Non-hydrolytic Sol Gel Process Research Articles

Confinement Effects on the Ionic Liquid Dynamics in Ionosilica Ionogels: Impact of the Ionosilica Nature and the Host/Guest Ratio

Ionosilica ionogels have been lately introduced as emerging all-ionic designer materials. They consist of an ionic liquid (IL) guest trapped within a solid ionosilica support host. In this work, we investigate the influence of the (i) ionosilica nature and (ii) the ionosilica/IL ratio on the mobility of the confined IL. We report the elaboration of various ionosilica ionogels via a nonhydrolytic sol–gel process, using namely tris(3-(trimethoxysilyl)propyl)amine (TTA), methyl-tris(3-(trimethoxysilyl)propyl)ammonium iodide (MTTA), and tetrakis(3-(trimethoxysilyl)-propyl)ammonium iodide (TKTA) as ionosilica precursors, with the IL butyl-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([BMIM] TFSI). Various ionogels were prepared from different ratios between the ionosilica host and the IL guest. The host/guest interactions, i.e., the change in the conformational contribution of the IL counter-anion, were explored by means of Raman spectroscopy. In addition, the transport properties of the confined species were probed via spin echo solid-state NMR experiments and Complex Impedance Spectroscopy (CIS) measurements. Raman experiments revealed different conformational equilibrium for the TFSI anion in the various ionosilica ionogels, with an increase in the cisoid form compared to the bulk IL due to confinement effects. The TFSI anion seems to experience different degrees of confinement and thus different interactions with the ionosilica scaffold as a function of the investigated parameters. Concomitantly, the 1H spin echo NMR and CIS measurements revealed a significantly higher ionic mobility in the materials synthesized from the tris-trialkoxysilylated ammonium precursor compared to the one synthesized from the tetra-trialkoxysilylated ammonium precursor. These results may reflect stronger host–guest interactions in the latter case related to the higher degree of the network reticulation. All these techniques give concordant results and highlight an effect of the chemical constitution of the ionosilica scaffold and the amount of confined IL on its dynamics within the network.

Tuning Polymer/TiO2 Nanocomposites Morphology by In Situ Non-Hydrolytic Sol-Gel Syntheses in Viscous Polymer Medium: Influence of the Polymer Nature and Oxygen Donor.

Herein, we reported the synthesis of TiO2 through different non-hydrolytic sol-gel (NHSG) routes in viscous polymer media. For the first time, the influence of the polymer nature (Polystyrene (PS) or Polypropylene (PP)) on the morphology of synthesized inorganic domains was investigated. The non-hydrolytic sol-gel reactions between titanium isopropoxide Ti(OiPr)4 and acetic anhydride in molten polypropylene lead to the formation of microfillers with a mean diameter of about 1 μm, while the same synthesis carried out in viscous polystyrene lead to the formation of nanofillers with diameter lower than 10 nm forming aggregates of approximately 200 nm. We have also investigated the influence of the oxygen donor nature on the morphology of synthesized fillers using aromatic oxygen donors in a polystyrene matrix. The use of benzoic anhydride or acetophenone as oxygen donors with Ti(OiPr)4 in viscous polystyrene lead to respectively platelet-like morphology or aggregated nanofillers. We demonstrated that the affinity between polymer, reactants, and/or by-products had an influence on the morphology and the size of in situ synthesized TiO2 fillers. These results evidenced for the first time the possibility to control and to tune the morphology of in situ grown inorganic objects through the NHSG process by the appropriate choice of solvent, here a viscous polymer medium, and reactants.

Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO2-Al2O3 mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N2-physisorption, powder XRD, 29Si, 27Al MAS-NMR, and NH3-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to 27Al and 29Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.

