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Photocatalysts have been widely applied in the degradation of organic compounds using visible and ultraviolet radiation. Different synthesis approaches have been developed and optimized to produce efficient, eco-friendly, and inexpensive materials to photo-treat water samples contaminated with dyes, pigments, pesticides, and other organic pollutants. Over the last two decades magnetic materials have emerged as a potential alternative to facilitate catalyst isolation in heterogeneously catalyzed liquid-phase reactions. In this review, we focus on the discussion of several studies including the main synthesis processes and new protocol modifications for the fabrication of magnetic photocatalysts, and their impact on the catalyst morphology, efficiency, and recycling. Emphasis is given on the discussion of the synthesis strategies over last decade to produce photoactive catalysts including single-phase catalysts, composites, Multifunctional metal–organic framework materials, binary and ternary core–shell materials, and yolk–shell photocatalysts. Highlights A review on magnetic materials for photocatalysis is given. Emphasis is given on sol–gel preparation methods utilized for the fabrication of magnetic photocatalysts. Discussion on different material types of magnetic photocatalysts is presented. Magnetic separation properties and efficiency are discussed based on the material structures.

The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing the onset of peri-implant diseases. In this context, quercetin, a naturally occurring flavonoid, has been entrapped at different weight percentages in a silica-based inorganic material by a sol-gel route. The establishment of hydrogen bond interactions between the flavonol and the solid matrix was ascertained by Fourier transform infrared spectroscopy. This technique also evidenced changes in the stretching frequencies of the quercetin dienonic moiety, suggesting that the formation of a secondary product occurs. Scanning electron microscopy was applied to detect the morphology of the synthesized materials. Their bioactivity was shown by the formation of a hydroxyapatite layer on sample surface soaked in a fluid that simulates the composition of human blood plasma. When the potential release of flavonol was determined by liquid chromatography coupled with ultraviolet and electrospray ionization tandem mass spectrometry techniques, the eluates displayed a retention time that was 0.5 min less than quercetin. Collision-activated dissociation mass spectrometry and untraviolet-visible spectroscopy were in accordance with the release of a quercetin derivative. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods, whereas the 2,7-dichlorofluorescein diacetate assay highlighted their ability to inhibit the H 2 O 2 -induced intracellular production of reactive oxygen species in NIH-3T3 mouse fibroblast cells. Data obtained, along with data gathered from the MTT cytotoxicity test, revealed that the materials that entrapped the highest amount of quercetin showed notable antioxidant effectiveness.

Sol–gel process is a very unique wet chemical method for producing advanced materials in various areas of research. An increasingly evolution trend of this process is to combine with other technologies, such as surface modification, hybridization, templating induction, self-assembly, and phase separation, for preparing new materials possessing controllable shape, unique microstructure, superior properties, and special application. The review aims to present the synthesis of several typical sol–gel-derived materials (monodisperse nanoparticles, hybrid coatings, hollow microspheres, aerogels, and porous monoliths) via sol–gel process combining with other technologies . Some examples of application of the sol–gel-derived materials are also included.

The use of nanostructured coatings is crucial to maintain clean surfaces in public transport, shopping malls, parks, and hospitals. Megacities produce large amounts of pollutants in water and air, making it necessary to develop strategies to prevent diseases caused by accumulation of organic compounds, bacteria, viruses, and other harmful microorganisms on surfaces. This concise review analyzes the fundamental deposition techniques based on the sol–gel process for the preparation of TiO 2 films and coatings. In this regard, methodologies such as dip-coating, spin coating, spray pyrolysis, and electrophoretic sol–gel deposition are reviewed in detail. Outstanding properties such as chemical stability, reusability, hydrophilicity, and activation by sunlight or simulated solar radiation position these TiO 2 thin films and coatings as a suitable technology for commercial devices that keep public surfaces clean. Environmental and energy applications including water and air purification, gas sensing, production of renewable fuels from water splitting and CO 2 photoreduction, as well as antimicrobial features of the sol–gel-based TiO 2 coatings can be considered as potential and valuable strategies to control pollution in the actual worldwide societies. Highlights Sol–gel methodologies are essential techniques for preparation of TiO 2 thin films and coatings. Dip/spin coating, spray pyrolysis and electrophoretic sol–gel deposition are reviewed in detail. Physical and chemical properties of TiO 2 films are modified according to the sol–gel methodology. Several photocatalytic applications of TiO 2 films derived from sol–gel techniques are discussed.

