A.S.M. Iftekhar Uddin

The effect of reduced graphene oxide on the dielectric and ferroelectric properties of PVDF–BaTiO3 nanocomposites

The fabrication and evolution of a high performance piezoelectric and ferroelectric material based on poly(vinylidene fluoride)–reduced graphene oxide–barium titanate (PVDF–RGO–BTO(BaTiO3)) nanocomposites have been investigated. The nanocomposites were obtained by the polymerization of graphene oxide (GO) into the PVDF matrix to achieve an insulator–conductor–insulator sandwich structure, and BTO was then carefully added to the composite. The as-prepared PVDF–RGO–BTO nanocomposite (PRB2) showed a dielectric constant of 98 and relatively low dielectric loss of 0.081 at a frequency of 1 MHz. A very low leakage current density (1.29 × 10−7 A cm−2) was measured at 80 MV m−1, suggesting the high breakdown strength of the PRB2 nanocomposite. Additionally, it exhibited a high energy density of 4.5 J cm−3 at an electric field of 50 MV m−1. This high performance piezoelectric–ferroelectric material can be a promising building block for its application in energy harvesting and high frequency capacitors.

A self-powered active hydrogen sensor based on a high-performance triboelectric nanogenerator using a wrinkle-micropatterned PDMS film

A triboelectric nanogenerator powered room-temperature hydrogen (H2) sensor was fabricated using ZnO nanorod (NR) arrays decorated with Pd nanoparticles (NPs) and a wrinkle-micropatterned polydimethylsiloxane (PDMS) nanogenerator. A generated open-circuit voltage of 16.2 V and short-circuit current of 0.512 μA were obtained when the device was exposed to a 5.3 N contact force at a fixed pressing frequency of 3 Hz. The instantaneous output power density from the device was 15.81 μW cm−2 when connected to a load resistor of 1 MΩ. The triboelectric output of the as-fabricated device was attributed to the enhanced triboelectrification of the wrinkle-micropatterned PDMS and the synergistic interplay of Pd/ZnO heterojunctions, which effectively acted as both the energy source and H2 sensing signal. Upon exposure to 3 vol% H2 at room temperature under the same applied force and deformation frequency, the triboelectric output voltage of the device decreased from 16.2 V (in dry air) to 1.04 V, through which a response value (sensitivity) up to 1457.69% was obtained. The device also showed an excellent low limit of detection (20 ppm), but a relatively slow response–recovery time (115–126 s). These results suggest that the device can be used in practical applications and can stimulate new research for the development of next-generation portable self-powered active H2 sensors.

High performance acetylene sensor based on ZnO/reduced graphene oxide nanocomposite

Sensing of acetylene (C2H2) has been carried out through synthesizing ZnO/reduced graphene oxide (rGO) nanocomposite using a solvothermal method with graphene oxide (GO) and Zn(NO3)2.6H2O as the precursors. The morphology, crystal structure, and the compositional analysis of the synthesized materials were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The physical properties of the as-synthesized material exhibited rGO layers assorted with tiny ZnO nanoparticles (NPs), where rGO supposedly acted as a template in the synthesis process for promoting the preferential attachment of ZnO nanoparticles with rGO sheets and preventing agglomeration of the ZnO nanoparticles without significantly changing its morphology and crystal structure. From the experimental results, it was evident that the synthesized nanocomposite had a preferential detection of C2H2 gas with a high response value of 34%, good selectivity, low detection limit (30 ppm), and response/recovery time of ~ 100/28 sec at 250oC. The results suggested that graphene oxide (GO) addition might be an effective method for improving C2H2 sensing performance of the ZnO based sensors which may provide challenges as well as more opportunities in the near future.

