Sol-gel Calcination Research Articles

Theoretical and experimental investigations of vanadium pentoxide–based electrocatalysts for the hydrogen evolution reaction in alkaline media

A key approach towards better realization of intermittent renewable energy resources, namely, solar and wind, is green electrochemical hydrogen production from water electrolysis. In recent years, there have been increasing efforts aimed at developing noble metal-free electrocatalysts that are earth-abundant and electroactive towards hydrogen evolution reaction (HER) in alkaline electrolytes, wherein an initial water dissociation step is followed by a two-electron transfer cathodic reaction. Although relatively earth-abundant, vanadium-based electrocatalysts have been sparsely reported due to subpar electroactivity and kinetics towards water electrolysis in general and alkaline electrolysis in specific. Herein, we investigate the fine-tuning of orthorhombic V2O5-based electrocatalysts as candidates for HER through a scalable two-step sol–gel calcination procedure. Briefly, surface-induced anionic oxygen deficiencies and cationic dopants are synergistically studied experimentally and theoretically. To that end, first-principle facet-dependent density function theory (DFT) calculations were conducted and revealed that the coupling of certain dopants on V2O5 and co-induction of oxygen vacancies can enhance the catalytic HER performance by the creation of new electronic states near the Fermi level (EF), enhancing conductivity, and modulating surface binding of adsorbed protons, respectively. This was reflected experimentally through kinetically non-ideal alkaline electrochemical HER using Zn0.4V1.6O5 whereby − 194 mV of overpotential was required to attain − 10 mA/cm2 of current density, as opposed to pristine V2O5 which required 32% higher overpotential requirement at the same conditions. The disclosed work can be extended to other intrinsically sluggish transition metal (TM)–based oxides via the presented systematic tuning of surface and bulk microenvironment modulation.Graphical

Self-driven degradation of TC-HCl by CuFe2O4/Bi2O3 activated peroxymonosulfate

CuFe2O4/Bi2O3 (hereinafter CFBO) was successfully synthesized by a straightforward sol–gel calcination approach based on citrate complexation in order to efficiently break down tetracycline hydrochloride (TC-HCl) in organic effluent. When there was no light, the degradation rate of 60 min TC-HCl increased from 56.2% to 95.7%, and it had a wide pH application range (3–11). The degrading capacity of activated CFBO by peroxymonosulfate (PMS) was substantially superior than that of the Bi2O3/PMS system. The activation and recoverability of Bi2O3 were significantly enhanced by the magnetic transition metal composite CuFe2O4. The key reaction mechanism of the catalytic process of the CFBO/PMS system was the cycling of Cu(I) and Cu(II), Fe(II) and Fe(III), Bi(III), and Bi(V) species. This efficiently drove the formation of reactive oxygen radicals by CFBO/PMS. In addition, CFBO/PMS possesses strong chemical stability and only exhibits a 6.8% decline in degrading performance after four magnetic recoveries. A potential catalytic mechanism for the self-driven breakdown of TC-HCl by CFBO composite activated PMS is suggested in light of the aforementioned findings.

Catalytic Degradation of Ciprofloxacin in Aqueous Solution by Peroxymonosulfate Activated with a Magnetic CuFe2O4@Biochar Composite

A magnetic copper ferrite and biochar composite (CuFe2O4@BC) catalyst was prepared by an improved sol-gel calcination method and initially used for the removal of antibiotics ciprofloxacin (CIP) by activated peroxymonosulfate (PMS). Using CuFe2O4@BC as the activator, 97.8% CIP removal efficiency could be achieved in 30 min. After a continuous degradation cycle, CuFe2O4@BC catalyst still exhibited great stability and repeatability and could also be quickly recovered by an external magnetic field. Meanwhile, the CuFe2O4@BC/PMS system presented good stability for metal ion leaching, which was far less than the leaching of metal ions in the CuFe2O4/PMS system. Moreover, the effects of various influencing factors, such as initial solution pH, activator loading, PMS dosage, reaction temperature, humic acid (HA), and the inorganic anions were explored. The quenching experiments and the electron paramagnetic resonance (EPR) analysis manifested that hydroxyl radical (•OH), sulfate radical (SO4•-), superoxide radical (O2•-), and singlet oxygen (1O2) were generated in the CuFe2O4@BC/PMS system, while 1O2 and O2•- are mainly involved in the degradation process. The synergistic effect between CuFe2O4 and BC enhanced the structural stability and electrical conductivity of the material, which promoted the bonding between the catalyst and PMS, resulting in the enhanced catalytic activity of CuFe2O4@BC. This indicates that CuFe2O4@BC activating PMS is a promising remediation technique for CIP-contaminated water.

