Preparation and characterization of tungsten-loaded titanium dioxide photocatalyst for enhanced dye degradation

Preparation and modification methods of defective titanium dioxide-based nanoparticles for photocatalytic wastewater treatment-a comprehensive review

The rapid population growth and industrial expansion worldwide have created serious water contamination concerns. To curb the pollution issue, it has become imperative to use a versatile material for the treatment. Titanium dioxide (TiO₂) has been recognized as the most-studied nanoparticle in various fields of science and engineering due to its availability, low cost, efficiency, and other fascinating properties with a wide range of applications in modern technology. Recent studies revealed the photocatalytic activity of the material for the treatment of industrial effluents to promote environmental sustainability. With the wide band gap energy of 3.2 eV, TiO₂ can be activated under UV light; thus, many strategies have been proposed to extend its photoabsorption to the visible light region. In what follows, this has generated increasing attention to study its characteristics and structural modifications in different forms for photocatalytic applications. The present review provides an insight into the understanding of the synthesis methods of TiO₂, the current progress in the treatment techniques for the degradation of wide environmental pollutants employing modified TiO₂ nanoparticles, and the factors affecting its photocatalytic activities. Further, recent developments in using titania for practical applications, the approach for designing novel nanomaterials, and the prospects and opportunities in this exciting area have been discussed.

Removal of Methylene Blue by Metal Oxides Supported by Oily Sludge Pyrolysis Residues

As a typical pollutant, methylene blue poses a serious threat to the environment and human health. Oily sludge pyrolysis residue loaded with metal oxides could be used to prepare composite materials, which is not only an effective way to treat oily sludge, but also a possible method to treat methylene blue pollutants. In this paper, composite materials (AC-CuO, AC-ZnO, and AC-TiO2) were prepared by oily sludge pyrolysis residue-loaded CuO, ZnO, and TiO2 directly, and characterized by XRD, SEM, EDS, BET, FT-IR, and XPS, and it was shown that the metal oxides were successfully supported on the pyrolysis residue. Then, the composite materials were applied to the removal of methylene blue solution. The removal effect of composite materials on methylene blue with respect to the impregnation time, impregnation ratio and dosage, and the contact time and number of regenerations were investigated, and the removal parameters were optimized by response surface methodology. The removal process for methylene blue was described by applying Lagergren, McKay, Langmuir isotherm, Freundlish isotherm and intraparticle diffusion models. According to the response surface methodology and the main factors affecting the removal effect of methylene blue, the results indicate that the removal effect of 5 mg/L methylene blue could reach 95.28%, 94.95%, and 96.96%, respectively, and the corresponding removal capacities were 4.76, 4.75, and 4.85 mg/g. In addition, kinetic studies showed that the removal process of methylene blue was mainly constituted by chemical adsorption. The intraparticle diffusion showed that the removal of methylene blue may be controlled by both liquid film diffusion and intraparticle diffusion. The isotherms showed that the adsorption sites of composites for methylene blue were uniformly distributed and had the same affinity. Furthermore, regeneration experiments showed that the composite materials were stable and had relatively reusability.

Azo dye removal by acid pretreated biomass and its regeneration by visible light photocatalysis with incorporated CuO

In this work, we synthesized self-regenerative biosorbent BM-H₃PO₄-(CuO) by combining the photocatalyst CuO and acid pre-treated biomass (BM-H₃PO₄), the hybrid material BM-H₃PO₄-(CuO) was used for the removal of azo dye Direct Red 89 (DR-89). The morphology, texture phase, composition of the samples was characterized with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, elemental diffraction analysis X-ray (EDAX). That confirms the presence of CuO into the pretreated biomass BM-H₃PO_4. The results reveal that when the biomass was loaded with a proper CuO/BM-H₃PO₄ weight ratio of 60%, the biosorption capacity was enhanced to 5.5 times compared to BM-H₃PO₄. The maximum adsorption capacity of BM-H₃PO₄-(CuO)_60% was 30.3 mg g^-1 determined from the Langmuir isotherm. The pseudo-second-order kinetic model was more appropriate for describing dye biosorption. The hybrid material BM-H₃PO₄-(CuO)_60% demonstrated a better photocatalytic activity under visible light irradiation then pure CuO. Incorporation of the CuO particles into the biosorbent, offers the possibility to harvest visible light for oxidative photodegradation. The prepared material also showed good reusability in the cyclic of biosorption-photocatalysis experiments and the biosorption efficiency was higher than 90% over four cycles. This study provides an eco-friendly way to fabricate self-regenerative biosorbents.

