Non-aqueous Sol Gel Route Research Articles

Comparative study of eriochrome black T (EBT) dye adsorption utilizing direct growth of cost-effective efficient materials: S-doped ZnO nanoparticles, ultrathin nanoflakes, and nanowalls

In the present studies, zinc oxide (ZnO) nanoparticles were synthesized by the non-aqueous sol-gel route and incorporated with diverse amounts of the nonmetal element like sulfur with different concentration (1, 2, 4, and 6 wt%). Furthermore, the physicochemical properties of all synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), N2 adsorption/desorption isotherms, and ultra violate visible (UV-Vis) absorption spectra. Powder XRD analysis shows the formation of hexagonal wurtzite phase of ZnO and the incorporation of S atom in ZnO lattice was confirmed by the XPS analysis. FESEM results reveal that the synthesised S-doped (2, 6 wt%) ZnO samples possess the growth of 1D ultra-thin nanoflakes with sharp edge and vertically aligned 1D thin nanowalls morphology. Moreover, UV-Visible transmission spectral studies showed that the optical energy band gap of ZnO NPs were reduced by S doping. After that, pure ZnO, 1, 4, and 6 wt% S-containing ZnO samples were examined as for adsorption study of eriochrome black T (EBT) dye. Among the S-containing samples, 50 mg of the adsorbent, doped with 4 wt% S (4 wt% S-ZnO) could adsorb up to 95.13 % of EBT dye (15 ppm) in 90 min. Therefore, such a sulfure doped ZnO samples in the form of nanoparticles (NPs), nanoflakes (nanosheets) as well as nanowalls could be used as a promising material for the application in industrial wastewater treatment processes.

Organic Modification of Silica-Based Ionogels Improves the Electrolyte/Electrode Contact and Influences Their Functional Properties

The energy transition necessitates sustainable energy storage to address the mismatch between the production and consumption of renewable electricity. Sodium-ion batteries (SIBs) are a promising candidate for stationary energy storage as an alternative for lithium-ion batteries (LIBs). In spite of their lower energy density, SIBs have advantages over LIBs.1 Sodium is considerably more abundant than lithium (2.83% versus 0.01%) and, evenly distributed across the Earth, implying that SIBs may be less expensive and more sustainable than LIBs.1,2 Conventional LIBs contain flammable organic liquid electrolytes (e.g. alkyl carbonates) with limited thermal stability. Thermal runaway can therefore lead to cell ignition, causing a significant safety hazard. Non-flammable electrolytes can be based on ionic liquids, which are molten salts with flame retarding properties and negligible vapor pressures. However, the possibility of leakage and related environmental hazards remains a concern.3 This risk can be mitigated by the use of solid electrolytes. Apart from circumventing safety issues, solid electrolytes may allow a significant increase in energy density. After all, they take up less dead volume than liquid electrolytes and can allow the use of alkali metals as negative electrodes.An attractive type of solid electrolyte is the class of silica-based ionogels, owing to their high ionic conductivity, thermal stability, and broad electrochemical window.4 They comprise an ionic liquid electrolyte (ILE, a salt dissolved in ionic liquid) confined in the pores of a solid silica matrix. The silica matrix is electrochemically inactive but influences the functional properties of the resulting solid material. Ionogels based on solely silica (SiO2) as matrix tend to crack easily when subjected to pressure as the rigid Si-O-Si bonds result in high Young’s modulus materials. Furthermore, materials with high Young’s moduli cannot adapt easily to electrode surfaces, resulting in higher charge-transfer resistances (Rct) between the solid electrolyte and electrode. One way to reduce the stiffness of silica-based ionogels is to modify the silica matrix with e.g. organic groups. Ormosils® are a class of materials completely consisting of organically modified silica and show mechanical properties from glassy to rubbery depending on the amount of organic modification.5 Here, the concepts of ionogels and Ormosils® are combined to produce sodium-ion conducting organically modified ionogels. Two different phenyl-bearing silanes (phenyltrimethoxysilane, PhTMS, or diphenyldimethoxysilane, DPhDMS) are for the first time used as organic modifiers in silica-based ionogels. A non-aqueous sol-gel route with formic acid (FA) is used to synthesize the monoliths. Incorporating phenyl groups allow to reduce the Young’s modulus from 29 MPa down to 6 MPa. The charge-transfer resistances (Rct) of Na|ionogel|Na2Ti3O7 half cells, determined with electrochemical impedance spectroscopy (EIS), followed the trend of the ionogels’ Young’s modulus. Through NMR spectroscopy, pi-stacking was observed between the matrix phenyl moieties and IL imidazolium cations. Furthermore, the organic modification diminished the formation of hydrogen bonds between IL anions and matrix silanol groups. This shows that the organic modification of the matrix can have a pronounced effect on the coordination of the ILE components, which ultimately determine the solid electrolyte’s functional properties. In summary, incorporating phenyl groups in the silica matrix of ionogels improves the mechanical properties and charge transfer resistances, but impairs ionic conductivity. Acknowledgments: This research is made possible by the Research Foundation Flanders (FWO, project G053519N and 1S08921N) and the Special Research Fund (BOF) of Hasselt University (BOF20INCENT19). This work is further supported by Hasselt University and FWO Vlaanderen via the Hercules project AUHL/15/2 - GOH3816N.

