Encyclopedia
Scanning Electron Microscopy (SEM) micrograph of a diatomite fragment. As visible, the ordered porosity (close-packed cylindrical pores) of diatomite allows to achieve the highest porosity possible for a solid.
01 Dec 2023
Meet Non-Newtonian Fluids, the rule-breaking liquids that behave like solids when you least expect it! From the ketchup on your fries to slime in your hands, these quirky fluids are everywhere!
Encyclopedia Editorial Office
24 Sep 2024
A map of a pistachio orchard segmented using random forest to classify vegetation, soil and shadows.
20 Mar 2023
Usually, nanostructures have an artificial origin, indeed they are fabricated by top-down (e.g., ball milling, laser ablation in liquids, sputtering, etc.) or bottom-up (i.e., chemical synthesis) approaches. However, nanostructures are occasionally available also in nature. The clinoptilolite mineral is the most relevant example of a nanostructured material made by nature. Clinoptilolite is a very common type of natural zeolite, widely available on the market at low cost. Zeolites are silicoaluminate compounds, containing charge-balancing cations of alkali (Na+, K+) and alkaline-heart (Ca2+, Mg2+) metals. Owing to their microporous structure, these substances are technologically very useful; indeed, zeolites have cavities (cages) in the crystalline lattice, that are connected together to form a regular array of channels. Clinoptilolite has a finely-grained texture made of lamellar crystals with a thickness of 40nm and containing a two-dimensional array of channels placed in parallel with the lamellar basal planes. These lamellas are compactly staked together, leading to a structure resembling the ‘Opus Latericium’ used in the ancient Roman architecture. This highly robust microstructure allows the clinoptilolite mineral to exhibit good mechanical properties and mesoporosity (inter-lamellar porosity), in addition to the typical microporosity (molecularly-sized porosity), which characterizes all zeolite types [1]. To observe the nano-sized texture of clinoptilolite, made of identical lamellas with a thickness of 40nm, the surface of the mineral needs to be polished, chemically etched, and investigated by Scanning Electron Microscopy (SEM) at very high magnification. In order to achieve a flat surface, the sample has to be first grained and then polished by a P4000 silicon carbide paper. Owing to the larger number of Si atoms contained in clinoptilolite compared to the Al atoms (5.4:1 for our zeolite sample), the chemical etching reaction needs to be based on the desilication process (dissolution of the framework silica with formation of soluble sodium silicate). In particular, a sodium hydroxide (NaOH) aqueous solution (0.2M) can be conveniently used for the clinoptilolite mineral etching with an etching time of a few hours (at room temperature). An etching treatment based on the dealumination reaction is not adequate since it can cause only lattice defects formation.
06 Dec 2023
The diatomite microstructure can be conveniently visualized by using the simple transmitted light optical microscopy (OM) technique. Diatomite is a soft sedimentary rock made of siliceous shells of diatoms, a type of hard shelled unicellular microalgae, and its structure can be conveniently visualized by transmitted light microscope (namely biological microscope) because this device is typically used for investigating biological structures like cells, bacteria, fungi, etc. Actually diatomite consists mostly of tinny fragments of fossilized remains of diatoms and their ordered porosity can be clearly identified, however the inner structure of pores can be seen only at very high magnification by using a scanning electron microscope (SEM). Diatomite is a low density and high porous solid made of hydrated silica (SiO2.xH2O), it is slightly colored since it contains iron oxide and therefore it appears in transmission-light observation as colored or transparent glass pieces. Here, micrographs have been obtained simply by using the camera of a smartphone (Samsung, Galaxy S8) without adapter or additional lens.
18 Dec 2023
Scanning electron microscopy (SEM) micrograph showing the expanded graphite structure.
20 Nov 2023
Transmission electron microscopy (TEM) micrograph of gold nanoparticles dispersed in polyvinylpyrrolidone (PVP).
04 Dec 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
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
SEM micrograph of an expanded graphite flake.
09 Nov 2023
Monoclonal antibodies (Mab) staining of jaagsiekte sheep retrovirus (JSRV)-infected sheep lung tumors from around the world. Sheep numbers and countries of origin are: A, 96238 from South Africa; B, 95234 from South Africa; C, 92K3 from Kenya; D, 81R16 from Peru; E and F, 85RS1 from the USA (experimentally-infected); G, 84RS28 from the USA; and H, B-96/00 from Spain. Sections were stained with Mab B3, C9, or both. Scale bars indicate a distance of 100 μm. [1]
Wikimedia Commons
08 Feb 2024
During my PhD project, it was very common to make organolthiums form tolylphosphines. Their colours were quite amazing to see!