SiC/SiC mini-composites with multilayer ZrSiO4 interphase: Room-temperature properties and toughening mechanism

SiC/SiC mini-composites reinforced with SiC fibers coated with different numbers of ZrSiO4 sublayers prepared via a non-hydrolytic sol-gel process were fabricated. The tensile strength and work of fracture of the prepared SiC/SiC mini-composites were determined, and the relationship between their mechanical properties and fracture morphologies was discussed. The toughening mechanism and the variation tendency of their mechanical properties were further elaborated by analyzing the interfacial debonding morphologies of the SiC/SiC mini-composites with 1 and 4 layers of ZrSiO4 interphase as well as the results of prior studies. A relatively rare phenomenon—the delamination of the multilayer ZrSiO4 interphase in the SiC/SiC mini-composites but not on the SiC fibers—was observed, which clearly demonstrated the weak bonding between the ZrSiO4 sublayers in the SiC/SiC mini-composites. The ZrSiO4 sublayer delamination mechanism was then explained based on the high-magnification morphologies found in and beside the ZrSiO4 interphase.

Self-assembled block copolymer electrolyte membranes with silica network-derived nanochannels for all-solid-state supercapacitors

Amphiphilic Block copolymer (BC) membranes, where the BC hydrophilic domain offers a continuous pathway for fast ion transport, while the BC hydrophobic domain provides a scaffold for high mechanical strength, are being widely studied as promising materials for energy storage applications due to their unique morphology with 3-dimensionally continuous macropores. We design silica network-derived poly(styrene)-b-poly(2-vinylpyridine) BC-based hierarchically porous membranes containing high-conducting ionic liquids (ILs) as solid-state electrolytes via nonsolvent-induced phase separation and nonhydrolytic sol–gel process. The introduction of a silica nanoparticle network within the self-assembled BC leads to micro- and nano-scale porous structures. This provides the functionalized BC/IL-based electrolytes (BCEs) with high IL uptake (87 wt%), high dielectric constant (123), low activation energy for ion conduction (6.8 kJ/mol), and high room temperature ionic conductivity (∼10-3 S/cm, comparable to pure IL). The optimized BCE is assembled with activated carbon electrodes, allowing us to fabricate an all-solid-state supercapacitor. The device delivers a broad voltage window (2.5 V), high specific capacitance (∼90 F/g at 0.2 A/g), large energy (E) and power (P) densities (a maximum of E=19 Wh/kg, observed at P=224 W/kg, and a maximum of P=1.3 kW/kg, observed at E=4 Wh/kg), and remarkable electrochemical stability (capacitance retention = 90% for 600 cycles and 76% for 1000 cycles and coulombic efficiency = 100% for 1000 cycles at 0.2 A/g). Therefore, the combination of self-assembly, phase inversion, and in-situ hybridization-derived hierarchical dual-pore construction, providing rapid ion migration, could be a new approach to powering next-generation energy storage devices.

Metallocene encapsulated within a hybrid silica-polystyrene support

A series of heterogeneous metallocene catalysts were prepared by encapsulating Cp2ZrCl2 within silica-polystyrene hybrid support. Immobilization was performed through a non-hydrolytic sol–gel process in which polystyrene (PS) dissolved in toluene and metallocene (1% by wt) were combined. The effect of PS (0 to 5% by wt) and silicon tetrachloride (0.5 to 1.6 [TEOS]/[SiCl4]) was evaluated in terms of catalyst activity in ethylene polymerization with methylaluminoxane as the cocatalyst. According to FTIR measurements, an increase in PS content promoted a decrease in (SiO)6 content, which indicated the formation of more compact structures. Furthermore, homogeneous distributions of polymer and silica phases were observed both in bulk and on the support surface. The results showed very small surface areas (< 20 m2 g−1), probably because PS would fill the silica pores. The catalytic activity for ethylene polymerization was shown to decrease with increasing polystyrene content within the catalyst support of low surface area. A positive correlation was found between the (SiO)6 content and catalyst activity. The increase in the PS content was followed by an increase in the degree of polyethylene crystallization, which ranged from 77 to 84%.

