Study of the sol-gel reaction mechanism in supercritical CO2 for the formation of SiO2 nanocomposites

Towards a mechanistic understanding of the sol–gel syntheses of ternary carbides

The formation mechanism during the sol–gel synthesis of MAX phase Cr2GaC is unraveled using a combination of complementary techniques.

Role of supercritical carbon dioxide (scCO2) in fabrication of inorganic-based materials: a green and unique route

In recent times, the supercritical carbon dioxide (scCO₂) process has attracted increasing attention in fabricating diverse materials due to the attractive features of environmentally benign nature and economically promising character. Owing to these unique characteristics and high-penetrability, as well as diffusivity conditions of scCO₂, this high-pressure technology, with mild operation conditions, cost-effective, and non-toxic, among others, is often applied to fabricate various organic and inorganic-based materials, resulting in the unique crystal architectures (amorphous, crystalline, and heterojunction), tunable architectures (nanoparticles, nanosheets, and aerogels) for diverse applications. In this review, we give an emphasis on the fabrication of various inorganic-based materials, highlighting the recent research on the driving factors for improving the quality of fabrication in scCO₂, procedures for production and dispersion in scCO₂, as well as common indicators utilized to assess quality and processing ability of materials. Next, we highlight the effects of specific properties of scCO₂ towards synthesizing the highly functional inorganic-based nanomaterials. Finally, we summarize this compilation with interesting perspectives, aiming to arouse a more comprehensive utilization of scCO₂ to broaden the horizon in exploring the green/eco-friendly processing of such versatile inorganic-based materials. Together, we firmly believe that this compilation endeavors to disclose the latent capability and universal prevalence of scCO₂ in the synthesis and processing of inorganic-based materials.

Metal Oxide-Related Dendritic Structures: Self-Assembly and Applications for Sensor, Catalysis, Energy Conversion and Beyond

In the past two decades, we have learned a great deal about self-assembly of dendritic metal oxide structures, partially inspired by the nanostructures mimicking the aesthetic hierarchical structures of ferns and corals. The self-assembly process involves either anisotropic polycondensation or molecular recognition mechanisms. The major driving force for research in this field is due to the wide variety of applications in addition to the unique structures and properties of these dendritic nanostructures. Our purpose of this minireview is twofold: (1) to showcase what we have learned so far about how the self-assembly process occurs; and (2) to encourage people to use this type of material for drug delivery, renewable energy conversion and storage, biomaterials, and electronic noses.

Synthesizing 1D and 2D metal oxide nanostructures: using metal acetate complexes as building blocks

1D and 2D metal oxide nanostructures are important for potential applications in alternative energy, batteries, supercapacitors, catalysts, biomaterials, and electronic nanodevices. Many current approaches for making the desired nanomaterials require multiple steps, which are often exotic and complex for production on a commercial scale. In contrast, the sol-gel reactions between metal alkoxides and organic acids have emerged as a simple protocol for producing metal oxides and inorganic/organic hybrid materials with a controllable 1D or 2D architecture. Our knowledge of this process continues to evolve through the fundamental goal of designing a desired nanostructure from the corresponding molecular building blocks. Our research was driven by the discovery of various morphologies by fine-tuning the synthesis parameters, such as the reaction temperature and molar ratio of the reactants, as well as switching solvents. These discoveries lead to several quesions: What are the building blocks of the 1D and 2D nanostructures and how does the self-assembly occur? What are the reaction kinetics and the mechanisms of nanostructure formation? What role does the solvent play in the assembly process? What are the effects of reaction temperature and pressure? How can we manipulate the nanostructure-for example, the parallel growth of 1D semiconductors-from a substrate surface? And lastly, what are the industrial applications of macroporous aerogels and xerogels? This minireview will highlight documented research accounts to answer these questions.

Bioactive Pigments from Isolated Bacteria and Its Antibacterial, Antioxidant and Sun Protective Application Useful for Cosmetic Products

Bacterial pigments are the unique and sustainable source of bioactive colour compounds used in cosmetics, food, textiles, printing and pharmaceutical products. Here, we report the pigment-producing isolates and their biological activities that could be benefited for different industries including cosmeceuticals. In this study, a total of 19 pigment-producing bacteria were isolated and purified from collected soil and water samples. The colour production ability of purified bacteria was observed up to 5 transfers. Of the 19 isolates, two isolates lost colour production ability in subsequent transfers. Crude pigments extracted from the remaining 17 isolates showed sunscreen activity in the range of 0.4-8.34. However, only 6 of them showed significant antibacterial and antioxidant activities. In the media optimization experiment, these 6 bacteria showed optimum growth in neutral to alkaline pH, while optimum temperatures for growth were different for different bacteria. One isolate produces the promising pigment, out of all six potential pigments. It is stable up to 5 transfers, having antioxidant and antibacterial activity with Sun protective activity; the strain was identified using 16srRNA gene sequencing and obtained accession number as MK770403 (probable strain is Staphylococcus xylosus) from National Center for Biotechnology Information (NCBI) database. The results of this study suggested that these bioactive pigments can further be developed and used as antibacterial, antioxidant and sun-protective ingredients in cosmeceuticals.

Insulating oxide film formation with acid catalyzed hydrolysis of alkoxide precursors in supercritical fluid carbon dioxide

Insulating oxide films can be produced by hydrolysis of metal alkoxide precursors in the presence of an acid catalyst in supercritical fluid carbon dioxide (sc-CO₂).