Effective Removal of Methylene Blue on EuVO4/g-C3N4 Mesoporous Nanosheets via Coupling Adsorption and Photocatalysis

In this study, we first manufactured ultrathin g-C₃N₄ (CN) nanosheets by thermal etching and ultrasonic techniques. Then, EuVO₄ (EV) nanoparticles were loaded onto CN nanosheets to form EuVO₄/g-C₃N₄ heterojunctions (EVCs). The ultrathin and porous structure of the EVCs increased the specific surface area and reaction active sites. The formation of the heterostructure extended visible light absorption and accelerated the separation of charge carriers. These two factors were advantageous to promote the synergistic effect of adsorption and photocatalysis, and ultimately enhanced the adsorption capability and photocatalytic removal efficiency of methylene blue (MB). EVC-2 (2 wt% of EV) exhibited the highest adsorption and photocatalytic performance. Almost 100% of MB was eliminated via the adsorption–photocatalysis synergistic process over EVC-2. The MB adsorption capability of EVC-2 was 6.2 times that of CN, and the zero-orderreaction rate constant was 5 times that of CN. The MB adsorption on EVC-2 followed the pseudo second-order kinetics model and the adsorption isotherm data complied with the Langmuir isotherm model. The photocatalytic degradation data of MB on EVC-2 obeyed the zero-order kinetics equation in 0–10 min and abided by the first-order kinetics equation for10–30 min. This study provided a promising EVC heterojunctions with superior synergetic effect of adsorption and photocatalysis for the potential application in wastewater treatment.     

Visible light-induced photocatalytic activity of delafossite AgMO2 (M = Al, Ga, In) prepared via a hydrothermal method

Delafossite-structured oxides AgMO₂ (M = Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO₂ > AgGaO₂ > AgAlO₂. The relative high photocatalytic activity of AgInO₂ can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO₂ was proposed and its stability was also investigated.     

Structure and photocatalytic performance of magnetically separable titania photocatalysts for the degradation of propachlor

A magnetic photocatalyst was prepared by modification of TiO₂ nanoparticles (Degussa P25) with nanocrystalline γ-Fe₂O₃ nanoparticles through a protective lining made up of two oppositely charged polyelectrolytes. As-prepared magnetically separable photocatalysts differing in γ-Fe₂O₃ loading (3, 8, 13, 20 and 30 wt.%) were characterized by XRD, TEM, thermal analysis, Mössbauer and magnetic measurements. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (propachlor) in water as model compound. The primary degradation of propachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Generally, all magnetic photocatalysts exhibit good catalytic activity towards organic pollutants, do not suffer from photodissolution and can be reused several times without any decrease in their photocatalytic activity.     

Preparation, characterization and activity evaluation of p–n junction photocatalyst p-CaFe2O4/n-ZnO

p–n junction photocatalyst p-CaFe₂O₄/n-ZnO was prepared by ball milling of ZnO in H₂O doped with p-type CaFe₂O₄. The structural and optical properties of the p–n junction photocatalyst p-CaFe₂O₄/n-ZnO were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectrum (DRS) and fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic degradation of methylene blue (MB). The results showed that the photocatalytic activity of the p-CaFe₂O₄/n-ZnO was higher than that of ZnO. When the amounts of doped p-CaFe₂O₄ were 0.0 wt.% and 1.0 wt.%, the photocatalytic degradation efficiencies were 50.1 and 73.4%, respectively. Effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

Prevention of photocatalytic deterioration of resins using TiO2 pillared fluoromica

The TiO₂ pillared fluoromica powder was kneaded with polylactic acid resin. The composite showed high photocatalytic activity for degradation of acetaldehyde and toluene gas, especially at the range of 1–3 wt.% pillared mica powder, and this photocatalytic activity was higher than that of resins containing even higher amounts of commercial TiO₂ (P-25, Degussa). The composite test pieces of pillared mica showed smaller photocatalytic deterioration than the samples with P-25 powder in out-door weathering tests. Thus, the TiO₂ pillared clay resin composite shows excellent prevention of photocatalytic deterioration and high photocatalytic activity in comparison with P-25.     

Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

Preparation and characterization of TiO2 photocatalysts by Fe doping together with Au deposition for the degradation of organic pollutants

Fe³⁺ doped TiO₂ deposited with Au (Au/Fe–TiO₂) was successfully prepared with an attempt to extend light absorption of TiO₂ into the visible region and reduce the rapid recombination of electrons and holes. The samples were characterized by X-ray diffraction (XRD), N₂ physical adsorption, Raman spectroscopy, atomic absorption flame emission spectroscopy (AAS), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The photocatalytic activities of the samples were evaluated for the degradation of 2,4-chlorophenol in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. The results of XRD, XPS and high-resolution transmission electron microscopy (HRTEM) analysis indicated that Fe³⁺ substituted for Ti⁴⁺ in the lattice of TiO₂, Au existed as Au⁰ on the surface of the photocatalyst and the mean particle size of Au was 8 nm. Diffuse reflectance measurements showed an extension of light absorption into the visible region for Au/Fe–TiO₂, and PL analysis indicated that the electron–hole recombination rate has been effectively inhibited when Au deposited on the surface of Fe-doped TiO₂. Compared with Fe doped TiO₂ sample and Au deposited TiO₂ sample, the Au/Fe–TiO₂ photocatalyst exhibited excellent visible light and UV light activity and the synergistic effects of Fe³⁺ and Au was responsible for improving the photocatalytic activity.     

Various TiO2 microcrystals: Controlled synthesis and enhanced photocatalytic activities

Titania microspheres with higher photocatalytic activity have been synthesized using TiCl₄ and FeCl₃ as the precursor in the presence of Span-80. The products were characterized with XRD, TEM and UV–vis DRS. XRD and TEM indicated that the microsphere was a mixture of rutile, brookite and anatase with a diameter of about 5–7 μm. The photocatalytic experiments revealed that the microspheres exhibited high photocatalytic activities under UV-light and solar irradiation. The degradation rate of methyl orange (MO) was 100% under UV-light irradiation for 3 h and 91% under solar irradiation for 6 h. In particular, the catalysts could be readily separated by sedimentation after the photocatalytic reaction.     

Evaluation of atrazine degradation in UV/FeZSM-5/H2O2 system using factorial experimental design

Degradation of atrazine in model wastewater by UV/FeZSM-5/H₂O₂ system chosen as optimal for application of advanced oxidation process (AOP) has been studied in a batch photo reactor. The statistical study of the process was performed using two-level full factorial experimental design with the three process parameters. Individual parameters and their interaction effects on atrazine degradation were determined and statistical model of process was developed. The optimal operating conditions were established. This approach has also given a broader insight of the processes that were occurring in the reaction system, and it has finally led to simplification in terms of kinetics. Atrazine degradation was described by pseudo-first-order kinetics with observed rate constant k′ = 2 × 10⁻³ s⁻¹.     

TiO2 nanotubes and CNT–TiO2 hybrid materials for the photocatalytic oxidation of propene at low concentration

In this work, we investigated titanium dioxide (TiO₂) nanotubes and CNT–TiO₂ hybrid materials for the photocatalytic oxidation (PCO) of propene at low concentration (100 ppmv) in gaseous phase. The materials were prepared via sol–gel method using sacrificial multi-walled carbon nanotubes (CNT) as templates and subsequent heat treatments to obtain the desired crystalline phase (anatase, rutile or a mixture of both) and eventually to remove the carbon template. We also studied rutile nanotubes for the first time and demonstrate that the activity strongly depends on the crystalline composition, following rutile < anatase < anatase/rutile mixture. The enhanced activity of the anatase–rutile mixture is attributed to the decrease in the electron–hole pair recombination due to the multiphasic nature of the particles. The key result of this work is the exceptional performance of the CNT–TiO₂ hybrid, which yielded the highest observed photocatalytic activity. The improved performance is attributed to synergistic effects due to the hybrid nature of the material, resulting in small anatase crystalline sizes (CNT act as heat sinks) and a reduced electron–hole pair recombination rate (CNTs act as electron traps). These results demonstrate the great potential of hybrid materials and stimulate further research on CNT-inorganic hybrid materials in photocatalysis and related areas.     

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics

Crystallization kinetics of amorphous alumina–zirconia–silica ceramics was studied by nonisothermal differential scanning calorimetry (DSC). Different amorphous materials were produced by plasma spraying of near-eutectic Al₂O₃–ZrO₂–SiO₂ mixtures. Phase composition and microstructure of the amorphous materials and nanocrystalline products were analyzed. All of the investigated materials show an exothermic peak between 940 and 990 °C in the DSC experiments. The activation energies calculated from DSC traces decrease with increasing SiO₂ concentration. Values of the Avrami coefficients together with results of the microstructural observations indicate that tetragonal zirconia crystallization from materials containing more than 10 wt.% SiO₂ proceeds by a diffusion-controlled mechanism with nucleation occurring predominantly at the beginning of the process. In contrast, material with almost no SiO₂ exhibited a value of the Avrami exponent consistent with the crystal growth governed by processes at the phase boundary.     

