64
L. Ponomarova et al.
tion of Pb 2+ [20–22], Cu 2+ , Zn 2+ , Ni 2+ [22], and UO 2
2+ [23, 24] cations
and H 2 PO 4
− (HPO 4
2− ) [25], ReO 4
− [26], and H 2 AsO 4
− (HAsO 4
2− ) [27–29]
anions. As opposed to strongly acidic or strongly basic ion-exchange resins,
which are traditionally applied to sorption processes, such inorganic materials
as hydrophosphates [30–34] or hydrated oxides of multivalent metals [35–39]
demonstrate high selectivity toward toxic ions. Regarding organic-inorganic ion
exchangers based on the mentioned resins, small size of the embedded inorganic
particles causes rather high sorption rate [23, 40]. The inorganic ion exchangers
are also used for modification of macroporous ceramic membranes [41–43]. As a
result, inert separators are transformed into ion-exchange materials, which can be
used for electromembrane separation. Insertion of nanoparticles into polymer ionexchange membranes improves their charge selectivity and accelerates ion transport
particularly due to stability of the composites against fouling with organics [44,
45]. Moreover, the embedded particles prevent fouling of polymer materials during
baromembrane processes [46–48].
Strongly acidic polymers were mainly applied to preparation of organicinorganic ion-exchangers. In swollen state, ion-exchange polymers are characterized
by complex porous structure. This structure involves hydrophilic pores (nanosized
clusters and channels), where ions move [49–52]. These pores are formed from
heterogeneities of air-dry polymers [49, 53, 54]. The heterogeneities are caused by
fragments of polymer chains, which contain functional groups. During swelling,
these fragments form so-called gel regions penetrated by a continuous system of
hydrophilic clusters and channels (transport pores). Ion-exchange polymers contain
also hydrophobic pores (voids between gel regions, structure defects). Depending
on location, the embedded particles change size and volume of one or other pores
[23, 40, 55]. This affects functional properties of the composites.
Weakly acidic ion-exchange resins show better selectivity toward toxic ionic
components due to formation of complexes with functional groups [56, 57].
However, the composites based on these resins are practically unknown. The aim
of the research involves obtaining nanocomposite using weakly acidic resin as a
polymer matrix. Another purpose is to compare porous structure and functional
properties of the composites based on strongly and weakly acidic resins.
4.2 Synthesis and Characterization of Nanocomposites
Following cation exchange resins that are produced by Dow Chemical Company
were used for modification with nanoparticles of zirconium hydrophosphate (ZHP):
Dowex MAC-3 (weakly acidic macroporous resin) and Dowex HCR-S (strongly
acidic gel-like resin). The weakly acidic resin is polyacrylic polymer containing
−COOH groups, and the strongly acidic ion-exchanger is styrene-divinylbenzene
polymer with −SO 3 H groups.
The modification procedure was similar to [40, 55]; it involved impregnation of
a resin with 1 M ZrOCl 2 solution followed by treatment with 1 M H 3 PO 4 solution,
L. Ponomarova et al.
tion of Pb 2+ [20–22], Cu 2+ , Zn 2+ , Ni 2+ [22], and UO 2
2+ [23, 24] cations
and H 2 PO 4
− (HPO 4
2− ) [25], ReO 4
− [26], and H 2 AsO 4
− (HAsO 4
2− ) [27–29]
anions. As opposed to strongly acidic or strongly basic ion-exchange resins,
which are traditionally applied to sorption processes, such inorganic materials
as hydrophosphates [30–34] or hydrated oxides of multivalent metals [35–39]
demonstrate high selectivity toward toxic ions. Regarding organic-inorganic ion
exchangers based on the mentioned resins, small size of the embedded inorganic
particles causes rather high sorption rate [23, 40]. The inorganic ion exchangers
are also used for modification of macroporous ceramic membranes [41–43]. As a
result, inert separators are transformed into ion-exchange materials, which can be
used for electromembrane separation. Insertion of nanoparticles into polymer ionexchange membranes improves their charge selectivity and accelerates ion transport
particularly due to stability of the composites against fouling with organics [44,
45]. Moreover, the embedded particles prevent fouling of polymer materials during
baromembrane processes [46–48].
Strongly acidic polymers were mainly applied to preparation of organicinorganic ion-exchangers. In swollen state, ion-exchange polymers are characterized
by complex porous structure. This structure involves hydrophilic pores (nanosized
clusters and channels), where ions move [49–52]. These pores are formed from
heterogeneities of air-dry polymers [49, 53, 54]. The heterogeneities are caused by
fragments of polymer chains, which contain functional groups. During swelling,
these fragments form so-called gel regions penetrated by a continuous system of
hydrophilic clusters and channels (transport pores). Ion-exchange polymers contain
also hydrophobic pores (voids between gel regions, structure defects). Depending
on location, the embedded particles change size and volume of one or other pores
[23, 40, 55]. This affects functional properties of the composites.
Weakly acidic ion-exchange resins show better selectivity toward toxic ionic
components due to formation of complexes with functional groups [56, 57].
However, the composites based on these resins are practically unknown. The aim
of the research involves obtaining nanocomposite using weakly acidic resin as a
polymer matrix. Another purpose is to compare porous structure and functional
properties of the composites based on strongly and weakly acidic resins.
4.2 Synthesis and Characterization of Nanocomposites
Following cation exchange resins that are produced by Dow Chemical Company
were used for modification with nanoparticles of zirconium hydrophosphate (ZHP):
Dowex MAC-3 (weakly acidic macroporous resin) and Dowex HCR-S (strongly
acidic gel-like resin). The weakly acidic resin is polyacrylic polymer containing
−COOH groups, and the strongly acidic ion-exchanger is styrene-divinylbenzene
polymer with −SO 3 H groups.
The modification procedure was similar to [40, 55]; it involved impregnation of
a resin with 1 M ZrOCl 2 solution followed by treatment with 1 M H 3 PO 4 solution,