Photoreduction of CHCl₃ in Aqueous SPEEK/HCO₂^- Solutions Involving Free Radicals

Exposure of sulfonated poly(ether etherketone), SPEEK, in aqueous solutions to 350 nm photons induced reduction of CHCl₃ to CH₂Cl₂ and chloride ions in the presence of HCO₂H/HCO₂^- buffers or poly(vinyl alcohol), PVA. The kinetics of the SPEEK-sensitized photoreaction was characterized by quantum yields of halide ion formation, ϕ(Cl^-), evaluated from in situ determinations of [Cl^-]. Particularly efficient reductions took place when formate buffers served as H atom donors in the absence of air and with excess CHCl₃. The dependence of ϕ(Cl^-) on the inverse square root of the light intensity together with postirradiation formation of Cl^- in the dark indicated that the CHCl₃ photoreduction occurred via a chain process. EPR determinations identified the α-hydroxy radical of SPEEK and ^•CHCl₂ as chain carriers. Most of the kinetic findings were rationalized in terms of a free radical mechanism where dimerizations of the radicals acted as termination steps. Photoreduction of CHCl₃ was also detected in the presence of air albeit with lower quantum efficiencies. Observations made during postirradiation experiments indicated that a chain process was also operative under such conditions.