Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable ...efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.
Schematic diagram for the preparation of silica nanoparticles via Sol-Gel process Display omitted
•Synthesis of silica nanoparticles using surfactants for desirable size and shape.•Mechanism proposed for the synthesis of SNPs.•Influence of temperature, pH, concentration, drying techniques, solvents etc.•Applications of SNPs in drug delivery, HPLC, biosensors, construction etc.
This work investigates a modified sol-gel method for the preparation of interlayer-free nickel oxide silica membranes for desalination applications. The sol–gels were synthesized using TEOS, nickel ...nitrate hexahydrate, ethanol as solvent and water with and without peroxide (H2O2). The effect of the nickel embedded in the silica matrix as Ni/Si molar ratio was varied from 5 to 50mol% and systematically studied. The sols prepared with H2O2 resulted in microporous structures and lower pore volume, contrary to the mesoporous structures derived from sols without H2O2. The modified sol-gel method proved to be robust enough for coating directly on α-alumina substrates, as opposed to conventional methods which required substrates with interlayers. All interlayer-free nickel oxide silica membranes delivered high salt rejection ranging from 91.5 to 99.9%, and reaching water flux as high as 7.3kgm−2h−1. The membranes prepared using sols with H2O2 gave lower water flux and slightly higher salt rejection, attributed to lower pore volume and smaller pore size, respectively. The membranes prepared with Ni/Si molar ratio of 25% achieved the highest water flux, though salt rejection slightly decreased with the increase of feed salt concentration from brackish (NaCl 0.3wt%) to sea water (NaCl 3.5wt%).
•Interlayer-free nickel oxide silica membranes for desalination applications•Sols prepared with and without H2O2 formed micro and mesoporous structures.•Higher silanol/siloxane ratio for sols prepared with H2O2, and smaller pore sizes.•Membranes gave high water fluxes and salt rejection up to 7.3kgm−2h−1 and 99.9%.•Membrane with H2O2 sols gave lower water fluxes and higher salt rejections.
Soaking up s'more: Marshmallow‐like flexible gels synthesized from organoalkoxysilanes by a facile process show superior oil/water separation properties. The gels are superhydrophobic and can be used ...to remove organic compounds from water through absorption; they can then be recovered by squeezing them out of the gel, as if it were a sponge. The gel retains flexibility over a wide temperature range, even in liquid nitrogen (see photo).
This reprint is a compilation of the articles submitted in the Special Issue entitled, “Heterogeneous Photocatalysis: A Solution for a Greener Earth”, from the journal Catalysts, which presents an ...overview of the latest advances in the development of innovative photocatalytic processes.
This reprint is a compilation of the articles submitted in the Special Issue entitled, “Heterogeneous Photocatalysis: A Solution for a Greener Earth”, from the journal Catalysts, which presents an ...overview of the latest advances in the development of innovative photocatalytic processes.
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.
A formaldehyde‐assisted metal–ligand crosslinking strategy is used for the synthesis of metal–phenolic coordination spheres based on sol–gel chemistry. A range of mono‐metal (Co, Fe, Al, Ni, Cu, Zn, ...Ce), bi‐metal (Fe‐Co, Co‐Zn) and multi‐metal (Fe‐Co‐Ni‐Cu‐Zn) species can be incorporated into the frameworks of the colloidal spheres. The formation of coordination spheres involves the pre‐crosslinking of plant polyphenol (such as tannic acid) by formaldehyde in alkaline ethanol/water solvents, followed by the aggregation assembly of polyphenol oligomers via metal–ligand crosslinking. The coordination spheres can be used as sensors for the analysis of nucleic acid variants with single‐nucleotide discrimination, and a versatile precursor for electrode materials with high electrocatalytic performance.
A formaldehyde‐assisted metal–ligand crosslinking strategy is developed for the synthesis of metal–phenolic coordination spheres with uniform diameter and tunable compositions. The coordination spheres can be used as sensors for the analysis of nucleic acid variants with single‐nucleotide discrimination, and a versatile precursor for electrode materials with high electrocatalytic performance.
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.
Inspired by the anti‐freezing mechanisms found in nature, ionic compounds (ZnCl2/CaCl2) are integrated into cellulose hydrogel networks to enhance the freezing resistance. In this work, cotton ...cellulose is dissolved by a specially designed ZnCl2/CaCl2 system, which endows the cellulose hydrogels specific properties such as excellent freeze‐tolerance, good ion conductivity, and superior thermal reversibility. Interestingly, the rate of cellulose coagulation could be promoted by the addition of extra water or glycerol. This new type of cellulose‐based hydrogel may be suitable for the construction of flexible devices used at temperature as low as −70 °C.
“Hotspot” in materials science: Anti‐freezing and thermally reversible cellulose hydrogels were fabricated in an aqueous ZnCl2/CaCl2 solution, whereby the Zn2+ ions contribute to the cellulose dissolution and the Ca2+ ions act as a gelling agent. These new cellulose‐based hydrogels may find application in flexible and wearable devices for use at temperatures as low as −70 °C.
A new type of multistimuli‐responsive hydrogels cross‐linked by metal ions and biopolymers is reported. By mixing the biopolymer chitosan (CS) with a variety of metal ions at the appropriate pH ...values, we obtained a series of transparent and stable hydrogels within a few seconds through supramolecular complexation. In particular, the CS–Ag hydrogel was chosen as the model and the gelation mechanism was revealed by various measurements. It was found that the facile association of Ag+ ions with amino and hydroxy groups in CS chains promoted rapid gel‐network formation. Interestingly, the CS–Ag hydrogel exhibits sharp phase transitions in response to multiple external stimuli, including pH value, chemical redox reactions, cations, anions, and neutral species. Furthermore, this soft matter showed a remarkable moldability to form shape‐persistent, free‐standing objects by a fast in situ gelation procedure.
Turning to jelly: A series of metal–biopolymer hydrogels is obtained by ultrafast supramolecular complexation. The hydrogels are easily prepared, have high water content, and are stable at room temperature. The multistimuli‐responsive Ag‐based hydrogel can be molded to form shape‐persistent, free‐standing objects.
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