Discovering the Determining Parameters for the Photocatalytic Activity of TiO₂ Colloids Based on an Anomalous Dependence on the Specific Surface Area

Abstract

The photocatalytic (PC) performance of titanium dioxide (TiO 2 ) nanoparticles strongly depends on their specific surface, the presence of crystal defects, their crystal phase, and the exposed crystal facets. In order to understand which of these factors contributes most significantly to the PC activity of TiO 2 colloids, all of them have to be individually analyzed. This study entails the synthesis of five anatase nanocrystal samples. By maintaining the same reactant ratios as well as hydrothermal sol-gel synthesis route and only varying the autoclaving time or temperature, different crystallite sizes are obtained under comparable experimental conditions. A decrease in PC performance with increase in specific surface area is found. Such an unexpected counterintuitive result establishes the basis for a better understanding of the crucial factors that ultimately determine the PC activity. These are investigated by studying nanocrystals bulk and surface structure and morphology using a selection of complementary analysis methods (X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), X-ray diffraction (XRD)…). It is found that a change in the nanocrystal morphology from an equilibrium state truncated tetragonal bipyramid to a more elongated rod-like structure accompanied by an increase in oxygen vacancies is responsible for an augmented PC activity of the TiO 2 nanocrystals. PhotocatalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Functionalisation of TiO2 nanoparticles with a fluorescent organosilane: A synergy enabling their visualisation in biological cells and an enhanced photocatalytic activity

“…Synthesis of TiO 2 NPs functionalised with a luminescent silylated coupling agent: TiO 2 @4 Anatase NPs were hydrothermally synthesised in order to obtain a diameter of around 8 nm. [26] Their chemical and physical properties have previously been reported by our group (including X-ray diffraction, transmission electron microscopy, DLS, zeta potential, nitrogen sorption, IR spectroscopy and thermogravimetric analysis). [26] The NPs were functionalised with the luminescent silylated coupling agent 4 in order to implement luminescent properties to the system.…”

“…[26] Their chemical and physical properties have previously been reported by our group (including X-ray diffraction, transmission electron microscopy, DLS, zeta potential, nitrogen sorption, IR spectroscopy and thermogravimetric analysis). [26] The NPs were functionalised with the luminescent silylated coupling agent 4 in order to implement luminescent properties to the system. This coupling agent was designed to contain an anchoring group, a spacer moiety and a chromophore.…”

“…TiO 2 NPs synthesis has already been described in detail elsewhere. [25,26] Briefly, titanium(IV) butoxide, 2-[2-(2-methoxyethoxy)ethoxy] acetic acid and water were used as reactants in a molar ratio of 1.00/ 1.89/3.33. Water was dropped into the mixture of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid and titanium(IV) butoxide and stirred overnight.…”

“…The PC activity of the synthesised samples was assessed via measuring the produced Cl-during the dichloroacetic acid degradation under UV light application as already described before. [26] The only modification was the reduction of the reactor volume and thus, of the measured solution to 0.5 L (water, 100 mg/L NP and 1 g/L dichloroacetic acid).…”

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage

“…Wintzheimer et al. studied the valence state and composition of synthesized TiO 2 nanoparticle using XPS and XAFS [69] . In their work, XPS spectra showed no signal of oxygen defect, indicating the absence of defects in the shallow layer.…”