Design of responsive cellulose-block copolymer memebranes for the remediation of organic emerging contaminants: a selective adsorption approach for electron-deficient aromatic compounds.

Abstract

Organic emerging contaminants (OECs) or contaminants of emerging concern (CECs) are molecules that were previously unaccounted for in term of water quality standards and are known now to have adverse ecological and human health effects. The primary source of OECs includes, among others, active pharmaceutical ingredients and personal care products discarded to the environment through the regular municipal wastewater plants. These contaminants keep building up over time, mainly owing to the lack of cost-efficient technologies; activated carbon (AC) is the choice of preference for the removal of EOCs due to its high adsorption capacity. Nevertheless, the adsorption efficiency of AC rapidly decreases due to organic fouling. Besides, the regeneration of AC is time-consuming and power-intensive; therefore, reuse of this material is somewhat limited. An alternative approach lies in water filtration using selective and reusable membranes. However, research in this area is still limited, and consequently, it is imperative to close the knowledge gap related to the rational design of membranes for the remediation of EOCs. Following that ideal, this research focused on the study and optimization of responsive membranes based on alternative materials, named, block copolymer (BCP)-cellulose conjugates. BCPs are polymers with a wide variety of molecular architectures based on the composition and molecular weight of its constituting monomers. This versatility allows BCPs to interact with organic contaminants through physical and chemical interactions selectively and reversibly that can be triggered by external stimulus. On the other hand, cellulose is an abundant, inexpensive, and renewable biopolymer that in this case is intended to provide structural support to the BCPs.

This thesis has been developed through three main objectives. Initially, it was evaluated the use of nanocellulose and polyethylene glycol-based BCP to prepare composites for sorption of EOCs. Experimental and theoretical results suggested that the material was able to adsorb EOCs via electrostatic interactions (H-bonds and Van der Waals). For the second objective, it was prepared low-cost, nanocellulose-BCP films modified with an alkoxysilane where the BCP, Poly(4-vinyl pyridine-b-ethylene oxide) (P4VP-PEO) was the active adsorption material. This BCP allowed the adsorption of sulfamethoxazole via electron donor-aceptor (EDA) interactions, which are selective and reversible, a key characteristic for the reuse of the films. In addition, the hydrophobic alkoxysilane, Trimethoxy (2-phenyl ethyl)silane provided aqueous stability to the films against dispersion through several adsorption cycles. Finally, cellulose tri acetate-P4PV-PEO membranes were prepared and optimized using non-solvent induced phase separation (NIPS) methods. These membranes presented high surface porosity with internal interconnected hierarchical pores containing P4VP-PEO for competitive adsorption of EOCs while allowing reusability. In this study was evaluated the adsorption selectivity of the membranes toward EOCs. Results suggested that higher electron-deficient aromatic EOCs translated to higher adsorption capacity of the membrane. Overall results of this study led into an efficient, low-cost, and eco-friendly method to produce selective and reusable absorption membranes that contribute to further development of large-scale EOCs remediation applications.