Nanostructured organometallic polymer and palladium/polymer hybrid: surface investigation and sensitivity to relative humidity and hydrogen in surface acoustic wave sensors

The nanostructured conjugated polymer poly[1,1'-bis(ethynyl)-4,4'-biphenyl-(bis-tributylphosphine) Pd(II)], known as Pd-DEBP and the hybrid system Pd/Pd-DEBP, made by dispersion of Pd(0) nanoclusters into the organometallic conjugated polymer Pd-DEBP, have been studied as active membranes for the development of surface acoustic wave (SAW) based chemical sensors. X-ray photoelectron spectroscopy (XPS), scanning tunnelling microscopy (STM) and scanning electron microscopy (SEM) characterizations of thin films of Pd-DEBP and Pd/Pd-DEBP proved the Pd/polymer interaction and the particle dispersion into the nanostructured polymer matrix. The propagation of SAWs and the perturbational approach were used to characterize the membranes and to estimate the thickness and the shear modulus of the polymeric films. The sensitivity of the nanostructured Pd-DEBP polymer and the Pd/Pd-DEBP hybrid to relative humidity (RH) and to hydrogen concentration was investigated by means of high frequency SAW resonator based sensors in the 0-80% RH range and 150-800 ppm H-2 range, at room temperature. The sensors based on Pd-DEBP and Pd/Pd-DEBP membranes showed a RH sensitivity of 600 and 320 Hz/RH%, and a H-2 sensitivity of 650 and 670 Hz/ppm, respectively. These values were compared with literature results, showing an enhancement of the sensitivity in the low RH range 0-30%.