Peroxymonosulfate activation by graphitic carbon nitride co-doped with manganese, cobalt, and oxygen for degradation of trichloroethylene: Effect of oxygen precursors, kinetics, and mechanism

• Graphitic carbon nitride co-doped with manganese, cobalt, and oxygen was synthesized with different oxygen precursors. • Citric acid proved to be effective oxygen precursor doped in the PMS activator. • The atom ratio of carbon to nitrogen and the metal content on the surface of the catalysts effected the activation of PMS. • The underestimation of SO 4 ·- contribution due to excess scavengers was proposed by competitive kinetics model. Graphitic carbon nitride (g-C 3 N 4 ) doped with metals and nonmetals has been widely applied to activating peroxymonosulfate (PMS) for removing organic pollutants. Herein, g-C 3 N 4 co-doped with manganese, cobalt, and oxygen (MCOCN) was prepared via a facile sol–gel calcination protocol for PMS activation to eliminate trichloroethylene (TCE). The influence of different oxygen precursors, namely citric acid, oxalic acid, and barbituric acid, on the catalytic capability of the MCOCN was investigated. Superior performance was found when the MCOCN was synthesized by the citric acid as the oxygen precursor; 100% TCE removal was achieved within 10 min by adding a 0.5 g/L catalyst and 1 mM of the PMS without a pH adjustment. The difference in the activity of the resultant catalysts could be ascribed to the carbon-to-nitrogen ratio and the content of metal on the surface of prepared catalysts. The impacts of parameters such as the concentration of the PMS, the initial pH, and the dose of the catalyst on the kinetics of trichloroethylene degradation were also investigated. A competitive kinetic model was employed to confirm that contribution of the sulfate radicals in TCE degradation was underestimated when the concentration of the quencher was set at 100 times the concentration of the oxidant. The quenching experiments demonstrated that OH ∙ and SO 4 ∙ - were the main reactive species, while 1 O 2 and O 2 ∙ - played a minor role in the degradation of the TCE by the MCOCN–PMS system. Furthermore, the reusability and ion leaching of the prepared catalysts were evaluated. Our results provide fundamental insights into applying the MCOCN to PMS activation for eliminating trichloroethylene in groundwater.

Synthesis, structure, and optical properties of nanopowders CdS: xAl (x=0, 1, 5, 10, 15 and 20%) via the sol–gel technique

The nanocrystalline Al-doped CdS semiconductors were produced accurately by the sol-gel calcination process. The aluminum was added with different percent’s (0, 1, 5, 10, 15, and 20 wt%) to the synthesized CdS. Both FT-Raman analysis and UV–VIS-NIR absorption measurements were utilized to characterize the studied semiconductors' structural and optical characteristics. The detected X-ray diffraction (XRD) patterns of the prepared CdS present a polycrystalline structure, and Al-doping does not significantly impact this range. Optical bandgaps were determined for undoped and Al-doped CdS, showing a significant change with the percentage of Al-dopants. With increasing Al-doping up to (20 percent), the optical bandgap for CdS (2.38 eV) grows to reach (2.47 eV) and the allowed transitions were found to be direct for the investigated samples. The blue shift may be the reason for the optical bandgap variations. Scanning Electron Microscope (SEM) micrographs were performed to establish the Al-doped CdS nanostructure to identify the morphological characteristics.

