Limits...
Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

No MeSH data available.


Related in: MedlinePlus

(a) 27Al, (b) 29Si MAS NMR spectra for Al/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Al/Si-5.0, -6.5, and -8.0), and (c) 29Si MAS NMR spectra for the Fe/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Fe/Si-5.0, -6.5, and -8.0) under an electrolyte concentration of 0.01 M NaNO3, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4837376&req=5

f5: (a) 27Al, (b) 29Si MAS NMR spectra for Al/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Al/Si-5.0, -6.5, and -8.0), and (c) 29Si MAS NMR spectra for the Fe/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Fe/Si-5.0, -6.5, and -8.0) under an electrolyte concentration of 0.01 M NaNO3, respectively.

Mentions: Solid-state 27Al and 29Si MAS NMR spectra for the Al/Si and Fe/Si coprecipitates were shown in Fig. 5. The 27Al NMR spectra for the Al/Si coprecipitates synthesized at various pH (Fig. 5a) showed a discernible crest at 58 ppm and a significant peak around 5 ppm. The feature at around 58 and 5 ppm suggested tetrahedral (AlO4) and octahedral (AlO6) Al coordination environments, respectively4041. Regarding the peak at 58 ppm, the decreasing intensity with increasing pH indicated a fewer amount of AlO4 at alkaline condition, agreed with what Houston et al. reported17, wherein the amount of AlO4 tended to decrease and transform to the precipitated AlO6 on the surface of silica as pH increased. Such result was in line with the shift of the 5 ppm peak to the higher magnetic field with increasing pH, which suggested more bonding was formed between Al and Si at higher pH42.


Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

(a) 27Al, (b) 29Si MAS NMR spectra for Al/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Al/Si-5.0, -6.5, and -8.0), and (c) 29Si MAS NMR spectra for the Fe/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Fe/Si-5.0, -6.5, and -8.0) under an electrolyte concentration of 0.01 M NaNO3, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837376&req=5

f5: (a) 27Al, (b) 29Si MAS NMR spectra for Al/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Al/Si-5.0, -6.5, and -8.0), and (c) 29Si MAS NMR spectra for the Fe/Si coprecipitates synthesized at pH 5.0, 6.5, and 8.0 (Fe/Si-5.0, -6.5, and -8.0) under an electrolyte concentration of 0.01 M NaNO3, respectively.
Mentions: Solid-state 27Al and 29Si MAS NMR spectra for the Al/Si and Fe/Si coprecipitates were shown in Fig. 5. The 27Al NMR spectra for the Al/Si coprecipitates synthesized at various pH (Fig. 5a) showed a discernible crest at 58 ppm and a significant peak around 5 ppm. The feature at around 58 and 5 ppm suggested tetrahedral (AlO4) and octahedral (AlO6) Al coordination environments, respectively4041. Regarding the peak at 58 ppm, the decreasing intensity with increasing pH indicated a fewer amount of AlO4 at alkaline condition, agreed with what Houston et al. reported17, wherein the amount of AlO4 tended to decrease and transform to the precipitated AlO6 on the surface of silica as pH increased. Such result was in line with the shift of the 5 ppm peak to the higher magnetic field with increasing pH, which suggested more bonding was formed between Al and Si at higher pH42.

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

No MeSH data available.


Related in: MedlinePlus