Highly efficient photocatalytic degradation of methylene blue using carbonaceous WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> composites

Recent improvements in the performance of photocatalysts made it possible to tackle pollution through environment friendly methods. This study investigates the modification of the photocatalytic activity of TiO₂ by employing WO₃ and conductive polymers, namely, polyaniline (Pani) and polypyrrole (Ppy). Basing on our previous improvement of TiO₂ using a conductive polymer and activated carbon (AC), this study determines the activated carbon forms of TiO₂. The prepared composites are characterized using X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, Brunauer–Emmet–Teller, and UV–Vis spectroscopy. The specific surface area of the mesoporous composites is as follows: WO₃/TiO₂·AC (Pani) > WO₃/TiO₂·AC (Ppy) > WO₃/TiO₂·Pani > WO₃/TiO₂·Ppy (127 > 98 > 68 > 44 m² g^?1), which exhibited a similar trend to the photocatalytic performances (100 > 95 > 91 > 72 % conversion rate). This result could be attributed to higher porosity, surge of charge separation, and photo-responding range extension induced by the synergistic effect of WO₃, conducting polymers, and TiO₂ in the samples.     

Photoelectrocatalytic degradation of phenol using a TiO<Subscript>2</Subscript>/Ni thin-film electrode

As a new type of photoelectrode, TiO₂/Ni thin-film electrode was prepared by dip-coating technique. The structural and surface morphology of electrode was examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). Effects of initial phenol concentration, pH value, number of film layers, voltage of electrical bias applied, variation of inorganic salt type and types of dissolved gas on the photoelectrocatalytic (PEC) degradation of phenol using ultraviolet (UV) illuminated TiO₂/Ni thin-film electrode were investigated. The mechanism of PEC degradation of phenol was also studied by analyzing reaction intermediates.     

Effect of TiO<Subscript>2</Subscript> loading on the activity of V/TiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the catalytic oxidehydrogenation of ethylbenzene with carbon dioxide

TiO₂-Al₂O₃ mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO₂ were prepared by sol-gel method and impregnated with different amounts of VO _x . Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H₂-TPR), and ammonia temperature programmed desorption (NH₃-TPD). TiO₂ content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO₂ content was 50 wt-%.     

PLS-based kinetics modeling and optimization of the oxidative coupling of methane over Na<Subscript>2</Subscript>WO<Subscript>4</Subscript>/Mn/SiO<Subscript>2</Subscript> catalyst

Reactor modeling for the oxidative coupling of methane over Na₂WO₄/Mn/SiO₂ catalyst was addressed in the present study. The catalyst loading part was designed to be thicker than the inlet and outlet parts to reduce the rates of side reactions in the gas phase, and the optimal aspect ratio (L to D ratio) for no pressure drop and minimum side reactions was determined in experimental studies. Experiments were also conducted under a variety of operating conditions such as gas hourly space velocity (GHSV), CH₄/O₂ ratio and reaction temperature, and partial least-squares model was applied to predict the performance of the reactor. The validity of the developed model was corroborated by the comparison with experimental data, and normalized parametric sensitivity analysis was carried out. Finally, the genetic algorithm (GA) was applied to determine the optimal conditions for maximum production of ethane and ethylene.     

Comparison of physically mixed and separated MgO and WO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> catalyst for propylene production via 1-butene metathesis

We examined the catalyst bed design of MgO and WO₃/SiO₂ for production of propylene via metathesis of 1-butene. WO₃/SiO₂ was used as a bi-functional catalyst for isomerization and metathesis reactions. Addition of MgO was proposed to help improve the isomerization activity and hence the propylene yield. Experimental studies were carried out to determine activity and reaction kinetics of 1-butene isomerization over MgO isomerization catalyst and 1-butene metathesis over WO₃/SiO₂ bi-functional catalyst for designing a suitable catalyst bed. Two types of catalyst bed arrangement—physically mixed bed and separated bed—were considered and compared by computer simulation. The simulations reveal that adding MgO in the separated bed by packing MgO before WO₃/SiO₂ offers superior propylene yield to the physically mixed bed. The appropriate %MgO loading in catalyst bed which offers a maximum propylene yield was found to vary (3 and 23%), depending on operating condition.     

