Microwave-assisted sol-gel method has proven to be a better alternate to conventional chemical approaches. In the present research work, chromium (Cr) doped thin films of iron oxide are prepared by modified sol-gel method, i.e. by using microwaves. Samples are prepared with microwave power of 720 W, whereas doping is varied in the range of 0 to 14 wt%. Maghemite phase (γ-Fe2O3) is observed for undoped sample, whereas hematite (α-Fe2O3) is observed for the samples prepared with 2–4 wt% Cr doping. Magnetite (Fe3O4) phase of iron oxide is observed at relatively higher doping concentrations, i.e. 6–10 wt%. Ferromagnetic behaviour along with high saturation magnetization is observed with the increase in Cr doping concentration. Increased value of squareness is observed at higher Cr concentration, i.e. 6–14 wt%. Higher value of saturation magnetization (Ms) is observed with 10 wt% Cr doping i.e. ~83 emu/g, whereas decrease in Ms is witnessed with further increase in dopant concentration to 12–14 wt%. Impedance measurements show that transport mechanism in Cr doped Fe3O4 is governed by tunnelling across the grain boundaries. Room temperature coupling of magnetic and dielectric behavior is observed under the effect of different frequency values.Graphical Abstract

Tunable manufacturing using flexible building blocks to bring functionalities while providing long-term stabilization for small-sized nanomaterials occupies a forefront position in nanoscience and nanotechnology. Iron oxide nanoparticles are among the most promising nano-objects, owing to their inherent magnetic properties. The propensity of iron oxide to aggregate constitutes a serious drawback for many of their potential properties that need to keep their size at the nanoscale. Hosting iron oxide in porous supports, intercalation in layered nanostructures or shelling with tunable partners are common approaches used for their stabilization. We herein report the controlled growth of iron oxide using cleverly crafted sol-gel transformable siloxane precursors. These flexible building blocks provide an entry to iron oxide encapsulated in hydrophobic silica, denoted as Fe3O4@PMSiO2, while the use of commercially available TEOS afforded Fe3O4@SiO2. Owing to the presence of PDMS-like segments, the grown Fe3O4 exhibits distinctive features in terms of the crystal size, restricted growth and dispersion in organic solvents compared to native iron oxide and those grown in conventional silica supports. Upon calcination at 500 °C, the size of the crystal expands by 25.4 nm in the case of native Fe3O4 reaching 35.9 nm. Comparatively, marginal expansion was observed using our siloxanes, with the size of those grown in Fe3O4@OMSiO2 and Fe3O4@PMSiO2 being restricted to 14.3 nm and 11.7 nm, because of the stabilization brought by the siloxane layers. Furthermore, Fe3O4@OMSiO2 and Fe3O4@PMSiO2 are fully soluble in apolar heptane and hexane, which convincingly substantiate the hydrophobic nature of the resulting mixed oxide materials.Graphical Abstract

