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

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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.


Comparison of the arrangement of nanoparticles on flat alumina substrate.(a) Nanoparticles without peptide (PS-COOH). (b) Nanoparticles with peptide (PS-COO-(RF)4).
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f5: Comparison of the arrangement of nanoparticles on flat alumina substrate.(a) Nanoparticles without peptide (PS-COOH). (b) Nanoparticles with peptide (PS-COO-(RF)4).

Mentions: The nanoparticles are polystyrene (PS), which were pretreated with carboxyl (COOH) groups on the surfaces. So we could functionalize their surfaces with arginine/phenylalanine peptide ((RF)4). This is a positively charged peptide, consisting of alternating sequence of arginine (R) and phenylalanine (F) amino acids, which can be used to fabricate fibers and hydrogel matrices for potential biological applications2122. This peptide of (RF)4 has high affinity to react with carboxyl groups on the polystyrene nanoparticles (PS-COOH) to form strong crosslinking bonds (PS-COO-(RF)4) (Fig. 4a). The functionalized nanoparticles were characterized by Fourier transform infrared (FTIR) spectroscopy as seen in Fig. 4b. Several specific peaks at 633, 1236, and 3435 cm−1 reveal the presence of N-H wag, C-N stretch and N-H stretch functional groups on nanoparticles (PS-COO-(RF)4), respectively. Moreover, there are strong absorption bands at 1045 and 1706 cm−1, which indicate the formation of C-O, C=O, and C=N stretch. So this result shows that the carboxylated nanoparticles are functionalized with the peptide group (RF)4 successfully. In this study, influence of the peptide on the size of the nanoparticles can be negligible, but it has significant influence on the surface properties. Figure 5 shows the arrangement of nanoparticles, which have been dispensed on a flat alumina (Al2O3) substrate in the solution and then dried on the hot plate. The particles without the peptide of (RF)4 are arranged in good order, or self-assembled (Fig. 5a), but the particles with (RF)4 are placed randomly (Fig. 5b). This difference has been caused by the electric charge of the nanoparticles and that of the alumina surface. The nanoparticles with carboxyl group (COOH) are charged negatively and those with peptide ((RF)4) are charged positively, while the surface of alumina is charged positively. When the particles and the substrate have different charge, the particles are arranged as crystal growth, or self-assembled. But when the particles and the substrate have the same charge, the particles are repelled from the surface and maintain their mobility in aqueous solution15, which results in the random arrangement of the nanoparticles as seen in Fig. 5b. Since the working template in this study is aluminum oxide also, the nanoparticles with (RF)4 will have higher mobility than those without it while they are injected into the pores. This means that the nanoparticles with (RF)4 can move more freely with the injected flow, resulting in higher chances for them to be stacked, or embedded, more densely in the pores.


Nano sand filter with functionalized nanoparticles embedded in anodic aluminum oxide templates
Comparison of the arrangement of nanoparticles on flat alumina substrate.(a) Nanoparticles without peptide (PS-COOH). (b) Nanoparticles with peptide (PS-COO-(RF)4).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120303&req=5

f5: Comparison of the arrangement of nanoparticles on flat alumina substrate.(a) Nanoparticles without peptide (PS-COOH). (b) Nanoparticles with peptide (PS-COO-(RF)4).
Mentions: The nanoparticles are polystyrene (PS), which were pretreated with carboxyl (COOH) groups on the surfaces. So we could functionalize their surfaces with arginine/phenylalanine peptide ((RF)4). This is a positively charged peptide, consisting of alternating sequence of arginine (R) and phenylalanine (F) amino acids, which can be used to fabricate fibers and hydrogel matrices for potential biological applications2122. This peptide of (RF)4 has high affinity to react with carboxyl groups on the polystyrene nanoparticles (PS-COOH) to form strong crosslinking bonds (PS-COO-(RF)4) (Fig. 4a). The functionalized nanoparticles were characterized by Fourier transform infrared (FTIR) spectroscopy as seen in Fig. 4b. Several specific peaks at 633, 1236, and 3435 cm−1 reveal the presence of N-H wag, C-N stretch and N-H stretch functional groups on nanoparticles (PS-COO-(RF)4), respectively. Moreover, there are strong absorption bands at 1045 and 1706 cm−1, which indicate the formation of C-O, C=O, and C=N stretch. So this result shows that the carboxylated nanoparticles are functionalized with the peptide group (RF)4 successfully. In this study, influence of the peptide on the size of the nanoparticles can be negligible, but it has significant influence on the surface properties. Figure 5 shows the arrangement of nanoparticles, which have been dispensed on a flat alumina (Al2O3) substrate in the solution and then dried on the hot plate. The particles without the peptide of (RF)4 are arranged in good order, or self-assembled (Fig. 5a), but the particles with (RF)4 are placed randomly (Fig. 5b). This difference has been caused by the electric charge of the nanoparticles and that of the alumina surface. The nanoparticles with carboxyl group (COOH) are charged negatively and those with peptide ((RF)4) are charged positively, while the surface of alumina is charged positively. When the particles and the substrate have different charge, the particles are arranged as crystal growth, or self-assembled. But when the particles and the substrate have the same charge, the particles are repelled from the surface and maintain their mobility in aqueous solution15, which results in the random arrangement of the nanoparticles as seen in Fig. 5b. Since the working template in this study is aluminum oxide also, the nanoparticles with (RF)4 will have higher mobility than those without it while they are injected into the pores. This means that the nanoparticles with (RF)4 can move more freely with the injected flow, resulting in higher chances for them to be stacked, or embedded, more densely in the pores.

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.