This study was conducted to investigate the potential of using sodium silicate with nanosilica as a treatment to inhibit the progress of corrosion in steel specimens that are already corroded. Steel specimens measuring 16 mm in diameter and 4 mm in thickness were prepared and subjected to pre-corrosion by immersion to 3.5% NaCl solution. Two sets of specimens were then dip-coated with sodium silicate containing nanosilica. One set was coated with 1% nanosilica, and the other was coated with 2.5% nanosilica. The coated specimens were then subjected to Complex Impedance Spectroscopy (CIS) at 20 Hz to 20 MHz frequency range. Compared with the sodium silicate coating with 1% nanosilica, the sodium silicate coating with 2.5% nanosilica had a larger semi-circle curve in the Nyquist plot. Similarly, the sodium silicate coating with 2.5% nanosilica also showed larger magnitudes of impedance at the low-frequency region and larger phase angles at the high-frequency regions in the Bode plot. These results imply that the sodium silicate coating with 2.5% nanosilica coating demonstrated better capacitive behavior. In addition, equivalent circuit modelling results also showed that the sodium silicate coating with 2.5% nanosilica had higher coating resistance and lower coating capacitance as compared to the sodium silicate coating with 1% nanosilica. Doi: 10.28991/cej-2021-03091761 Full Text: PDF
The electrical conductivity of simulated cement paste matrixes with water-to-cement ratios of 0·50 and 2·0% amorphous nanosilica, synthesized from rice hull ash, has been related to the effect of hydration stages on the ions dissociated in the capillary pore solution of the cement paste mesostructure. The increase in ions, as the hydration proceeded, has also been implied by the increasing trend of the conductivity spectra obtained from the complex impedance spectroscopy in the frequency region from 100 kHz to 20 MHz. In the 105–107 Hz spectra, the conductivity was also found to exhibit a power-law behavior. To consider the effect of capillary pores, a comparable set of cement pastes with a similar macrostructure has been established using a modified method of simple grinding and pelletizing with a similar techniques. From the results of the Kramers–Kronig validation test, the impedance data have been found to exhibit a causal, linear and stable behavior in the high-frequency region from 6 to 20 MHz.
Phycocyanin (PC), the major phycobiliprotein found in the cyanobacterium Spirulina platensis, was explored as a biosorbent for cadmium removal in contaminated water. It was isolated from commercially available Spirulina tablets using 0.1 M phosphate buffer with 0.15 M NaCl (pH 7) and was purified using two-stage ammonium sulfate precipitation followed by gel filtration chromatography using Sephadex G-75. The water-soluble pigment protein thus obtained could not be directly used as a biosorbent and was subsequently immobilized on rice hull nanosilica using 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde as linkers resulting in a blue-green powder composite material (SAGPC). Optimum immobilization of PC on rice hull nanosilica was achieved by using 5% v/v APTES, 1.5% v/v glutaraldehyde, and 6 mg/mL PC solution. The immobilized PC was then prepared in the form of calcium-alginate beads (SAGPCAlg beads) to allow easy separation from effluents. The Cd adsorption efficiency (99.80 ± 0.20 %) and adsorption capacity (19.72 ± 0.38 mg/g) of SAGPC-Alg beads were determined through batch sorption experiments at room temperature using the optimum working conditions at pH 7, 0.1 g wet beads, 0.5 ppm initial Cd concentration, and 60-min shaking time.
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