Luminescence properties of ZrO2: Dy3+ phosphor for solid-state lighting applications

Herein, we report Dy3+-activated ZrO2 phosphors synthesized via the sol-gel technique. The structural, morphological, and optical properties of the synthesized powder samples annealed at 900 °C were investigated. The monoclinic phase of the synthesized phosphor was confirmed by recording the X-ray powder diffraction (XRPD) pattern. Ultraviolet–visible analysis was performed for the reflectance and bandgap measurements of the phosphors. Field emission scanning electron microscope and X-ray energy dispersive spectroscopy analyses were used to study the morphology and elemental composition of the phosphors, respectively. The distribution of ions in the undoped and Dy3+-doped samples was confirmed using time-of-flight secondary ion mass spectroscopy. The photoluminescence (PL) behavior of the synthesized phosphors was investigated by recording the excitation and emission spectra. When the synthesized phosphors were exposed to UV light at 353 nm, we observed characteristic blue and yellow Dy3+ PL emissions, corresponding to the transition 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. Additionally, we observed low-intensity red and brown-red emission peaks corresponding to 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2. These observations indicate that the non-aqueous sol-gel route, coupled with the suitable post-synthesis heat treatment, resulted in the development of a monophase (monoclinic) zirconia. This makes it a strong candidate for phosphor applications due to its high room temperature stability and efficient characteristic features of the monoclinic phase. These findings strongly suggest that Dy3+-doped ZrO2 can serve as a superior phosphor material for white light-emitting diode applications.

Revealing the Dependency of Dye Adsorption and Photocatalytic Activity of ZnO Nanoparticles on Their Morphology and Defect States.

ZnO is an effective photocatalyst applied to the degradation of organic dyes in aqueous media. In this study, the UV-light and sunlight-driven photocatalytic activities of ZnO nanoparticles are evaluated. A handheld Lovibond photometer was purposefully calibrated in order to monitor the dye removal in outdoor conditions. The effect of ZnO defect states, i.e., the presence of zinc and oxygen defects on the photocatalytic activity was probed for two types of dyes: fuchsin and methylene blue. Three morphologies of ZnO nanoparticles were deliberately selected, i.e., spherical, facetted and a mix of spherical and facetted, ascertained via transmission electron microscopy. Aqueous and non-aqueous sol-gel routes were applied to their synthesis in order to tailor their size, morphology and defect states. Raman spectroscopy demonstrated that the spherical nanoparticles contained a high amount of oxygen vacancies and zinc interstitials. Photoluminescence spectroscopy revealed that the facetted nanoparticles harbored zinc vacancies in addition to oxygen vacancies. A mechanism for dye degradation based on the possible surface defects in facetted nanoparticles is proposed in this work. The reusability of these nanoparticles for five cycles of dye degradation was also analyzed. More specifically, facetted ZnO nanoparticles tend to exhibit higher efficiencies and reusability than spherical nanoparticles.