THE INVESTIGATION OF VARIATIONS IN OPTICAL PROPERTIES DEPENDING ON SINTERING TEMPERATURE OF Ni:ZNO NANO POWDERS

In this study, Ni:ZnO nano powders were produced by the sol-gel calcination method to investigate and improve the interaction between sintering temperature and optical properties. ZnO based nano-ceramic materials with superior properties which can be used in several scientific researches and high technology applications and can be easily synthesized were produced by this method. The effect of Ni doping on the optical properties of ZnO nanopowders was investigated through spectrophotometric measurements. The optical band gaps of the samples were calculated from the diffuse reflectance curves using Kubelka-Munk function. It was observed that E g values of the samples changed depending on the Ni dopant and sintering temperature. As a result of the investigations, it was determined that Ni doping and different sintering temperature have significant effects on the optical properties of ZnO nano powders, and the produced samples can be used in high temperature conductive electrode applications, optoelectronic devices, and sensor production.

Synthesis of Magnesium Oxide Nanoplates and Their Application in Nitrogen Dioxide and Sulfur Dioxide Adsorption

In this research, nanostructured magnesium oxide was synthesized through the sol-gel calcination or hydrothermal calcination method using various surfactants. The X-ray diffraction pattern of the materials confirmed that all the prepared magnesium oxide samples were single phase without any impurity. The scanning electron microscopy images and specific surface area values showed that sodium dodecyl sulfate was the most suitable surfactant for the synthesis of magnesium oxide nanoplates with the diameter of 40–60 nm, the average thickness of 5 nm, and a specific surface area of 126 m2/g. This material was utilized for nitrogen dioxide and sulfur dioxide adsorption under ambient condition. The saturated adsorption capacities of magnesium oxide were 174 mg/g for nitrogen dioxide and 160 mg/g for sulfur dioxide, making the magnesium oxide nanoplates a promising candidate for toxic gas treatment.

Tin Oxide Based Nano Electroceramics Obtained from Sol–Gel Process: The Modified of the Structural and Opto-Electrical Properties with the Al Doping

Nano electroceramic samples of undoped and Al doped SnO2 were synthesized by the sol–gel calcination process. The structural, morphological, electrical and optical properties of samples were characterized. X-ray diffraction analysis results confirm that all of the synthesized nanopowders are polycrystalline with a tetragonal structure. The crystallite size values of the prepared nanocomposites were calculated in the range of 21.32–34.33 nm. The values of crystallite size indicate that the prepared powders have nanostructure. The grain size and morphological parameters of the undoped and Al-doped SnO2 nanopowders calculated. AFM measurements suggest that Al dopants ratio could be an effect to control surface parameters of the SnO2 nanomaterials. The optical band gap (Eg) of prepared nanomaterials were calculated using Tauc plot method for the various atomic ratios of Al. The calculated Eg values for samples are found to be in the range from 3.51 to 3.69 eV. The electrical conductivity of undoped and Al doped Tin oxide nanopowders were carried out at the temperature range from 290 to 420 K. It demonstrates that the electrical conductivity at room temperature and the activation energy of samples increase with the Al doping. The obtained results suggest that the structural, morphological, optical and electrical properties of SnO2 based nanomaterials can be controlled and changed with Al content.

Biocompatible Er:(Na,K)NbO3 nanofibers

Dense homogeneous fabric composed from continuous bead-free erbium-doped sodium potassium niobate (Er:NKN) 100 μm long and 100-200 nm in diameter nanofibers was sintered by sol-gel calcination assisted electrospinning technique. Er doping with the concentration of 2 at.% provides readily detectable room-temperature broad-band photoluminescence (PL) centered at λPL = 0.55 and 0.98 μm being pumped, respectively, with 532 and 785 nm lasers. Electric field induced resistance switching and strong electric rectification effect were found in nanoporous sandwich Au/Er:NKN/Pt capacitive cell. Memristor-type current-voltage I-V characteristics originate from the electrochemical migration of oxygen vacancies at the n-type Er:NKN oxide/high work function Pt cathode junction interface.

