-ray diffraction (WAXD) pattern and fourier transform infrared (FTIR) spectroscopy. These features proved that IMT-MBG system is effective for bone tissue regeneration and bone cancer treatment.

Synthesis of nano-textured polystyrene/ZnO coatings with excellent transparency and superhydrophobicity

Transparent superhydrophobic polystyrene/ZnO nanocoating, possessing an average roughness of 28 nm and high contact angle (>150°) has been synthesized through a modified facile sol–gel route. The anticipated hierarchical roughness of the coating was obtained using dual functionalized ZnO nanoparticles. Chlorotrimethylsilane and 3-mercaptopropyltrimethoxy silane were espoused as nanoparticle surface functionalizing agents to generate superhydrophobic coating. The effect of experimental parameters on transparency and superhydrophobicity of developed coatings was examined to obtain optimum conditions. Such developed coatings can prove to have substantial industrial applications.

Synthesis and electrochemical characteristics of isostructural LiMTiO4 (M = Mn, Fe, Co)

Isostructural LiMTiO4 (M = Mn, Fe, Co) have been successfully synthesized by a facile sol-gel route and evaluated their possibility as an anode materials for lithium ion batteries (LIBs). All the samples exhibit high operating potential plateaus (>1.7V vs. Li+/Li), which can prevent the formation of the solid electrolyte interphase (SEI) film on the electrode surface effectively. In addition, electrochemical investigations show that LiCoTiO4 has a superior cycling performance, better rate capability, lower charge transfer resistance and higher lithium-ion diffusion coefficient than those of LiMnTiO4 and LiFeTiO4. These electrochemical results indicate that LiCoTiO4 is the most promising lithium storage material among all the examined spinel-type LiMTiO4 samples.

Na3V2(PO4)3 coated by N-doped carbon from ionic liquid as cathode materials for high rate and long-life Na-ion batteries.

A facile and simple hydrothermal assisted sol-gel route was developed to prepare nitrogen doped carbon coated Na3V2(PO4)3 nanocomposites (denoted as NVP@C-N) as cathodes for sodium ion batteries (NIBs). An ionic liquid (EMIm-dca) was used as the nitrogen doped carbon source. The optimized N-doped carbon coated Na3V2(PO4)3 (denoted as NVP@C-N150) displays a very thin and uniform N-doped carbon coating layer (thickness: ∼2 nm), showing an excellent sodium storage performance (85 mA h g-1 at 20 C after 5000 cycles) and high rate capability (71 mA h g-1 at 80 C). Such a superior sodium storage performance derives from the nitrogen doping carbon coating, triggering amounts of extrinsical defects and active sites in the N-doped amorphous carbon layer, which highly accelerates Na-ion and electron transport. This approach is simple, facile and shows easy scale-up. It could be extended to other materials for energy storage.

A facile sol–gel route to prepare functional graphene nanosheets anchored with homogeneous cobalt sulfide nanoparticles as superb sodium-ion anodes

A facile sol–gel route to prepare functional graphene nanosheets/cobalt sulfide hybrid nanocomposites as high-speed-stable sodium-ion anodes.

Enhancing the electron transfer and band potential tuning with long-term stability of ZnO based dye-sensitized solar cells by gallium and tellurium as dual-doping