Synthesis of tungsten oxide/ amino-functionalized sugarcane bagasse derived-carbon quantum dots (WO3/N-CQDs) composites for methylene blue removal

In this present study, the tungsten oxide/amino-functionalized sugarcane bagasse derived-carbon quantum dots (WO₃/N-CQDs) composite has successfully been prepared through a simple mixing process. The WO₃ was synthesized through a precipitation method, and CQDs were amino-functionalized using ethylenedinitrilotetraacetic acid (EDTA) and ethylenediamine (EDA) through one-pot hydrothermal method. It is revealed that N-CQDs incorporation into WO₃ alters the bandgap energy, crystallinity, surface area, and photoluminescence (PL) properties. The produced composites exhibit higher monoclinic WO₃ crystallinity, larger surface area, lower bandgap energy and quenched photoluminescence intensity. The as-prepared WO₃/N-CQDs composites exhibit better adsorption and photocatalytic degradation performance of methylene blue (MB) than the pristine WO₃. It shows that the combination of N-CQDs and WO₃ enhanced visible light absorption, by lowering the bandgap energy of WO₃ from 2.175 to 1.495 eV. The best performance composite is WO₃/N-CQDs EDA 2.5% with an efficiency of 96.86%, removal rate constant of 0.02017/min, and chemical oxidation demand (COD) removal efficiency achieved 84.61%. Moreover, the WO₃/N-CQDs EDA 2.5% shows a significant photocatalytic activity even at higher MB initial concentration with 92.93% removal for 50 ppm MB. Subsequently, the composite also has good stability after a sequential 3-times cycle of degradation with 86.85% removal. The increasing photocatalytic performance is affected by the quenching effect of PL and lower bandgap energy. The lower intensity of the PL indicates the reduced charge carrier recombination resulting in increased photocatalytic activity. The combination of N-CQDs and WO₃ resulted in improved photodegradation, which shows its significant potential to be utilized for wastewater treatment.

Improved photocatalytic oxidation of arsenic (III) with WO3/TiO2 nanomaterials synthesized by the sol-gel method

Photocatalytic oxidation of arsenite (As(III)) to arsenate (As(V)) was studied in aqueous solution using a series of WO₃/TiO₂ semiconductors readily synthesized through sol-gel method with WO₃ content in the range of 1-5 wt%. The resulting materials showed enhanced photocatalytic activity towards As(III) photo-oxidation compared to their individual counterparts under UV radiation. The amount of As(III) and As(V) species in the irradiated solution was determined using the molybdenum blue method. The efficiency of photoinduced carriers separation was further affirmed by electrical impedance spectroscopy (EIS) and photocurrent tests. The maximum catalytic efficiency was observed when the binary oxide 3%WO₃/TiO₂ (TW3) was used, reaching a 99% conversion of As(III) to As(V) within the first 25 min under UV irradiation. The enhanced photocatalytic performance of the heterostructures could be explained as consequent to an improved charge separation due to the migration of photoproduced holes in TW3 photocatalyst. Based on the electric band structure of WO₃ and TiO₂, a reasonable mechanism for the photo-oxidation of As(III) over TW3 novel catalyst has been proposed.

