Catalytic surfaces from Langmuir-Blodgett films of Tris(4,4'-diisopropyldibenzylideneacetone)palladium(0) as precursor .1. Study of the thermal complex decomposition and formation of palladium particles
Langmuir 12(23): 5595-5600
A detailed study is presented on Langmuir and Langmuir-Blodgett (LB) films of tris(4,4'-(diisopropyldibenzylideneacetone)palladium(0)(1) and the thermal decomposition of these LB films under formation of catalytic palladium particles. Monolayers of 1 at the air-water interface were characterized by their rr-A isotherms, while LB film formation was studied using UV-vis spectroscopy. Thermal decomposition was investigated using spectroscopic methods (X-ray photoelectron spectroscopy, UV-vis spectroscopy, and attenuated total reflectance infrared spectroscopy) and microscopic methods (scanning force microscopy). It was found that the spreading of cyclohexane solutions of 1 at the air-water interface leads to stable monolayers, which can be deposited on hydrophobic supports (e.g., silanized quartz, polyarylate) according to the LB technique. Transfer conditions are optimum at a surface pressure of 7.5 mN m(-1) and a subphase temperature of 7.5 degrees C. Monolayers are transferred during the downstroke and upstroke, the transfer ratio being 1. If the LB films are annealed at 100 degrees C or higher, they gradually decompose under formation of palladium particles whose size is controlled by time and temperature of the annealing process. For example, annealing at 120 degrees C for up to 3 min leads to formation of palladium clusters with absorption maxima at 280, 380, and 420 nm, while a thermal treatment for 10 min or longer favors the growth of metallic palladium particles with an average diameter of 22 nm. Simultaneously, the ligand molecules are set from the complex and crystallize on the surface under formation of large particles with an average diameter of 250 nm.