Novel nanograined ZnO/Au heterostructured nanofibers have been successfully prepared using two‐step process via electrospinning method followed by thermal oxidation and their surface bound NO2 sensing properties were analyzed. The ZnO/Au heterojunction nanofibers exhibited typical nanograined structure with 1D morphology consisting of two distinct lattice fringes with d spacing values of 0.14 ± 0.5 nm and 0.28 ± 0.5 nm corresponding to Au [111] and ZnO [101] respectively. Defects and surface bound properties were examined using Room temperature Photoluminescence (RTPL) spectroscopy, X‐ray photo‐electron spectroscopy (XPS) and X‐ray diffraction analysis. The existence of Au, Zn and O in 4 f, 2p and 1 s states and chemisorbed oxygen species on the surface were structurally confirmed after the careful evaluation and proves the purity of synthesis. NO2 gas sensor property analysis of ZnO/Au heterojunction nanofibers showed an extraordinary sensor response (S=98) and selectivity at a lower operating temperature of 350°C than pristine ZnO nanofibers (450 °C). The enhanced sensing behavior of the heterostructured nanofibers are ascribed to the synergetic effect of Au nanoclusters at the interface which act as spill‐over zone favoring physisorption and defect mediated sensing process.

An ultrasensitive and selective chemiresistive sensor interface based on Ag nanocluster integrated polyaniline functionalized multi-walled carbon nanotubes (AgNC@PANI/MWCNTs) has been developed for trace-level detection of NH 3 gas at room temperature. AgNC@PANI/MWCNTs was synthesized using surfactant-free, one-pot wet-chemical process, by controlled integration of active Ag sites onto MWCNTs. The structure and morphology of AgNC@PANI/MWCNTs nanocomposite have been extensively studied by various characterization techniques. The gas sensing properties of AgNC@PANI/MWCNTs nanocomposite towards trace-level concentrations NH 3 (2-10 ppm), an important biomarker in exhaled human breath, was systematically evaluated. The sensor exhibited dramatic enhancement in the sensor response (26 %), fast response (5 s) and recovery (~4 s) characteristics with good reproducibility and selectivity upon exposure to NH 3 gas. The excellent performance of the sensor towards NH 3 could be attributed to the rapid electronic sensitization of surface engineered active AgNC sites in the composite in which oxidized AgNC were found to play a critical role. Effect of humidity and the kinetics of the NH 3 gas adsorption on nanocomposite were analyzed. The possible interactions between NH 3 and AgNC@PANI/ MWCNTs nanocomposite were discussed. This investigation can pave the way to novel strategies for designing and fabricating low-cost, high performance NH 3 gas sensors for clinical breath analyzer application.[a] S.

A comparative analysis of NO2 gas-sensing performances of geometry-controlled Au-decorated ZnO heterojunction nanostructures (nanospheres, nanorods, ultralong nanorods, and nanofibers) has been demonstrated with an emphasis toward exploration of their mechanistic pathways using in situ electrical and Raman spectroscopic studies. Room-temperature photo luminescence (RT-PL) studies indicate that the electron transfer from ZnO nanorods to Au nanocluster develops high resonant electron density with higher energy states. Among the investigated ZnO-Au heterojunction nanostructures, ultralong ZnO-Au nanorods possess superior sensing properties because of their directed electron transport, active heterojunctions, favorable band-bending, and spillover sensitization, which have been justified by performing in situ measurements. The investigation implies that enhanced gas sensing properties of ultralong ZnO-Au heterojunction nanorods mainly originate from a combined effect of spillover and back spillover based electron transfer mechanism along with higher activation energy. Understanding the complex mechanistic aspects of the gas-sensing process prevailing on metal-oxide-based heterojunction nanostructures can open a new paradigm toward the design of novel sensing materials, facilitating commercialization of nanomaterial-based gas sensors.