FUNCTIONALIZED CARRAGEENAN BASED NANOMATERIALS FOR MITIGATION OF HAZARDOUS ENVIRONMENTAL POLLUTANTS

Abstract

Water pollution is a repercussion of human activities accountably industrialization, urbanization, and population overgrowth that contaminate the water resources with biological (bacteria, viruses, fungi, algae, weeds, etc.), inorganic (toxic heavy metals and metals), and organic pollutants (hydrocarbons, antibiotics, dyes). The wastewater reclamation strategies reckon conventional methods, however nanomaterials due to their unique properties, small size, high surface area, and reactivity are relevant for water pollution remediation. The nanocomposites such as nano-adsorbents, antimicrobial nanomaterials, nanocatalysts, photo-anocatalysts, nanogels, aerogels, and nanocomposite membranes have been exploited for their effectiveness in removing pollutants such as heavy metals, organic compounds, and microorganisms from water sources. Between chemical and green synthesis routes of nanoparticles, the latter is a pertinent approach towards sustainability, the green route most commonly uses biopolymers such as polysaccharides, proteins, nucleic acids, proteoglycans, and lipids for the fabrication of metal, metal oxide nanoparticles, and nanocomposite materials. In particular, polysaccharide-coated nanoparticles because of their excellent biocompatibility and additional properties such as antimicrobial, anticoagulation, antiviral, and anti-cancerous activities, have been used in various applications notably for biomedical purposes such as drug delivery, tissue engineering, catalysis, sensing and imaging. Polysaccharides including heparin, cellulose, chitosan, alginate, gum Arabic, and carrageenan are being utilized in the fabrication of various metal (Ag, Au, Pd, Pt) and metal oxide (ZnO, Fe3O4, CuO, MnFe2O4, NiO) nanoparticles. Carrageenans are anionic linear forms of sulfated carbohydrates from red algae. Three major carrageenan types including kappa (κ-C), iota (ι-C), and lambda (λ-C) possess one, two, and three negatively charged sulfate groups along their backbone respectively. Carrageenan-based nanocomposites nanofibers, hydrogel, aerogels, films, coatings, nano-catalysts, nanosensors, and fabrics have been used in various fields such as food, pharmaceuticals, cosmetics, and biomedical engineering. The current thesis focuses on developing carrageenan-based nanoparticles and nanocomposites to provide sustainable techniques for the remediation of water pollution. Chapter 1 focuses on the pollutants, especially water pollutants which were defined, classified, and addressed along with their sources of pollution, and their impact on the ecosystems and living being health. The role of nanotechnology in the management of water quality was discussed in the gamut of different structural types of nanomaterials. The intricacy of nanomaterials synthesis and nanocomposite formulations were elaborate where top-down and bottom-up methods were discussed and compared concurrently with chemical and green nanocomposite synthesis routes were compared. The different components of green synthesis were included with examples with detailed discussion on carrageenans and carrageenan-based nanoparticles and nanocomposite formulation used in various applications. Coherently carrageenan nanocomposites in water pollution management were discussed with existing research work and upcoming challenges or research gaps. Chapter 2 targets the textile industry effluents contaminated with azo dyes through development of a carrageenan based nanocatalytic platform towards sustainable technology. Nanocomposite was fabricated with a facile one-pot synthesis method with κ-carrageenan capped silver nanocatalyst (CSNC), and was immobilized on 2D bentonite (BT) sheets to generate nano catalytic platform (BTCSNC) for the degradation of anionic azo dyes. The nanocomposite(s) were physicochemically characterized using UV–Vis, DLS, TEM, FESEM, PXRD, ATR-FTIR, TGA, BET and XPS etc., to obtain insights into the nanocomposite composition, structure, stability, morphology and mechanism of interaction. The obtained CNSC are monodispersed, spherical and were stabilized by κ-Crg. The broadening of peak PXRD spectra established its exfoliation upon addition of CSNC. XPS and ATR-FTIR data evidenced the absence of covalent interactions between CSNC and BT. The catalytic efficiency of CSNC and BTCSNC composites were compared for the degradation of methyl orange (MO) and congo red (CR). The reaction followed a pseudo first order kinetics, and immobilization of CSNC on BT resulted in a 3–4 fold enhancement in degradation rates. Further, a degradation mechanism has been proposed by analyzing the products identified through LC-MS. The reusability studies of the BTCSNC evidenced the complete activity of the nanocatalytic platform for six cycles, and the gravitational separation method for catalyst recycling. In a nutshell, the current chapter provided an environmentally friendly, sizable, and sustainable nano catalytic platform” for