PNNL

Abstract

We report the synthesis and characterization of a new vapochromic platinum compound, [Pt(CN-cyclododecyl)4][Pt(CN)4]. The vapor response characteristics of this material were investigated by simultaneous optical reflectance and quartz crystal microbalance (QCM) measurements, using water(0-13,000 mg/m3) as the test vapor. The sensing film on the QCM consisted of a mixture of the solid vapochromic powder dispersed in a hydrophobic vapor permeable polymer (vapochromic compound:polymer ratio of 80:20). The polymer was incorporated as a binder to adhere the sensing material to the QCM surface. Reflectance (I/I0) measurements were taken from the film on the QCM surface using a fiber optic bundle incorporated into the flow cell. The vapor sorption characteristics of the vapochromic compound as determined by the QCM were closely correlated with the observed spectral changes. At low concentrations (up to about 5,000 mg/m3) the response is linear; at about 6,000 mg/m3 a dramatic step response occurs and at concentrations above 6,000 mg/m3 a linear response is again obtained. The response of the sensor is rapid (minutes) and reversible. The distinctly non linear, step-function response is interpreted as a reversible transition from a non-hydrated form of [Pt(CN-cyclododecyl)4][Pt(CN)4] to a hydrated form with at least two water molecules per formula unit.