Preparation and Characterization of Pr<sub>2</sub>Ti<sub>2</sub>O<sub>7</sub> by Sol-Gel Process

Using Pr (NO3)3, butyl titanate, ethylene glycol and citric acid as main raw materials, praseodymium titanate (Pr2Ti2O7) was prepared by the sol-gel process. The samples were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravity-differential thermal analysis (TG-DTA), diffuse-reflection spectra (DRS) and Fourier transform infrared (FT-IR). The effect of different calcination temperature and illumination time on the photocatalytic properties of Pr2Ti2O7 was investigated. It was found that the single phase Pr2Ti2O7 could be obtained through sol-gel process and calcination at 1000 °C. The Pr2Ti2O7 samples calcination at 1000 °C were uniform , and the resulting product had a particle size of 200 nm and an optical band gap of 3.26 eV. Under ultraviolet light, the degradation of methyl orange arrived to 80.11% after 180 min of photocatalytic reaction. The Pr2Ti2O7 samples showed good photocatalytic activity for decomposition of methyl orange.

A Facile Preparation Process of Magnetic Aldehyde-Functionalized Ni(0.5)Zn(0.5)Fe₂O4@SiO₂ Nanocomposites for Immobilization of Penicillin G Acylase (PGA).

A facile sol combustion and gel calcination process has been reported for the preparation of core– shell magnetic Zn0.5Fe₂O₄@SiOnanocomposites. The morphology, chemical composition, structure and magnetic property of as-prepared nanocomposites were investigated by XRD, VSM, BET, SEM, and TEM, and the magnetic Ni0.5Zn0.5Fe₂O₄@SiO₂ nanocomposites were characterized with average size of about 25 nm, saturation magnetization of 90.8 Am²/kg and the specific surface area of 67.1 m2/g. The surface of Ni0.5Zn0.5Fe₂O₄@SiO₂ nanocomposites was functionalized with glutaraldehyde to form the aldehyde-functionalized magnetic Ni0.5Zn0.5Fe₂O4@SiO₂ nanocomposites, and penicillin G acylase (PGA) was successfully immobilized onto them. And the immobilized PGA exhibited high effective activity, good stability of enzyme catalyst and good reusability, and could retain 63.5% of initial activity after 12 consecutive operations. The kinetic parameters were determined, and the value of K m for the immobilized PGA (161.7 mmol/L) is higher than that of the free PGA (3.5 mmol/L), while v max (1.626 mmol/min) is also larger than that of the free PGA (0.838 mmol/min), which revealed that the immobilization of PGA onto Ni0.5Zn0.5Fe₂O₄@SiO₂ nanocomposites was an efficient and simple way for preparation of stable PGA.

Broadband luminescent ferroelectric biocompatible Er:(Na,K)NbO3 nanofibers

AbstractDense homogeneous fabric composed from continuous bead‐free erbium‐doped sodium potassium niobate (Er:NKN) 100 μm long and 100‐200 nm in diameter nanofibers was sintered by sol‐gel calcination assisted electrospinning technique. X‐ray diffraction revealed preferential cube‐on‐cube [001]‐directional growth of fibers containing predominantly monoclinic Na0.35K0.65NbO3‐type phase and significantly less of tetragonal NbO2, cubic Er2O3, and monoclinic ErNbO4 phases. Er doping with the concentration of 2 at.% provides readily detectable room‐temperature broad‐band photoluminescence (PL) centered at λPL = 0.55 and 0.98 μm being pumped, respectively, with 532 and 785 nm lasers. Impedance spectroscopy and static electrical tests revealed ferroelectric properties, electric field induced resistance switching and strong rectification effect in nanoporous sandwich Au/Er:NKN/Pt capacitive cell. Memristor‐type current‐voltage (I‐V) characteristics originate from the electrochemical migration of oxygen vacancies at the n‐type NKN oxide/high work function Pt cathode junction interface.

Synthesis and Characterization of LiZn Ferrites/Carbon Nanotubes (CNTs) Temperature Control Biomaterials

In this study, LiZn ferrites with different content of CNTs (1%-9%) were successfully prepared by a sol-gel method. X-ray diffraction pattern exhibit a relatively high crystallinity of the Li0.25Zn0.5Fe2.25O4/CNTs composite, and the CNTs still exist after acid treatment and subsequent heat treatment. Then the composite was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), the results demonstrate that the particles are nearly spherical in shape and agglomerated to some extent. By a sol-gel method and subsequent calcination, the temperature of LiZn ferrites/CNTs temperature control biomaterials gradually increase and maintain at a certain temperature in the alternating magnetic field, so it can be a potential material used for hyperthermia applications.

