Control of Volume‐Responsive Properties of Hydrogels through Molybdenum Disulfide Nanosheet Incorporation

Abstract

efforts have been devoted to remove the aforementioned limitations of the PNIPAM hydrogel sensors by incorporating nanomaterials. [17,18] Recently, low dimensional nanomaterials with a large specific surface area such as carbon nanotubes and graphene oxide have been incorporated to hydrophilic polymers such as PNIPAM, chitosan, and polyacrylic acid hydrogels to enhance the adsorption of substances and chemical storage capacity. [19][20][21] In this study, we demonstrate a composite hydrogel of MoS 2 nanosheets functionalized with 4-mercaptobenzoic acid (MBA) and PNIPAM (MBAMS-PNIPAM hydrogel) for the detection of water-soluble phenols. Herein, MoS 2 nanosheets have been shown to be promising candidate components for various fields, such as the detection of water-soluble substances, humidity, and gas species. [22][23][24][25][26] MBAMS was prepared via MoS 2 exfoliation processes and subsequent chemical functionalization process with 4-MBA for realizing the reactivity and selectivity toward the target substance. Here, 4-MBA, a small ligand molecule with a thiol and a carboxyl group, was used to modify the surface of MoS 2 nanosheets. We also verified that we can adjust the phenol detection range by controlling the adsorption and responsivity of the MBAMS-PNIPAM hydrogel through the amount of the incorporated MoS 2 . In addition, we demonstrate an in situ detection strategy of watersoluble phenols by developing an effective transduction strategy to convert the hydrogel volume change into electronic signals. The novel transduction strategy uses a liquid metal-based capacitive transduction method. Furthermore, combined with a handheld signal processor and home-built data-visualization software, we demonstrate a portable detection instrument for phenolic molecules. The instrument successfully detected resorcinol concentrations as low as 10 mg L −1 . As an example, compared to other sensors using optical or electrical mechanisms, [27][28][29] our hydrogel can be readily integrated with existing ducts, containers, or pipe systems without any additional process. Furthermore, above certain concentrations, the hydrogel color change will be large enough to enable detection with the naked eye. As this strategy enables the simple, one-step, and easy detection, it can be easily extended to detect water-soluble chemicals other than phenols in the future. Figure 1a depicts the molecular structure of MBAMS-PNIPAM hydrogels and the detection mechanism of phenols. The surface of MoS 2 was functionalized with 4-MBA molecules to enhance the reactivity and selectivity toward the target phenolic substance and stabilize the hydrogel structure. The target phenolic molecule A composite structure of molybdenum disulfide (MoS 2 ) nanosheets and poly(N-isopropylacrylamide) (PNIPAM) hydrogel is demonstrated for the selective detection of phenols. The incorporation of MoS 2 with a hydrogel system enhances its adsorption and its volume-change response to phenols. It is verified that the phenol detection range can be adjusted by controlling the ...

Multifunctional Role of MoS2 in Preparation of Composite Hydrogels: Radical Initiation and Cross-Linking

“…In particular, soft, nanocomposite hydrogels have benefited from the elastic, cross-linked networks that confine a considerable amount of water and additive nanomaterials that induce tailored, complex properties, and now hold privileged positions in the development of smart, elastic materials. − Typically, colloidal nanoparticles including nanowires or carbon dots have been widely used, − and more recently, two-dimensional layered materials such as ceramic nanosheets, carbides, graphene oxides, and covalent organic framework have been extensively researched. − They have relatively weak intermolecular interactions between the layers and thus show large surface areas and accessible active sites that are exposed on the surface, which imparts sophisticated yet essential properties to the polymeric networks. , Among many layered materials, molybdenum disulfide (MoS 2 ) has been incorporated in hydrogel networks due to its mechanical or electronic properties; recently, the embedded hydrogels have been used as a functional platform for energy-related or environmental applications such as separation or catalysis under aqueous conditions. − When designing the materials via a bottom-up approach, MoS 2 and other monomeric components are dispersed on a molecular level; thereafter, the composite networks are set, usually, by radical polymerization while leaving the inorganic material as an exogenous additive in most cases. Conversely, from the perspective of polymer chemistry, the chemical function of MoS 2 that can play a significant role as a reactive component in the formation of hydrogels through radical polymerization has been rarely investigated.…”

Near-Infrared Light-, Magneto-, and pH-Responsive GO–Fe3O4/Poly(N-isopropylacrylamide)/alginate Nanocomposite Hydrogel Microcapsules for Controlled Drug Release

“…Therefore, the stimulus-responsive hydrogel composite systems, that is, nanocomposite hydrogels (NCHs) that incorporated responsive nanostructures into hydrogels, have been proposed as a novel strategy to reinforce the versatility and flexibility of responsive hydrogels. − Among a variety of NCHs, near-infrared (NIR) light-responsive hydrogels are of considerable interest, as the NIR light can penetrate tissues and the light intensity can be remotely regulated . In general, NIR light-responsive hydrogels have been formed by the integration of photosensitive nanomaterials such as gold nanoparticles, graphene oxide (GO), carbon nanotubes, and MoS 2 nanosheets into a hydrogel polymer network. − The NIR-absorbing nanoparticles inside the hybrid hydrogels can generate heat to trigger the temperature-sensitive hydrogels, offering a noninvasive and remote control method. Although promising, the stimulus responsiveness is not as quick as required in some cases, and furthermore, the cooperation of multiple stimuli provides an innovative avenue to achieve a faster response in comparison to a single trigger .…”