Click-functionalized inverse-opal structured membranes for organocatalytic reactions

Abstract

Three-dimensional (3D) porous polymeric inverse-opal (IO) structures have unique structural characteristics for various applications. The combined benefit of highly interconnected pores with facilitated mass transfer properties imparts a strong potential for use as catalytic reactive membranes. Although research has developed methods for immobilizing catalysts at the internal surface of reactive membranes, there are still problems of catalyst leaching and issues with post-separation of catalysts from reaction products. In this work, we present a straightforward and robust method for generating irreversible chemical bonds by employing click chemistry, using copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition in particular. We used a combination of an azide-functionalized 3D-IO surface and an alkyne-end-modified 2,2,6,6-Tetramethyl-1-piperidineyloxy (TEMPO) organocatalyst. The TEMPO-embedded 3D-IO structures performed significantly better as catalytic membranes for oxidizing alcohols into their corresponding aldehyde derivatives in the presence of an oxidant and co-catalyst. The synergistic effects contribute to the outstanding membrane performance and high conversion efficiency (>97% depending on the type of alcohol) while maintaining a permeation flux greater than 300 L/m2⋅h@1 bar. This novel approach can be extended to the design and development of various reactive membranes for biomedical, environmental, and scaled-up synthetic purposes.