24 Jul 2023
The astonishing aspect of diatomite that can be observed by scanning electron microscope (SEM) is principally related to the highly regular arrangement of pores in the frustules. However, color is another consequence of this highly ordered porosity, but it can be revealed only by using transmitted-light optical microscopy (OM). Indeed, diatomite frustules are nature-made photonic crystals and for such a reason the diatomite frustules appear variously colored under transmitted-light microscopy observation. Diatomite frustules are a mixture of glass (hydrated silica, SiO2.xH2O) and air. Glass and air are two perfectly transparent optical phases characterized by very different refractive indices and in addition they are organized in the frustules in a very regular manner. Owing to destructive light interference phenomena among the light beams reflected and refracted at glass-air interface, the frustules appear slightly colored for the extinction of most light components contained in the incident white radiation. Since color strictly depends on the refractive index of the optical phase contained in the frustules holes, these natural materials can be used as optical sensors. Photonic crystals are quite common in nature indeed the colors of scarabs, butterflies, and other insect types are due to this optical phenomenon. This natural phenomenon has inspired the fabrication of many artificial devices, however to make very miniaturized photonic crystals is a quite difficult process. To copy this functional porosity of natural systems like diatomite frustules is a particular approach of materials science known as biomimetics.
25 Dec 2023
The figure shows the schematics of the methods traditionally used for the deposition of electrode layers: (a) slurry application; (b) spraying; (c) screen printing; (d) film casting [1].
25 Jul 2023
Scanning electron microscopy (SEM) micrograph of microporous palladium generated by thermal decomposition of palladium dodecylthiolate.
20 Nov 2023
Scanning electron microscopy (SEM) micrograph of platinum deposited on a carbon substrate. Platinum has been produced by thermal decomposition of platinum-dodecylthiolate.
20 Nov 2023
Graphene single-sheet is quite difficult to be prepared and, in order to take it in a stable form, it requires to be supported on an inert substrate or to be dispersed in a liquid under very dilute conditions. Differently, few-layer graphene, which is known also as quasi-graphene, can be easily obtained by applying some sono-acoustic energy to a low-cohesion graphite solid form, known as expanded graphite, dispersed in a volatile organic liquid capable to wet the graphite solid. Acetone is typically used as dispersing medium for the expanded graphite. The exact number of graphite sheets contained in the resulting graphite nanoplatelets (GNPs) depends on the nature of the dispersing medium and the intensity/duration of the sonication treatment. Such an approach is very common in nanotechnology; indeed, many other 2D-materials can be prepared simply by applying sono-acoustic energy to a suspension of a layered material in an adequate dispersing medium (e.g., MoS2 can be easily exfoliated by sonication in N-methyl-pyrrolidone, NMP). Graphite nanoplatelets (GNP) is an important precursor for the preparation of other graphite-derivatives. For example, it can be used for coating the surface of a non-polar polymeric substrate (e.g., low-density polyethylene, polydimethylsiloxane, poly(methyl methacrylate)) by a micromechanical method based on friction and also as precursor of graphene oxide (GO); indeed, it can be used as reactant for the Hummers’ method (in this case, a quantitative oxidation of the graphene sheets with formation of graphene oxide is obtained).
13 Dec 2023
Thiol salts (that is, Me(SR)x), named ‘metal thiolates’ or ‘mercaptides’, are organic compounds capable to thermally decompose leading to the pure metal (Me) or to a metal sulfide (MexSy) and an organic by-product (that is, an organic disulfide, RSSR, or a sulfide, RSR, respectively). These chemical substances can be conveniently used in different ways to produce nanostructures of pure metals or semiconductors (i.e., sulfides). In particular, noble-metal thiolates generate the elemental metal (zero-valent metal) by thermal decomposition at temperatures ranging between 150°C and 200°C. Noble-metal thiolates are non-polar compounds (covalent molecules), that easily dissolve in non-polar polymers, like the amorphous polystyrene (PS). These solid solutions are thermally unstable and transform in a metal-polymer nanocomposite by heating at temperature values compatible with the thermal stability of most polymers. The metallic phase precipitates in the molten polymer in form of hyperfine zero-valent metal. Controlling the precursor concentration and the thermal annealing temperature (low concentration and high temperature values), it is possible to generate highly monodispersed nanometric particles, known as metallic clusters. For example, this technique has been used to generate clusters of elemental gold (Aun, with n<1000) in an amorphous polystyrene matrix by thermal decomposition of gold dodecyl-thiolate (Au-SC12H25). Such metallic thiolate has been synthesized by reacting tetrachloroauric acid (HAuCl4) with the dodecylthiol. Metal-polymer nanocomposites of gold and other coin metals are optically transparent and have very useful functional properties like surface plasmon resonance (SPR), fluorescence, thermocromism based on SPR, etc. and therefore they can be exploited for many technological applications [1].
13 Nov 2023
Scanning electron microscopy (SEM) micrograph of expanded graphite.
06 Dec 2023
