Sol-gel Synthesis Research Articles

Production of cost-effective green energy using Mn/Gd co-substituted cobalt ferrites hydroelectric cells and their oxygen evolution reaction

A thorough investigation into hydroelectric cells (HECs) composed of spinel ferrites, aiming to generate environmentally friendly electricity through the dissociation of water molecules into H3O+ and OH- ions without producing any harmful by-products has been reported. Utilizing a modified sol-gel auto-combustion synthesis method, we synthesized highly porous Mn2+/Gd3+ co-substituted cobalt ferrites (CFO) with the formula) [Co1-xMnxFe2-yGdyO4, 0≤x≤0.30 and y = 0.10]. X-ray diffraction (XRD) analysis revealed a singular-phase cubic structure, while Rietveld refinement provided essential parameters such as crystallite size, lattice constant, density, porosity percentage, and unit-cell volume. Morphological examination using Field emission scanning electron microscopy (FESEM) confirmed nanoparticle formation with an average size of 60.418 nm, and porosity increasing from 30 % to 51 % with Mn2+ ion doping, indicating enhanced water adsorption. XPS analysis highlighted increased lattice defects due to Mn/Gd co-substitution, boosting water adsorption capacity. Vibrating Sample Measurements showed a rise in Ms value with increasing Mn2+ concentration. Fabricated HECs delivered a maximum output current density of 13.906 mA/cm2, with 20 % Mn-substituted gadolinium cobalt ferrites-based HEC achieved a peak short-circuit current of 9.16 mA. These cells exhibited pseudo-capacitive behaviour, characterized by rapid and reversible faradaic reactions near electrode surfaces, while ionic diffusion mechanisms confirmed ion diffusion over the material's surface. Co1-xMnxGd0.1Fe1.9O4 (x = 0.20) is the optimal composition to get best OER performance having an overpotential of 342 mV at 10 mA/cm2 with a Tafel slope of 48 mV/dec in alkaline medium. This study underscores the potential of Mn2+/Gd3+ co-substituted cobalt ferrite as a promising alternative in green energy conversion applications, potentially replacing conventional fuel and solar cells. It has been concluded that the x = 0.20 is the composition that exhibits the best OER as well as HEC performance.

Effect of N-Doped Carbon on the Morphology and Oxygen Reduction Reaction (ORR) Activity of a Xerogel-Derived Mn(II)O Electrocatalyst

This work synthesizes a xerogel from a sol–gel synthesis strategy and supports it on N-doped carbon support from spent coffee biomass (Mn(II)O/N-CC, hereafter MnO) as an efficient oxygen reduction reaction (ORR) catalyst in alkaline electrolytes. The effects of N-CC carbon content on MnO nanoparticle size, dispersion, distribution, morphology, and electrochemistry on ORR are discussed. The SEM and TEM measurements show that increasing the N-CC content during the MnO gelation reaction improved MnO dispersion and particle size during thermal treatment, increasing the ORR’s electrochemical active surface area. Several physiochemical and electrochemical characterizations show a clear relationship between N-CC catalysts and ORR activities. The best catalyst, MnO/N-CC-5, had an even distribution of 27 nm MnO nanoparticles on the N-CC support. The MnO/N-CC-5 catalyst had almost identical ORR kinetics and stability to those of the state-of-the-art Pt/C catalyst in 0.1 M KOH electrolytes, losing only 10 mV in half-wave potential after 5000 potential cycles and retaining 96% of current for over 10 h of continuous chronoamperometric stability. By measuring the electrochemical active surface areas of various catalysts by cyclic voltammetry at different scan rates and measuring the double layer capacitance (Cdl) and ECSA, MnO/N-CC-5 catalysts were shown to have enhanced ORR activity. The XPS analysis explains the ORR activity in terms of the Mn3+/Mn4+ ratio, and a mechanism was proposed. These findings suggest that the MnO/N-CC-5 catalyst could be a cathode catalyst in fuel cells, biofuel cells, metal–air batteries, and other energy conversion devices.

Transition Metal-Doped Layered Iron Vanadate (FeV3-xMxO9.2.6H2O, M = Co, Mn, Ni, and Zn) for Enhanced Energy Storage Properties.