Photocatalytic Decolorization and Biocidal Applications of Nonmetal Doped TiO2: Isotherm, Kinetic Modeling and In Silico Molecular Docking Studies

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO₂ against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO₂ with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO₂. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m² g⁻¹ specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g⁻¹ with K_ads of 0.113 mg⁻¹. The LH model yielded a higher coefficient K_C (1.15 mg L⁻¹ h⁻¹) compared to the adsorption constant K_LH (0.3084 L mg⁻¹). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol⁻¹) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Design a new photocatalyst of sea sediment/titanate to remove cephalexin antibiotic from aqueous media in the presence of sonication/ultraviolet/hydrogen peroxide: Pathway and mechanism for degradation

The aim of the current study was directed to develop a new sea sediment/titanate photocatalyst to remove cephalexin from aqueous media in the presence of ultraviolet (UV) light, hydrogen peroxide (H₂O₂), and ultrasonic waves. The influence of furnace temperature (300, 350, 400, and 500 °C), furnace residence time (1, 2, 3, and 4 h), and ratio of sea sediment: titanium (0-6 v: w) on the physicochemical properties and the cephalexin removal by the sea sediment/titanate photocatalyst was explored. The technique of FTIR, SEM/EDX, XRD, BET, BJH, and Mapping was used to determine the physicochemical properties of the generated photocatalyst. The maximum cephalexin removal (94.71%) was obtained at the furnace temperature of 500 °C, the furnace residence time of 2 h, and the sea sediment: titanium ratio of 1:6 (=12 mL TiO₂/2 g sea sediment). According to the acquired results, the surface area of the optimized catalyst, namely Cat-500-2-12, was computed to be 52.29 m²/g. The crystallite size of titanium oxide on the optimum photocatalyst was calculated ~17.68 nm. The FTIR test confirmed the presence of C=C, O-H, C=O, C-S, and C-H functional groups in the photocatalyst. The transformation pathway for the degradation of cephalexin by the developed system was drawn. The present investigation showed that the developed technique (sea sediment/titanate-UV-H₂O₂-ultrasonic) could be used as a promising alternative for attenuating cephalexin from aqueous solutions.

Elnouby M, Gouda MH, Elessawy NA, Santos DMF. Effect of the Morphology of Tungsten Oxide Embedded in Sodium Alginate/Polyvinylpyrrolidone Composite Beads on the Photocatalytic Degradation of Methylene Blue Dye Solution

Tungsten oxide nanostructures were modified by oxygen vacancies through hydrothermal treatment. Both the crystalline structure and morphological appearance were completely changed. Spherical WO₃·H₂O was prepared from tungstic acid solution by aging at room temperature, while rod-like WO₃·0.33H₂O was prepared by hydrothermal treatment of tungstic acid solution at 120 °C. These structures embedded in sodium alginate (SA)/polyvinylpyrrolidone (PVP) were synthesized as novel porous beads by gelation method into calcium chloride solution. The performance of the prepared materials as photocatalysts is examined for methylene blue (MB) degradation in aqueous solutions. Different operation parameters affecting the dye degradation process, such as light intensity, illumination time, and photocatalyst dosage are investigated. Results revealed that the photocatalytic activity of novel nanocomposite changed with the change in WO₃ morphology. Namely, the beads with rod nanostructure of WO₃ have shown better effectiveness in MB removal than the beads containing WO₃ in spherical form. The maximum degradation efficiency was found to be 98% for WO₃ nanorods structure embedded beads, while the maximum removal of WO₃ nanospheres structure embedded beads was 91%. The cycling-ability and reuse results recommend both prepared structures to be used as effective tools for treating MB dye-contaminated wastewaters. The results show that the novel SA/PVP/WO₃ nanocomposite beads are eco-friendly nanocomposite materials that can be applied as photocatalysts for the degradation of cationic dyes in contaminated water.

Solvothermal synthesis of WO3 /TiO2 /carbon fiber composite photocatalysts for enhanced performance under sunlight illumination

Carbon fiber (CF)-based WO₃ /TiO₂ composite catalysts (WO₃ /TiO₂ /CF) were successfully synthesized by solvothermal method. The catalysts were characterized by XPS, SEM, BET, XRD, FTIR, Raman and UV-Vis. The analyses confirmed the WO₃ /TiO₂ nanoparticles with high crystallinity deposited on the carbon structure. The photocatalytic degradation of Orange II azo dye under UV and sunlight illumination with the synthesized catalyst was explored. The composite catalyst displayed high performance (85%) for Orange II degradation while that of for WO₃ /TiO₂ was found as 76%. The effects of CF amount, solution pH, initial dye concentration and catalyst dose on photocatalytic performance were studied. It was found that the degradation efficiency increased from 68% to 90% with the increasing CF amount from 3 wt% to 5 wt%, while the further increase in CF amount (7-10 wt%) decreased the photodegradation due to the blocking the active sites of WO₃ /TiO₂ . The enhanced photocatalytic efficiency was mainly attributed to the electrical properties of the CF and reduced bandgap.

