Photodegradation of benzothiazole ionic liquids catalyzed by titanium dioxide and silver-loaded titanium dioxide

In recent years, ionic liquids(ILs) have been widely used in extraction, synthesis, electrochemistry and other fields.Meanwhile, the environmental impact of ILs has been attracting a lot of attention, and eco-friendly treatment for ILs is becoming a necessary subject. In this study, photocatalytic degradations of benzothiazole ILs catalyzed by titanium dioxide(TiO_2) and silver-loaded titanium dioxide(Ag/TiO_2) were studied for the first time. The degradation of benzothiazole hexafluorophosphate([C4 Bth]PF6) could reach more than 99% within 240 min with the catalysis of TiO_2. To improve catalytic efficiency, Ag/TiO_2 was synthesized and characterized by UV–Vis diffuse reflectance absorption spectra(DRS) and X-ray photoelectron spectroscopy(XPS). The degradation of [C4 Bth]PF6 could reach more than 99% within 120 min in the degradation catalyzed by Ag/TiO_2. The photodegradation products of benzothiazole ILs are composed of inorganic substances or organic substances with simpler structures, which are easier to decompose and less toxic. The degradation system proposed by this study could provide a simple, green,safe, and economical method for the efficient treatment of benzothiazole ILs.     

Factors affecting the interfacial adsorption of stabilisers on to titanium dioxide particles (flow microcalorimetry, modelling, oxidation and FTIR studies): Nano versus pigmentary grades

A series of nano and micron particle size anatase and rutile titanium dioxide (TiO₂) were prepared with various densities of surface treatments in order to examine the influence of the particle size on the photoactivity of the titania particle surface and their degree and nature of interfacial interaction with polymer stabilisers namely, Irganox 1010 (Phenolic type) and Tinuvin 770 (hindered piperidine type). The surface characteristics of the synthesized powders were studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The surface area was determined using the Brunauer Emmett Teller (N₂ BET) method, and particle size measurements using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photochemical activities of the titania particles have been examined by monitoring the oxygen consumption during photo-oxidation of 2-propanol. Surface activity of the titania with stabilisers has also been examined by flow microcalorimetry (FMC) and DRIFTS in order to determine the nature of the interfacial interactions with different polymer stabilisers. Photoactivity assessment verified the higher activity of the nanoparticles. Hydroxyl groups were also found to be accountable for the higher photoactivity of the nanoparticles. The rutile crystal form conferred an inherent photostabilising effect that was further improved by surface coating with alumina. FMC studies revealed that the calcination of nanoanatase increased adsorption activity of hindered phenol and hindered amine probes, with the latter being more strongly adsorbed due to the higher basicity of the amine functionality. DRIFTS indicated adsorption may also occur through the ester functionalities. Calcination of the titania causes a reduction in the surface concentration of Ti–OH and hence a reduction in the amount of strongly adsorbed water blocking the adsorption sites and possibly bridging the amorphous primary particles on the uncalcined sample. With the calcined samples the adsorption activity was proportional to surface area. The physical and chemical nature of these intermolecular forces are assessed and discussed in relation to the potential effects on polymer stabilisation processes.     

A study of the adsorption properties of commercial carbon dioxide corrosion inhibitor formulations

Corrosion rate data for several commercial carbon dioxide corrosion inhibitors have been fitted to the Temkin adsorption isotherm and van't Hoff equation, enabling a determination of the enthalpy of adsorption (H _ad ). It has been found that experimentally determined H _ad values for commercial inhibitor formulations can provide valuable insights into the behaviour of the inherent active components. The temperature sensitivities along with the mechanism of adsorption (physi- or chemisorption) and the minimum concentration required for activity of inhibitors is determinable by this approach. Additionally, FTIR has been used to identify those inhibitors that are tenaciously adsorbed to steel, and suitable for use in batch treatment applications.     

