Classic Sol-gel Method Research Articles

The N-doped carbon coated Na3V2(PO4)3 with different N sources as cathode material for sodium-ion batteries: Experimental and theoretical study

NASICON (super ion conductor)-type Na3V2(PO4)3 (NVP) is considered to be one of the most promising cathode materials for sodium-ion batteries (SIBs) due to its good structural stability, fast Na+ diffusion coefficient, and excellent electrochemical properties. However, the poor intrinsic conductivity and electronic conductivity and severe volume shrinkage of NVP, resulting in serious limitations in the practical application of NVP materials. Carbon, especially N-doped carbon modification, is the most effective method and strategy to improve the conductivity of NVP. The study of N source and N content in carbon plays a very important role in improving the electronic properties. Herein, N-doped carbon coated NVP composites was synthesized via the classical sol-gel method using common, green and inexpensive urea and polyvinylpyrrolidone (PVP) as N sources, respectively. According to EIS tests and GITT tests, N-doped carbon layers with urea as the N source significantly improved the conductivity of the carbon layers and the Na+ diffusion kinetics. The effects of N-doped carbon layers on the electrode kinetics and electrochemical properties of NVP materials were investigated in detail. The optimized U-NC15@NVP composite exhibited a maximum discharge capacity of 114.2 mAh g−1 at 0.2C and 92.1% capacity retention after 400 cycles at 1C. When the optimal U-NC15@NVP electrode was selected to assemble a symmetric full cell, the reversible discharge capacity was 75.0 mAh g−1 after 100 cycles at 1C. The density functional theory (DFT) calculations establish that N-doped carbon can generate lots of active sites and external defects, which is beneficial to reduce the energy bandwidth of the carbon layer and thus improve the conductivity of the carbon layer. Additionally, it can also reduce the Na+ diffusion barrier and improve the adsorption energy for Na+. Experimental tests and theoretical calculations show that N-doped carbon can significantly increase the conductivity of the carbon layer and improve the electrochemical properties of NVP.

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped NaxMnO2.

Sodium-ion batteries have recently aroused the interest of industries as possible replacements for lithium-ion batteries in some areas. With their high theoretical capacities and competitive prices, P2-type layered oxides (NaxTMO2) are among the obvious choices in terms of cathode materials. On the other hand, many of these materials are unstable in air due to their reactivity toward water and carbon dioxide. Here, Na0.67Mn0.9Ni0.1O2 (NMNO), one of such materials, has been synthesized by a classic sol-gel method and then exposed to air for several weeks as a way to allow a simple and reproducible transition toward a Na-rich birnessite phase. The transition between the anhydrous P2 to the hydrated birnessite structure has been followed via periodic XRD analyses, as well as neutron diffraction ones. Extensive electrochemical characterizations of both pristine NMNO and the air-exposed one vs sodium in organic medium showed comparable performances, with capacities fading from 140 to 60 mAh g-1 in around 100 cycles. Structural evolution of the air-exposed NMNO has been investigated both with ex situ synchrotron XRD and Raman. Finally, DFT analyses showed similar charge compensation mechanisms between P2 and birnessite phases, providing a reason for the similarities between the electrochemical properties of both materials.

Microdroplet-based synthesis of polymethylsilsesquioxane microspheres with controllable size, surface morphology, and internal structure

Monodispersed polysilsesquioxane (PSQ) microspheres are generally synthesized by the classical sol–gel method. Using this method, the particle size is limited to the range of several hundred nanometers to several microns. The preparation of monodispersed large-sized PSQ microspheres remains technically challenging. Herein, with the polymethylsilsesquioxane (PMSQ) microspheres as the model product, a microdroplet-based strategy was developed for the synthesis of PSQ microspheres with larger particle sizes. According to the properties of the reactants, a W/O microdroplet reaction system was realized, i.e., with the mixture of methyltrimethoxysilane (MTMS) and liquid paraffin as the continuous phase and ammonia solution as the dispersed phase. The monodispersed W/O microdroplets were generated in a step T-junction microfluidic device, and solidified into PMSQ microspheres via in-situ interfacial polycondensation (∼2 min) in a microtube reactor. The size, surface morphology and internal structure of the PMSQ microspheres could be tuned by adjusting the synthesis conditions, mainly including the two-phase flow rates, MTMS concentration, NH4OH concentration, and the structural parameters of the microfluidic device. Various PMSQ microspheres with corrugated or smooth surface morphology, and loose or dense internal structure could be synthesized. The microsphere size could be tuned from tens of microns (∼20 μm) to hundreds of microns.

