Towards a large scale aqueous sol-gel synthesis of doped TiO2: Study of various metallic dopings for the photocatalytic degradation of p-nitrophenol (original) (raw)
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Effect of N-doping on the photocatalytic activity of sol–gel TiO2
In order to study the visible light photocatalytic activity of nitrogen doped titanium dioxide, the interaction between nitrogen dopant sources and titania precursors during sol–gel synthesis is investigated. N–TiO2 was synthesised using the sol–gel method using 1,3-diaminopropane as a nitrogen source. Samples were annealed several temperatures and the percentage of rutile present determined by X-ray diffraction to be 0% (500 ◦C), 46% (600 ◦C), and 94% (700 ◦C). The reducing amounts of anatase at higher temperatures are studied using FTIR, which suggests the absence of any polymeric chains formed by the chelating agents, which would normally extend anatase-to-rutile transformation temperatures. Differential scanning calorimetry shows that crystalliation occurs before 500 ◦C, providing the crystalline form determined by XRD at 500 ◦C. Increased temperature also resulted in diminished visible light absorption capability, with only the 500 ◦C sample showing significant absorption in the visible region. XPS studies revealed that nitrogen remained within the TiO2 lattice at higher temperatures. Consequent with the reduced visible light absorption capacity, photocatalytic activity also reduced with increased annealing temperature. Degradation kinetics of methylene blue, irradiated with a 60 W house-bulb, resulted in first order degradation rates constants of 0.40 × 10−2, 0.19 × 10−2, and 0.22 × 10−2 min−1 for 500, 600, and 700 ◦C respectively. Degradation of Degussa P25 was minimal under the same conditions, and that of undoped TiO2 was 0.02 × 10−2 min−1. Similarly, using 4-chlorophenol under solar irradiation conditions, the N-doped sample at 500 ◦C substantially out-performed the undoped sample. These results are discussed in the context of the effect of increasing temperature on the nature of the band gap.
The Journal of Physical Chemistry B, 2002
A set of polycrystalline TiO 2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the particles, and a not homogeneous distribution of the metal species onto the surface of catalyst particles. The impregnated samples revealed recombination rates always higher than that of bare TiO 2 . The photoactivity of TiO 2 was reduced by the presence of transition metal ions with the exception of W, which instead played a beneficial role. The results of femtosecond pumpprobe diffuse reflectance spectroscopy appear quite in accord with the observed photocatalytic activity only for the lowest values of electron-hole recombination rate of the samples.
Synthesis, characterization and activity of photocatalytic sol–gel TiO 2 powders and electrodes
Applied Catalysis B-environmental, 2009
The efficiency of photoelectrocatalytic processes is strongly influenced by the electrode type and synthesis procedure. This work reports the sol-gel synthesis and characterization of TiO 2 and Fe-doped TiO 2 powders and electrodes as a function of pH and preparation temperatures and the correlation of their photoelectrochemical properties with their activity for azo dye decolourization. pH is shown to be the variable that most influences the formation of the TiO 2 crystalline phases, the photocurrents of the electrodes, and consequently their photocatalytic activity.
Green Synthesis of N/Zr Co-Doped TiO2 for Photocatalytic Degradation of p-Nitrophenol in Wastewater
Catalysts
TiO2 prepared by a green aqueous sol–gel peptization process is co-doped with nitrogen and zirconium to improve and extend its photoactivity to the visible region. Two nitrogen precursors are used: urea and triethylamine; zirconium (IV) tert-butoxide is added as a source of zirconia. The N/Ti molar ratio is fixed regardless of the chosen nitrogen precursor while the quantity of zirconia is set to 0.7, 1.4, 2, or 2.8 mol%. The performance and physico-chemical properties of these materials are compared with the commercial Evonik P25 photocatalyst. For all doped and co-doped samples, TiO2 nanoparticles of 4 to 8 nm of size are formed of anatase-brookite phases, with a specific surface area between 125 and 280 m2 g−1 vs. 50 m2 g−1 for the commercial P25 photocatalyst. X-ray photoelectron (XPS) measurements show that nitrogen is incorporated into the TiO2 materials through Ti-O-N bonds allowing light absorption in the visible region. The XPS spectra of the Zr-(co)doped powders show the p...
Journal of Cleaner Production, 2019
Nitrophenols are used extensively in the chemical, pharmaceutical, and pesticide industries. Recently, water pollution caused by nitrophenols has gained worldwide attention. Significant efforts have been made over the past years to develop effective treatment options for the removal of nitrophenols in aqueous phase. Photocatalysis using titanium dioxide (TiO 2) is regarded as one of the most effective options to degrade nitrophenols in contaminated water. This review deals with the performance of TiO 2 photocatalysis for the degradation of nitrophenols and related mechanisms. The performance of TiO 2 photocatalysts is assessed by comparing basic performance metrics such as quantum yields and reaction rates before and after modification (e.g., pristine vs. modified forms). Results suggest that TiO 2-based photocatalysis is a promising treatment option for degrading nitrophenol.
The advancements in sol–gel method of doped-TiO 2 photocatalysts
A critical review on the advancements in sol-gel method of doping TiO2 photocatalysts is provided. Various sol-gel and related systems of doping were considered, ranging from co-doping, transition metal ions doping, rare earth metal ions doping to other metals and non-metals ions doping of TiO2. The results available showed that doping TiO2 with transition metal ions usually resulted in a hampered efficiency of the TiO2 photocatalyst, though in some few cases, enhancements of the photocatalytic activity of TiO2 were recorded by doping it with some transition metal ions. In most cases, co-doping of TiO2 increases the efficiency of its photocatalytic activity. The review reveals that there are some elemental ions that cannot be used to dope TiO2 because of their negative effects on the photocatalytic activity of the catalyst, while others must be used with caution as their doping will create minimal or no impacts on the TiO2 photocatalytic efficiency.