J. A. Santaballa

Bio: J. A. Santaballa is an academic researcher from University of A Coruña. The author has contributed to research in topics: Aqueous solution & Photodegradation. The author has an hindex of 20, co-authored 67 publications receiving 2074 citations. Previous affiliations of J. A. Santaballa include University of Santiago de Compostela.

Reaction pathways and mechanisms of photodegradation of pesticides.

Abstract: The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.

Kinetics and mechanism of aqueous degradation of carbamazepine by heterogeneous photocatalysis using nanocrystalline TiO2, ZnO and multi-walled carbon nanotubes-anatase composites

Abstract: The photocatalytic degradation of Carbamazepine (CBZ), 5H-dibenzo[b,f]azepine-5-carboxamide, under near UV–Vis and UV irradiation is studied using P25, synthesized TiO2 (anatase and rutile), mechanical mixtures and composites of oxidized-multi-walled-carbon-nanotube:anatase, and ZnO suspensions as catalyst, to identify intermediates, and to elucidate its degradation mechanism. Factors affecting the kinetics of the process, such as the type and load of photocatalyst, and the presence of dissolved O2 or addition of co-oxidants (H2O2), have been compared. Optimal conditions for degradation were obtained using P25 (0.5 g/L), 5 mM of H2O2 or 50% O2 (v/v), with rate constants ca. 0.3144 min−1 and 0.2005 min−1, respectively. Complete removal of CBZ was achieved, showing the efficiency of the photocatalytic process. Ten photoproducts of CBZ were assigned by using high-resolution mass spectrometry, the most important of which identified as 10,11-dihydro-CBZ-10,11-epoxide, in accordance with the literature. The reaction mechanism includes previous proposals, and accounts for the pathways giving rise to the identified photoproducts.

Aqueous degradation of diclofenac by heterogeneous photocatalysis using nanostructured materials

Abstract: The photocatalytic degradation of diclofenac (DIC), 2-[2′, 6′-(dichlorophenyl)amino]phenylacetic acid is investigated under near UV–Vis and UV irradiation, using commercial TiO 2 P25, synthesized TiO 2 (anatase and rutile) and functionalized multi-walled carbon nanotube (MWCNT ox ): anatase (10-MWCNT ox –TiO 2 ) suspensions as catalysts. Factors affecting the kinetics of the process, such as the type and load of photocatalyst, and the presence of dissolved O 2 , or addition of H 2 O 2 as co-oxidant have been compared. The degradation under UV irradiation is more effective than under near UV–Vis. Optimal conditions for a complete removal were obtained using synthesized anatase (0.5 g L −1 ) and 50% O 2 (v/v) under UV irradiation, with rate constants ca . 0.9 min −1 (half-life time ca. 0.8 min). Eight photoproducts were observed from DIC photodegradation, mainly corresponding to photocyclisation (2-(8-chloro-9H-carbazol-1-yl)acetic acid, 1-chloro-8-methyl-9H-carbazole), decarboxylation (2,6-dichloro-N-o-tolylbenzenamine) and dehalogenation.

Aqueous chemistry of N-halo-compounds

Abstract: Halogens in aqueous solution are still used world-wide as disinfectants. During the process of halogenation, the substances present in water undergo several chemical processes, yielding relatively unstable intermediate species; their life-times in the medium depend on their structure and on the physico-chemical conditions. Several low molecular weight hydrocarbons are formed during water halogenation, some of them potent mutagens and/or carcinogens. Halogenation also takes place in vivo involving the system myeloperoxidase/H2O2/halide, which increases the relevance of such reactions and opens new research fields.

On the mechanism of TiO2-photocatalyzed degradation of aniline derivatives

Abstract: Interaction between aromatic amines and TiO 2 takes place preferentially through the amino group when pH > p K a (BH + ) and, as a minor but mechanistically relevant mode, via a π-interaction if pH K a (BH + ). No significant direct photodegradation of aniline or N , N -dimethyl-aniline is detected in acidic medium using λ > 290 nm, but it is enhanced in alkaline medium. 2-Aminophenol and benzoquinone are the main photoproducts of direct irradiation of aniline. The main photoproducts of photocatalytic degradation of aniline at the pH of maximum adsorption are 2-aminophenol and phenol. Scavenging HO • with t -BuOH shows that adsorbed aniline is oxidized by positive holes (h + ), with participation of the anilinium radical cation. In the case of N , N -dimethyl-aniline at the pH of maximum adsorption, N -methyl-aniline is the main photoproduct, formed also via the dimethyl anilinium radical cation. Photocatalytic degradation in acid medium is inhibited due to electrostatic repulsion between the positively charged surface and the protonated amines. Aniline is mainly transformed into phenol and 2-aminophenol, and N , N -dimethyl-aniline into aniline, that undergoes hydroxylation to phenol. In alkaline medium the main photoproduct of degradation of aniline is nitrobenzene, formed with involvement of the anilinyl radical.

TiO2-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations A review

Abstract: The photocatalytic degradation of azo dyes containing different functionalities has been reviewed using TiO2 as photocatalyst in aqueous solution under solar and UV irradiation. The mechanism of the photodegradation depends on the radiation used. Charge injection mechanism takes place under visible radiation whereas charge separation occurred under UV light radiation. The process is monitored by following either the decolorization rate and the formation of its end-products. Kinetic analyses indicate that the photodegradation rates of azo dyes can usually be approximated as pseudo-first-order kinetics for both degradation mechanisms, according to the Langmuir–Hinshelwood model. The degradation of dyes depend on several parameters such as pH, catalyst concentration, substrate concentration and the presence of electron acceptors such as hydrogen peroxide and ammonium persulphate besides molecular oxygen. The presence of other substances such as inorganic ions, humic acids and solvents commonly found in textile effluents is also discussed. The photocatalyzed degradation of pesticides does not occur instantaneously to form carbon dioxide, but through the formation of long-lived intermediate species. Thus, the study focuses also on the determination of the nature of the principal organic intermediates and the evolution of the mineralization as well as on the degradation pathways followed during the process. Major identified intermediates are hydroxylated derivatives, aromatic amines, naphthoquinone, phenolic compounds and several organic acids. By-products evaluation and toxicity measurements are the key-actions in order to assess the overall process.