Preparation of BiVO4/bentonite catalysts and their photocatalytic properties under simulated solar irradiation

A series of BiVO₄/bentonite catalysts calcined at different temperatures were prepared by the solution combustion method and characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Brunauer–Emmett–Teller (BET) specific surface area and ultraviolet–visible diffuse reflectance (UV–vis DRS) spectra. The results of BET analysis showed that BET specific surface area of BiVO₄/bentonite crystallite decreased with increasing calcination temperature. The results of XRD, FE-SEM and UV–vis DRS analysis indicated that BiVO₄ on bentonite calcined at 300 °C was in a monoclinic structure with a diameter of around 30 nm, as well as strong absorbance in a region of 350–500 nm. The photocatalytic activities of as-prepared catalysts were discussed by the degradation of C.I. Reactive Blue 19 (RB19) under simulated solar irradiation. It was found that the catalyst could be separated from aqueous suspensions by sedimentation after reaction, and maintained almost the same activity after being used five times.     

Solar photocatalytic activity of chemical solution-prepared barium tungstate nanostructures

Nanostructured barium tungstate (BaWO₄) as a solar photocatalyst has been successfully synthesized by a chemical solution method. The sample was characterized using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and UV–vis diffuse reflectance spectroscopy. Then, the photocatalytic degradation of methylene blue (MB) in an aqueous medium was evaluated with nanostructured BaWO₄ under direct sunlight irradiation. The effects of the initial pH, and the catalyst dosage on the dye degradation were studied in order to achieve maximum degradation efficiency. The nanostructured BaWO₄ exhibited good photocatalytic activity for degradation of MB under sunlight irradiation at pH 10 after 3 h of irradiation. Also, the optimal catalyst loading of 25 mg/L obtained throughout the present study. The degradation of the dye followed the first-order reaction and the adsorption obeyed the Langmuir model.     

Size,morphology and optical properties of SnO2 nanoparticles synthesized by facile surfactant-assisted solvothermal processing

Spherical and dumbbell-shaped SnO₂ nanoparticles were grown by a facile solvothermal using different amounts (0.5, 1 and 1.5 g) of three different surfactants (cetyltrimethylammonium bromide, polyethylene glycol and sodium dodecyl sulfate) in ethylenediamine, serving as both a coordinating and an alkaline reagent. The average particle size, measured by powder X-ray diffraction, was determined to be ∼3–6 nm and was confirmed by transmission electron microscopy. The chemical structure of products was studied by Fourier transform infrared spectroscopy. Morphologies and composition of products were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Optical properties of products were investigated by ultraviolet–visible (UV–vis) absorption and photoluminescence spectroscopies. Finally, the formation mechanism of SnO₂ nanoparticles is discussed.     

Photocatalytic degradation of methylene blue by Zn2SnO4-SnO2 system under UV visible radiation

Zn₂SnO₄-SnO₂ system was successfully synthesized by co-precipitation under ultrasonic radiation combined with high temperature calcination. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy and UV–visible absorption spectroscopy revealed the presence of cubic particles mixed with nanoparticles of Zn₂SnO₄-SnO₂ composites which were synthesized from Zn:Sn molar ratios of 1:1 and 3:2. Upon using Zn:Sn molar ratios of 3:1 and 2:1, additional ZnO minor phase was detected. In addition, the calculated pseudo-first-order rate constant of the product synthesized from 3:2 molar ratio of Zn:Sn was the highest at 12.244×10^–3 min^–1.     

Electrical,optical and visible light-photocatalytic properties of monoclinic BiVO4 nanoparticles synthesized hydrothermally at different pH

Monoclinic BiVO₄ nanoparticles were synthesized hydrothermally at pH 0.5, 2.0, 5.0 and 7.0. They were characterized by high resolution scanning electron microscopy or field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction, powder X-ray diffraction, Raman spectroscopy, solid state impedance spectroscopy, UV–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. While BiVO₄ nanoparticles synthesized at pH 0.5 and 2.0 provide perfect semicircular Nyquist plots the nanocrystals prepared at pH 5 show a semicircular arc. The nanocrystals obtained at pH 7 exhibit a quasi-linear dependence of Z_Im on Z_Re. The absorption edge of BiVO₄ nanoparticles is red-shifted on decrease of the pH of synthesis; BiVO₄ synthesized at pH 0.5 is an exception. The synthesized nanoparticles show band gap emission at 483 nm and defect emissions at 534 and 578 nm. The band gap emission of BiVO₄ nanocrystals synthesized at pH 0.5 is much less than those of others. The photocatalytic activity of BiVO₄ nanoparticles decreases with increase of the pH of synthesis and nanocrystalline BiVO₄ synthesized at pH 0.5 is an exception. The photocatalytic activities of BiVO₄ nanoparticles synthesized at different pH are explained in terms of the charge transfer resistance, band gap energy, photoluminescence due to charge carrier recombination and preferential orientation of 040-plane in BiVO₄ nanocrystals synthesized at pH 2.     

Synthesis,characterization and optical band gap of La2CuO4 nanoparticles

Pure La₂CuO₄ nanoparticles were synthesized via sol–gel process using stearic acid as complexing reagent. This method consists of the formation of an organic precursor, with metallic cations homogeneously distributed throughout the matrix. The gel was calcined at 700 °C, 800 °C and 900 °C for 4 h. The as-prepared La₂CuO₄ nanoparticles were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and diffuse reflectance spectroscopy. Results show that the purity of La₂CuO₄ crystallites increases with the increase of heat treatment temperature from 700 °C to 900 °C. Optical properties show that La₂CuO₄ crystallites have broad absorption in the UV–vis region and the corresponding band gap is 1.24 eV.     

