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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

PXRD patterns and TEM images of raw SiO2 and Al/Si, Fe/Si coprecipitates synthesized at pH 5.0 and pH 8.0 (Al/Si-5.0, -8.0, Fe/Si-5.0 and -8.0). The white bars represent 20-nm scales and the white arrows pointed out the plausible Fe precipitates.
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f2: PXRD patterns and TEM images of raw SiO2 and Al/Si, Fe/Si coprecipitates synthesized at pH 5.0 and pH 8.0 (Al/Si-5.0, -8.0, Fe/Si-5.0 and -8.0). The white bars represent 20-nm scales and the white arrows pointed out the plausible Fe precipitates.

Mentions: The BET surface area (SBET) for Fe hydroxides (283 and 284 m2 g−1 for Fe-5.0 and Fe-8.0) are greater than that of Al hydroxides (54 and 158 m2 g−1 for Al-5.0 and Al-8.0), wherein the Al-5.0 sample showed the lowest SBET (Table S1). While coprecipitated with silica, the SBET for the Al/Si samples were increased substantially. Especially for the Al/Si-5.0 sample, its SBET (155 m2 g−1) was almost three times greater than that of pure Al hydroxides. In Fe systems, however, the SBET was slightly decreased while coprecipitated with SiO2. Figure 2(a) showed the PXRD patterns for Al/Si and Fe/Si samples, which indicated that all samples were non- or poorly crystalline. For Al/Si and SiO2 samples, the broad peak centered at 4.1 Å (2θ = 23°) demonstrated the presence of SiO2 structures2324. However, no discernable peak was found in Fe/Si samples. While no discrete phase was found in Al/Si samples (Fig. 2cd), there were significant precipitates (dark spots in Fig. 2e,f) in Fe/Si samples. The single phase in Al/Si sample implied a strong association between Al and SiO2 surfaces. On the other hand, Fe precipitates and SiO2 might form separate phases in Fe/Si systems.


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)

PXRD patterns and TEM images of raw SiO2 and Al/Si, Fe/Si coprecipitates synthesized at pH 5.0 and pH 8.0 (Al/Si-5.0, -8.0, Fe/Si-5.0 and -8.0). The white bars represent 20-nm scales and the white arrows pointed out the plausible Fe precipitates.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: PXRD patterns and TEM images of raw SiO2 and Al/Si, Fe/Si coprecipitates synthesized at pH 5.0 and pH 8.0 (Al/Si-5.0, -8.0, Fe/Si-5.0 and -8.0). The white bars represent 20-nm scales and the white arrows pointed out the plausible Fe precipitates.
Mentions: The BET surface area (SBET) for Fe hydroxides (283 and 284 m2 g−1 for Fe-5.0 and Fe-8.0) are greater than that of Al hydroxides (54 and 158 m2 g−1 for Al-5.0 and Al-8.0), wherein the Al-5.0 sample showed the lowest SBET (Table S1). While coprecipitated with silica, the SBET for the Al/Si samples were increased substantially. Especially for the Al/Si-5.0 sample, its SBET (155 m2 g−1) was almost three times greater than that of pure Al hydroxides. In Fe systems, however, the SBET was slightly decreased while coprecipitated with SiO2. Figure 2(a) showed the PXRD patterns for Al/Si and Fe/Si samples, which indicated that all samples were non- or poorly crystalline. For Al/Si and SiO2 samples, the broad peak centered at 4.1 Å (2θ = 23°) demonstrated the presence of SiO2 structures2324. However, no discernable peak was found in Fe/Si samples. While no discrete phase was found in Al/Si samples (Fig. 2cd), there were significant precipitates (dark spots in Fig. 2e,f) in Fe/Si samples. The single phase in Al/Si sample implied a strong association between Al and SiO2 surfaces. On the other hand, Fe precipitates and SiO2 might form separate phases in Fe/Si systems.

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