Growth of Graphitic Carbon Nitride-Incorporated ZnO Nanorods on Silicon Pyramidal Substrates for Enhanced Hydrogen Sensing Applications.

Monitoring the hydrogen gas (H2) level is highly important in a wide range of applications. Oxide-carbon hybrids have emerged as a promising material for the fabrication of gas sensors for this purpose. Here, for the first time, graphitic carbon nitride (g-C3N4)-doped zinc oxide nanorods (ZNRs) have been grown on silicon (Si) pyramid-shaped surfaces by the facile hydrothermal reaction method. The systematic material analyses have revealed that the g-C3N4 nanostructures (NS) have been consistently incorporated into the ZNRs on the pyramidal silicon (Py-Si) surface (g-C3N4-ZNRs/Py-Si). The combined properties of the present structure exhibit an excellent sensitivity (∼53%) under H2 gas exposure, better than that of bare ZNRs (12%). The results revealed that the fine incorporation of g-C3N4 into ZNRs on the Py-Si surface improves the H2 gas sensing properties when compared to that of the planar silicon (Pl-Si) surface. The doping of g-C3N4 into ZNRs increases the electrical conductivity through its graphene-like edges (due to the formation of delocalized bonds in g-C3N4 during carbon self-doping), as revealed by FESEM images. In addition, the presence of defects in g-C3N4 induces the gas adsorption properties of ZnO through its active sites. Moreover, the integration of the 1D structure (g-C3N4-ZNRs) into a 3D pyramidal structure opens up new opportunities for low-cost H2 gas sensing at room temperature. It is an easy way to enhance the gas sensing properties of ZNRs at room temperature, which is desirable for practical H2 sensor applications.

Role of Nanodiamond Grains in the Exfoliation of WS2 Nanosheets and Their Enhanced Hydrogen-Sensing Properties.

Herein, for the first time, a combination of detonation nanodiamond (DND)-tungsten disulfide (WS2) was devised and studied for its selective H2-sensing properties at room temperature. DND-WS2 samples were prepared by a sonication-assisted (van der Waals interaction) liquid-phase exfoliation process in low-boiling solvents with DND as a surfactant. The samples were further hydrothermally treated in an autoclave under high pressure and temperature. The as-prepared samples were separated as two parts named DND-WS2 BH (before hydrothermal) and DND-WS2 AH (after hydrothermal). The exfoliated bilayer to few-layer DND-doped WS2 nanosheets were confirmed by ultraviolet-visible spectra, atomic force microscopy, and transmission electron microscopy studies. It was observed that the DND powder not only acted as a surfactant but also doped and expanded on WS2 nanosheets. The difference between samples BH and AH treatment was further investigated using Raman spectroscopy. The WS2 and DND-WS2 samples on SiO2/Si were fabricated using a sputtered Pd/Ag interdigitated electrode and utilized for H2 gas-sensing measurements. Surprisingly, the DND-WS2 exhibits an ultrahigh sensor response of 72.8% to H2 at 500 ppm when compared to only 9.9% for WS2 alone. Also, the DND-WS2 shows a fast response/recovery time, high selectivity, and stability toward H2 gas. It can be attributed to the correlation of the intergrain phase of DND nanoparticles and WS2 nanosheets, which contributes to the easy transportation of charge carriers when exposed to the air and H2 gas atmosphere. Moreover, it is believed that DND-induced WS2 exfoliation might inspire future synthesis of transition metal dichalcogenides induced by DND in green solvents.

Superficial Edge Effect of N2-Doped Nanodiamond on the Highly Stable Nonenzymatic Glucose Detection Properties of Dispersed Graphene Flakes/Ni Nanostructures.

In this study, we report nitrogen-doped nanodiamond (ND)-integrated crushed graphene (Gr) nanoflakes on nickel hydroxide (Ni(OH)2, named NH) nanostructures for highly stable nonenzymatic glucose sensors. A chemical vapor deposition route with a simple hydrothermal method was devised in the fabrication of ND-Gr-NH nanostructures. Thus, the results depict that the best sensitivity of 13769 µA mM-1 cm-2 was detected for Gr-NH, while NH shows 10,358 µA mM-1 cm-2. The salient improvement in the sensitivity of ND-Gr-NH is 15,431.2 µA mM-1 cm-2, with a limit of detection of 0.1 µm. The enhancement in ND-integrated Gr-NH is due to the synergistic influence of ND and graphene on NH. Furthermore, the ND-Gr-NH electrode shows a good stability (95%), while Gr-NH exhibits a stability of 82% over 21 days. In addition, the present ND-based electrode shows high selectivity toward glucose among additional interfering compounds including sodium chloride (NaCl), uric acid, and ascorbic acid. These outstanding enzymeless glucose sensing results could be ascribed to the synergistic influence that provides more active sites and further enhances the electron-transfer reaction.

