Bio-Inspired Iron-Loaded Polydopamine Functionalized Montmorillonite as an Environmentally Friendly Flame Retardant for Epoxy Resin

As an important thermosetting material, flame-retardant epoxy resin has various applications in the aerospace, chemical, and electronics industry, and other fields. However, the flame retardancy of epoxy resins is often improved at the expense of mechanical performance. The contradiction between flame retardancy and mechanical properties seriously impedes the practical applications of epoxy resin (EP). Herein, iron-loaded polydopamine functionalized montmorillonite (D-Mt-Fe³⁺), which was prepared by dopamine, iron chloride and montmorillonite in an aqueous solution, was introduced to prepare iron-loaded polydopamine functionalized montmorillonite/epoxy resin composites (D-Mt-Fe³⁺/EP). As expected, D-Mt-Fe³⁺/EP-10 with 10 phr of D-Mt-Fe³⁺ passed the UL-94 V-0 rating, achieved a limiting oxygen index (LOI) value of 31.0% and reduced the smoke production rate (SPR) and total smoke production (TSP), indicating that the introduction of D-Mt-Fe³⁺ could endow EP with satisfactory flame retardancy through the radical scavenging function of dopamine in the gas phase and the catalytic charring effect of iron ions, respectively. Encouragingly, the mechanical property was also enhanced with the flexural strength increased by 25.5%. This work provided an attractive strategy for improving both the mechanical properties and fire resistance of EP, which greatly broadened their applications in the chemical industry and electronics field, etc.

Molecular Organization in Exponentially Growing Multilayer Thin Films Assembled with Polyelectrolytes and Clay

Multilayer thin film assembly by the layer-by-layer (LbL) technique offers an inexpensive and versatile route for the synthesis of functional nanomaterials. In the case of polymer-clay systems, however, the technique faces the challenges of low clay loading and lack of tunability of the film characteristics. This is addressed in the present work that achieves exponential growth in clay-containing polyelectrolyte films having high clay loading and tailored properties. Our approach involves the incorporation of a weak polyelectrolyte and a clay with relatively high charge density and small particle size. The system of investigation comprises poly(diallyldimethylammonium chloride) (PDDA) as the polycation and laponite clay and poly(acrylic acid) (PAA) or poly(sodium-4-styrene sulfonate) (PSS) as polyanions that are used alternately to create multilayers. Successful high clay loading and exponential growth were achieved by two different approaches of polyanion incorporation in the multilayers. A progressive increase in the degree of ionization of PAA was shown to contribute to the exponential growth. Our findings also include novel pathways to manipulate thickness, surface topography, and clay content. The strategy presented here can lead to novel approaches to fabricate tailor-made nanomaterials for distinct applications.

Multifunctional ZnO-Co3O4 @ polymer hybrid nanocoatings with controlled adsorption, photocatalytic and anti-microbial functions for polluted water systems

Triple action pollutant responsive multi-layer hybrid nanocoatings of architecture PEI(PAA/ZnO-Co3O4)n were constructed through ZnO-Co3O4 binary oxide co-precipitation followed by its inclusion in multi-layer polymeric thin films using Layer-by-Layer (LbL) deposition. Characterization of the designed architecture was carried out via FTIR, XRD, UV-Vis, and Raman spectroscopic studies to evaluate the chemical nature, bonding, and crystallographic behavior of ZnO-Co3O4. Peaks of ZnO-Co3O4 were recorded at 586.38, 486.08, and 443.64 cm-1 while pronounced shifting of ZnO characteristic E2 (high) peak ~ 450 cm-1 and appearance of modes around 495, 530, 630, and 719 cm-1 indexed via Raman studies validated Co3O4 impregnation into ZnO structure. XRD patterns of ZnO-Co3O4 compared to their previously reported pristine structures also justified the formation of binary oxide as unit composite. SEM micrographs confirmed homogenous multi-layered depositions while EDX analysis confirmed their uniform elemental distribution in the unit structure. Sequential multi-layer buildup up to 48 layer pairs was monitored using ellipsometry with maximum film thickness ~ 89 nm and by UV-Vis at 376 nm. The prepared thin films exhibited significant photodegradation of methylene blue ~ 91% and Cu (II) adsorption capacity ~ 89% within first 90 min of contact, along with prominent bactericidal efficiency against E. coli within 24 h of reaction time. FAAS, ICP-OES, and UV-Vis spectroscopy analyses make these multifunctional hybrid nanocoatings promising for industrial wastewater as well as drinking water purification setups. Furthermore, protuberant recycling and regenerative capacity make these hybrid nanocoatings an eco-friendly system for hydro-remediation.

Inclusion of organic species in exfoliated montmorillonite nanolayers towards hierarchical functional inorganic-organic nanostructures

Montmorillonite (Mt) can readily undergo spontaneous delamination or exfoliation into nanolayers by various physical and chemical processes, which allow various strategies to engineer hierarchical functional inorganic-organic nanostructures. This review aims to discuss the recent progress in the liquid-phase exfoliation of Mt into individual nanolayers and the inclusion chemistry of functional organic species, ions, or molecules into the exfoliated Mt nanolayers to produce hierarchical functional inorganic-organic nanostructures. The exfoliation methods include mechanical force, ultrasonication, and intercalation-assisted exfoliation. Techniques for quickly assessing the quality of the exfoliated Mt nanolayers are still needed. Layer-by-layer (LbL) deposition, template, and evaporation-induced inclusions are examined to fabricate hierarchical Mt-organic species nanocomposites with unique functionalities and properties. The nanocomposites can be produced as multilayered porous films, brick-and-mortar coatings, hydrogels with a house-of-cards structure, core-shell materials, and hollow and mesoporous spherical nanocomposites, which exhibit significant potential for adsorption, catalysis, targeted delivery and controlled drug release, highly sensitive sensors, flame retardant coatings, and thermal energy storage and release (i.e. phase change materials). Finally, the challenges and prospects for the future development of hierarchical nanocomposites of exfoliated Mt nanolayers and organic species, particularly in hierarchical supramolecular nanostructured composites, are highlighted.

Indirect X-ray Detectors Based on Inkjet-Printed Photodetectors with a Screen-Printed Scintillator Layer

Organic photodetectors (PDs) based on printing technologies will allow to expand the current field of PD applications toward large-area and flexible applications in areas such as medical imaging, security, and quality control, among others. Inkjet printing is a powerful digital tool for the deposition of smart and functional materials on various substrates, allowing the development of electronic devices such as PDs on various substrates. In this work, inkjet-printed PD arrays, based on the organic thin-film transistor architecture, have been developed and applied for the indirect detection of X-ray radiation using a scintillator ink as an X-ray absorber. The >90% increase of the photocurrent of the PDs under X-ray radiation, from about 53 nA without the scintillator film to about 102 nA with the scintillator located on top of the PD, proves the suitability of the developed printed device for X-ray detection applications.