Photocatalytic Activity Of Titanate Nanotubes Research Articles

Factors Determining the Removal Efficiency of Procion MX in Waters Using Titanate Nanotubes Catalyzed by UV Irradiation

The treatment of wastewater from the textile industry containing organic dyes faces many challenges since these compounds resist the biodegradation process in conventional treatment units. Among the physicochemical processes, photocatalysis is considered a facile, cheap, and environmental-friendly technology for treating persistent organic pollutants in waters at low concentrations. This study investigated several physicochemical factors determining the photocatalytic activity of titanate nanotubes (TNTs) to remove Procion MX 032 (PMX), an azo dye, in waters. Degradation of PMX by photocatalytic oxidation process at room temperature (30°C) was set up with the UV irradiation in the presence of different types of photocatalyst such as ST-01 (100% anatase), industrial TiO2, TNTs calcined at 120°C and 500°C. Effect of reaction time, catalyst amount, pH, light wavelength and intensity, and oxidants was investigated. Consequently, TNTs calcined at 500°C provided the highest removal efficiency. The photocatalytic oxidation of PMX by TNT calcined at 500°C was affected by pH variation, getting the highest removal at pH of 8, and inhibited with the presence of H2O2 and O2. Particularly, the PMX degradation using titanate nanotubes was optimized under the UV-A intensity of 100 W/m2. The dye was degraded by more than 95% at the TNTs concentration of 75 mg/L and pH 8.0 after 90 min. The results suggest that photocatalysis using TNTs can be a simple but efficient treatment method to remove PMX and potentially be applied for the treatment of wastewaters containing dyes.

Effects of environmental factors and synthesis conditions on the photocatalytic activity of titanate nanotubes for removal of gaseous formaldehyde

The increase in indoor air pollution problems stimulates the necessity for the development of photocatalytic removal processes, especially for the application of new and effective photocatalysts. In this study, we aimed to prepare and modify various types of titanate nanotubes (TNTs) synthesized by hydrothermal method and apply them for the removal of indoor formaldehyde by photocatalysis. The effect of environmental factors such as inlet concentration, exposed surface area, residential time, light intensity, and catalyst amount was investigated. The effects of various synthesis conditions such as acid treatment (i.e., at pH 1–9) and heat treatment (i.e., at temperatures of 120–900 °C) on the properties and the photocatalytic activity of the TNTs materials were also determined. Preliminary results showed that the highest removal efficiency of around 99% was found at the condition of 2 UV light bulbs, 29 s for retention time, 0.11 g of TNTs, 15 mg/m3 of formaldehyde, and 3 glass substrates. Regarding the synthesis condition, the TNTs material treated at pH 1.6 and annealed at 400 °C had the highest formaldehyde removal efficiency, which could be due to the suitable condition of mixed nanorods and nanotubes structure, anatase crystallinity, surface area, sodium content, and surface acidity the material.

Rapid Formation of 1D Titanate Nanotubes Using Alkaline Hydrothermal Treatment and Its Photocatalytic Performance

One-dimensional (1D) titanate nanotubes (TNT) were successfully synthesized using alkaline hydrothermal treatment of commercial TiO2nanopowders in a Teflon lined stainless steel autoclave at 150°C. The minimum time required for the formation of the titanate nanotubes was 9 h significantly. After the hydrothermal processing, the layered titanate was washed with acid and water in order to control the amount of Na+ions remaining in the sample solutions. In this study, the effect of different reaction durations in a range of 3 h to 24 h on the formation of nanotubes was carried out. As the reaction duration is extended, the changes in structure from particle to tubular shapes of alkaline treated TiO2were obtained via scanning electron microscope (SEM). Also, the significant impact on the phase transformation and crystal structure of TNT was characterized through XRD and Raman analysis. Indeed, the photocatalytic activity of TNT was investigated through the degradation of methyl orange aqueous solution under the ultraviolet light irradiation. As a result, TNT with reaction duration at 6 h has a better photocatalytic performance than other samples which was correlated to the higher crystallinity of the samples as shown in XRD patterns.

