Facile Sol-gel Synthesis Research Articles

Ultrasonically modified P25-TiO2 /In2O3 heterostructured nanoparticles: An efficient dual- responsive photocatalyst for solution and gas phase reactions

BackgroundDesigning and fabricating an efficient heterostructured photocatalyst for degrading organic pollutants is a major concern for environmental remediation researchers. In that series we fabricated a P25-TiO2/In2O3 (PT/In) heterostructured nanocomposite via the facile ultrasonication and sol-gel synthesis method. MethodsIn both solution and gas-phase methods, the photocatalytic efficiency of the obtained PT/In nanocomposite was investigated. DRIFT-IR was measured at room temperature with the effect of adsorbed ethanol molecules, which would be used as a different approach to confirm the photocatalytic reaction mechanism. Significant FindingsUnder UV-Visible light illumination, the PT/In-4 nanocomposite was found to be an excellent photocatalyst for degrading Acid Blue (AB) dye. The calculated degradation rate constant (k) of PT/In-4 was 4.0 × 10−2 min−1, which was 13.3 and 5.7 times higher than that of PT-4 (0.3 × 10−2 min−1) and bare In2O3 (0.7 × 10−2 min−1) materials, respectively. The enhancement in photocatalytic performance is owing to the synergistic effect of the heterojunction between TiO2 and In2O3 and a reduction in the recombination rate. Furthermore, the PT/In-4 nanocomposite showed high stability even after five consecutive cycles. The photocatalytic mechanism was proposed based on experimental results obtained through the gas phase photocatalytic studies via DRIFT-IR technique.

Synthesis and Characterisation of Organo-Modified Silica Nanostructured Films for the Water-Repellent Treatment of Historic Stone Buildings

This study presents the facile sol-gel synthesis of nanostructured coatings for use in water-repellent treatment of travertine stone. The synthesized materials combine surface roughness characteristics with particular chemical compositions to give different hydrophobicity results. The influence of the silica particle coating precursor on the hydrophobicity of the polymeric film was investigated, and the octyl-modified silane was selected for further fabrication of the hybrid coatings. The water repellent properties, together with composition and structural properties of the silane-based hybrid material were measured on model glass surface. The coating with the best characteristics was subsequently deposited onto the travertine stone. The potential applicability of the nanostructured material was evaluated considering both the properties of the coating film and those of the travertine stone subjected to the treatment. The surface texture of the film, water repellent properties and uniformity were determined using scanning electron microscopy, atomic force microscopy, dynamic light scattering and contact angle measurements. The coating’s potential for use in stone conservation was evaluated by assessing its impact on the stone’s visual aspect. All the results obtained from the different types of analyses showed that the octyl-modified silica nanostructured material was highly hydrophobic and compatible both with the travertine stone and with the requirements for use on cultural heritage monuments.

Structural, morphological and optical properties of cobalt-substituted MgMoO4 ceramics prepared by pyrolysis of citric acid precursors

Magnesium-cobalt molybdate composites (Mg1–xCoxMoO4: x = 0, 0.3, 0.4, 0.6, 0.8 and 1) were successfully synthesized through a facile sol-gel synthesis at low temperature, and characterized by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), UV-Vis spectroscopy and colorimetric measurements using the CIE L*a*b* colour system. The surface specific area was calculated using the Brunauer–Emmett–Teller analysis in the adsorption/desorption isotherm. The examination of the X-ray diffractograms of the unground milled solid solutions of Mg1–xCoxMoO4 (0 ≤ x ≤ 1) presented a single continuous system related to monoclinic β-MgMoO4. The absorbance spectra of the Mg1–xCoxMoO4 pigments confirmed the insertion of cobalt in the β-MgMoO4 matrix. The CIE-L*a*b* colour coordinates indicated that the intense purple colour was obtained for x = 0.6.

A facile sol–gel synthesis of chitosan–boehmite film with excellent acid resistance and adsorption performance for Pb(II)

A chitosan–boehmite (CS–boehmite) film with excellent acid resistance for effective Pb(II) removal was successfully synthesized via a facile sol–gel method. The composite, corresponding boehmite and CS films were characterized by XRD, ATR-FT-IR, TG, SEM and XPS. The static adsorption experiment showed that their adsorption well matched the pseudo-second order model on chemisorption adsorption, and the modified Langmuir model on homogenously surface for monolayer adsorption. Especially, the composite film with cross-linking mass ratio of 1:1 did not dissolve after shaking in an acidic solution of pH=2.0 for 1h due to formation of the monodentate C(O−Al)2 ligand, while the boehmite and CS films dissolved 24wt% and 100wt%, respectively. The maximum adsorption capacity of the composite film is 33.00mg/g from the modified Langmuir model which is much higher than 19.57mg/g of the boehmite film and 17.48mg/g of the CS film, respectively, and these values are highly close to their calculated values from the pseudo-second order model and also from the experiment values. Furthermore, the composite film shows strong capability of resisting disturbance for the coexisting cations (Na+, Mg2+, K+ and Ca2+); its adsorption mechanisms involve electrostatic attraction, complexation to form PbOH and the chemical precipitation of Pb3(CO3)2(OH)2.

