Arsonic Acid As a Robust Anchor Group for the Surface Modification of Fe₃O₄

In order to use iron oxide nanoparticles (Fe₃O₄) in various applications, a surface modification that provides colloidal stability and additional functionality to the nanoparticles is necessary. For the modification of the nanoparticle surface with ligand molecules, the ligand molecule should contain an anchor group that has a strong affinity for the surface. However, currently used anchor groups have shown some problems such as low affinity and stability as well as reactivity with the surface. In this study, arsonic acid (RAsO­(OH)₂) was investigated as a novel anchor group. It was possible to introduce azide groups on the surface of iron oxide nanoparticles using 4-azidophenylarsonic acid, and the desired functional molecules could be chemically attached to the surface via copper-catalyzed azide–alkyne cycloaddition (click chemistry). By quantifying and comparing the amount of attached anchors on the surface, it was found that arsonic acid displays better affinity than other currently used anchors (catechol, carboxylic acid). Furthermore, we examined the binding reversibility, long–term anchoring stability, and anchoring stability at various pH values. It was revealed that arsonic acid is a stable anchor in various conditions

Variation in Crystalline Phases: Controlling the Selectivity between Silicon and Silicon Carbide via Magnesiothermic Reduction using Silica/Carbon Composites

Magnesiothermic reduction of various types of silica/carbon (SiO₂/C) composites has been frequently used to synthesize silicon/carbon (Si/C) composites and silicon carbide (SiC) materials, which are of great interest in the research areas of lithium-ion batteries (LIBs) and nonmetal oxide ceramics, respectively. Up to now, however, it has not been comprehensively understood how totally different crystal phases of Si or SiC can result from the compositionally identical parent materials (SiO₂/C) via magnesiothermic reduction. In this article, we propose a formation mechanism of Si and SiC by magnesiothermic reduction of SiO₂/C; SiC is formed at the interface between SiO₂ and carbon when silicon intermediates, mainly <i>in situ</i>-formed Mg₂Si, encounter carbon through diffusion. Otherwise, Si is formed, which is supported by an <i>ex situ</i> reaction between Mg₂Si and carbon nanosphere that results in SiC. In addition, the resultant crystalline phase ratio between Si and SiC can be controlled by manipulating the synthesis parameters such as the contact areas between silica and carbon of parent materials, reaction temperatures, heating rates, and amount of the reactant mixtures used. The reasons for the dependence on these synthesis parameters could be attributed to the modulated chance of an encounter between silicon intermediates and carbon, which determines the destination of silicon intermediates, namely, either thermodynamically preferred SiC or kinetic product of Si as a final product. Such a finding was applied to design and synthesize the hollow mesoporous shell (ca. 3–4 nm pore) SiC, which is particularly of interest as a catalyst support under harsh environments

Bioinspired Synthesis of Melaninlike Nanoparticles for Highly N‑Doped Carbons Utilized as Enhanced CO₂ Adsorbents and Efficient Oxygen Reduction Catalysts

Highly N-doped nanoporous carbons have been of great interest as a high uptake CO₂ adsorbent and as an efficient metal-free oxygen reduction reaction (ORR) catalyst. Therefore, it is essential to produce porosity-tunable and highly N-doped carbons through cost-effective means. Herein, we introduce the bioinspired synthesis of a monodisperse and N-enriched melaninlike polymer (MP) resembling the sepia biopolymer (SP) from oceanic cuttlefish. These polymers were subsequently utilized for highly N-doped synthetic carbon (MC) and biomass carbon (SC) spheres. An adequate CO₂ activation process fine-tunes the ultramicroporosity (<1 nm) of N-doped MC and SC spheres, those with maximum ultramicroporosities of which show remarkable CO₂ adsorption capacities. In addition, N-doped MC and SC with ultrahigh surface areas of 2677 and 2506 m²/g, respectively, showed excellent ORR activities with a favored four electron reduction pathway, long-term durability, and better methanol tolerance, comparable to a commercial Pt-based catalyst

