Recent Progress in the Electrochemical Exfoliation of Colloidal Graphene: A Review

Graphene is a wonder nanomaterial which is used in a wide variety of electronics applications because of its excellent electrical, optical, chemical and mechanical properties. For the efficient use of graphene in the preparation of modern electronics devices it is imperative to first prepare a colloidal solution of graphene. Although various techniques are being used for the synthesis of colloidal form of graphene, the synthesis of colloidal graphene via electrochemical exfoliation is time saving and easy, facile method which can be easily performed in the laboratory without any expensive and sophisticated equipment as required in other techniques. Through electrochemical exfoliation of colloidal graphene, high quality graphene can be obtained within short time. Further, after the electrochemical exfoliation of colloidal graphene, the colloidal solution is stable in the organic solvent for few weeks. The conducting electrodes prepared by this colloidal solution of graphene have wide application in the areas of flexible energy storage devices and sensors fabrication.

Physical Properties Investigation on Sunscreens with Colloidal Gold and Moringa oleifera Extract

Botanicals were known as active ingredients in sunscreens due to their dermal protecting. Gold in colloidal form has a completely unique property for the reason that it may be used as photoaging material. The exposure of UV radiation to skin can cause erythema and skin cancer. The aim of this study was to determine the physical properties of the sunscreens made from Au/ZnO and antioxidant from Moringa oleifera extract such as the sun protection factor (SPF), pH, spreadability, and adhesion. The Moringa oleifera were extracted by maceration. Maceration with 70% ethanol of dried leaves exhibited DPPH scavenging activity (EC50 235.01 μg/mL). Diffuse reflectance UV-Vis spectra of ZnO and Au/ZnO revealed absorption at λex of 385 nm which were equivalent to a bandgap energy of 3.22 eV. Au/ZnO posed a localized state at λex of 385 (3.65 eV). The sunscreens with formulations F1, F2, F3, and F4 showed high SPF number of 20.1479, 21.0008, 22.3872, and18.4631. Kruskal-Wallis test showed significant differences between sunscreen formulations.

Organic matter of sediments of South Chukotka

The article discusses data on paleosol, mineralogy, and paleobotany obtained as a result of studying material collected from the Maastricht-Early Paleocene sediments of the Tanyurer Formation of South Chukotka. The burial of organic matter in the sedimentary rock of the Tanyurer Formation is associated with deflationary processes during the period of activation of volcanic activity. On the drained volcanic plateau of soil formation, a sod humus-accumulative process prevailed under the steppe vegetation. Humic substance dispersed in sedimentary rock was represented by a group of humins resistant to microbial decomposition. As a result of exposure to high pressures and temperatures, the colloidal form of humus was transformed into kerogen. Organic compounds (cellulose, lignin) in the plant tissue of buried tree trunks were replaced by silicon compounds. Weathering processes have affected the thin surface layer of dense sedimentary rock. Under the influence of the temperature and humidity gradient, loosening of loose rock and disintegration of clots of colloidal forms of humus occurred.

Activity of photosynthetic Reaction Centers coated with polydopamine

Dilute aqueous solutions of dopamine buffered to an alkaline pH and in the presence of dissolved oxygen undergo to a series of autoxidation and rearrangement reactions that lead to the formation of a dark insoluble material called polydopamine (PDA) with melanin reminiscent properties. In this work we carried out this reaction in the presence of the photosynthetic reaction center (RC), a transmembrane pigment-protein complex responsible for the first light-induced reactions in the photosynthetic process. We have found that PDA grows in colloidal form around the RC and in the appropriate conditions the protein is entrapped in the PDA matrix without loss of functionality. The protein is still capable to perform its natural photocycle leading to the generation of photocurrents and the ubiquinone acceptor complex function is modulated by the PDA/RC ratio.

Preparation and Characterization of PMMA-AgNPs Polymer Composite as a Dental Prosthesis

Silver nanoparticles (AgNPs) have been used for centuries in the field of medicine due to the antimicrobial properties. AgNPs has been synthesized and incorporated in different aspects of biomaterials. It is reported that AgNPs as a result of its small size, it provides sufficient antimicrobial effect at lower filler level, thus can be used in dentistry for prevention and reduction of biofilm formation on a surfaces of dental prosthesis. The purpose of this study is to develop AgNPs antimicrobial acrylic resin for dental prosthesis. The effect of AgNPs incorporated into acrylic resin poly methyl methacrylate (PMMA) on the bacterial biofilm was studied in terms of bacterial growth and the incorporating effect on the thermal stability of these polymeric biocides was evaluated. Silver nanoparticles in colloidal form was added to PMMA(ONDA-CRYL) using microwave and make four dental prosthesis at the different concentration. The specimens were delivered to the four toothless patients for 21 days. The formed biofilm was tested for microbiological study (taxonomic profile). After setting, the specimens were characterized to determine the spatial distribution of AgNPs on the PMMA matrix through scanning electron microscope and the thermal stability was examined using TGA and DSC. The modified PMMA prosthesis base containing AgNPs, which exhibited good in vivo antimicrobial properties without altering their thermal properties of degradation as well as their mechanical properties and minimize the maximum infectious signs by reducing the formation of microbial biofilm forming on the surfaces of dental prostheses. As the modification of PMMA with AgNPs improved the anti-biofilm properties without altering its mechanical and thermals properties to the degradation, it could be used as a dental prosthesis.