Highly efficient and visible light–driven nickel–doped vanadium oxide photocatalyst for degradation of Rhodamine B Dye

Water pollution has become serious threat for environment and society. Due to failure of different methods, semiconductor photocatalyst based advance oxidation process has attracted a huge interest for wastewater treatment. In this work, Nickel-doped vanadium pentaoxide (Ni doped-V2O5) is synthesized using easy and facile sol–gel synthesis route and the synthesized material is characterized through various characterization tools. The orthorhombic phase was detected in which decrease in crystallite size is observed with addition of dopant. The SEM analysis revealed that layered structure is formed with sufficient surface area and Energy Dispersive X-ray spectroscopy (EDX) represented the purity of samples. UV–Vis and Photoluminescence spectroscopies provide the information about the absorption and band gap of material and confirm the visible light response of the prepared catalysts. The photodegradation of RhB was evaluated through employing Ni doped-V2O5 photocatalyst which exhibited the 100% dye removal and high photostability. The factors which can affect the performance of catalytic activity are also studied to optimize the parameters for maximum dye removal. The kinetic study was also performed which showed that the synthesized materials follows pseudo first order kinetics.

One-pot facile sol-gel synthesis of W, N, C and S doped TiO2 and its application in the photocatalytic degradation of thymol under the solar light irradiation: Reaction kinetics and degradation mechanism

The ions W6+, N3−, C4+ and S6+ were incorporated into TiO2 lattice (WNCST) by sol-gel method. Sodium tungstate and l-cysteine were the precursors for these dopant ions. Energy dispersive X-ray studies confirmed the stoichiometry of the WNCST samples. Powder X-ray diffraction studies confirmed the anatase structure for TiO2, W6+-doped TiO2 and WNCST samples. The preferential sites for the occupation of dopant ions in the TiO2 lattice, the oligomeric octahedral chain growth mechanism and the mechanism of retention of anatase phase in the WNCST photocatalysts was explained in detail. The WNCST samples showed extended absorption in the visible region due to the creation of various dopant/defect energy levels. The plot of crystal density versus dopant concentration implied that the WNCST samples were omission solid solutions containing various defects such as neutral/ionized vacancies of Ti and O. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of carbonate and sulfate groups on the surface of WNCST samples. Photoluminescence confirmed the optimum dopant concentration of cysteine as 0.17 mol %. The enhanced visible light photocatalytic activity of WNCST samples was mainly attributed to extended light absorption in the visible region due to the presence of 5d energy levels of W6+ ions and 2p states of S6+ and N3− dopant ions, surface adsorbed electron withdrawing sulfate groups and surface adsorbed carbonaceous content acting as a sensitizer. The thymol degradation reaction intermediates were identified using high performance liquid chromatography, UV–visible absorption spectroscopy and gas chromatography-mass spectrometry.

Low-temperature catalytic oxidation of benzene over nanocrystalline Cu–Mn composite oxides by facile sol–gel synthesis

We prepare a series of nanocrystalline copper–manganese oxides by a facile citric acid sol–gel method, and test their activities for catalytic oxidation of benzene.

Green and facile sol-gel synthesis of the mesoporous SiO2-TiO2 catalyst by four different activation modes.

The most environmentally friendly protocol for obtaining mesoporous SiO2–TiO2 catalysts has been sought. Water has been employed as a green solvent, the energy input has been minimized, and three further principles (1, 3, and 12) of Green Chemistry have been considered. Four different modes for promoting the reaction have been comparatively evaluated, namely near-infrared and microwave electromagnetic irradiations, ultrasound, and traditional mantle heating. Brunauer–Emmett–Teller (BET) analyses of the catalysts produced revealed that the non-conventional activation modes afforded both large surface areas (335–441 m2 g−1) and smaller crystal sizes (7.2–15.3 nm) than the mantle heating process. These modes also generated the catalysts in shorter reaction times than traditional mantle heating, 10–30 min versus 3 h, with anatase as the sole crystalline phase. The photocatalytic degradation of 4-chlorophenol has been carried out to assess the catalytic efficiencies of the hybrid materials. The catalyst synthesized with microwave assistance showed the best mineralization activity (97%), followed by those prepared with ultrasound, near-infrared, and mantle heating. The materials have been extensively characterized by FTIR, XRD, DRS-UV/Vis, SEM, 29Si MAS NMR, and BET analyses. To the best of our knowledge, this is the first such comparative assessment of green energetic alternatives in developing a sol–gel process.

