Ambient temperature ZrO2-doped TiO2 crystalline photocatalysts: Highly efficient powders and films for water depollution

Abstract

In this paper, several TiO2 materials doped with zirconia precursor (0.7, 1.4, 1.6 and 2.0 mol%) were synthesized by an easy aqueous sol-gel synthesis at ambient temperature. This method consisted in the peptization of the TiO2 colloid in presence of HNO3. The corresponding pure TiO2 material was also synthesized for comparison. The performances and the physicochemical properties of these materials were compared to the well-known Evonik P25 photocatalyst.The physico-chemical characterizations showed that nano-crystalline anatase-brookite particles were produced with the sol-gel process, with higher specific surface area than P25 (~ 200 m 2 g -1 vs. 47 m 2 g -1 ). All samples presented a higher visible absorption than P25. The XPS spectra showed that all the samples were doped with nitrogen and that mixed TiO2-ZrO2 oxide materials were obtained when doping with zirconia precursor.Photoactivity was evaluated through the degradation of p-nitrophenol in water. On the one hand, under UV/visible light, the ZrO2 doping increased the degradation efficiency of the pure TiO2 catalyst due to a better charge separation in the mixed TiO2-ZrO2 oxides. The activity of the sample with the highest dopant content was even higher than the one of P25. On the other hand, under visible light, all samples were much more efficient than P25. This activity shift towards visible range was due to the N-doping of the catalysts, with a slight improvement for the doped ones.Finally, the feasibility of producing films starting from an aqueous suspension of the photocatalyst was assessed on P25, pure TiO2 and the best doped material. The photoactivity of these films, evaluated on the degradation of methylene blue under UV-A light, showed that the sample with the highest dopant concentration had an efficiency 4 times higher than pure TiO2 and 20 times higher than P25.

Green Synthesis of N/Zr Co-Doped TiO2 for Photocatalytic Degradation of p-Nitrophenol in Wastewater

“…Thus, the crystallization of amorphous TiO 2 into anatase and brookite structures is less favored with a higher zirconium loading, as reported by other authors [41]. It is also observed in Table 2 that the TiO 2 crystallite sizes, d XRD , slowly increase from 4 to 6 nm with increasing zirconium content, as already observed by Mahy et al [14]. Table 2.…”

“…These textural properties are typical of TiO 2 samples doped with zirconium and prepared with the peptization-precipitation method [14]. This is due to the spherical shape of the nanoparticles in between which small voids (<2 nm) lie [14]. It is possible to see on TEM micrographs (see next section, Figure 5C) these small TiO 2 nanoparticles.…”

“…From the specific surface area, S BET , it is possible to estimate the elementary TiO 2 particle size, d BET , with Equation 2 For the pure TiO2 sample and all samples only doped with Zr (TiO2/Zr0.7, TiO2/Zr1.4, TiO2/Zr2 and TiO2/Zr2.8), the isotherms are similar: a strong increase in adsorbed volume at low pressure, followed by a plateau, corresponding to a microporous solid (type I isotherm from the BDDT classification) [14,51]. The values of the specific surface area, SBET, and microporous volume, VDR, are similar for all samples, between 195 and 210 m 2 g −1 for SBET and equal to 0.11 cm 3 g −1 for VDR (Table 2).…”

“…To reach these goals, modifications of TiO 2 were envisaged with the incorporation of metallic or non-metallic atoms. The list of doping elements in literature is long and includes transition metal ions such as Zr [14], Cu [15], Co [16], Ni [17], Cr [18], Mn [19], Mo [20], Nb [21], V [22], Fe [23], Ru [24], Au [25], Ag [26], and Pt [11], or nonmetallic ions such as N [27], S [28], C [29], B [30], P [31], I [32], and F [33]. The combination with other semiconductors, having a lower band gap energy, was also studied [34], as well as the sensitization of TiO 2 with organic or organometallic dyes [35].…”

“…In this study, TiO 2 powders were doped with two nitrogen precursors (urea and triethylamine) and with a zirconium source. The photocatalysts were prepared by an aqueous sol-gel method, combining and optimizing two methods developed previously in Mahy et al [14,27]. Emphasis was placed on the development of a green process by using water as solvent and no calcination step to crystallize the titania.…”