Effectively Modified Surface Microstructure and Properties of Carbon Fiber via In-situ Growth of Nano-SiO2

Design and adjustment of surface microstructure is an essential step forward in enhancing the interfacial properties of carbon fiber composites. Based on the classical Sol-Gel method, the silica was successfully introduced on the carbon fiber (CF) surface by the In-situ growth strategy. Scanning electron microscopy (SEM) and Electron Probe Microanalysis (EPMA) showed squid-like tentacle-like silica protrusions covered the CF surface uniformly. Fourier transform infrared spectra (FT-IR) result showed that the In-situ growth method introduced more silica on the CF surface. The interfacial layer is well preserved under mild condition and the tensile strength of CF increased by a 4.42%. Additionally, this investigation has the potential value not only focus on improved its smooth surface and chemical inertness but also solved the problems such as non-dispersible silica and time-consuming during the preparation process.

Integrated approach: Al2O3-CaO nanocatalytic biodiesel production and antibacterial potential silver nanoparticle synthesis from Pedalium murex extract

Pedalium murex, a less-utilized traditional plant, has high lipid content, which ranges from 21 mg/gfw (milligram per gram fresh weight) in leaf, 32 mg/gfw in stem and 19 mg/gfw in callus. Lipids from different parts of the plant were extracted and employed for biodiesel production. Al2O3-CaO nanocatalyst was synthesized by the classical Sol-gel method, characterized by XRD, HR-SEM, and was applied for biodiesel production. In transesterification, the influence of methanol-lipid was evaluated by varying the ratio from 1:6 to 1:16, and the FAME converted yield was calculated to be 60% using Gas chromatography. The biomass was subjected to lipid extraction and was then used for the synthesis of AgNPs, analyzed through the UV–Visible absorption spectrum, XRD, HR-SEM, and SAED. AgNPs of Pedalium murex plant extract were examined for their antimicrobial activity against various bacterial pathogens such as Staphylococcus aureus, Klebsiella pneumonia, Bacillus subtilis and Escherichia coli. AgNPs showed the best antibacterial activity against E. coli at 5.0 mM concentration. This study is promising in the identification of a cheap source for biodiesel production with the added advantage of antimicrobial drug formulation from the medicinal plant Pedalium murex.

Physicochemical properties of La3+-doped TiO2 monolith prepared by sol–gel approach: application to adsorption and solar photodegradation of ibuprofen

This study investigated the adsorption and photocatalytic performance of La3+-doped titanium dioxide for the removal of drug contaminants from wastewater using ibuprofen salt as contaminant model. La3+-doped TiO2 transparent monolith was synthesized by classic sol–gel method. Transparent materials crystallized under anatase form with great thermal stability. Doping of TiO2 using La3+ cations increases the specific surface area. Diffuse reflectance spectroscopy characterization of the prepared photocatalysts indicated that La3+ doping shifts the absorbance spectra of photocatalysts to the visible range. Adsorption modeling indicated that ibuprofen adsorption follows the Langmuir model. Dubinin–Radushkevich model confirms that adsorption of IBPF drug on La3+-doped TiO2 was physic-sorption phenomena. Solar light photocatalytic oxidation of IBPF using x% La3+–TiO2 catalysts follows the pseudo-first-order kinetic model. The photocatalytic degradation rate increased with the La3+ amount in TiO2 catalysts, which was attributed to the enhanced visible light absorption capacity. The recyclability of catalysts shows that 1 and 2% La–TiO2 have a good response after ten photodegradation cycles.

