Semiconducting Polymer Interfaces for Electrochemically Assisted Mercury Remediation

Self-Standing Biohybrid Xerogels Incorporating Nanotubular Clays for Sustainable Removal of Pollutants

In this work, it is reported a scalable and systematic protocol for the preparation of xerogels based on the use of green, highly available, and low-cost materials, i.e. halloysite nanoclay and chitosan, without the need for any expensive equipment or operational/energetic demands. Starting from colloidal dispersions, rheological studies demonstrate the formation of hydrogels with zero-shear viscosities enhanced by ≈9 orders of magnitude and higher storage moduli. Hence, the corresponding self-standing xerogels are prepared by a simple solvent casting method and their properties depend on the concentration of halloysite, possessing enhanced thermal stability and outstanding mechanical performances (elastic modulus and ultimate elongation of 165 MPa and 43%, respectively). The resulting biohybrid materials can be exploited for environmental remediation. High removal efficiencies are reached for the capture of organic molecules from aqueous media and the CO2 capture from the atmosphere is also investigated. Most importantly, the presence of an inorganic skeleton within the xerogels prevents the structure from collapsing upon drying and it allows for the control over their morphology and shape. Therefore, taking advantage of the overall features, the designed xerogels offer an attractive strategy for sustainably tackling pollution and for environmental remediation in a plethora of different domains.

Unraveling the Role of Solvation and Ion Valency on Redox-Mediated Electrosorption through In Situ Neutron Reflectometry and Ab Initio Molecular Dynamics

Solvation and ion valency effects on selectivity of metal oxyanions at redox-polymer interfaces are explored through in situ spatial-temporally resolved neutron reflectometry combined with large scale ab initio molecular dynamics. The selectivity of ReO4- vs MoO42- for two redox-metallopolymers, poly(vinyl ferrocene) (PVFc) and poly(3-ferrocenylpropyl methacrylamide) (PFPMAm) is evaluated. PVFc has a higher Re/Mo separation factor compared to PFPMAm at 0.6 V vs Ag/AgCl. In situ techniques show that both PVFc and PFPMAm swell in the presence of ReO4- (having higher solvation with PFPMAm), but do not swell in contact with MoO42-. Ab initio molecular simulations suggest that MoO42- maintains a well-defined double solvation shell compared to ReO4-. The more loosely solvated anion (ReO4-) is preferably adsorbed by the more hydrophobic redox polymer (PVFc), and electrostatic cross-linking driven by divalent anionic interactions could impair film swelling. Thus, the in-depth understanding of selectivity mechanisms can accelerate the design of ion-selective redox-mediated separation systems for transition metal recovery and recycling.

The key role of unsaturated olefin content on polysulfides prepared via inverse vulcanization of waste plant oils for mercury removal from wastewater

Three waste plant oils (olive oil, coconut oil, and soybean oil) were utilized as monomer crosslinking agents to synthesize polysulfides by inverse vulcanization with elemental sulfur, for mercury removal from wastewater. NMR analysis showed that 92.1% of the olefins participated in the inverse vulcanization reaction, indicating that the quantity of unsaturated olefins in plant oil mainly affects the ring-opening ratio of sulfur for the formation of sulfur-based polymers. The experimental results showed that olive oil polysulfide (S-r-olive) achieved 100% Hg2+ removal within 2 h at a pH of 6. The S-r-olive, S-r-soybean, and S-r-coconut exhibited adsorption capacities of 130.23, 42.72, and 28.08 mg/g, respectively. The kinetic and adsorption isotherm illustrated that the Hg2+ adsorption by polysulfides conformed to the pseudo-second-order and Freundlich models, showing that the reaction rate constant of S-r-olive is approximately 14 times and 4.6 times greater than that of S-r-soybean and S-r-coconut, respectively. The adsorption mechanism is concluded that Hg2+ first enters the suspended S-r-olive by physical adsorption, then combined with sulfur to form HgS by chemical action and fixed in the S-r-olive adsorbent. This study demonstrates that utilizing waste plant oils as monomer crosslinking agents to synthesize adsorbents for Hg2+ removal is feasible and effective.