Effects of heat and peroxide treatment on photocatalytic activity of titanate nanotubes

The influence of structural, morphological and surface properties on photocatalytic activity of pristine and modified titanate nanotubes was carefully described and discussed in the following study. Titanate nanotubes (TNTs) were prepared via alkaline hydrothermal synthesis route followed by acid washing at ambient conditions. The resulting high specific surface area nanotubular solids were further modified by two distinguished post-treatments: (i) heat-treatment in the temperature range from 300 to 700°C, and (ii) peroxide-treatment at room temperature. Bisphenol A (BPA), a well-known endocrine disrupting compound (EDC), was selected as a testing molecule to evaluate the photodegradation potency of the modified TNTs. The resulting BPA and TOC removals confirmed that crystallinity and BET surface area of examined heat-treated solids play a crucial role in governing the photooxidation reaction. Regarding the peroxide-treated TNTs, a nearly three-fold improvement in BPA removal was attained in comparison to the pristine TNTs, which can be attributed to the redox reaction of surface titanium(IV) peroxo groups. However, the exposure of anatase-based samples to the H2O2 medium resulted in deteriorated photocatalytic oxidation of the model compound, due to recovery of surface Ti3+ defect sites, leading to increased e−–h+ recombination and decreased oxygen adsorption. In addition, a carbon-based elemental analysis of the heat-treated TNTs (TNT_500) and standard TiO2 P25 stressed the potential of tailor-made crystalline TNTs to be applied as photocatalysts for long-term removal of aqueous organics, due to low accumulation of carbonaceous deposits during the photodegradation runs.

A review on TiO2-based nanotubes synthesized via hydrothermal method: Formation mechanism, structure modification, and photocatalytic applications

TiO2 nanotubes or titanate nanotubes (TNTs), which are produced by hydrothermal synthesis, have received increasing attention for photocatalytic applications due to their unique physicochemical properties, such as nanotubular structure with layered walls, high surface area, ion-exchange ability, and photocatalytic activity. The hydrothermal method that has been widely applied for preparation of catalysts in industry like zeolites, is a simple and mature synthesis technique, in which the properties of products depend on the formation mechanism and hydrothermal conditions. Focusing on the structure of TNTs including crystallography and morphology from the extensive literature, this paper discusses the formation mechanisms of TNTs during hydrothermal synthesis. The effects of synthesis conditions (TiO2 precursor, hydrothermal temperature and duration), auxiliary methods (ultrasonication and microwave-assistance), and post treatment (acid washing and calcination) on the formation of titanate nanotubes are reviewed. Furthermore, structural modifications and current progress toward photocatalytic activity of TNTs as photocatalysts are also summarized in this review.

Hydrothermal temperature as a morphological control factor: Preparation, characterization and photocatalytic activity of titanate nanotubes and nanoribbons

Layered titanate nanotubes (TNTs) and titanate nanoribbons (TNRs) were synthesized via hydrothermal treatment from commercial TiO2. Formation of nanotubes and nanoribbons were monitored by varying the hydrothermal reaction temperature and time. The two parameters hydrothermal reaction temperature and time was 100°C for 24h/72h, 150°C for 24h/72h and 200°C for 24h/72h. The morphology, structure and optical properties were systematically analyzed, with samples are characterized by TEM, XRD, XPS, SEM, N2 adsorption–desorption isotherm (BET) as well as Raman, FT-IR and UV–Vis/DR spectroscopy. The study revealed that reaction temperature is the parameter for morphological control of the product. Structure and physical properties of TNTs and TNRs are summarized. Further, dense products are obtained by increase the reaction time for the same temperature. The photocatalytic activities were assessed under UV light by degradation of rhodamine B aqueous solution. Results revealed that, degradation of TNTs and TNRs was observed, after samples annealed once at 400°C, which is due to occurrence of phase transformation from titanate to anatase TiO2 and TiO2 (B) respectively.

Photocatalytic Activity of (B, N)‐Codoped Titanate Nanotubes

The multi‐walled (B, N)‐codoped titanate nanotubes (TNTs) have been prepared via a simple hydrothermal route. Such (B, N)‐codoped TNTs showed a decrease in band gap energy as compared with the undoped TNTs. The effect of the doping amounts of B and N on the photocatalytic activity of TNTs was studied. Among the as‐prepared samples, (1% B, 1% N)‐codoped TNTs exhibited the best photocatalytic activity for methyl orange decomposition under Ultraviolet–Visible (UV–Vis) light irradiation. The photocatalytic activity of (1% B, 1% N)‐codoped TNTs is twice as high as that of the undoped TNTs.

