Stable Cu(2)O nanocrystals of around 3 nm were uniformly and densely grown on functionalized graphene sheets (FGS), which act as molecular templates instead of surfactants for controlled nucleation; the distribution density of nanocrystals can be easily controlled by FGS with different C/O ratios. The nanocomposite displays improved stability of the crystalline phase in wet air, which is attributed to finite-size effects that the high-symmetry crystalline phase is to be more stable at smaller size. Meanwhile, we conjecture that the oxygen adsorbed on the interfacial surface prefers to extract electrons from FGS, thus the interfacial bonding also makes a contribution in alleviating the process of corrosion to some extent. More importantly, the Cu(2)O-FGS nanocomposite based sensor realizes room temperature sensing to H(2)S with fantastic sensitivity (11%); even at the exposed concentration of 5 ppb, the relative resistance changes show good linearity with the logarithm of the concentration. The enhancement of sensitivity is attributed to the synergistic effect of Cu(2)O and FGS; on the one hand, surfactant-free capped Cu(2)O nanocrystals display higher surface activity to adsorb gas molecules, and on the other hand, FGS acting as conducting network presents greater electron transfer efficiency. These observations show that the Cu(2)O-FGS nanocomposite based sensors have potential applications for monitoring air pollution at room temperature with low cost and power consumption.
The coffee ring effect is reduced effectively and a hydrogen sensor with platinum-decorated single-walled carbon nanotubes (SWCNTs) is prepared by aerosol jet printing (AJP) technology. The stable aqueous solution of platinum functional SWCNTs is prepared by a series of chemical and physical processes and the electrode array is formed by micro-fabrication technology. The AJP process is also researched in detail including the number of printing passes and the printing distance between electrodes. Then, the functional SWCNT aqueous solution is printed on the electrode array and the response of this sensor to the hydrogen is measured carefully. The results show that a functional SWCNT sensor has excellent sensing properties toward hydrogen.
Large-area and uniform three-dimensional (3D) β-Ni(OH)2 and NiO nanowalls were synthesized on a variety of rigid and flexible substrates via a simple aqueous chemical deposition process. The β-Ni(OH)2 nanowalls consist of single-crystal Ni(OH)2 nanosheets that were vertically grown on different substrates. The height, crystallinity, and morphology of the Ni(OH)2 nanowalls can be readily modified by adjusting the reaction time and concentration of the NiCl2 solution. The synthesis mechanism of the Ni(OH)2 nanowalls was determined through heterogeneous nucleation and subsequent oriented crystal growth. 3D NiO nanowalls were obtained by thermal decomposition of the Ni(OH)2 nanowalls at 400 °C in Ar atmosphere. Highly sensitive, selective gas sensors and electrochemical sensors based on these NiO nanowalls were developed. The chemiresistive gas sensors based on the NiO nanowalls grown on ceramic substrates exhibited an excellent performance with low detection limit for formaldehyde (8 ppb) and NO2 (15 ppb). The electrochemical sensor based on the NiO nanowalls grown on an FTO glass substrate had a superior selectivity to non-enzymatic glucose with a detection limit of 200 nm.
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