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Nano sand filter with functionalized nanoparticles embedded in anodic aluminum oxide templates

View Article: PubMed Central - PubMed

ABSTRACT

Since the ancient Egyptians had used sand as filter media for water purification, its principle has been inherited through generations and it is still being used now in industries. The sand filter consists of sand literally, and the voids within the sand bed are the pores for filtration. Here we present a filtration principle using nanoparticles, so that the voids between the nanoparticles can be considered as effective pores in nanoscale dimension. Anodic aluminum oxide (AAO) membrane has been used as the working template, and the nanoparticles have been injected and embedded within the pores of the AAO template. Nanoparticles with multiple sizes have been used in order to obtain smaller voids. Moreover, the nanoparticles have been functionalized, or electrically charged, with arginine/phenylalanine (RF) peptide group. In this way, filtration performance for charged particles or molecules, such as methylene blue, has been enhanced. Consequently, this study is expected to provide a new principle for fabrication of nano voids, or nano pores, and for filtration in nanoscale dimension.

No MeSH data available.


Pictures of the AAO templates after the methylene blue filtration test.(a–d) AAO templates with nanoparticles with peptide (PS-COO-(RF)4). (e–h) AAO templates with nanoparticles without peptide (PS-COOH). The particles of 150, 60 and 24 nm are embedded together for all templates. The flow flux through membrane has been increased from left to right.
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f9: Pictures of the AAO templates after the methylene blue filtration test.(a–d) AAO templates with nanoparticles with peptide (PS-COO-(RF)4). (e–h) AAO templates with nanoparticles without peptide (PS-COOH). The particles of 150, 60 and 24 nm are embedded together for all templates. The flow flux through membrane has been increased from left to right.

Mentions: Methylene blue is a common dye for biological stain, which is soluble in water and measurable with spectroscopic method2324. In this study, this dye was used as an indicator for filtration characteristics because it is charged positively in aqueous solution. And the nanoparticles in this study may have negative charge with carboxyl group, or positive charge with peptide ((RF)4). So filtration characteristics have been investigated with the nanoparticle-embedded templates using this dye solution. The nanoparticle-embedded AAO templates were prepared by using the particles of 150, 60 and 24 nm in diameter and they were made into two groups according to the surface functionalization with (RF)4 on the particles. The dye solution of 10 mg/L was pressurized in a stirred cell. And the concentration of the solution was measured with ultraviolet (UV)-visible spectroscopy as seen in Supplementary Fig. 3. Firstly, the rejection rates were measured using different combination of nanoparticles as seen in Fig. 7. The rejection rates are quite poor unless the smallest particles (24 nm) were embedded. In other words, the rejection is increased much when all of the particles are embedded together. Furthermore, it is also noticeable that the highest rejections from each group are quite different, which are 94.6% for the particles with peptide and 57.6% for those without it. This result means that the charge of the nanoparticles is effective on filtration performance, as long as the size of voids is comparable to that of the filtration target. Then, further tests were performed only using the templates which have all of the particles (150, 60 and 24 nm) inside. The rejection rate has been obtained for various mass fluxes as seen in Fig. 8. As the flux increases, the rejection decreases slightly for all cases. However, it is evident that the rejection is much higher when the nanoparticles with peptide ((RF)4) were used. As discussed in the above paragraph, the templates with peptide-treated particles have produced higher pressure drop, which means that the nanoparticles with peptide are embedded more closely, resulting in smaller voids. So this difference of rejection is partially caused by the embedment, or stacking, of the nanoparticles. However, the rejection is also influenced much by the electric charge of the particles and dye molecules. Since the dye and peptide ((RF)4) have the same charge, higher rejection (between 94.8% and 87.9% in Fig. 8a~8d) has been obtained as seen in the result. Meanwhile, the templates without peptide, which have carboxyl group on the nanoparticles instead, have opposite charge to the dye molecules, so the rejection is low and it degrades as the flux increases (between 60.0% and 36.6% in Fig. 8e~8h). These dye tests (Figs 7 and 8) suggest that the void size is critical to the filtration characteristics. So the particle size and its combination need to be selected considering the target. Moreover, it has been also investigated that matching of charges between the target and the nanoparticles can enhance the filtration greatly. For more investigation on the charge-matching issue, the templates have been inspected after the tests as seen in Fig. 9. It shows the templates, which have been disassembled from the stirred cell after experiments and then dried out. Color of the residue is much darker on the templates without the peptide (Fig. 9e~9h), while it is lighter on those with the peptide (Fig. 9a~9d). So these pictures explain that the templates without peptide have produced poor rejection rate because of the negative charge of the nanoparticles and its consequent adsorption of dye onto the nanoparticles.