Non-hydrolytic Sol–Gel Route: a Powerful Process to Develop UV-Vis-IR Luminescent YVO4 Phosphors

The spectroscopic properties of lanthanide ions stem from absorption and emission radiation in the solar spectrum range, which promotes numerous applications in areas such as white light emission, bio-imaging, biological markers, and photovoltaic cells, among others. To intensify these properties, several matrixes have been studied, particularly the yttrium vanadate matrix due to its structural, mechanic, and physicochemical properties. The non-hydrolytic sol-gel process is a versatile way to prepare inorganic oxides doped with lanthanide ions. In this work, we describe the synthesis of yttrium vanadate matrixes doped with Eu3+, Er3+, and/or Yb3+ ions (containing 1% lanthanide ions with respect to Y3+ (molar ratio)) by the non-hydrolytic sol-gel, annealed at 800°C for 4h, and their characterization by X-ray diffraction and photoluminescence spectroscopy. The X-ray diffraction patterns display the peaks corresponding to the yttrium vanadate tetragonal phase. Laser excitation at 980nm elicits Er3+ emission bands in the green and red regions and Eu3+ emission at 620nm. Laser excitation at 322nm; i.e., the charge transfer band, provides emission in the same regions, as well as infrared emission. This system is a promising candidate for applications in solar cells, optical amplifiers, and biomarkers because it can be excited at different wavelengths. Graphical Abstract Schematic diagram of the energy level of lanthanides and vanadate ions, and energy transfer.

Preparation of Nanocomposite Polymer Electrolyte via In Situ Synthesis of SiO2 Nanoparticles in PEO

Composite polymer electrolytes provide an emerging solution for new battery development by replacing liquid electrolytes, which are commonly complexes of polyethylene oxide (PEO) with ceramic fillers. However, the agglomeration of fillers and weak interaction restrict their conductivities. By contrast with the prevailing methods of blending preformed ceramic fillers within the polymer matrix, here we proposed an in situ synthesis method of SiO2 nanoparticles in the PEO matrix. In this case, robust chemical interactions between SiO2 nanoparticles, lithium salt and PEO chains were induced by the in situ non-hydrolytic sol gel process. The in situ synthesized nanocomposite polymer electrolyte delivered an impressive ionic conductivity of ~1.1 × 10−4 S cm−1 at 30 °C, which is two orders of magnitude higher than that of the preformed synthesized composite polymer electrolyte. In addition, an extended electrochemical window of up to 5 V vs. Li/Li+ was achieved. The Li/nanocomposite polymer electrolyte/Li symmetric cell demonstrated a stable long-term cycling performance of over 700 h at 0.01–0.1 mA cm−2 without short circuiting. The all-solid-state battery consisting of the nanocomposite polymer electrolyte, Li metal and LiFePO4 provides a discharge capacity of 123.5 mAh g−1, a Coulombic efficiency above 99% and a good capacity retention of 70% after 100 cycles.

Mechanistic insight into the non-hydrolytic sol–gel process of tellurite glass films to attain a high transmission

The development of amorphous films with a wide transmission window and high refractive index is of growing significance due to the strong demand of integrating functional nanoparticles for the next-generation hybrid optoelectronic films. High-index TeO2-based glass films made via the sol–gel process are particularly suitable as their low temperature preparation process promises high compatibility with a large variety of nanoparticles and substrates that suffer from low thermal stability. However, due to the lack of in-depth understanding of the mechanisms of the formation of undesired metallic-Te (highly absorbing species) in the films, the preparation of high-transmission TeO2-based sol–gel films has been severely hampered. Here, by gaining insight into the mechanistic chemistry of metallic-Te formation at different stages during the non-hydrolytic sol–gel process, we identify the chemical route to prevent the generation of metallic-Te in a TeO2-based film. The as-prepared TeO2-based film exhibits a high transmission that is close to the theoretical limit. This opens up a new avenue for advancing the performance of hybrid optoelectronic films via incorporating a large variety of unique nanoparticles.

