Electrochemical conversion of CO2 to fuels and chemicals as a sustainable solution for waste transformation has garnered tremendous interest to combat the fervent issue of the prevailing high atmospheric CO2 concentration while contributing to the generation of sustainable energy. Monometallic palladium (Pd) has been shown promising in electrochemical CO2 reduction, producing formate or CO depending on applied potentials. Recently, bimetallic Pd-based materials strived to fine-tune the binding affinity of key intermediates is a prominent strategy for the desired product formation from CO2 reduction. Herein, the recent emerging trends on bimetallic Pd-based electrocatalysts are reviewed, including fundamentals of CO2 electroreduction and material engineering of bimetallic Pd-electrocatalysts categorized by primary products. Modern analytical techniques on these novel electrocatalysts are also thoroughly studied to get insights into reaction mechanisms. Lastly, we deliberate over the challenges and prospects for Pd-based catalysts for electrochemical CO2 conversion.

Hypothesis Chemically or physically distinct patches can be induced on the micelles of amphiphilic block copolymers, which facilitate directional binding for the creation of hierarchical structures. Hence, control over the direction of patches on the micelles is a crucial factor to attain the directionality on the interactions between the micelles, particularly for generating colloidal molecules mimicking the symmetry of molecular structures. We hypothesized that direction and combination of the patches could be controlled by physical confinement of the micelles. Experiments We first confined spherical micelles of diblock copolymers in topographic templates fabricated from nanopatterns of block copolymers by adjusting the coating conditions. Then, patch formation was conducted on the confined micelles by exposing them with a core-favorable solvent. Microscopic techniques of SEM, TEM, and AFM were employed to investigate directions of patches and structures of combined micelles in the template. Findings The orientation of the patches on the micelles was guided by the physical confinement of the micelles in linear trenches. In addition, by confining the micelles in a circular hole, we obtained a specific polygon arrangement of the micelles depending on the number of micelles in the hole, which enabled the formation of cyclic colloidal molecules consisting of micelles.

Precise control of the width and length of one-dimensional (1D) semiconducting nanostructures is a topic of attention owing to the potential applications of such nanostructures in optoelectronics. However, regulating both the length and width of the 1D nanostructures using conjugated polymers or block copolymers is a significant challenge. To solve this problem, we synthesized a unique conjugated polyacetylene homopolymer via living cyclopolymerization, which spontaneously formed 1D nanoribbons via in situ nanoparticlization. Interestingly, their widths could be controlled from 11 to 42 nm, which is directly proportional to their degree of polymerization. Furthermore, a self-seeding technique via crystallization-driven self-assembly (CDSA) was adopted to control the length of the nanoribbons up to 2.3 μm with narrow distributions. Interestingly, adding a block copolymer unimer to these nanoribbons produced triblock comicelles by the living CDSA mechanism. The nanoribbons were visualized directly by super-resolution optical fluorescence microscopy. The proposed approach allows us to tune the length and width of 1D nanoribbons up to a certain degree.

Despite the remarkable breakthroughs in the catalyst-transfer polymerization (CTP) technology in the precision synthesis of conjugated polymers, modulating the monomer reactivity is still challenging. We report that, by boronate tuning, we can modulate the rate of the Suzuki–Miyaura CTP (SCTP) of 3-hexylthiophene with high control. First, cyclic boronate esters showed different polymerization rates depending on their diol subunit structure. Additionally, the rates of the N-coordinated boronates were differentiated by tuning their O- or N-substituents. Notably, the origin of the difference in reactivity could be explained by the N → B bond lengths. The detailed structural analysis of the resulting polymers by 1H nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometry showed that the slower and more stable boronate monomers were less prone to homocoupling and protodeboronation, thereby producing poly(3-hexylthiophene) (P3HT) with higher control (i.e., molecular weight, dispersity, end-group fidelity, and yield). By rational optimizations to suppress homocoupling and protodeboronation, well-defined P3HT were prepared at various monomer-to-initiator ratios (M/I ratios).

