A study on the degradation of methamidophos in the presence of nano-TiO<Subscript>2</Subscript> catalyst doped with Re

A new Re-doped nano-TiO₂ photocatalyst was synthesized by immersion method. The novel doped nano-TiO₂ photocatalyst utilizing visible light was firstly prepared. The doped nano-TiO₂ powder was charactered by XRD, FTIR, UV-Vis, and its photocatalytic activity was tested through the photocatalytic degradation of methamidophos as a model compound under ultraviolet irradiating and in sunlight, respectively. In order to compare the photocatalytic activities, the same experiment was carried out for undoped nano-TiO₂. The degradation ratio of methamidophos in the presence of doped nano-TiO₂ reached 64.40% under sunlight for 12 h, which was 2.64% in the presence of undoped nano-TiO₂. The degradation ratio of methamidophos in the presence of doped nanoTiO₂ reached 90.39% under UV irradiationat 2.5 h, which was 51.29% in the presence of undoped nano-TiO₂. All the results show that the doped TiO₂ is a promising photocatalyst using sunlight for treating the organophosphorous pesticide wastewater. The article is published in the original.     

Enhanced photocatalytic activities of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> nanohybrids immobilized on cement-based materials for dye degradation

Using cement-based material as a matrix for photocatalytic hybrids is an important development for the large-scale application of photocatalytic technologies. In this work, photocatalytic activity of nanosized hybrids of TiO₂/SiO₂ (nano-TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was highlighted. For this purpose, an optimal inorganic sol–gel precursor was firstly applied to prepare the composites of nano-TiO₂–SiO₂ which was characterized by XRD, SEM and UV–Vis. Then, a thin layer was successfully coated on white Portland cement (WPC) blocks using a dipping process in a nano-TiO₂–SiO₂ solution. The effect of nano-TiO₂–SiO₂-coated WPC blocks on photocatalytic decomposition of three dyes, including Malachite green oxalate (MG), Methylene blue (MB) and Methyl orange (MO) were studied under UV irradiation and monitored by chemical oxygen demand tests. The results showed an increase in photocatalytic effects which depends on the structure and pH of the applied cement.     

Catalytic Properties of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles in Plasma Chemical Treatment

We proposed here a new process coupling dielectric barrier discharge (DBD) plasma with magnetic photocatalytic material nanoparticles for improving yield in DBD degradation of methyl orange (MO). TiO₂ doped Fe₃O₄ (TiO₂/Fe₃O₄) was prepared by the sol-gel method and used as a new type of magnetic photocatalyst in DBD system. It was found that the introduction of TiO₂/Fe₃O₄ in DBD system could effectively make use of the energy generated in DBD process and improve hydroxyl radical contributed by the main surface Fenton reaction, photocatalytic reaction and catalytic decomposition of dissolved ozone. Most part of MO (88%) was degraded during 30 min at peak voltage of 13 kV and TiO₂/Fe₃O₄ load of 100 mg/L, with a rate constant of 0.0731 min^?1 and a degradation yield of 7.23 g/(kW h). The coupled system showed higher degradation efficiency for MO removal.     

Kinetic studies of direct blue photodegradation over flower-like TiO<Subscript>2</Subscript>

The kinetics of photocatalytic oxidation reaction for direct blue solution was studied by using flower-like TiO₂ under the irradiation of ultraviolet (UV) light. A series of possible affecting factors were studied, including pH value, the additive amount of light catalyst, H₂O₂ and with or without Ag modification. The kinetics of photocatalytic degradation under UV was found following a pseudo-second-order reaction kinetic model with high regression coefficients (R ²). It has been demonstrated that the initial concentration and its related factors have influenced the photocatalytic degradation efficiency and corresponding kinetic parameters. Also, the kinetic parameter k is increasing with the degradation efficiency.     

Structural characterization and photocatalytic properties of novel Bi<Subscript>2</Subscript>FeVO<Subscript>7</Subscript>

Bi₂FeVO₇ was prepared by a solid-state reaction technique for the first time and the structural and photocatalytic properties of Bi₂FeVO₇ were studied. The results shows that this compound crystallized in the tetragonal crystal system with space group I4/mmm. Moreover, the band gap of Bi₂FeVO₇ was estimated to be about 2.22(6) eV. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water with Bi₂FeVO₇ as the photocatalyst by ultraviolet light irradiation. Degradation of aqueous methylene blue (MB) dye by photocatalytic way over this compound was further studied under visible light irradiation. Bi₂FeVO₇ shows higher catalytic activity compared to TiO₂ (P-25) for MB photocatalytic degradation under visible light irradiation. Complete removal of aqueous MB was realized after visible light irradiation for 170 min with Bi₂FeVO₇ as the photocatalyst. The reduction of the total organic carbon (TOC) and the formation of inorganic products, SO ₄ ²⁻ and NO ₃ ⁻ revealed the continuous mineralization of aqueous MB during the photocatalytic course.     

