Biomimetic Nanowire Structured Hydrogels as Highly Active and Recyclable Catalyst Carriers

Abstract

Nanowire hydrogels with high specific surface areas have great promise in many practical applications. However, the preparation of nanowire hydrogels using common materials and inexpensive means remains an outstanding challenge. This paper reports a novel method for creating aligned nanowire structured hydrogels by directional freezing and γ-radiation initiated polymerization of 2-hydroxyethyl methacrylate (HEMA) using <i>t</i>-butyl alcohol (TBA) as the solvent. The hydrogels prepared at a monomer concentration lower than 2.0 mol L^–1 and a freezing rate higher than 10 mm min^–1 are structured of nanowires, mimicking the microstructure of jellyfish mesogloea. Silver (Ag) nanoparticles (NPs) are introduced into the hydrogels with a chemical reduction method, and the Ag NPs are formed and deposited on the nanowires. Both size and content of Ag NPs in the hydrogels increase with increasing AgNO₃ concentration. The PHEMA and PHEMA/Ag nanocomposite hydrogels all possess very good compressive properties, and the composite hydrogels show higher compressive strengths and excellent deformation recovery. The PHEMA/Ag NPs composite hydrogels show excellent catalytic activity and reusability for the conversion of <i>o</i>-nitroaniline to 1,2-benzenediamine, with an apparent rate constant (<i>k</i>_app) up to 0.165 min^–1. This facile and efficient method can be applied to fabricate more nanowire hydrogels for many practical applications