A series of ZnO nanoparticles with Ga and Te dual-doping were successfully synthesized by using a facile sol–gel route, and their performance as the photoanode material in DSSCs was employed for the first time. The effects of simultaneously Ga–Te dopants into ZnO host (GaxTe1-xZnO where the values of x ranging from 0 to 1mol % with increments of 0.25mol %) on the structural, optical, morphological, and compositional properties of the resulting samples were characterized via XRD, Raman, UV–vis–NIR spectrometer, PL, BET, AFM, FE–SEM, EDX, and XPS measurements. The incorporation of Ga–Te enlarges the surface area of the photoanodes, leading to higher dye-loading capability. Moreover, the PL intensity of pure ZnO drastically decreases by Ga–Te dopants, which demonstrates the reduction of oxygen vacancies, indicating the slow recombination of photoinduced charge carriers. Owing to the doping effect of Ga–Te, the energy conversion efficiencies of the DSSCs based on these photoanodes lie in the range of 4.79–7.08%, which is higher than that of pure ZnO (3.53%). This improvement of efficiency can be mainly ascribed to the combined effects of faster electron transport rate, retarded charge recombination, enhanced dye adsorption capability, longer electron lifetime as well as shifted negatively of conduction band edge in dual-doped ZnO films. Furthermore, it is noteworthy that after 1200h, the degraded Ga0.25Te0.75ZnO device still shows 86% of their initial efficiency. This study provides a strategy for constructing self-powered systems using a device such as GaxTe1-xZnO based DSSC described here for the first time.

Mixed oxide semiconductor CuInAlO4 nanoparticles: synthesis, structure and photocatalytic properties

CuInAlO4 nanoparticles were synthesized via the facile sol–gel route. The phase formations were investigated by x-ray powder diffraction and structure refinements. The morphological characteristic of the nano-oxides was tested with scanning electron microscopy, transmission electron microscopy, energy-dispersive spectra, N2-adsorption–desorption isotherms and the x-ray photoelectron spectrum. The optical absorption, band energy and structures of the nanoparticles were measured. CuInAlO4 has wide optical absorption from UV to visible wavelength. The nano-oxides have a narrow band energy of 2.191 eV. The photocatalysis ability of CuInAlO4 nanoparticles was confirmed by its efficient photodegradation on methylene blue (MB) dye under the excitation of the visible wavelengths: CuInAlO4 demonstrates efficient photocatalysis on MB photodegradation.

Improved structural stability and electrochemical performance of Na3V2 (PO4)3 cathode material by Cr doping

Cr-doped sodium vanadium phosphate (NVP) in the form of Na3V2-xCrx(PO4)3 (x = 0, 0.02, 0.04, 0.08, 0.10) is synthesized via a facile sol-gel route as cathode materials for sodium ion batteries. The structure and morphology of these materials are systematically characterized by x-ray diffraction (XRD), Fourier-infrared spectra (FT-IR), and scanning electron microscope (SEM). XRD analysis reveals that with the increasing amount of Cr, the crystallographic parameters show a descending trend. Electrochemical tests show that the cycle stability and the specific capacity of the sodium ion batteries can be significantly improved by doping Cr into NVP. Among all the Cr-doped cathode materials, Na3V1.92Cr0.08(PO4)3 achieves the highest capacity of 112.2 mAh g−1 and the capacity retention is 97.2 % after 50 cycles. Electrochemical impedance spectroscopy measurements demonstrate that Cr doping is an effective method to reduce the contact resistance of interparticles by suppressing irreversible phase transformation at low sodium contents.

Nucleation-growth induced phase transformation during delithiation/lithiation of ‘ultra-small’ LiFePO4 nanoparticles decorating carbon nanotubes

‘Ultra-small’ LiFePO4 nanoparticles (~5nm) ‘decorating’ multi-walled carbon nanotubes (MWCNTs) have been developed, possibly for the first time, via engineered but facile sol-gel route. During delithiation/lithiation, nucleation-growth induced first-order phase transformation between LiFePO4 and FePO4 could be experimentally evidenced, albeit only in the presence of MWCNTs, even for these particle sizes, which are significantly finer compared to the predicted lower limit of ~20nm for complete disappearance of the concerned miscibility gap. This first report on experimental evidences for occurrences of these (LiFePO4↔FePO4) phase transformations at such (nano)particle sizes is expected to throw new insights into the still debated phenomenon.

Enhanced visible light photocatalytic activity of Gd-doped BiFeO3 nanoparticles and mechanism insight.