Enhanced adsorption of methylene blue by mixed-phase bismuth ferrite prepared by non-aqueous sol-gel route

We report here a non-aqueous sol-gel synthesis of bismuth ferrite (BFO) particles in THF, DMF, and DMSO solvents, their subsequent utilization in adsorption of methylene blue, and a comparison of their adsorption efficiencies. BFO is attractive for adsorption because of its excellent dispersion in water. XRD data shows that all the solvents yield a mixture of a primary rhombohedral and a secondary orthorhombic phases with varying fractions. The DMSO yields the most impure samples having the highest fraction of secondary phase. However, the adsorption efficiencies of the samples order as DMF < THF < DMSO, with DMF showing 26.28 %, THF 51.63 %, and DMSO 96.54 %. A higher refractive index and donicity of DMSO leads to better solvation of the sol and incorporation of sulfur in the metal-oxide network during the sol-gel reaction. DMSO aids in columnar growth of orthorhombic phase, which, due to sulfur incorporation, forms a more open and less crystalline phase, which are the factors responsible for DMSO samples showing enhanced adsorption. Analysis of adsorption kinetics and isotherm on the DMSO samples confirms diffusive regimes pertaining to film-diffusion and intra-particle diffusion with the diffusive kinetics becoming faster at higher dye concentration. Fitting to Langmuir isotherm yields maximum monolayer coverage of 7.14 mg of dye per g of the adsorbent. The DMSO samples also show excellent adsorption at high pH conditions.

Enhanced electrochemical properties of Zn and V-doped TiO2 nanoparticles synthesized via non-aqueous sol–gel route for supercapacitor application

Enhanced electrochemical properties of Zn and V-doped TiO2 nanoparticles synthesized via non-aqueous sol–gel route for supercapacitor application

Significance of Hydroxyl Groups on the Optical Properties of ZnO Nanoparticles Combined with CNT and PEDOT:PSS.

We report on the synthesis of ZnO nanoparticles and their hybrids consisting of carbon nanotubes (CNT) and polystyrene sulfonate (PEDOT:PSS). A non-aqueous sol–gel route along with hydrated and anhydrous acetate precursors were selected for their syntheses. Transmission electron microscopy (TEM) studies revealed their spherical shape with an average size of 5 nm. TEM also confirmed the successful synthesis of ZnO-CNT and ZnO-PEDOT:PSS hybrid nanocomposites. In fact, the choice of precursors has a direct influence on the chemical and optical properties of the ZnO-based nanomaterials. The ZnO nanoparticles prepared with anhydrous acetate precursor contained a high amount of oxygen vacancies, which tend to degrade the polymer macromolecule, as confirmed from X-ray photoelectron spectroscopy and Raman spectroscopy. Furthermore, a relative increase in hydroxyl functional groups in the ZnO-CNT samples was observed. These functional groups were instrumental in the successful decoration of CNT and in producing the defect-related photoluminescence emission in ZnO-CNT.

Self-assembled hierarchical microporous ZrO2 nanoparticles and Mg-doped ZrO2 nanodiscs synthesized by non-aqueous sol–gel route

Self-assembled hierarchical microporous ZrO2 nanoparticles and Mg-doped ZrO2 nanodiscs synthesized by non-aqueous sol–gel route

Enhancing the UV Emission in ZnO-CNT Hybrid Nanostructures via the Surface Plasmon Resonance of Ag Nanoparticles.

