Water-Chloroform Interface Assisted Microstructure Tuning of Polypyrrole-Silver Sheets

Emerging trends and future challenges of advanced 2D nanomaterials for combating bacterial resistance

The number of multi-drug-resistant bacteria has increased over the last few decades, which has caused a detrimental impact on public health worldwide. In resolving antibiotic resistance development among different bacterial communities, new antimicrobial agents and nanoparticle-based strategies need to be designed foreseeing the slow discovery of new functioning antibiotics. Advanced research studies have revealed the significant disinfection potential of two-dimensional nanomaterials (2D NMs) to be severed as effective antibacterial agents due to their unique physicochemical properties. This review covers the current research progress of 2D NMs-based antibacterial strategies based on an inclusive explanation of 2D NMs' impact as antibacterial agents, including a detailed introduction to each possible well-known antibacterial mechanism. The impact of the physicochemical properties of 2D NMs on their antibacterial activities has been deliberated while explaining the toxic effects of 2D NMs and discussing their biomedical significance, dysbiosis, and cellular nanotoxicity. Adding to the challenges, we also discussed the major issues regarding the current quality and availability of nanotoxicity data. However, smart advancements are required to fabricate biocompatible 2D antibacterial NMs and exploit their potential to combat bacterial resistance clinically.

Precisely Controlled Polymerization of Two-Dimensional Conducting Polymers in Quasi-Liquid Layer Enables Ultrahigh Sensing Performance

Gas sensors based on conducting polymers offer great potential for high-performance room temperature applications due to their cost-effectiveness, high-sensitivity, and operational advantage. However, their current performance is limited by the deficiency of control in conventional polymerization methods, leading to poor crystallinity and inconsistent material properties. Here, the quasi-liquid layer (QLL) on the ice surface acts as a self-regulating nano-reactor for precise control of thermodynamics and kinetics in the polymerization, resulting in a 7.62 nm thick two-dimensional (2D) polyaniline (PANI) film matching the QLL thickness. The ultra-thin film optimizes the exposure of active sites, enhancing the detection of analyte gases at low concentrations. It is validated by fabricating a chemiresistive gas sensor with the 2D PANI film, demonstrating stable room-temperature detection of ammonia down to 10 ppt in ambient air with an impressive 10% response. This achievement represents the highest sensitivity among sensors of this kind while maintaining excellent selectivity and repeatability. Moreover, the QLL-controlled polymerization strategy offers an alternative route for precise control of the polymerization process for conducting polymers, enabling the creation of advanced materials with enhanced properties.

In Situ Engineering of Conducting Polymer Nanocomposites at Liquid/Liquid Interfaces: A Perspective on Fundamentals to Technological Significance

The conducting polymers have continuously been hybridized with their counterparts to overcome the intrinsic functional limitations compared to the metallic or inorganic analogs. Remarkably, the liquid/liquid interface-assisted methods represent an efficient and facile route for developing fully tunable metamaterials for various applications. The spontaneous adsorption of nanostructures at a quasi-two-dimensional interface is energetically favorable due to the reduction in interfacial tension, interfacial area, and interfacial energy (Helmholtz free energy). This Perspective highlights the fundamentals of nanostructure adsorption leading to hierarchical architecture generation at the interface from an experimentalist's point of view. Thereafter, the essential applications of the conducting polymer/nanocomposites synthesized at the interface emphasize the capability of the interface to tune functional materials. This Perspective also summarizes the future challenges and the use of the known fundamental aspects in overcoming the functional limitations of polymer/nanomaterial composites and also provides some future research directions.

Self-assembly of random networks of zirconium-doped manganese oxide nanoribbons and poly(3,4-ethylenedioxythiophene) flakes at the water/chloroform interface

Owing to their magnificent chemical and physical properties, transition metal-based heterostructures are potential materials for applications ranging from point-of-care diagnostics to sustainable energy technologies. The cryptomelane-type octahedral molecular sieves (K-OMS-2) are extensively studied porous materials with a hollandite (2 × 2 tunnel of dimensions 4.6 × 4.6 Å2) structure susceptible to the isovalent substitution of metal cations at the framework of MnO6 octahedral chains. Here we report a facile in situ synthesis of framework-level zirconium (Zr)-doped K-OMS-2 nanoribbons in poly(3,4-ethylenedioxythiophene) (PEDOT) nanoflakes at a water/chloroform interface at ambient conditions. An oxidant system of KMnO4 and ZrOCl2·8H2O initiated the polymerisation at temperatures ranging from 5° to 50 °C. The lattice distortions arising from the framework-level substitution of Mn4+ by Zr4+ in the K-OMS-2 structure were evidenced with powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption studies. Transmission electron microscopic and mapping images confirmed that PEDOT/Zr-K-OMS-2 comprises a highly crystalline random network of two-dimensional PEDOT flakes and Zr-doped K-OMS-2 nanoribbons. In this regard, the proposed interfacial strategy affirms an in situ method for the morphological tuning of heterostructures on polymer supports at low temperatures.