Corrugated-core sandwich-structured self-powered active gas sensor workable under wide range of external impacts

Herein, we present a self-powered active hydrogen (H2) sensor using a corrugated-core sandwich-structured triboelectric nanogenerator (CS-TENG). The working capability of the sensor can be tuned by varying the corrugated sheets orientation in the sandwich plates and/or stacking two single-unit TENGs in parallel. The sensor offers superior sensing properties (responsemax: 79%; detection: 0.001–1 vol%) with high stability using ambient mechanical forces (3–7.6 N) and without the requirement of any external power sources. We expect that the proposed sensor will show enhanced workability under a broad variety of impacts and will pave the way for a next-generation self-powered active sensor for integrated systems.

A self-powered active hydrogen sensor using triboelectric effect

In this work, we presented a self-powered active hydrogen (H2) sensor based on triboelectric effect using Pd nanoparticles (NPs) decorated ZnO nanorods (NRs) array and micropatterned (wrinkle) poly-dimethylsiloxane (PDMS). The triboelectric output of the as-fabricated device was used as the nanogenerator output as well as the sensor output. Under 5.3 N contact force and at a fixed pressing frequency of 3 Hz, generated open-circuit voltage and short-circuit current of the device can reach to 16.2 V and 0.5 μA, respectively. The output power density was measured to be nearly 15.8μW/cm2 when connecting to a load resistor of 1 ΜΩ. Upon exposure to 3 vol% H2 gas under the optimum conditions, the device output voltage dropped from 16.2 V (in dry air) to 1.04 V, showing a maximum sensor response of 1457.7%. The device also showed minimum detection of H2 down to 20 ppm. The proposed work suggests that the device can be used as a possible mean for the development of next-generation portable self-powered active sensors.

A novel flexible C2H2 gas sensor based on Ag-ZnO nanorods on PI/PTFE substrate

In this work a novel flexible acetylene (C2H2) gas sensor based on Ag nanoparticles decorated vertical ZnO nanorods (Ag-ZnO NRs) on PI/PTFE substrate has been investigated. The grown structure was synthesized through a simple, rapid, and low-temperature hydrothermal-RF magnetron sputtering method. The successful immobilization of Ag nanoparticles (NPs) onto the surface of ZnO nanorods contributed large effective surface area and facilitated the charge transfer process. The as-fabricated sensor exhibited enhanced C2H2 sensing performances at low temperature (200°C) including a broad detection range (3 - 1000 ppm), and short recovery time (39 sec). Mechanical robustness and device flexibility were investigated at different curvature angle (0 - 90°) and several times bending-relaxing process (0 – 5 × 105 times). The sensor exhibited stable response magnitude with a negligible drift of ~ 2.1% for a maximum bending angle of 90o and a response drop of 8% after 5 × 104 bending/relaxing processes. The superior sensing features along with outstanding flexibility to extreme bending stress indicate the sensor a promising candidate for the development of practical flexible C2H2 gas sensors.

Acetylene gas sensing properties of silver nanoparticles decorated ZnO morphologies with reduced graphene oxide hybrids

In the current work, in order to investigate the acetylene (C2H2) gas sensing behaviors of different ZnO morphologies; ZnO nanoparticles (NPs), hierarchical ZnO (Hrc), silver (Ag)-loaded ZnO NPs-reduced graphene oxide (Ag/ZnO NPs-rGO) hybrid and Ag-loaded ZnO Hrc-rGO (Ag/ZnO Hrc-rGO) hybrid were successfully synthesized via hydrothermal and chemical method. Addition of small amount of additives (Ag: 3 wt%; rGO: 12 wt%) with the pristine ZnO has boosted the sensing performance within the temperature range of 25-300°C, in which Ag/ZnO NPs-rGO hybrid showed the best result among the tested samples. Low operating temperature (150°C), high response magnitude (21.2 to 100 ppm gas concentration) and fast response/recovery time (25/80 sec) of the Ag/ZnO NPs-rGO hybrid might be attributed to the specific surface area, crystalline quality, surface defects and uniformity of the ZnO NPs, and the active catalytic effect of Ag and rGO with ZnO NPs in the hybrid.