Improved photocatalytic degradation of organic dye using Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>/MoS<Subscript>2</Subscript> nanocomposite

Highly efficient Ag₃PO₄/MoS₂ nanocomposite photocatalyst was synthesized using a wet chemical route with a low weight percentage of highly exfoliated MoS₂ (0.1 wt.%) and monodispersed Ag₃PO₄ nanoparticles (~5.4 nm). The structural and optical properties of the nanocomposite were studied using various characterization techniques, such as XRD, TEM, Raman and absorption spectroscopy. The composite exhibits markedly enhanced photocatalytic activity with a low lamp power (60 W). Using this composite, a high kinetic rate constant (k) value of 0.244 min^-1 was found. It was observed that ~97.6% of dye degrade over the surface of nanocomposite catalyst within 15 min of illumination. The improved photocatalytic activity of Ag₃PO₄/MoS₂ nanocomposite is attributed to the efficient interfacial charge separation, which was supported by the PL results. Large surface area of MoS₂ nanosheets incorporated with well dispersed Ag₃PO₄ nanoparticles further increases charge separation, contributing to enhanced degradation efficiency. A possible mechanism for charge separation is also discussed.     

Ag<Subscript>2</Subscript>S/Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> co-sensitized TiO<Subscript>2</Subscript> nanorod arrays prepared on conductive glass as a photoanode for solar cells

TiO₂ nanorod arrays (TiO₂ NRAs) were synthesized through a hydrothermal method. Ag₂S and Bi₂S₃ were then grown on the surface of TiO₂ NRAs with successive ionic layer adsorption and reaction method. The pristine rutile TiO₂ NRAs, Ag₂S/TiO₂, Bi₂S₃/TiO₂, and Bi₂S₃/Ag₂S/TiO₂ electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible absorption spectroscopy, and electrochemical analysis. According to photoelectrochemical (PEC) measurement, an enhanced short circuit current density was obtained for the co-sensitized TiO₂ NRAs under simulated sunlight illumination, which was 10.7 times higher than that of the TiO₂ NRAs. Appropriate potential positions of conduction band and valence band of Bi₂S₃ that match well those of rutile TiO₂ NARs and Ag₂S lead to the improved PEC performance. In addition, the PEC property of the co-sensitized TiO₂ NRAs under visible light irradiation was also investigated and showed a dramatically enhanced photocurrent response.     

Photocatalysis of several organic dyes by a hierarchical Ag<Subscript>2</Subscript>V<Subscript>4</Subscript>O<Subscript>11</Subscript> micro–nanostructures

Hierarchical Ag₂V₄O₁₁ nano-protuberance-assembled submicrofibers have been successfully synthesized through a facile and surfactant-free hydrothermal strategy. Morphology and microstructures of as-fabricated products are carefully examined using TEM, SA-ED, HRTEM, FE-SEM, XPS and X-ray diffraction. A possible growth mechanism of the as-obtained Ag₂V₄O₁₁ hierarchical submicrofibers is proposed by a time dependent experiments and the dosage of Ag. The as-prepared Ag₂V₄O₁₁ products are further regarded as a kind of photocatalyst for the catalytic degradation of three toxic organic dyes, methyl blue (MB), methyl orange and rhodamine blue. Radical trapping experiments have been applied to confirm the photoreaction mechanism. Compared with N-doped TiO₂ and P25, the catalyst Ag₂V₄O₁₁ prepared at 24 h reaction time exhibited much higher photocatalytic activity for MB degradation under visible-light illumination. It was ascribed to the formation of superoxide radicals species, and hierarchical structure. The use of ESI-MS analyses showed that the MB dye molecules were broken up by the action of the Ag₂V₄O₁₁ photocatalyst, indicating the occurrence of a mineralization process. Additionally, kinetic results showed that the degradation process follows Langmuir–Hinshelwood (L–H) first-order kinetic reaction.     

Oxidizing catalysts supported on nanostructured TiO<Subscript>2</Subscript>

This paper compares the catalytic performance of platinum catalysts supported on different forms of TiO₂. A composite material in the form of Pt supported on titanium dioxide nanotubes is shown to possess the highest catalytic performance for CO oxidation. It exhibits stable catalytic activity at temperatures from 65 to 300°C.     

