Preparation and applications of silver nanoparticle decorated block copolymer nanocomposite particles

Abstract

This thesis explores the preparation and characterisation of Ag/polymer nanocomposite hybrids via in-situ synthesis. Functionalised diblock copolymer nanoparticles were synthesised using polymerisation-induced self-assembly (PISA) by reversible addition-fragmentation chain-transfer (RAFT) polymerisation and subsequently employed as templates for the in-situ formation of silver nanoparticles (AgNPs). The morphologies and functional properties of these materials were systematically investigated, and their potential applications were demonstrated. Firstly, anionic poly(potassium 3-sulfopropyl methacrylate) (PKSPMA) macro chain-transfer agents (macro-CTAs) were synthesised via RAFT solution polymerisation and chain-extended with hydrophobic benzyl methacrylate (BzMA) monomer to form sulfonate-functional diblock copolymer nanoparticles. The effect of polymer functionality, solution pH, and the molar ratio of silver ions [Ag+] to functional groups [-SO3-] were investigated for the subsequent in-situ synthesis of AgNPs. The long-term colloidal stability of Ag/polymer nanocomposites with a silver loading of 10 % w/w was demonstrated at pH 5. These particles had a mean diameter of ~180 nm and a low polydispersity index (< 0.1), as judged by dynamic light scattering. The resulting Ag/PKSPMA25-PBzMA300 (Ag/S25-B300) nanoparticles, with a [Ag+] to [-SO3-] ratio of 2:1, were investigated in terms of their antimicrobial performance against Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli). Broad-spectrum antibacterial performance was indicated by >99.99% colony-forming units (CFU) reduction for both E.coli and S. epidermidis. Furthermore, it was demonstrated for the first time that silver-decorated PISA-derived nanoparticles could be formulated and printed onto a glass substrate via inkjet printing, forming stable and continuous patterns. Subsequently, the catalytic performance of Ag/S25-B300 nanoparticles was investigated for potential applications in industrial wastewater treatment. Reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) served as a model to assess the catalytic activity. This reduction followed pseudo-first-order kinetics, and the mechanism of catalytic performance of AgNPs was studied using the Langmuir-Hinshelwood model. 4-NP could be completely reduced to 4-AP in presence of NaBH4 and Ag/S-B catalyst within 55 s with a maximum apparent rate constant (kapp) of 0.038 s-1 and turnover frequency (TOF) of 631 h-1. The recovery and recyclability of the nanoparticle catalyst was also demonstrated for at least five dye degradation cycles. Additionally, rapid dye degradation was demonstrated for Rhodamine B (RhB), methylene blue (MB) and methyl orange (MO) dyes, with complete degradation within 2 mins, 0.5 mins, and 1 min, respectively. Furthermore, to investigate a ‘recovery-free’ mode of nanoparticle catalyst use, Ag/S25-B300 nanoparticles were diluted in a dialysis tube and immersed into dye (colloquially referred to as the ‘tea-bag’ procedure). This method successfully reduced the 4-NP to 4-AP but longer times were required for complete dye degradation. These results demonstrate an efficient, stable, recoverable and cost-effective nanoparticle catalyst for potential industrial applications. Follow-up studies aimed to enhance the silver loading of these block copolymer nanocomposite particles by investigating the in-situ synthesis of AgNPs using carboxylic-functionalised poly(methacrylic acid)-poly(benzyl methacrylic) (M-B) diblock copolymer nanoparticles as templates. In addition, tannic acid (TA) was introduced to modify the surface functionality of diblock copolymer nanoparticles. It was anticipated that this would increase the interactions of the nanoparticles with the Ag precursors and provide more active sites for AgNP nucleation. The coating efficiency was highly pH-dependent due to the protonation and deprotonation of the phenolic groups in TA and carboxylic functional groups of PMAA. The preparation of TA-coated M-B nanoparticles with good colloidal stability was achieved at pH 9. Comparative experiments were also conducted using the M-B nanoparticles without TA as templates with a [Ag+] to [-COOH] ratio of 8:1. The catalytic performance these two types of silver-decorated nanocomposites were investigated towards the reduction of 4-NP, and degradation of RhB, MB and MO. Notably, both materials exhibited significantly enhanced catalytic performance compared to Ag/S-B catalyst, corresponding to a maximum kapp for the reduction of 4-NP of 0.14 s-1 and 0.20 s-1. TA-coated M-B catalysts exhibited superior catalytic activity when compared to uncoated M-B catalysts in all cases of dye degradation studied. In summary, this thesis presents the synthesis of two novel Ag/polymer nanocomposite hybrids. These materials demonstrate long-term colloidal stability, have high catalytic performance and broad-spectrum antibacterial activity. In addition, they are inkjet printable and recoverable from dispersion, making them promising candidates for industrial applications such as wastewater treatment and antibacterial coatings.

Date of Award	26 Mar 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lee Fielding (Main Supervisor) & Stephen Edmondson (Co Supervisor)