Formation of moth-eye-like structures on silicon through in situ crystallization of layered Mg silicate

Coating subwavelength-scale pinnacles/thorns on surfaces usually results in antireflection, known as "moth-eye effect". However, fabrication of such coatings is often complicated and expensive. Herein, we present a bottom-up approach for forming a moth-eye-like structure on Si by directly growing layered Mg silicate using a one-step process. When an aqueous solution containing LiF, MgCl2, and urea is heated at 150 °C in the presence of Si, fine crystals of the layered silicate completely cover the Si surface. The resulting thorn-like structures reduce the reflectance of Si in the visible-wavelength range, exhibiting a graded-refractive index profile from air to the Si substrate. The antireflection feature is observed when the height of the thorns is 0.1 μm, which is equivalent to the crystal size of Mg silicate and is influenced by the heating temperature. The heating period is optimized to be 48 h to avoid coprecipitation of light-scattering fine particles, such as amorphous silica and Mg silicate, in excess quantities.

Fabrication and Mechanical Properties of High-Durability Polypropylene Composites via Reutilization of SiO2 In-Situ-Synthesized Waste Printed Circuit Board Powder

This paper focuses on the characterization of the physico-chemical properties, surface modification, residual copper content and in situ hybrid inorganic particle modification of polypropylene (PP) composites reinforced by waste printed circuit board powder (WPCBP). A series of WPCBP/SiO2 hybrids (TSW) were prepared by a sol–gel method at different pH values. Characterization results revealed the in situ generation of SiO2 on the surface of WPCBP, and showed that with an increase in pH value, the size of SiO2 particles increased gradually and the copper content decreased in the TSW powder. The mechanical properties, oxidation induction time (OIT) and thermal properties of PP composites were improved by reinforcement with TSW, which might be ascribed to the formation of serrated interfaces. This work not only develops a powerful method to enhance the properties of PP/WPCBP composites, but also provides an environmentally sustainable approach to the high-added-value reutilization of WPCBP.

Caffeine removal from aqueous media by adsorption: An overview of adsorbents evolution and the kinetic, equilibrium and thermodynamic studies

Caffeine is an emerging pollutant and is considered the most representative pollutant of the Pharmaceutical Active due to its high consumption by the general population. It can be used to track pollution caused by humans. Different technologies have been employed to remove the caffeine from aqueous media, however the adsorption has been preferred due to its simplicity, high removal efficiency, operational and implementation facility and low cost. This paper provides a systematic review of the published peer-reviewed literature concerned with caffeine removal by the adsorption process. The Scopus and ScienceDirect databases were used to identify relevant articles researches on caffeine removal. Many authors have studied caffeine's adsorption equilibrium in aqueous media, different conditions, and different adsorbents. This paper aims to uncover the overall trend of adsorbent used, kinetic and thermodynamic studies. The impact of pH, temperature, adsorbent dosage and competitive effect were presented and analyzed. It was observed that the adsorption capacities ranged between 10 and 1000 mg g^-1, according to the nature and properties of the adsorbent. The pseudo-second order (kinetic model) and the Langmuir isotherm model showed the best adjustment of the experimental data from caffeine adsorption in most studies. The mechanistic understanding of adsorption and the development of new adsorbents are still a matter of future research, as well as the use of other kinetic models based on statistical factors and the thermodynamic studies should be considered.

Hydrated Silicate Layer Formation on Mica-Type Crystals

This study aims to investigate the growth of a cation-exchangeable hydrated layer on the surface of mica-type silicates based on a synthetic fluorophlogopite and a natural muscovite. Through the reaction of a synthetic fluorophlogopite using LiF, MgCl₂, and a silica sol in water at 373 K for 48 h in the presence of urea, a hydrated phyllosilicate was formed on the fluoromica. As a result of examining the reaction in the alkali solution in the absence of Mg²⁺, the uptake of the silica sol would be included as a chemical process to begin the crystallization on fluorophlogopite because the lithium and ammonium ions (generated by urea hydrolysis) are known to contribute to enhanced adsorption. We found that the urea hydrolysis increased the pH, which, in turn, assisted the formation of magnesium hydroxide after the isomorphic substitution of Li⁺ for Mg²⁺. Bridging tetrahedral SiO₄ with a magnesium-lithium double hydroxide afforded a 1 nm silicate layer. This facilitated the hectorite-like hydrated silicate layer to adhere closely to both the crystal edge and the cleaved face of the synthetic mica, which was found to coat the surface homogeneously. Only surface crystals were found to form through this process. The layered silicates included exchangeable hydrated cations for the cation-exchange reactions to expand the interlayer space by a cationic surfactant, dimethyldistearylammonium. The layered silicate also adsorbed methylene blue as a cationic dye in the aqueous phase. Apart from fluoromica, the natural muscovite also provided the surface to grow hydrated silicate layers, as a crystal turned dense blue when reacted with methylene blue.