Interfacial Tension-Impelled Self-Assembly and Morphology Tuning of Poly(3,4-ethylene dioxythiophene)/Tellurium Nanocomposites at Various Liquid/Liquid Interfaces

Compared to the enormous number of nanostructures that have been documented, the variety of nanostructures produced by organic polymerization is rather limited. We devised an unconventional route and a sustainable approach to distribute tellurium nanoparticles (Te NPs) in a poly(3,4-ethylene dioxythiophene) (PEDOT) matrix to form semiconducting organic-inorganic nanocomposites for potential applications in electrochemical sensing. The adopted strategy of in situ liquid/liquid interface-assisted polymerization aids in the formation of intimately tethered Te NPs on the PEDOT polymer chains, thereby preventing the aggregation of Te NPs. The untapped versatility inherent to using biphasic systems for interfacial polymerization is explored at three interface systems of immiscible solvents: chloroform/water, dichloromethane/water, and hexane/water, giving rise to PEDOT/Te nanocomposite (PTeNC) of distinct morphology. Chemical nature, crystallinity, and morphology investigations proved the successful formation of PTeNC in different interface systems. Consequently, the temporal evolution of interfacial tension in the preferential adsorption of nanoparticles and final product morphology was monitored by pendant drop tensiometry. Owing to the role of morphology, PTeNC synthesized at the hexane/water interface showcased the best electrocatalytic behavior toward nonenzymatic detection of l-ascorbic acid, an essential nutritional factor, and a neuromodulator with a limit of detection of 0.66 μM and excellent sensitivity, selectivity, and reproducibility. Hence, we envision that interface-assisted polymerization offers a nascent and robust strategy for encapsulating unusual electrode materials in polymeric matrices.

Interfacial tension driven adsorption of MnO2 nanoparticles at the liquid/liquid interface to tailor ultra-thin polypyrrole sheets

An emerging aspect of research is designing and developing fully tunable metamaterials for various applications with fluid interfaces. Liquid/liquid interface-assisted methods represent an efficient and facile route for synthesizing two-dimensional (2-D) thin films of potential materials. The underlying mechanism behind thin film formation at the liquid/liquid interface involves the preferential adsorption of nano-sized particles at the interface to minimize high interfacial tension. Here, a water/chloroform interface-assisted method is employed for the one-pot synthesis of highly crystalline polypyrrole/manganese dioxide (PPy/MnO₂) sheets. The temporal evolution in the dynamic interfacial tension (from 32 mN m^-1 to 17 mN m^-1) observed in pendant drop tensiometry proved the preferential adsorption of MnO₂ atttached PPy oligomers at the water/chloroform interface. An ultra-thin sheet-like morphology and uniform distribution of ∼6 nm highly crystalline MnO₂ nanoparticles are evidenced by transmission and atomic force microscopy techniques. The predominance of interfacial polymerization in retaining the electrochemical activity of the PPy/MnO₂ sheets is elucidated for the electrochemical detection of nicotine. This study opens a new avenue for the realization of ultra-thin sheets of polymer-nanomaterial hybrids, enabling applications ranging from new classes of sensors to optics.

Design and Characterization of a Novel ZnO-Ag/Polypyrrole Core-Shell Nanocomposite for Water Bioremediation

Incorporating nanostructured metal and metal oxide in a polymer matrix is a strategic way to develop a novel candidate for water bioremediation. In this study, under microwave irradiation, a ZnO–Ag/polypyrrole (PPy) nanocomposite with a core/shell structure was prepared by interfacial polymerization of pyrrole in the presence of ZnO nanoparticles and AgNO₃ as an oxidant. The antimicrobial behavior of the ZnO–Ag core combined with the electrical properties of the conducting PPy shell created a special ZnO–Ag/PPy nanocomposite with inherent adsorption behavior and antimicrobial properties. More impressively, the as-prepared ZnO–Ag/PPy displayed enhanced adsorption of Cd²⁺ and PO₄³⁻ ions in the mixed solution. At pH 8, it had overall removal efficiencies of 95% and 75% for Cd²⁺and PO₄³⁻ ions, respectively. The Freundlich adsorption model, rather than the Langmuir adsorption model, better fits the adsorption isotherm results. The adsorption kinetics also followed the pseudo-second-order kinetic model. Additionally, the engineered nanocomposite demonstrated antifungal activity against different fungi, as well as remarkable antibacterial activity against Gram-negative and Gram-positive bacteria. The synergistic combination of crystallinity, coherence of the ZnO–Ag core in the PPy matrix, and the negative zeta potential all contribute to this nanocomposite’s high efficiency. Our results have significant consequences in the wastewater bioremediation field using a simple operation process.