Molecularly Selective Polymer Interfaces for Electrochemical Separations

The molecular design of polymer interfaces has been key for advancing electrochemical separation processes. Precise control of molecular interactions at electrochemical interfaces has enabled the removal or recovery of charged species with enhanced selectivity, capacity, and stability. In this Perspective, we provide an overview of recent developments in polymer interfaces applied to liquid-phase electrochemical separations, with a focus on their role as electrosorbents as well as membranes in electrodialysis systems. In particular, we delve into both the single-site and macromolecular design of redox polymers and their use in heterogeneous electrochemical separation platforms. We highlight the significance of incorporating both redox-active and non-redox-active moieties to tune binding toward ever more challenging separations, including structurally similar species and even isomers. Furthermore, we discuss recent advances in the development of selective ion-exchange membranes for electrodialysis and the critical need to control the physicochemical properties of the polymer. Finally, we share perspectives on the challenges and opportunities in electrochemical separations, ranging from the need for a comprehensive understanding of binding mechanisms to the continued innovation of electrochemical architectures for polymer electrodes.

Spark Discharge Synthesis and Characterization of Ge/Sn Janus Nanoparticles

Germanium-tin nanoparticles are promising materials for near- and mid-infrared photonics thanks to their tunable optical properties and compatibility with silicon technology. This work proposes modifying the spark discharge method to produce Ge/Sn aerosol nanoparticles during the simultaneous erosion of germanium and tin electrodes. Since tin and germanium have a significant difference in the potential for electrical erosion, an electrical circuit damped for one period was developed to ensure the synthesis of Ge/Sn nanoparticles consisting of independent germanium and tin crystals of different sizes, with the ratio of the atomic fraction of tin to germanium varying from 0.08 ± 0.03 to 0.24 ± 0.07. We investigated the elemental and phase composition, size, morphology, and Raman and absorbance spectra of the nanoparticles synthesized under different inter-electrode gap voltages and the presence of additional thermal treatment directly in a gas flow at 750 °C. The research shows that the in-flow thermal treatment of aerosol-agglomerated nanoparticles produced special individual bicrystalline Janus Ge/Sn nanoparticles with an average size of 27 nm and a decreasing absorption function with a changing slope at 700 nm.

Electrochemical recycling of homogeneous catalysts

Homogeneous catalysts have rapid kinetics and keen reaction selectivity. However, their widespread use for industrial catalysis has remained limited because of challenges in reusability. Here, we propose a redox-mediated electrochemical approach for catalyst recycling using metallopolymer-functionalized electrodes for binding and release. The redox platform was investigated for the separation of key platinum and palladium homogeneous catalysts used in organic synthesis and industrial chemical manufacturing. Noble metal catalysts for hydrosilylation, silane etherification, Suzuki cross-coupling, and Wacker oxidation were recycled electrochemically. The redox electrodes demonstrated high sorption uptake for platinum-based catalysts (Q_max up to 200 milligrams of platinum per gram of adsorbent) from product mixtures, with up to 99.5% recovery, while retaining full catalytic activity over multiple cycles. The combination of mechanistic studies and electronic structure calculations indicate that selective interactions with anionic intermediates during the catalytic cycle played a key role in the separations. Last, continuous flow cell studies support the scalability and favorable technoeconomics of electrochemical recycling.

Mechanistic Study of Controlled Zinc Electrodeposition Behaviors Facilitated by Nanoscale Electrolyte Additives at the Electrode Interface

Nanoparticle organic hybrid materials (NOHMs) are liquid-like materials composed of an inorganic core to which a polymeric canopy is ionically tethered. NOHMs have unique properties including negligible vapor pressure, high oxidative thermal stability, and the ability to bind to reactive species of interest due to the tunability of their polymeric canopy. This makes them promising multifunctional materials for a wide range of energy and environmental technologies, including electrolyte additives for electrochemical energy storage (e.g., flow batteries) and the electrochemical conversion of CO₂ to chemicals and fuels. Due to their unique transport behaviors in fluid systems, an understanding of the near-electrode surface behavior of NOHMs in electrolyte solutions and their effect on electrochemical reactions is still lacking. In this work, the complexation of zinc (Zn) by NOHMs with an ionically tethered polyetheramine canopy (HPE) (NOHM-I-HPE) was studied using attenuated total reflectance Fourier transform infrared and Carbon-13 nuclear magnetic resonance spectroscopy. Additionally, various electrochemical techniques were employed to discern the role of NOHM-I-HPE during zinc electrodeposition, and the results were compared to those of the electrochemical system containing untethered HPE polymers. Our findings confirmed that NOHM-I-HPE and HPE reversibly complex zinc in the aqueous electrolyte. NOHM-I-HPE and HPE were found to block some of the electrode active sites, reducing the overall current density during electrodeposition, while facilitating the formation of smooth zinc deposits, as revealed by surface imaging and diffraction techniques. Observed variations in the current density responses and the degree of passivation created by the NOHM-I-HPE and HPE adsorbed on the electrode surface revealed that their different packing behaviors at the electrode-electrolyte interface influence the zinc deposition mechanism. The presence of the nanoparticle and ordering offered by the NOHMs as well as the structured conformation of the polymeric canopy allowed the formation of void spaces and free volumes for enhanced transport behaviors. These findings provided insights into how structured electrolyte additives such as NOHMs can allow for advancements in electrolyte design for controlled deposition of metal species from energy-dense electrolytes or for other electrochemical reactions.

