Ionic Surfactant-Triggered Renewal of the Structures and Properties of Polyelectrolyte Multilayer Films

The present study investigated the effects of ionic surfactants on polyelectrolyte multilayer (PEM) films, consisting of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), prepared using a sequential layer-by-layer (LbL) technique. The electrostatic interaction between sodium dodecyl sulfate (SDS) and the PEMs resulted in desorption of the polyelectrolytes from the PEM films, and consequently the thickness of the PEM films was altered, as confirmed by UV−vis, XPS, and AFM studies. Two critical features of this phenomenon include the porous morphology of the SDS-treated films and the simultaneous increase in the thickness of the film. Furthermore, both the rate and amount of polyelectrolytes desorbed from the PEM films could be controlled by varying the surfactant, the outermost layer, and the reaction time. The surface morphology and thickness of the PEM films could be retuned even after formation of PEMs. Thus, controlled desorption of PEs could be an effective tool for the renewal of the structures and properties of PEMs

Self-Assembly of a Metal–Phenolic Sorbent for Broad-Spectrum Metal Sequestration

Metal contamination of water bodies from industrial effluents presents a global threat to the aquatic ecosystem. To address this challenge, metal sequestration via adsorption onto solid media has been explored extensively. However, existing sorbent systems typically involve energy-intensive syntheses and are applicable to a limited range of metals. Herein, a sorbent system derived from physically cross-linked polyphenolic networks using tannic acid and ZrIV ions has been explored for high-affinity, broad-spectrum metal sequestration. The network formation step (gelation) of the sorbent is complete within 3 min and requires no special apparatus. The key to this system design is the formation of a highly stable coordination network with an optimized metal–ligand ratio (1.2:1), affording access to a major fraction of the chelating sites in tannic acid for capturing diverse metal ions. This system is stable over a pH range of 1–9, thermally stable up to ∼200 °C, and exhibits a negative surface charge (at pH 5). The sorbent system effectively sequesters 28 metals in single- and multielement model wastes, with removal efficiencies exceeding 99%. Furthermore, it is demonstrated that this system can be processed as membrane coatings, thin films, or wet gels to capture metal ions and that both the sorbent and captured metal ions can be regenerated or directly used as composite catalysts

Metal Ion-Enriched Polyelectrolyte Complexes and Their Utilization in Multilayer Assembly and Catalytic Nanocomposite Films

The mixing of Ag ion-doped poly­(ethyleneimine) (PEI) and poly­(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts

Nanoengineering Particles through Template Assembly

The nanoengineering of particles is of interest for both fundamental and applied science. How particles are made substantially affects their properties and quality, and therefore usefulness. Disseminating current understanding of particle engineering can help facilitate the use of existing technologies, as well as guide future developments. Herein, we describe three methods used in our laboratory for the nanoengineering of particles, based on template assembly, and discuss important considerations for each. First, we describe the use of layer-by-layer assembly for depositing multilayered nanofilms on particle surfaces to generate core–shell particles and hollow capsules. Second, we detail the use of mesoporous silica templating for the engineering of porous polymer replica particles. Third, we describe how the coordination of phenolic compounds and metal ions can be used to fabricate thin films via metal–phenolic network formation on particle templates. We provide stepwise, easy-to-follow guides for each method and discuss commonly encountered challenges and obstacles, with considerations for how to alter these protocols to achieve desired particle properties. While we intend for these guides to be easily accessible to researchers new to particle engineering, we believe they can also provide useful insight to experienced researchers working in the field of engineering advanced particles

Nanoengineering Particles through Template Assembly

The nanoengineering of particles is of interest for both fundamental and applied science. How particles are made substantially affects their properties and quality, and therefore usefulness. Disseminating current understanding of particle engineering can help facilitate the use of existing technologies, as well as guide future developments. Herein, we describe three methods used in our laboratory for the nanoengineering of particles, based on template assembly, and discuss important considerations for each. First, we describe the use of layer-by-layer assembly for depositing multilayered nanofilms on particle surfaces to generate core–shell particles and hollow capsules. Second, we detail the use of mesoporous silica templating for the engineering of porous polymer replica particles. Third, we describe how the coordination of phenolic compounds and metal ions can be used to fabricate thin films via metal–phenolic network formation on particle templates. We provide stepwise, easy-to-follow guides for each method and discuss commonly encountered challenges and obstacles, with considerations for how to alter these protocols to achieve desired particle properties. While we intend for these guides to be easily accessible to researchers new to particle engineering, we believe they can also provide useful insight to experienced researchers working in the field of engineering advanced particles

Coordination-Driven Multistep Assembly of Metal–Polyphenol Films and Capsules

We report the assembly of metal-polyphenol complex (MPC) films and capsules through the sequential deposition of iron­(III) ions (Fe^(III)) and a natural polyphenol, tannic acid (TA), driven by metal–ligand coordination. Stable Fe^(III)/TA films and capsules were formed, indicating lateral and longitudinal cross-linking of TA by Fe^(III) in the film structure. Quartz crystal microbalance, ultraviolet–visible (UV-vis) spectrophotometry, and X-ray photoelectron spectroscopy were carried out to quantitatively analyze the film growth. A comparison of the MPC capsules prepared through multistep assembly with those obtained through one-step deposition, as reported previously [Ejima et al., <i>Science</i> <b>2013</b>, <i>341</i>, 154–156], reveals substantial differences in the nature of complexation and in their physicochemical properties, including permeability, stiffness, and degradability. This study highlights the importance of engineering MPC films with different properties through implementing different assembly methods

