Enhanced gas sensing properties of chemiresistors based on ZnO nanorods electrodecorated with Au and Pd nanoparticles
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Enhanced gas sensing properties of chemiresistors based on ZnO nanorods electrodecorated with Au and Pd nanoparticles E. Dilonardo1,2*, M. Alvisi3, G. Cassano,3 M. Penza3 1 Department of Chemistry, Università degli Studi di Bari Aldo Moro, Bari, Italy. 2 Department of Electrotechnics and Electronics (DEE), Politecnico di Bari, Bari, Italy. 3 ENEA, - Brindisi Research Center, Brindisi, Italy *Corresponding authors: Elena Dilonardo ([email protected]). ABSTRACT Colloidal Au and Pd nanoparticles (NPs) were directly electrochemically synthesized, by sacrificial anode electrolysis (SAE), on hydrothermal ZnO nanostructures, previously desiccated; further, the functionalized ZnO nanostructures were subjected to thermal annealing at 550°C to obtain stable ZnO nanorods (NRs), superficially decorated by naked metal NPs. The both pristine and metal functionalized ZnO NRs were proposed as active layer in chemiresistive sensors for environmental monitoring to detect pollutant gases (e.g. NO2, C4H10). The effect of the presence and of the chemical nature of the deposited metal NPs on the performance of ZnO NRs-based gas sensor (e.g. sensitivity, selectivity and recovery) was evaluated, comparing the sensing results with those of pristine ZnO NRs. In particular, the gas sensing properties of pristine and metal-functionalized ZnO NRs were studied at an operating temperature of 300°C towards a various range of concentration of different gaseous pollutants. INTRODUCTION The use of ZnO nanostructures as sensing layer in chemiresistive gas sensors is promising, although the limited selectivity, high response/recovery time, high-power consumption, and lack of long-term stability have limited their use in more demanding applications [1, 2]. Nowadays, many strategies have been developed to improve the gas sensing properties of ZnO-based gas sensors, including the use of catalysts and promoters. Specifically, the loading of ZnO with noble metals (e.g., Au, and Pd), that act as sensitizers or promoters, has been widely considered as an effective method to catalyze the gas-sensing reactions [3]. Therefore, various processes have been proposed to decorate ZnO nanostructures with noble metal NPs [3, 4], although they are often complex, time-consuming, and can produce an undesired clustering of metal NPs with the consequent reduction of their catalytic activity. To overcome these drawbacks, different functionalization procedures have been developed [5, 6]. In this contribution, we propose a one-step electrochemical functionalization process based on sacrificial anode electrolysis (SAE) to synthesize stabilized Au and Pd NPs [7], directly deposited on the surface of sol-gel pre-synthesized ZnO nanostructures [8], with a subsequent annealing at 550°C to obtain ZnO NRs. The preparation and the characterization of chemiresistive gas sensors based on ZnO NRs, electrochemically functionalized with Au and Pd NPs, to improve the sub-ppm detection of gaseous pollutants, compared to pristine ones, are reported. Both, pristine and metal functionali
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