The crystal quality and surface states are two major factors that determine optical properties of ZnO nanoparticles (NPs) synthesized through nonaqueous sol–gel routes, and both are strongly dependent on the growth conditions. In this work, we investigate the influence of the different growth temperatures (240 and 300 °C) on the morphology, structural and crystal properties of ZnO NP. The effects of conjoining ZnO NP with carbon nanotubes (CNT) and the role of surface states in such a hybrid nanostructure are studied by optical emission and absorption spectroscopy. We demonstrate that depending on the synthesis conditions, activation or passivation of certain surface states may occur. Next, silver nanoparticles are incorporated into ZnO–CNT nanostructures to explore the plasmon–exciton coupling effect. The observed enhanced excitonic and suppressed defect-related emissions along with blue-shifted optical band gap suggest an intricate interaction of Burstein–Moss, surface plasmon resonance and surface band-bending effects behind the optical phenomena in hybrid ZnO–CNT–Ag nanocomposites.

Crystallization Pathway of Size-Controlled SnO2 Nanoparticles Synthesized via a Nonaqueous Sol–Gel Route

This paper deals with the crystallization pathway of tin dioxide nanoparticles of a few nanometers synthesized via a nonaqueous sol–gel route based on the etherolysis of a tin tetrachloride (SnCl4) precursor. Two different ethers were used as oxygen donors: diisopropyl ether (iPr2O) and dibenzyl ether (Bn2O). The solvothermal treatments of SnCl4 in iPr2O at different temperatures and reaction times revealed in the early stages of the reaction the formation of an organic polymeric phase in which crystalline nanoparticles are embedded. In the case of the SnCl4–Bn2O system, the formation of a brownish polymer containing crystalline oxidic nanoparticles and the production of water were evidenced. With both ethers, an unexpected intermediate disordered nanocrystalline phase is formed, which progressively transforms into rutile-type SnO2 nanoparticles. The formation of the polymeric phase, which is suspected to act as a trap for the nanoparticles, freezes the intermediate phase, limits the particle growth, and delays the restructuration into the rutile-type structure. The degradation of the polymer phase in the case of iPr2O and/or the water action in the case of Bn2O are finally able to destabilize the nanoparticle–polymer assembly and to induce the restructuration of the nanoparticles.

Time evolution of ZnO-CNT photoluminescence under variable ambient and temperature conditions

ZnO-CNT hybrid materials were prepared by non-aqueous sol-gel routes at 240ºC. The morphology and defects have been studied by transmission electron microscopy and photoluminescence spectroscopy. The hybrid nanostructures manifest a broad luminescence emission covering the visible spectrum. Variations in photoluminescence with time are observed for the ZnO-CNT hybrid structures exposed to different ambient and temperatures. The studies show that photoluminescence from adsorbed oxygen dominates the emission emanating from other intrinsic defects and also affects the stability of the latter over time.

Effect of cerium on electrochemical properties of V2O5 nanoparticles synthesized via non-aqueous sol-gel technique

Pure, 1%, 3%, and 5% of cerium-doped vanadium pentoxide (V2O5) nanoparticles were synthesized by non-aqueous sol-gel route. Synthesized samples were employed to various characterizations such as structural, morphological, optical, and electrochemical studies using XRD, SEM, FTIR, RAMAN, and UV-Vis DRS and cyclic voltammetry, charge-discharge, and cycle stability for supercapacitor applications. XRD analysis revealed the phase purity and crystallinity of the powder samples with a crystallite size 89–84 nm. SEM images show that the synthesized nanoparticles are highly monodispersed and homogenous in size. FTIR and RAMAN spectra ensured the presence of functional groups in synthesized V2O5. Then, the UV-Vis DRS spectra depict that the synthesized nanoparticles are red shifted. Ce(5%):V2O5 nanoparticles provided high specific capacitance about 555 Fg−1 at 1 Ag−1 and cycling stability up to 10,000 cycles with capacity retention up to 85% compared with pure, 1%, and 3% cerium-doped V2O5 nanoparticles. Thus, cerium-doped V2O5 nanoparticles were considered potential cathode materials for supercapacitor applications.