Facile sol-gel synthesis of LiMn0.5Fe0.5PO4 cathode materials fostered by bio-derived natural agar

Olivine-structured LiMn0.5Fe0.5PO4 cathode materials were successfully synthesized via the bio-derived agar-assisted sol-gel method. Rietveld analysis revealed that the structure of the synthesized materials was orthorhombic with the Pbnm space group. The addition of agar in the precursors significantly reduced the calcination temperature and impurity phases. When increasing the temperature from 400 to 700 °C, the particle size of LiMn0.5Fe0.5PO4 was increased from 1 to 3 μm. Among all the samples, LiMn0.5Fe0.5PO4 synthesized with agar at 700 °C delivered better electrochemical performances due to its lower charge transfer resistance. The same sample exhibited specific discharge capacities of 143, 123, 110, 96, and 88 mAh/g at C/10, C/5, C/3, C/2, and 1C rates, respectively. The retention in capacity was observed to be 95% for 40 cycles at C/3 rate. The obtained results indicated the feasibility to synthesize phase pure LiMn0.5Fe0.5PO4 powders by the addition of agar.

Facile Sol-Gel Synthesis of Co3O4 Nanoparticles — An Efficient and Recyclable Catalyst for the Synthesis of 1,2-Disubstituted Benzimidazoles Under Solvent-Free Conditions

High-surface-area Co3O4 nanoparticles have been prepared as a potential heterogeneous catalyst by the sol-gel method using starch as an inexpensive and a nontoxic starting material. Evidence showing that the cobalt precursor had been completely coverted into a pure crystalline Co3O4 phase with a cubic structure was obtained by X-ray diffraction analysis. The average particle size was estimated at 24 nm. The prepared catalyst was used in the synthesis of benzimidazoles. The developed methodology offers the advanvages of high yields (70–95%) and short reaction times (35–95 min) and avoids the use of toxic organic solvents. All of the reactions were carried out in the presence of Co3O4 nanoparticles (0.01 g) at 80°C under solvent-free conditions. The catalyst could be recovered and reused without any significant loss of activity.

Doping TiO2 with CuSO4 enhances visible light photocatalytic activity for organic pollutant degradation.

Photocatalysis is one of the most promising advanced oxidation processes due to the capability of solid catalyst to continuously produce oxidant species under light irradiation. The use of conventional UV lamps is high cost intensive, which undermines the possible implementation in developing countries. Visible light active photocatalysts can overcome these challenges and find a market opportunity for competitive technology implementation. This work proposes the synthesis of visible light active catalyst following a facile sol-gel synthesis that introduces CuSO4 as dopant in TiO2. Results present complete abatement of methylene blue in 120min of treatment under 50mWcm-2 of blue light (λ = 450nm), while commercial P25 TiO2 presented null abatement under identical conditions. Synthesis parameters including dopant level and calcination temperature allowed defining optimum synthesis conditions based on material characteristics modification and catalytic activity enhancement. A doping level of 0.21mol% CuSO4 was identified as optimum condition to enable visible light photocatalysis of doped TiO2 catalysts calcined at 300°C. Finally, operational parameters were evaluated defining a wide range of pH operation under 3.0gL-1 of catalyst dose to treat up to 20gL-1 of highly recalcitrant phenothiazine dye. These optimum conditions allowed complete dye removal under visible light after 120min of treatment.

Improving the performance of sulphur doped LiMn2O4 by carbon coating

Sulphur-doped spinel LiMn2O3.99S0.01 is a promising cathode material for lithium-ion batteries. It can be obtained in a form of nanocrystals by a facile, eco-friendly and water-based sol-gel synthesis. In this work, LMOS was successfully coated with a 2–3 nm conductive carbon layer fabricated from pyrolysis of modified poly(N-vinylformamide) - water-soluble polymer precursor. Carbon coated material exhibits greatly increased performance under high currents and improved cyclability in long-term charge-discharge tests. Pristine and carbon-coated samples are characterized by X-ray diffraction, thermogravimetric analysis, elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical performance of the materials is examined by galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. Carbon coated sample present a highly enhanced rate capability, withstanding up to 100C rate and maintaining up to 67.5% of initial 1C discharge capacity at 50C rate (1C - 148 mA g−1 – current required to fully charge a cell in time of 1 h). Li+ ion apparent diffusion coefficient in carbon coated sample is approximately twice increased. Electrochemical impedance spectroscopy has shown, that carbon coating decreases internal resistances of the cell caused by material passivation and charge-transfer reactions.

