Suspended Particles as Photoelectrochemical Systems

Abstract

Investigations on the fundamentals concerning three types of fine particles that can serve potentially as minute photoelectrochemical reaction centers in form of suspensions have been carried out for InP powders, colloidal CdS, and tris(2,2'-bipyridine)ruthenium(II) complex assembled in particles of zeolite X in this work.

Theoretical analysis based on the Pourbaix potential-pH method shows that InP is intrinsically unstable in aqueous solutions. Strong ionic complexations of indium(III) with halides, thiocyanate, and acetate are the main causes responsible for the observed rapid dissolutions. Surface modification with ferri- or ferrocyanide by forming a layer of insoluble InFe(CN)(,6) was found useful to stabilize the powder against dissolution in aqueous sulfuric acid. Thermal annealing of InP powders effects the stability by promoting the crystallinity, reducing the surface defects, and improving the stoichiometric ration in composition.

Preparation and stabilization of colloidal CdS suspensions in CH(,3)CN were discovered for the first time in this work. The stabilizing effect of halides via surface adsorption follows the decreasing order of SCN('-) >(' )Br('-) > I('-) > Cl('-). Addition of the stabilizing agents also affects the particle(' )sizes and the intensity of luminscences. The latter was found, for CdS prepared with halides added before the reaction, to follow the decreasing order of Br('-) > Cl('-) > I('-) > SCN('-). Surface adsorptions of quenchers are found mandatory for effectively scavenging the photogenerated short-lived charge carriers at concentrations lower than 1 x 10('-4) M.

Tris(2,2'-bipyridine)ruthenium(II), Ru(bpy)(,3)('2+), synthesized in the zeolite X was found to reach a maximum loading of ('(TURN))1.5 complexes per supercage. Fluorescence lifetimes of the encapsulated complex were deconvoluted by curve-fitting method into two components. The long-lived components decreased from ('(TURN))1100 ns to ('(TURN))200 ns due to self quenching as Ru(bpy)(,3)('2+) in zeolites increased from 10('-5) to 10('-4) moles/gram zeolite X. The short ones, smaller than 80 ns, are considered arising from the paired complexes. Quenching by tetramethyl-p-phenyldiamine was ineffective because the complexes could only be accessed in the matrice with difficulty.