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Titanate nanotubes (NTs) were synthesised by the hydrothermal method and later calcined at temperatures between 100–500°C. The calcined NTs were characterised and evaluated in the physicochemical adsorption of the safranin dye and photocatalytic degradation of caffeine. The materials calcined at low temperatures displayed a tubular structure and the H2Ti3O7 crystalline phase, which was transformed into anatase nanoparticles at 400°C. The NTs treated at 100°C showed the highest adsorption capacity (94%). Safranin was adsorbed through an ion-exchange mechanism, following the Langmuir isotherm and a pseudo-second-order kinetic model. While NTs calcined at lower temperatures were better for adsorption, the photocatalytic degradation of caffeine increased in samples calcined at higher temperatures with a maximum removal of 72%. The photocatalytic behaviour of the NT samples confirmed that the crystalline anatase structure in conjunction with structural OH groups enhanced the photocatalytic activity. The addition of isopropanol as a scavenger confirmed the important role played by the •OH radicals in the photocatalytic process. NTs calcined at 300°C were efficient for both adsorption and photocatalytic processes. Due to its efficiency, this sample was reused after dye adsorption for the photocatalytic degradation of caffeine under visible light due to its enhanced absorbance in the visible region. This research work shows the potential of NTs for wastewater purification. [ABSTRACT FROM AUTHOR]

Titanate nanotubes (TNTs) were prepared by the hydrothermal method and rinsed at different pH values (2, 5, 8, 11 and 14). The material TNT-11 reached the best copper removal (98.1 mg·g−1) with a TNT dosage of 200 mg·L−1, [Cu(II)] of 20 mg·L−1 and pH 7. This material presented H2Ti3O7 and Na2Ti3O7 as crystalline phases, a surface area of 250 m2·g−1, and 13 wt.% of sodium content. The adsorbed TNT-11@Cu material was reutilized in the water splitting reaction with hydrogen production of 2139 µmolH2·g−1 after 5 h. It was found that the outstanding behavior stemmed from the formation of Cu2O. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation of Rhodamine B was carried out by decorated V2O5/NT and WO3/NT titanate nanotubes with Pt (0.3 wt. %) under visible light irradiation. The effect of parameters such as titanic acid phase, surface area and photocatalyst load on the deactivation of the photocatalytic degradation of Rhodamine B were studied. Photoatalysts were characterized by SBET, XRD, UV‐vis, XPS, HR‐TEM, and H2‐TPR. We found that Pt‐WO3/NT photocatalyst reached 90% of dye degradation in 60 min. WO3/NT reached 60% after 90 min under 450‐nm visible light irradiation and pH neutral. The incorporation Pt nanoparticles into WO3/NT and V2O5/NT supports increased remarkably the photocatalytic activity during degradation of Rhodamine B. After reaction, an evolution from VO2 to V2O5 was observed. We also found the transition from W5+ to W6+. The transition from Pt0 to Pt2+ was also observed. We concluded that the presence of Pt hinders the oxidation of the oxygen species on the surface of the titanate nanotubes. Addition of Pt nanoparticles enhances the reduction process from V5+ to V4+ and V3+ for Pt‐V2O5/NT and from W+6 to W+5 on Pt‐WO3/NT photocatalyts. After 60 min of reaction under visible light, Pt hinders the oxidation process of V and W to promote the conversion of Rhodamine B. [ABSTRACT FROM AUTHOR]

Nickel-doped TiO2 (0.1, 0.5, 1.0, 2.5, 5.0, and 10.0 wt%) photocatalysts were prepared by the sol-gel method. Physicochemical properties were determined by the characterization using X-ray diffraction, Raman and UV-vis diffuse reflectance spectroscopies, N2 physisorption, and zeta potential determination (PZC). The synthesized materials exhibited the photocatalytically active anatase crystalline phase and the catalysts exhibited stronger absorption in the visible light region with a red shift in the adsorption edge with the increase of Ni doping. The photocatalytic evaluation of TiO2−Ni materials was carried out on p-arsanilic acid (p-ASA, 10 mg L−1) degradation in aqueous suspension under visible radiation. Compared with bare TiO2, the TiO2-Ni 1.0 material (1 wt% Ni-doped TiO2) exhibited higher photocatalytic activity on p-ASA degradation under visible light irradiation allowing a 76% degradation percentage in 180 min reaction time while 60% degradation percentage was achieved with undoped TiO2. The TiO2-Ni 1.0 material showed the highest surface area in comparison with the other prepared materials. Meanwhile, the photocatalytic activity of TiO2-Ni 1.0 can keep even after three cycles with not loss of activity since nickel was not leached from the TiO2-based catalyst into the solution during photocatalytic reaction. Therefore, the doping of the nickel into the TiO2 lattice by the sol-gel method allowed its activation under visible radiation and an efficient photoexcited charge separation to prevent electron-hole recombination showing high chemical stability. [ABSTRACT FROM AUTHOR]