the remediation of industrial wastewater contaminated with hazardous azo dyes”. Chapter 3 aims a sustainable approach towards the fabrication of a nanocatalyst system or platform for the mitigation of the existing global water crisis is portentous. In this work, the development of a polymer nanocomposite (PNC) membrane with the incorporation of green synthesized nano-catalytic materials and its effect on the performance of the membrane has been dissected. The biopolymer carrageenan-coated cuprous oxide nanocubes (CCNC) were synthesized in the presence of kappa (κ-C), iota (ι-C), lambda (λ-C) carrageenans which affected the size and dispersity of the nanocubes. Among all three carrageenans, λ-C shows better dispersity and well-defined shape of the nanocubes, which as efficient nanocatalysts were able to degrade toxic pollutant azo dyes methyl orange (MO) and congo red (CR) via both reductive and oxidative degradation methods. The characterization of the nanocubes was performed using UV-Vis spectroscopy, FESEM, ATR-FTIR, XPS, and P-XRD. The catalytic mechanism of λ-CCNC4 to degrade MO and CR with reductive and oxidative methods was compared using LC-MS. Further, the λ-CCNC4 incorporated PVDF nanocomposite membrane’s porosity, flux, rejection, and fouling were analyzed. The nanocomposite membrane was characterized using FESEM, ATR-FTIR, TGA, and P-XRD. The catalytic anti-biofouling and antimicrobial performance of the membrane were tested against dyes, BSA, and bacterial contamination, respectively and found to be effective. Chapter 4 addresses bacterial contamination and its resistant aggregation to biofilm formation which possesses a global industrial, environmental, and health concern. This chapter focuses on the synthesis, characterization, and functional assessment of two carbohydrate/sulfated polysaccharide (ι-carrageenan and λ-carrageenan)-capped silver nanocomposites (ι-CrgAgNPs and λ-CrgAgNPs). The nanocomposite syntheses were designed and optimized using RSM-based FCCCD. The synthesized nanocomposites were characterized using an array of physicochemical techniques to study their morphological, structural, compositional, and molecular interaction features. Spherically shaped nanoparticles were obtained for ι-CrgAgNPs and λ-CrgAgNPs. As evident from FTIR, silver nanocomposites were stabilized by various functional groups present in carrageenans. Antibacterial and anti-biofilm studies performed using the Gram-negative strain Pseudomonas aeruginosa and Gram-positive strain Staphylococcus aureus suggested that both the nanocomposites were potent in inhibiting and eradicating the bacterial biofilms; however, their potency for eradicating the P. aeruginosa biofilm is much higher as compared to the S. aureus biofilm. Furthermore, within the nanocomposites, λ-CrgAgNPs was observed to be more stable, while ι-CrgAgNPs exhibited enhanced biofilm inhibition/eradication properties. These results confirm the broad-spectrum anti-biofilm features of the synthesized carrageenan nanocomposites, which can be further developed as functional industrial formulations as potent antimicrobial agent. Chapter 5 elaboratively discusses the recalcitrance of antibiotics exacerbating the world water crisis menacing humanity along with the entire ecosystem. The remediation of antibiotics has been attempted with various techniques comprising an array of materials. The focus has been the development of materials with environmental safety, sustainability, scalability and economic viability. Aerogels have been widely utilized for adsorption-based pollutant removal, additionally the aerogels were imparted with nanocatalysts to provide a functional catalytic system. Requisitely in this work, the 2D hexagonal boron nitride nanosheets (BNNS) were exfoliated and stabilized in the presence of biopolymer carrageenans. The carrageenan stabilized BBNS were further used for in situ immobilization core Cu2O nanocubes along with Ag2S shell structure to obtain a catalytic platform. The catalytic platform was converted into aerogels. The nanocomposite and the aerogels were characterized using FESEM, ATR-FTIR, PXRD, and XPS. The fabricated aerogels were deployed for the catalytic degradation of antibiotics due to their excellent catalytic properties. The biocompatible, hydrophilic, and functional catalytic properties of the aerogels conferred a sustainable platform for antibiotic degradation through advanced oxidative processes. In summary the present thesis focuses on the potential of carrageenan as stabilizing agents for metal, metal oxide and 2D nanosheets. The structural difference between carrageenans kappa, iota and lambda shows effect on nanoparticles sizes, shapes, stabilizing efficiency, yield, and antimicrobial potentials, concluded to nanocomposites membrane and aerogels materials fabrication. Elliptically this thesis work endows carrageenans based nanocomposite materials towards sustainable remediation of water pollutants azo dyes, bacterial biofilms, and antibiotics for a sustainable and safer environment.