Effects of sintering temperature on physicochemical properties and photocatalytic activity of titanate nanotubes modified with sulfuric acid

Titanate nanotubes were prepared by using a hydrothermal treatment of TiO2 (Degussa P25) with NaOH aqueous solutions. The as-prepared titanate nanotubes were treated with H2SO4, subsequently sintered at different temperatures. The results of physicochemical characterization and photoactivity analysis revealed that the sintering temperature remarkably altered the phase composition, specific surface area, microstructure, sulfate species as well as photocatalytic activity of the titanate nanotubes modified with sulfuric acid. The sample sintered at 500°C exhibited much higher activity and better stability than P25, this can be attributed to the suitable crystallization, the porous structure and the abundant surface hydroxyl groups as well as the active sulfate species. As the sintering temperature increased to 600°C or above, the sulfate species in the samples decomposed, TiO2 particles grew and pore structure shrank, resulting in the poor activities of the samples.

Visible-Light Photocatalytic Property of Titanate Nanotubes Sensitized by Several Porphyrins

The visible-light photocatalytic activity of titanate nanotubes (TiNTs) sensitized by 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetraphenylporphyrin manganese (MnTPP), 5,10,15,20-tetraphenylporphyrin nickel (NiTPP) and 5,10,15,20-tetraphenylporphyrin zinc (ZnTPP), respectively, was investigated by the photocatalytic degradation of methyl orange (MO) as a probe reaction. The results showed that the central ions of porphyrins had an important influence on the photocatalytic activity of the samples. The activity was in the order of TiNTs-ZnTPP > TiNTs-TPP > TiNTs-NiTPP > TiNTs-MnTPP. Combined the result of absorption spectra with that of fluorescence spectra, it was demonstrated that various visible-light absorption and photoelectron transfer caused by the central ions of porphyrins were the decisive factor for the visible-light photocatalytic activity of the sensitized TiNTs.

Preparation of cadmium-zinc sulfide nanoparticles modified titanate nanotubes with high visible-light photocatalytic activity

Titanate nanotubes (TiNTs) were modified in situ with cadmium-zinc sulfide nanoparticles by an ultrasound ion-exchange method combined with a hydrothermal process. The target product (TiNTs/Cd 0.8Zn 0.2S) showed a wide visible-light response and high visible-light photocatalytic activity. Degradation efficiency of rhodamine B in water was up to 96.6% with 1 mg mL −1 of TiNTs/Cd 0.8Zn 0.2S photocatalyst under visible-light illumination for 90 min. The result demonstrated that the photocatalytic activity of TiNTs under visible-light illumination could be increased dramatically by modification with the ternary sulfide Cd 0.8Zn 0.2S nanoparticles.

Study on the formation and photocatalytic activity of titanate nanotubes synthesized via hydrothermal method

Titanate and titania (TiO 2 ) nanotubes were synthesized by hydrothermal method. The effect of NaOH to TiO 2 ratio, reaction temperature, reaction time and annealing temperature on the formation of nanotubes was investigated using X-ray diffraction, field emission microscope and Transmission electron microscope. Titanate nanotubes with 10 nm diameter was formed for NaOH to TiO 2 ratio >27 treated at 110 °C for 24 h. Increasing the synthesis temperature to 150 °C, the titanate nanotubes transformed to anatase phase and it was found minimum of 15 h is required for completing transformation from nanoparticles to nanotubular structure. With increasing annealing temperature, titanate nanotubes undergo dehydration and form anatase phase. Besides, the sintegration of the nanotubes was observed at 500 °C and the structure completely converted to nanoparticles at 600 °C. The photocatalytic activity of the sample was evaluated by degradation of methyl orange aqueous solution. The results indicate the photocatalytic activity of titanate is low and once the formation of anatase phase begins with increasing temperature, the photocatalytic activity increases dramatically. However, the deterioration in the tubular structure and increase in oxygen vacancies which act as a recombination centre of electron–holes with increasing annealing temperature need to be controlled to avoid the reduction in the photocatalytic behavior of anatase phase.