Study on the electrochemical performance of ZnO nanoparticles synthesized via non-aqueous sol-gel route for supercapacitor applications

Pure zinc oxide (ZnO) nanoparticles have been synthesized by non-aqueous sol-gel route and electrochemical properties were studied for pseudocapacitor applications. The structural, morphological and functional studies were done by XRD, SEM and FTIR respectively. The results showed that the synthesized nanoparticles have good crystallinity, phase pure hexagonal wurtzite structure with highly dispersed nanoparticles with crystallite size about 85 nm. UV–vis DRS spectroscopy results depict that the absorption wavelength gets red shifted. The electrochemical analysis was carried out in three electrode system with the potential window from −0.4 to +0.6 V under 3M KOH aqueous electrolyte. The calculated specific capacitance is very much high about 776 F g−1 at 4 A g−1 current density with 98% capacity retention upto 2500 cycles. Electrochemical impedance spectrum exhibited low ESR value revealed the fast charge transfer kinetics with superior electrical conductivity. These enhanced electrochemical performance highlight the potential of ZnO electrode for the development of supercapacitor applications.

Ion conducting polymer-silica hybrid ionogels obtained via non-aqueous sol-gel route

One pot synthesis of high ion-conducting polymer based organic-inorganic hybrid ionogels via non-aqueous sol-gel route is being reported here. These hybrid ionogel films have been obtained using copolymer, poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), silica precursor, tetraethyl orthosilicate (TEOS), salt, lithium trifluoromethanesulfonate (LiTf) and ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMTf). The use of non-aqueous sol-gel route facilitates the confinement of large amount of electrolyte solution in the hybrid matrix. The highest value of ionic conductivity achieved at room temperature for these hybrid ionogels (encompassing 65 wt% of electrolyte solution) is 3 mS/cm (comparable to that of liquid electrolyte), which is a desirable value for many electrochemical applications. Deconvolution of the ATR-IR spectra in the range 980–1100 cm−1 has provided information about the varying concentration of free ions (CF3SO3−) in the hybrid ionogels and evidence of ion-pair formation while the spectra in the 2900–3300 cm−1 range throws light on the interaction of the electrolyte solution (trapped in the organic-inorganic matrix) with the other constituents of the hybrid film (i.e., polymer and silica). These hybrid ionogels exhibit a wide electrochemical stability window (~4.63 V) and high thermal stability (~320 °C) along with increased amorphisity. The value of tLi+ has been found to be in the range. The value of tLi+ has been found to be in the range ~0.41 to 0.48 for all the films. The maximum value of tLi+ ~ 0.48 has been obtained for the hybrid ionogel film containing 60 wt% of electrolyte solution (PVdF-HFP/silica/ES-60). Mechanical properties indicate that higher amount of the electrolyte solution in the matrix reduces the mechanical strength. However, for films with same amount of electrolyte solution, the film without SiO2 has higher mechanical strength as compared to the one with SiO2.

Cotton functionalized with nanostructured TiO2-Ag-AgBr layer for solar photocatalytic degradation of dyes and toxic organophosphates.

The functionalization of cotton fabric with photoactive TiO2-Ag-AgBr nanostructured layer has been successfully developed using a low temperature non-aqueous sol-gel route and aqueous suspension of AgBr. Evidence for the growth of TiO2 layer and the immobilization of AgBr nanoparticles have been confirmed by Raman, XRD and XPS. GSDR analysis revealed a strong absorption in the visible region brought by surface Plasmon resonance (SPR) of Ag nanocrystals generated at the surface of AgBr. The XPS evidenced the presence of Ag+, Ag0 and bromine, suggesting that Ag0 formed a shell around the deposited AgBr. The immobilized TiO2-Ag-AgBr heterostructured layer imparts a strong photocatalytic activity under visible light for the degradation of dyes in aqueous solution as well as of dimethyl methylphosphonate (DMMP), a chemical warfare agent simulant. These new catalytically active functionalized fabrics, with self-detoxification properties, have great potential for application in chemical protective clothes and might offer new opportunities for the design of functional materials for toxic chemical protection.

