Preparation of Chitin Nanofibers and Natural Rubber Composites and Their Triboelectric Nanogenerator Applications.

Triboelectric nanogenerators (TENGs) have gained significant attention as promising energy-harvesting devices that convert mechanical energy into electrical energy through charge separation induced by friction and electrostatic induction. In this study, we explore the utilization of biowaste shrimp shell-extracted chitin nanofiber (ChNF) as a viable eco-friendly material for TENG applications. Composite materials were prepared by incorporating ChNF into natural rubber (NRL) at loading levels of 0.1 and 0.2 wt% (NRL/ChNF) to form the TENG triboelectric layer. ChNFs with a uniform width of approximately 10-20 nm were successfully extracted from the shrimp shells through a simple mechanical procedure. The NRL/ChNF composites exhibited enhanced mechanical properties, as evidenced by a higher Young's modulus (3.4 GPa) compared to pure NRL. Additionally, the NRL/ChNF composites demonstrated an increased dielectric constant of 3.3 at 0.1 MHz. Moreover, the surface potential difference of NRL increased from 0.182 V to 1.987 V in the NRL/ChNF composite. When employed as the triboelectric layer in TENG, the NRL/ChNF composites exhibited significant improvement in their output voltage, with it reaching 106.04 ± 2.3 V. This enhancement can be attributed to the increased dielectric constant of NRL/ChNF, leading to enhanced charge exchange and charge density. This study presents a straightforward and environmentally friendly technique for preparing sustainable natural materials suitable for energy-harvesting devices.

Electrochemical and electrical characteristics of ball milled Cs2Ti6O13 modified by the surface-to-bulk migration of hydroxyl groups.

Ball milling of solids under benign conditions leads to surface functionalization without altering the crystal structure and morphology. However, these additional surface functional groups are rarely fixed but instead mobilized across such ball milled solids. This phenomenon, including its effects on electrochemical and electrical properties, has received limited attention. We report herein that dry vibratory ball milling of lepidocrocite-type Cs2Ti6O13 generated hydroxyl groups which subsequently migrated from surfaces to bulk. The increased number of bulk hydroxyl groups is deduced from Raman, IR, and solid state 1H nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. In contrast, the decrease in the relative proportion of surface hydroxyl groups/water and carbon-oxygen species was deduced from X-ray photoelectron spectroscopy. The inaccessible hydroxyl groups in ball milled Cs2Ti6O13 lead to a smaller amount of stored charge and increased charge transfer resistance, according to galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy studies in 1 M Na2SO4. The alternating current electrical properties were also measured, revealing fundamental insights such as the one-dimensional conduction pathway and the relaxation time in microseconds. A model has been proposed for this surface-to-bulk migration of the hydroxyl groups, which competes with surface dangling bonds leading to particle agglomeration.

Carbon nanotube/polydimethylsiloxane composite micropillar arrays using non-lithographic silicon nanowires as a template for performance enhancement of triboelectric nanogenerators.

Carbon nanotube/polydimethylsiloxane composite micropillar (CNT/PDMS MP) arrays were successfully fabricated using non-lithographic silicon nanowire (SiNW) arrays as a template for performance enhancement of triboelectric nanogenerators (TENG). The CNT/PDMS MP arrays were obtained by pouring CNT/PDMS composites on the SiNW arrays and peeled off. Surface topology of CNT/PDMS composites directly depends on morphology of SiNW arrays, which can be varied by the etching time of the typical metal-assisted chemical etching process. The micropatterned CNT/PDMS composites was mostly depicted to the SiNW array template pattern when the morphologies of the SiNW were optimized with a length of approximately 10 mm. Next, the CNT/PDMS MP arrays were utilized as a triboelectric layer of TENGs, generating the maximum output voltage of 22.84 ± 0.85 V, enabling an approximately 18-fold improvement in an electrical output compared to the flat PDMS-based TENG. The performance enhancement of TENGs based on CNT/PDMS MP arrays are attributed to synergic effects of (1) an enhancement of electrostatic induction by CNT composites, increasing dielectric constant, and (2) an enhancement of electrification by surface texturing using non-lithographic pattern and CNT composites.

Comparison of acid exfoliators in carbon nanosheets synthesis from stinging nettle (Urtica dioica) for electrochemical applications.

Carbon nanosheets (CNs) were successfully synthesized from nettle stem (NS) which is an inexpensive material with a high carbon content that is abundantly available in nature. CNs were produced using chemical (potassium hydroxide activation and acid exfoliation) and thermal treatments. Sulfuric (H2SO4), phosphoric (H3PO4) and nitric (HNO3) acid solutions were used for exfoliation. CNs exfoliated by H3PO4 have higher specific surface area (789 m2 g-1) compared to CNs exfoliated by H2SO4 (705 m2 g-1) and HNO3 (106 m2 g-1). In this work, NSCNs were found to be a potential candidate for electrode material in electrochemical capacitors. The maximum specific capacitance of the NSCNs exfoliated by H3PO4 is found to be 27.3 F g-1 at a current density of 0.05 A g-1, while the specific capacitance of NSCNs exfoliated by H2SO4 and HNO3 is 9.34 F g-1 and 1.71 F g-1, respectively. Energy density (0.06-0.95 Wh kg-1) and power density (20.9-26.7 W kg-1) of NSCNs are confirmed to be supercapacitor materials and can be applied in energy storage devices.

Graphene nanosheet-grafted double-walled carbon nanotube hybrid nanostructures by two-step chemical vapor deposition and their application for ethanol detection.

