P. Davydovskaya

Analyte Detection with Cu-BTC Metal–Organic Framework Thin Films by Means of Mass-Sensitive and Work-Function-Based Readout

Metal-organic frameworks (MOFs) constitute a new generation of porous crystalline materials, which have recently come into focus as analyte-specific active elements in thin-film sensor devices. Cu-BTC--also known as HKUST-1--is one of the most theoretically and experimentally investigated members of the MOF family. Its capability to selectively adsorb different gas molecules renders this material a promising candidate for applications in chemical gas and vapor sensing. Here, we explore details of the host-guest interactions between HKUST-1 and various analytes under different environmental conditions and study the vapor adsorption mechanism by mass-sensitive and work-function-based readouts. These complementary transduction mechanisms were successfully applied for the detection of low ppm (2 to 50 ppm) concentrations of different alcohols (methanol, ethanol, 1-propanol, and 2-propanol) adsorbed into Cu-BTC thin films. Evaluation of the results allows for the comparison of the amounts of adsorbed vapors and the contribution of each vapor to the changes of the electronic properties of Cu-BTC. The influence of the length of the alcohol chain (C1-C3) and geometry (1-propanol, 2-propanol) as well as their polarity on the sensing performance was investigated, revealing that in dry air, short chain alcohols are more likely adsorbed than long chain alcohols, whereas in humid air, this preference is changed, and the sensitivity toward alcohols is generally decreased. The adsorption mechanism is revealed to differ for dry and humid atmospheres, changing from a site-specific binding of alcohols to the open metal sites under dry conditions to weak physisorption of the analytes dissolved in surface-adsorbed water reservoirs in humid air, with the signal strength being governed by their relative concentration.

Ethanol Sensing with Cu-BTC Metal Organic Framework: Mass Sensitive, Work Function Based and IR Investigations

Cu-BTC, also known as H-KUST 1, belongs to Metal Organic Frameworks (MOFs). Nanoporosity, relatively good thermal stability and unsaturated metal sites are some of its properties that make this MOF promising for application as a gas sensing material. In this work we chose different experimental approaches to examine trace gas sensing (5 to 50 ppm) of ethanol with Cu-BTC. Measurements with mass sensitive, as well as work function based readout, were successfully performed in dry synthetic air at room temperature. Strong, fast and concentration dependent response to ethanol was observed. In-situ measurements with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were additionally applied to visualize the adsorption of ethanol molecules on the Cu-BTC sensing layer.

4.1.2 MetalOrganicFrameworks as an aldehyde sensing layer in workfunction based gas sensing devices

Metal-Organic Frameworks (MOFs) are porous crystalline materials with a characteristic large surface area. These materials were mainly investigated for applications as gas storage and separation and catalysis. The approach for using MOFs for sensing application was already done. MOFs show high potential for applications involving work function based gas sensing devices. In this work the Cu-BTC MOF was investigated as an aldehyde sensing material for work function readout based gas sensors at ambient conditions. The cross-sensitivity to humidity was proved. It is shown that Cu-BTC MOF sensing layers allow the distinguishing of molecules with similar chemical properties but different lengths.