Controllable synthesis of Ho-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> porous nanotubes by electrospinning and their application as an ethanol gas sensor

Pure and Ho-doped In₂O₃ nanotubes (NTs) and porous nanotubes (PNTs) were successfully synthesized by conventional electrospinning process and the following calcination at different temperatures. X-ray diffractometry (XRD), thermogravimetric analysis (TGA), Raman spectrometer, energy-dispersive spectroscopy, scanning and transmission electron microscopy were carefully used to investigate the morphologies, structures and chemical compositions of these samples. Their sensing properties toward ethanol gas were studied. Compared with pure In₂O₃ NTs (response value is 17), pure In₂O₃ PNTs (response value is 20) demonstrated enhanced sensing characteristics. What’s more, the response of Ho-doped In₂O₃ PNTs sensors to 100 ppm ethanol was up to 60 at 240 °C, which increased three times more than that of the pure In₂O₃ PNTs. Additionally, the minimum concentration for ethanol was 200 ppb (response value is 2). The increased gas-sensing ability was attributed not only to the hollow and porous structure, but to the Ho dopant. Furthermore, Ho-doped In₂O₃ PNTs enable sensor to discriminate between ethanol and the other gas distinctly, particularly acetone that is usually indistinguishable from ethanol. Also, by analyzing XRD, TGA and Raman spectrometer, a possible formation mechanism of porous nanotubes and sensing mechanism were put forward.     

Solar photocatalytic generation of hydrogen under ultraviolet-visible light irradiation on (CdS/ZnS)/Ag<Subscript>2</Subscript>S + (RuO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>) photocatalysts

In order to efficiently use the UV-vis light in the photocatalytic reaction, a novel (CdS/ZnS)/Ag₂S + RuO₂/TiO₂ was synthesized by chemical coprecipitation and metal ion implantation. The composition and structure of this composite were characterized by BET, UV-vis spectroscopy, SEM, XRD and EDX. This composite exhibited much higher photocatalytic activity for the generation of hydrogen (H₂).     

Effect of cerium additive and secondary phase analysis on Ag<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> ceramics

Cerium-doped silver bismuth titanate—Ag_0.5Bi_0.5TiO₃ (ABT) ceramics have been synthesized by the high-temperature solid-state reaction method. The structure and elemental examination of the prepared ceramic was analysed by X-ray diffraction (XRD), Fourier transform infrared, scanning electron microscopy and energy-dispersive spectroscopy. XRD analysis showed the presence of pyrochlore structure and secondary phase when more than 5 mol% cerium was added. The impact of temperature on cerium-doped silver bismuth titanate samples was analysed by differential thermal analysis and differential scanning calorimetry. Cerium doping caused the flaky morphology comparing with undoped sample. The homogeneity of all the samples was discussed in detail by diffuse reflectance spectrum. This is the first time the reflection process is analysed for the cerium-doped ABT system to the best of our knowledge.     

Preparation and Physical Properties of Ag<Subscript>5</Subscript>Pb<Subscript>2</Subscript>O<Subscript>6</Subscript>-Ag Ceramics

A new process for Ag₅Pb₂O₆ synthesis is described. Ag₅Pb₂O₆-Ag ceramics are prepared and characterized using x-ray diffraction, thermal analysis, and scanning electron microscopy. The room-temperature resistivity of Ag₅Pb₂O₆ ceramics is 0.35–0.37 m cm, and that of Ag₅Pb₂O₆-Ag ceramics is 0.03–0.04 µ cm.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 628–634.Original Russian Text Copyright © 2005 by Akimov, Savchuk.     

Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/TiN composites produced from TiO<Subscript>2</Subscript>-Modified Si<Subscript>3</Subscript>N<Subscript>4</Subscript> powders

Si₃N₄/TiN composites have been produced by hot pressing at temperatures from 1600 to 1800°C in a nitrogen atmosphere, using silicon nitride powders prepared by self-propagating high-temperature synthesis and surface-modified with titanium dioxide nanoparticles. We examined the effect of TiO₂ content on the microstructure, phase composition, and mechanical strength of the ceramics. It is shown that titanium nitride can be formed by the reaction Si₃N₄ + TiO₂ → TiN + NO + N₂O + 3Si. The Si₃N₄/TiN composites containing 5–20% TiN have a low density, high porosity, and a bending strength of 60 MPa or lower. In Si₃N₄/TiN ceramics produced using calcium aluminates as sintering aids, the silicon nitride grains are densely packed, which ensures an increase in strength to 650 MPa.     