Photocatalytic inactivation of bacteria by photocatalyst Bi2WO6 under visible light

The photocatalytic inactivation of Escherichia coli under visible light irradiation (λ > 420 nm) was performed with Bi₂WO₆ to investigate the photocatalytic bactericidal capability. Our work shows that the single phase oxide photocatalyst Bi₂WO₆ is effective in photocatalytic inactivation on E. coli. And the results revealed that the photocatalytic inactivation rate of E. coli with Bi₂WO₆ followed pseudo-first-order kinetics. The bactericidal action was directly observed by TEM and further proved by the measurement of K⁺ leakage from the inactive E. coli through the ICP-OES analysis. The results demonstrated that the photocatalysis could cause drastic damage in E. coli cells.     

Synergistic effect of TiO2 and iron oxide supported on fluorocarbon films: Part 2: Long-term stability and influence of reaction parameters on photoactivated degradation of pollutants

The degradation of hydroquinone (HQ) and nalidixic acid (NA) mediated by TiO₂ and iron oxide immobilized on functionalized polyvinyl fluoride films (PVF^f–TiO₂–Fe oxide) in the presence of H₂O₂ under simulated solar light has been examined. The results show that the contribution of homogeneous photo-Fenton oxidation to the initial mineralization process was low. The degradation rates were not dependant of initial pH. Heterogeneous photocatalytic activity of PVF^f–TiO₂–Fe oxide was enhanced by increasing temperature, NaCl addition and by long-term utilization.The PVF^f–TiO₂–Fe oxide surface was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) at different states of utilization. Correlations between the catalyst surface composition and degradation kinetics are discussed. Long-term stability evaluated by repetitive pollutant degradations was outstanding. The presence of TiO₂ seems to (i) limit contact between polymer film and highly reactive radicals in the solution and (ii) act as a charge trap. Moreover, during the photocatalysis mediated by PVF^f–TiO₂–Fe oxide, some leaching of supported iron increased the amount of the top TiO₂ layer exposed to the light increasing the synergistic effects between the two oxides leading to enhanced pollutant degradation.     

Preparation, characterization and photocatalytic activity of TiO2 impregnated with the heteropolyacid H3PW12O40: Photo-assisted degradation of 2-propanol in gas–solid regime

Both commercial and home prepared TiO₂ samples impregnated with tungstophosphoric acid (H₃PW₁₂O₄₀) were prepared and used for the photo-assisted degradation of 2-propanol in gas–solid regime. The characterization results evidenced a good coverage of the polyoxometalate (POM) onto the surface of both types of TiO₂ samples along with a marginal effect of the presence of ethanol or HCl during the POM impregnation step on the specific surface area, porosity, morphology, crystallinity and acidity of the samples. Propene was the main intermediate product found in 2-propanol photocatalytic degradation by using the samples containing POM as the photocatalyst, whereas propanone was mainly obtained when the photocatalyst was bare TiO₂. Acetaldehyde was also an intermediate product and its amount was always significantly smaller with respect to propanone and propene (when formed). Carbon dioxide and water were the ultimate oxidation products. The selectivity to propene has been attributed to the acidity of the POM supported samples.     

Boosting the photoconversion efficiency of TiO2 nanotubes using UV radiation-assisted anodization as a prospective method: An efficient photocatalyst for eliminating resistant organic pollutants

1D TiO₂ nanotube arrays (TNTs), as versatile nanostructures, have attracted a considerable amount of scientific attention, particularly in photocatalytic applications. In the present study, UV radiation-assisted anodization method with various irradiation times (30–120 min) was employed as a preferable approach to fabricating TNTs with remarkable optical property and photocatalytic activity. The results revealed that in situ irradiation not only improved the surface area (from 30.10 to 48.5 m²), but also increased the roughness factor (from 77.27 to 124.73). Furthermore, UV radiation had a significant impact on optical property and by altering elemental composition, led to a red shift in absorption edge (from 3.2 to 1.4eV). Meanwhile, voltammetric experiments showed that 120 min UV radiation during anodization was able to substantially cause a surge of the photocurrent density and the photoconversion efficiency of TNTs from 0.15 to 0.55 mA cm⁻² and from 13% to 40%, respectively. As a consequence of the improvement in optical property and photochemical features, anodic TNTs fabricated under 120 min UV radiation could increase the photocatalytic degradation of 2,4-DCP from 75% to 100%. Moreover, the kinetics study showed that all photocatalytic reactions followed zero-order kinetics which rate constant over the synthesized TNTs under 120 min UV radiation was about 5.1 times greater than that of conventionally fabricated TNTs. Likewise, the pathway of photocatalytic degradation and the proportion of reactive species in this process were assessed by scavenging tests. The results confirmed that holes (h⁺) play the main role that 53% of photocatalytic degradation occurred via both direct and indirect reactions with h⁺ species. The rest of the degradation pathways were also allocated to e⁻ and ^•O₂⁻ species by accounting for 37% and 10%, respectively.     