Here, we present a facile technique for synthesis of graphene nanosheet (GNS)-grafted double-walled carbon nanotube (DWCNT) hybrid carbon nanostructures (here after referred to as G-DWCNTs) by directly growing GNSs along the sidewalls of DWCNTs using a two-step chemical vapor deposition (CVD). DWCNTs were synthesized by floating catalyst CVD at 1300 °C using ferrocene and thiophene dissolved in ethanol. Then, GNSs were grafted onto the synthesized DWCNT bundles by thermal CVD at 1300 °C using ethanol. The sharp-edged petal-like structure of GNSs were grown along the sidewalls of DWCNT bundles while maintaining the one-dimensional structure of DWCNT. Next, DWCNTs and G-DWCNTs were dispersed in ethanol, then deposited on the paper using vacuum filtration method and used for ethanol detection. G-DWCNTs sensor exhibited a 3-fold improvement in the response to ethanol vapor compared to the DWCNTs sensor. The sensing mechanism of DWCNTs and G-DWCNTs can be described in terms of charge transfer between the gas molecules and sensing material. These results demonstrate that the facile technique by two-step CVD method provides a promising approach for simple and low-cost technique to synthesize the hybrid nanostructure of GNSs and DWCNTs. The new hybrid carbon nanostructures are attractive for gas sensing application.

Nitrogen self-doped activated carbons via the direct activation of Samanea saman leaves for high energy density supercapacitors.

In this study, nitrogen self-doped activated carbons (ACs) obtained via the direct activation of Samanea saman green leaves (SSLs) for high energy density supercapacitors were investigated. The SSL-derived direct-activated carbons (hereinafter referred to SD-ACs) were synthesized by impregnating sodium hydroxide as an activating agent and heating up to 720 °C without a hydrothermal carbonization or pyrolysis step. The optimum condition was investigated by varying the weight ratio of raw SSLs to NaOH. Surpassing the ACs derived from the two-step convention method, SD-ACs showed superior properties, including a higher surface area (2930 m2 g-1), total pore volume (1.37 cm3 g-1) and nitrogen content (4.6 at%). Moreover, SD-ACs exhibited enhanced electrochemical properties with specific gravimetric and volumetric capacitances of 179 F g-1 and 88 F cm-3 in an organic electrolyte, respectively, a high capacitance retention of approximately 87% at a current density of 0.5 A g-1 and excellent cycling stability of 97.5% after 3000 cycles at a current density of 5 A g-1. Moreover, the potential window of the supercapacitor cell was extended to 3.5 V with a significantly enhanced energy density of up to 79 W h kg-1. These results demonstrate that the direct activation of nitrogen-enriched SSLs offers advantages in terms of simplicity, low-cost and sustainable synthetic route to achieve nitrogen self-doped ACs for high energy density supercapacitors, which exhibit superior properties to that of ACs prepared via the conventional method.

Preparation and electrochemical performance of nitrogen-enriched activated carbon derived from silkworm pupae waste.

In this study, nitrogen-enriched activated carbon from silkworm pupae waste (P-AC) was successfully prepared and its electrochemical performances in aqueous and organic electrolytes were investigated. Silkworm pupae waste is beneficial because it is a nitrogen-enriched, inexpensive, and locally available material. The preparation process includes hydrothermal treatment of the silkworm pupae waste at 200 °C, and chemical activation using zinc chloride at activation temperatures of 700, 800 and 900 °C (P700, P800, and P900, respectively). The nitrogen content in the P-ACs was approximately 3.8-6.4 at%, decreasing with activation temperature, while the surface area was approximately 1062-1267 m2 g-1, increasing with activation temperature. Compared to a commercial AC, the P-ACs show higher nitrogen content but lower surface area. Furthermore, the P800 exhibited superior specific capacitance (154.6 and 91.6 F g-1 in aqueous and organic electrolytes) compared to a commercial AC despite possessing smaller surface area. The high nitrogen content enhanced the pseudocapacitance and improved the electrical conductivity of the P-ACs. These properties were confirmed by relatively low series and charge transfer resistances, a capacity retention higher than 88% at a current density of 0.5 A g-1 and excellent cycling stability demonstrated by maintaining 97.6% of its capacitance after 3000 cycles. These results demonstrate that silkworm pupae waste is a viable source of nitrogen-enriched AC for application in supercapacitors.

Piezoelectric-Induced Triboelectric Hybrid Nanogenerators Based on the ZnO Nanowire Layer Decorated on the Au/polydimethylsiloxane-Al Structure for Enhanced Triboelectric Performance.

Here, we demonstrate a novel device structure design to enhance the electrical conversion output of a triboelectric device through the piezoelectric effect called as the piezo-induced triboelectric (PIT) device. By utilizing the piezopotential of ZnO nanowires embedded into the polydimethylsiloxane (PDMS) layer attached on the top electrode of the conventional triboelectric device (Au/PDMS-Al), the PIT device exhibits an output power density of 50 µW/cm2, which is larger than that of the conventional triboelectric device by up to 100 folds under the external applied force of 8.5 N. We found that the effect of the external piezopotential on the top Au electrode of the triboelectric device not only enhances the electron transfer from the Al electrode to PDMS but also boosts the internal built-in potential of the triboelectric device through an external electric field of the piezoelectric layer. Furthermore, 100 light-emitting diodes (LEDs) could be lighted up via the PIT device, whereas the conventional device could illuminate less than 20 LED bulbs. Thus, our results highlight that the enhancement of the triboelectric output can be achieved by using a PIT device structure, which enables us to develop hybrid nanogenerators for various self-power electronics such as wearable and mobile devices.

Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains.

A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 µm to more than 100 µm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.