Ionic liquid microemulsion-assisted synthesis and improved photocatalytic activity of ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript>

This paper reported the fabrication of high-performance ZnIn₂S₄ photocatalysts using ionic liquid microemulsion-mediated hydrothermal method under facile conditions. The influences of reaction temperature and aging time on the catalytic properties of the specimens were investigated. The crystal phase, optical property, and morphological structure of the obtained catalysts were characterized using X-ray diffraction, UV–visible spectrometer, electronic microscope, and N₂ adsorption–desorption techniques. The results indicated that all of the ZnIn₂S₄ samples prepared by this method consisted of the hexagonal phase and exhibited excellent photoresponse capability and photocatalytic performance. The sample prepared at 60 °C with an aging time of 6 h showed the best photocatalytic performance, and the corresponding degradation rate of methyl orange was measured as 98.5% after 10 min. The current study highlights an efficient and environmental method for the formulation of high-performance ZnIn₂S₄.     

Construction of 3D marigold-like Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Ag<Subscript>2</Subscript>O/CQDs heterostructure with superior visible-light active photocatalytic activity toward tetracycline degradation and selective oxidation

A novel visible-light-driven photocatalyst Bi₂WO₆/Ag₂O/CQDs (BWO/Ag₂O/CQDs), which possesses hierarchical superstructure with marigold-like appearance, was fabricated via a hydrothermal method, followed by a simple precipitation process. Ag₂O nanoparticles sized around 25 nm and CQDs with diameters of about 10 nm were evenly deposited on Bi₂WO₆ to form a unique heterostructure. The obtained BWO/Ag₂O/CQDs heterostructure showed excellent adsorption and remarkably enhanced photocatalytic performance in the photodegradation of antibiotic tetracycline (TC) under visible-light irradiation compared to pristine Bi₂WO₆. The degradation rate of TC over BWO/Ag₂O/CQDs photocatalyst is 16.2 times higher than that of pristine Bi₂WO₆ and a possible mechanism for the enhanced photocatalytic performance was discussed. In addition, BWO/Ag₂O/CQDs was applied in the selective oxidation of benzyl alcohol to benzaldehyde under visible-light illumination. The result demonstrated that the conversion rate and product selectivity are greatly improved over BWO/Ag₂O/CQDs compared to pristine Bi₂WO₆ in the same reaction conditions, making it a promising photocatalyst in the application of green chemical transformation. The co-coupling of CQDs and Ag₂O with matched band potentials gives a substantial promotion for the light harvesting ability and effective separation of photogenerated charge carriers, synergistically accounting for the improvement of photocatalytic efficiency.     

The microwave absorbing properties of CoFe<Subscript>2</Subscript> attached single walled carbon nanotube/BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanocomposites

The CoFe₂ attached single-walled carbon nanotubes (CoFe₂@SWCNTs) and BaFe₁₂O₁₉ ferrite nanocomposites with different CoFe₂@SWCNTs weight ratios (1, 3, 5, 7 wt%) were synthesized by a simple combination process. Then, the electromagnetic and microwave absorption properties were systematically investigated by a vector network analyzer in the frequency range of 2–18 GHz. High-quality CoFe₂@SWCNTs were prepared by a direct current arc discharge method in one-step. BaFe₁₂O₁₉ nanocrystals were synthesized by a nitrate citric acid sol–gel auto-ignition method. The CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposites exhibited an efficient reflection loss (RL) and a wide absorption bandwidth. The minimum RL of ?54.13 dB was observed at 11.84 GHz for the nanocomposite (5 wt% CoFe₂@SWCNTs) with a thickness of 2.8 mm, 3.4 times greater than those without CoFe₂@SWCNTs, and a broad absorption bandwidth of 4.64 GHz (<?10 dB) was achieved. In addition, the nanocomposite (1 wt% CoFe₂@SWCNTs) shows a broader effective microwave absorption bandwidth of 7.12 GHz with a thickness of 1.9 mm. The experimental results reveal that the absorbing properties of the nanocomposites are greatly improved by controlling the CoFe₂@SWCNTs weight ratio and the matching thickness of the absorber. This CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposite is anticipated to be applied in advanced microwave absorbers.     

Synthesis of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composites with core/shell/shell nano-structure and evaluation of their photo-catalytic efficiency for degradation of methylene blue

The SrFe₁₂O₁₉/SiO₂/TiO₂ nanostructures with hard magnetic core were successfully synthesized through the facile and efficient wet chemical processes. At first, nanocrystalline strontium hexaferrite (SrFe₁₂O₁₉) powder was prepared using a new co-precipitation route in ethanol/water media. In the next step, SrFe₁₂O₁₉/SiO₂ composites were produced by well-known Stöber method using tetraethyl orthosilicate as precursor. Finally titania was coated on SrFe₁₂O₁₉/SiO₂ composite particles using titanium n-butoxide precursor. The core/shell/shell nanostructures have been characterized by means of X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy detector. The catalytic activity of SrFe₁₂O₁₉/SiO₂/TiO₂ composites has been investigated in the degradation of methylene blue dye under UV illumination. The results indicated that the obtained SrFe₁₂O₁₉/SiO₂/TiO₂ composite has photo-catalytic properties and can be retrieved by magnetic separation. The photo-degradation of methylene blue dye was about 80% in the presence of photo-catalyst powder at irradiation time of 180 min. Recycled composite particles could be used again.     