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.     

TiO2 photoactivity in vis and UV light: The influence of calcination temperature and surface properties

A series of TiO₂ photocatalysts were obtained using several calcination temperatures ranging from 350 to 750 °C. The photocatalysts’ characteristics by X-ray diffraction, UV–vis and FTIR diffuse reflectance spectroscopies, X-ray photoelectron spectroscopy, BET and BJH methods showed that sample active in vis region had anatase structure, about 200 m²/g specific surface area, absorbed light for λ > 400 nm and contained 10.1 at.% of C–C species. The photocatalytic activity of the catalysts was estimated by measuring the decomposition rate of phenol in 0.21 mM aqueous solution in visible and ultraviolet light. The experimental data clearly indicate correlation between the absorption intensity of irradiation by obtained powders and their photocatalytic performance in phenol degradation. An increase in absorbance over the entire vis region and the highest photocatalytic activity for phenol degradation in visible light (λ > 400 nm) occurred for photocatalyst calcinated at 350 °C. Photocatalyst processed at 450 °C had the best activity in UV light (250 < λ < 400 nm).     

Synthesis of highly active nanocrystalline WO3 and its application in laser-induced photocatalytic removal of a dye from water

Tungsten oxide nanoparticles were synthesized using the sol–gel process and applied for heterogeneous photocatalytic removal of a dye using a 355 nm laser radiation generated from Nd:YAG for the first time. Effect of various parameters, such as calcination temperature, calcination time, catalyst concentration and laser energy on the photocatalytic removal of dye has been investigated. The study showed that almost complete degradation of dye can be achieved within very short time of reaction (within few minutes) in presence of nanocrystalline WO₃ under laser irradiation. The removal process obeys first-order kinetics with an appreciable rate constant 0.146 min⁻¹. The main reason of high efficiency is the nanostructure nature of WO₃ and the laser as an excitation source as compared with the conventional setups using lamps and conventional microstructure catalysts.     

Fabrication and photoactivities of spherical-shaped BiVO4 photocatalysts through solution combustion synthesis method

Spherical-shaped BiVO₄ photocatalysts were prepared by the solution combustion synthesis method. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), nitrogen absorption for the BET specific surface area, field emission scanning electron microscopy (FE-SEM) and ultraviolet–visible diffraction reflection spectroscopy (UV–vis). The BiVO₄ crystallites show a monoclinic structure with diameter of about 400–600 nm. UV–vis diffusion absorption spectra indicate that the band gap absorption edge of pure BiVO₄ crystallites prepared by the SCS method and the SSR method are 523 nm and 540 nm, corresponding to the band gap energies of 2.45 eV and 2.40 eV, respectively. It is also found that the photocatalytic activity of degradation of methylene blue improves when the molar ratio of fuels to oxidizer is 5.     

Photo-catalytic degradation of Rhodamine B on C-, S-, N-, and Fe-doped TiO2 under visible-light irradiation

C-, S-, N-, and Fe-doped TiO₂ photocatalysts were synthesized by a facile sol–gel method. The structure and properties of catalysts were characterized by N₂ desorption–adsorption, X-ray diffraction (XRD), UV–vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results revealed that the surface area of the multi-doped TiO₂ was significantly increased and the crystallite size was smaller than the pure TiO₂ obtained by a similar route. Compared with TiO₂, the peak position in doped-TiO₂ XRD patterns was slightly shifted, which could be attributed to the distortion by the substitution of carbon, nitrogen, and sulfur dopants for some oxygen atoms and Fe³⁺ for Ti⁴⁺ in the lattice of TiO₂. These substitutions were confirmed by XPS. In addition, these dopants were responsible for narrowing the band gap of TiO₂ and shifting its optical response from ultraviolet (UV) to the visible-light region. The photocatalytic reactivities of these multi-doped TiO₂ catalysts were investigated by degrading Rhodamine B (RB) in aqueous solution under visible-light irradiation (λ > 420 nm). It was found out that the reactivity was significantly enhanced and the catalyst doped with nitrogen, carbon, sulfur, and 0.3 wt% iron had the highest photocatalytic activity.