Simulating the redox potentials of unexplored phenazine derivatives as electron mediators for biofuel cells

In this research, we aimed to establish a guideline for designing electron mediators suitable for biofuel cells. A redox potential simulator was fabricated by combining density functional theory calculation and experiment, allowing us to select molecules with appropriate redox potentials efficiently. Previously, mediators have been developed depending on the trials and errors; thus, our strategy will speed up the development of biofuel cells with outstanding performances

Structural Optimization of Alkylbenzenes as Graphene Dispersants

Among the several methods of producing graphene, the liquid-phase exfoliation of graphite is attractive because of a simple and easy procedure, being expected for mass production. The dispersibility of graphene can be improved by adding a dispersant molecule that interacts with graphene, but the appropriate molecular design has not been proposed. In this study, we focused on aromatic compounds with alkyl chains as dispersing agents. We synthesized a series of alkyl aromatic compounds and evaluated their performance as a dispersant for graphene. The results suggest that the alkyl chain length and solubility in the solvent play a vital role in graphene dispersion

Bipolar anodic electrochemical exfoliation of graphite powders

The electrochemical exfoliation of graphite has attracted considerable attention as a method for large-scale, rapid production of graphene and graphene oxide (GO). As exfoliation typically requires direct electrical contact, and is limited by the shape and/or size of the starting graphite, treatment of small graphite particles and powders, the typical form available commercially, is extremely difficult. In this study, GO nanosheets were successfully prepared from small graphite particles and powders by a bipolar electrochemical process. Graphite samples were placed between two platinum feeder electrodes, and a constant current was applied between the feeder electrodes using dilute sulfuric acid as the electrolyte. Optical microscopy, atomic force microscopy, X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy were employed to examine the samples obtained after electrolysis. The results obtained from these analyses confirmed that anodic electrochemical exfoliation occurs in the graphite samples, and the exfoliated samples are basically highly crystalline GO nanosheets with a low degree of oxidation (C/O = 3.6–5.3). This simple electrochemical method is extremely useful for preparing large amounts of graphene and GO from small particles of graphite

Stacking order reduction in multilayer graphene by inserting nanospacers

Toward macroscopic applications of graphene, it is desirable to preserve the superior properties of single-layer graphene in bulk scale. However, the AB-stacking structure is thermodynamically favored for multilayer graphene and causes strong interlayer interactions, resulting in property degradation. A promising approach to prevent the strong interlayer interaction is the staking order reduction of graphene, where the graphene layers are rotated in-plane to form a randomly stacking structure. In this study, we propose a strategy to effectively decrease the stacking order of multilayer graphene by incorporating nanospacers, cellulose nanofibers, or nano-diamonds (NDs) in the formation process of porous graphene sponges. We conducted an ultrahigh temperature treatment at 1500 °C with ethanol vapor for the reduction and structural repair of graphene oxide sponges with different concentrations of the nanospacers. Raman spectroscopy indicated an obvious increase in the random-stacking fraction of graphene by adding the nanospacers. The x-ray diffraction (XRD) analysis revealed that a small amount of the nanospacers induced a remarkable decrease in ordered graphene crystalline size in the stacking direction. It was also confirmed that a layer-number increase during the thermal treatment was suppressed by the nanospacers. The increase in the random-stacking fraction is attributed to the efficient formation of randomly rotated graphene through the ethanol-mediated structural restoration of relatively thin layers induced by the nanospacers. This stacking-order-reduced graphene with bulk scale is expected to be used in macroscopic applications, such as electrode materials and wearable devices.Zizhao Xu, Taiki Inoue, Yuta Nishina, and Yoshihiro Kobayashi, "Stacking order reduction in multilayer graphene by inserting nanospacers", Journal of Applied Physics 132, 174305 (2022) https://doi.org/10.1063/5.010382

Adsorption enhancement of nitrogen gas by atomically heterogeneous nanospace of boron nitride

In this study, porous boron nitride (p-BN) with hexagonal phase boron nitride (h-BN) pore walls was synthesized using high-temperature calcination. Negligible variation in pore-wall structure can be observed in powder X-ray diffraction (XRD) profiles and infrared (IR) spectra. However, a highly stable p-BN with a stable pore structure even at 973 K under the oxidative conditions is obtained when synthesized at higher than 1573 K under nitrogen gas flow. For p-BN, this stability is obtained by generating h-BN microcrystals. Nitrogen adsorption–desorption isotherms at 77 K provide type-IV features and typical adsorption–desorption hysteresis, which suggests micropore and mesopore formation. Moreover, adsorption–desorption isotherms of Ar at 87 K are measured and compared with those of nitrogen. The relative adsorbed amount of nitrogen (i.e., the amount of nitrogen normalized by that of Ar at each relative pressure or adsorption potential value) on p-BN is considerably larger than that on microporous carbon at low-pressure regions, which suggests the existence of strong adsorption sites on the p-BN surface. In fact, the relative number of adsorbed nitrogen molecules to that of Ar on p-BN is, at most, 150%–200% larger than that on microporous carbon for the same adsorption potential state. Furthermore, additional adsorption enhancement to nitrogen between P/P0 = 10−5 and 10−3 can be observed for p-BN treated at 1673 K, which suggests the uniformly adsorbed layer formation of nitrogen molecules in the vicinity of a basal planar surface. Thus, unlike typical nanoporous sp2 carbons, p-BN materials have the potential to enhance adsorption for certain gas species because of their unique surface state