With its distinctive multiple electrochemical reaction, iron vanadate (FeV3O9.2.6H2O) is considered as a promising electrode material for energy storage. However, it has a relatively low practical specific capacitance. Therefore, using the low temperature sol-gel synthesis process, transition metal doping was used to enhance the electrochemical performance of layered structured FeV3O9.2.6H2O (FVO). According to this study, FVO doped with transition metals with larger interlayer spacing exhibited superior electrochemical performance than undoped FVO. The Mn-doped FVO electrode showed the highest specific capacitance and retention of 143 Fg-1 and 87%, respectively, while the undoped FVO showed 78 Fg-1 and 54%.

Ionogels in Aqueous Media: From Conductometric Probing of the Ionic Liquid Washout to the Design of More Stable Materials

Although the most promising applications of ionogels require their contact with aqueous media, few data are available on the stability of ionogels upon exposure to water. In this paper, a simple, easy-to-setup and precise method is presented, which was developed based on the continuous conductivity measurements of an aqueous phase, to study the washout of imidazolium ionic liquids (IL) from various silica-based ionogels immersed in water. The accuracy of the method was verified using HPLC, its reproducibility was confirmed, and its systematic errors were estimated. The experimental data show the rapid and almost complete (>90% in 5 h) washout of the hydrophilic IL (1-butyl-3-methylimidazolium dicyanamide) from the TMOS-derived silica ionogel. To lower the rate and degree of washout, several approaches were analysed, including decreasing IL content in ionogels, using ionogels in a monolithic form instead of a powder, constructing ionogels by gelation of silica in an ionic liquid, ageing ionogels after sol–gel synthesis and constructing ionogels from both hydrophobic IL and hydrophobic silica. All these approaches inhibited IL washout; the lowest level of washout achieved was ~14% in 24 h. Insights into the ionogels’ structure and composition, using complementary methods (XRD, TGA, FTIR, SEM, NMR and nitrogen adsorption), revealed the washout mechanism, which was shown to be governed by three main processes: the diffusion of (1) IL and (2) water, and (3) IL dissolution in water. Washout was shown to follow pseudo-second-order kinetics, with the kinetic constants being in the range of 0.007–0.154 mol−1·s−1.

Structural, optical, luminescent and magnetic properties of Gd2O3 nanoparticles: A comparative study on the effect of different green fuels in the sol–gel synthesis tactics

In this study, five samples of Gd2O3 NPs (size range: 4–33 nm) were synthesized by five different green facile and diverse natural products acting as reducing & stabilizing agents such as: fresh juices of sugarcane, lemon, tomato & orange fruits and citric acid via self combustion sol–gel tactics. Powder X-ray diffraction (PXRD), High resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) and Raman analysis affirmed cubic-C type crystal structure of Gd2O3 NPs prepared using citric acid, lemon juice and sugarcane juice. Mixed cubic and monoclinic phases were observed in Gd2O3 NPs prepared using tomato and orange juices. Notably, NPs of Gd2O3 in quantum dot regime (size: 6 ± 2 nm) were produced in the fresh sugarcane juice mediated synthesis protocol. Fresh lemon juice and sugarcane juice were appeared to be the most efficient green fuel for producing quality samples of Gd2O3 NPs. Optical absorption studies showed that bandgap in these Gd2O3 NPs is strongly dependent on the preparation protocol and type of green fuel. Interestingly, highest and lowest band gap of 4.91 eV and 4.43 eV were obtained for Gd2O3 NPs fabricated with orange and lemon juices, respectively. Photoluminescence (PL) and electron spin resonance (ESR) analysis affirmed formation of Schottky and Frenkel surface defects along with self trapped excitons and oxygen vacancies in these Gd2O3 NPs. Paramagnetic character of these Gd2O3 NPs at 300 K is validated by dc-magnetization and ESR studies. Present study demonstrated that microstructural, optical absorption and photoluminescence properties of Gd2O3 NPs can be easily customized by choice of natural products in the synthesis tactics.