The sol–gel process has become a rapidly growing research area in materials science. A variety of materials prepared via sol–gel routes have shown unique properties and characteristics that are difficult to achieve using conventional methods. In recent years, tremendous progress in sol–gel R&D has been made not only in the world but also in China. Here, this review provides a retrospective overview of the sol–gel history in China and summarizes recent progress and applications of sol–gel research in Chinese universities, institutes, and industries. It highlights some of the recent developments published by Chinese researchers in the last 5 years, ranging from the sol–gel synthesis of nanomaterials, bulk materials, and functional coatings, to their applications in the fields of energy conversion, energy storage, photocatalysis, etc. It is evident that sol–gel technology nowadays in China has evolved into a vibrant research area both in academia and industry. Graphical abstract Highlights A brief overview of sol–gel history in China is given. Some of the recent developments of fundamental sol–gel research in China are highlighted. The commercialization of sol–gel technology in China is introduced.

The preparation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-functionalised polysilsesquioxane (Si-DOPO)-coating was described and its flame retardant efficiency for cotton fabric was thoroughly investigated. The 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide–vinyltrimethoxysilane (DOPO–VTS) was synthesized and applied to cotton fabrics at different concentrations using a sol–gel process. The structure of the synthesized DOPO–VTS was characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The characteristics of the Si-DOPO coatings formed on the cotton fibres were investigated using X-ray photoelectron spectroscopy, time-of-flight-secondary ion mass spectrometry and scanning electron microscopy. The flame retardant properties of the Si-DOPO-coated cotton samples were evaluated by thermogravimetric analyses, vertical flame spread tests and cone calorimetry analyses. The Si-DOPO coating increased the thermo-oxidative stability of the cotton fibres by increasing the stability of the protective char and inhibited cellulose fibres degradation. The Si-DOPO coating did not decrease the time of flaming combustion but did completely stop the vigorous combustion of the fibres. The results also suggest that the flame retardation by the Si-DOPO coating is due to the quenching of active radicals from the decomposing cellulose and the cellulose phosphorylation by the DOPO component as well as the silicon oxide formation by the silsesquioxane component on the fibre surface. These findings indicate that the flame retardant efficiency of the Si-DOPO coating can be ascribed to the combined activity of phosphorus acting in both gas and condensed phases and silicon acting in the condensed phase.

In this work, hydrophobic surfaces on cotton fabrics were obtained using a sol–gel technique to produce coatings applied using a spray of precursor solution followed by drying and heat treatments. Different types of treatments using the sol–gel process were performed in order to assess the influence on fabric hydrophobicity, with alteration of parameters including the concentrations of citric acid and tetraethyl orthosilicate (TEOS), the number of sprays, and curing of the fabric after obtaining the hydrophobic coating. The absorption of water into material samples were tested according to the AATCC test method 79. Scanning electron microscopy, contact angle, and Fourier-transform infrared spectroscopy (FT-IR) analysis were also studied. Excellent results were obtained for the contact angle (>150°), hence characterizing all the treatments as super-hydrophobic. FT-IR analyses revealed differences according to the citric acid concentration employed. The best results were obtained for samples treated using a higher concentration of citric acid and spraying the sol–gel solution twice. Mathematical models of the contact angle and the time for water absorption by the fabric treated with TEOS and citric acid showed good agreement with the experimental data. Highlights A hydrophobic coating on porous materials was achieved using a simple, single-step, and inexpensive procedure employing TEOS, citric acid, and ethanol, without any fluorinated compounds. The hydrophobic solution was applied using a spray of fine droplets released at a distance of 15 cm from the porous material. Better resistance to washing processes was obtained using higher concentrations of citric acid for formation of the hydrophobic solution employed for the porous coating on the cotton fabric.