AbstractDesigning luminescent nanohybrids for bioimaging proposes has been explored by different approaches in the literature. In this context, here silica luminescent nanohybrids containing Eu3+-complexes were synthesized in three different approaches to determine the better methodology to obtain the most efficient emissive final hybrid and its applicability in cell imaging by using the Eu3+ luminescent probe properties. For this, the synthesized dense Stöber silica nanoparticles, SiO2, had their surface functionalized with APTES, in which its amine group reacted with salicylaldehyde to form a Schiff base ligand (SB), yielding the SiO2-SB system. Then, Eu3+ ion was coordinated to the SB, followed by the displacement of coordinated water molecules by dibenzoylmethane (dbm), resulting in the SiO2-[Eu1] hybrid. SiO2-[Eu2] hybrid, in turn, was obtained from tris-[Eu(dbm)3] complexes coordinated to the imine groups grafted on the SiO2-SB surface. For the third hybrid, SiO2-[Eu3], a new Eu3+-Schiff base complex displaying a triethoxysilyl group was grafted onto the SiO2 surface. The three luminescent hybrids are spheroidal shaped with 100 nm-size and they are red emitters with long lifetime (0.34–0.61 ms) and high photostability when exposed to continuous 340 nm UV radiation. Quantum efficiency (\(Q_{{\rm{Eu}}}^{{\rm{Eu}}}\)) as well as the number of coordinated water molecules (qH2O) to the Eu3+ was estimated using the LUMPAC software package and Horrocks equation, respectively. Although the three strategies exhibited suitable photophysical results, SiO2-[Eu1] was classified as the best hybrid considering its higher \(Q_{{\rm{Eu}}}^{{\rm{Eu}}}\) and color purity values, and it was evaluated as non-toxic according to its bio-viability in CHO-k1 cells in different doses. Exploratory cell imaging tests using such hybrid indicated cell marking near the nucleus with the internalization of nanoparticles in the cell confirmed by Eu3+ (5D0 → 7FJ) narrow emission bands. Therefore, SiO2-[Eu1] hybrid manifested suitable shape and size, optical, and biocompatibility features that make it promising to be applied as a luminescent stain for cell imaging.Graphical abstract

In this study, the effect of strontium (Sr) concentration on the ultrafast humidity sensing performance of Sr doped zinc oxide (SrxZn1–xO) nanostructured thin films was reported. The sol gel method was used in the synthesis of undoped zinc oxide (ZnO) and SrxZn1–xO (x = 0.01, 0.02, 0.03, 0.04, and 0.10) nanoparticles. According to the x-ray diffraction analysis, all films had a hexagonal wurtzite structure. By doping Sr into the ZnO lattice, the preferential orientation changed from the (002) plane to the (101) plane. Scanning electron microscopy micrographs showed that all films had a structure containing nanosized grains and capillary-nanopores, and the nanosized grains were homogeneously and uniformly distributed on the surface of films. The presence of zinc, oxygen and Sr elements in nanostructured thin films was proved by energy dispersive x-ray spectra. The relative humidity sensing performances of undoped ZnO and SrxZn1–xO films were tested with electrical resistance measurements in the range of 40–90% RH at room temperature. SrxZn1–xO films had high sensitivity, excellent stability, reliable and reproducible character, and fast response and recovery times. Sr0.10Zn0.90O was accepted as the best sample in terms of having the highest humidity sensitivity (657.59x) and the fastest response (0.8 s) and recovery (9.8 s) times. This study clearly revealed that SrxZn1–xO nanostructured thin films have great potential for high performance humidity sensor applications due to their ultrafast humidity sensing performance.Graphical Abstract

Nanocomposites based on Keggin-type polyoxometalate H5PV2Mo10O40 (POM) and organically modified silicate (Ormosil) were prepared by sol-gel processes. The physical properties of the Ormosil/POM composites were examined using FTIR, UV, SEM, TEM and XRD. These techniques indicated that the POM was bond to the Ormosil matrix after impregnation. The antibacterial effects of Ormosil/POM and the Ormosil+POM were assessed by the zone of inhibition, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). A higher POM proportion used in the Ormosil/POM yielded a stronger antimicrobial effect that was superior to Ormosil+POM. The excellent antibacterial performance of Ormosil/POM-10 compositean was discovered. Ormosil/POM composites were therefore believed to have great potential for use as an antibacterial material.Graphical Abstract

Air pollution surrounds us outdoors as well as indoors, with significant health consequences. Addressing this issue starts with a widespread reporting of ambient pollutants concentrations, which inevitably relies in part on miniaturized sensors that are affordable, light and easy to deploy and operate. Besides widespread electrochemical or CMOS miniaturized sensors, optical sensors based on functional porous materials represent an interesting alternative. We show in this article the fabrication and use of a miniaturized colorimetric sensor thanks to a microfluidic method known as anchored droplet generation. By capillary trapping of sub-millimeter sol droplets at predefined position within a microfluidic chamber, we obtain a silica porous bead array. This method is compatible by design with operando monitoring of key parameters of the sol-gel process, such as gelation or shrinkage. This monitoring capability was used to seek optimal fabrication conditions of microarrays with a density of ~125 beads/cm². Microarrays of porous beads functionalized with a formaldehyde probe were produced and a low-cost homemade system was used to monitor beads color, directly within the microfluidic chip, upon exposure to formaldehyde.Graphical Abstract