Efficient removal of basic yellow 28 dye from water using facilely synthesized ZnO and Mg3B2O6 nanostructures

Basic yellow 28 dye, used extensively in the textile and leather industries, poses significant environmental and health risks, including allergic reactions, skin irritation, and respiratory problems. This study reports the Pechini sol-gel synthesis of novel ZnO/Mg3B2O6 nanostructures for the decontamination of basic yellow 28 dye from aqueous solutions. The nanostructures were synthesized by calcining at 650 and 850 °C for 5 h, producing ZM650 and ZM850, respectively. The average crystallite sizes were 39.28 nm for ZM650 and 51.03 nm for ZM850. BET surface areas were 70.71 m2/g for ZM650 and 48.13 m2/g for ZM850. FE-SEM and HR-TEM analyses revealed distinct morphological structures, with ZM650 exhibiting a dense aggregation of rod-like particles and ZM850 showing larger clusters. The maximum adsorption capacities were 381.68 mg/g for ZM650 and 303.03 mg/g for ZM850. The optimum adsorption was observed at a pH of 10, a contact time of 70 min, and a temperature of 298 K. Regeneration using a 6 M HCl solution demonstrated efficient reusability over five cycles. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm, indicating monolayer adsorption. Also, the adsorption process was found to be physical and exothermic.

Dysprosium chromite nanoparticles: A promising photocatalyst for the remediation of ciprofloxacin and methylene blue from wastewater

A facile sol-gel synthesis method was employed to synthesize dysprosium chromite (DyCrO3) nanoparticles (NPs), which were subsequently calcined at 750 ∘C to investigate their structural, optical, and photocatalytic properties. Rietveld refinement of powder X-ray diffraction patterns revealed a single-phase orthorhombic structure for the DyCrO3 NPs, exhibiting good crystallinity and belonging to the Pbnm space group. Furthermore, Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy imaging revealed a promising morphology with an average particle size of 30 ± 7 nm. Optical assessments indicated an energy band gap of 2.72 eV, suggesting potential for solar light harvesting as a photocatalyst. Mott-Schottky plots confirmed the n-type semiconductor behavior of the DyCrO3 NPs, and valence band X-ray photoelectron spectroscopy analysis supported these findings. Electronic band structure calculations showed a substantial conduction band minimum and a positive valence band maximum, essential for promoting oxygen reduction and oxidation reactions, respectively, which are crucial for photocatalytic activity. Moreover, the synthesized DyCrO3 NPs demonstrated significant potential as efficient photocatalysts, effectively decomposing the antibiotic ciprofloxacin (CIP) under solar light. Notably, the DyCrO3 NPs achieved 83 % degradation of CIP within 240 min of solar irradiation. Similarly, under identical conditions, the DyCrO3 NPs photocatalyst showed promise in degrading 70 % of the colored organic pollutant methylene blue (MB). Interestingly, during the first 120 min, the degradation of CIP was approximately 25 % greater than that of MB. The ability of DyCrO3 NPs to efficiently degrade both colored and colorless pollutants highlights the catalyst’s inherent photocatalytic nature, rather than merely relying on dye-sensitization effects. Furthermore, the presence of DyCrO3 NPs reduced the activation energy for CIP degradation from 31.657 kJ mol−1 K−1 to 20.846 kJ mol−1 K−1, providing additional evidence of their true catalytic efficacy. Apparent quantum yield values of 40 % for CIP and 35 % for MB degradation further illustrate their superior solar energy harvesting ability. A comprehensive mechanism was developed to explain the impressive photocatalytic performance of the synthesized NPs, highlighting their potential in degrading pharmaceutical antibiotics.

Sol-gel synthesis, characterizations of efficient Y3+ doped ZnO nanoparticles for photocatalytic dye degradation and energy storage applications

Sol-gel synthesis, characterizations of efficient Y3+ doped ZnO nanoparticles for photocatalytic dye degradation and energy storage applications

Synthesis and Applications of Nanocomposites in Food Packaging Industry: A Review

The current review focuses on the applications of polymer nanocomposites in the packing industry. Nanocomposite fabrication may be carried out through several synthetic techniques based on the type of material required. Basically, it is the composite formation of polymeric matrix and a reinforcing nanofiller. The nanoclay used for the modification of nanocomposites acts as a reinforcement or filler. Montmorillonite (MMT) is the most frequently used clay material to obtain the desired properties of nanocomposite. Clay reinforcement enhances the food packing properties of the material because of its properties as flame retardant, tensile features, barrier properties, and biodegradability. Among bottom-up and top-down techniques, sol-gel synthesis, self-assembly, and polymerization are the most common techniques used for the synthesis of nanocomposites. Nanocomposites derived from bio-polymers make the material biodegradable which, in turn, is one of the most desirable features for their future use. Owing to improved characteristics, clay nanocomposites form a superior class of materials for food packaging, yet much finer dispersion of nanofillers and compatibility may be devised.

Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems

The results are summarised of the Seventh International Conference of CIS countries “Sol-gel synthesis and research of inorganic compounds, hybrid functional materials and disperse systems “Sol-gel 2023”, the key reports are discussed within the scientific sections: Theoretical aspects of sol-gel process; Films, coatings and membranes obtained using sol-gel technology; Hybrid organic-inorganic sol-gel materials; Xerogels, glasses and bulk ceramic materials synthesized by sol-gel method; Nano- and microstructured materials, nanotechnology; Methods of research of structure and properties of materials obtained using sol-gel synthesis.

Sol-gel synthesis, structure and adsorption properties of LiMgxMn(2-x)O4 (0 ≤ x ≤ 0.7) Oxides

Lithium manganese оxides with a spinel structure LiMgxMn(2–x)O4, doped with Mg2+ ions in the range 0 ≤ x ≤ 0.7, were obtained by sol-gel synthesis. Phase composition and morphology of obtained оxides were studied by using X-ray phase analysis and scanning electron microscopy. It is shown, that in the studied range 0 ≤ x ≤ 0.7 Mg-doped lithium manganese оxides saved the structure of the original cubic spinel LiMn2O4, while an increase in parameter a was observed from 8.175 to 8.309 Å and average crystallite size practically unchanged (30–36 nm). Samples of the initial LiMn2O4 and Mg-doped spinels were represented by prismatic particles of submicron (0.1–0.2 µm) and micron (1.0–3.0 µm) sizes, respectively. The effect of the adsorbent dose (0.05–0.3 g/l) and pH (3.0–13.0) of the solution on the adsorption efficiency was studied. The adsorption isotherms of the LiMg0.3Mn1.7O4 samples were described by the Langmuir monomolecular adsorption equation. An increase in the temperature of the model solution from 25 to 45°C was accompanied by an increase in the maximum adsorption of the LiMg0.3Mn1.7O4 samples from 10.50 to 10.98 mmol/g, which indicates the endothermic nature of the adsorption process. The kinetics of adsorption was well described by a pseudo-second order equation, which indicates the occurrence of chemical interaction during the adsorption process.

Engineering hard ferrite composites by combining nanostructuring and Al3+ Substitution: From nano to dense bulk magnets

We have investigated the bottom-up sol-gel synthesis of nanocomposite powders comprising two magnetic phases (hexagonal Sr ferrite and spinel Co ferrite) in order to outline a strategy to obtain permanent magnets with large coercivities via low-cost and scalable syntheses. The correlation between morphological, structural and macroscopic magnetic properties of Al-substituted SrFe12O19 and SrFe12O19/CoFe2O4 nanocomposites was analyzed in detail. The hysteretic behavior can be tuned by cation substitution and/or modulation of the super-exchange coupling at the interface of the constituting phases. The magnetic data, supported by Monte Carlo simulations, indicates enhanced magnetic coupling within the composite: this observation underscores the significance of soft crystallite size and epitaxial growth quality at the interface as key factors influencing super-exchange coupling strength, ranging from fully coupled to essentially decoupled composites. Bulk magnets with high density were manufactured by compacting these nanostructured phases using spark plasma sintering, without an applied magnetic field. Consolidation of powders significantly impacted magnetic properties, by increasing remanent magnetization and decreasing coercivity due to enhanced super-exchange coupling. The presence of two phases hindered reciprocal growth, influencing coercivity differently in various compositions. Overall, the compaction enhanced magnet performance through improved particle alignment and super-exchange coupling, offering the potential for optimized magnet design.