Liquid-liquid interfaces: a unique and advantageous environment to prepare and process thin films of complex materials

Thin film technology is pervasive for many fields with high impact in our daily lives, which makes processing materials such as thin films a very important subject in materials science and technology. However, several paramount materials cannot be prepared as thin films through the well-known and consolidated deposition routes, which strongly limits their applicability. This is particularly noticeable for multi-component and complex nanocomposites, which present unique properties due to the synergic effect between the components, but have several limitations to be obtained as thin films, mainly if homogeneity and transparence are required. This review highlights the main advances of a novel approach to both process and synthesize different classes of materials as thin films, based on liquid/liquid interfaces. The so-called liquid/liquid interfacial route (LLIR) allows the deposition of thin films of single- or multi-component materials, easily transferable over any kind of substrate (plastics and flexible substrates included) with precise control of the thickness, homogeneity and transparence. More interesting, it allows the in situ synthesis of multi-component materials directly as thin films stabilized at the liquid/liquid interface, in which problems related to both the synthesis and processing are solved together in a single step. This review presents the basis of the LLIR and several examples of thin films obtained from different classes of materials, such as carbon nanostructures, metal and oxide nanoparticles, two-dimensional materials, organic and organometallic frameworks, and polymer-based nanocomposites, among others. Moreover, specific applications of those films in different technological fields are shown, taking advantage of the specific properties emerging from the unique preparation route.

Interface-assisted synthesis: a gateway to effective nanostructure tuning of conducting polymers

The interface-assisted polymerization technique can be viewed as a powerful emerging tool for the synthesis of conducting polymers (CPs) on a large scale. Contrary to other bulk or single-phase polymerization techniques, interface-assisted synthesis strategies offer effective nanostructure control in a confined two-dimensional (2-D) space. This review focuses on the types of interfaces, mechanism at the interface, advantages and future perspectives of the interfacial polymerization in comparison to conventional polymerization techniques. Hence, the primary focus is on briefing the different types of the chemical methods of polymerization, followed by uniqueness in the reaction dynamics of interface polymerization. The classification of interfaces into four types (liquid/solid, gas/liquid, liquid/liquid, and gas/solid) is based on the versatility and underlying mechanistic pathway of the polymerization of each type. The role of interface in tuning the nanostructure of CPs and the performance evaluation of pristine CPs based on the electrical conductivity are also discussed. Finally, the future outlook of this emerging field is discussed and proposed in detail through some multifunctional applications of synthesized conducting polymers.

n-Butanol/Water Interface-Aided Physicochemical Tuning of Two-Dimensional Transition-Metal Oxides

Herein, we report a facile regulation of the interface of two immiscible solvents, n-butanol and water, to achieve the physicochemical tuning of the transition-metal oxide nickel cobaltite. The crystal nucleation and the growth of nickel cobaltite into distinct morphology are highly dependent on the orientation and the mass transfer of the reactive species through the reactive interface layer. A distinct two-dimensional flakelike (1 nm thickness) nickel cobaltite is formed at the interface of n-butanol/water in a 1:1 solvent ratio. Rather, one-dimensional needles and irregular interconnected networks are achieved, as aqueous and organic counterparts are, respectively, increased. The impact of the solvent ratio on doping metal ions (Co²⁺ and Ni²⁺) at the interstitial sites of fcc spinel structure is evident from the X-ray and electronic absorption investigations. It is presumed that the interface-assisted synthesis may provide a simple and novel way to develop and adopt various transition-metal oxides for wide applications.

Two-dimensional nanomaterials beyond graphene for antibacterial applications: current progress and future perspectives

The marked augment of drug-resistance to traditional antibiotics underlines the crying need for novel replaceable antibacterials. Research advances have revealed the considerable sterilization potential of two-dimension graphene-based nanomaterials. Subsequently, two-dimensional nanomaterials beyond graphene (2D NBG) as novel antibacterials have also demonstrated their power for disinfection due to their unique physicochemical properties and good biocompatibility. Therefore, the exploration of antibacterial mechanisms of 2D NBG is vital to manipulate antibacterials for future applications. Herein, we summarize the recent research progress of 2D NBG-based antibacterial agents, starting with a detailed introduction of the relevant antibacterial mechanisms, including direct contact destruction, oxidative stress, photo-induced antibacterial, control drug/metallic ions releasing, and the multi-mode synergistic antibacterial. Then, the effect of the physicochemical properties of 2D NBG on their antibacterial activities is also discussed. Additionally, a summary of the different kinds of 2D NBG is given, such as transition-metal dichalcogenides/oxides, metal-based compounds, nitride-based nanomaterials, black phosphorus, transition metal carbides, and nitrides. Finally, we rationally analyze the current challenges and new perspectives for future study of more effective antibacterial agents. This review not only can help researchers grasp the current status of 2D NBG antibacterials, but also may catalyze breakthroughs in this fast-growing field.