Constructing stable and reliable interfaces around pseudo two-dimensional clay materials is a key process in achieving advanced and reliable performance of related composite materials. However, the effective surface modification of pseudo two-dimensional clay has been a challenging research topic. In this study, we have developed an effective and facile method for the interfacial modification of magnetic montmorillonite (MMT) nanocomposite by using covalent layer-by-layer (LbL) assembly. The method involves conventional LbL assembly around the magnetic MMT followed by infiltration of a bifunctional photoactive small molecule and then covalent cross-linking of the LbL multilayers upon UV irradiation. After covalent LbL modification, the nanocomposite presented ample organic species around its interfaces and displayed stable organic interfaces even in extreme solution conditions such as in basic (pH =14) solutions. The covalent cross-linking of the multilayers proved to be indispensable in keeping the LbL multilayers stable around the MMT composites. After modification, the composite particles kept their magnetic properties. In addition, the release profile of the composite particles for methyl blue indicated that the composite particles preserved the capacity to carry loads and release them in retarded speed. This method will potentially integrate the merits of LbL multilayers with MMT to achieve advanced functional materials.
A stable drug release system with magnetic targeting is essential in a drug delivery system. In the present work, layered double hydroxide assemblies stabilized by layer-by-layer polymer multilayers were prepared by alternative deposition of poly(allylamine hydrochloride) and poly(acrylic acid) species on composite particles of Fe3O4 and ZnAl-LDH and then covalent cross-linkage of the polymer multilayers by photosensitive cross-linker. The successful fabrication was recorded by Zeta potential and Fourier transform infrared spectrum measurements. The formed assemblies were stable in high pH solutions (pH > 7). The drug loading capacity and release behavior of the assemblies could be controlled by treatment with appropriate acidic solution, and were confirmed by loading and release of a simulated drug, methylene blue. The formed assemblies possessed enough saturated magnetic strength and were sensitive to external magnetic field which was essential for targeting drug delivery. The formed assemblies were multifunctional assemblies with great potential as drug delivery system.
The electronic structures and catalytic efficacies of molybdenum disulfide (MoS2)‐based catalysts are sensitive to embedding environment. In order to develop a finely tunable strategy, a “layer‐by‐layer and Nafion capping” strategy for the scalable preparation of interfacial (MoS2)‐based catalytic structures is developed. The study shows that the assembly partner influences the electronic structures of the Zn&N co‐doped (MoS2) (Zn‐N‐(MoS2)) catalysts. Poly(allylamine hydrochloride) (PAH) decreases the catalytic efficacy, whereas when PAH‐rGO (rGO [reduced graphene oxide]) is the assembly partner, effective interfacial catalysts are prepared. The superior catalytic efficacy of (PAH‐rGO/Zn‐N‐(MoS2))n can be attributed to the fact that rGO effectively activates the basal plane S2− as the active sites. The catalytic efficacy of the multilayers at 16 assembly cycles due to a balance between the number of active sites and low resistance. After capping with Nafion layer, the interfacial catalysts exhibit high stability. Compared with the widely used drop‐casting methods, the layer‐by‐layer strategy possesses unique benefits, including fine‐tune the structures, free choice of the partner, and planar homogeneity. It is expected that this layer‐by‐layer catalyst immobilization strategy will benefit fundamental understandings regarding the finely controlled scalable interfacial immobilization of catalysts with superior efficacy, and assist in promoting the practical utilization of various catalysts.
The fixation of the catalyst interface is an important consideration for the design of practical applications. However, the electronic structure of MoS2 is sensitive to its embedding environment, and the catalytic performance of MoS2 catalysts may be altered significantly by the type of binding agents and interfacial structure. Interfacial engineering is an effective method for designing efficient catalysts, arising from the close contact between different components, which facilitates charge transfer and strong electronic interactions. Here, we have developed a layer-by-layer (LbL) strategy for the preparation of interfacial MoS2-based catalyst structures with two types of conducting polymers on various substrates. We demonstrate how the assembled partners in the LbL structure can significantly impact the electronic structures in MoS2. As the number of bilayers grows, using polypyrrole as a binder remarkably increases the catalytic efficacy as compared to using polyaniline. On the one hand, the ratio of S2 2– (or S2–), which is related to the remaining active hydrogen evolution reaction (HER) species, is further increased. On the other hand, density functional theory calculations indicate that the interfacial charge transport from the conducting polymers to MoS2 may boost the HER activity of the interfacial structure of the conducting polymer/MoS2 by decreasing the adsorption free energy of the intermediate H* at the S sites in the basal plane of MoS2. The optimized catalytic efficacy of the (conducting polymer/MoS2) n assembly peaks is obtained with 16 assembly cycles. In preparing interfacial catalytic structures, the LbL-based strategy exhibits several key advantages, including the flexibility of choosing assembly partners, the ability to fine-tune the structures with precision at the nanometer scale, and planar homogeneity at the centimeter scale. We expect that this LbL-based catalyst immobilization strategy will contribute to the fundamental understanding of the scalability and control of highly efficient electrocatalysts at the interface for practical applications.
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