Photoreduction of Chlorinated Organic Pollutants Using Solutions or Films of a Polymeric System via a Free Radical Mechanism

Abstract

Efficient reduction of chlorinated organics took place upon exposure to 350 nm photons in aqueous solutions containing sulfonated poly(ether etherketone), SPEEK, and either poly(vinyl alcohol), PVA, or HCO2H/HCO2- buffers. Chloride ions together with H+ were photogenerated and the rate of Cl- formation, r(Cl-), was a linear function of time. The efficiency of the photoreaction increased in air-free solutions, since oxygen is a scavenger of the reducing species, SPEEK•. Using formate buffers as H-atom donors not only generated Cl- as a reaction product but also induced reductions at least 10 times faster than in the presence of PVA. Differences in obtained quantum yield, Φ(Cl-), were also noticed when SPEEK samples were prepared from poly(ether etherketone) precursors supplied by Evonik (called E-SPEEK) or Victrex (known as V-SPEEK) or Solvay (known as S-SPEEK). Efficiency for the reduction of the chlorinated organics increases more than 20 fold using SPEEK/PVA film as a reducing system instead of aqueous SPEEK/PVA solution. Drastic Φ(Cl-) increases were noticed in neutral solutions and at pH = 7.3 the quantum yield reached maximum values exceeding one irrespective of the nature of SPEEK. The dependence of r(Cl-) on (I0)1/2, I0 = light intensity, and the occurrence of post-irradiation formation of Cl- via reduction of CCl4/CHCl3 in the dark are further evidence that the photoreaction proceeded via a chain process.