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The oxidative degradation of phenolic compounds (4-chlorophenol and 4-nitrophenol) was studied using different electrochemical systems involving ozone formation at PbO 2 anodes: (i) direct electrolysis at constant current; (ii) ex-situ use of O 3 and (iii) combined use of anodically generated stream of O 3 /O 2 fed into the cathode where H 2 O 2 is electrogenerated by O 2 reduction. We show that the latter advanced oxidation method gives the best results: it is a Fenton-type degradation of the target pollutants taking place in the cathodic compartment by reason of the highly oxidizing environment brought about by radicals that are formed mainly in the reactions of O 3 with OH À and HO 2 À . Electrochemistry along with the microbial and photochemical approaches is a well established method for the degradation of wastes. It has been frequently stressed, however, that often these methods cannot bring about complete mineralization of several compounds, 1 and to this end various methods broadly classified as AOPs (Advanced Oxidation Processes) 2 provide complementary and alternative means of environment remediation, as outlined in comprehensive recent surveys. 3,4 These AO systems include ozone, hydrogen peroxide as well as a mixture of them called "Peroxone" 5 which can be activated by Fenton reactions leading to formation of a large amount of OH radicals and, consequently, to a highly oxidizing environment.In our previous work, 6 H 2 O 2 was electrogenerated at the cathode which was fed by a gaseous mixture of O 2 and O 3 that are, in turn, electrogenerated at the PbO 2 anode of the same electrochemical cell; the cathode also contained the target organic species to be degraded. Ozonization combined with electrolysis has been later investigated in other laboratories. 7 Herein we report on the oxidation of phenol derivatives in aqueous solutions using conventional electrolysis as well as and indirect electrochemical methods that generate the active oxidants such as O 3 and/or H 2 O 2 . In particular, we compare the results obtained using different oxidation methods: (i) the conventional electrolysis at PbO 2 anodes; (ii) the ex-situ method, whereby the electrochemical system is used only for the electrogeneration of O 3 at PbO 2 ; (iii) a combined use of electrogenerated O 3 and H 2 O 2 in a Fenton-like AOP.It is now well recognized that, in the direct electrolysis process, the oxidation of a large number of organic and inorganic compounds on different electrode materials, including PbO 2 , proceeds simultaneously with the evolution of oxygen. Highly oxidizing oxygen species, such as OH radicals, formed during the anodic oxidation of water are able, in turn, to oxidize most organic compounds. There is a vast literature on this subject, concerning both conducting 8-16 and semiconductor anodes. [17][18][19][20] At the high anodic potentials involved, the same oxygen species may react to form O 3 in addition to O 2 , as illustrated by the pathway below 21-26 H 2 O ! H þ þð:OHÞ ads þe À [1] ð:OHÞ ads ! ðOÞ ads þH þ þe À [...

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The preparation of cobalt-modifiedTiO2(Co-TiO2) was carried out by the incipient impregnation method starting from commercialTiO2(Degussa, P-25) and cobalt acetate. XPS data show that cobalt is incorporated as divalent ion, and it is likely present within few subsurface layers. No appreciable change in structural-morphologic properties, such as surface area and anatase/rutile phase ratio, was observed. Conversely, Co addition brings about conspicuous changes in the point of zero charge and in surface polarity. Diffuse reflectance spectra feature a red shift in light absorption that is dependent on the amount of cobalt. The influence of cobalt addition on the performance ofTiO2as a photocatalyst in the degradation of 4-chlorophenol and Bisphenol A is investigated. The results show that the modified oxide presents a higher photoactivity both for illumination with UV-visible (λ>360 nm) and visible light (λ>420 nm;λ>450 nm), and that this enhancement depends on the amount of the added species and on the final thermal treatment in the preparation step. We also show that Co-TiO2is a more active catalyst than pureTiO2for the reduction ofO2in the dark, which is an important reaction in the overall photocatalytic processes.