Photocatalytic hydrogenation of acetophenone derivatives and diaryl ketones on polycrystalline titanium dioxide

In the absence of molecular oxygen, various aromatic ketones such as acetophenone derivatives and diaryl ketones were photocatalytically hydrogenated on polycrystalline titanium dioxide (Degussa P25) under UV light irradiation (> 340 nm). The desired secondary alcohols were obtained with excellent chemical efficiency (almost 100% yields for 10 examples) by choosing ethanol as a sacrificial hole scavenger, which was oxidized into acetaldehyde.     

A comparative photocatalytic activity of titanium dioxide and zinc oxide by investigating the degradation of vanillin

The photocatalytic degradation of an organic pollutant such as vanillin has been investigated in aqueous suspensions of titanium dioxide and zinc oxide by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation of the model compound was studied under different conditions such as pH, catalyst concentration, substrate concentration and in the presence of an electron acceptor such as hydrogen peroxide besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts, Hombikat UV100 and ZnO.     

Efficient adsorption and photocatalytic degradation of organic pollutants diluted in water using the fluoride-modified hydrophobic titanium oxide photocatalysts: Ti-containing Beta zeolite and TiO2 loaded on HMS mesoporous silica

Using the F⁻ media, the hydrophobic zeolite and mesoporous silica can be synthesized. These hydrophobic porous materials exhibit the high ability for the adsorption of organic compounds diluted in water and become the useful supports of photocatalyst. The hydrophobic Ti-Beta(F) zeolite prepared in the F⁻ media exhibited high efficiency than the hydrophilic Ti-Beta(OH) zeolite prepared in OH⁻ media for the liquid-phase photocatalytic degradation of 2-propanol diluted in water to produce CO₂ and H₂O. The TiO₂ loaded on the hydrophobic mesoporous silica HMS(F) (TiO₂/HMS(F)), which was synthesized using tetraethyl orthosilicate, tetraethylammonium fluoride as the source of the fluoride and dodecylamine as templates, also exhibited the efficient photocatalytic performance for the degradation. The amount of adsorption of 2-propanol and the photocatalytic reactivity for the degradation increased with increasing the content of fluoride ions on these photocatalysts. The efficient photocatalytic degradation of 2-propanol diluted in water on Ti-Beta(F) zeolite and TiO₂/HMS(F) mesoporous silica can be attributed to the larger affinity for the adsorption of propanol molecules on the titanium oxide species depending on the hydrophobic surface properties of these photocatalysts.     

Kinetic study of the direct causticization reaction involving titanates and titanium dioxide

The solid state reaction between titanium dioxide and sodium carbonate forming sodium titanates was investigated. Reactions between sodium carbonate and titanium dioxide and/or sodium tri-titanate play a key role in the direct causticization of kraft black liquor. Experiments were carried out in a microdifferential reactor made of quartz glass at varying temperatures up to a maximum of 880 °C. Kinetic data were obtained by measuring the release of carbon dioxide. The physical and chemical properties of the reactants and products were analysed in order to obtain a maximum understanding of the reaction path. Scanning electron microscopy (SEM) and the specific surface area of the reactants and products were applied for morphology determination. X-Ray diffraction (XRD) was employed to characterize the phase composition of the product. The results showed that 100% conversion can be obtained at temperatures above 830 °C. Different kinetic models were taken into consideration, such as the Jander and Valensi-Carter models for diffusion-controlled reaction rates and the phase-boundary model for first-order reaction kinetics. One model was based on the theory that the kinetics can be described by the phase-boundary theory at the beginning of the reaction but, as the reaction proceeds, the rate becomes diffusion controlled. This model gave a good fit to the experimental data collected at 840 °C. However, this model did not work as well at high temperature (880 °C) or at lower temperatures as at 840 °C. This was explained by the fact that the reaction path is different at these temperatures, i.e. other reaction products are involved.     