Chitosan/ Alginate /Gellan Gum Hybrid Hydrogel as a Vehicle for Controlled Release of Drug

Hybrid hydrogel was fabricated by a classic sol-gel method using EDC/NHS as crosslink reagent grafting onto the thermoplastic polyurethane (TPU), nonwoven fabric, for controlled release of drug. In this study, precursor acetic acid (AA) was used to plasma deposit on the surface of TPU to form a hydrophilic thin film. Hybrid hydrogel was investigated through scanning electron microscopy (SEM), water contact angle (WCA) measurement, Fourier transform infra-red (FTIR) spectroscopy, UV/V is spectroscopy, equilibrium swelling ratio, MTT assay and drug delivery system studies. This polyelectrolyte complexes (PECs) formed hydrogel, pH-sensitive type, was evaluated at pH value of 1.2 and 7.4 of buffer solution and at temperature of 37C to observe its rate of swelling and drug release features with caffeine. Moreover, the mechanism of caffeine release from membrane devices (n=0.58) are anomalous transport, non-Fickian diffusion, the value of n lies between 0.43 and 0.85. It has an excellent release ratio up to about 90% absorption cumulative amounts of caffeine at pH 7.4 after 8h and could be a beneficial carrier for fragile drugs.

Preparation of hydrophobic antireflective SiO2 coating with deposition of PDMS from water-based SiO2-PEG sol

The classic sol-gel method for preparing antireflective coatings (ARCs) known for decades often employs an organic liquid as the solvent, so it is necessary to develop an environmental- friendly and feasible procedure for commercial ARC fabrication. Herein, self-cleaning ARCs were prepared from water-based silica hydrosols followed by a chemical vapor deposition process. The average transmittance rose remarkably after the dip-coating of silica hydrosols. Polyethylene glycols (PEGs) with molecular weights of 1000, 2000 and 4000 were adopted as template agents to lower the refractive index of the coatings and thus enhance the antireflective performance. The PEG1000-modified coating has the highest average transmittance of 96.44%. Field-emission scanning electron microscopy and atomic force microscopy showed the surface roughness increased with the rise of molecular weight of PEG and the coating from PEG1000 is relatively smooth. Water contact angle measurement and anti-smudge test showed the chemical vapor deposition endowed the ARCs with hydrophobicity and self-cleaning ability.

Performance of Bi2O3/TiO2 prepared by sol-gel on p-Cresol degradation under solar and visible light.

Photocatalytic degradation of p-Cresol was evaluated using the mixed oxide Bi2O3/TiO2 (containing 2 and 20% wt. Bi2O3 referred as TB2 and TB20) and was compared with bare TiO2 under simulated solar radiation. Materials were prepared by the classic sol-gel method. All solids exhibited the anatase phase by X-ray diffraction (XRD) and Raman spectroscopy. The synthesized materials presented lower crystallite size and Eg value, and also higher surface area as Bi2O3 amount was increased. Bi content was quantified showing near to 70% of theoretical values in TB2 and TB20. Bi2O3 incorporation also was demonstrated by X-ray photoelectron spectroscopy (XPS). Characterization of mixed oxides suggests a homogeneous distribution of Bi2O3 on TiO2 surface. Photocatalytic tests were carried out using a catalyst loading of 1gL-1 under simulated solar light and visible light. The incorporation of Bi2O3 in TiO2 improved the photocatalytic properties of the synthesized materials obtaining better results with TB20 than the unmodified TiO2 under both radiation sources.

Influence of Diamond Particles Coated with TiO2 Film on Wettability of Vitrified Bond and Transverse Rupture Strength (TRS) of Vitrified Bond Composites

TiO2 films were prepared on the surface of the diamond particles using a classical sol-gel method. The results showed that the TiO2 covered on the diamond surface as a rough and dense film with anatase phase, and tightly combined with the diamond substrates via the Ti-O-C bond. The initial oxidation temperature and compression strength of diamond were improved to 725 °C and 23.8 N with TiO2 film coated. TiO2 film increased the roughness of the diamond surface, promoted its mutual solubility, and formed the chemical bonding (Ti-O-Si) between the vitrified bond and the diamond. Therefore, the TiO2 film decreased the interface energy of the diamond, and promoted the wetting angle of vitrified bond with diamond to 36.7°. As a result, the TRS of vitrified bond diamond composites was increased to 76.3 MPa.

