Fabrication of rGO nano-sheets wrapped on Ni doped ZnO nanowire p-n heterostructures for hydrogen gas sensing

In this work, two types of van der Waals p-n heterostructure nanocomposite materials (nano-sheet/nanowire) are fabricated, and their gas sensing performances are analyzed. A hydrothermal process and Hummers' method are used for nanowire (NW) growth (Ni doped ZnO (Ni-ZnO-NWs) and ZnO (ZnO-NWs)), and rGO nano-sheet (rGO-NS) synthesis, respectively. Then, (1) rGO-NSs + Ni-ZnO-NWs (Ni-ZnO-rGO) and (2) rGO-NSs + ZnO-NWs (ZnO-rGO), as nanocomposite materials, and (3) Ni-ZnO-NWs, (4) ZnO-NWs, and (5) rGO-NSs as pristine materials are electro-sprayed on interdigitated electrodes to study their gas sensing performances. Characterization of the (1) and (2) materials shows that the nanowires are wrapped by nano-sheets. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), elemental mapping by EDX spectroscopy and X-ray photoelectron spectroscopy (XPS) are used for structural, morphological, and material characterization. Different concentrations of rGO (0.8 wt%, 1.2 wt%, 1.6 wt%, and 2 wt%) in the ZnO-rGO and Ni-ZnO-rGO nanocomposites are also studied, and the gas-sensing responses of Ni-ZnO-rGO and ZnO-rGO with 1.6 wt% rGO concentration are 29.9% and 16%, respectively, toward 50 ppm of hydrogen gas at 150 degrees C. Subsequently, response/recovery times are analyzed in various concentrations of gases at different temperatures. Also, gas sensing selectivity toward ethanol, nitrogen dioxide and ammonia gases is studied.