Sulfonated Pentablock Copolymer (NexarTM) for Water Remediation and Other Applications

Abstract

This review focuses on the use of a sulfonated pentablock copolymer commercialized as Nexar^TM in water purification applications. The properties and the use of sulfonated copolymers, in general, and of Nexar^TM, in particular, are described within a brief reference focusing on the problem of different water contaminants, purification technologies, and the use of nanomaterials and nanocomposites for water treatment. In addition to desalination and pervaporation processes, adsorption and photocatalytic processes are also considered here. The reported results confirm the possibility of using Nexar^TM as a matrix for embedded nanoparticles, exploiting their performance in adsorption and photocatalytic processes and preventing their dispersion in the environment. Furthermore, the reported antimicrobial and antibiofouling properties of Nexar^TM make it a promising material for achieving active coatings that are able to enhance commercial filter lifetime and performance. The coated filters show selective and efficient removal of cationic contaminants in filtration processes, which is not observed with a bare commercial filter. The UV surface treatment and/or the addition of nanostructures such as graphene oxide (GO) flakes confer Nexar^TM with coating additional functionalities and activity. Finally, other application fields of this polymer are reported, i.e., energy and/or gas separation, suggesting its possible use as an efficient and economical alternative to the more well-known Nafion polymer.

Keywords: NexarTM; adsorption; antibiofouling; coating; energy; filtration; photocatalysis; sulfonated copolymer; water.

Figure 1

Scheme of water treatment methodologies.

Figure 2

Scheme of advantages and disadvantages of using polymers in water treatment.

Figure 3

Scheme of selective sulfonation of a block copolymer.

Figure 4

Scheme of the possible use of sulfonated block copolymers.

Figure 5

Nexar^TM structure as reported in [93].

Figure 6

Scheme of all the processes (adsorption, filtration, and photocatalysis) involved in water contaminant removal by Nexar nanocomposites.

Figure 7

Cross SEM images and photos (insets) of a s-PBC membrane (a) and sPBC-GO composite membrane (b), respectively. In (c), the amount of adsorbed ions (mg) per gram of sPBC or sPBC-GO membrane, respectively, is reported. Images are reported from [108].

Figure 8

Photos (on the left) of membranes before and after the MO and MB adsorption experiments and the residual amount (%) of dyes after membrane adsorption (on the right). The adsorption experiment of MO was conducted at both neutral and acidic pH values. Blue, orange and pink bars refer, respectively, to the MB, MO at pH = 6 and MO at pH = 2 solutions before being in contact with the membranes. Reproduced from [29] with permission from the Royal Society of Chemistry.

Figure 9

Scheme of photodegradation of water contaminants by Nexar nanocomposites under light irradiation. A scheme of the photocatalytic process is shown in the box.

Figure 10

Percentages of MO removal by different s-PBC nanocomposite films under UV or visible light irradiation (on the top). Images of membranes after adsorption or photocatalytic processes (on the bottom). Experiments were conducted at pH = 2. Partially reproduced from [29] with permission from the Royal Society of Chemistry and from [31] with permission from Elsevier.

Figure 11

Consecutive cycles of adsorption and/or photocatalytic processes for MO (a,c) and MB (b) removal by different polymeric nanocomposites after their regeneration. Partially reproduced from [29] with permission from the Royal Society of Chemistry and from [31] with permission from Elsevier.

Figure 12

Scheme of the Nafion^® and Nexar^TM polymer, respectively. Reproduced from [93].

Figure 13

Modified Zone of Inhibition Test of P. aeruginosa after 24 h incubation with coated (A) and uncoated (B) filters in the presence of water. Partially reproduced from [32].

Figure 14

Photos and SEM images (a,b) of polypropylene (PP) (on the left) and sulfonated pentablock copolymer (s-PBC)@PP (on the right) coupons. Fluorescence optical microscopy images of reference PP and s-PBC@PP coupons before (c,d, respectively) and after (e,f, respectively) 20 days of incubation with Pseudomonas aeruginosa in water. Partially reproduced from [32].

Figure 15

The modified Zone of Inhibition test (on the left) and biofilm formation tests (on the right) using coated and uncoated polypropylene (PP) coupons (named A and B, respectively) against Legionella pneumophila SG 2–16. A reference was used for biofilm formation tests. Partially reproduced from [33].

Figure 16

Schematic representation of P. aeruginosa death induced by s-PBC@PP and water: (A) acid s-PBC@PP in a small volume system; (B) neutralized s-PBC@PP in a small volume system; (C) acid s-PBC@PP in a large volume system. Physiological (blue), damaged (red), and dead (gray) bacteria are indicated with different colors. Partially reproduced from [32].

Figure 17

(a) Photos of PP and s-PBC coatedPP filters before the filtration of MB, MO, and mixed (Green) solutions, as well as (b) coated filters after filtration of MB and MO dye solutions. For each dye, the scheme of the dye and the images of initial and filtered solutions are reported. (c) UV-Visible spectra of dye solutions before and after filtration through a coated filter.

Figure 18

Scheme of the selective adsorption of positively charged molecules (MB) with respect to negative ones (MO) by Nexar coated PP filters during an adsorption/filtration test of mixed dyes solution (Green).

Figure 19

Q_t values of Fe³⁺ ions versus adsorption time for uncoated and coated filters immersed in FeCl₃ solutions. The composite layer was investigated considering three different amounts of dispersed GO flakes.

Figure 20

Images of commercial (PP) and coated filters untreated (s-PBC@PP) or UV-treated (s-PBC@PP_UV) after the removal of MB molecules by adsorption (a). UV-Visible spectra of cobalt solution where UV-treated and untreated filters coated with s-PBC/sPBCGO were immersed to remove Co ions (b). Reproduced [139,140].