A tetraphenylporphyrin/WO3/exfoliated graphite nanocomposite for the photocatalytic degradation of an acid dye under visible light irradiation

Charge carrier separation in visible light photocatalytic degradation of a dye was achieved by the fabrication of a tetraphenylporphyrin/WO₃/exfoliated graphite nanocomposite.

Synthesis, Surface Acidity and Photocatalytic Activity of WO3/TiO2 Nanocomposites – An Overview

Titania has been studied to be one of the best photocatalysts for the decomposition of many organic pollutants present in aqueous medium. Because of the wide band gap energy of TiO2 (3.2 eV) it can be activated only under UV light region which is present 4 % in the solar light spectrum. The photocatalytic activity of TiO2 was enhanced by means of several methods. TiO2 coupled with other semiconductor has gained additional importance, owing to improving the efficient charge separation by trapping the photogenerated electrons. WO3 is a better semiconductor having relatively lower band gap energy (2.8 eV) and absorb broad solar light spectrum. The formation of WOx monolayer on TiO2 notably increases the surface acidity of TiO2. This increasing the surface acidity of WO3/TiO2 photocatalyst facilitates the adsorption of the more hydroxyl group in addition to more organic reactants on its surface which obviously facilitate the enhancement of photocatalytic activity. In this review, the synthesis methods and photocatalytic activity of some selected and unique results related to WO3/TiO2 photocatalyst were discussed. The efficient charge separation, increased absorption of the reactants by increasing the surface acidity and high aspect ratio structures of WO3/TiO2 are also reviewed.

Synthesis of iron-doped TiO2 for degradation of reactive Orange16

In this study the optimum conditions for preparing the iron-doped TiO2 nanoparticles were investigated. Samples were synthesized by sol-gel impregnation method. Three effective parameters were optimized using Taguchi method, consisted of: (i) atomic ratios of Fe to Ti; (ii) sintering temperature; (iii) sintering time. The characterization of samples was determined using X-ray diffraction, BET- specific surface area, UV- Vis reflectance spectra (DRS) and scanning electron microscope (SEM). The XRD patterns of the samples indicated the existence of anatase crystal phase in structure. UV- Vis reflectance spectra showed an enhancement in light absorbance in the visible region (wavelength > 400 nm) for iron-doped samples. The photocatalytic activity of samples was investigated by the degradation of RO 16 (RO 16) dye under UV irradiation. The results illustrated that the photocatalytic activity of iron-doped TiO2 was more than pure TiO2, because of the smaller crystal size, grater BET surface area and higher light absorption ability.

Solar photocatalytic activity of TiO2 modified with WO3 on the degradation of an organophosphorus pesticide

In this study, the solar photocatalytic activity (SPA) of WO3/TiO2 photocatalysts synthesized by the sol-gel method with two different percentages of WO3 (2 and 5%wt) was evaluated using malathion as a model contaminant. For comparative purpose bare TiO2 was also prepared by sol-gel process. The powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectance UV-vis spectroscopy (DRUV-vis), specific surface area by the BET method (SSABET), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy with a high annular angle dark field detector (STEM-HAADF). The XRD, Raman, HRTEM and STEM-HAADF analyses indicated that WO3 was present as a monoclinic crystalline phase with nanometric cluster sizes (1.1 ± 0.1 nm for 2% WO3/TiO2 and 1.35 ± 0.3 nm for 5% WO3/TiO2) and uniformly dispersed on the surface of TiO2. The particle size of the materials was 19.4 ± 3.3 nm and 25.6 ± 3 nm for 2% and 5% WO3/TiO2, respectively. The SPA was evaluated on the degradation of commercial malathion pesticide using natural solar light. The 2% WO3/TiO2 photocatalyst exhibited the best photocatalytic activity achieving 76% of total organic carbon (TOC) abatement after 300 min compared to the 5% WO3/TiO2 and bare TiO2 photocatalysts, which achieved 28 and 47% mineralization, respectively. Finally, experiments were performed to assess 2% WO3/TiO2 catalyst activity on repeated uses; after several successive cycles its photocatalytic activity was retained showing long-term stability.

