Encyclopedia
Diatomite: a 'water-like' substance
Water is only a tinny molecule but it results the most important chemical substance in the physical world. Such statement follows to the consideration that living matter excels in the physical world and it is made substantially of water (up to 75%), thus the transitive property suggests that water should excel in the physical world. Biomimetics is a new approach in material science, that consists in finding technological solutions by emulating the nature. Therefore, water-like solids should be substances with great technological potentialities. Hydroxyls (O-H) represent the only water fragment characterized by chemical/physical behaviors quite close to water. Owing to such huge similarity with water, hydroxyl-containing substances are important matter forms. Diatomite (hydrated silica, amorphous solid known as: opaline, SiO2.xH2O) is an inorganic chemical compound extremely rich of hydroxyl groups (i.e., silanols, Si-OH) and therefore this water-like substance should have a number of great technological potentialities.
01 Apr 2024
Under the electron microscope, a capillary reveals red blood cells transporting oxygen and white blood cells engaged in immune surveillance. The vessel's thin walls and endothelial cells facilitate nutrient exchange, highlighting its vital role in circulation and immune defense
05 Jul 2024
Noble-metals are stable only in their zero-valent state, consequently noble-metal cations can oxidize organic molecules like alcohols to get in their zero-valent state. Alcoholic reduction is the simplest 'chemie douce' technique available to produce metallic colloids. In this process, a vicinal-diol is preferred as reducing agent because its reducing capability is stronger than that of simple alcohols. Ethylene glycol is the typical polyol used for the noble-metal cation reduction, and it is used in combination with a polymeric surface stabilizing agent, like polyvinylpyrrolidone (PVP). The polymeric stabilizing agent side-groups adsorb on the electrophilic surface of metal particles and avoid particle aggregation by steric stabilization; in addition, the stabilizing agent favors the cation reduction process because it forms coordination-complexes with the zero-valent noble-metal atoms that get closer and easily precipitate. When a large amount of a non-solvent liquid for PVP (like anhydrous acetone) is added to the noble metal colloidal suspension at the end of the reaction, a metal-polymer nanocomposite is generated by co-precipitation of PVP and metal nanoparticles. These PVP-embedded metal clusters are ‘model systems’ that can be very usefully used to study the nanoscopic properties of nano-sized metals, like the surface plasmon resonance (SPR), spin-glass transition, and many other physical phenomena characterizing the nano-world. The reducing ability of polyols significantly increases with rising of temperature and therefore also some transition metals like copper, cobalt [1], nickel, etc. can be obtained by the polyol process (in this case, a refluxing high boiling point glycol, like dietylene glycol, triethylene glycol, and tetraethylene glycol is used) with or without the use of a stabilizing agent.
13 Nov 2023
Several strategies have been developed for preparing freestanding noble-metal aerogels with high specific surface area; a very simple approach is based on the combustion of metal clusters embedded in poly(vinylpyrrolidone) (PVP) [1]. In particular, this noble-metal/PVP solid system is prepared by co-precipitation with acetone of a metal colloid (e.g., silver colloid), that has been obtained by reduction of a noble-metal salt (e.g., silver nitrate, AgNO3) with ethylene glycol in presence of PVP [2]. A very critical factor of such preparative approach is represented by the metallic filler percentage in the precursor system. Indeed, the metallic percentage must be conveniently low for allowing neighbor particles to coalesce together (sintering process) generating a fibrous morphology, during the polymeric matrix elimination process by combustion. In particular, when the metal content is close to ca. 5% by weight, a continuous and uniform highly porous 3D network of silver is generated. Spherical metal nanoarticles aggregate in form of short filaments (i.e., nanoparticle chains with necklace-like structures), which randomly interconnect together, thus producing a trees-like morphology (arborescent structure). Owing to the very good electrical conductivity of noble metals (e.g., Au, Ag, Pt) and the extremely high porosity of these metallic aerogels, they result very adequate for technological applications where a high current density value is required, like for example electrodes for supercapacitors, current collectors, hydrogen sensors, etc. Also very effective heterogeneous catalysts can be prepared by this quite general approach (e.g., palladium aerogels [3]).
31 May 2024
Artistic rendering of Cassava Mosaic Virus - graphic design on fabric in Guinea-Bissau.
William M. Brown Jr., Bugwood.org
01 Mar 2024
Frequency of using of chemical elements in high-entropy alloys accordinh to Scopus data to period of 2010–2022 (shown as vertical lines with corresponding numbers, elements used less than 10 times shown without numbers). [1]
30 May 2024
Thiol-derivatized gold nanoparticles have been prepared by alcoholic reduction of AuCl4- in presence of PVP, followed by PVP replacement with thiol
19 Jul 2023
Encyclopedia now accepts Field Guides! Showcase plants, animals, fungi, and more from specific regions with high-quality images for easy identification. No length limits—just include at least five images.
Encyclopedia Editorial Office
24 Sep 2024
Owls are some of the most fascinating creatures in the animal kingdom! With their stealthy flight, powerful grip, and unique adaptations, they’ve earned a reputation as expert hunters.