Facile Synthesis of Polyethylenimine and Nano-TiO<Subscript>2</Subscript> Particles Functionalized PolyHIPE Beads for CO<Subscript>2</Subscript> Capture

Polyethylenimine (PEI) and titanium dioxide nanoparticles (nano-TiO₂) functionalized poly- HIPE beads were synthesized by suspension polymerization of styrene/divinylbenzene high internal phase emulsion (HIPE) containing PEI and nano-TiO₂ particles in inner phase. The products are uniform and spherical beads with average diameter of 1 mm. Characterization results showed good thermal stability and desired mechanical strength. CO₂ adsorption tests were performed with CO₂/H₂O/N₂ (1 : 1 : 8) gas mixture. Nano-TiO₂ particles distinctly improved the CO₂ adsorption performance of the polyHIPE beads, resulting in enhanced CO₂ adsorption capacity and fast adsorption/desorption kinetics. Besides, the functionalized polyHIPE beads exhibited remarkable cycle stability.     

UV-Assisted Fabrication of Reduced Graphene Oxide Doped SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript> Nanocomposites as Efficient Photocatalyst for Photodegradation of Rhodamine B

The core-shell nanostructure materials have gained great interests because of its excellent photocatalytic properties and promising applications in several fields. In this work, we prepared the core-shell SiO₂@TiO₂ nanocomposites by the versatile kinetics-controlled coating method. The graphene oxide (GO) was further reduced over SiO₂@TiO₂ using UV-assisted photocatalytic reduction method. The physicochemical properties of the as-prepared SiO₂@TiO₂/RGO nanocomposites were characterized by SEM, XRD, BET, EDS, and FTIR. Results showed that, TiO₂ was mainly composed of anatase phase with high crystallinity. Their photocatalytic activities were examined by the degradation of Rhodamine B (RhB) under UV light irradiation. The presence of RGO obviously improved the adsorption ability and photodegradation performance of the composites to RhB. The degradation kinetics of RhB can be described by the pseudo-first-order model. The optimum mass ratio of SiO₂@TiO₂ to RGO in the composite was 1/0.05 and the rate constant was about 4 times greater than that of the SiO₂@TiO₂.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

One-dimensional porous Ag/AgBr/TiO<Subscript>2</Subscript> nanofibres with enhanced visible light photocatalytic activity

One-dimensional (1D) Ag/AgBr/TiO₂ nanofibres (NFs) have been successfully fabricated by the one-pot electrospinning method. In comparison with bare TiO₂ NFs and Ag/AgBr/PVP (polyvinylpyrrolidone) NFs, the 1D Ag/AgBr/TiO₂ NFs photocatalyst exhibits much higher photocatalytic activity in the degradation of a commonly used dye, methylene blue (MB), under visible light. The photocatalytic removal efficiency of MB over Ag/AgBr/TiO₂ NFs achieves almost 100 % in 20 min. The photocatalytic reaction follows the first-order kinetics and the rate constant (k) for the degradation of MB by Ag/AgBr/TiO₂ NFs is 5.2 times and 6.6 times that of Ag/AgBr/PVP NFs and TiO₂ NFs, respectively. The enhanced photocatalytic activity is ascribed to the stronger visible light absorption, more effective separation of photogenerated electron-hole pairs, and faster charge transfer in the long nanofibrous structure. The Ag/AgBr/TiO₂ NFs maintain a highly stable photocatalytic activity due to its good structural stability and the self-stability system of Ag/AgBr. The mechanisms for photocatalysis associated with Ag/AgBr/TiO₂ NFs are proposed. The degradation of MB in the presence of scavengers reveals that h⁺ and ^?O ₂ ^? significantly contribute to the degradation of MB.     

