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Dynamic working temperature modulation has received considerable attention as a way to enable metal oxide-based gas sensors to recognize the detected gases. Previous reports mainly focused on heating-voltage waveform manipulation and algorithm improvement, not involving the insight of the temperature modulation sensing behavior correlated with fine nanostructures of metal oxide. Here, three types of SnO2 nanoparticles with different percentages of high-energy {221} and low-energy {110} crystal facets were synthesized and assembled as gas sensors. Under a working temperature modulation by applying a square wave pulse heating voltage, their dynamic response behaviors toward volatile organic compounds (VOCs) including alcohols, aldehydes, ketones, amines, and aromatic compounds were systematically explored. The results indicated that they exhibited different characteristic response curves toward different VOCs, presenting the crystal facet-dependent temperature modulation sensing behaviors. This effect was analyzed further and explored in conjunction with the characteristic response curves. Based on their different characteristic response curves that occurred on the three types of SnO2 nanoparticles, the detected gases, and even some congeners, were well discriminated along with a simple PCA recognition algorithm. Additionally, their quantitative analysis was also achieved. [ABSTRACT FROM AUTHOR]

This work investigates the adsorption of organosulfur compounds in model fuels over metal-organic frameworks (MOFs) using a combined experimental/computational approach. Adsorption isotherms of three MOFs, MIL-101(Cr), MIL-100(Fe), and Cu-BTC, follow the Langmuir isotherm models, and Cu-BTC shows the highest adsorption capacity for both dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), ascribing to the highest density of adsorption sites and fairly strong adsorption sites on Cu-BTC. Experimental results show adsorption selectivity of various compounds in model fuels follows the order of quinoline (Qu) > indole (In) > DBT > 4,6-DMDBT > naphthalene (Nap), which is consistent with the order of calculated binding energies. Adsorption capacities of thiophenic compounds decrease significantly with the introduction of Qu, In, or water due to their strong competitive adsorptions over the coordinatively unsaturated Cu sites on Cu-BTC. The binding energies of Qu, In, H2O, and DBT are calculated as -56.04, -41.01, -50.27, and -27.52 kJ/mol, respectively. The experimental and computational results together suggest that the adsorption strength of thiophenic compounds over Cu-BTC is dominated by the interaction of both the conjugated π system (π-M) and the lone pair of electrons on sulfur atom (σ-M) of thiophenes, with the coordinatively unsaturated sites (CUS) on Cu-BTC. Alkyl groups on 4- and/or 6-positions of thiophenic compounds function as both eletron donor to increase π-M interaction and steric inhibitor to decrease σ-M interaction. MOFs with strong and highly dense CUS can be promising materials for ADS of fuels.