Flexible electrospun MWCNTs/Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>/PAN ternary composite fiber membranes with enhanced photocatalytic activity and stability under visible-light irradiation

Semiconductor photocatalysis is a promising technology for removing contaminants from water. Particularly, visible-light photocatalysis has attracted much attention because of its potential to utilize solar energy. However, nano-sized visible-light-driven photocatalysts easily aggregate during water treatment. Besides, it is difficult to recycle them from treated systems. Therefore, it is of great importance to develop visible-light-responsive immobilized photocatalysts with high activity. In this work, MWCNTs/Ag₃PO₄/polyacrylonitrile (PAN) ternary composite fiber membranes (TCFMs) with good photocatalytic performance were fabricated by electrospinning technique combined with in situ Ag₃PO₄ forming reaction. Due to the addition of MWCNTs, the band gap of MWCNTs/Ag₃PO₄/PAN TCFMs became narrower than that of Ag₃PO₄/PAN binary composite fiber membranes (BCFMs), which made MWCNTs/Ag₃PO₄/PAN TCFMs be able to use light at longer wavelengths. Compared with Ag₃PO₄/PAN BCFMs, the as-prepared MWCNTs/Ag₃PO₄/PAN TCFMs showed enhanced photocatalytic activity and stability for degrading rhodamine B (RhB) in batch processing systems, which mainly ascribed to fast electron transfer from Ag₃PO₄ to MWCNTs and the resulting high electron–hole (e^?–h⁺) separation efficiency. Radical trapping experiments revealed that holes (h⁺) and superoxide radicals (^·O₂^?) played primary roles in RhB degradation. In addition, the flexible MWCNTs/Ag₃PO₄/PAN TCFMs also showed potential practical application in the continuous wastewater treatment by a suitable photocatalytic membrane reactor. This work provides a facile approach to prepare flexible supported photocatalytic membrane with visible-light response, high activity and good stability.     

Fabrication of nanocomposites based on carbon nanotubes containing Pt nanoparticles and TiO<Subscript>2</Subscript>

Using conical multiwalled carbon nanotubes (CNTs), we have prepared Pt/CNT and Pt/TiO₂/CNT nanocomposites with an average platinum particle size of 3–5 nm, Pt/Ti molar ratio on the surface in the range 3.5–4, and C/Pt = 21–22. Titania was deposited onto the CNTs through titanium tetrachloride (TiCl₄) hydrolysis. Platinum particles were produced by reducing chloroplatinic acid (H₂PtCl₆) with sodium borohydride (NaBH₄) in the presence of CNTs. The composition and structure of the composites have been studied using X-ray photoelectron spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. The results demonstrate that the modification of Pt/CNT with titania enhances the catalytic activity of the material.     

Facile preparation of Ag<Subscript>2</Subscript>V<Subscript>4</Subscript>O<Subscript>11</Subscript> nanoparticles via low-temperature molten salt synthesis method

Nanosized Ag₂V₄O₁₁ powders have been prepared via the low-temperature molten salt method using LiNO₃ as a reaction medium. The powders have been characterized by x-ray diffraction and transmission electron microscopy. The discharge properties of the powders have been assessed by the galvanostatic discharge test using CR2016 coin cells. The powder made at 300°C for 2 h is composed of nearly spherical particles about 40 nm in size. The discharge test shows that the powders prepared by the low-temperature molten salt method exhibit high discharge capacities.     

Highly ordered Ag–TiO<Subscript>2</Subscript> nanocomposited arrays with high visible-light photocatalytic activity

TiO₂ is active only in the ultraviolet region. To enhance the active ability, a combined method consisting of the anodic oxidation method and the hydrothermal method was developed to prepare highly ordered Ag-TiO₂ nanocomposited arrays. The anodic oxidation was used to synthesize amorphous nanotubes with high chemical activity that subsequently served as highly ordered templates in preparing the final sample. The amorphous nanotubes got converted to highly ordered Ag-TiO₂ (anatase) arrays in the silver nitrate & glucose aqueous solution via hydrothermal treatment. SEM and TEM results show that the Ag-TiO₂ nanocomposite was composed of a large number of Ag nanoparticles and anatase TiO₂ nanoparticles, and the morphology of those at the top of the arrays was found different from that of its trunk. The morphology evolution mechanism of the obtained sample was discussed. It is also revealed that the Ag-TiO₂ nanocomposite has high visible-light photocatalytic activity.     