Role of chelating agents on the sol-gel synthesis of bismuth ferrite nanoparticles

Role of chelating agents on the sol-gel synthesis of bismuth ferrite nanoparticles

Chemical synthesis, structural and magnetic properties of Al-doped neodymium orthoferrite

Crystalline and single phase of Al doped orthoferrite with stoichiometry NdFe1-xAlxO3 was synthesized by a hydrothermal method. The effect of Al doping on the structure features was investigated by powder X-ray diffraction (PXRD) technique. In this sense, Rietveld refinement was applied in refining the PXRD data. Scanning electron microscopy (SEM) was used to characterize the morphology. And from image analyses show a sub-micron particle size distributions for all samples. Using hydrothermal synthesis method, a micro-sized particle distribution is reached. Measurement of magnetic hysteresis loops showed that the highest coercivity (Hc) obtained was 5.2 kOe for the sample with x=2. Compared to previous results using sol-gel synthesis, the hydrothermal method used in this study showed improved magnetization properties.

The Sol-Gel Process, a Green Method Used to Obtain Hybrid Materials Containing Phosphorus and Zirconium.

The sol-gel process is a green method used in the last few decades to synthesize new organic-inorganic phosphorus-containing hybrid materials. The sol-gel synthesis is a green method because it takes place in mild conditions, mostly by using water or alcohol as solvents, at room temperature. Therefore, the sol-gel method is, among others, a promising route for obtaining metal-phosphonate networks. In addition to phosphorus, the obtained hybrid materials could also contain titanium, zirconium, boron, and other elements, which influence their properties. The sol-gel process has two steps: first, the sol formation, and second, the transition to the gel phase. In other words, the sol-gel process converts the precursors into a colloidal solution (sol), followed by obtaining a network (gel). By using the sol-gel method, different organic moieties could be introduced into an inorganic matrix, resulting in organic-inorganic hybrid structures (sometimes they are also referred as organic-inorganic copolymers).

Non-hydrolytic sol-gel synthesis of amine-functionalized silica: Template- and catalyst-free preparation of mesoporous catalysts for CO2 valorization

Carbon dioxide utilization presents an important and topical research topic. However, the performance of catalysts needed for CO2 transformations does not achieve the necessary levels for their widespread application. To this end, we decided to study non-aqueous condensations providing amine-functionalized silica catalysts, possibly active in CO2-epoxide cycloaddition reaction. While non-hydrolytic sol-gel method is well-known for its efficiency in providing highly porous Lewis and Brønsted acid metallosilicates, here we show for the first time its application for the preparation of silica-based catalysts containing basic groups. First, the reaction conditions were screened to reproducibly obtain porous materials with preserved amine moieties. These were identified as follows: silicon tetraacetate and bridging tertiary amine silanes as precursors, toluene as a solvent, and temperature between 160 and 180 °C. In such a way, materials with up to 776 m2 g−1 and 1.58 cm3 g−1 were obtained in one-step process, without any template, after conventional drying step. Next, the amine-functionalized materials were tested in CO2-epoxide coupling providing cyclic organic carbonates with high selectivity (>99 %) and moderate activity (up to 86 % epichlorohydrin conversion after 1 h at 120 °C and 10 bar CO2). The characterization of spent catalysts revealed a presence of cyclic organic carbonates at the catalyst surface as well as conversion of tertiary amine groups to quaternary ammonium moieties.

Nitrogen doped TIO2/g-C3N4 nanocatalyst for photodegradation of methylene blue dye

In this study, the ethanol dispersion procedure was implemented to prepare the g-C3N4/N–TiO2 nanocatalyst structure. Sol-gel synthesis is utilized for synthesizing N–TiO2 and g-C3N4 via urea thermal decomposition. Physicochemical properties of produced photocatalysts were revealed using PL imaging, UV–vis DRS, XRD, FTIR, SEM, BET, and TEM. Evaluation of photocatalytic activity of synthetic photocatalysts by exposure to sunlight and degradation of methylene blue (MB) dye. g-C3N4/N–TiO2 NCs showed excellent photocatalytic activity, reaching 96 % MB degradation efficiency in 80 min. g-C3N4 and N–TiO2 doped form a nanocomposite structure that increases photocatalytic activity, affecting charge separation performance and service life. The system also exhibits the ability to collect visible and ultraviolet light. Even after four consecutive cycles, the efficiency of the MB is still above 85 %. Capture experiments showed that the decomposition of MB was mainly caused by h+ and O22− radicals. The results of kinetic investigations indicate that the degradation rate of g-C3N4/N–TiO2 nanocomposites surpasses that of N–TiO2 nanoparticles.