Electrochemical preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite film and its high activity toward the photoelectrocatalytic degradation of methyl orange

Uniform TiO₂/SiO₂ composite films were prepared on ITO substrates by electrodeposition, and highly photoelectrocatalytic (PEC) activity of the composite films was observed toward the degradation of methyl orange (MO) in aqueous solutions. It was further found that their PEC activity was dependent on the electrodeposition parameters including deposition time, solution pH and SiO₂ content. Under the optimized condition, the PEC degradation of MO on TiO₂/SiO₂ composite film electrode could be enhanced about 14 times relative to that on neat TiO₂ film electrode. The high PEC activity of the TiO₂/SiO₂ composite film electrode was mainly attributed to the enhancement of the charge separation of photo-generated electron-hole pairs by the dispersion of SiO₂ nanoparticles in the TiO₂ matrix with the aid of the applied electric field.     

Li<Subscript>2</Subscript>Cu<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> + SiO<Subscript>2</Subscript>/Ti compositions for the catalytic afterburning of diesel soot

Two methods were used to obtain a catalytically active oxide coating on the surface of titanium for the catalytic afterburning of diesel soot: plasma electrochemical formation of an oxide film on the surface of titanium and extraction pyrolytic deposition of the Li₂Cu₂(MoO₄)₃ compound. The Li₂Cu₂(MoO₄)₃/TiO₂ + SiO₂/Ti compositions synthesized by the single-step extraction pyrolytic treatment of the oxidized surface of titanium ensured a high burning rate of soot of ∼300°C. The subsequent deposition of Li₂Cu₂(MoO₄)₃ lowers the activity of the catalyst, due probably to the growth of molybdate phase crystallites and the filling of open oxide film pores. Double lithium-copper molybdate is able to reduce appreciably the concentration of CO in the oxidation products of soot. The advantages of these methods are the possibility of forming high-cohesion durable coatings on surfaces of any complexity, the simplicity of their implementation, and high productivity and low cost. The obtained results can be recommended for use in developing methods for creating composite coatings on catalytic soot filters.     

A multipath peroxymonosulfate activation process over supported by magnetic CuO-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles for efficient degradation of 4-chlorophenol

Heterogeneous catalysts with low cost, environmentally friendly, highly effective and ready separation from aqueous solution are highly desirable. Magnetic CuO-Fe₃O₄ nanoparticles, a type of non-toxic bimetallic transition metal oxide, is a promising heterogeneous catalyst for activation of peroxymonosulfate (PMS) to generate reactive oxygen species (ROS) that has not been previously investigated. In this study, the activation of PMS by CuO-Fe₃O₄ nanoparticles was evaluated using the degradation of 4-chlorophenol as a model reaction. Several critical factors such as pH, catalyst dosage and PMS concentration were investigated. CuO-Fe₃O₄/PMS system demonstrated a wide effective pH range to degrade 4-chlorophenol, namely 5.5 to 9.5. With the increase of the catalyst dosage, the degradation efficiency of 4-chlorophenol appeared to increase first and then decrease, that the inflection point was 0.5 g/L. Elevated PMS concentration obviously improved the decomposition of 4-chlorophenol; however, the plateau was reached when the PMS concentration was 8 mM. Further increase in PMS concentration would not significantly improve the removal efficiency. Through examining the effects of scavengers and electron spin resonance (ESR) analyses, CuO-Fe₃O₄ nanoparticles were proven to activate PMS through a non-radical and radical pathway to generate singlet oxygen, sulfate radicals and hydroxyl radicals. Based on results, CuO-Fe₃O₄ nanoparticles were effective, environmentally friendly and low cost catalysts for efficient activation of PMS. These features make CuO-Fe₃O₄ nanoparticles a readily available heterogeneous catalyst to activate PMS for refractory organic pollutants degradation in advanced oxidation processes (AOPs).     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite oxide and its photocatalytic degradation of rhodamine B