Encyclopedia Editorial Office
02 Jan 2025
Mechanisms of action of sunitinib (VEGF-tyrosine kinase inhibitor) and mechanisms of drug resistance in renal cell carcinoma.
Sunitinib is a small molecule TKI, inhibiting activation of VEGF-R and PDGF-R, blocking intracellular pathways mediating cellular growth and angiogenesis. Mechanisms of resistance include upregulation of HIF pathways to stimulate angiogenesis and subsequent tumor growth. Lysosome sequestration of sunitinib contributes to reduced drug efficacy and resistance. Pro-angiogenic factors are inhibited by ICI-mediated anti-angiogenic therapy, which contributes to hypoxia. VEGF, Vascular endothelial growth factor; TKI, tyrosine kinase inhibitor; ICI, immune checkpoint inhibitor; HIF, hypoxia-inducible factor; PI3K, phosphoinositide 3-kinase; VEGF-R, vascular endothelial growth factor receptor; PDGF-R, platelet-derived growth factor receptor; mTOR, mammalian target of rapamycin; AKT, protein kinase B.
28 Sep 2023
Therapeutic approaches for colorectal cancer, with conventional treatment (i.e., surgery, radiation, hormone therapy, targeted therapy, and chemotherapy), as well as the use of flavonoids, tannins, and non-flavonoids in colorectal cancer treatment [1].
06 Sep 2023
Artemisia herba alba, also known as "Desert Wormwood" or "White Sagebrush," is a medicinal plant native to North Africa, including Morocco. This remarkable herb has gained attention for its potential beneficial effects on various health conditions, including liver injury, diabetes, heart disease, and arthritis. With a long history of traditional use and ongoing scientific research, Moroccan Artemisia herba alba holds promise as a natural remedy for promoting overall well-being and managing these health concerns.
04 Sep 2023
Image captured from Xflow postprocessing for vortices behind C130H at 160 m/s speed.
18 Jul 2023
Recently, the development of techniques to prepare and characterize carbon nano-materials has attract a great attention. In particular, low-density and porous exfoliated graphite is a widely investigated industrial product. Exfoliated graphite is generated as a result of an 'intermolecular explosion' during expandable graphite momentary heating, which causes the vaporization of water and some acid compounds, thus generating a dispersion pressure [1]. Exfoliated graphite according to XRD corresponds to graphite but it is represented by a number of chaotically located worm-like particles. Exfoliated graphite combines initial graphite properties with high specific area, porosity, low thermal conductivity, adsorption ability to various gasses and organic compounds, ability to be pressed without binder into materials with controlled density, gas permeability, etc. Exfoliated graphite is characterized by a X-ray density of 2.26 g/cm3 and a bulk density (determined as mass/volume ratio) of 1-10 g/l. Such difference in densities is caused by the high material porosity that varies from 95 to 98% with an estimated open pores of 98-99%. The exfoliated graphite porosity is represented by micro-, meso- and macropores, which determine its application areas. The production of graphite foils represents the most common use. These graphite foils are obtained simply by pressing the exfoliated graphite worm-like particles without binder; the obtained graphite-based product show perfect cohesion. Mesopores provides high sorption ability for heavy oils, while micropores makes exfoliated graphite a very promising material for hydrogen sorption. Indeed, exfoliated graphite adsorbs 0.11-0.25 wt. % under 1 bar of hydrogen at 77K.
12 Jan 2024
When caffeine crystals are magnified 900x under a microscope, they exhibit a striking, needle-like structure with sharp, elongated edges. The crystals appear as slender, interwoven shards or rods that often form intricate patterns, resembling a crystalline forest or a delicate mesh. Depending on the lighting, the crystals can appear transparent or display a shimmering, reflective quality. The geometric precision of the crystals reflects the orderly arrangement of caffeine molecules within the solid state. These microscopic details highlight the purity and characteristic morphology of caffeine, providing insight into its chemical structure and crystallization properties.
09 Aug 2024
Did you know that wombats are much more than just cute marsupials? These fascinating creatures are full of surprising traits, from their cube-shaped poop to their super digging skills.
Encyclopedia Editorial Office
02 Jan 2025
Scanning electron microscopy (SEM)-micrograph showing the microstructure of a natural clinoptilolite sample. The clinoptilolite crystals are 40 nanometer thick.
03 Nov 2023
Researchers take 100mL of sample with 100mL of water, after filtering researchers add the solution of bromophenol blue + 50% NH4OH which gives the color blue and researchers add 20mL HCl N/10 + 15mL HCl 1.6 pH so the solution must be yellow.
29 May 2023
Cristobalite (silica polymorth, SiO2) forms octahedral crystals. Micronic cristobalite crystals are frequently embedded in natural zeolites like clinoptilolite. In this scanning electron microscopy (SEM) micrograph a regular array of micrometric cristobalite crystals is clearly visible. This clinoptilolite crystal system have been extract from a continuous matrix of clinoptilolite mineral by dissolving the zeolite component with an aqueous solution of sodium hydroxide (NaOH). Zeolite is a silicoalluminate compound and it can react with sodium hydroxide forming water-soluble sodium silicate molecules. Such chemical reaction is named desilication.
04 Jan 2024
