Photocatalytic activity of multielement doped TiO2 in the degradation of congo red

TiO₂ although considered a promising photocatalyst for the degradation of aqueous pollutants, it suffers from poor absorption in the visible region and hence requires ultraviolet (UV) light for activation. To make TiO₂ a visible active photocatalyst, multielement (C, N, B, and F) doping has been done. The synthesised CNBF/TiO₂ catalysts were calcined at different temperatures and characterized by XRD, BET surface area, UV DRS, XPS, HRSEM-EDAX, and TEM techniques. These catalysts found to show less band gap values when compared to bare TiO₂. These catalysts were tested for their catalytic activity towards the degradation of a textile dye - congo red (CR) under different reaction conditions. It was found that the photocatalytic activity was dependent on both doping of multielement and the calcination temperature of CNBF/TiO₂. The co-doped catalysts which were calcined at 400 °C and 600 °C (100% intensity in anatase phase) were found to be the best catalysts (100% decolourisation of CR in 21/2 h and 2 h respectively). TOC analysis carried out for the samples at the reaction time of 5 h showed very high percentage (83%) degradation of CR over CNBF/TiO₂ catalysts calcined at 600 °C when compared to the other catalysts calcined at different temperatures. CNBF/TiO₂ (1000 °C) showed very less photocatalytic activity due to the formation of rutile phase.     

Photocatalytic abilities of gel-derived P-doped TiO2

P-doped TiO₂ nanoparticles were synthesized through hydrolysis and condensation of Ti(OC₂H₅)₄ with H₃PO₄ additions. Effects of [H₃PO₄]/[Ti(OC₂H₅)₄] molar ratios on the anatase-to-rutile phase transformation, crystallite sizes, surface areas, and photocatalytic abilities of the gel-derived P-doped TiO₂ were investigated. The P-doped TiO₂ nanoparticles prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 were composed of anatase monophase even at 900 ^oC and possessed very strong photocatalytic ability. Kinetic studies on the P-doped TiO₂ to photocatalytically decompose methylene blue under irradiation of 365 nm UV light found that the P-doped TiO₂ prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 and calcined at 800 ^oC had the specific reaction rates, at 25 °C, k_A,m=0.76 m³/(kg min) (based on the mass of P-doped TiO₂) and k_A,BET=46.2×10⁻⁶ m/min (based on the BET surface area of P-doped TiO₂), which is superior to the performance of a commercial product, P25 (k_A,m=0.22 m³/(kg min) and k_A,BET=4.8×10⁻⁶ m/min).     

Photocatalytic behavior of heavy La-doped TiO2 films deposited by pulsed laser deposition using non-sintered target

We have investigated the control of photocatalytic behavior under deposited conditions of non-sintered target of different molar ratios with TiO₂ and La₂O₃ from 1:0 to 1:2 for heavily La doping, and post-annealing temperature from 600 °C to 1000 °C for crystallizing by pulsed laser deposition. We have successfully crystallized heavily La-doped TiO₂ films with post-annealing temperature over 800 °C and with molar ratio of TiO₂:La₂O₃ over 1:1 on a quartz substrate. Heavily La-doped TiO₂ films are observed the decomposition of methylene blue and a water-splitting reaction in photocatalytic behavior under Xe light irradiation. When stoichiometric La-doped TiO₂ (TiO₂:La₂O₃ = 1: 1) is synthesized with heat-treatment at 900 °C, the best results are obtained under photocatalytic behavior and pure La₂Ti₂O₇ crystalline were obtained.     