Growth Kinetics and Sensing Features of Colloidal Silver Nanoplates

This paper presents the growth mechanisms and the plasmon sensing features for a large class of silver nanoplates obtained in the colloidal form. The synthesis is conducted by seed-mediated growth and leads to plates with aspect ratios as large as 20, having localized surface plasmon resonances extending deeply into the infrared spectral region (1000 nm and above). We measure plasmon sensitivity by varying the colloidal local refractive index, and Δλ/Δn sensitivity values up to 500 nm/RIU are obtained. Theoretical considerations regarding the correlation between the refractive index sensitivity and the position of the main localized plasmon resonance band demonstrate that plasmon sensitivity does not depend directly on the nanoparticle shape and aspect ratio.

pH-induced phase transition and crystallization of soft-oxometalates (SOMs) into polyoxometalates (POMs): a study on crystallization from colloids

In this work, we demonstrate a simple approach for growing 1D (one-dimensional) inorganic chains of K(C6H16N)3Mo8O26·H2O polyoxometalates (POMs) from its colloidal soft-oxometalate (SOM) phase through the variation of pH. The structure is composed mainly of a 1D inorganic chain with a β-Mo8O26 4− binding node linked using K+ via Mo—O—K linkages, which results in a cuboctahedral geometry for the K+ ions. Crystal structure and Hirshfeld surface studies reveal the role of triethylammonium cations in restricting the growth of the 1D chain into 2D/3D (two-/three-dimensional) structures. During the nucleation process from the heterogeneous SOM phase, some of the intermolecular interactions in the dispersion phase are retained in the crystal structure, which was evidenced from residual O...O interactions. The crystallization of the species from its colloidal form as a function of pH was studied by the use of Raman spectroscopy and it was found that the increase in volume fraction of the β-Mo8O26 4− species in the crystallizing colloidal mixture with the decrease in pH is responsible for the nucleation. This was monitored by time-dependent DLS (dynamic light scattering) measurement and zeta-potential studies, revealing the co-existence of both the crystal and the colloidal forms at pH 3–2. This brings us to the conclusion that in the crystallization of POMs, the colloidal SOM phase precedes the crystalline POM phase which occurs via a phase transition. This work could open up avenues for the study of POM formation from the stand-point of colloidal chemistry and SOMs.

The hydrothermal Waterberg platinum deposit, Mookgophong (Naboomspruit), South Africa. Part 1: Geochemistry and ore mineralogy

ABSTRACTThe Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal quartz-hematite-PGE (platinum-group element) mineralization. This study concentrates on the geochemical character of the ores and the platinum-group mineral (PGM) assemblage by application of reflected-light and scanning electron microscopy followed by electron probe microanalysis.The PGM-bearing quartz veins show multiple banding indicating numerous pulses of fluid infiltration. Mineralization was introduced contemporaneously with the earliest generation of vein quartz and hematite. High oxygen and low sulfur fugacities of the mineralizing fluids are indicated by hematite as the predominant opaque mineral and the lack of sulfides.The ‘Waterberg type’ mineralization is characterized by unique metal proportions, namely Pt>Pd>Au, interpreted as a fingerprint to the cradle of the metals, namely rocks and ores of the Bushveld Complex, or reflecting metal fractionation during ascent of an oxidized, evolving fluid. The PGM assemblage signifies three main depositional and alteration events. (1) Deposition of native Pt and Pt–Pd alloys (>90% of the PGM assemblage) and Pd–Sb–As compounds (Pt-rich isomertieite and mertieite II) from hydrothermal fluids. (2) Hydrothermal alteration of Pt by Cu-rich fluids and formation of Pt–Cu alloys and hongshiite [PtCu]. (3) Weathering/oxidation of the ores producing Pd/Pt-oxides/hydroxides.Platinum-group element transport was probably by chloride complexes in moderately acidic and strongly oxidizing fluids of relatively low salinity, and depositional temperatures were in the range 400–200°C. Alternatively, quartz and ore textures may hint to noble metal transport in a colloidal form and deposition as gels.The source of the PGE is probably in platiniferous rocks or ores of the Bushveld Complex which were leached by hydrothermal solutions. If so, further Waterberg-type deposits may be present, and a prime target area would be along the corridor of the Thabazimbi-Murchison-Lineament where geothermal springs are presently still active.

Astromimetics

Composite, multifunctional fine particles are likely to be at the frontier of materials science in the foreseeable future. Here we present a submicron composite particle that mimics the stratified structure of the Earth by having a zero-valent iron core, a silicate/silicide mantle, and a thin carbonaceous crust resembling the biosphere and its biotic deposits. Particles were formulated in a stable colloidal form and made to interact with various types of healthy and cancer cells in vitro. A selective anticancer activity was observed, promising from the point of view of the intended use of the particles for tumor targeting across the blood–brain barrier. As an extension of the idea underlying the fabrication of a particle mimicking the planet Earth, we propose a new field of mimetics within materials science: astromimetics. The astromimetic approach in the context of materials science consists of the design of particles after the structure of celestial bodies. With Earth being the most chemically diverse and fertile out of all the astral bodies known, it is anticipated that the great majority of astromimetic material models will fall in the domain of geo-inspired ones.