Facile Synthesis of r-GO@Pd/TiO2 Nanocomposites and Its Photocatalytic Activity Under Visible Light.

Reduced Graphene Oxide Wrapped Pd/TiO2 (r-GO@Pd/TiO2) which exhibited high photocatalytic activity under visible light was synthesized from commercial chemicals. The classic sol-gel method and the Ar gas bubbling composition was used in the preparation of the catalyst. Furthermore, the best Pd-doping concentration in crystals, the wrapping concentration of r-GO over nanoparticles, and the optimal calcination temperature were investigated to enhance the photocatalytic activity of the hybrid catalyst. The experimental results showed that the catalytic efficiency of r-GO@Pd/TiO2 reached maximum value at the optimum synthesis conditions: 0.7 wt% Pd-doped TiO2 by sol-gel process, calcination temperature of 550 °C, 1 mg of GO for 100 .gram wrapped Pd/TiO2. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques were conducted to determine the nanostructure of the catalysts. The average crystallite size of nanoparticles was 14 nm with perfect dispersion of Pd dots and wraps of r-GO membrane. Methyl Blue was used as an organic dye model to test the ability in wastewater treatment of the catalysts. A comparison between different catalysts' characteristics was also studied. The r-GO@Pd/TiO2 showed a higher photocatalytic activity compared to Pd/TiO2 and commercial P25. Additionally, the complete dye reduction under visible light excitation indicated that wrapping r-GO round Pd/TiO2 improved the photocatalytic activity of catalysts. The determination of the stability of r-GO@Pd/TiO2 showed that its photocatalysis was persistent over several times of recycling examination. Therefore, r-GO@ Pd/TiO2 in wastewater treatment.

Gas sensing properties and modeling of YCoO3 based perovskite materials

YCoO3 perovskite powder was prepared by the classical sol–gel method, which was extended to the preparation also of non stoichiometric materials or samples containing platinum or palladium, incorporated either during synthesis or a posteriori through impregnation. The prepared powders were characterized in terms of composition and structure, using X-ray diffraction (XRD) and Rietveld refinement. The compounds show a tunnel structure with octahedral framework.The surface properties of these powders were investigated studying their catalytic activity in CO oxidation, as well as their adsorptive features towards oxygen and their redox behavior by means of TPD and TPR respectively. Sensing films of the prepared powders were realized by a screen-printing technique. The electrical properties and response to various gases were studied and found to be correlated to composition and structure of the different materials. Moreover the influence of the mictrostructure was analyzed and a model was developed.The responses to both oxidizing and reducing gases such as CO, NO2, NO, and CH4 were evaluated and discussed both in an inert environment (nitrogen) and in the presence of oxygen (air). All the YCoO3 based sensors show p-type semiconducting properties in the tested environments within the temperature range of 100–380°C. All the studied materials respond to CO in the high temperature range with a limited response but a large response speed. The response to NOx is optimum in the low temperature range between 160°C and 200°C; moreover even at these temperatures both the response and the recovery time are satisfactory. The response towards CH4 results much lower. Finally, the gas sensor properties of the proposed materials proved to be insensitive to ambient humidity.

Structure–activity relationship of nanosized porous PEG-modified TiO2 powders in degradation of organic pollutants

This study aims to gain insights in structure–activity relationship of TiO2 photocatalysts. For this purpose photocatalysts were synthesized via classical sol–gel method using titanium isopropoxide as a precursor and polyethylene glycols (PEGs) of different molecular mass (Mn=200, 600, 2000, 10,000) as a template agents. Incorporating PEG into TiO2 network enhanced not only catalyst porous structure, but also increased the fraction of anatase phase. The use of low-molecular-weight PEGs resulted in catalysts with increased anatase content and enlarged specific surface area. The catalyst photoactivity was estimated through degradation of organic pollutants: Reactive Black 5, arylazo pyridone dye and phenol. The results revealed that the photoactivity was following the same order independently of target pollutant: TiO2/P600>TiO2/P200>TiO2/P2000>TiO2/P10000>TiO2. BET surface area and anatase fraction, rather than pore diameter or pore volume, were found to be predominant catalyst property determining the activity for particular reaction system. The existence of synergistic effect between anatase and rutile phases was confirmed for the most active catalysts TiO2/P200 and TiO2/P600. These catalysts showed similar activity in dye degradation, while TiO2/P200 displayed significantly lower activity in phenol degradation, which was attributed to its lower sorption capacity and lower UV light utilization. The difference in the reactivity between investigated pollutants was discussed in relationship with their size, structure and sorption ability.

