[en] Here we present a vacuum spacetime with closed null geodesics (CNGs). These CNGs are obtained by analytically solving the geodesic equations. This spacetime is locally isometric to the plane wave spacetime and has very different global properties from metrics of the latter type. - Highlights: ► Closed null geodesics are found in a vacuum spacetime. ► These are obtained by analytically solving the geodesic equations. ► The nature of the spacetime is fully analysed.

[en] Highlights: • Imidazolium-based ionic salt (LiFSMIPFSI) was prepared as an electrolyte for LIBs. • LiFSMIPFSI electrolyte showed good ionic conductivity and LIB performance. • LiFSI and LiTFSI were added as additives to enhance the performance of LiFSMIPFSI. • LiFSMIPFSI with LiFSI additive delivered a maximum capacity of 147 mAhg⁻¹. • The electrolyte without/with additives showed good capacity retention. -- Abstract: Herein, we report the synthesis of a novel imidazolium-based ionic salt, lithium (fluorosulfonyl) ((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl) bis(fluorosulfonyl)imide (LiFSMIPFSI) as an electrolyte for the application in lithium-ion battery (LIB). The as-synthesized LiFSMIPFSI exhibited high purity and yield, which was characterized by various spectroscopic techniques. The LiFSMIPFSI electrolyte with a mixed solvent of ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) showed a wide electrochemical stability (ca. 4.5 V vs. Li/Li⁺) and high thermal stability (300 °C), good Li⁺ conductivity (ca. 8.02 mS/cm at 30 °C), and low intrinsic viscosity, which concurrently delivered a specific discharge capacity of ca. 125 mAhg⁻¹ at 0.1 C with the full LIB configuration of LiFePO₄/electrolytes/graphite. The performance of this LiFSMIPFSI electrolyte was enhanced further by the addition of conventional lithium bis(fluoro-sulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) ionic salts (20% each) as additives with the specific discharge capacity of ca. 147 and 139 mAhg⁻¹, respectively, at 0.1 C. This is mainly due to the additional enhancement of Li⁺ conductivity and its concentrations in the electrolytes induced by the additives. The LiFSMIPFSI electrolyte with LiFSI additive based LIB showed the highest cycling stability (capacity retention ca. 97%) among the electrolytes after 500 charge-discharge cycles. Thus, the present work contributes to the development of new ionic salts and its effects upon the addition of additives on LIB performance.

[en] The synthesis of boron nitride nanodisks (BNNDs) with reducing the size and having fewer disk layers, and low optical band gap (E _g) is essential for practical applications in electronics and optoelectronic devices. So far, the large-scale preparation of hydroxyl (–OH) and hydroperoxyl (–OOH) functionalized boron nitride nanosheets and BNNDs with reduced E _g is still a challenge. This research demonstrates the scalable and solution process synthesis of hydroxyl (–OH) and hydroperoxyl (–OOH) functionalization of BNNDs at the edges and basal planes from pristine hexagonal boron nitride (h–BN) by the combination of modified Hummer’s method and Fenton’s chemistry. Modified Hummer’s method induces exfoliation and cutting of the h–BN into BNNDs with a low percentage of –OH functionalization (6.90%), which is further exfoliated and cut by Fenton’s reagent with improved –OH and –OOH functionalization (ca. 17.25%). The combination of these two methods allows us to reduce the size of the OH/OOH–BNNDs to ca. 200 nm with the number of disk layers in the range from ca. 6–11. Concurrently, the E _g of h–BN was decreased from ca. 5.10 to ca. 3.58 eV for OH/OOH–BNNDs, which enables the possible application of OH/OOH–BNNDs in semiconductor electronics. The high percentage of –OH and –OOH functionalizations in the OH/OOH–BNNDs enablesg them to disperse in various solvents with high long-term stability. (paper)

[en] 2,4-Dinitrophenylhydrazine (DNPH) was electropolymerized on the surface of an anodized glassy carbon electrode by cyclic voltammetry. The anodized electrode has a highly electroactive surface due to the creation of chemically functionalized graphitic nanoparticles, and this facilitates the formation of poly-DNPH via radical polymerization. Poly-DNPH displays excellent redox activity due to the presence of nitro groups on its backbone. These catalyze the electro-oxidation of hydroquinone (HQ) and catechol (CT). The peak-to-peak separation is around 109 mV, while a bare GCE cannot resolve the peaks (located at 165 and 274 mV vs. Ag/AgCl). Sensitivity is also enhanced to ∼1.20 and 1.19 μA·cm⁻²·μM⁻¹, respectively. The sensor has a linear response that covers the 20–250 μM concentration range for both HQ and CT, with 0.75 and 0.76 μM detection limits, respectively, at simultaneous detection. Commonly present species do not interfere. .

[en] Highlights: • A Cr-MOF (MIL-53-Cr^III) was utilized for H₂O₂ sensing for the first time. • The Cr-MOF exhibits high chemical and electrochemical stability in NaOH solution. • The redox processes of Cr^III/II in MIL-53-Cr^III have induced the direct reduction of H₂O₂. • The sensor shows a wide linear range, good sensitivity, and low method detection limit. Stability of metal-organic frameworks (MOFs) in aqueous medium and extreme solution conditions (acidic or basic) are important for the development of stable, reproducible, and sensitive electrochemical biosensors. Herein, a base-stable chromium(III) dicarboxylate MOF was synthesized by microwave assisted solvothermal method for non-enzymatic detection of hydrogen peroxide (H₂O₂). The as-synthesized MOF exhibited excellent base stability without any obvious changes in crystallinity, morphology, and spectroscopic behaviors after base treatment. This MOF-modified glassy carbon electrode showed negligible change in charge transfer resistance at the electrode|electrolyte interface after redox cycling and good catalytic activity for the reduction of H₂O₂ in 0.1 M NaOH_(aq.). The enhanced catalytic activity of H₂O₂ reduction is enabled by the redox process of Cr^III/II in the chromium (III) dicarboxylate. The sensor showed the sensitivity of ca. 11.9 μA mM⁻¹, wide linear range from 25 to 500 μM, and a method detection limit of ca. 3.52 μM. The validation of this sensing platform was evaluated by standard addition method. Thus, the present biosensor could be used for the point of care detection of H₂O₂.