To investigate the effect of Gd doping on photocatalytic activity of BiFeO3 (BFO), Gd-doped BFO nanoparticles containing different Gd doping contents (Bi(1−x)GdxFeO3, x = 0.00, 0.01, 0.03, 0.05) were synthesized using a facile sol-gel route. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, and ultraviolet-visible diffuse reflectance spectroscopy, and their photocatalytic activities were evaluated by photocatalytic decomposition of Rhodamine B in aqueous solution under visible light irradiation. It was found that the Gd doping content could significantly affect the photocatalytic activity of as-prepared Gd-doped BFO, and the photocatalytic activity increased with increasing the Gd doping content up to the optimal value and then decreased with further enhancing Gd doping content. To elucidate the enhanced photocatalytic mechanism of Gd-doped BFO, the trapping experiments, photoluminescence, photocurrent and electrochemical impedance measurements were performed. On the basis of these experimental results, the enhanced photocatalytic activities of Gd-doped BFO could be ascribed to the increased optical absorption, the efficient separation and migration of photogenerated charge carriers as well as the decreased recombination probability of electron-hole pairs derived from the Gd doping effect. Meanwhile, the possible photocatalytic mechanism of Gd-doped BFO was critically discussed.

Selective adsorption of amaranth dye on Fe3O4/MgO nanoparticles

This research work is concerned with investigation of removal amaranth food stuff dye on magnetic Fe3O4/MgO nanoparticles synthesized by facile sol–gel route. The crystalline feature and the nanostructure of the magnetic nanoparticles were investigated by X-ray diffraction (XRD), N2-adsorption–desorption isotherm, field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM). FESEM and HRTEM analysis illustrate the existence of MgO nanoparticles with rod-like structure of average size about 14nm in diameter and 22nm in length. However, N2 adsorption–desorption isotherm reveals the existence of mesoporous nanoparticles with ink-bottle pore shape. It is obvious to notice a change in sample crystallography from cubic MgO to hexagonal Mg(OH)2 crystals after adsorption of amaranth dye which reveal the full hydration of the magnetic nanoparticles. The influence of reaction parameters affecting dye uptake including contact time, catalyst dosage, initial dye concentration and temperature were investigated for proper choosing the optimization parameters of the removal process. Different types of adsorption isotherms equations were performed for the better fit to get a clear picture on the mechanism of the adsorption process. The kinetics of the adsorption process was analyzed using different models to indicate the rate determine step. Thermodynamic parameters such as free energy, entropy, and enthalpy were estimated. The intra-particle diffusion was identified to be the rate-limiting step in addition to the film diffusion. The experimental results have pointed out that the adsorption equilibrium data are fitted well to the Langmuir isotherm rather than Freundlich isotherm reflecting favor formation of monolayer of this dye on MgO surface. The adsorption isotherm indicates that the adsorption capacities are 37.98mg/g. The value of enthalpy change is17.03kJ/mol indicating that the removal process is endothermic. The adsorption process follows pseudo-second order rate equation and the negative values of standard free energy (ΔG°) suggested that the adsorption process is spontaneous. The existence of magnetic Fe3O4 facilitates the recovery of solid catalyst after adsorption process. Overall; this research work promotes the possible use of Fe3O4/MgO as an effective magnetic adsorbent for removal of dye from aqueous solution and recovery the catalyst to be used for several cycles.

Mg-substitution for promoting magnetic and ferroelectric properties of BiFeO3 multiferroic nanoparticles

Mg-substituted BiFeO3 (BFO) multiferroic nanoparticles were synthesized by a facile sol-gel route and their magnetic and ferroelectric properties were investigated. Due to Mg2+ ion substitution, the magnetization is dramatically increased and higher than the other A-site substituted BFO reported with similar doping level. Such strong magnetization improvement originates from the release of latent magnetization locked within the cycloid, which is caused by the substitution of small-radius Mg2+ ion at the edge of the perovskite-structure tolerance factor. Compared to the pristine BFO, the as-doped Bi0.98Mg0.02FeO3 exhibits five-fold improved magnetization with simultaneously improved ferroelectric properties at room temperature. Increased magnetic and ferroelectric properties suggest the doped BFO possesses great potential for data storage and magnetoelectric devices.