In-situ carbon integration on atomically dispersed platinum metal oxide nanocomposites for hydrogen evolution reaction

In this study, a novel in-situ carbon growth technique by a modified sol gel synthesis method is presented. The carbon support developed on a transition metal oxide composite transforms the electronic conductivity and is engineered for hydrogen evolution reaction by a dispersion of unit atomic concentration of platinum. Through two different synthesis techniques, platinum dispersion is implemented on the metal oxide-carbon system, one by direct sol-gel technique and another by chemical reduction technique, whereby a homogeneous dispersion of the noble metal on the composite is achieved. Carbon-based cerium oxide and titanium oxide composites are used as the base material, and one atomic percentage of platinum metal is ensured while synthesizing each of the carbon composites. The functionality of these catalysts towards hydrogen evolution reaction in a 0.5 M H2SO4 acidic media revealed the synthesis technique's uniqueness and the effect of metal support interaction that plays a vital role in the electrocatalytic activity. The intrinsic activity of the titania system, along with enhanced metal support interaction due to highly enriched platinum availability on the surface of the substrate, provides for strong electrochemical activity. The titanium oxide carbon composite with platinum dispersed by hydrazine reduction exhibited the finest activity with an overpotential of just 44 mV at j = 10 mA/cm2 and a tafel slope of 118 mV/dec. The gas chromatographic analysis on platinum supported titania catalyst showcased better performance by a margin of four times than the commercial three weight percentage platinum supported carbon.

A study on bacterial inactivation using green synthesized photocatalytically active TiO2, MgO, TiO2/MgO nanoparticles

Madhuca longifolia (Mahua) flower extracts were utilised to perform the green synthesis of titanium dioxide (TiO2), magnesium oxide (MgO) nanoparticles, and a nanocomposite consisting of TiO2/MgO. Mahua flower extracts were used as both reducing and capping agents in a sol-gel synthesis method. The effectiveness of the green reducing agent in improving the surface structure of the green nanoparticles was demonstrated. FTIR, XRD, FESEM, and UV vis spectroscopy were employed to analyse the successful synthesis of TiO2, MgO, and TiO2/MgO nanocomposites. A study was done to examine the process of employing these nanoparticles to deactivate Escherichia coli (E. coli) by photocatalysis. The effectiveness of these nanoparticles in inhibiting the growth of the bacterial species was demonstrated. The optimisation of the bacterial inactivation experiment was performed using Design Expert's RSM CCD model on all three nanoparticle samples. The optimisation study investigated the impact of nanoparticle concentration and exposure duration on the inhibition of bacterial growth. The highest levels of percent inhibition (%I) were recorded as 85.4 % for TiO2/MgO, 82.8 % for TiO2, and 65.14 % for MgO at a concentration of 50 mg/2 ml and an exposure time of 2 h. The effectiveness of these nanoparticles in exhibiting inhibition has been limited, indicating their prospective use in the advancement of antimicrobial coatings and other applications, such as disinfectants, in the future.

Polypropylene Crystallinity Reduction through the Synergistic Effects of Cellulose and Silica Formed via Sol-Gel Synthesis.

This study focuses on the development of environmentally sustainable polypropylene (PP)-based composites with the potential for biodegradability by incorporating cellulose and the oligomeric siloxane ES-40. Targeting industrial applications such as fused deposition modeling (FDM) 3D printing, ES-40 was employed as a precursor for the in situ formation of silica particles via hydrolytic polycondensation (HPC). Two HPC approaches were investigated: a preliminary reaction in a mixture of cellulose, ethanol, and water, and a direct reaction within the molten PP matrix. The composites were thoroughly characterized using rotational rheometry, optical microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Both methods resulted in composites with markedly reduced crystallinity and shrinkage compared to neat PP, with the lowest shrinkage observed in blends prepared directly in the extruder. The inclusion of cellulose not only enhances the environmental profile of these composites but also paves the way for the development of PP materials with improved biodegradability, highlighting the potential of this technique for fabricating more amorphous composites from crystalline or semi-crystalline polymers for enhancing the quality and dimensional stability of FDM-printed materials.