Ag- and Cu-Promoted Mesoporous Ta-SiO2 Catalysts Prepared by Non-Hydrolytic Sol-Gel for the Conversion of Ethanol to Butadiene

The direct catalytic conversion of bioethanol to butadiene, also known as the Lebedev process, is one of the most promising solution to replace the petro-based production of this important bulk chemical. Considering the intricate reaction mechanism—where a combination of acid-catalyzed dehydration reactions and metal-catalyzed dehydrogenation have to take place simultaneously—tailor-made bifunctional catalysts are required. We propose to use non-hydrolytic sol-gel (NHSG) chemistry to prepare mesoporous Ta-SiO2 materials which are further promoted by Ag via impregnation. An acetamide elimination route is presented, starting from silicon tetraacetate and pentakis(dimethylamido)tantalum(V), in the presence of a Pluronic surfactant. The catalysts display advantageous texture, with specific surface area in the 600–1000 m² g−1 range, large pore volume (0.6–1.0 mL g−1), an average pore diameter of 4 nm and only a small contribution from micropores. Using an array of characterization techniques, we show that NHSG allows achieving a high degree of dispersion of tantalum, mainly incorporated as single sites in the silica matrix. The presence of these monomeric TaOx active sites is responsible for the much higher dehydration ability, as compared to the corresponding catalyst prepared by impregnation of Ta onto a pristine silica support. We attempt to optimize the butadiene yield by changing the relative proportion of Ta and Ag and by tuning the space velocity. We also demonstrate that Ag or Cu can be introduced directly in one step, during the NHSG process. Copper doping is shown to be much more efficient than silver doping to guide the reaction towards the production of butadiene.

Supported metallocenes produced by a non-hydrolytic sol-gel process: Application in ethylene polymerization

The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxides SiO2-CrO3, SiO2-MoO3 and SiO2-WO3 using a non-hydrolytic sol-gel route. Catalyst performance was evaluated in ethylene polymerization. The highest catalyst activity was found with a lower metal chloride:Si ratio and catalyst bearing W moieties. The catalyst and oxide matrices were characterized by complementary techniques (nitrogen porosimetry, small angle X-ray scattering, Fourier Transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential pulse voltammetry). The interaction between the binary oxide support and the immobilized metallocene reduced the electron density on the Zr centers, enabling the activation reaction to occur with lower concentrations of the methylaluminoxane (MAO) co-catalyst (Al/Zr = 500). The catalytic activity showed a direct relationship with the size and shape of the mass fractal. The results demonstrate that the entrapping method allows for the generation of a catalyst system in which part of the activation process may be attributed to the support.

Synthesis of High Refractive Index Epoxy Modified Methyl Phenyl Silicone Resin and Amine Phenyl Silicone Resin for LEDs Packaging

A series of epoxy modified methyl phenyl silicone resins with different epoxy values were prepared by an approach of combination of hydrolytic sol-gel and non-hydrolytic sol-gel process. Then, in order to solve poor compatibility between epoxy modified silicone resins and commercial amine curing agents, amine phenyl silicone resin curing agent was synthesized by non-hydrolytic sol-gel method. The test results exhibited that the process of combination of hydrolytic sol-gel and non-hydrolytic sol-gel process had a significant effect on the elimination of hydroxyl groups. A lot of experiments and mechanism analysis exhibited that the activity and content of hydroxyl groups are two important factors for ring-opening of epoxy groups and gelation of product. So, epoxy groups can be stably and efficiently introduced in the terminal of product in the course of non-hydrolytic sol-gel process, which hugely avoided ring-opening of epoxy groups. Subsequently, epoxy modified silicone materials were obtained by thermal curing reaction between epoxy modified silicone resins with different epoxy values and amine phenyl silicone resin. And the curing reaction can be completed at 80 °C for 2 h. Transmittance of light, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and reliability test were used to analyze performance of epoxy modified silicone materials. The results exhibited that prepared silicone materials had a high transmittance (>90%), strong adhesive strength, good thermal stability and mechanical performance. Therefore, epoxy modified silicone material can be applied in high-power LEDs packaging.