Molecularly Imprinted TiO2/WO3-Coated Magnetic Nanocomposite for Photocatalytic Degradation of 4-Nitrophenol Under Visible Light

In this paper, a molecularly imprinted TiO2/WO3-coated magnetic Fe3O4@SiO2 nanocomposite was developed for photocatalytic degradation. Fe3O4 nanoparticles were first prepared by a traditional co-precipitation method, and then a SiO2 shell was grown on the surface of the Fe3O4 nanoparticles. Finally, a 4-nitrophenol imprinted TiO2/WO3 coating was obtained on the surface of the Fe3O4@SiO2 nanocomposite via a sol-gel method and subsequent calcination. The new composite was characterised by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and vibrating sample magnetometry (VSM). In addition, the adsorption ability and photocatalytic activity of the composite were investigated. Results showed that the imprinted composite had higher adsorption ability for the template than the non-imprinted composite. The imprinted catalyst could degrade 4-nitrophenol under visible light with a first-order reaction rate of 0.1039 h–1, which was ~2.5 times that of the non-imprinted catalyst. The new imprinted catalyst showed good catalytic selectivity, an ease of being recycled by an external magnetic field, good reusability, no need for additional chemicals, and allows the possibility of utilising solar light as energy resource. Therefore, the catalyst can be potentially applied for ‘green’, low-cost and effective degradation of 4-nitrophenol in real wastewater.

Band Gap Engineering of In2TiO5 for H2 Production under Near-infrared Light.

In2TiO5, containing both early transition metal (d(0)) and p-block metal (d(10)), is a very promising candidate for possible application in H2 production because of its suitable edges of conduction and valence bands and the crystal structure, which is considered to favor mobility of charge carriers. Herein we report, for the first time, the synthesis of novel oxygen vacancies (OV), N-doped In2TiO5 (OV,N-In2TiO5) with controllable band gap. The resultant OV,N-In2TiO5 sample was prepared by a multistep sol-gel calcination process and studied as a near-infrared (NIR) light-driven photocatalyst for H2 production. OV and N-doping can effectively extend the photoresponse of In2TiO5 to the NIR region due to an interband springboard and the reduced band gap, thus leading to efficient NIR light photocatalytic H2 production activity with Pt as a cocatalyst.

Gadolinia nanofibers as a multimodal bioimaging and potential radiation therapy agent

Continuous bead-free C-type cubic gadolinium oxide (Gd2O3) nanofibers 20-30 μm long and 40-100 nm in diameter were sintered by sol-gel calcination assisted electrospinning technique. Dipole-dipole interaction of neighboring Gd3+ ions in nanofibers with large length-to-diameter aspect ratio results in some kind of superparamagnetic behavior: fibers are magnetized twice stronger than Gd2O3 powder. Being compared with commercial Gd-DTPA/Magnevist®, Gd2O3 diethyleneglycol-coated (Gd2O3-DEG) fibers show high 1/T1 and 1/T2 proton relaxivities. Intense room temperature photoluminescence, high NMR relaxivity and high neutron scattering cross-section of 157Gd nucleus promise to integrate Gd2O3 fibers for multimodal bioimaging and neutron capture therapy.