Enhanced electrical, magnetic and optical behaviour of Cr doped Bi0.98Ho0.02FeO3 nanoparticles

It remains a challenge to enhance the multiferroic properties of perovskite materials. Herein, we demonstrate a facile sol-gel synthesis of BiFeO3 and Bi0.98Ho0.02Fe1-xCrxO3 (x = 0.01, 0.02, 0.03 and 0.04) nanoparticles with an average size range of 71–35 nm. The crystal phase and structure of as-synthesized powders are studied using Rietveld refinement, which reveal 100% perovskite phase with rhombohedral R3c structure. A saturated loop with small remnant magnetization (Mr) reflects weak ferromagnetism in all the samples. The dc magnetization along with Mössbauer spectroscopy confirms ferromagnetic nature of the compounds. Further, it is to be noted that the co-doping enhances the saturation magnetization to almost three times more than that of pure BiFeO3 and related mechanism was studied in details. Simultaneously, the ferroelectric polarization (Pm) was found to increase from 0.44 μC/cm2 (pure BiFeO3) to 2.08μC/cm2 (Cr doped Bi0.98Ho0.02FeO3). The co-doped samples show high resistivity which is confirmed by the decrease of loss tangent (tanδ) from 3.6 to 0.17 due to the reduction of oxygen vacancies. The band gap of as prepared samples was also found to increase at higher Cr concentration. To the best of our knowledge, for the first time, we have attempted to enhance the multiferroic properties of BiFeO3 using Cr and Ho as co-dopants.

Selenium-enriched flower-like of bismuth ferrite nanosheets assembly with associated magnetic properties

Facile sol-gel synthesis method was used to prepare Selenium (Se) and Lanthanum (La) co-doped BiFeO3 nanoparticles for soft and hard ferromagnetic applications. La and Se doped bismuth ferrite nanostructures were fabricated using facile double-solvent sol-gel technique for, BiFe1-xSexO3 (BFSex) and Bi0.92La.08Fe1-xSexO3 (L8Sex), (where, x=0.1, 0.25, 0.5, 0.75, 1) nanocomposites. The structural, morphological and magnetic properties of BFSex and L8Sex were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. Structural and morphological analysis reveals that BFSex and L8Sex transform from perovskite rhombohedral crystal structure of pure BiFeO3 to orthorhombic crystal structure by the co-substitution of Se and La. The SEM results revealed that the shape of the nanocomposites is continuously changed with increasing Se concentration starting first from nanoparticles shape to needle-like to the nanosheets and ending up to the self-growth flower-like structure under the same synthesis conditions. The magnetization of BFSex and L8Sex is large at initial Se concentration but the coercivity and squareness of the magnetic hysteresis increase with increases in Se concentration. The results revealed that various co-doped BFO novel nanostructures can be synthesized using simple and economical method for variable magnetic properties.

Facile Sol-Gel Synthesis of Calcium Phosphates: Influence of Ca/P Ratio and Calcination Temperature

Calcium phosphates (CP) have been synthesized by sol-gel method in various calcium to phosphorus molar ratio and calcination temperatures. The objective of this study was to understand the influence of molar ratio Ca/P and calcination temperature on crystalline phase of CP. Sol-gel synthesis of calcium phosphates have been performed at room temperature by mixing calcium nitrate and phosphoric acid at Ca/P molar ratio 1.0, 1.3 and 1.5. Gel of synthesis products were dried at 110°C to produce powder then measured by thermal analysis of Differential Scanning Calorimetry-Thermogravimetric Analysis (DSC-TGA). Powders of CP were calcined at 110, 400 and 600°C based on thermal analysis result. Crystalline phase and chemical bonds of calcined CP powders were characterized by X-Ray Diffractometer (XRD) and Fourier Transform Infrared Spectrophotometer (FTIR).

Facile sol-gel synthesis of C@MoSe2 core-shell composites as advanced hydrogen evolution reaction catalyst

In this work, we show the successful synthesis of MoSe2 particle and C@MoSe2 core-shell composite electrocatalysts by a simple sol-gel approach. The carbon sphere shells can effectively prevent the aggregation of MoSe2 nanosheets and greatly improve the conductivity of the hybrid structure, making the C@MoSe2 has good HER activity with an onset overpotential of ∼−170 mV and a Tafel slope of ∼72 mV dec−1. This work paves a new way to synthesize MoSe2-based electrocatalyst and can be extended as a general strategy to prepare other two-dimensional materials, such as WSe2 and VSe2.