Preparation of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO<Subscript>2</Subscript> and acquirement of efficient photocatalyst

ZnFe₂O₄ nanoparticles sensitized by C-modified TiO₂ hybrids (ZnFe₂O₄–TiO₂/C) were successfully prepared by a feasible method. The ZnFe₂O₄ nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO₂ were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N₂ adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO₂ lattice but adhered to the surface of TiO₂. The photocatalytic activity of the as-prepared C-modified TiO₂ (TiO₂/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe₂O₄ into the TiO₂/C could enhance the absorption spectrum range. The ZnFe₂O₄–TiO₂/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO₂ and TiO₂/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe₂O₄–TiO₂/C composites. The optimum photocatalytic performance was obtained from the ZnFe₂O₄(0.8 wt%)–TiO₂/C sample.     

Photocatalytic degradation on Disperse Blue with modified nano-TiO<Subscript>2</Subscript> film electrode

Sol–gel and dip-coating methods were used to prepare the modified nano-TiO₂ film electrode; its photocatalytic and electrochemical properties were investigated under both UV light and sunlight for the degradation of Disperse Blue. The results showed that the effect of co-doping metal and non-metal ions was better than that of single metal ion doping or no doping. Y–F co-doping could better take advantage of sunlight so as to decrease the energy gap of semiconductor and to improve the utilization of visible light, while Ce–F co-doping served to separate photo-generated h ⁺ /e ⁻ pairs, which resulted in better degradation of dye under UV light. The grain size of prepared electrode was from 15 to 25 nm, and nano particles were arranged smoothly as well as closely with each other, confirming to be an effective binder. The final decolorization extents reached 44.43% under sunlight and 96.86% under UV light within 30 min, respectively.     

One-pot sequential synthesis of magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/AgCl photocatalysts with enhanced activity and stability

Magnetically separable Fe₃O₄/AgCl photocatalysts were prepared by a one-pot sequential method. A series of techniques proved the hybrid structure of Fe₃O₄/AgCl composites. Fe₃O₄/AgCl composites had a much higher photocatalytic activity toward Rhodamine B (RhB) degradation than pure AgCl under the simulated solar light irradiation. The existence of metal Ag resulted in high photocatalytic activity of Fe₃O₄/AgCl, which was related with the amount of metallic Ag. The scavenging experiments showed that the degradation reaction most probably was initiated by the photoinduced single-electron transfer, and the generation of superoxide anion (O ₂ ^-· ) played a significant role. The composite photocatalysts could be recycled by applying an external magnetic field, and the reused composites maintained their original photocatalytic activity. Fe₃O₄/AgCl composites were highly efficient, magnetically separable, and recoverable. This proves their potential applications in the photodegradation of organic pollutants.     

A novel WO<Subscript>3</Subscript>/MoS<Subscript>2</Subscript> photocatalyst applied to the decolorization of the textile dye Reactive Blue 198

A novel FTO/WO₃ electrode decorated with MoS₂ was constructed using two simple and low-cost techniques involving a modified single-step sol-gel method for the WO₃ film together with the electrodeposition of amorphous MoS₂. The photoelectrocatalytic performance of the material was investigated by monitoring the degradation of Reactive Blue 198 dye under visible-light irradiation. The FTO/WO₃/MoS₂ electrode exhibited excellent photocatalytic activity and afforded total decolorization of the dye after 90 min at low applied current density (5 mA cm^?2). The results described herein support the view that MoS₂ acts as a noble metal-free cocatalyst by promoting H₂ evolution and assisting in the suppression of electron/hole pair recombination in the photocatalytic material (WO₃), thereby improving the process of decolorization of the dye solution. The novel approach of combining of the WO₃ and MoS₂ materials shows particular promise and may prove to be very effective in the photocatalytic degradation of other hazardous organic compounds.     

Solvothermal synthesis and photocatalytic activity of S-doped TiO<Subscript>2</Subscript> and TiS<Subscript>2</Subscript> powders

The photocatalytic activity of S-doped TiO₂ powder depends on the S content. To synthesize S-doped TiO₂ powders with high S content, solvothermal processes were used in this work. The S-doped TiO₂ powder contains 2.0 M% sulfur and has an absorption edge of 460 nm (2.7 eV). The pure TiS₂ powder also synthesized by a solvothermal process has an absorption edge of 595 nm (2.08 eV) and broad absorption above 595 nm. The photocatalysis experiments indicate that the degradation of methyl orange is associated with the light adsorption edge. The photocatalytic activity is much larger for the pure TiS₂ powder than for partially S-doped TiO₂ powder.     