Synthesis, characterization and fuel cell performance tests of boric acid and boron phosphate doped, sulphonated and phosphonated poly(vinyl alcohol) based composite membranes

The aim of this study is to synthesize a composite membrane having high proton conductivity, ion exchange capacity and chemical stability. In order to achieve this aim, poly(vinyl alcohol) (PVA) based composite membranes are synthesized by using classic sol–gel method. Boric acid (H3BO3) and boron phosphate (BPO4) are added to the membrane matrix in different ratios in order to enhance the membrane properties. Characterization tests, i.e; FT-IR analysis, mechanical strength tests, water hold-up capacities, swelling properties, ion exchange capacities, proton conductivities and fuel cell performance tests of synthesized membranes are carried out.As a result of performance experiments highest performance values are obtained for the membrane containing 15% boron phosphate at 0.6 V and 750 mA/cm2. Water hold-up capacity, swelling ratio, ion exchange capacity and proton conductivity of this membrane are found as 56%, 8%, 1.36 meq/g and 0.37 S/cm, respectively. These values are close to the values obtained ones for perfluorosulphonic acid membranes. Therefore this membrane can be regarded as a promising candidate for usage in fuel cells.

Fast Sol–Gel Method to Prepare Mesoporous TiO2 with High Photocatalytic Activity

Mesoporous TiO 2 nanoparticles were synthesized via a fast and classical sol–gel method, respectively. Polyacrylamide was used as the template in the fast sol–gel route; the polymerization crosslink by hydrogen bonds between the template and hydrolysates of Ti alkoxides shortens the reaction time from several days to several hours. The X-ray diffraction results testified that only anatase was obtained in the samples, and the crystallite sizes of the samples prepared by fast and classical sol–gel method were 13.6 nm and 20 nm, respectively. Transmission electron microscopy and N 2 adsorption–desorption reveal that the nanocrystals have typical mesoporous structure and high surface areas. The pore sizes and surface areas of the samples prepared by fast and classical sol–gel method are 17.3 nm and 28.2 nm, 154.7 m2/g and 102.6 m2/g, respectively. The photocatalytic degradation of methyl orange solution under UV light irradiation suggests that the mesoporous TiO 2 photocatalyst prepared by the fast sol–gel method exhibits higher photocatalytic activity than the mesoporous TiO 2 prepared via classical sol–gel method.

Fabrication, structural morphology and photocatalytic activity of mesoporous TiO2 prepared by fast sol–gel method

Mesoporous TiO2 photocatalysts were prepared by fast and classical sol–gel method respectively, while polyacrylamide was used as the template in the fast sol–gel route. Reaction time has been shortened from several days for classical sol–gel method to several hours for the fast sol–gel route. This is because of the polymerisation crosslink by hydrogen bonds between the polyacrylamide and hydrolysates of Ti alkoxides in the fast route. Only anatase TiO2 was obtained in the samples from the X-ray diffraction results. The results of transmission electron microscopy and N2 adsorption–desorption show that the photocatalysts have typical mesoporous structure and high surface areas. The surface areas of the samples prepared by the fast and classical sol–gel method are 154·7 and 102·6 m2 g−1 respectively. The photocatalytic degradation of methyl orange solution under UV light irradiation suggests that compared with the sample prepared via classical sol–gel method, mesoporous TiO2 prepared via fast sol–gel method exhibits higher photocatalytic activity.