Enhancement of UV Photodetection Properties of Hierarchical Core-Shell Heterostructures of a Natural Sericin Biopolymer with the Addition of ZnO Fabricated on Ultra-Nanocrystalline Diamond Layers.

A novel self-assembled hierarchical heterostructure is derived from cocoon-derived sericin biopolymer (CSP) biowaste with ZnO deposited on ultra-nanocrystalline diamond (UNCD) substrates using a scalable chemical deposition technique. Then, high-performance long-life UV photodetectors are fabricated using this hybrid sericin, diamond, and ZnO (SDZ) nanostructure. The microstructural analysis reveals a several nanometer-thick CSP shell coated with a highly uniform ZnO nanorod (ZNR) array grown on the UNCD substrate. The CSP shell also contains columnar nanograins on top of the ZNR as well as vertical sidewalls with unique alignments. The hierarchical core-shell SDZ heterostructures reveal superior UV diode performance, with an ultrahigh UV switching ratio of 1.1 × 105 at 5 V, an increase of up to 49 900% greater than that of as-grown ZNRs (220). High UV responsivity is observed around 3.6 A W-1 under 365 nm UV light illumination. The perfect distribution of the sericin in the ZNRs on the UNCD substrates resulted in the ultrafast electron-hole recombination. The sericin dopants and the UNCD interlayer enabled the device to reach new energy levels in the conduction band, with the reduced barrier height allowing for improved charge carrier transportation during UV light illumination. It is believed that the sericin dopants and the UNCD layer increased the UV adsorptivity and the amount of conducting carbon dopants within the ZNRs was sufficient for s0tability. These noteworthy features make the SDZ heterostructures promising candidates for the fabrication of cost-efficient biopolymers and UNCD hybrid-based UV photodetectors.

Bio-industrial Waste Silk Fibroin Protein and Carbon Nanotube-Induced Carbonized Growth of One-Dimensional ZnO-based Bio-nanosheets and their Enhanced Optoelectronic Properties.

High performance UV/Visible photodetectors are successfully fabricated from ZnO/fibroin protein-carbon nanotube (ZFPCNT ) composites using a simple hydrothermal method. The as-fabricated ZnO nanorods (ZnO NRs) and ZFPCNT nanostructures were measured under different light illuminations. The measurements showed the UV-light photoresponse of the as-fabricated ZFPCNT nanostructures (55,555) to be approximately 26454 % higher than that of the as-prepared ZnO NRs (210). This photodetector can sense photons with energies considerably smaller (2.75 eV) than the band gap of ZnO (3.22 eV). It was observed that the finest distribution of fibroin and CNT into 1D ZnO resulted in rapid electron transportation and hole recombination via carbon/nitrogen dopants from the ZFPCNT . Carbon dopants create new energy levels on the conduction band of the ZFPCNT , which reduces the barrier height to allow for charge carrier transportation under light illumination. Moreover, the nitrogen dopants increase the adsorptivity and amount of oxygen vacancies in the ZFPCNT so that it exhibits fast response/recovery times both in the dark and under light illumination. The selectivity of UV light among the other types of illumination can be ascribed to the deep-level energy traps (ET ) of the ZFPCNT . These significant features of ZFPCNT lead to the excellent optical properties and creation of new pathways for the production of low-cost semiconductors and bio-waste protein based UV/Visible photodetectors.

Interfacial Effect of Oxygen-Doped Nanodiamond on CuO and Micropyramidal Silicon Heterostructures for Efficient Nonenzymatic Glucose Sensor.