Preparation of Nano-TiO2/Diatomite Composites by Non-hydrolytic Sol–Gel Process and its Application in Photocatalytic Degradation of Crystal Violet

The dispersion of anatase TiO2 on diatomic material was a prospective route to avoid agglomerates of these particles. In this work, the TiO2/diatomite composites were prepared using a solvothermal process and a non-hydrolytic sol-gel method at low temperature on the raw (TDB) and the purified (TDS) diatomite. The synthesized samples were characterized utilizing various techniques. These given that TiO2 anatase was impregnated well on the surface of diatomite, and the immobilization of these particles tends to increase the thermal stability of the composite as compared to the raw diatomite. In addition, the photodegradation of crystal violet (CV) in solution was in the direction of TDB > TDS > TiO2. The 99.996% of CV can be degraded in 210 min of irradiation time at pH 10. These results revealed that the immobilization of titanium on diatomite improves the photocatalytic degradation by reducing the crystallite size of anatase TiO2.

Synthesis of High-Refractive-Index Epoxy-Modified Vinyl Methyl Phenyl Silicone Resins for Encapsulation of LEDs

A series of high-refractive-index epoxy-modified vinyl methyl phenyl silicone resins with different content of vinyl groups have been synthesized by a combination of hydrolytic and nonhydrolytic sol–gel processes to improve their adhesion. The products were characterized by Fourier-transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The results showed that epoxy and vinyl groups were successfully introduced into the products while the content of hydroxyl groups was low. Then, epoxy-modified silicone materials were manufactured by addition reaction between the epoxy-modified vinyl methyl phenyl silicone resins and hydrogen-containing phenyl silicone resin. The epoxy-modified silicone materials were characterized by thermal aging (250°C for 2 h) experiments, light transmittance measurements, thermogravimetric analysis, red dye penetration tests, reflow soldering (270°C for 10 cycles), and lumen depreciation (50 mA for 165 h) tests. The results showed that the epoxy-modified silicone materials exhibited high transmittance (> 90%) and good thermal stability. The epoxy-modified silicone materials showed better resistance to high temperature and ultraviolet (UV) radiation than commercial epoxy resin (6103). The introduced epoxy groups greatly improved the adhesion of the silicone resin. The epoxy-modified silicone material prepared using epoxy-modified vinyl methyl phenyl silicone resin with higher content of vinyl groups showed better mechanical performance (50 Shore D). The epoxy-modified silicone material EVMPS-3′ is expected to be applicable in packaging of high-power light-emitting diodes (LEDs).

Stimuli-responsive amphoteric ion exchange polymers bearing carboxylic and amine groups grafted to a cross-linkable silica network

Stimuli-responsive hybrid organic-inorganic amphoteric ion exchange polymers were synthesized via a non-hydrolytic sol–gel process with carboxylic acid and amine groups in silica side chains. Structural characterization of samples with a ratio carboxylic acid/amine 1:2 (PSU-SiCA(1:2)) and 2:2 (PSU-SiCA(2:2)) showed a degree of functionalization of 0.5 in both cases. The ion exchange capacity, analysed by acid-base titration, elemental analysis and thermogravimetric analysis, was 1.8 meq/g for PSU-SiCA(1:2) and 1.2 meq/g for PSU-SiCA(2:2). pH-Dependent properties for acidic, basic and zwitterionic forms were studied including hydration isotherms, ionic conductivity and selective deposition on acidic and basic substrates. The water uptake and ionic conductivity of the acidic and basic forms were highest for PSU-SiCA(1:2), due to the higher IEC. The zwitterionic forms, which contain a minimum of mobile ions, showed the lowest water uptake and ionic conductivity. The acidic form deposited on basic Al2O3 substrates and the basic form on acidic SiO2, whereas the zwitterionic polymer was deposited on neither. The stimulus-dependent ionic conductivity and hydration and the selective deposition depending on interfacial charges are striking properties, which make these hybrid bio-friendly ionomers compelling for applications.