Structural control of siloxane-based materials at multiple length scales is important for various applications. In this study, we report the controlled assembly of cage oligosiloxane building blocks by both intermolecular hydrogen bonding and hydrophobic interactions. A cage siloxane molecule modified with seven dimethylsilanol groups and an octadecyldimethylsilyl group was synthesized by stepwise silylation of double-four-ring (D4R) cage octasilicate anions. This molecule self-assembled to form a molecularly and mesoscopically ordered structure by solvent evaporation. Furthermore, the silanol groups in the assembled solids were cross-linked by silylation with dichlorodimethylsilane. This approach will allow for the creation of various hierarchically ordered siloxane-based materials by molecular design.Graphical Abstract

Adsorption based materials play a rather important prospect in the treatment of petroleum. Currently, most of the adsorbent materials work based on substrates such as sponges and aerogels, to endow super-hydrophobic/super-oleophilic properties on the membrane surface. As the adsorbent material reaches the end of its useful life, it undoubtedly further exacerbates the burden on the environment from an environmental protection perspective. Here, we modified the recycled discarded air filter with polydimethylsiloxane (PDMS), γ-aminopropyltriethoxysilane (KH-550), TiO2, SiO2, and Ag. The results showed that the prepared PDMS-1 (TiO2/SiO2/Ag)@ discard air filter has excellent super-hydrophobicity and enhanced antibacterial properties, and possesses mechanical durability and chemical stability. The modified discarded air filter had an absorption capacity of up to 23.2 g/g of carbon tetrachloride. This research provides a new oil-absorbent substrate with a secondary use strategy to reduce environmental damage. Ultimately, it exhibits excellent performance almost indistinguishable from other adsorbent materials.Graphical Abstract

In this study, MgFe2O4 nanoparticles with different Mg/Fe molar ratios were synthesized by a sol-gel (Pechini) method and a Support Vector Regression (SVR) as a predictive model has been used in this context for the first time. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the nanoparticles synthesized using this methodology. According to the results obtained by XRD, nanoparticles with a Mg/Fe ratio of 0.75 heat-treated at 700oC have an inverse spinel structure, which corresponds to the pure magnesium ferrite phase. The use of the SVR predictive model allowed the efficient synthesis of a pure magnesium ferrite phase, providing data that could be experimentally validated to obtain a pure phase without additional phases.Graphical Abstract

This paper studies how electrochemically inserting or extracting lithium ions in TiO2 can trigger and orient solar hydrogen evolution reaction. LixTiO2 is envisioned as a photo(electro)catalyst, whose rejuvenation can be achieved by in situ potential control. The investigations are conducted in a half-battery cell design where a mesoporous, anatase TiO2 thin film (negative electrode candidate) is deposited onto a transparent conducting oxide (FTO) substrate, water-in-salt (WiSE) is used as an electrolyte. Changing the state of charge of the working electrode material, will adjust the ratio between the Li-rich phase (Li0.5TiO2 blue) and the Li-poor phase (Li0.01TiO2 uncolored), which will tune the opto-electronic properties of the material, potentially changing the light-matter interaction. The impact of light on the interplay between hydrogen evolution reaction and lithium insertion/extraction in TiO2 is investigated using classical electrochemical characterizations inspired from both battery and photoelectrode communities. With a minimum of Li-rich phase solar hydrogen is produced at the working or at the counter electrode while lithium in photo-extracted of the Li-rich phase to reform TiO2.Graphical Abstract

