Single-walled carbon nanotubes (SWNTs) have been used extensively for sensor fabrication due to its high surface to volume ratio, nanosized structure and interesting electronic property. Lack of selectivity is a major limitation for SWNTs-based sensors. However, surface modification of SWNTs with a suitable molecular recognition system can enhance the sensitivity. On the other hand, porphyrins have been widely investigated as functional materials for chemical sensor fabrication due to their several unique and interesting physico-chemical properties. Structural differences between free-base and metal substituted porphyrins make them suitable for improving selectivity of sensors. However, their poor conductivity is an impediment in fabrication of prophyrin-based chemiresistor sensors. The present attempt is to resolve these issues by combining freebase- and metallo-porphyrins with SWNTs to fabricate SWNTs-porphyrin hybrid chemiresistor sensor arrays for monitoring volatile organic carbons (VOCs) in air. Differences in sensing performance were noticed for porphyrin with different functional group and with different central metal atom. The mechanistic study for acetone sensing was done using field-effect transistor (FET) measurements and revealed that the sensing mechanism of ruthenium octaethyl porphyrin hybrid device was governed by electrostatic gating effect, whereas iron tetraphenyl porphyrin hybrid device was governed by electrostatic gating and Schottky barrier modulation in combination. Further, the recorded electronic responses for all hybrid sensors were analyzed using a pattern-recognition analysis tool. The pattern-recognition analysis confirmed a definite pattern in response for different hybrid material and could efficiently differentiate analytes from one another. This discriminating capability of the hybrid nanosensor devices open up the possibilities for further development of highly dense nanosensor array with suitable porphyrin for E-nose application.
Zinc oxide (ZnO) nanoparticles decorated single walled carbon nanotubes (SWNTs) were electrochemically synthesized where the deposition conditions were systematically explored to tailor the size, density, and microstructure of the ZnO nanoparticles and correlated to the gas sensing performance. Room temperature conductometric detection of various analytes including CO, CO2, NO2, NH3, SO2, H2S with ZnO/SWNT hybrid nanostructures demonstrated uncharacteristic selectivity towards H2S with little to no response for the other analytes examined. Optimal ZnO/SWNTs gas sensor devices showed a significantly increased in H2S sensitivity over unfunctionalized SWNT networks (i.e. 4.96 % per ppmV vs. 0.225 % ppmV) with a lower detection limit in the ppb range. Additionally, the H2S sensing performance was greatly improved by enhancing the crystallinity of ZnO nanoparticles.
The title compound, [ReCl(C10H11NO2)2(CO)3]·CHCl3, has Re—N distances of 2.202 (8) and 2.237 (7) Å, an N—Re—N angle of 84.1 (3)° and 2‐hydroxy‐4‐oxopent‐2‐en‐3‐yl (acacH) units which are uncoordinated. The acacH units are in the enol tautomeric form, with delocalized single and double bonds.
The title compound, C21H15O4P·0.5C4H8O, contains an ordered phosphane oxide in a general position and a tetrahydrofuran solvent molecule disordered about a twofold axis. All three aldehyde substituents are nearly coplanar with their attached benzene rings, with C—C—C—O torsion angles in the range 1.64 (17)–4.24 (19)°. All three have different conformations with respect to the P=O group, one syn, one anti, and one gauche. Two of the aldehyde substituents form intermolecular C—H⋯O contacts.
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