Clay-supported TiO 2 photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a bench-top photocatalytic flow reactor was used to evaluate the efficiency of hectorite-TiO 2 and kaolinite-TiO 2 , two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (λ max = 365 nm) or UVC (λ max = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay-TiO 2 composites was compared with that of pure TiO 2 (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO 2 composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of ~170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33 and 66 % relative humidity (RH). be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, T r /I λ , the UV/TiO 2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO 2 (P25 and Hecto-TiO 2 ), but not for Kao-TiO 2 . In all cases, reaction rates

We studied the synthesis and photocatalytic activity of small-sized TiO 2 supported on hectorite and kaolinite. Deposition of TiO 2 on the clay mineral surface was conducted by using a sol-gel method with titanium isopropoxide as precursor. Anatase TiO 2 particles formation was achieved by hydrothermal treatment at 180 °C. Material characterization was conducted using XRD, SEM, XPS, ICP-OES, BET and porosimetry analysis.Efficiency in synthesizing clay-TiO 2 composites depended strongly on the clay mineral structure. Incorporation of anatase in hectorite, an expandable clay mineral, was found to be very significant (> 36 wt.% Ti) and to be followed by important structural changes at the clay mineral surface. Instead, no major structural modifications of the clay were observed for kaolinite-TiO 2 , as compared with the untreated material. Photocatalytic performance of clay-TiO 2 composites was evaluated with ATR-FTIR following the oxidation of adsorbed toluene and d-limonene, two model air pollutants. In either case, the photocatalytic removal efficiency of these hydrophobic substrates by the synthesized clay-TiO 2 composites was comparable to that observed using pure commercial TiO 2 (Degussa P25).

We investigated the adsorption capacity and photocatalytic removal efficiency of formaldehyde using a hectorite-TiO 2 composite in a bench flow reactor. The same experimental conditions were applied to pure TiO 2 (Degussa P25) as a reference. The catalysts were irradiated with either a UVA lamp (365 nm) or with one of two UVC lamps of 254 nm and 254+185 nm, respectively.Formaldehyde was introduced upstream at concentrations of 100 -500 ppb, with relative humidity (RH) in the range 0 -66 % and residence times between 50 and 500 ms. Under dry air and without illumination, saturation of catalyst surfaces was achieved after ~200 min for P25 and ~1000 min for hectorite-TiO 2 . The formaldehyde uptake capacity by hectorite-TiO 2 was 4.1 times higher than that of P25, almost twice the BET surface area ratio. In the presence of humidity, the difference in uptake efficiency between both materials disappeared, and saturation was achieved faster (after ~200 min at 10% RH and ~60 min at 65% RH). Under irradiation with each of the three UV sources, removal efficiencies were proportional to the Ti content and increased with contact time. The removal efficiency decreased at high RH. A more complete elimination of formaldehyde was observed with the 254+185 nm UV source.

Small-sized environmental particles such as 2:1 phyllosilicates induce oxidative stress, a primary indicator of cell damage and toxicity. Herein, potential hazards of clay particle uptake are addressed. This paper reports that the content and distribution of structural Fe influence the ability of expandable clay minerals to induce lipid peroxidation (LP), a major indicator of oxidative stress, in biological matrices. Three smectite clays, hectorite (SHCa-1) and two nontronites (NAu-1) and (NAu-2) containing varying total content and coordination environment of structural Fe, were selected. Screening and monitoring of LP was conducted using a thiobarbituric acid reactive substances (TBARS) assay. The higher content of TBARS in nontronites than that in SHCa-1 suspensions was explained because structural Fe contributes to LP. The observed lack of correlation between TBARS content and the extent of Fe dissolution indicated that the formation of TBARS is surface controlled. Results showing a high TBARS content in SHCa-1 but not in nontronite supematant solutions was explained because the former contains distinct, soluble chemical component(s) that could (i) induce LP by its (their) own right and (ii) whose chemical affinity for organic ligands used as inhibitors is weak. Clays serve as stronger inductors than 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) but are much weaker than FeSO4. The outcome of this work shows that LP is clay surface-controlled and dependent on clay structural composition.

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