Maintaining particle size in the transformation of anatase to rutile titania nanostructures

We study the temperature-dependent transformation of two distinctly synthesized TiO₂ nanoparticles from the anatase to the rutile phase. These studies are carried out over the temperature range extending from room temperature to an excess of 800 °C where the anatase to rutile conversion is found to occur. Results obtained for both a sol-gel-generated nanocolloid (3-20 nm) and a sol-gel-generated micelle nanostructure (∼40 nm) are evaluated. While the TiO₂ nanocolloid structures aggregate to form larger crystallites as a function of increasing temperature with sizes comparable to the sol-gel-generated micelle structures, the resulting anatase crystallites, which are of a diameter 40-50 nm, appear to transform to comparable or slightly smaller rutile structures at 800 °C. This is in contrast to the transformation to larger rutile structures, observed for larger anatase particles. The importance of kinetic effects is considered as it enhances the rate of anatase to rutile conversion. These characteristics are established using a combination of Raman spectroscopic, X-ray diffraction, and scanning electron microscopy. The relative playoffs of the Raman and X-ray diffraction techniques are considered as they are used for the analysis of particles at the nanoscale, especially when phase transformations are evaluated.     

Reasons for the deactivation of Pt/TiO2 photocatalyst treated by inert gas N2

The effect of N₂ treatment on the photocatalytic activity of Pt⁰/TiO₂ was investigated. The results showed that after treatment at 500 °C in N₂, 70% of the photocatalytic activity of 1.0 wt.% Pt⁰/TiO₂ was lost by the evaluation of photocatalytic oxidation reaction of C₃H₆. Transmission electron microscopy (TEM) and Ar⁺ ion sputtering tests revealed that in the course of high-temperature N₂ treatment, the size of Pt⁰ particles on TiO₂ increases and a strong interaction between metal and support, i.e. Pt⁰ particles encapsulated by Ti_xO_y, happens, which are the reasons for the deactivation of Pt⁰/TiO₂ photocatalyst treated by high-temperature N₂.     

A novel approach towards high-performance composite photocatalyst of TiO2 deposited on activated carbon

TiO₂ photocatalysts deposited on activated carbon (TiO₂/AC) were prepared by dip-hydrothermal method at 180 °C using peroxotitanate as a precursor, then calcinated at 300-800 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and the nitrogen absorption. Their photocatalytic activity was evaluated by degradation of methyl orange (MO). The results showed that TiO₂ particles of anatase type were well deposited on the activated carbon surface. TiO₂/AC calcinated at 600 °C exhibited the best photocatalytic performance. For the comparison, the same photocatalysis experiment was carried out for two mixtures of commercial TiO₂ (Degussa P25) with AC and synthetic TiO₂ with AC. It was found that the composite catalyst TiO₂/AC was better than the two mixtures. Besides, different from fine powdered TiO₂, the granular TiO₂/AC photocatalysts could be easily separated from the bulk solution and reused; indeed, its photocatalytic ability was hardly decreased after a five-cycle for MO degradation. The kinetics of the MO degradation fitted well the Langmuir-Hinshelwood model.     

Optical and photocatalytic properties of nanocrystalline TiO2 synthesised by solid-state chemical reaction

Nanoparticulate TiO₂ is of interest for a variety of technological applications, including optically transparent UV-filters and photocatalysts for the destruction of chemical waste. The successful use of nanoparticulate TiO₂ in such applications requires an understanding of how the synthesis conditions effect the optical and photocatalytic properties. In this study, we have investigated the effect of heat treatment temperature on the properties of nanoparticulate TiO₂ powders that were synthesised by solid-state chemical reaction of anhydrous TiOSO₄ with Na₂CO₃. It was found that the photocatalytic activity increased with the heat treatment temperature up to a maximum at 600 °C and thereafter declined. In contrast, the optical transparency decreased monotonically with the heat treatment temperature. These results indicate that solid-state chemical reaction can be used to prepare powders of nanoparticulate TiO₂ with properties that are optimised for use as either optically transparent UV-filters or photocatalysts.     

Structure and photocatalytic properties of copper-doped rutile TiO2 prepared by a low-temperature process

Copper-doped titania with variable Cu/Ti ratios have been prepared via a simple aqueous-phase method at 85 °C. The obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectra analysis. The photocatalytic properties of the products were tested by photocatalytic degradation of aqueous brilliant red X-3B solution. The results showed that the sample with 2% copper doping has the best photocatalytic activity, which is 3 times that of undoped rutile titania. The effect of the doped copper on the structure and property of TiO₂ has also been discussed.     