Nano sand filter with functionalized nanoparticles embedded in anodic aluminum oxide templates
Pictures of the AAO templates after the methylene blue filtration test.(a–d) AAO templates with nanoparticles with peptide (PS-COO-(RF)4). (e–h) AAO templates with nanoparticles without peptide (PS-COOH). The particles of 150, 60 and 24 nm are embedded together for all templates. The flow flux through membrane has been increased from left to right.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC5120303&req=5

f9: Pictures of the AAO templates after the methylene blue filtration test.(a–d) AAO templates with nanoparticles with peptide (PS-COO-(RF)4). (e–h) AAO templates with nanoparticles without peptide (PS-COOH). The particles of 150, 60 and 24 nm are embedded together for all templates. The flow flux through membrane has been increased from left to right.
Mentions: Methylene blue is a common dye for biological stain, which is soluble in water and measurable with spectroscopic method2324. In this study, this dye was used as an indicator for filtration characteristics because it is charged positively in aqueous solution. And the nanoparticles in this study may have negative charge with carboxyl group, or positive charge with peptide ((RF)4). So filtration characteristics have been investigated with the nanoparticle-embedded templates using this dye solution. The nanoparticle-embedded AAO templates were prepared by using the particles of 150, 60 and 24 nm in diameter and they were made into two groups according to the surface functionalization with (RF)4 on the particles. The dye solution of 10 mg/L was pressurized in a stirred cell. And the concentration of the solution was measured with ultraviolet (UV)-visible spectroscopy as seen in Supplementary Fig. 3. Firstly, the rejection rates were measured using different combination of nanoparticles as seen in Fig. 7. The rejection rates are quite poor unless the smallest particles (24 nm) were embedded. In other words, the rejection is increased much when all of the particles are embedded together. Furthermore, it is also noticeable that the highest rejections from each group are quite different, which are 94.6% for the particles with peptide and 57.6% for those without it. This result means that the charge of the nanoparticles is effective on filtration performance, as long as the size of voids is comparable to that of the filtration target. Then, further tests were performed only using the templates which have all of the particles (150, 60 and 24 nm) inside. The rejection rate has been obtained for various mass fluxes as seen in Fig. 8. As the flux increases, the rejection decreases slightly for all cases. However, it is evident that the rejection is much higher when the nanoparticles with peptide ((RF)4) were used. As discussed in the above paragraph, the templates with peptide-treated particles have produced higher pressure drop, which means that the nanoparticles with peptide are embedded more closely, resulting in smaller voids. So this difference of rejection is partially caused by the embedment, or stacking, of the nanoparticles. However, the rejection is also influenced much by the electric charge of the particles and dye molecules. Since the dye and peptide ((RF)4) have the same charge, higher rejection (between 94.8% and 87.9% in Fig. 8a~8d) has been obtained as seen in the result. Meanwhile, the templates without peptide, which have carboxyl group on the nanoparticles instead, have opposite charge to the dye molecules, so the rejection is low and it degrades as the flux increases (between 60.0% and 36.6% in Fig. 8e~8h). These dye tests (Figs 7 and 8) suggest that the void size is critical to the filtration characteristics. So the particle size and its combination need to be selected considering the target. Moreover, it has been also investigated that matching of charges between the target and the nanoparticles can enhance the filtration greatly. For more investigation on the charge-matching issue, the templates have been inspected after the tests as seen in Fig. 9. It shows the templates, which have been disassembled from the stirred cell after experiments and then dried out. Color of the residue is much darker on the templates without the peptide (Fig. 9e~9h), while it is lighter on those with the peptide (Fig. 9a~9d). So these pictures explain that the templates without peptide have produced poor rejection rate because of the negative charge of the nanoparticles and its consequent adsorption of dye onto the nanoparticles.

View Article: PubMed Central - PubMed

ABSTRACT

Since the ancient Egyptians had used sand as filter media for water purification, its principle has been inherited through generations and it is still being used now in industries. The sand filter consists of sand literally, and the voids within the sand bed are the pores for filtration. Here we present a filtration principle using nanoparticles, so that the voids between the nanoparticles can be considered as effective pores in nanoscale dimension. Anodic aluminum oxide (AAO) membrane has been used as the working template, and the nanoparticles have been injected and embedded within the pores of the AAO template. Nanoparticles with multiple sizes have been used in order to obtain smaller voids. Moreover, the nanoparticles have been functionalized, or electrically charged, with arginine/phenylalanine (RF) peptide group. In this way, filtration performance for charged particles or molecules, such as methylene blue, has been enhanced. Consequently, this study is expected to provide a new principle for fabrication of nano voids, or nano pores, and for filtration in nanoscale dimension.

No MeSH data available.