Interface-Controlled Phase Separation of Liquid Metal-Based Eutectic Ternary Alloys

Liquid metals (LMs) are immiscible in many common electrolytic solutions and, when immersed in them, establish phase boundaries that display intriguing interfacial characteristics. The application of a cathodic potential to such interfaces may trigger phase separation of solute elements out of the LMs. Here, we investigate this possibility in two of the most researched and industrially used eutectic ternary LMs of Galinstan (Ga-In-Sn) and Field’s metal (FM, In–Bi–Sn). We observe that upon surface perturbation by an applied electric potential, solute elements compete to segregate out of the LM alloys according to their energy levels. The nature of the electrolytic solutions plays a key role in the separation process as they dictate whether solute metals are expelled selectively in their pure form or as binary compounds. For example, in a phosphate-based aqueous electrolyte, nano-sized Sn-based entities are selectively expelled from Galinstan, while only Bi-based structures leave the surface of FM. In contrast, in a non-aqueous electrolyte, nano-sized binary compounds of Sn–In and Bi–Sn are separated from the surfaces of Galinstan and FM, respectively. We show that selectivity in the surface separation process, achieved by the alteration of the electrolytic solutions, is due to the interplay between the electrodynamic interactions and the electrocapillary effect. This study presents two key findings: (a) it is essential to carefully consider the possibility of component separation in electrochemical systems based on LMs and (b) it demonstrates interfacial metallurgical pathways to process alloys for refining metals into specific purities, component ratios, and dimensions

Insights into the Interfacial Contact and Charge Transport of Gas-Sensing Liquid Metal Marbles

Understanding the interfacial contacts between liquid metals and substrate materials is becoming increasingly important for the fast-rising liquid metal-enabled technologies. However, for such technologies, probing the contact behavior and interfacial charge transport has remained challenging due to the deformable nature of liquid metals and the presence of the surface oxide layer. Here, we encapsulate eutectic gallium indium (EGaIn) micro-/nanodroplets with tungsten trioxide (WO3) nanoparticles to form a WO3/EGaIn liquid metal marble network, in which the interfacial contact of the intrinsically semiconducting WO3 governs the charge transport. We investigate the interfacial structures and charge transport characteristics under different contact conditions and various gaseous environments. The results suggest that establishing a WO3/EGaIn heterostructure leads to near-ohmic contact behaviors and also the emergence of localized surface plasmon resonance. Density functional theory calculations of the WO3/EGaIn interface support the experiments by revealing atomistic attractions between EGaIn alloy and the O atoms from WO3, resulting in a Fermi level shift. We also show that the efficient interfacial charge transport of the liquid metal marble network results in an enhanced gas-sensing response. This work paves the way for the possibility of studying other liquid metal/semiconductor contacts for applications in soft electronics and optics

Passivation-Free, Liquid-Metal-Based Electrosynthesis of Aluminum Metal–Organic Frameworks Mediated by Light Metal Activation

The production of aluminum (Al) metal–organic frameworks (MOFs) by electrosynthesis using solid-state Al electrodes always faces significant challenges due to the formation of a passivating aluminum oxide layer in the process. Here, we developed a liquid-metal-based method to electrosynthesize an aluminum Al-MOF (MIL-53). This method uses a liquid-state gallium (Ga) anode as a reservoir and activator for a light metal, Al, in the form of Al-Ga alloys that releases Al3+ for the electrosynthesis of Al-MOFs. Introducing Ga into the system inhibits the formation of aluminum oxide passivation layer and promotes the electrochemical reaction for Al-MOF synthesis. The electrosynthesis using liquid Al-Ga alloy is conducted at ambient temperatures for long durations without requiring pretreatment for aluminum oxide removal. We show that the Al-MOF products synthesized from 0.40 wt % Al in liquid Ga lead to the highest crystallinity and possess a specific surface area greater than 800 m2 g–1 and a low capacity for CO2 adsorption that can be used as a potential matrix for CO2/N2 separation. This work provides evidence that employing liquid-metal electrodes offers a viable pathway to circumvent surface passivation effects that inevitably occur when using conventional solid metals. It also introduces an efficient electrosynthesis method based on liquid metals for producing atomically porous materials

Surface-Confined Amorphous Films from Metal-Coordinated Simple Phenolic Ligands

Coordination chemistry of natural polyphenols and transition metals allows rapid self-assembly of conformal coatings on diverse substrates. Herein, we report that this coordination-driven self-assembly process applies to simple phenolic molecules with monotopic or ditopic chelating sites (as opposed to macromolecular, multitopic polyphenols), leading to surface-confined amorphous films upon metal coordination. Films fabricated from gallic acid, pyrogallol, and pyrocatechol, which are the major monomeric building blocks of polyphenols, have been studied in detail. Pyrocatechol, with one vicinal diol group (i.e., bidentate), has been observed to be the limiting case for such assembly. This study expands the toolbox of available phenolic ligands for the formation of surface-confined amorphous films, which may find application in catalysis, energy, optoelectronics, and the biomedical sciences