Synergic effect of graphene oxide and boron nitride on the mechanical properties of polyimide composite films

The addition of two-dimensional (2D) materials into polymers can improve their mechanical properties. In particular, graphene oxide (GO) and hexagonal boron nitride (h-BN) are expected to be potential nanoplatelet additives for polymers. Interactions between such nanoplatelets and polymers are effective in improving the above properties. However, no report has investigated the effect of using two types of nanoplatelets that have good interaction with polymers. In this study, we fabricated polyimide (PI) films that contain two types of nanoplatelets, amine-functionalized h-BN (BNNH2) and GO. We have elucidated that the critical ratio and the content of BNNH2 and GO within PI govern the films' mechanical properties. When the BNNH2/GO weight ratio was 52 : 1 and their content was 1 wt% in the PI film, the tensile modulus and tensile strength were increased by 155.2 MPa and 4.2 GPa compared with the pristine PI film

Non-enzymatic detection of glucose levels in human blood plasma by a graphene oxide-modified organic transistor sensor

We herein report an organic transistor functionalized with a phenylboronic acid derivative and graphene oxide for the quantification of plasma glucose levels, which has been achieved by the minimization of interferent effects derived from physical protein adsorption on the detection electrode

Size, polyglycerol grafting, and net surface charge of iron oxide nanoparticles determine their interaction and toxicity in Caenorhabditis elegans

The widespread application of engineered nanoparticles (NPs) in environmental remediation has raised public concerns about their toxicity to aquatic organisms. Although appropriate surface modification can mitigate the ecotoxicity of NPs, the lack of polymer coating to inhibit toxicity completely and the insufficient knowledge about charge effect hinder the development of safe nanomaterials. Herein, we explored the potential of polyglycerol (PG) functionalization in alleviating the environmental risks of NPs. Iron oxide NPs (ION) of 20, 100, and 200 nm sizes (IONS, IONM and IONL, respectively) were grafted with PG to afford ION-PG. We examined the interaction of ION and ION-PG with Caenorhabditis elegans (C. elegans) and found that PG suppressed non-specific interaction of ION with C. elegans to reduce their accumulation and to inhibit their translocation. Particularly, IONS-PG was completely excluded from worms of all developmental stages. By covalently introducing sulfate, carboxyl and amino groups onto IONS-PG, we further demonstrated that positively charged IONS-PG-NH3+ induced high intestinal accumulation, cuticle adhesion and distal translocation, whereas the negatively charged IONS-PG-OSO3– and IONS-PG-COO– were excreted out. Consequently, no apparent deleterious effects on brood size and life span were observed in worms treated by IONS-PG and IONS-PG bearing negatively charged groups. This study presents new surface functionalization approaches for developing ecofriendly nanomaterials

Improved performance of strain sensors constructed from highly crystalline graphene with nanospacer

This is the version of the article before peer review or editing, as submitted by an author to Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1347-4065/ad0cdb.Xu Zizhao, Himura Yuna, Ishiguro Chikako, et al. Improved performance of strain sensors constructed from highly crystalline graphene with nanospacer. Japanese Journal of Applied Physics 63, 015001 (2023); https://doi.org/10.35848/1347-4065/ad0cdb.Graphene shows promise as an alternative material for strain sensors due to its excellent properties and could overcome the limitations of conventional metal sensors. However, current graphene-based strain sensors are fabricated from chemically reduced graphene oxide (rGO) and suffer from low linearity and large hysteresis in the sensor response as well as high initial resistance. These issues are caused by functional groups and defects remaining on the rGO. Herein, highly crystalline rGO is employed for the fabrication of the strain sensor. Porous rGO sponge with low defect density is prepared in bulk scale via the ethanol-associated thermal process at ultra-high temperature. The obtained rGO sensor exhibits improved linearity, low initial resistance, and very small hysteresis owing to the high crystallinity of the rGO. The composite of rGO with nano-diamond, which has the role of a nanospacer to separate the rGO layers, is found to be highly effective in enhancing the sensitivity