A full palette: Crystal chemistry, polymorphism, synthetic strategies, and functional applications of lanthanide oxyhalides

Ionic compounds wherein lanthanide cations are arrayed alongside anions adopt a wide range of crystal structures as a result of the variation of ionic radii and electronic configurations across the lanthanide series. Owing to the constricted nature of 4f orbitals, local coordination environments and structural preferences in such compounds are primarily dictated by electrostatic interactions and steric considerations with the primary driving force being the minimization of the crystal lattice energy. In this review, we examine a broad class of dianionic rare-earth compounds, lanthanide oxyhalides that present a multidimensional design space for tuning of functional properties by dint of the possibilities for extensive alloying on cationic and anionic sublattices; the considerable span of ionic radii and hardness across the lanthanide series and down the halide group, respectively; a large tolerance window for point defects such as oxide and halide vacancies; as well as multiple accessible polymorphs. In addition to their structural versatility, control over functional properties is accessible based on alteration of microstructure and surface chemistry. Synthetic strategies for accessing atomistic, nanoscale, and mesoscale control are discussed using illustrative examples placing particular emphasis on non-hydrolytic sol—gel processes that provide access to well-defined solid-solution nanocrystals. The reactivity and post-synthetic modification of these compounds is further delineated. Methods for defining color centers within these compounds, cooperativity of the optical response of the color centers with the host lattice (determined by overlap integrals specific to each structure type and the polarization and ligand field effects of different halide ions) and adjacent color centers (reliant on energy transfer schema), and their practical application in phosphors are further detailed. Mechanisms facilitating down- and up-conversion of energy absorbed from incident electromagnetic radiation or high-energy particles are delineated with particular emphasis on X-ray and electron-beam excitation. The accessible energy conversion mechanisms, efficacious radiative recombination channels, and opportunities for systematically tuning color through compositional modulation have led to the emergence of these materials as potential candidates for phosphors. These materials have potential applications in solid-state lighting, radiation detection, and as the active elements of imaging devices. The tolerance towards large concentrations of anion vacancies and the facile diffusivity of anions in these compounds further underpins the function of lanthanide oxyhalides as ion conductors, gas sensors, and heterogeneous catalysts. Increasing interest has focused on utilization of well-defined color centers for quantum information science and multiplexed sensing in biological systems. Such applications require additional control of the positioning of dopant atoms and understanding of their interactions with the host lattice and other dopant atoms.

Carbon Quantum Dots Encapsulated Molecularly Imprinted Fluorescence Quenching Particles for Sensitive Detection of Zearalenone in Corn Sample.

An eco-friendly and efficient one-step approach for the synthesis of carbon quantum dots (CDs) that encapsulated molecularly imprinted fluorescence quenching particles (MIFQP) and their application for the determination of zearalenone (ZEA) in a cereal sample are described in this study. CDs with high luminescence were first synthesized, and then encapsulated in the silica-based matrix through a non-hydrolytic sol-gel process. The resulting ZEA-imprinted particles exhibited not only an excellent specific molecular recognition of ZEA, but also good photostability and obvious template binding-induced fluorescence quenching. Under the optimized conditions, the fluorescence intensity of MIFQP was inversely proportional to the concentration of ZEA. By validation, the detection range of these fluorescence quenching materials for ZEA was between 0.02 and 1.0 mg L−1, and the detection limit was 0.02 mg L−1 (S/N = 3). Finally, the MIFQP sensor was successfully applied for ZEA determination in corn with recoveries from 78% to 105% and the relative standard deviation (RSD %) was lower than 20%, which suggests its potential in actual applications.