Electrochromic glass, one of the green energy-saving building materials, get more and more attention. The advancement of efficient ion storage film become a hot topic of research. The porous V2O5 ion-storage film was prepared by sol-gel method using polyethylene glycol (PEG) as the pore-former. The peak current of porous V2O5 films heated at 300 °C increased substantially due to the volatility temperature of PEG at 285 °C. The mutual effects of the PEG content, heat treatment temperature, and heat treatment time on the structure and electrochromic properties of porous V2O5 film were investigated by the response surface method (RSM). The results show that the influence extent on ion storage is: heat treatment temperature > PEG content > heat treatment time. Under optimized process parameters of PEG content 6.2 g/100 mL sol, heat treatment time 4 h, heat treatment temperature 310 °C, the porous V2O5 film exhibited excellent ion storage capacity (87.28 mC·cm−2). The electrochromic device (ECD) with optimized porous V2O5 ion-storage film as the counter electrode of electrochromic WO3 film has been successfully assembled, which shows fascinating performance with high optical contrast (87.8% at 550 nm) and fast response time (bleaching/coloring: 4.5/3.7 s).Graphical Abstract

Hydroxyapatite (HA) embedded in polymer-based bone scaffold exhibits excellent medical properties for bone healing. Indeed, limited studies have reported on the addition of HA into starch/polyvinyl alcohol (PVA) scaffold system, especially HA role as bio-additive releasing Ca2+ ion promoting biomineralization. Herein, HA derived from chicken bone with the particles size ranging from 100 to 600 nm loaded starch/PVA composite scaffold with different amount was fabricated using a salt-leaching method. XRD and SEM-EDS analysis indicated the presence of HA in starch/PVA composite. FTIR results showed that the chemical bondings in starch/PVA matrices were not affected by the introduction of HA. Morphology and architecture of scaffolds characterized by SEM demonstrated pore size and their structure satisfying the needs of bone scaffolds. Young modulus of composite scaffold increased with the increase of HA loading content. The Ca2+ release analyzed by ion chromatography system showed the increasing trend with amount of HA addition into scaffold, which improved mineralization of composite scaffold in in-vitro observed by SEM-EDS. HA-loaded starch/PVA scaffold demonstrated a similar biodegradation rate and amount to the starch/ PVA scaffold. According to the result, loading starch/PVA with HA can be proposed a potential candidate for bone regeneration.Graphical Abstract

The production of the zinc oxide (ZnO) particle still has a great challenge due to the disadvantage of the latest method such as high temperature and long reaction time. To this end, a rapid method was developed to produce the ZnO particle by the simple ultrasonication method that can be applied as a photocatalyst of dyes waste produced by industries. We investigated the effect of the ultrasonic wave amplitude (0, 25, 50 and 75%) and irradiation time (0, 10, 30 and 45 min) on the structural, surface morphology, optical and photocatalytic activity on the produced ZnO particle. TEM micrographs showed that free-agglomerate and smaller ZnO particle size (compared with non-ultrasound ZnO sample) were obtained by just increasing the ultrasonic wave amplitude and irradiation time, which correlate with ultrasonication energy. This suggested a morphological control of the ZnO production through the ultrasonication method. The wurtzite-type ZnO crystal and its size estimation determined from the Rietveld-refined XRD patterns confirm that the crystal size increases as the ultrasonication time and wave amplitude increase. The FTIR spectra confirm the chemical bond of ZnO particle. The photocatalytic activity of ZnO particle under sunlight irradiation revealed that the application of ultrasonication tremendously increased the photocatalytic activity. It was measured by degradation of methylene blue and methyl orange using ZnO particles prepared with and without ultrasonication up to 98% and 78% in 90 min, respectively. This is the highest value compared with other previous results.Graphical Abstract