The composite semiconductor photocatalyst TiO₂/SiO₂ was prepared by template-hydrothermal method using carbon spheres as the template. The structural and optical properties of TiO₂/SiO₂ were characterized by XRD, SEM, BET, UV–Vis DRS, TG-DTA, PL techniques. The formation of hydroxyl radical on the surface of TiO₂/SiO₂ was studied with terephthalic acid as the probe molecule, combined with fluorescence technique. The results showed that the specific surface area of TiO₂/SiO₂ composite was 327.9 m²/g, and the specific surface area of TiO₂/SiO₂ was larger than that of pure TiO₂. Photocatalytic degradation of rhodamine B showed that TiO₂/SiO₂ composite oxide under visible light illumination 40 min, the degradation rate was 98.6 % and the degradation rate of pure TiO₂ was only 11.9 %. The apparent first-order rate constant of TiO₂/SiO₂ was 33 times that of pure TiO₂ and more than 6 times that of P25 when the molar ratio of Ti to Si was 1:1 under visible light irradiation. Moreover, it’s also as much as 5 times that of pure TiO₂ and is more than 1 times that of P25 under UV light irradiation 25 min. Based on the experimental results, ^·O₂ ^? and h⁺ were suggested to be the major active species which was responsible for the degradation reaction. The increased photocatalytic activity of TiO₂/SiO₂ may be mainly attributed to effectively suppressing the recombination of hole/electron pairs. After the photocatalyst TiO₂/SiO₂ was reused 5 times, the degradation rate of rhodamine B could reach 89.2 % under visible light irradiation. Moreover, The composite semiconductor photocatalyst TiO₂/SiO₂ was selective towards the degradation of rhodamine B.     

CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> catalyst prepared by physical mixing for NH<Subscript>3</Subscript> selective catalytic reduction: Evidence about the migration of sulfates from TiO<Subscript>2</Subscript> to CeO<Subscript>2</Subscript> via simple calcination

A mechanical mixture of CeO₂ and TiO₂ powder with a small amount of sulfate was applied for the selective catalytic reduction (SCR) of NO with NH₃. After calcination at 500 oC, the mixed sample showed significantly enhanced activity and selectivity compared to the uncalcined one and, moreover, demonstrated even higher activity than the conventional V₂O₅/TiO₂ catalyst above 300 °C. Combined characterization results revealed that the main active sites were newly formed sulfate species on CeO₂, the number of which increased with calcination. Temperatureresolved DRIFT spectra provided convincing evidence about the migration of sulfate species from TiO₂ to CeO₂, as confirmed from the shift of v(S=O) band as a result of the mechanical mixing and the subsequent calcination.     

Catalytic performance of CuCl<Subscript>2</Subscript>-modified V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> catalyst for Hg<Superscript>0</Superscript> oxidation in simulated flue gas

CuCl₂-SCR catalysts prepared by an improved impregnation method were studied to evaluate the catalytic performance for gaseous elemental mercury (Hg⁰) oxidation in simulated flue gas. Hg⁰ oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl₂. Nitrogen adsorption, XRD, XRF and XPS were used to characterize the catalysts. The results indicated that CuCl₂ was well loaded and highly dispersed on the catalyst surface, and that CuCl₂ played an important role for Hg⁰ catalytic oxidation. The effects of individual flue gas components on Hg⁰ oxidation were also investigated over CuCl₂-SCR catalyst at 350 oC. The co-presence of NO and NH₃ remarkably inhibited Hg⁰ oxidation, while this inhibiting effect was gradually scavenged with the decrease of GHSV. Further study revealed the possibility of simultaneous removal of Hg⁰ and NO over CuCl₂-SCR catalyst in simulated flue gas. The mechanism of Hg⁰ oxidation was also investigated.     

