Photocatalytic degradation of humic acids using substrate-supported Fe3+-doped TiO2 nanotubes under UV/O3 for water purification

Abstract

In this paper, Fe 3+ -doped TiO 2 nanotubes (FeTNTs) were successfully synthesized using hydrothermal method. Four different types of substrates, more specifically, ceramsite, zeolite, activated alumina, and activated carbon (AC), have been investigated in the study. The substratesupported Fe-TNTs were used to effectively decompose humic acids (HAs) in water under O 3 /UV conditions. The experiment results show that the highest photocatalytic activity was obtained in the presence of AC-supported 1.0 atomic percent (at.%) Fe-TNTs calcined at 500°C, as HAs was removed by 97.4 %, with a pseudo-first-order rate constant of 0.126/min. The removal efficiencies of HAs reduced when the catalysts was repeatedly used, since the amount of adsorption sites of the supporting substrates decreased. However, even after the catalyst was repeatedly used for five times, the removal efficiency of HAs in the presence of AC-supported catalyst, which was 78.5 %, was still sufficient in water treatment. The enhanced photocatalytic activity of AC-supported Fe-TNTs was related to a synergistic effect of AC adsorption and Fe-TNT photocatalytic ozonation.

The Role of Catalytic Ozonation Processes on the Elimination of DBPs and Their Precursors in Drinking Water Treatment

“…As a difference from catalytic ozonation, so far literature only reports just one work dealing with the combination of ozone, catalyst and light, that is, photocatalytic ozonation (PhCatOz) to remove natural organic matter, NOM, or humics from water [194]. Photocatalytic ozonation is an emerging AOP where hydroxyl radicals may generate from different mechanisms including adsorption and oxidation of water or hydroxyl groups on the valence band of the catalyst, ozone decomposition, reactions of ozone and oxygen with electrons of the conduction band of the catalyst or even reaction of ozone with possible hydrogen peroxide formed from superoxide ion recombination or from direct ozone-organics reactions [27].…”

“…According to WOS data base there are 160 works on photocatalytic ozonation so far published. As said before, however, only the work of Yuan et al [194] treats photocatalytic ozonation for the removal of humics to reduce THM and TOX formation potential. Nonetheless, treatment of humics or NOM with photocatalysis and ozone as a sequence of processes has some antecedents due to Kerc et al [202], Bekbolet et al [203], and Uyguner et al [204].…”

“…The results show the better performance of the sequential oxidation process (ozonation followed by photocatalytic oxidation) to decrease TOXFP. Coming back to the work of Yuan et al [194], PhCatOz is applied, in this case, to remove a humic acid (its origin is not reported) with ozone, UVC radiation (250-260 nm with 254 nm as main wavelength) and different TiO 2 catalysts in powder or supported form. Supported materials were ceramsite, zeolite, alumina, and activated carbon (AC), while the composite prepared was Fe on TiO 2 nanotubes (Fe-TNT).…”