Facile NiOx Sol-Gel Synthesis Depending on Chain Length of Various Solvents without Catalyst for Efficient Hole Charge Transfer in Perovskite Solar Cells.

Nickel oxide (NiOx)–based perovskite solar cells (PSCs) have recently gained considerable interest, and exhibit above 20% photovoltaic efficiency. However, the reported syntheses of NiOx sol-gel used toxic chemicals for the catalysts during synthesis, which resulted in a high-temperature annealing requirement to remove the organic catalysts (ligands). Herein, we report a facile “NiOx sol-gel depending on the chain length of various solvents” method that eschews toxic catalysts, to confirm the effect of different types of organic solvents on NiOx synthesis. The optimized conditions of the method resulted in better morphology and an increase in the crystallinity of the perovskite layer. Furthermore, the use of the optimized organic solvent improved the absorbance of the photoactive layer in the PSC device. To compare the electrical properties, a PSC was prepared with a p-i-n structure, and the optimized divalent alcohol-based NiOx as the hole transport layer. This improved the charge transport compared with that for the typical 1,2-ethanediol (ethylene glycol) used in earlier studies. Finally, the optimized solvent-based NiOx enhanced device performance by increasing the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF), compared with those of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)–based devices.

Preparation, Structural Characteristics, and Catalytic Performance of Cu–Co Alloy Supported on Mn–Al Oxide for Higher Alcohol Synthesis via Syngas

A series of Mn–Al oxide supported Cu–Co alloy catalysts having various molar ratios of Cu/Co were prepared using the facile sol–gel synthesis, with the aim of investigating the effects of the chemical, physical properties in the catalytic behavior on higher alcohol synthesis (HAS). The as-prepared samples were characterized through utilizing XRD, BET, TEM, XPS, H2-TPD/TPR, CO-TPD, in-situ CO adsorption DRIFTS, and CO-TPSR techniques. The study suggests that the proper ratio of Cu/Co could adjust the amount of adsorbed hydrogen and nondissociatively adsorbed CO at the surface of catalyst on CO hydrogenation and insertion, improve the reducibility, and ameliorate the catalytic behavior for HAS. Especially, the 3Cu–5Co/(Mn–Al) catalyst showed the best catalytic behavior with a CO conversion of 33.4%, total alcohol selectivity of 39.7%, C2+ alcohol selectivity in the total alcohols of 57.3% at GHSV of 5000 h–1, 260 °C, and 5 MPa.

Facile sol-gel synthesis and enhanced photocatalytic activity of the V2O5-ZnO nanoflakes

Abstract The structural, optical and photocatalytic properties of V2O5-ZnO nanoflakes are reported. A facile sol-gel method was employed for the synthesis of ZnO and V2O5-ZnO nanostructures. Structural characterizations revealed a flake-type structure of V2O5-ZnO obtained from ZnO nanorods. A decrease in the band gap from 3.28 eV for ZnO to 2.64 eV for V2O5-ZnO was observed by Ultraviolet (UV)-Visible spectroscopy. The V2O5-ZnO based photodegradation of methylene blue (MB) dye indicated that the anchoring of V2O5 in the ZnO composite improved the photocatalytic efficiency of the composite under irradiation of the visible light.

Polyethylene glycol assisted facile sol-gel synthesis of lanthanum oxide nanoparticles: Structural characterizations and photoluminescence studies

In this study, lanthanum oxide nanoparticles (La2O3 NPs) synthesised via the facile sol-gel method, using a solution of micro-sized lanthanum oxide powders containing 20% nitric acid and high molecular weight polyethylene glycol (PEG). The as synthesised La2O3 NPs were then characterized using X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), energy-dispersive X-ray (EDS) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy. Our findings indicated that the concentration of PEG strongly influences the particle size and the lattice strain of the La2O3 NPs. A single phase hexagonal crystal structure was confirmed via XRD studies with lattice constants, a = b = 0.3973 nm and c = 0.6129 nm. The average crystallite size and lattice strains estimated were in the range of approximately 25–28 nm and 0.0050–0.0055 respectively. The incremental nature of the crystallinity and lattice strains of the NPs was observed with the subsequent enhancement of PEG-contents, while the average particle size was reduced. The average particle size of La2O3 NPs estimated from ESEM imaging was consistent with that obtained from the XRD data. The photoluminescence spectra revealed a strong emission band located at a wavelength of 365 nm (typical green band) for all La2O3NPsamples. This is ascribed to the recombination of delocalized electrons around the conduction band with a single charged state of a surface oxygen vacancy.