Synthesis of LLDPE/TiO<Subscript>2</Subscript> nanocomposites by in situ polymerization with zirconocene/dMMAO catalyst: effect of [Al]/[Zr] ratios and TiO<Subscript>2</Subscript> phases

This article reveals the dependence of crystalline phases in titania on the intrinsic activity during in situ polymerization of ethylene/1-hexene using the zirconocene/dMMAO catalyst to produce LLDPE/TiO₂ nanocomposites. First, the TiO₂ nanoparticles having different crystalline phases were employed as the nanofillers by impregnation with dMMAO to obtain dMMAO/TiO₂. Then, copolymerization of ethylene/1-hexene using zirconocene catalyst was performed in the presence of dMMAO/TiO₂. It was found that the catalytic activity derived from the anatase TiO₂ (A) was about four times higher than that obtained from the rutile TiO₂ (R). This was likely due to higher intrinsic activity of the active species present on the TiO₂ (A). In addition, increased [Al]_dMMAO/[Zr]_cat ratios apparently resulted in enhanced activities for both TiO₂ (A) and TiO₂ (R). However, the TiO₂ (R) showed less deactivation upon increased [Al]_dMMAO/[Zr]_cat ratios. This can be attributed to strong interaction between dMMAO and TiO₂ (R) as proven by the TGA measurement. The microstructure of the LLDPE/TiO₂ obtained was found to be random copolymer for both TiO₂ (A) and TiO₂ (R).     

Template-free preparation of TiO<Subscript>2</Subscript> microspheres for the photocatalytic degradation of organic dyes

TiO₂ microspheres were successfully synthesised by simple solution phase method by using various amount of titanium butoxide as precursor. The prepared TiO₂ were characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance absorption spectra (UV-DRS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XRD analysis revealed that the as-synthesized TiO₂ microsphere poses an anatase phase. The photocatalytic degradation experiments were carried out with three different dyes, such as methylene blue, brilliant black, reactive red-120 for four hours under UV light irradiation. The results show that TiO₂ morphology had great influence on photocatalytic degradation of organic dyes. The experimental results of dye mineralization indicated the concentration was reduced by a high portion of up to 99% within 4 hours. On the basis of various characterization of the photocatalysts, the reactions involved to explain the photocatalytic activity enhancement due to the concentration of titanium butoxide and morphology include a better separation of photogenerated charge carriers and improved oxygen reduction inducing a higher extent of degradation of aromatics.     

Synthesized Hollow TiO<Subscript>2</Subscript>@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> Composites for Carbon dioxide Reduction Under Visible Light

The hollow TiO₂@g-C₃N₄ composites were synthesized by a facile stirring method. The phase compositions, optical properties, and morphologies of the samples were characterized via X-ray diffraction, scanning electron microscope, transmission electron microscopy, high resolution transmission electron microscopy, fourier transform infrared spectroscopy, N₂ adsorption–desorption, UV–Vis diffuse reflectance spectroscopy and Photoluminescence. The photocatalyitc performance was evaluated by reduction carbon dioxide under visible light irradiation. The results indicated that TiO₂@g-C₃N₄ nanocomposites displayed higher photocatalytic activity compared with pure g-C₃N₄. The increased photocatalytic activity of TiO₂@g-C₃N₄ nanocomposites can be attributed to facilitating the photo-induced electron–hole separation efficiency and enhancing the photo-induced electron migration.

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Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Photoactive WO<Subscript>3</Subscript> and Se-WO<Subscript>3</Subscript> thin films for photoelectrochemical oxidation of organic compounds

Thin films of bare and Se-containing tungsten trioxide (WO₃) on AISI304-type stainless steel were prepared by electrochemical deposition using peroxy-tungstate solutions. The obtained films were characterized by X-ray diffraction, photoelectron spectroscopy, scanning electron microscopy, thermal and photovoltammetry analyses. The oxidation of methylene blue, phenol, and methanol was used to evaluate the photoelectrocatalytic activity of the prepared films. It has been established that the incident photon-to-current efficiency (IPCE) in 0.1-M K₂SO₄ decreases as the concentration of methylene blue and phenol increases. On the contrary, the IPCE values increase with the increase in initial concentration of methanol. The bulk electrolysis experiments revealed that the prepared films are stable and can be used for photoelectrochemical oxidation of methanol.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.