Synthesis, structure and magnetic properties of multipod-shaped cobalt ferrite nanocrystals

A non-aqueous sol–gel route followed by oriented attachment to make multi-pod CoFe2O4 nanocrystals showing large room temperature saturation magnetization.

Effect of Zn2+, Ti2+ dopants on structural, optical and electrochemical properties of V2O5 nanoparticles synthesized via non-aqueous sol–gel route

Transition divalent metal cations (Zn2+, Ti2+) doped V2O5 nanoparticles were synthesized via non-aqueous sol–gel route. The influence of dopant materials on the characteristics of V2O5 nanoparticles was studied. XRD studies ensure that all the prepared samples possess phase pure orthorhombic structure. From the FESEM images, it was noted that the products possess uniform particle size around 20–30 nm. The presence of functional groups and dopants was confirmed by FTIR, Raman, and elemental analysis respectively. From UV–Vis spectra, the significant blue shift was observed for doped samples compared to pure V2O5 nanoparticles, which is attributed to the quantum confinement effect. The high capacity retention of the intercalation compound was measured by using C–V study and implies that the prepared samples are very promising electrode materials for supercapacitor.

Synthesis and Characterization of NiO Nanoparticles by Non-Aqueous Sol-Gel Route

Synthesis and Characterization of NiO Nanoparticles by Non-Aqueous Sol-Gel Route

Nonaqueous Sol-Gel Synthesis of Anatase Nanoparticles and Their Electrophoretic Deposition in Porous Alumina.

Titanium dioxide (TiO2) nanoparticles were synthesized by nonaqueous sol-gel route using titanium tetrachloride and benzyl alcohol as the solvent. The obtained 4 nm-sized anatase nanocrystals were readily dispersible in various polar solvents allowing for simple preparation of colloidal dispersions in water, isopropyl alcohol, dimethyl sulfoxide, and ethanol. Results showed that dispersed nanoparticles have acidic properties and exhibit positive zeta-potential which is suitable for their deposition by cathodic electrophoresis. Aluminum substrates were anodized in phosphoric acid in order to produce porous anodic oxide layers with pores ranging from 160 to 320 nm. The resulting nanopores were then filled with TiO2 nanoparticles by electrophoretic deposition. The influence of the solvent, the electric field, and the morphological characteristics of the alumina layer (i.e., barrier layer and porosity) were studied.

Mechanistic Aspects in the Formation, Growth and Surface Functionalization of Metal Oxide Nanoparticles in Organic Solvents.

The synthesis of metal oxide nanoparticles in organic solvents, so-called nonaqueous (or nonhydrolytic) processes represent powerful alternatives to aqueous approaches and have become an independent research field. 10 Years ago, when we published our first review on organic reaction pathways in nonaqueous sol-gel approaches, the number of examples was relatively limited. Nowadays, it is almost impossible to provide an exhaustive overview. Here we review the development of the last few years, without neglecting pioneering examples, which help to follow the historical development. The importance of a profound understanding of mechanistic aspects of nanoparticle crystallization and formation mechanisms can't be overestimated, when it comes to the design of rational synthesis concepts under minimization of trial-and-error experiments. The main reason for the progress in mechanistic understanding lies in the availability of characterization tools that make it possible to monitor chemical reactions from the dissolution of the precursor to the nucleation and growth of the nanoparticles, by ex situ methods involving sampling after different reaction times, but more and more also by in situ studies. After a short introduction to experimental aspects of nonaqueous sol-gel routes to metal oxide nanoparticles, we provide an overview of the main and basic organic reaction pathways in these approaches. Afterwards, we summarize the main characterization methods to study formation mechanisms, and then we discuss in great depth the chemical formation mechanisms of many different types of metal oxide nanoparticles. The review concludes with a paragraph on selected crystallization mechanisms reported for nonaqueous systems and a few illustrative examples of nonaqueous sol-gel concepts applied to surface chemistry.