Surging interests in point-of-care diagnostics have led to the development of many lightweight and cost-effective paper-based sensors. Particularly, sensors using colorimetric readouts are considered highly advantageous because no additional detector or device is required for signal display. Herein, we introduce an electrochemically operated colorimetric sensor that can compensate for the disadvantages of traditional colorimetry, hence enhancing response time, reusability and color uniformity. On a single paper substrate, carbon/graphite paste was screen printed to form the working and counter electrodes, and Ag/AgCl ink was applied for the reference electrode. Prussian blue and Glucose oxidase were employed on the one of the carbon electrodes for the detection of analytes, hydrogen peroxide and glucose. For the colorimetric readout, indium tin oxide nanoparticles and polyaniline were consecutively introduced on the other carbon electrode, which is used as the counter electrode. The color change of electrochromic polyaniline could be clearly observed, and its application as a colorimetric sensor was demonstrated by the quantitative analyses of hydrogen peroxide and glucose. This paper-based electrochromic glucose sensor showed a short response time of 30 s and exhibited a detection limit of 126 μM for glucose. Along with its rapid and easy detection by incorporating the merits of electrochemical sensing and colorimetry, the paper-based electrochromic sensor could potentially contribute to the development of point-of-care devices by combination with portable power sources.

The spiral shape of intestinal pathogen Campylobacter jejuni is critical for invasion of intestinal mucosa epithelial cells. Insofar as this cell morphology plays a role in the pathology of C. jejuni infection, its restructuring by pharmacological intervention could be an unexplored means to prevention of infection. We recently described that peptidoglycan hydrolase 3 (Pgp3) is involved in the spiral-shape formation of C. jejuni. We report herein the design and synthesis of the hydroxamate-based inhibitors targeting Pgp3. C. jejuni cells exposed to these inhibitors changed from the helical- to rod-shaped morphology, comparable to the case of the pgp3-deletion mutant. Evidence for the mechanism of action was provided by crystal structures of Pgp3 in complex with inhibitors, shedding light into the binding modes of inhibitors within the active site, supported by kinetics and molecular-dynamics simulations. C. jejuni exposed to these inhibitors underwent the morphological change from helical- to rod-shaped bacteria, an event that reduce the ability for invasion of the host cells. This proof of concept suggests that alteration of morphology affects the interference with the bacterial infection.

Recently, there have been urgent demands for decentralized, point-of-care (POC) diagnostics for digital healthcare, telemedicine, and individual self-assessment. A chemosensor producing electrochemiluminescence (ECL) upon molecular recognition is distinctly advantageous as it offers sensitive target signals without the need for bulky instrumentation and highly trained personnel. Herein, we report an Ir(III)-based chemosensor (1) that selectively generates ECL signal only at the content of glutathione (GSH) among various interferences. Our sensing strategy is based on the binding stability between the 1 and GSH. 1 possesses the terpyridine-Cu(II) branch as a recognition unit undergoing complexation reaction by various biothiols in human serum. The binding motif of 1 is structurally less selective and weak to be easily broken by dissolved oxygen. However, 1 exhibits long-lasting stability only with GSH enabling quantitative chemosensing for GSH. Time-resolved fluorescent assay along with the NMR and mass spectrometry study reveals that GSH permits the stable complexation with 1. The ECL approach additionally provides high detection sensitivity and selectivity towards GSH, which is challenging in fluorescence assay. Various coreactant ECLs, including oxalate (C2O42-), tri-n-propylamine (TPA), and peroxydisulfate (S2O82-), were investigated to find optimal conditions for the ECL chemosensing. After 15 min incubation in a 40 μL deproteinized serum sample, 1 successfully reports the GSH content by yielding an efficient ECL signal in a compact, homemade ECL device. The ECL “turn-on” signal provides a linear correlation only to the GSH level, which is 0–25 μM under a detection limit of 1.47 μM.