Role of the TiO6 octahedra on the ferroelectric and piezoelectric behaviour of the poled PbMg1/3Nb2/3O3-xPbTiO3 (PMN-PT) single crystal and textured ceramic

Field cooling (FC) poled/unpoled PMN-29%PT single crystal and room temperature (RT) poled/unpoled PMN-34.5%PT textured ceramic were investigated between ∼0 and 300 °C by thermal expansion, dielectric and Raman spectroscopy. New phase transitions are evidenced at 40, 91 and 180 °C in the case of FC PMN-29%PT as well as at 70 and 200 °C for RT PMN-34.5%PT and their order is discussed. The physical properties of the textured ceramics are rather similar to the ones observed for the single crystals that make them low-cost alternative for a wide range of applications. However, the temperatures and character of the phase transitions strongly depend on the kind of the poling conditions. Temperature dependences of the Raman line parameters show that the NbO₆ octahedra remain stable during temperature increase, while TiO₆ ones evolve quasi-continuously. The step transitions of the Pb²⁺ ion sublattice are evidenced. This suggests that the TiO₆ and Pb²⁺ sublattices are especially coupled. The role of the TiO₆ clusters on the structural phase transitions and dielectric properties of the PbMg_1/3Nb_2/3O₃-xPbTiO₃ (PMN-PT) system is discussed. The presence of the Raman modes above the maximum dielectric permittivity reveals that the local symmetry is lower than the cubic one (Pm3m). The decrease of the Raman line intensities vs. temperature indicates precisely the continuous evolution of the local symmetry towards the cubic one. The temperature evolution of the Rayleigh wing parameters appears sensitive to the phase transitions’ presence.     

Hydrothermal synthesis and characterization of nanocrystalline Zn-Mn spinel

Hydrothermal method had been used to successfully synthesize the nanocrystalline spinel zinc manganese oxide (ZnMn₂O₄) directly from Zn(CH₃COO)₂·2H₂O, NaOH, Mn(NO₃)₂ and H₂O₂ at 170 °C for the reaction time of 48 h. The effects of the synthesis conditions, such as the Zn/Mn molar ratio, the reaction temperature, the reaction time, the zinc source and the concentrations of NaOH and H₂O₂, on the formation of the Zn-Mn spinel were investigated. The products were characterized by means of X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The results indicated that the compositions of the Zn-Mn spinel with the tetragonal structure were Zn_1.14Mn_1.86O₄. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) images showed that the products at 170 °C were with square-shaped nanocrystalline spinel with the particle size of about 20-50 nm. The thermal behaviors of the products were investigated by thermogravimetric analysis (TG).     

Characterization of nanosized TiO2 synthesized inside a porous glass-ceramic monolith by metallo-organic decomposition process

This work reports the preparation of TiO₂ by decomposition of a metallo-organic precursor (MOD process) in the pores of an α-NbPO₅ glass-ceramic monolith (PGC-NbP) and the study of the TiO₂ anatase-rutile transition phase. The impregnation of titanium di-(propoxy)-di-(2-ethylhexanoate) in the PGC-NbP was confirmed by diffuse reflectance infrared spectroscopy. In the restrictive porous environment the decomposition of the metallo-organic compound exhibits a lower initial decomposition temperature but a higher final decomposition temperature, in comparison to the free precursor. The pure TiO₂ rutile phase is formed only above 700 °C when the titanium precursor is decomposed outside the pores. The TiO₂ anatase obtained inside the PGC-NbP was stabilized up to 750 °C and exhibits a smaller average crystallite size in comparison with the MOD process performed without PGC-NbP. Furthemore, the temperature of the TiO₂ anatase-rutile transformation depends on crystallite size, which was provided by XRD and Raman spectroscopy. The precursor impregnation-decomposition cycle revealed a linear mass increment inside PGC-NbP. Micro-Raman spectroscopy shows the presence of a gradient concentration of the TiO₂ inside the PGC-NbP. The use of the MOD process in the PGC-NbP pores has several advantages: control of the amount and the nature of the phase formed and preservation of the pore structure of PGC-NbP for subsequent treatments and reactions.     

Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with lanthanum and iodine

The novel visible-light-activated La/I/TiO₂ nanocomposition photocatalyst was successfully synthesized using precipitation-dipping method, and characterized by X-ray powder diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG-DSC) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of La/I/TiO₂ was evaluated by studying photodegradation of reactive blue 19 as a probe reaction under simulated sunlight irradiation. Photocatalytic experiment results showed that the maximum specific photocatalytic activity of the La/I/TiO₂ photocatalyst appeared when the molar ratio of La/Ti was 2.0 at%, calcined at 350 °C for 2 h, due to the sample with good crystallization, high BET surface area and small crystal size. Under simulated sunlight irradiation, the degradation of reactive blue 19 aqueous solution reached 98.6% in 80 min, which showed La/I/TiO₂ photocatalyst to be much higher photocatalytic activity compared to standard Degussa P25 photocatalyst. The higher visible light activity is due to the codoping of lanthanum and iodine.     

Effect of post heat treatment on microstructure and photocatalytic activities of TiO2 nanoribbons

Low-dimensional TiO₂ nanoribbons were synthesized by a simple one-step hydrothermal method. The TiO₂ nanoribbons were calcined over the temperature range 200-800 °C in order to enhance their photocatalytic properties by altering their crystal phase and increasing crystallization. Effects of hydrothermal temperature, calcinated temperature and calcination time on the formation of nanostructures have been observed and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The (BET) specific surface area of the samples which with different post treatments were determined by N₂ absorption-desorption experiment. In addition, photocatalytic activities of the nanoribbons were evaluated by photodegradation of organic dyes methyl orange under the radiation of UV light. The results reveal that the post-treatments have great effects on the microstructures and the photocatalytic activities of TiO₂ nanoribbons.     

Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO2 nanotubes on Ti substrate and freestanding membrane

Highly ordered titanium oxide (TiO₂) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO₂ nanotubes on a Ti substrate and that of freestanding TiO₂ membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO₂ nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO₂ membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO₂ nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO₂ nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.     

Mesoporous TiO2-B nanowires synthesized from tetrabutyl titanate

Ultralong mesoporous TiO₂-B nanowires were synthesized via a hybrid hydrothermal-ion exchanging-thermal treatment using tetrabutyl titanate (TBOT) as a raw material. The phase transformations and porous structures of TiO₂-B nanowires were characterized and studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption-desorption measurement. Mesoporous TiO₂-B nanowires showed a length of several micrometers and diameter of about 25 nm. The porous structures of obtained TiO₂-B nanowires were demonstrated by BJH pore distribution measurement. The wirelike morphologies and porous structures of monodisperse nanowires calcined at 600 °C showed little change, which indicated that such nanowires possessed high thermal stability. The formation mechanism of TiO₂-B nanowires with mesoporous structures were also discussed based on our experimental results.     

Catalytic activity of Fe, Co and Fe-Co-MCM-41 for the growth of carbon nanotubes by chemical vapour deposition method

Iron, cobalt and a mixture of iron and cobalt incorporated mesoporous MCM-41 molecular sieves were synthesised by hydrothermal method and used to investigate the rules governing their nanotube producing activity. The catalysts were characterised by XRD and N₂ sorption studies. The effect of the catalysts has been investigated for the production of carbon nanotubes at an optimised temperature 750 °C with flow rate of N₂ and C₂H₂ is 140 and 60 ml/min, respectively for a reaction time 10 min. Fe-Co-MCM-41 catalyst was selective for carbon nanotubes with low amount of amorphous carbon with increase in single-walled carbon nanotubes (SWNTs) yield at 750 °C. Formation of nanotubes was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Transmission electron microscope and Raman spectrum was used to follow the quality and nature of carbon nanotubes formed and the graphitic layers and disordered band, which shows the clear evidence for the formation of SWNTs, respectively. The result propose that the diameter of the nanotubes in the range of 0.78-1.35 nm. Using our optimised conditions for this system, Fe-Co-MCM-41 showed the best results for selective SWNTs with high yield when compared with Fe-MCM-41 and Co-MCM-41.     