Simultaneous Separation and Recovery of Gold and Copper from Electronic Waste Enabled by an Asymmetric Electrochemical System

Exploiting efficient strategies for the selective separation and extraction of valuable metals from e-waste is in urgent demand to offset the ever-increasing depletion of metal resources, satisfy the sustainable supply of metal resources, and reduce the environmental impact from toxic metals. Herein, an asymmetric electrochemical system, constructed by polyaniline (PANI) nanofibers grown on carbon cloth (CC) and CC as the respective counter and working electrodes, is presented for the simultaneous and selective extraction of gold and copper from e-waste leachate solution. Harnessing the established CC/PANI//CC system, CC/PANI as the anode electrode is capable of selectively and rapidly extracting gold with high efficiency, accompanied by excellent reusability. Meanwhile, cathodic CC electrode is found to achieve almost 100% recovery of copper at a voltage of -1.2 V. Furthermore, the feasibility of the proposed asymmetric electrochemical system is further exemplified in waste central processing unit (CPU) leaching solution, enabling to recover simultaneously gold and copper with high purity. This work will provide meaningful guidance for simultaneous separation and recovery of multiple valuable metals from real e-waste.

Electrosorption of cadmium ions in aqueous solutions using a copper-gallate metal-organic framework

Recently, there is a recognized need for green technologies for the effective decontamination of toxic heavy metal ions in wastewater. This study demonstrates the electrochemically assisted uptake and release of cadmium ions (Cd²⁺) using a redox-active Cu-based metal-organic framework (MOF) electrode. Copper gallate (CuGA), which was synthesized in an aqueous solution, is a water-stable and cost-effective MOF adsorbent in which naturally abundant gallic acid is used as a linker. This work utilized copper within the CuGA structure as a redox center to attract Cd²⁺ by means of Cu²⁺/Cu⁺ reduction, exhibiting rapid uptake kinetics and a much higher capacity (>60 mg g^-1) compared to the case without electrochemical assistance (~15 mg g^-1). In addition, by applying an opposite overpotential to induce the re-oxidation of copper, the facile recovery of Cd²⁺ and the regeneration of the electrode were possible without regenerants. Physicochemical characterizations including XPS were conducted to investigate the chemical oxidation states and stability of the electrode after the effective electrosorption-regeneration process. This work presents the feasibility of a Cu-based MOF electrode as a reusable platform for the efficient removal of Cd²⁺, supporting the continued discovery and development of new Faradaic electrodes for electrochemical wastewater treatments.

Au nanoclusters-decorated WO3 nanorods for ultrasensitive photoelectrochemical sensing of Hg2+

Ultrasensitive photoelectrochemical sensing of Hg2+ is achieved using Au nanocluster-decorated WO3 nanorods as photoactive materials.

Electrochemical approaches for selective recovery of critical elements in hydrometallurgical processes of complex feedstocks

Critical minerals are essential for the ever-increasing urban and industrial activities in modern society. The shift to cost-efficient and ecofriendly urban mining can be an avenue to replace the traditional linear flow of virgin-mined materials. Electrochemical separation technologies provide a sustainable approach to metal recovery, through possible integration with renewable energy, the minimization of external chemical input, as well as reducing secondary pollution. In this review, recent advances in electrochemically mediated technologies for metal recovery are discussed, with a focus on rare earth elements and other key critical materials for the modern circular economy. Given the extreme heterogeneity of hydrometallurgically-derived media of complex feedstocks, we focus on the nature of molecular selectivity in various electrochemically assisted recovery techniques. Finally, we provide a perspective on the challenges and opportunities for process intensification in critical materials recycling, especially through combining electrochemical and hydrometallurgical separation steps.