Synergistic photosensitized removal of Cr(VI) and Rhodamine B dye on amorphous TiO2 under visible light irradiation

Amorphous TiO(2) (Am-TiO(2)) was prepared at room temperature by hydrolysis of Ti(OBu)(4) in water without addition of strong acids or organic solvents. Results from XRD and TEM revealed that the as-prepared Am-TiO(2) was composed of amorphous structure. For the simultaneous photosensitized removal of Cr(VI) and zwitterionic Rhodamine B (RhB) dye, Am-TiO(2) exhibited more significant synergistic effect than commercial P25-TiO(2). The removal efficiencies for RhB and Cr(VI) after 100 min visible light irradiation were 97.8% and 53.5% on Am-TiO(2), respectively. While 88.2% RhB and 42.1% Cr(VI) were removed on P25-TiO(2). Decreased synergistic activities as well as smaller surface areas were observed when Am-TiO(2) was pretreated at high temperatures (200-700°C). Thus, it was the larger specific surface area rather than better crystallinity dominated the synergistic degradation dynamics under visible light irradiation with lower pH (2), greater catalyst loading amount (2g/L), proper RhB/Cr(VI) ratios (1:8) and higher light intensity (500 W). Better synergistic performance was also obtained on Am-TiO(2) than P25-TiO(2) when Cr(VI) coexists with cationic dyes, while negligible difference was observed in the presence of anionic dyes. Superior stability and simplicity of Am-TiO(2) was also exhibited in the cyclic runs.

Synthesis and photo-degradation application of WO3/TiO2 hollow spheres

A WO(3)/TiO(2) composite, hollow-sphere photocatalyst with average diameter of 320 nm and shell thickness of 50 nm was successfully prepared using a template method. UV-vis diffuse reflectance spectra illustrated that the main absorption edges of the WO(3)/TiO(2) hollow spheres were red-shifted compared to the TiO(2) hollow spheres, indicating an extension of light absorption into the visible region of the composite photocatalyst. The WO(3) and TiO(2) phases were confirmed by X-ray diffraction analysis. BET isotherms revealed that the specific surface area and average pore diameter of the hollow spheres were 40.95 m(2)/g and 19 nm, respectively. Photocatalytic experiments indicate that 78% MB was degraded by WO(3)/TiO(2) hollow spheres under visible light within 80 min. Under the same conditions, only 24% MB can be photodegraded by TiO(2). The photocatalytic mineralization of MB, catalyzed by TiO(2) and WO(3)/TiO(2), proceeded at a significantly higher rate under UV irradiation than that under visible light, and more significant was the increase in the apparent rate constant with the WO(3)/TiO(2) composite semiconductor material which was 3.2- and 3.5-fold higher than with the TiO(2) material under both UV and visible light irradiation. The increased photocatalytic activity of the coupled nanocomposites was attributed to photoelectron/hole separation efficiency and the extension of the wavelength range of photoexcitation.

The pH-dependent surface charging and points of zero charge: V. Update

The points of zero charge (PZC) and isoelectric points (IEP) from the recent literature are discussed. This study is an update of the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC, Boca Raton, FL, 2009] and of its previous update [J. Colloid Interface Sci. 337 (2009) 439]. In several recent publications, the terms PZC/IEP have been used outside their usual meaning. Only the PZC/IEP obtained according to the methods recommended by the present author are reported in this paper, and the other results are ignored. PZC/IEP of albite, sepiolite, and sericite, which have not been studied before, became available over the past 2 years.