Herein, the novel strategy of copper oxide (CuO) deposited oxygen-doped nitrogen incorporated nanodiamond (NOND)/Si pyramids (Pyr-Si) heterostructure is studied for high-performance nonenzymatic glucose sensor. The combined properties of surface-modified NOND/Pyr-Si induced by different growth durations (5 to 20 min) of CuO is envisioned to improve glucose sensitivity and stability. For comparison, the same methods and parameters were deposited on the plane silicon wafers. The systematic analysis reveals the best glucose sensing properties of 15 min grown CuO/NOND/Pyr-Si based sensor, with a high sensitivity of 1993 µA mM-1 cm-2, a lower limit of detection of 0.1 µm, and a longer stability of 28 d (∼96%). In addition, the present sensor exhibits good selectivity of glucose among other analytes such as sodium chloride, ascorbic acid, uric acid, and so on. The enhancement in glucose sensing performances of the as-fabricated CuO/NOND/Pyr-Si is ascribed to the interfacial effect of NOND and the synergistic effect of CuO and NOND/Pyr-Si. Moreover, the oxygen dopant in NOND and CuO stimulates the reactive oxygen species while measuring glucose and affords rapid recovery (<2 s). This promotes fast electron kinetics in the electrocatalytic solutions, which enhances the electroactive area and thereby contributes to a high sensitivity. These salient results suggested that the as-fabricated CuO/NOND/Pyr-Si sensor is more suitable for high-performance biosensors and effective energy storage device applications.

Natural Biowaste-Cocoon-Derived Granular Activated Carbon-Coated ZnO Nanorods: A Simple Route To Synthesizing a Core-Shell Structure and Its Highly Enhanced UV and Hydrogen Sensing Properties.

Granular activated carbon (GAC) materials were prepared via simple gas activation of silkworm cocoons and were coated on ZnO nanorods (ZNRs) by the facile hydrothermal method. The present combination of GAC and ZNRs shows a core-shell structure (where the GAC is coated on the surface of ZNRs) and is exposed by systematic material analysis. The as-prepared samples were then fabricated as dual-functional sensors and, most fascinatingly, the as-fabricated core-shell structure exhibits better UV and H2 sensing properties than those of as-fabricated ZNRs and GAC. Thus, the present core-shell structure-based H2 sensor exhibits fast responses of 11% (10 ppm) and 23.2% (200 ppm) with ultrafast response and recovery. However, the UV sensor offers an ultrahigh photoresponsivity of 57.9 A W-1, which is superior to that of as-grown ZNRs (0.6 A W-1). Besides this, switching photoresponse of GAC/ZNR core-shell structures exhibits a higher switching ratio (between dark and photocurrent) of 1585, with ultrafast response and recovery, than that of as-grown ZNRs (40). Because of the fast adsorption ability of GAC, it was observed that the finest distribution of GAC on ZNRs results in rapid electron transportation between the conduction bands of GAC and ZNRs while sensing H2 and UV. Furthermore, the present core-shell structure-based UV and H2 sensors also well-retained excellent sensitivity, repeatability, and long-term stability. Thus, the salient feature of this combination is that it provides a dual-functional sensor with biowaste cocoon and ZnO, which is ecological and inexpensive.

Self-Assembled Hierarchical Interfaces of ZnO Nanotubes/Graphene Heterostructures for Efficient Room Temperature Hydrogen Sensors.

Herein, we report the novel nanostructural interfaces of self-assembled hierarchical ZnO nanotubes/graphene (ZNT/G) with three different growing times of ZNTs on graphene substrates (namely, SH1, SH2, and SH3). Each sample was fabricated with interdigitated electrodes to form hydrogen sensors, and their hydrogen sensing properties were comprehensively studied. The systematic investigation revealed that SH1 sensor exhibits an ultrahigh sensor response even at a low detection level of 10 ppm (14.3%) to 100 ppm (28.1%) compared to those of the SH2 and SH3 sensors. The SH1 sensor was also found to be well-retained with repeatability, reliability, and long-term stability of 90 days under hydrogenation/dehydrogenation processes. This outstanding enhancement in sensing properties of SH1 is attributed to the formation of a strong metalized region in the ZNT/G interface due to the inner/outer surfaces of ZNTs, establishing a multiple depletion layer. Furthermore, the respective band models of each nanostructure were also purposed to describe their heterostructure, which illustrates the hydrogen sensing properties. Moreover, the long-term stability can be ascribed by the heterostructured combination of ZNTs and graphene via a spillover effect. The salient features of this self-assembled nanostructure are its reliability, simple synthesis method, and long-term stability, which makes it a promising candidate for new generation hydrogen sensors and hydrogen storage materials.