One-Minute Synthesis of a Supramolecular Hydrogel from Suspension-Gel Transition and the Derived Crystalline, Elastic, and Photoactive Aerogels

Peng Meng; Yanan Xu; Cheng Yan; Jingsan Xu

doi:10.1021/acsami.0c16009

One-Minute Synthesis of a Supramolecular Hydrogel from Suspension-Gel Transition and the Derived Crystalline, Elastic, and Photoactive Aerogels

ACS Appl Mater Interfaces. 2020 Nov 25;12(47):53125-53133. doi: 10.1021/acsami.0c16009. Epub 2020 Nov 10.

Authors

Peng Meng¹, Yanan Xu², Cheng Yan^{3

4}, Jingsan Xu^{1

4}

Affiliations

¹ School of Chemistry and Physics, Queensland University of Technology, Brisbane QLD 4000, Australia.
² Institute for Future Environments, Queensland University of Technology, Brisbane QLD 4000, Australia.
³ School of Mechanical Medical and Process Engineering, Queensland University of Technology, Brisbane QLD 4000, Australia.
⁴ Centre for Materials Science, Queensland University of Technology, Brisbane QLD 4000, Australia.

PMID: 33169961
DOI: 10.1021/acsami.0c16009

Abstract

Solutions or sols are commonly employed as the starting materials for the preparation of supramolecular hydrogels; however, suspension-based synthesis has been much less reported because of inhomogeneity and quick sedimentation of large particles in a suspension. Further, it remains a technical challenge to derive supramolecular aerogels directly from the parental hydrogels owing to the ease of structural collapse during water removal. Herein, we report a suspension-gel transition for the ultrafast synthesis of a new supramolecular hydrogel simply by adding AgNO₃ into the aqueous suspension of cyanuric acid-melamine (CAM) aggregates. With the activation of preadded ammonia, Ag ions instantly reacted with the CAM particles, transforming into N-Ag(I)-N coordinating bonded supramolecular nanofibers; simultaneously, the suspension converted to a hydrogel without the use of polymer cross-linkers or external stimulus. Upon simple freeze-drying, a highly crystalline fibrous aerogel with a cellular network was obtained, which possessed a porosity up to 99.7% and a density as low as 4.8 mg/cm³, enabling remarkable oil uptake capacities (100 times of its weight). The supramolecular aerogel demonstrated intrinsic elasticity, which should arise from the cellular structure and elastic character of the nanofiber skeletons. Notably, the aerogel showed high compatibility to incorporate a range of external substances for further functionalization exemplified by polymeric carbon nitride (PCN, a metal-free semiconductor) included gels. The loaded PCN resulted in enhanced mechanical strength and endowed the aerogel unique photoactivity, i.e., in situ reducing Ag(I) into Ag nanoparticles upon light illumination and thus forming a plasmonic shell over the aerogel with potential applications in sensing and catalysis.

Keywords: crystalline and elastic aerogels; cyanuric acid-melamine polymer; photocatalysis; supramolecular hydrogels; ultrafast suspension−gel transition.