Effect of M-doping (M = Fe,V) on the photocatalytic activity of nanorod rutile TiO2 for Congo red degradation under the sunlight

Nanorods TiO₂, Fe-TiO₂ (3 and 2 at.% Fe), V-TiO₂ (5 at.% V) were prepared by a low temperature method and characterized by powder X-ray diffraction, thermal analysis, transmission electron microscope and BTE surface area analysis. The as-prepared samples were evaluated as catalysts for photodegradation of Congo red aqueous solution under the sunlight. Nanorods Fe-doped TiO₂ shows higher adsorption and also higher photocatalytic degradation of Congo red solution compared to pure nanorods TiO₂ rutile. A higher activity is obtained when the amount of doped Fe is 2 at.%, compared to 3 at.%. However, nanorods V-TiO₂ does not show neither adsorption nor photodegradation activity of Congo red solution.     

Ag/αFe2O3-rGO novel ternary nanocomposites: Synthesis,characterization, and photocatalytic activity

In this research, novel ternary Ag/αFe₂O₃-rGO nanocomposites with various contents of GO were synthesized via a facile one-pot hydrothermal method. Ag/αFe₂O₃-rGO nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDX), photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR). The results showed that hematite nanoparticles and Ag nanoparticles were well decorated on the graphene surface. Photocatalytic activity of Ag/αFe₂O₃-rGO ternary nanocomposites and pure Ag/αFe₂O₃ was investigated for photodegradation of Congo red dye solution as a model pollutant under UV light irradiation. The ternary nanocomposite with 1.8?mg/ml GO aqueous solution concentration shows higher degradation efficiency under UV light irradiation than the pure Ag/αFe₂O₃ and the nanocomposites with other GO aqueous solution concentrations. It was observed that the adsorption of the dyes on the nanocomposites surface is dependent on the graphene content due to a decrease in the recombination rate, particles size, and increase charge carrier transfer. The results show that the Ag/αFe₂O₃-rGO nanocomposite can be used as an excellent photocatalytic material for degradation of Congo red dye in wastewater. A possible photocatalytic mechanism was proposed for degradation of Congo red dye.     

Fe- and Eu-doped TiO2 Photocatalytical Materials Prepared by High Energy Ball Milling

TiO₂ nanopowders, doped with Fe³⁺ and Eu³⁺ were obtained by high-energy ball milling and their physical properties were investigated as a function of the doping content and ball milling time. A noticeable red shift and high photoactivity in the degradation and catalytic oxidation reactions of styrene and phenol were found for all doped specimens.     

Effect of hydrodynamics during sol–gel synthesis of TiO2 nanoparticles: From morphology to photocatalytic properties

In this study, the role of mixing hydrodynamics during the sol–gel synthesis of titania nanoparticles and the consequences on their photocatalytic properties were investigated. For the first time three different T-mixer geometries were tested. Alcoholic solutions of titanium tetra-isopropoxide and water were mixed in three different T-mixers with turbulence promoters and thus different mixing characteristics. The changes of nanoparticle sizes during the induction time of the sol–gel process were followed by dynamic light scattering and velocity and turbulence fields were simulated by Computational Fluid Dynamics (CFD) for the three T-mixer geometries. The results indicated that macro-mixing is crucial during the first step as it determines the nucleation rate and then the primary particle size. The micro-mixing has an influence on particle properties, especially on particle stability. Titanium dioxide nanoparticles synthesized by the sol–gel process were deposited on alumina supports. A homogeneous film of about 200 nm was deposited in all cases. Degradation of Acid Orange 7 (AO7) was used to evaluate the photocatalytic activity of TiO₂ coatings. No difference was observed between the photoactivity of synthesized TiO₂. Total mineralization of the dye occurred after 24 h irradiation.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).     

Surface modified nanostructured-TiO<Subscript>2</Subscript> thin films for removal of Congo red

We synthesized nanostructured TiO₂ thin films by the modified sol-gel template method using the polyethylene glycol as filler media. The TiO₂ surface modification for both the thin films, i.e., template and non-template, was done with the ascorbic acid. All the four thin film samples, S1 (TiO₂ (non-template), TiO₂ (template), S3 (S1 modified with ascorbic acid) and S4 (S2 modified with ascorbic acid), were characterized by various analytical methods. Phase evaluation was monitored by the X-Ray diffraction analysis. Moreover, the thin films particle sizes were obtained to be 22.32, 21.20, 14.52 and 16.77 nm, respectively for the samples S1, S2, S3 and S4. The changes in particle size and morphology due to the PEG and ascorbic acid were determined by scanning electron microscopy (SEM). Similarly, thermal gravimetric (TG) and differential scanning calorimetry (DSC) were performed to determine the decomposition behavior of organic compound present in the solid samples. The functional groups were determined by infrared (IR) analysis. The photocatalytic efficiency, as a reference of Congo red, was conducted using all the four samples of TiO₂ thin films. Complete photocatalytic degradation of Congo red was achieved by these samples within 130, 80, 40 and 30 mins of UV illumination.     