Influence of ThO<Subscript>2</Subscript> on the photocatalytic activity of TiO<Subscript>2</Subscript>

Microcomposites consisting of TiO₂ (or Ce-doped TiO₂) and ThO₂ (0.5–2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of ThO₂. X-ray diffraction study reveals the effects of ThO₂ (compared to the ThO₂-free TiO₂, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO₂ obtained at 550°C and containing 1% ThO₂. The composite exhibits activity in dark, also. The presence of Ce⁴⁺ ions is not an obligatory requirement for the realization of the ThO₂ effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO₂.      

Photocatalytic effect of nano-TiO<Subscript>2</Subscript> loaded cement on dye decolorization and <Emphasis Type="Italic">Escherichia coli</Emphasis> inactivation under UV irradiation

In the present study, titanium dioxide (TiO₂) nano-particles were synthesized by sol–gel technique and then used to provide nano-TiO₂ loaded cement samples at 1, 5, and 10 wt% for investigation of Malachite green pigment decomposition and Escherichia coli inactivation under UV irradiation. Surveys conducted on the synthesized TiO₂ nano-particles showed a 100 % anatase phase with a mean particle size of 66.5 nm, surface area of 64.352 m² g^?1, and a porosity volume of 0.1278 cm³ g^?1. Cement samples containing this catalyst exhibited stronger photocatalytic properties as compared to the same amount of pure catalyst. Considering both photocatalytic performance and cost of catalyst, 5 wt% titanium dioxide was suggested to be added to cement. By addition of 1 wt% polycarboxylic copolymer as super-plasticizer to the cement paste, the photocatalytic sample activities were reinforced so that a similar performance could be obtained at 1 wt% catalyst as compared to 5 wt% catalyst without super-plasticizer.     

Preparation of highly active photocatalyst anatase TiO<Subscript>2</Subscript> by mixed template method

TiO₂ nanocrystals with diameters 8–10 nm have been prepared through sol–gel method using a mixed template of polyethylene glycol (PEG) and cetytrimethylammonium bromide (CTAB) at low temperature. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR) TEM and fourier transform infrared spectroscopy (FT-IR) etc. XRD analysis showed the TiO₂ photocatalysts prepared with mixed template are pure anatase. FTIR spectrum revealed that the cationic surfactant provides CTA⁺ molecules and bonds to Ti–O to prevent the condensation reaction. PEG plays a dispersant role in controlling the structure of nano-TiO₂ particles. CTAB and PEG incorporated with each other to restrain the growth of crystal nucleus and control the size of grain. The self-assembling process has been confirmed by HRTEM. PEG played different role in mixed template from the single template. The photocatalytic activity of samples was determined by using as a model reaction. The results showed that TiO₂ photocatalysts with mixed template have higher photocatalytic activity than P25.     

Photocatalytic degradation of dichloroacetyl chloride adsorbed on TiO<Subscript>2</Subscript>

Dichloroacetyl chloride (DCAC) attracted our attention as an intermediate product of the photocatalytic degradation of trichloroethylene (TCE). The adsorption and photocatalytic reaction of DCAC on TiO₂ have been investigated by FTIR spectroscopy. The influence of the surface structure of several TiO₂s on the reaction mechanism was discussed in order to understand the complete degradation mechanism of TCE as well as DCAC. DCAC was transformed into dichloroacetic acid (DCAA) on the relatively hydrophobic TiO₂ surface by the small amount of the water molecules weakly adsorbed on the surface. This DCAA was degraded to phosgene, CO₂, and CO during UV irradiation. For the hydrophilic TiO₂, DCAC was mainly transformed into the dichloroacetate anion. UV irradiation allowed this species to produce chloroform in addition to phosgene, CO₂, and CO. It is suggested that DCAC easily reacts with the Ti–OH group on the hydrophilic TiO₂ and forms the bidentate titanium chelate of dichloroacetate, which efficiently degrades into chloroform.     

Preparation of Cu<Subscript>2</Subscript>O/AC photocatalysts and their photocatalytic activity in degradation of pyrocatechol

Cu₂O on active carbon (Cu₂O/AC) catalysts were prepared by impregnation of support with aqueous solutions of CuSO₄ in various concentrations and then treated with a mixture of glucose and NaOH. Photocatalytic activity of the prepared catalysts was investigated in the photocatalytic degradation of pyrocatechol. The catalyst prepared by dipping of 0.5 g of AC into 25 ml of 0.04 mol/l CuSO₄ was found to exhibit the best activity. The effects of the reaction time and the amount of catalyst on the photocatalytic degradation of pyrocatechol were also studied.