Elucidating Relationships between Structural Properties of Nanoporous Carbonaceous Shells and Electrochemical Performances of Si@Carbon Anodes for Lithium-Ion Batteries

The encapsulation of silicon in hollow carbonaceous shells (Si@C) is known to be a successful solution for silicon anodes in Li-ion batteries, resulting in many efforts to manipulate the structural properties of carbonaceous materials to improve their electrochemical performance. In this regard, we demonstrate in this work how both the shell thickness and pore size of nanoporous carbonaceous materials containing silicon anodes influence the electrochemical performance. Structurally well-defined Si@C materials with varying carbon-shell thicknesses and pore sizes were synthesized by a nanocasting method that manipulated the carbon shell and by a subsequent magnesiothermic reduction that converted the amorphous silica cores into silicon nanocrystals. When these materials were employed as anodes, it was verified that two opposite effects occur with respect to the thickness of carbon shell: The weight ratio of silicon and the electrical conductivity are simultaneously affected, so that the best electrochemical performance is not obtained from either the thickest or the thinnest carbon shell. Such countervailing effects were carefully confirmed through a series of electrochemical performance tests and the use of electrochemical impedance spectroscopy. In addition, the effect of pore size was elucidated by comparing Si@C samples with different pore sizes, revealing that larger pores can further improve the electrochemical performance as a result of enhanced Li-ion diffusion

Facile Sol–Gel-Derived Craterlike Dual-Functioning TiO₂ Electron Transport Layer for High-Efficiency Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PSCs) are considered promising materials for low-cost solar energy harvesting technology. An electron transport layer (ETL), which facilitates the extraction of photogenerated electrons and their transport to the electrodes, is a key component in planar PSCs. In this study, a new strategy to concurrently manipulate the electrical and optical properties of ETLs to improve the performance of PSCs is demonstrated. A careful control over the Ti alkoxide-based sol–gel chemistry leads to a craterlike porous/blocking bilayer TiO₂ ETL with relatively uniform surface pores of 220 nm diameter. Additionally, the phase separation promoter added to the precursor solution enables nitrogen doping in the TiO₂ lattice, thus generating oxygen vacancies. The craterlike surface morphology allows for better light transmission because of reduced reflection, and the electrically conductive craterlike bilayer ETL enhances charge extraction and transport. Through these synergetic improvements in both optical and electrical properties, the power conversion efficiency of craterlike bilayer TiO₂ ETL-based PSCs could be increased from 13.7 to 16.0% as compared to conventional dense TiO₂-based PSCs

Investigating Recombination and Charge Carrier Dynamics in a One-Dimensional Nanopillared Perovskite Absorber

Organometal halide perovskite materials have become an exciting research topic as manifested by intense development of thin film solar cells. Although high-performance solar-cell-based planar and mesoscopic configurations have been reported, one-dimensional (1-D) nanostructured perovskite solar cells are rarely investigated despite their expected promising optoelectrical properties, such as enhanced charge transport/extraction. Herein, we have analyzed the 1-D nanostructure effects of organometal halide perovskite (CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i>) on recombination and charge carrier dynamics by utilizing a nanoporous anodized alumina oxide scaffold to fabricate a vertically aligned 1-D nanopillared array with controllable diameters. It was observed that the 1-D perovskite exhibits faster charge transport/extraction characteristics, lower defect density, and lower bulk resistance than the planar counterpart. As the aspect ratio increases in the 1-D structures, in addition, the charge transport/extraction rate is enhanced and the resistance further decreases. However, when the aspect ratio reaches 6.67 (diameter ∼30 nm), the recombination rate is aggravated due to high interface-to-volume ratio-induced defect generation. To obtain the full benefits of 1-D perovskite nanostructuring, our study provides a design rule to choose the appropriate aspect ratio of 1-D perovskite structures for improved photovoltaic and other optoelectrical applications