Influence of Ca additives on the optical and dielectric studies of sol-gel derived PbTiO3 ceramics

Sintered ceramic powders of calcium-doped lead titanate [Pb_1−xCa_xTiO₃] ceramics with different Ca dopant concentration in the range (x=0-0.35) have been prepared using a sol-gel chemical route. The sol-gel technique is known to offer better purity and homogeneity, and can yield stoichiometric powders with improved properties at relatively lower processing temperature in comparison to conventional solid-state reaction. X-ray diffraction (XRD) and Raman spectroscopy studies have been carried out to identify the crystallographic structure and phase formation. The infrared absorption spectra in the mid-IR region (400-4000 cm⁻¹) show the band corresponding to the Ti-O bond at ∼576 cm⁻¹ and is found to shift to a higher wave number 592 cm⁻¹ with increasing Ca content. The dielectric properties as a function of frequency, and phase transition studies on sintered ceramic Pb_0.65Ca_0.35TiO₃ has been investigated in detail over a wide temperature range 30-600 °C and the results are discussed.     

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO2 films

Porous surface-fluorinated TiO₂ (F-TiO₂) films were prepared through PEG modified sol-gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV-vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO₂ film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO₂ film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO₂ film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO₂ film. Porous F-TiO₂ film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO₂ film had original water CA of 22.7°, which is much smaller than that of normal F-TiO₂ film. Under UV light irradiation, the water CA of porous F-TiO₂ film decreased to 5.1° in 90 min.     

Preparation and characterization of iodine-doped mesoporous TiO2 by hydrothermal method

Iodine-doped mesoporous TiO₂ (I/TiO₂) was prepared by hydrothermal method, using tetrabutyl titanate as precursor, potassium iodate as iodine sources. The as-prepared I/TiO₂ catalysts were characterized by UV-vis, XRD, TEM, BET, TG/DTA, XPS and photoluminescence (PL) spectroscopy. Production of OH radicals on the I/TiO₂ surface was detected by the PL technique using terephthalic acid as a probe molecule. The effects of hydrothermal reaction temperature, calcination temperature and iodine doping content on the structure and properties of the catalysts were investigated. The results showed that iodine-doped TiO₂ calcinated at 300 °C have good anatase crystal. The optimal hydrothermal conditions have been determined to be that reaction temperature 120 °C, calcinated temperature 300 °C and added 1.16 mmol iodine dopants. The average particle size of I/TiO₂ synthesized under optimal condition (I-3 sample) is about 3.9 nm. The I-3 photocatalyst contains 100% anatase crystalline phase of TiO₂. BET specific surface area of I-3 sample is184.8 m² g⁻¹ and is 3.67 times that of pure TiO₂ (50.37 m² g⁻¹). Iodine in I/TiO₂ catalyst mainly exists in the form of I₂, and photoactivity of I/TiO₂ catalyst in visible light comes from photosensitize of I₂. I/TiO₂ catalysis shows very high efficiency for the degradation of phenol under visible light.     

Hydrothermal synthesis of well-dispersed ultrafine N-doped TiO2 nanoparticles with enhanced photocatalytic activity under visible light

Ultrafine nitrogen-doped TiO₂ nanoparticles with narrow particle size distribution, good dispersion, and high surface area were synthesized in the presence of urea and PEG-4000 via a hydrothermal procedure. TEM observation, N₂ adsorption, XRD, UV-vis spectroscopy, the Raman spectroscopy and XPS analysis were conducted to characterize the synthesized TiO₂ particles. The synthesized TiO₂ particles were a mixture of 49.5% anatase and 50.5% rutile with a size of around 5 nm. The photocatalytic activities were tested in the degradation of an aqueous solution of a reactive Brilliant Blue KN-R under both UV and visible light. The synthesized TiO₂ particles showed much higher photocatalytic activity than a commercial P25 TiO₂ powder under both UV and visible light irradiations. The high performance is associated to N doping, the reduced particle size, good dispersion, high surface area, and a quantum size effect.