Synthesis of Eu-Doped Bi2O3/CeO2 Composite with Enhanced Photocatalytic Activity by a Facile Sol–Gel–Calcination Route

Eu-Doped Bi2O3/CeO2 composites were successfully synthesized by a facile sol–gel–calcination route. The as-prepared composites were prepared with different molar ratios of Bi/Ce/Eu by the sol–gel route, and then calcined at 500°C for 2 h. The photocatalytic efficiencies of all composites were tested by degradation of methyl orange (MO) under visible light irradiation. The result suggested that the best composite is the one that was prepared with a Bi/Ce/Eu mole ratio of 8 : 8 : 1, and achieved a MO degradation rate of nearly 98.5 % within 2 h of irradiation. The as-prepared composites were characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The X-ray diffraction and scanning electron microscopy results suggested that Eu doping may have led to some lattice distortion and particle aggregation that enhanced the photocatalytic activity of the photocatalyst. The UV-visible diffuse reflectance spectroscopy and photoluminescence spectroscopy results showed that Eu-doped Bi2O3/CeO2 exhibited higher visible light response properties and enhanced separation of the photogenerated electron–hole pairs, which is the main reason for the higher photocatalytic activity. In general, this study could provide a facile route to synthesize Eu-doped Bi2O3/CeO2 composites with enhanced photocatalytic activity by a sol–gel–calcination route for environmental purification.

Mo-Doped Cerium Gadolinium Oxide as Environmentally Sustainable Yellow Pigments

Mo-doped Gd1Ce1–xO3.5+Y (where x ranged from 0 to 0.3) oxides were synthesized as inorganic yellow pigments, which are benign and sustainable. The pigments exhibited good yellow color, with the yellowness value using the CIELAB 1976 system being around 39. In comparison to the existing reports on benign yellow pigments, which have been synthesized using high temperature calcination routes, this pigment has been synthesized through a low temperature sol–gel calcination route. The process also provided for a higher degree of size and shape control, leading to a bandgap of 2.82–2.52 eV. Size reduction to the nano level through the process provided a bottom up approach, where the presence of mineralizers enabled higher mass tone (b* value of around 80) at lower covering thickness. NIR solar reflectance, a measure of the ability of the pigment to contribute to energy savings by reflecting heat generating radiations of sunlight, was as high as 91%. The absence of toxic metal ions coupled with excellent chemical...

Synthesis Route for the Safe Production of Targets for Transmutation of Plutonium and Minor Actinides

Use of composites of actinide oxides dispersed in a Mo metal matrix is a recent inert matrix fuel concept for the transmutation of Pu and the minor actinides (Np, Am, and Cm). These elements are present in spent nuclear fuel, and their long-term radiotoxicity can be minimized if they are recovered from the fuel and irradiated in dedicated targets in nuclear reactors. The synthesis of such highly radioactive fuels is not simple, and given the high radiotoxicity of Am, the safety of operation of such a process must be examined for production of small-scale analytical batches. Infiltration of americium nitrate into porous PuO2 beads has potential safety bonuses. The beads are produced by a sol-gel external gelation route. Tests have been developed here with CeO2, as a surrogate for PuO2, and have been optimized for both bead production and pelletization of a blend of calcined beads and Mo powder. Addition of carbon to the sol-gel feed solution and its subsequent pyrolysis provides a means to optimize the porosity of the oxide beads. The carbon acts as a pore former. The highest-quality product meeting typical fuel specifications required addition of 20 g/l carbon in the sol-gel feed and calcination of the CeO2 beads at 800°C. Subsequent Mo cermet composites with 20 or 40 vol% of ceramic reached densities in excess of 90% of the theoretical value as is required for nuclear reactor applications. Finally, the step from CeO2 surrogates to (Pu, Am)O2 targets has been made and pellets of excellent quality produced.

Synthesis, diffused reflectance and electrical properties of nanocrystalline Fe-doped ZnO via sol–gel calcination technique

The nanocrystalline ZnO:Fe semiconductor oxides were successfully synthesized via the sol–gel calcination method. Structural, optical and electrical properties of the investigated samples were characterized by various techniques such as atomic force microscopy (AFM), UV–vis absorption and electrical transport measurements. The optical band gap for undoped ZnO (3.19eV) decreases (2.75eV) with increasing Fe-doped ZnO (20%). The temperature dependences of the electrical conductivities of undoped ZnO and Fe-doped ZnO were measured and analyzed by Arrhenius equation. The electrical conductivity of the samples decreases with the increase of Fe doping ratio; hence, the electrical conductivity mechanism is controlled by thermally activated processes. To support the nanostructure of Fe-doped ZnO, AFM micrographs were performed.