The synthetic parameters for the preparation of nanotubular titanate with highly photocatalytic activity

A detail study for the effects of synthetic parameters, including acid washing concentration, heat treatment, and synthesis temperature, on the photocatalytic degradation performance of hydrothermal method derived titanate nanotubes (TNT) was given. The alteration of microstructures of TNT was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption–desorption isotherms. The photocatalytic activity of TNT was evaluated by photocatalytic oxidation of basic dye (basic violet 10, BV10) in aqueous solution. The photocatalytic activity of TNT was found to be closely related to the specific surface area and pore volume of TNT as well as the amount of anatase phase and remnant sodium in TNT. TNT with high dye photodegradation efficiency was found to prepare with synthesis temperature smaller than 170 °C and subsequently washed with 0.01N HCl aqueous solution and calcined at temperatures smaller than 300 °C.

Characteristics of Titanate Nanotube and the States of the Confined Sodium Ions

The titanate nanotubes (TNTs) prepared by the reaction of titanium dioxide (TiO2) with NaOH were treated with acid (HNO3) solutions of various concentrations and/or heat treated at different temperatures. The properties of the treated TNTs were investigated in relation to the photocatalytic activities. The state and the role of Na ions confined in the TNTs were analyzed by means of 23Na and 1H NMR spectroscopy. It was revealed that there exist two states of Na ions, i.e. strongly and weakly interacting with the TNT system. The Na ions strongly bound to the interlayer of TNT play an important role to stabilize the tube structure. On the other hand, Na ions weakly interacting with the surface of the TNT suppress the photocatalytic activity but can be easily removed by a weak acid treatment with 50 mM HNO3 solution to lead the optimum photocatalytic activity. In addition, the Na ions on the surface of the TNT interfere with the crystalline transition to anatase on calcinations. Although the photocatalytic activity of TNT has been believed to be lower than that of conventional TiO2 photocatalysts of nanoparticles, it was also found that TNT showed specifically high photocatalytic activities, even higher than P25 TiO2 (Degussa P25), for some cationic reactant such as trimethylamine.

Effects of sodium content and calcination temperature on the morphology, structure and photocatalytic activity of nanotubular titanates

Titanate nanotubes (TNT) were prepared via a hydrothermal treatment of TiO 2 powders (P25) in a 10 M NaOH solution at 150 °C for 24 h and subsequently washed with HCl aqueous solution of different concentrations (0.1, 0.01, and 0.001 N). Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by transmission electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption isotherms. The photocatalytic activity of TNT was evaluated by photocatalytic oxidation of basic dye (basic violet 10 (BV10)) in water solution. It was found that if the sodium was not completely exchanged with proton, the removal of sodium increased the specific surface area (and pore volume), while the thermal stability was reduced. When the sodium content of TNT was approximately 0 wt% (nearly complete proton exchange), the nanotubular structure of titanates might be destroyed. The effects of the alterations of microstructures induced by the exchange of sodium and heat-treatment on the photocatalytic activity of TNT were discussed with the variations of specific surface area, pore volume, and the amounts of anatase phase in TNT.

Effects of calcination temperature on the microstructures and photocatalytic activity of titanate nanotubes

Titanate nanotubes were prepared via a hydrothermal treatment of TiO 2 powders (P25) in a 10 M NaOH solution at 150 °C for 48 h and then calcined at various temperatures. The as-prepared titanate nanotubes before and after calcination were characterized with XRD, TEM, HRTEM, SEM, FESEM, and nitrogen adsorption–desorption isotherms. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic oxidation of acetone in air. The effects of calcination temperature on the phase structure, crystallite size, morphology, specific surface area, pore structures and photocatalytic activity of the titanate nanotubes were investigated. The results indicated that at 400 to 600 °C, the calcined nanotube samples showed a higher photocatalytic activity than Degussa P25. Especially, at 400 and 500 °C, the photocatalytic activity of the calcined nanotubes exceeded that of P25 by a factor of about 3.0 times. This could be attributed to the fact that the former had a larger specific surface area and pore volume. With further increase in the calcination temperature from 700 to 900 °C, the photocatalytic activity of the calcined nanotube samples greatly decreased due to the formation of rutile phase, the sintering and growth of TiO 2 crystallites and the decrease of specific surface area and pore volume.