In the initial stage of the hydrolysis–condensation of tetraethoxysilane (TEOS), hexaethoxydisiloxane (HEDS) and octaethoxytrisiloxane (OETS) are formed. However, little is known about the hydrolysis–condensation of HEDS and OETS. In this study, the hydrolysis–condensation of TEOS, HEDS, and OETS was investigated. HEDS and OETS were synthesized from diethoxy(diisocyanato)silane, a raw material with controllable functionality. The hydrolysis of TEOS, HEDS, and OETS was analyzed by mass spectroscopy, gel permeation chromatography, and nuclear magnetic resonance. The hydrolysis–condensation product of TEOS was a three-dimensional network-type polysiloxane. The hydrolysis–condensation product of HEDS consisted mainly of four-membered cyclic siloxane. The hydrolysis–condensation product of OETS consisted mainly of various membered cyclic siloxanes.Graphical Abstract

This study reports a comparative characterization of Au/n-Si Schottky diodes/contacts (SDs) with hydrothermally synthesized ZnO–PVP and ZnO/Ag2WO4–PVP interfacial layers, which outperforms conventional metal-semiconductor Schottky diode structures. This characterization is important because these structures outperform traditional metal-semiconductor Schottky diodes due to the presence of an interfacial layer, allowing barrier height control, surface passivation, and leakage current reduction. Based on the thermionic emission (TE) theory assumed to be the dominant current mechanism across, SDs parameters were obtained. As expected, nonlinear rectifying behavior was observed for all SDs, and the divergence from linearity is caused by factors such as the interfacial layer thickness, the interface-state (Nss) density, and the bulk series resistance (Rs). It is important to note that the rectification ratio (RR) of the Au/(ZnO/Ag2WO4–PVP)/n-Si (MPS2) SD is 48 times more than the RR of the Au/n-Si SD and 11 times greater than the RR of the Au/ ZnO–PVP/n-Si (MPS1) SD. The ideality factor (n) and zero-bias barrier height (ΦB0) were found to be 7.73 and 0.563 for MS, 6.23 and 0.604 for MPS, 4.83 and 0.684 for MPS2 SD. Nearly an order of magnitude less Nss exists for the MPS2 diode than the MS diode. According to these findings, the ZnO–PVP and ZnO/Ag2WO4–PVP interfacial layers stop Au and n-Si from reacting or diffusing with one another while also passivating the active dangling bonds at the Si surface. The methods of Cheung and Norde were also used to extract the Rs, n, and ΦB. The inconsistency between the parameters obtained from these methods could be attributed to the regions where the methods are used differ.Graphical Abstract

A novel, fast, stable, and cost-effective colorimetric hydrogen peroxide (H2O2) sensor was prepared by the incorporation of silver nanoparticles (AgNPs) in chitosan-co-acrylic acid (CS-co-AAc) microgel. AgNPs were synthesized by green method by using Euphorbia Maculate (EM) leaf extract. Chitosan-co-acrylic acid/silver nanaoparticle (CS-co-AAc/AgNPs) hybrid microgel can be characterized by various analytical techniques. CS-co-AAc/AgNPs hybrid microgel exhibited UV-visible absorption band 436 nm. X-ray diffraction spectrum reveals that CS-co-AAc/AgNPs hybrid microgel are amorphous in nature and the crystalline nature of synthesized AgNPs. The hybrid microgels are highly selective towards H2O2 and the absorption band intensity is proportional to the concentration of H2O2 in solution. Over the concentration range of 0–50 nM, the intensity of the absorption peak decreases linearly,and the corresponding correlation coefficient is R2 -0.9063. The limit of detection is determined to be 3.2 nM. Antibacterial activities of the hybrid microgel were also observed against aquatic bacteria such as Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) isolated from river water samples taken from Kerala. Practical applicability of the hybrid microgel for the sensing of H2O2 in real milk samples was also investigated. AgNPs themselves can show similar behaviors, but they are destabilized because it undergo rapidly agglomerate. This hybrid microgel system offers numerous advantages, such as sample processing and extreme stability. This technique is ideal for assessing diverse biological and environmental materials since it is easy to use, inexpensive, and adaptable to complex matrices.Graphical Abstract

