O. González Díaz

Highly concentrated phenolic wastewater treatment by the Photo-Fenton reaction, mechanism study by FTIR-ATR

Phenol degradation by Photo-Fenton reaction has been studied in highly concentrated wastewaters and most intermediate species have been identified by Fourier Transform IR-Spectroscopy with ATR device. During the photodegradation of highly concentrated phenol solutions, the formation of dissolved and precipitate tannin has been observed. The possibility of a Fe3+-Pyrogallol complex formation, previous to the tannin formation, has been proposed too. The complex formation involving Fe3+ ions could be related to the observed Photo-Fenton activity decrease. Tannin formation inhibits the complete mineralization of phenol because *OH radicals attack will produce further condensation steps and the polymer size increase. This fact limits the applicability of the process for highly concentrated phenolic wastes mineralization. However, the tannin precipitation allows its separation from the solution by conventional filtration, and reduction of the corresponding dissolved organic carbon. These observations have been proved from the identification of primary degradation products, catechol and hydroquinone. Catechol is considered to be the first step for the formation of tannins. Degradation process for phenol, catechol and hydroquinone have been monitored by total organic carbon (TOC) measurements along the reaction time span. From these results, a global mechanism for the Photo-Fenton degradation of phenol is proposed.

Maleic acid photocatalytic degradation using Fe-TiO2 catalysts: Dependence of the degradation mechanism on the Fe catalysts content

Abstract The photocatalytic degradation of maleic acid by using Fe-doped (0.15, 0.5, 2 and 5% w/w in Fe) TiO2 catalysts has been studied. Catalysts with the lowest Fe content (0.15 and 0.5%) show a considerably better catalytic behavior than non-doped TiO2 and catalysts with higher Fe contents. Maleic acid molecules interact with the surface of the lowest Fe-containing catalysts and as a consequence, iron atoms are extracted from the catalyst surface as photoactive Fe3+–maleic acid complexes. When this complex is degraded, the resulting Fe2+ ions react with TiO2 holes (h+) and the iron return to the catalyst surface as Fe2O3. In catalysts with low Fe content (0.15 and 0.5% w/w in Fe) the quite and return of the metal to the surface occurs in a fast way. On the contrary, in catalysts with high Fe content (2 and 5% w/w in Fe) the formation of less photoactive complexes seems to predominate. FTIR studies have proven the formation of such complexes in the doped catalysts.

Comparative Study of Photocatalytic Degradation Mechanisms of Pyrimethanil, Triadimenol, and Resorcinol

The photocatalytic degradation of an endocrine disruptor (resorcinol) and of two fungicides (pyrimethanil and triadimenol) has been studied and compared. The effect of pH, oxygen, and H 2 O 2 on the photocatalytic degradation of these compounds has been established. The three organics were analyzed by means of high pressure liquid chromatography (HPLC) and their mineralization by total organic concentration (TOC) measurements. The evolution of the toxicity to Lemna minor of the aqueous solutions of the three organics during their photocatalytic treatment has also been studied. The obtained results have been interpreted according to Fourier transform infrared studies on the interaction of the molecules with the catalyst surface and their reaction mechanisms by gas chromatographpy-mass spectrometry (GC-MS) analyses. The toxicity studies have shown that some intermediates acted as nutrients or toxicity antagonists as negative growth rate inhibitions were obtained. After 30 min of reaction, the resorcinol and pyrimethanil solutions were detoxified, although some amount of the organics still remained. In the case of triadimenol, a 92% detoxification was achieved after 60 min of reaction. The solar photocatalytic degradations of the pollutants have resulted to be comparable with those obtained with UV lamp. The obtained results suggest that the type of interaction of pyrimethanil and triadimenol with the TiO 2 surface decides their degradation mechanism by which the effect of pH, H 2 O 2 , and dissolved oxygen is determined. It has also been confirmed that the photocatalytic techniques are very efficient at the detoxification of wastewaters contaminated with these fungicides.

The Effect of Modifying TiO2 on Catechol and Resorcinol Photocatalytic Degradation

The photocatalytic features of TiO 2 doped with ferric oxides or mixed with activated carbon (AC-TiO 2 ) are compared with those of the unmodified Degussa P-25 TiO 2 . These new catalysts show specific structural features that alter catechol and resorcinol photodegradabilities, according to their chemical structures. For instance, we have observed that Fe oxides located on the TiO 2 particle surface hamper these dihydroxybenzenes degradation. Likewise, AC-TiO 2 catalysts have shown improved catechol photodegradability with respect to that of TiO 2 , while that of resorcinol is not altered. These studies show that catechol and resorcinol adsorption patterns are different, i.e., they have different adsorption centres on the catalyst surface and are differently affected by photonic flux variations.