Iron doped TiO materials were prepared by the sol-gel method and used as supports of gold nanoparticles synthesized by the deposition-precipitation technique. The gold-iron-titania catalysts were characterized by X-ray diffraction, Raman spectroscopy, N physisorption, UV-Vis spectroscopy as a function of temperature, H-temperature programmed reduction, transmission electronic microscopy and X-ray photoelectron spectroscopy. The gold-iron catalysts were catalytically active during the CO oxidation reaction at low temperatures, reaching CO conversion percentages of almost 80% at room temperature. The Au/TiO-Fe catalyst surface was characterized through infrared spectroscopy (DRIFTS) during the CO oxidation reaction to elucidate the active sites and the real carbon monoxide interaction during the reaction. A 24-h deactivation test corroborated a final deactivation of the catalysts of only 25% for both Au/TiO-Fe 1 and the bare Au/TiO. The results here obtained corroborate that the activity of the iron-doped TiO catalyst was higher than that of the bare TiO due to the iron incorporation into the TiO lattice, which allows the formation of surface oxygen vacancies and new adsorption sites which favor the CO adsorption and its oxidation to CO. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The photocatalytic degradation/adsorption process of the β-blocker atenolol (ATL) under UV irradiation is described using two types of silver decorated catalysts: silver/titania and silver/titanates. The silver ions were reduced on the surface of TiO2-P25-Degussa using gallic acid. Silver/titanates were prepared by a microwave-assisted hydrothermal method using the silver/titania as the starting material to obtain the hydrogen titanate (H2Ti3O7) structure with tubular morphology. These materials were characterized by X-ray diffraction, UV-Vis spectroscopy, N2 physisorption, temperature programmed reduction, TEM, and FTIR spectroscopy. During the photocatalytic process, the ATL molecules were completely converted to amino-diol byproducts. It is the first time that these materials have been applied during the photocatalytic process in the degradation of pharmaceuticals products. The success of the silver nanoparticles (2 nm) consists of the homogeneous distribution over the surface of titanate nanotubes inhibiting the hole/electron recombination promoting the oxidation process. The Ag@H2Ti3O7 with a concentration of silver as 1.0% shows the highest adsorption/degradation of ATL than the Ag@TiO2 and the P25-Degussa. The great performance in the reuse test consists in the strong attachment of the silver nanoparticles on the titanium surface that inhibits the silver lixiviation during the photocatalytic tests. [ABSTRACT FROM AUTHOR]

Nickel-doped-TiO 2 catalysts were prepared by the sol–gel method and surface modified with gold nanoparticles (AuNPs) by the urea-deposition-precipitation technique. The as-synthesized catalysts were characterized by X-ray diffraction, Raman and XPS spectroscopies, N 2 physisorption, STEM-HAADF microscopy and TPR hydrogen consumption. The Au/TiO 2 -Ni catalysts were evaluated catalytically performing CO oxidation reactions. The catalyst with nickel content of 1 wt. % (Au/TiO 2 -Ni 1) showed the highest CO conversion with respect to the high-nickel-content or bare/commercial TiO 2 at 0 °C. In situ DRIFTS showed a strong participation of both nickel due to the presence of surface-nickel-metallic nanoparticles formed during the CO adsorption process at reaction temperatures above 200 °C, and surface-bridged-nickel-CO species. A minor deactivation rate was observed for the Au/TiO 2 -Ni 1 catalyst in comparison with the Au/TiO 2 one. The oxygen vacancies that were created on the sol–gel-doped TiO 2 improved the catalytic behavior during the performance of CO oxidation reactions, and inhibited the AuNP sintering. [ABSTRACT FROM AUTHOR]

Cu-TiO 2 photocatalysts were prepared by the sol-gel method. Copper loadings from, 1.0 to 5.0 wt % were used. The materials were annealed at different temperatures (from 400 to 600 °C) to study the formation of brookite and copper ionic species. The photocatalysts were characterized by X-ray diffraction, UV-vis, Raman and XPS spectroscopies, H 2 -temperature programmed reduction (TPR), N 2 physisorption, and SEM-EDS to quantify the actual copper loadings and characterize morphology. The photocatalysts were evaluated during the hydrogen photocatalytic production using an ethanolic solution (50% v/v) under UV and visible radiation. The best hydrogen production was performed by Ti-Cu 1.0 with an overall hydrogen production that was five times higher than that obtained with photolysis. This sample had an optimal thermal treatment at 500 °C, and at this temperature, the Cu 2 O and brookite/anatase ratio boosted the photocatalytic production of hydrogen. In addition, a deactivation test was carried out for the most active sample (TiO 2 -Cu 1.0), showing unchanged H 2 production for three cycles with negligible Cu lixiviation. The activity of hydrogen-through-copper production reported in this research work is comparable with the one featured by noble metals and that reported in the literature for doped TiO 2 materials., (Copyright © 2017 Elsevier Ltd. All rights reserved.)