Kinetics and isotherm studies for the adsorption of boron from water using titanium dioxide

Boron is a necessary element for plants that are generally found in the ground and seawater, but it can also be poisonous in large doses. Contamination of water with boric acid or borate ions is a global concern. Due to the absence of the chemical charge that boron possesses, its removal is often difficult. To investigate boron's adsorption characteristics, kinetic, isotherm, and isothermal studies were performed. The adsorption of boron was shown to be a pH-dependent mechanism, with the best results at around pH 9.0. About 47% of the boron from a solution of 50 mg L⁻¹ was removed using 5 g titanium dioxide in 30 min. It was also demonstrated that boron adsorption kinetics increased with temperature, which is best described by the pseudo-second-order kinetic model (R² > 0.98) and also fits well with Elovich and pseudo-first-order models (R² > 0.94) at pH 9.0. Equilibrium was reached in about 40 min for all the samples. The film boundary layer diffusion step limits the rate. Experimental results correspond well to the Freundlich isotherm (R² = 0.95–0.99). Langmuir and Temkin's isotherms also fitted reasonably well (R² = 0.94–0.98). The Freundlich and Langmuir constants indicate favourable adsorption. The Gibbs free energy (ΔG) values increased negatively (from −11.47 to −15.63 kJ mol⁻¹) with increasing temperature, signifying a feasible and spontaneous process. The enthalpy change (ΔH) value of about 30.35 kJ mol⁻¹ indicated endothermic physical adsorption. The results indicate that titanium dioxide is an excellent and safe adsorbent for the removal of boron from water.     

Using photoelectrochemical measurements for distinguishing between direct and indirect hole transfer processes on anatase: Case of oxalic acid

Photocurrents collected from an interface between polycrystalline anatase and an aqueous solution of oxalic acid were measured as a function of oxalic acid concentration and photon flux at 365 nm. According to a kinetic model previously developed, such data can be used as a diagnostic tool for distinguishing between direct oxidation involving valence band holes and an indirect process, involving (surface bound) OH radicals. In the case of oxalic acid studied here, from the linear relation between initial slopes of photocurrent versus concentration and photon flux, a direct process is indicated.     

Determination of the kinetic pathway in the electrochemical reduction of titanium dioxide in molten calcium chloride

An investigation into the kinetics of the electrochemical reduction of titanium dioxide (TiO₂) to titanium metal (Ti) in molten calcium chloride has been performed. Partially reduced samples were prepared by terminating the reduction process after different reaction times and characterised by means of X-ray diffraction analysis. Based on the time-dependent changes of phase composition as well as thermodynamic and kinetic considerations, the reaction path has been derived. The key result is that the reduction proceeds through a number of individual stages some of which involve the formation and decomposition of calcium titanates. Several of the partially reduced samples were examined further through scanning electron microscopy and energy-dispersive X-ray analysis. The results demonstrate that the electrochemical reduction of titanium dioxide to titanium metal is accompanied by substantial changes in the microstructure.     

Photocatalytic degradation of two volatile fatty acids in monocomponent and multicomponent systems: Comparison between batch and annular photoreactors

This study investigates the influence of the inlet concentrations on the degradation rates of a binary mixture of volatile fatty acids (propionic and butyric acids). TiO₂-coated non-woven fibre textile was used as the photocatalyst in a batch reactor and in an annular reactor at laminar flow regime. The humidity level, temperature, UV intensity and flow rate were kept constant. First, the adsorption isotherms were determined and these showed that the propionic acid is less adsorbed than the butyric acid onto the catalyst. Conversely to the adsorption, the photodegradation of pure propionic acid is better than the degradation of pure butyric acid. Photodegradation is greatly inhibited when the two acids are mixed in comparison to the pure compounds. The propionic acid is more affected. This inhibition is attributed to the competitive adsorption of the two species on the active sites of the catalyst. A model which takes into account the competitive adsorption is proposed in order to determine the outlet concentrations of the compounds knowing the inlet concentrations in the annular reactor.     