Aminoiron(III)–porphyrin–alumina catalyst obtained by non-hydrolytic sol-gel process for heterogeneous oxidation of hydrocarbons

An aminoiron(III) porphyrin immobilized on an alumina matrix was prepared and used as catalyst for the oxidation of organic substrates. Powder alumina had been prepared by a non-hydrolytic sol-gel method through condensation of aluminum chloride with anhydrous ethanol. Then, iron(III) [5,10,15,20-tetrakis(2,6-dichloro-3-aminophenyl)-porphyrin] was immobilized on the alumina powder under magnetic stirring, reflux, and inert atmosphere. Ultraviolet–visible and infrared spectroscopies, powder X-ray diffraction, scanning electron microscopy and thermal analysis were applied for characterizing the resulting material, confirming that the ironporphyrin was immobilized on the alumina support. The catalytic activity of ironporphyrin/alumina was evaluated in the oxidation of (Z)-cyclooctene and cyclohexane and in the Baeyer-Villiger oxidation of cyclohexanone using iodosylbenzene or hydrogen peroxide as oxygen donors. The novel immobilized catalyst proved to be a promising system for the efficient and selective oxidation of the organic substrates with 85–92% selectivity to the epoxide in the oxidation of alkenes and 25–41% to the ketone in the oxidation of cyclohexane. As for the Baeyer-Villiger oxidation of cyclohexanone, good conversion to ԑ-caprolactone was observed as well. The material is a reusable heterogeneous catalyst, which makes it more economically feasible than its homogeneous counterpart.

Surface Plasmon Assisted Luminescence Enhancement of Ag NP/NWs-Doped SiO2-TiO2-ZrO2:Eu3+ Ternary System

Non-hydrolytic sol-gel process was employed to prepare Eu3+-doped and silver nanoparticles/nanowires (Ag NP/NWs) co-doped SiO2-TiO2-ZrO2 ternary matrix. XRD, TEM, and SAED analyses revealed that the matrix is of amorphous nature even the crystalline nanoparticles/nanowires are embedded. The formation of ternary matrix is further evidenced by the characteristic peaks in FTIR spectrum and EDS analysis. The emission intensity is enhanced by sixfold for Ag NPs and eightfold for Ag NWs embedded matrix and is probably due to Surface Plasmon Coupled Emission (SPCE). Above the critical concentration of 1 wt.% Ag NP and 1.5 wt.% Ag NW, the emission intensity starts to diminish because of quenching effects. CIE chromaticity studies confirm that the addition of Ag NP/NWs into Eu3+-doped ternary matrix does not alter the color coordinates and purity of the present system. These Eu3+-Ag NP/NWs-doped ternary systems could be used as a promising material for efficient red light emitting sources, bio-detection, and plasmonic sensor applications.

Perceiving impressive optical properties of ternary SiO2-TiO2-ZrO2:Eu3+ sol-gel glasses with high reluctance for concentration quenching: An experimental approach

Eu3+-doped ternary SiO2-TiO2-ZrO2 glasses were prepared through a non-hydrolytic sol-gel process. Fourier transform infrared spectroscopy was employed to identify the vibrational modes present in the ternary glass. The phonon energies were calculated using excitation spectrum and complemented well with the vibrational modes in the Raman spectrum. Photoluminescence spectrum was used to assess the luminescent augmentation. The uniform distribution of dopant ions in the as prepared ternary glass aided in achieving a comparatively unmatched doping concentration of Eu3+ion (17.5wt%) without luminescence quenching and it can be attributed to reduced cluster formation. High concentration of rare earth ion incorporation leads to intense and tunable emission with higher brightness. Excellent color purity of the emission by means of CIE color gamut for the red color was observed, which is close to the National Television Standard Committee (NTSC) value. Theoretical investigations of the photophysical parameters and radiative decay time were carried out with Judd-Ofelt analysis. The double exponentially fitted decay curve gave a satisfactory experimental lifetime. These results indicate that tailor made europium doped ternary SiO2-TiO2-ZrO2 glasses have potential applications in the areas of photonic devices as well as biological sensors because of its intense tunable and efficient emission, high purity, and low toxicity.