Dielectric capacitors have been widely studied for energy storage applications in pulsed power electronic and electrical systems due to their fast charge/discharge rate and high power density. In this work, the lead-free ferroelectric BaZr0.2Ti0.8O3–0.02 MnO2 (BZT-0.02 Mn) thin films are prepared by a sol–gel method on Pt(111)/Ti/SiO2/Si(100) substrates. The crystal structure, surface morphology, ferroelectric properties, leakage behavior, energy storage properties and stability of the films are systematically investigated. The BZT-0.02 Mn thin films exhibit relatively high recoverable energy storage density of 32.3 J/cm3 and energy storage efficiency of 62% at 3700 kV/cm. In addition, the frequency-insensitive stability from 0.1 kHz to 10 kHz, long-term fatigue resistance up to 107 switching cycles and high temperature stability in a range of 20 °C to 120 °C are also achieved. The results show that the BZT-0.02 Mn thin film is a promising lead-free dielectrics for application in energy storage.Graphical Abstract

In this study, considering the good optical properties of CeO2 thin films, their anti-reflective effect on crystalline silicon solar cells was investigated. First molarity and then coating speed optimizations were carried out for the optimum thickness value. In addition, annealing temperature and annealing time optimizations were performed on CeO2 thin films, and the appropriate values for annealing temperature and annealing time were determined. As a result of all optimizations, it was found that 0.3 M concentration, 6000 rpm coating speed, 400 °C annealing temperature, and 120 min annealing time were optimum values for CeO2 thin films. The average reflectance value of CeO2 thin films obtained using these values was 14.32%, while the minimum reflectance value was 0.62%. When the optimum reflectance values were applied to c-Si solar cells with Afors-het simulation, it was observed that the efficiency value increased from 11.57 to 16.89% compared to the uncoated solar cell.

The highly efficient Cu doped TiO2/Yb2O3 (CTYO) photoactive nanocomposite were prepared by simple and straight sol-gel method. The structural, morphological and other properties of the prepared nanocomposite were studied. X-ray diffraction analysis revealed the existence of both Yb2O3 and TiO2 phases in crystalline structure of CTYO. UV-Vis diffuse reflectance spectroscopy confirmed the great potential of the prepared samples as the efficient visible light photocatalyst. The photoactivity of the prepared samples were evaluated using degradation of acid red 88 solution (AR88) under visible light irradiation. The 92.5% of the AR88 in solution was degraded after the 180 min illumination over CTYO photocatalyst. The degradation efficiency was studied under different pH of AR88 solution and amounts of the loaded photocatalyst. The stability and recyclability of the prepared photocatalyst were studied under 8 reaction cycles which revealed the superiority of CTYO as the visible light photocatalyst.Graphical Abstract

Zn-doped TiO2 (0,3,7% wt.) thin films were obtained by Sol-Gel method, deposited by spin-coating process on glass substrates, then heat treated at 500 °C for 90 min. Deposited films (Zn: TiO2) have been characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), UV–vis transmittance spectroscopy and m-lines spectroscopy (MLS). XRD analysis of the undoped TiO2 films showed the formation of both phases (anatase and brookite) with A(101) plan as preferential orientation. Increase of zinc concentration inhibited the crystal growth in the TiO2 films. SEM pictures of undoped TiO2 and Zn doped films indicate that zinc contents can lead to significant microstructure changes of TiO2 films. The average transmittance and the optical band gap of the films are 70–90% in the wavelength range 350–900 nm and 3.6–3.51 eV, respectively. M-lines spectroscopy put into evidence that Zn: TiO2 planar waveguides support single confined guided modes for both transverse electric (TE) and transverse magnetic (TM) polarizations. MLS measurements proved that doping zinc in TiO2 increased the index refraction of TiO2 thin films which enhances the waveguiding properties. Simultaneously, the birefringence decreases with increasing concentrations up to 7 wt%.Graphical Abstract