Efficient Adsorption of Chromium Ions from Aqueous Solutions by Plant-Derived Silica.

Nowadays, there is great interest in the use of plant waste to obtain materials for environmental protection. In this study, silica powders were prepared with a simple and low-cost procedure from biomass materials such as horsetail and common reed, as well as wheat and rye straws. The starting biomass materials were leached in a boiling HCl solution. After washing and drying, the samples were incinerated at 700 °C for 1 h in air. The organic components of the samples were burned leaving final white powders. These powders were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and low-temperature nitrogen sorption. The amorphous powders (biosilica) contained mainly SiO2, as indicated by FTIR analysis. Horsetail-derived silica was chosen for testing the removal of dichromate ions from water solutions. This biosilica had a good ability to adsorb Cr(VI) ions, which increased after modification of the powder with the dodecylamine surfactant. It can be concluded that the applied procedure allowed obtaining high purity biosilica from plant waste with good efficiency. The produced biosilica was helpful in removing chromium ions and showed low cytotoxicity to human endothelial cells, suggesting that it can be safely used in environmental remediation.

Amorphous Silicon Oxynitride-Based Powders Produced by Spray Pyrolysis from Liquid Organosilicon Compounds.

Silicon oxynitrides (SiOxNy) have many advantageous properties for modern ceramic applications that justify a development of their new and efficient preparation methods. In the paper, we show the possibility of preparing amorphous SiOxNy-based materials from selected liquid organosilicon compounds, methyltrimethoxysilane CH3Si(OCH3)3 and methyltriethoxysilane CH3Si(OC2H5)3, by a convenient spray pyrolysis method. The precursor mist is transported with an inert gas or a mixture of reactive gases through a preheated tube reactor to undergo complex decomposition changes, and the resulting powders are collected in the exhaust filter. The powders are produced at the tube at temperatures of 1200, 1400, and 1600 °C under various gas atmosphere conditions. In the first option, argon Ar gas is used for mist transportation and ammonia NH3 gas serves as a reactive medium, while in the second option nitrogen N2 is exclusively applied. Powder X-Ray Diffraction (XRD) results confirm the highly amorphous nature of all products except those made at 1600 °C in nitrogen. SEM examination shows the spheroidal particle morphology of powders, which is typical for this method. Fourier Transform Infrared (FT-IR) spectroscopy reveals the presence of Si-N and Si-O bonds in the powders prepared under Ar/NH3, whereas those produced under N2 additionally contain Si-C bonds. Raman spectroscopy measurements also support some turbostratic free carbon C in the products prepared under nitrogen. The directly determined O- and N-contents provide additional data linking the process conditions with specific powder composition, especially from the point of view of oxygen replacement in the Si-O moieties formed upon initial precursor decomposition reactions by nitrogen (from NH3 or N2) or carbon (from the carbonization of the organic groups).

Particle morphology of various SiC-based nanocomposite powders made by the aerosol-assisted synthesis method.

Herein, we present a part of a study on the preparation of SiC-based composite nanopowders by the two-stage Aerosol-Assisted Vapor Phase Synthesis (AAVS) method from organosilicon precursors (neat hexamethyldisiloxane, neat tetramethoxysilane, ethanol solutions of polydimethylsiloxane). Upon generation, liquid aerosol droplets were transported in a stream of argon through a ceramic reactor tube maintained at 1200 degrees C. The resulting solid by-products were collected on a nylon filter as bulk powders. Each raw powder was, subsequently, pyrolyzed in a furnace reactor heated to 1650 degrees C under a flow of argon. After the final pyrolysis at 1650 degrees C, mostly nanocrystalline silicon carbide powder with small quantities of free excess carbon was obtained from the neat hexamethyldisiloxane system, composite powder of not fully converted silica and SiC was prepared from the neat tetramethoxysilane system, and C-rich/SiC composite was made from the ethanol/polydimethylsiloxane solution system. The prevailing phase of the SiC component was the regular beta-SiC polytype. Most of the powders were composed of spheroidal particles--morphology imprinted during aerosol generation at 1200 degrees C and not much affected by the second-stage bulk pyrolysis at 1650 degrees C. The specifics of spheroidal morphology were characteristic of the applied precursor system.