In this review article the available results about application of sol–gel synthesis method for the preparation of different calcium phosphates and composite materials are summarized. The attention is paid to calcium phosphate-containing compounds which show the biological properties and could be used as potential phosphate bioceramics in medicine. It was demonstrated that the sol–gel synthesis method is a powerful tool for the synthesis of calcium hydroxyapatite and other phosphates, and different calcium phosphate-based composites at mild synthetic conditions resulted in high reproducibility, high phase purity, and desired morphology. Thus, the sol–gel synthesis method enables the researchers to develop biomaterials with superior features in terms of biomedical applications. For the synthesis of calcium phosphate biomaterials an effective sol–gel chemistry approaches have been developed. KI, EG, and AK. “Sol–gel synthesis of calcium phosphate-based biomaterials—A review of environmentally benign, simple, and effective synthesis routes”. Highlights The sol-gel chemistry approaches for synthesis of calcium phosphate biomaterials were observed. Calcium hydroxyapatite, different calcium phosphates, and composites are discussed. These CP biomaterials show a high biocompatibility and increased biological behaviour. The sol-gel synthesis method is a powerful tool for the synthesis of CP biomaterials. High reproducibility, high phase purity and desired morphology could be achieved.

The corrosion process is a major source of metallic material degradation, particularly in aggressive environments, such as marine ones. Corrosion progression affects the service life of a given metallic structure, which may end in structural failure, leakage, product loss and environmental pollution linked to large financial costs. According to NACE, the annual cost of corrosion worldwide was estimated, in 2016, to be around 3%–4% of the world’s gross domestic product. Therefore, the use of methodologies for corrosion mitigation are extremely important. The approaches used can be passive or active. A passive approach is preventive and may be achieved by emplacing a barrier layer, such as a coating that hinders the contact of the metallic substrate with the aggressive environment. An active approach is generally employed when the corrosion is set in. That seeks to reduce the corrosion rate when the protective barrier is already damaged and the aggressive species (i.e., corrosive agents) are in contact with the metallic substrate. In this case, this is more a remediation methodology than a preventive action, such as the use of coatings. The sol-gel synthesis process, over the past few decades, gained remarkable importance in diverse areas of application. Sol–gel allows the combination of inorganic and organic materials in a single-phase and has led to the development of organic–inorganic hybrid (OIH) coatings for several applications, including for corrosion mitigation. This manuscript succinctly reviews the fundamentals of sol–gel concepts and the parameters that influence the processing techniques. The state-of-the-art of the OIH sol–gel coatings reported in the last few years for corrosion protection, are also assessed. Lastly, a brief perspective on the limitations, standing challenges and future perspectives of the field are critically discussed.

The sol–gel process is used to prepare photocatalytic coatings with antibacterial properties. Also, doping with metallic or non-metallic elements has an impact on the antibacterial and photocatalytic activity of these coatings. Although there are many studies in this field, the effect of co-doping with Cu and N and their concentrations on the antibacterial properties of TiO 2 coatings against the E. coli and S. aureus bacteria has not been studied. In the present investigation, the sol–gel method was employed to deposit both undoped and Cu-N co-doped TiO 2 photocatalytic coatings on glass surface, which are expected to degrade bacterial and chemical contaminants in water while exposed to visible sunlight wavelengths. Before the coating process, an appropriate heat treatment was applied on the samples and the quality of coatings, band gap energy, and also photocatalytic and antibacterial properties were evaluated. Results showed that, in the presence of dopants, the band gap become narrower and the absorption spectrum is transferred from the ultraviolet to the visible light range. Also, it was demonstrated that, under the visible light radiation, all of the co-doped samples show higher photocatalytic activity than the undoped ones. Meanwhile, the antibacterial characteristics of TiO 2 coatings was enhanced by increasing the dopant concentration when exposing to sunlight. Highlights TiO 2 coatings co-doped with different concentrations of copper and nitrogen were applied on glass surface using sol–gel process. The influence of the dopant concentration on the photocatalytic activity and antibacterial properties was discussed. Under the visible light radiation, all of the co-doped samples have higher photocatalytic activities than the undoped ones, while the 0.75%Cu-N sample has the best photocatalytic activity, even better than the 1% Cu-N one.