Insight into the effect of surface carboxyl and amino groups on the adsorption of titanium dioxide for acid red G

In this study, TiO₂ functionalized with organic groups were prepared to study the effect of carboxyl and amino groups on the adsorption behavior of TiO₂ for the removal of acid red G (ARG) as an anionic dye from aqueous solution. TiO₂ was successfully modified with carboxyl and amino groups by using the hydrolysis method with oxalic acid (OAD, with two carboxyl groups), ethylenediamine (EDA, with two amino groups) and DL-alanine (DLA, with one carboxyl group and one amino group) at low temperature (65 °C) and labeled as OAD-TiO₂, EDA-TiO₂ and DLA-TiO₂, respectively. The ARG uptake by the functionalized TiO₂ samples was largely dependent on the functional groups. The interaction between ARG and the functional organic groups on the TiO₂ samples plays an important role in the adsorption process, which leads to the excellent adsorption performance (higher capacity and faster adsorption rate) of the functionalized TiO₂ samples than that of P25 (commercial TiO₂ without modification). Furthermore, there is no obvious loss of the adsorption capacity for the functionalized TiO₂ even after 5 adsorption-desorption cycles, which indicated the good reusability of the modified TiO₂ samples for anionic dye removal from aqueous solution.     

A photoelectrochemical and spectroscopic study of phenol and catechol oxidation on titanium dioxide nanoporous electrodes

The photoelectrochemical behavior of TiO₂ nanoporous thin film electrodes has been studied in the presence of phenol and catechol. Voltammograms, both in the dark and under illumination, as well as photocurrent transients were combined with Attenuated Total Reflection Infrared measurements. Particular attention has been paid to the way that photocurrent is sensitive to the organics concentration. A non-monotonic, unusual tendency has been observed in all cases. For low organics concentration (lower than 0.1 mM), there is a deactivation of the electrode toward the water photooxidation process. Parallel spectroscopic measurements prove that, in this concentration range, the amount of adsorbed phenol (or catechol) is very small (undetectable), which supports the existence of a low coverage of surface active sites for the water photooxidation process. In the high concentration range, an increase of the organics concentration leads to an unexpected decrease in the stationary photocurrent. This behavior, attributed to both the build-up of an intermediate acting as a recombination center and a fouling of the oxide surface, has rarely been observed in TiO₂ heterogeneous photocatalysis.     

Experimental study on the simultaneous adsorption of carbon dioxide and moisture from nitrogen in linde 5 a molecular sieves

Experimental data for the simultaneous adsorption of CO₂ and moisture with variations of some process variables, such as inlet adsorbate concentration, particle Reynolds number, and bed diameter to bed length ratio, have been generated to see their effects on the efficiency of adsorption of CO₂ and moisture. Presence of moisture strongly affects the CO₂ adsorption behaviour leading to roll up of CO₂ concentration breakthrough curves, whereas the presence of CO₂ has an insignificant effect on the moisture adsorption behaviour.     

Using H-titanate nanofiber catalysts for water disinfection: Understanding and modelling of the inactivation kinetics and mechanisms

The H-titanate nanofiber catalyst (TNC), which has a favourable morphological structure for mass transfer and energy access, was proven as a promising alternate titanium dioxide (TiO₂) carrier for photo-inactivation of a sewage isolated E. coli strain (ATCC 11775). This study revealed that the TNC loading is a key process parameter that radically influenced the photo-inactivation of bacteria in an annular slurry photoreactor (ASP) system. Variation in the TNC loadings was found to have a considerable impact on the dissolved oxygen (DO) concentration profiles and subsequently, on the photo-inactivation rates of bacteria in the ASP system. The photo-inactivation reaction in the ASP system was found to exhibit three different bacterial inactivation regimes of shoulder, log-linear and tailing. Resultant photo-inactivation kinetics data was evaluated using both empirical and mechanistic bacterial inactivation models. The modified Hom model was found to be the best empirical model that can represent the sigmoid-type bacterial inactivation pattern. An interesting correlation between the TNC loadings and DO concentration profiles was also established. From the correlation, it was found necessary to integrate a DO limiting reactant term in the newly proposed mechanistic Langmuir–Hinshelwood model to describe the bacterial inactivation mechanisms under two different TNC loading conditions of sub-optimal and optimal, respectively.     

