Polymeric Materials for Clean Water

Polymer can be defined as a macromolecule, and due to its broad range of properties, they could play an essential role in everyday life. This chapter defines some terms of polymer and its chemistry for chain formation, mechanism of polymerization, methods for polymer characterization, etc. It also highlights the summary of each chapter of this book, i.e., the uses of both natural and synthetic polymers for water purification.

This chapter is devoted to the observation of general methods of polymer synthesis including radical, ionic, coordination, and metathesis polymerization. The main advantages, possibilities, and drawbacks of each method are discussed. A special emphasis was placed to the modern methods of controlled polymer synthesis leading to well-defined polymers with desired structure, composition and properties. Such methods are considered as a way to the novel polymer materials for various high-tech applications.

This chapter discussed the characterization and properties of polymeric materials. Prominent characterization techniques used for analyzing polymeric materials are mass spectrometry (MS), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC), which are used for measuring mass-to-charge ratio (m/z) of analyte ions. Other methods used for this purpose include matrix-assisted laser desorption/ionization (MALDI), electrospray ionization (ESI), and secondary-ion mass spectrometry (SIMS). X-ray diffraction (XRD) is used for solid-state analysis such as degree of crystallinity and crystal structure as well as the unit cell parameters, while Fourier transform infrared spectroscopy (FTIR) is used for identification of the polymer functional groups. NMR helps to identify and characterize various polymers and also provides information on the mobility of their molecules, while X-ray photoelectron spectroscopy (XPS) provides information regarding the chemical composition of polymeric materials. The physical properties such as hydrophobicity, functional groups, and flexibility of the polymer chain structure and chemical properties such as chemical reactivity, toxicity, biocompatibility, chirality, adsorption capacities, chelation, and polyfunctionality of polymeric materials are also discussed.

The desires to improve on the operational efficiency of coagulation/flocculation (CF), a unit process in water and wastewater treatment, and to obviate the other challenges synonymous with the use of inorganic coagulants (i.e. aluminium- and iron-based alum) impelled the search for alternative coagulants that can ameliorate the identified shortcomings. Amongst the array of synthetic and natural origin materials that have been screened as alternatives to the conventional inorganic alum, polymeric coagulants have shown better promise. The inherent structural features of polymeric coagulants enhanced the CF process operation and economy. This treatise is an exposition on the variables that define the choice of polymeric coagulant as an alternative to the conventional inorganic coagulants. The theoretical bases for the choice of the different polymeric coagulants were discussed. Using the identified active coagulating species in the different polymeric coagulant as a premise, the underlying CF mechanisms in the use of this genre of coagulants were expounded. The research gap in the use of polymeric coagulant as substitute to the conventional inorganic coagulant was also highlighted.

In the past decades, polymer and polymer-based nanocomposite adsorbents have been emerging as promising materials for the removal of various pollutants from contaminated waters, in terms of strong mechanical strength, excellent hydraulics performance, high stability, and tunable surface chemistry. In general, the adsorption of target pollutant is highly dependent upon the physicochemical structure of adsorbent materials, such as skeleton chemistry, pore structure, surface functional groups as well as the encapsulated moieties. This chapter reviews the synthesis, structure, and adsorption mechanism of polymer and polymer-based nanocomposite adsorbents utilized for the removal of various organic and inorganic pollutants. Also, the application of these materials is particularly concerned.

The recent developments in the synthesis of polymer-based photocatalysts, photosensitizers, and hybrid photocatalysts along with their properties and potential applications in degradation of water pollutants have been presented. Polymer functions as photocatalysts, catalytic supports, and photosensitizers in pure as well as in composite form. The photocatalysts generate very reactive oxygen species (ROS), which efficiently oxidizes several pollutants such as dyes, pesticides, pharmaceuticals, and microorganism present in water. Polymeric and hybrid photocatalysts are especially well suited for removal of chemical compounds, which are present at low concentrations in water resources due to synergistic effect. The advantages for the use of photoactive polymeric are easy removal and long life, and control of the formation of secondary contamination is avoided.

Today, microbial infection appeared as one of the most critical environmental pollutions from our water stream. Indeed, the rising of public awareness for water pollution and water security has urged both researchers and industries to develop cost-effective antimicrobial polymer system. Although a range of polymers have antimicrobial properties, the most frequently studied polymer for water disinfection is chitosan. It offers several advantages, including biodegradable, non-toxic in nature, biocompatible and inexpensive, as compared to other low molecular weight antimicrobial polymers. In general, low molecular weight antimicrobial agents suffer several disadvantages, such as toxicity to the environment and short-term antimicrobial ability. Moreover, using chitosan biopolymer could enhance the efficacy of some existing antimicrobial agents and antifungal agents and minimize the environmental problems. In this chapter, the brief introduction of chitosan as well as modified chitosan on the development of water disinfection is extensively discussed. In particular, this chapter discusses the physicochemical properties of chitosan and different synthesis approaches for chitosan.

Polymers are sometimes preferred for membrane filtration because they are more flexible, easier to handle, and less expensive than inorganic membranes fabricated from oxides, metals, and ceramics. The polymers are used as the membrane active layer and porous support in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF) processes. However, the application of polymers for filtration suffers critical drawbacks, such as the chemical attack of polymers, membrane fouling, and hydrophobicity of most polymers. In this chapter, the polymers used for membrane filtration in recent studies and their fabrication procedures are presented and discussed. The polymers used in recent applications include cellulose acetate (CA), polyamide (PA), polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), polyvinyl chloride (PVC), polyimide (PI), polyacrylonitrile (PAN), polyethylene glycol (PEG), polyvinyl alcohol (PVA), poly(methacrylic acid) (PMAA), poly(arylene ether ketone) (PAEK), poly(ether imide) (PEI), and polyaniline nanoparticles (PANI). A new polymeric material named polyethersulfone amide (PESA) has also been presented recently. Most of the recent studies have focused on improving the specific energy consumption, salt rejection, water flux, chemical resistance and antifouling properties of polymeric membranes and nanocomposites through blending and surface modification techniques. These techniques involve the use of zwitterionic coatings, sulfonated poly(arylene ether sulfone) (SPAES), perfluorophenyl azide (PFPA), carbon nanotubes (CNTs) and graphene oxide (GO) as nanofillers, polyether ether ketone (PEEK), and nanoparticles such as titanium dioxide (TiO₂), and mesoporous silica. The use of polymers for filtration is still gaining tremendous attention, and further improvements of polymeric characteristics for enhanced membrane performance are expected in the coming years.