FTIR study of the photocatalytic degradation of NH4+ determination wastes

In this work we present the results of the application of photocatalytic techniques to organic pollutants in water. Such aqueous wastes are produced during the UV-Vis spectrophotometric determination of the NH 4 + ion in water. Processes taking place during the photocatalytic degradation of such organics have been studied by using FTIR, HLPC and TOC measurements. The obtained results suggest that in the presence of light, air and a catalyst (TiO 2 or Fe 2+ ) one of the existing organics, nitroprusside is decomposed to C≡N - , NO 2 - and NO 3 -. Free C≡N - ions react with other intermediates yielding nitrogen-containing compounds such as acetaloximes and acetamides. The photocatalytic degradation of this kind of N-containing compounds seems to be more complicated than the corresponding alcohols and carboxylic groups generated during the individual degradation of phenol, citrate or ethanol. A remarkable affinity of those nitrogenated species in adsorbing onto the TiO 2 surface has been observed. This may be the cause of the reduced catalyst activity observed in the process. It has been also determined that C≡N - ions tend to react with Fe 3+ ions to give complexes like [C≡N-Fe] 2+ and [R-C≡N-Fe] 2+ inhibiting this way the photo-Fenton reaction. In fact, no organic carbon reduction was observed during the application of the photo-Fenton reaction or TiO 2 photocatalysis. Toxicity of the samples was determined before and after the application of the photo-Fenton reaction and TiO 2 photocatalysis. Toxicity as determined by using the algal species Phaedactylum tricornutum after the photocatalytic treatment was higher. This suggests the possible above mentioned recombination of chemical species during the degradation of the samples.

Conventional and photocatalytic degradation of aromatic amines from nitrite determination wastes

Different methods such as KMnO4 oxidation, TiO2-photocatalysis and photo-Fenton reaction have been employed for the degradation of wastes from the spectrophotometric determination of in seawater. The optimisation of the degradation process was determined by total organic carbon (TOC) measurements. Experimental parameters such as pH, TiO2, H2O2, Fe3+ or Fe2+ concentrations have been checked. The highest TOC reduction was achieved by applying the photo-Fenton reaction with 0.02 g of FeSO4 and 3 mL of H2O2 for every 100 mL of sample. Mean TOC reductions of about 78 and 47% were achieved by photo-Fenton reaction and TiO2-photocatalysis, respectively. The addition of potassium oxalate to the photo-Fenton reaction enhanced the mineralisation efficiency. The mineralisation of individual components of the samples by photo-Fenton reaction was also attempted. Sulphanilamide was degraded to a large extent since TOC reductions of about 83% were achieved. In contrast N-(1-naphtyl-)-ethylenediamine degradation was negligible and TOC reduction was never larger than 6%. Degradation of N-(1-naphtyl-)-ethylenediamine by KMnO4 yielded a TOC reduction of 40.89%. The application of a KMnO4 pretreatment enhances the oxalate--photo-Fenton reaction efficiency by greatly reducing the irradiation time. The solar photo-Fenton reaction of the sample gave a TOC reduction of about 70%. After the treatment wastes lose their characteristic pink colour becoming nearly transparent or showing a very subtle yellowish colour.

Adsorption and Photocatalytic Degradation of Phthalic Acid on TiO2 and ZnO

Abstract The photocatalytic degradation of phthalic acid (H2Ph) with TiO2 (Degussa P-25) and ZnO (Aldrich) at different pHs and substrate concentrations (10-150 ppm) has been studied. The concentration and mineralization of H2Ph has been monitored. Results in optimal conditions are: ko = 6.63 · 10-4 s-1, %TOC = 86.02 for TiO2 and ko = 12.7 · 10-4 s-1, %TOC = 81.90 for ZnO. Dissolved zinc was monitored during reaction. Zinc concentration in solution showed a maximum when that of the organic compound was at its minimum. At this step zinc in solution decreases. Catalyst solubility, catalyst photocorrosion and extraction by the substrate, could be main processes explaining dissolved zinc concentration along the reaction. Adsorption and rate constants have been obtained by using the Langmuir-Hinselwood model. Adsorption constants in the dark and adsorption constants obtained from Langmuir-Hinselwood kinetic model have been compared. The adsorption constant values in TiO2 studies are greater than in ZnO ones. Considering the relationship between degradation rate and surface bonding FTIR studies have been performed. FTIR results show that H2Ph molecule interacts with ZnO and TiO2 surfaces. In both cases, H2Ph interaction occurred by means of the formation of a phthalate.

Valorisation of a by-product from the TiO2 pigment industry for its application in advanced oxidation processes

AbstractThe aim of this study was to find a recycling use for waste material (WTiO2) that results from the extraction process of TiO2 from ilmenite in the pigment industry. In view of its high TiO2 content, the photocatalytic activity of this material was tested in the degradation of humic and fulvic acid substances (HFAs) and showed low levels of photoactivity, as was the case for the commercial photocatalyst Aeroxide TiO2 P25 (P25). However, due to its high Fe3+ content, an important application was observed for WTiO2 as an HFA coagulant and catalyst in Fenton and photo-Fenton processes. A two-stage process of coagulation and photo-Fenton treatment was subsequently designed and conducted at laboratory and small pilot scale. High percentages (above 95%) were obtained in total organic carbon (TOC) removal.