Factors Affecting the Reductive Properties of the Core-Shell SiO2-Coated Iron Nanoparticles

Abstract

In this study, novel core-shell SiO 2 -coated iron nanoparticles (SiO 2 -nZVI) were synthesized using a one-step Stöber method. The Malachite green degradation abilities of the nanoparticles were investigated. The effects of ethanol/distilled water volume ratio, presence and absence of PEG, tetraethyl orthosilicate (TEOS) dosage, and hydrolysis time used in the nanoparticles preparation process were investigated. The results indicated that the SiO 2 -coated iron nanoparticles had the highest reduction activity when the particles synthesized with ethanol/H 2 O ratio of 2:1, PEG of 0.15 ml, TEOS of 0.5 ml and the reaction time was 4 h. The SiO 2 -nZVI nanoparticles were characterized using Transmission Electron Microscopy (TEM), Energy Dispersive Spectrometry (EDS) and powder X-Ray Diffraction (XRD). The results showed that the average particles diameter of the SiO 2 -nZVI was 20 -30 nm. The thickness of the outside SiO 2 film is consistent and approximately 10 nm. The results indicated that the nanoparticles coated completely with a transparent SiO 2 -film. Such nanoparticles could have wide applications in dye decolorization.

Synthesis of Silica-supported Nanoiron for Cr(VI) Removal: Application of Box-Behnken Statistical Design (BBD)

“…The XRD patterns of fresh and spent NZVI and NZVI/ SiO 2 are presented in Figure 4. The peaks at 2θ of 44.55° and 64.85° confirmed the existing of Fe 0 and the successful synthesis of NZVI and NZVI/SiO 2 (Wang et al 2009;Wu et al 2016). After 60 min of Cr(VI) removal, the peaks of the spent NZVI and NZVI/SiO 2 demonstrated the NZVI corrosion products including magnetite (Fe 3 O 4 ), maghemite (Fe 2 O 3 ) and lepidocrocite (FeOOH) (Shih et al 2015;Zhou et al 2015).…”

“…The addition of SiO 2 to the NZVI resulted in an increased dispersion of the NZVI particles which in turn provided a higher contact area between NZVI and Cr(VI). In addition, the EDX profiles showed that the major elemental components were O, Cl, Fe and Si for the NZVI/SiO 2 sample (Wu et al 2016) except Cl originated from the FeCl 3 •6H 2 O as a precursor of the NZVI synthesis. The BET results showed that the specific surface areas of the NZVI and NZVI/SiO 2 were 12.35 and 8.89 m 2 /g, respectively, while that of SiO 2 was 240.12 m 2 /g.…”

“…Because ethanol provides lower polarity than water, it can be used to stabilize the NZVI, which is neutral, during the synthesis. However, aggregation of the NZVI is rarely formed in the lower polar solvent (Wang et al 2009;Wu et al 2016) leading to the improvement of Cr(VI) removal efficiency by NZVI/SiO 2 synthesized in the ethanol/water solvent. On the other hand, while silica is capable of directly absorbing the precipitate of Cr(III), it also releases a proton from the silanol group (Oh et al 2007) that can increase the solubility of the precipitated Cr(III).…”

“…It was found that the higher reducing power of NZVI was obtained at the higher agitation speed because of more dispersion and higher surface area of NZVI particles. Concentration of ethanol in the ethanol/water solvent was the one of parameter concerned with NZVI synthesis (Wu et al 2016). Absolute ethanol concentration of 0-100 vol% showed the differences of NZVI characteristics (Wang et al 2009).…”