Kinetic behaviour of the adsorption and photocatalytic degradation of salicylic acid in aqueous TiO2 microsphere suspension

A new photocatalyst, named TiO₂ microspheres, prepared by a sol‐spraying‐calcination method, can freely suspend with air bubbling in its aqueous suspension and easily settle down from a water phase under gravity. The experimental results demonstrated that TiO₂ microspheres had better adsorption capacity than conventional TiO₂ powders, due to large surface area, large pore volume, and also a porous structure. The photocatalytic activity of TiO₂ microspheres in aqueous suspension was evaluated using salicylic acid (SA) as a model substrate. It was found that the Langmuir–Hinshelwood model in its integral form described the kinetics of SA photocatalytic degradation in the TiO₂ microsphere suspensions better than its simplified form as a first‐order reaction model, since the significant substrate adsorption on the catalysts was not negligible. The kinetics of SA photocatalytic degradation with different initial concentrations and pH was further investigated. The experiments demonstrated that the change of pH could significantly affect the adsorption of SA in the TiO₂ microsphere suspensions. The effects of substrate adsorption rate and photoreaction rate on the overall performance of photocatalytic degradation is also discussed on the basis of experimental data. Copyright © 2004 Society of Chemical Industry     

A new kinetic model for titanium dioxide mediated heterogeneous photocatalytic degradation of trichloroethylene in gas-phase

This paper focuses on the kinetics of photocatalytic removal and carbon mineralization of gaseous trichloroethylene (TCE) on near-UV irradiated TiO₂ Degussa P25. Experiments were carried out in a flat-plate photoreactor at TCE inlet concentrations of 100–500 ppmv, relative humidities (RH) of 0–62% and gas residence times of 2.5–60.3 s. Gas residence time distribution (RTD) curves revealed an axial dispersed plug flow in the photoreactor with Peclet numbers above 59.4. For all experimental conditions, the carbon mineralization efficiency (5.1–73.0%) was lower than the removal efficiency (8.6–99.9%) and dichloroacetylchloride (DCAC) was detected as a gas-phase degradation product. TCE removal efficiencies increased with lower TCE inlet concentrations, lower RH and higher gas residence times. Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir–Hinshelwood (LH) model could not give an adequate fitting to the experimental results. A new kinetic model, explicitly taking into account electron–hole pair reactions, was developed based on linear TCE adsorption–desorption equilibrium and first order reaction kinetics. The new kinetic model described the experimental results in a more accurate way, as exemplified by a more randomly distributed set of residuals and by a reduction of the sum of squares (SSQ) by a factor 1.7–8.5. The effect of TCE gas-phase concentration, RH and light intensity on adsorption–desorption kinetics, electron–hole concentrations and chemical conversion rates is discussed.     

可光助再生二氧化钛/层状双氢氧化物去除水体中有机染料

利用吸附-光催化技术去除水体中有机染料,是高效节能的方法之一。然而,碳基吸附剂在光催化降解污染物过程中,由于活性氧的攻击会发生自身的逐渐氧化。本研究中,采用尿素水解水热法制备二氧化钛/层状双氢氧化物(TiO₂/LDH)非碳基复合材料,不仅对水体中有机染料具有较高的吸附容量,也在光辐射后具有可重复的再生能力。对甲基橙的吸附量为527.5 mg/g,在4轮循环再生后仍具有88.6%的再生率;对亚甲基蓝的吸附量为208.3 mg/g,在4轮循环再生后仍具有94.7%的再生率。在吸附-光再生过程中,LDH基底自身具有强抗氧化能力和高吸附能力,同时提高了负载剂TiO₂的光吸收效率,为水中有机污染物去除和吸附-光催化复合材料设计优化提供了可行的策略。