Fabrication and performances of MWCNT/TiO<Subscript>2</Subscript> composites derived from MWCNTs and titanium (IV) alkoxide precursors

Multi-walled carbon nanotubes (MWCNTs)/TiO₂ composites were synthesized by sol-gel technique using titanium (IV) n-butoxide (TNB), titanium (IV) isopropoxide (TIP) and titanium (IV) propoxide (TPP) as different titanium alkoxide precursors. The as-prepared composites were comprehensively characterized by BET surface area, SEM, XRD, EDX and UV-Vis absorption spectroscopy. The samples were evaluated for their photocatalytic activity towards the degradation of methylene blue (MB) under UV irradiation. The results indicated that the sample MPB had best excellent photocatalytic activity among the three kinds of samples. Furthermore, we also used piggery waste to determine the photocatalytic activity for the MWCNT/TiO₂ composites by using a chemical oxygen demand (COD) method. It seemed all of the samples have an excellent removal effect of COD. From the results of the bactericidal test, MWCNT/TiO₂ composites with sunlight had a greater effect on E. coli than any other experimental conditions.     

Multifunctional performance of gC<Subscript>3</Subscript>N<Subscript>4</Subscript>-BiFeO<Subscript>3</Subscript>-Cu<Subscript>2</Subscript>O hybrid nanocomposites for magnetic separable photocatalytic and antibacterial activity

Highly active gC₃N₄-BiFeO₃-Cu₂O nanocomposites were successfully prepared via a facile, cost effective and eco-friendly method of hydrothermally wet precipitation combined with ultrasonic dispersion process. The prepared samples were characterized by XRD, FTIR, HRSEM, EDS, TEM, UV–Vis DRS, PL, VSM, BET and electrochemical properties. By means of these analysis for examine the crystal phase, nanostructure, band gap and light-harvesting properties were carried out. UV-DRS spectra indicate that the bandgap of g-C₃N₄ (2.7 eV) reduced to 2.59 and 2.21 eV by mixed with corresponds to BiFeO₃ and BiFeO₃/Cu₂O nanomaterials. The ideal photocatalytic activity of the gC₃N₄-BiFeO₃-Cu₂O nanocomposites, where RhB dye under visible light irradiation which was up to 4.36 and 2.52 times as the higher photodegradation ability to compare pristine g-C₃N₄ and gC₃N₄-BiFeO₃ catalyst. The magnetization was confirmed by VSM studies, and hence, after the photocatalytic reaction, the magnetically separable catalyst can be quickly separated from the water by an external magnetic field. The superior photocatalytic performance is due to the synergistic effect on the interface of BiFeO₃/Cu₂O in the gC₃N₄-BiFeO₃-Cu₂O nanocomposites has reduced the bandgap which enables high separation efficiency of the charge carrier, suppressed recombination rate and their high surface area. Moreover, the chief gC₃N₄-BiFeO₃-Cu₂O catalyst can exhibited the lesser charge transfer resistance (impedance), enhances of photocurrent responses, whereas exposed to the development of photocatalytic appearance and more charge carrier ability. Also, the antibacterial activity of the gC₃N₄-BiFeO₃-Cu₂O nanocomposite has showing a well deactivation in both G⁺ (S. aureus) and G^? (E. coli) bacteria’s whereas compare to other prepared samples.     

Fabrication of Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>-AgBr-PTh composite loaded on Na<Subscript>2</Subscript>SiO<Subscript>3</Subscript> with enhanced visible-light photocatalytic activity

A novel Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ was synthesized for enhanced visible-light photocatalytic activity. The photocatalytic activity of the samples was evaluated by photodegrading rhodamine B (RhB) under visible light irradiation. The main reactive species and possible photocatalytic mechanism were also discussed. As a result, the Ag₃PO₄-AgBr-PTh composite loaded on Na₂SiO₃ exhibited enhanced photocatalytic activity for RhB compared with Ag₃PO₄ under visible-light irradiation. Additionally, it was demonstrated that the hole (h⁺) and superoxide radical (?O ₂ ^? ) were the major reactive species involving in the RhB degradation. PTh played vital role for the enhanced photocatalytic activity of Ag₃PO₄-AgBr-PTh-Na₂SiO₃ composite, which offered an electron transfer expressway and accelerated the transfer of the electrons from the CB of AgBr into Ag₃PO₄. This work could provide a new perspective for the synthesis of Ag₃PO₄-based composites and the improvement of photocatalytic activity of Ag₃PO₄.