Enhancing Effects of Ultrasound Treatment on the Preparation of TiO2 Photocatalysts

TiO₂ nanoparticles were synthesized by the hydrolysis and condensation of TiCl₄ in a mixed solvent of iso-propyl alcohol and water with or without ultrasound treatment. As-prepared powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy filtering transmission electron microscopy (EF-TEM), particle size analysis and BET surface area analysis. The specific surface area, thermal stability and crystallization of the as-prepared samples treated with ultrasound were higher than those of samples treated without ultrasound. To examine the photocatalytic activity of the as-prepared TiO₂, the photodegradation of MB which is a typical dye resistant to biodegradation has been investigated on TiO₂ powders in aqueous heterogeneous suspensions. The photocatalytic degradation of a aqueous solution of methylene blue shows a remarkable increase when it is carried out with ultrasound in all cases.     

Visible light induced self-cleaning performance of iron-doped TiO2 nanoparticles for surface applications

This study aimed to enhance the visible light photosensitivity of TiO₂ nanoparticles for self-cleaning applications by doping with Fe³⁺. Nanocrystalline undoped and Fe-doped TiO₂ (Ti_1 − xFe_xO₂, x = .01–.04) were synthesized via sol–gel method. The results demonstrated that Fe-doped TiO₂ nanoparticles exhibited visible light sensitivity and self-cleaning properties. An increased Fe concentration resulted in a red shift in the absorption band edge. Fe_0.03-doped TiO₂ with an average particle size of ∼21 nm, a crystallite size of ∼12 nm, and a band gap of ∼2.86 eV showed the highest photocatalytic activity (60% methylene blue degradation) and super-hydrophilicity (water droplet contact angle 9°) under visible light radiation. These findings highlight the potential of Fe-doped TiO₂ nanoparticles as a promising material for self-cleaning applications.     

Hydrothermal preparation of Ag-TiO2 nanostructures with exposed {001}/{101} facets for enhancing visible light photocatalytic activity

Nano-composite materials of Ag nanoparticles dispersed TiO₂ nanocubes with exposed {001}/{101} crystal faces were fabricated mainly via a flexible one-step method of hydrothermal treatment with different content of Ag from 1 up to 3 mol%. Prepared photocatalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. These analysis was carried out for understanding the contribution of different content of silver for enhancing the photocatalytic activity of TiO₂ nanocubes. Prepared silver nanoparticles had small particle size and grafted to the {101} crystal face of TiO₂ with the role of template control agent and linking agent. The photocatalytic performance of Ag-TiO₂ nanocubes were researched via Rhodamine B dye removal under visible light irradiation ( ≧420 nm). Ag-TiO₂ composite materials with the content of 2 mol% Ag showed the best photocatalytic activity for degradation of Rhodamine B, which was five times more than bare TiO₂ and associated with the localized surface plasmon resonance (LSPR) propelled effect. The mechanism by which silver enhanced the photocatalytic activity of TiO₂ was also demonstrated.     

Effect of calcination temperature on the structural properties and photocatalytic activities of solvothermal synthesized TiO2 hollow nanoparticles

TiO₂ hollow nanoparticles were prepared by the solvothermal method, calcined at different temperatures and characterized by XRD, BET, SEM, PL and FT-IR. The effects of morphology, size and calcination temperature on the photocatalytic activity of the prepared materials were discussed in detail. It was found that the calcination temperature altered the crystallinity, morphology, surface area, and the porous structure. The photocatalytic activity of the TiO₂ powders evaluated through photocatalytic degradation of gaseous acetone under UV-light irradiation, showed TiO₂ calcined at 250 °C to exhibit a higher photocatalytic activity than commercial powders (Degussa P25).     