The encoding of information by defining the sequence of monomers is a highly anticipated strategy for controlling the three-dimensional structures of polymers via information-driven chain folding and self-assembly. In this paper, we report the controlled chain folding of stereoblock poly(lactic acid)s (PLAs) composed of two oligo(lactic acid) domains, [DLAn] and [LLAn], constructed by using precisely defined numbers of d- and l-lactic acids, respectively. Under the crystallization-driven self-assembly (CDSA) condition, block copolymers (BCPs) of stereoblock PLA and poly(ethylene glycol) formed planar nanostructures having unilamellar crystalline cores of stereoblock PLA. [DLAn]-[LLAn] stereoblocks were folded predominantly by intramolecular stereocomplexation (SCN) in dilute solutions in which the intermolecular interaction between BCPs was suppressed. The thickness of the planar nanostructures was precisely defined by the number of repeating units constituted of [DLAn] and [LLAn] domains. The convergent synthesis of PLA permitted the addition of a single monomer unit between the [DLAn] and [LLAn] domains, resulting in the introduction of a desired functional group at the apex of the folded chain. Our results demonstrate that information encoded in the form of a monomer sequence may shape the polymer chain and guide its self-assembly toward specific nanostructures having the desired dimensions and functions.

Catalytic methylation utilising methanol as a sustainable C1 building block and hydrogen source continues to attract attention due to its atom-economical, cost-effective, and simple one-pot method. So far, research on heterogeneous systems has been limited to noble monometallic catalysts such as Ir, Pd, and Pt. A bimetallic catalyst containing a non-noble metal can be an ideal tool to modulate the reactivity and economic feasibility. Reported herein is a bimetallic PdCu–Fe3O4 nanoparticle (NP) catalyst for the selective N-methylation of aniline with methanol as a carbon source in the presence of K2CO3 via a “hydrogen-borrowing strategy”. The PdCu alloy showed synergistic catalytic activity, superior to monometallic Pd and Cu catalysts. The best catalytic activity for N-methylation of aniline was achieved when the Pd/Cu metal ratio was 1 : 0.6 and on an Fe3O4 support. To explain the details of the synergistic effect according to the metal composition, we investigated the electronic properties of the catalytic surface of PdxCuy on Fe3O4 NPs through the density functional theory (DFT). DFT calculation and kinetic studies successfully delineated the catalytic activities of N-methylation depending on varying Pd/Cu ratios. Highly efficient monomethylation of a wide range of aromatic amines was possible using the optimally chosen Pd1Cu0.6 catalyst. Furthermore, the catalyst could be recycled and reused owing to the magnetic nature of the Fe3O4 support.

Precise size control of semiconducting nanomaterials from polymers is crucial for optoelectronic applications, but the low solubility of conjugated polymers makes this challenging. Herein, we prepared length-controlled semiconducting one-dimensional (1D) nanoparticles by synchronous self-assembly during polymerization. First, we succeeded in unprecedented living polymerization of highly soluble conjugated poly(3,4-dihexylthiophene). Then, block copolymerization of poly(3,4-dihexylthiophene)-block-polythiophene spontaneously produced narrow-dispersed 1D nanoparticles with lengths from 15 to 282 nm according to the size of a crystalline polythiophene core. The key factors for high efficiency and length control are a highly solubilizing shell and slow polymerization of the core, thereby favoring nucleation elongation over isodesmic growth. Combining kinetics and high-resolution imaging analyses, we propose a unique mechanism called crystallization-driven in situ nanoparticlization of conjugated polymers (CD-INCP) where spontaneous nucleation creates seeds, followed by seeded growth in units of micelles. Also, we achieved “living” CD-INCP through a chain-extension experiment. We further simplified CD-INCP by adding both monomers together in one-shot copolymerization but still producing length-controlled nanoparticles.