Influence of the chemical synthesis on the physicochemical properties of N-TiO2 nanoparticles

Nitrogen doped TiO2 materials were successfully prepared following three different preparation routes (sol–gel, hydrothermal and pyrolysis) and characterized by various spectroscopic techniques. All samples absorbed radiation in the visible range and were active in the photocatalytic degradation of cyanotoxin microcystin-LR under visible light and in acidic conditions. The different preparation routes led to the formation of various impurities into the solids. In the case of hydrothermal and sol–gel samples, these impurities were weakly bound at the surface whereas the materials prepared by pyrolysis, the impurities showed a relevant stability and could not be removed even at high temperature. These species can affect the photocatalytic performance in different ways depending on their bulk or surface nature. On the basis of the photocatalytic data illustrated in this paper, the presence of such species at the surface was not detrimental for the photocatalytic activity of nitrogen doped TiO2 but actually contributed to a higher interaction with the target cyanotoxin; leading to a higher photocatalytic activity than that observed for samples prepared via the classic sol–gel method.

Low-temperature sintering behavior of nanocrystalline indium tin oxide prepared from polymer-containing sols

Indium tin hydroxide (ITH) xerogel powders and thin films with different polyvinylpyrrolidone (PVP) contents (0–22%, w/w) were prepared by a classical sol–gel method. To obtain nanocrystalline indium tin oxide (ITO), the ITH xerogels were calcined at 550°C. The effect of the initial polymer content on the structure of the ITO powders was studied by means of N2-sorption measurements, small-angle X-ray scattering (SAXS), transmission and scanning electron microscopy. The N2-sorption measurements revealed that the ITO powders obtained contained micropores and both their porosity and specific surface area decreased with increasing PVP content of the ITH xerogels. The SAXS measurements confirmed the enhanced sintering of the particles in the presence of PVP. The calculated mass fractal dimensions of the ITO powders increased significantly, indicating a significant compaction in structure. The pre-sintered structure could be achieved at relatively low temperature, which induced a significant decreasing (three orders of magnitude) in the electrical resistance of the ITO films.

Electrical properties and reactivity under air–CO flows of composite systems based on ceria coated carbon nanotubes

Nanocomposite systems of ceria nanoparticles and Double Walled Carbon Nanotubes (DWNTs) coated with nano-ceria (n-CeO 2) were elaborated using a classical sol gel method. Three samples noted as [n-CeO 2 + xDWNTs] with variable weight fractions x = 0, 5 and 15 wt.% of DWNTs were obtained. The samples were characterized by X-ray diffraction and electron microscopy. The electrical conductivity of [n-CeO 2 + xDWNTs] compacted pellets systems was determined from electrical impedance spectrometry, under air, between 120 and 400 °C. In this temperature range, all samples were semi-conducting with a weak variation of activation energy. However, the conductivity strongly increased with the weight fraction of ceria coated carbon nanotubes. Finally, the solid–gas interactions between air–CO flows and these systems were studied as a function of time and temperature, by means of Fourier transform infrared (FTIR) spectroscopy. The oxidation kinetics of CO into CO 2 was analyzed from the evolutions of FTIR absorption band intensities. As the carbon nanotube fraction x increased, the conversion efficiency was strongly improved.

Photocatalytic ozonation of dimethyl phthalate with TiO 2 prepared by a hydrothermal method

TiO 2 was prepared by a hydrothermal method at a low temperature and used to degrade and mineralize dimethyl phthalate (DMP). TiO 2 was characterized by XRD, TEM, BET and UV–vis techniques. The characteristics of TiO 2 prepared by a hydrothermal method (h-t TiO 2) included a good crystalline anatase phase, greater surface area, stronger absorption to UV light wavelength and lower agglomeration than TiO 2 prepared by a classic sol–gel method (s–g TiO 2). The photocatalytic activity of h-t TiO 2 prepared under optimal hydrothermal condition (180 °C for 10 h) was 2.5 times higher than that of s–g TiO 2 in degrading DMP. The process of photocatalysis combined with UV irradiation and ozonation (TiO 2/UV/O 3) considerably improved the mineralization and degradation of DMP compared to photocatalysis combined with UV irradiation (TiO 2/UV), ozonation combined with UV irradiation (UV/O 3), and ozonation alone (O 3). A kinetic study showed the mineralization in TiO 2/UV/O 3 followed the Langmuir–Hinshelwood model.