Effect of mineral acids on the production of alumina nanopowder from raw bauxite

In this study a novel synthetic method for the large-scale production of spherical, high surface area and ultra-fine alumina (Al₂O₃) powder has been described. Synthetic Bayer liquor was extracted by alkali fusion of raw bauxite with sodium hydoxide. Alumina nanopowders were synthesised through a ball mill-aided precipitation method using the synthetic Bayer liquor and mineral acid precipitants. The powders produced were characterised by X-ray diffraction (XRD), particle size distribution (PSD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller surface area and pore size analysis, energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this article, the effects of precipitants such as H₂SO₄, HCl and HNO₃ on crystallite and particle size, surface area, pore volume, and pore size and shape are reported. The experimental results prove that precipitation leads to an aggregated particle that is disaggregated by the ball-milling method. The ball milling process strongly influences the formation of uniform-sized spherical particles with a high surface area. It was revealed that nitric acid is an effective precipitant for controlling particle size and textural properties of Al₂O₃ powder. A nanopowder of γ-Al₂O₃ with an average crystallite size of 3 nm and an average particle size of 58 nm with a specific surface area (SSA) of 190 m² g^− 1 is produced. This article elucidates a new method with a simple reaction scheme for the mass production of Al₂O₃ nanoparticles from raw bauxite for various commercial applications.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Photoassisted mineralization of remazole red F3B over NiO/TiO2 and CdO/TiO2 nanoparticles under simulated sunlight

In this work, a series of titania-supported NiO and CdO materials were synthesized by a modified sol-gel process. The prepared photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). The activities of titania-supported NiO and CdO photocatalysts for photocatalytic degradation of Remazole Red F3B (RR) dye, under simulated sunlight, were investigated. The photocatalytic mineralization of an RR dye solution over various NiO-x/TiO₂ and CdO-x/TiO₂ photocatalysts under simulated sunlight was investigated. It was worthy noticing that the photocatalytic activity of titania improved using the prepared catalysts. The prepared TiO₂, NiO-5/TiO₂, and CdO-2/TiO₂ photocatalysts exhibited higher photocatalytic activity under simulated sunlight than did commercial TiO₂. The prepared photocatalysts were stable after photocatalytic degradation of the dye. The observed photocatalytic mineralization of the dye was 51 and 71% over NiO-10/TiO₂ and CdO-2/TiO₂ after 180 min of irradiation, respectively. Juxtaposing a p-NiO-5/TiO₂ semiconductor provided a potential approach for decreasing charge recombination. The prepared photocatalystsNiO-5/TiO₂ and CdO-2/TiO₂ are promising composites for the solar detoxification of textile wastewater.     

Removal of the herbicide Bentazon from contaminated water in the presence of synthesized nanocrystalline TiO2 powders under irradiation of UV-C light

A solution-based processing method has been used to synthesize nanocrystalline TiO₂ powders by controlling the hydrolysis of TiCl₄ in an aqueous solution in both anatase and rutile phases. The primary particle sizes of the powders were in the range of 5-15 nm. To determine the crystal phase composition and size of the prepared photocatalysts, X-ray diffraction (XRD) measurements were used. We also studied the photocatalytic removal of the herbicide, Bentazon, from contaminated water in the presence of synthesized nanocrystalline TiO₂ powders under UV light illumination (30 W). The removal efficiency of Bentazon was 16% when the photolysis was carried out in the absence of TiO₂ and it was negligible in the absence of UV light. We have studied the influence of the basic operational parameters such as the different kinds of TiO₂, amount of TiO₂, irradiation time and initial concentration of Bentazon on the photocatalytic removal efficiency of Bentazon. Our results indicated that 99% removal of the herbicide from the solution containing 15 ppm of Bentazon after selecting desired operational parameters could be achieved in a relatively short time, about 90 min. A kinetic model was successfully established for the prediction of removal of Bentazon by the UV/TiO₂ system with any concentration of the herbicide. In this work, we also compared the photocatalytic activity between the commercial TiO₂ and synthesized nanocrystalline TiO₂ powders. The photocatalytic activities of different photocatalysts were tested using the herbicide solution.     

Enhanced photocatalytic activity of highly transparent superhydrophilic doped TiO2 thin films for improving the self-cleaning property of solar panel covers

Undoped and metal doped nanocrystalline TiO₂ transparent thin films were synthesized on glass substrates via sol-gel/dip-coating method. TiO₂ thin film coatings can be applied to the surfaces of solar panels to impart self-cleaning properties to them. The structural and optical properties of few nanometer-thick films were characterized by XRD, SEM, CA, AFM, XPS, and UV–Vis spectrophotometry techniques. The stoichiometric TiO₂ films crystallized in anatase phase, with a particle size of ～100 nm, which were uniformly distributed on the surface. The prepared films with a roughness of ～1–5 nm, increased the hydrophilicity of the glass surface. Reducing the amount of Ti precursor (X) favored the improvement of film quality. To improve the photocatalytic activity of the TiO₂ thin film, it was doped with Ni, Cd, Mo, Bi and Sr metal ions. The effect of metal doping on the photocatalytic activity of the films was investigated using the degradation process of methylene blue (MB) dye as the model contaminant. Among the prepared coatings, the Sr–TiO₂ film showed the highest efficiency for MB degradation. It increased the dye degradation efficiency of the films under both UV and Vis lights. The kinetic investigations also showed that the degradation of MB by TiO₂ and M ? TiO₂ films obeyed the pseudo-first order kinetics.     

Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A simple and straightforward approach to prepare TiO₂-coated carbon nanotubes (CNTs) is presented. Anatase TiO₂ nanoparticles (NPs) with the average size ~8 nm were coated on CNTs from peroxo titanic acid (PTA) precursor even at low temperature of 100 °C. We demonstrate the effects of CNTs/TiO₂ molar ratio on the adsorption capability and photocatalytic efficiency under UV–visible irradiation. The samples showed not only good optical absorption in visible range, but also great adsorption capacity for methyl orange (MO) dye molecules. These properties facilitated the great enhancement of photocatalytic activity of TiO₂ NPs-coated CNTs photocatalysts. The TiO₂ NPs-coated CNTs exhibited 2.45 times higher photocatalytic activity for MO degradation than that of pure TiO₂.     

Visible photocatalytic activity and photoelectrochemical behavior of TiO2 nanoparticles modified with metal porphyrins containing hydroxyl group

TiO₂ nanoparticles modified with 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin (HTPP), 5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin zinc (ZnHTPP) and trans-dichloro-5-(p-hydroxylphenyl)-10,15,20-triphenylporphyrin tin (SnHTPP) were prepared in order to improve the visible photocatalytic activity of TiO₂ nanoparticles. The photocatalytic activity of the modified TiO₂ nanoparticles was investigated by carrying out the photodegradation of methyl orange in aqueous solution under visible light irradiation. The TiO₂ nanoparticles modified with SnHTPP show the highest visible photocatalytic activity with a degradation ratio of 86% of methyl orange after 180 min irradiation among three catalysts. This result indicates that the central metal ions in porphyrins can significantly influence the sensitization efficiency of porphyrins. In addition, the photoelectrochemical behavior of the modified TiO₂ nanoparticles was examined and related to their photocatalytic activity. Finally, the photocatalytic mechanism was discussed preliminarily.     

The role of the diluent phase in the mechanochemical preparation of TiO2 nanoparticles

Anatase and rutile TiO₂ nanoparticles were synthesized via mechanochemical reaction and subsequent annealing of the products. TiO₂ nanoparticles were prepared by the use of planetary ball milling of titanyl sulphate (TiOSO₄.xH₂O.yH₂SO₄) and NaCl powders as the reactant and diluent phases, respectively. In this paper, the effect of volume fraction of diluent phase (NaCl) on the particle size distribution and agglomeration of TiO₂ nanoparticles is studied. Final products were obtained by annealing the milled powders at 700 °C for half an hour and subsequent washing out the water-soluble NaCl. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) investigations showed that the increase in NaCl:TiOSO₄ weight ratio (NTR) leads to the formation of nanocrystalline anatase and rutile particles with more uniform size distribution, lower weight ratio of rutile phase and lower agglomeration of particles.     

Synthesis of TiO2 nano-particles and their photocatalytic activity for formaldehyde and methyl orange degradation

TiO₂ nano-particles were synthesized by sol-gel technique and characterized by X-ray diffractometer (XRD) and transmission electron microscope (TEM). Their photocatalytic activities for formaldehyde (FA) and methyl orange (MO) degradation were tested using degradation rate (η) as an evaluation index. Based on the orthogonal test results, the optimal condition for TiO₂ preparation was obtained. Results showed that particle sizes were in the range of 10–40 nm, and that prepared TiO₂ had better photocatalytic activity than P25. A simplified model was developed to evaluate the apparent quantum efficiency (Φ _app) of this photocatalytic reaction system.     

Synthesis, characterization and optical properties of Zn1−xTixO nanoparticles prepared via a high-energy ball milling technique

Zn_1−xTi_xO (x = 0, 0.01, 0.03 and 0.05) nanoparticles were prepared by high-energy ball milling at 400 rpm. The milled powders were characterized by X-ray diffractometer (XRD) and the results exhibited that Ti-doped ZnO nanoparticles consisted of single phase with hexagonal structure when the mixtures of ZnO and TiO₂ powders were milled for 20 h. The crystallite size reduced as a function of the doping content and milling time from 1 to 10 h then increased after milling for 20 h and when the annealing temperature increased. The strain changed inversely to the crystallite size. A wider band-gap was obtained by increasing the doping content and annealing temperature because of a reduction in defect concentration. Both ZnO- and Ti-doped ZnO nanoparticles caused damage to S. aureus, E. coli, P. mirabilis, S. typhi and P. aeruginosa.