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi₂MoO₆/g-C₃N₄ heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi₂MoO₆/g-C₃N₄ composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20 wt% Bi₂MoO₆/g-C₃N₄ sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20 wt% Bi₂MoO₆/g-C₃N₄ is about 5 and 2.5 times higher than that over pure Bi₂MoO₆ and g-C₃N₄ nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.     

Photocatalytic and antimicrobial activity of NiWO4 nanoparticles stabilized by the plant extract

In recent years, biosynthesis of nanoparticles using plant extract has attracted great attention owing to its cost effective, non-toxic, eco-friendly and as an alternative approach to physical and chemical methods. Nickel tungstate (NiWO₄) nanoparticles were synthesised via the aqueous leaf extract of Azadirachta indica plant. The prepared nanoparticles were characterized using UV–visible diffuse reflectance spectroscopy (UV–vis-DRS), fourier transform infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. SEM results showed that plant extract modified NiWO₄ (PNT) was composed of tiny sphere in shape. XRD results revealed that the average crystallite size of PNT was smaller (12.12 nm) when compared to the bare NiWO₄ (NT) prepared using precipitation method (31.11 nm). The photocatalytic activity of NiWO₄ nanoparticles were investigated using methylene blue (MB) as a model organic pollutant under visible light irradiation. PNT showed high efficiency for the degradation of MB compared to NT. The effect of operation parameters such as initial dye concentration, pH and catalyst concentration has been investigated in detail. PNT was subjected to antimicrobial studies and significant results were obtained.     

Synthesis of novel NiZn-ferrite/Polyaniline nanocomposites and their microwave absorption properties

Novel Ni_0.5Zn_0.5Fe₂O₄ (NiZn-ferrite)/Polyaniline (PANI) nanocomposites with NiZn ferrite nanoparticles on the surface of PANI nanofibers were successfully prepared by hydrothermal method. The composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and UV–vis spectra. The results indicate that the PANI nanofibers (80 nm in thickness) are attached by NiZn ferrite nanoparticles. Compared with pure PANI, the thermal stability of composites is improved clearly. The NiZn-ferrite/PANI nanocomposites exhibit ferromagnetic behavior with high saturation magnetization (Ms=43.7 emu/g) and coercivity (Hc=138.7 Oe) at room temperature. The microwave absorption properties of these composites were measured, and the absorption bandwidth with reflection loss below ?10 dB is up to 5 GHz. The composites could further extend the potential application in microwave absorption and electromagnetic interference shielding fields.     

Influence of propyl alcohol addition during processing of molybdenum trioxide powders: Observation of novel dual-wavelength excitation photochromism

The novel dual-wavelength excitation photochromic molybdenum trioxide (MoO₃) powders are fabricated successfully via the hydrothermal method by the addition of propyl alcohol. The samples were fully characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis), and colorimetry. The characteristic spectrum of XRD demonstrates that the as-obtained products are highly pure. The results show that the flowerlike MoO₃ sample with the inducer of propyl alcohol has better photochromic properties, which was analyzed by colorimetry. It is shown that both of the samples exhibit a strong adsorption band between 250 and 400 nm in the UV range. Moreover, the UV–vis spectra shows that MoO₃ synthesized with added propyl alcohol absorbs light not only between 250 and 400 nm but also displays an additional band between 500 and 800 nm, demonstrating novel dual-wavelength excitation photochromic properties.     

Thin films of silica imbedded silicon and germanium quantum dots by solution processing

Hydrophilic silicon (0.9 nm) and germanium (2.7 nm) quantum dots (QDs), synthesized utilizing micelles to control particle size, were coated with silica using liquid phase deposition. The use of dodecyltrimethylammonium bromide as a surfactant yielded uniform spheres (Si@SiO₂=57 nm; Ge@SiO₂=32 nm), which could then be arrayed in three dimensions using a vertical deposition method on quartz plates. The silica coated QDs were characterized by UV–visible spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The thin films were characterized by UV–visible spectroscopy, scanning electron microscopy, and the measurement of a photocurrent.     

Studies on structural,morphological, magnetic and optical properties of chromium sesquioxide (Cr2O3) nanoparticles: Synthesized via facile solvothermal process by different solvents

Chromium sesquioxide (Cr₂O₃) nanoparticles have been successfully synthesized via the facile solvothermal process, by using CrO₃ in different solvents. The as-synthesized nanoparticle sizes are calculated and confirmed to be 25–45 nm, by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The functional groups of the samples were tested by the Fourier transform infrared (FTIR) spectroscopy. Fine and spherical-like morphologies and compositional elements of the products were observed by the scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. A weak ferromagnetic (WFM) property was observed for sample by the vibrating sample magnetometer (VSM). The observed band gap values (E_g=4.33–3.54 eV) higher than that of bulk Cr₂O₃ (~3.4 eV) indicated that the particles had been successfully synthesized in the nano region, and measured by ultra-violet visible (UV–vis) absorption spectroscopy. The broad visible emission at ~399 nm, in the photoluminescence spectroscopy revealed the high purity and perfect crystallinity of the samples.     

Effect of temperature on crystallite sizes of copper sulfide nanocrystals prepared from copper(II) dithiocarbamate single source precursor

We report the synthesis of CuS nanoparticles using [Cu(butdtc)₂] as single source precursor thermolysed at two different temperatures. The products were characterized by UV–vis absorption spectroscopy, X-ray diffraction, Transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis and atomic force microscopy. The absorption spectra of the CuS nanocrystals are blue shifted and the XRD were indexed to the hexagonal phase of CuS with nanoparticles obtained at 120 °C showing well defined crystalline structure compared to those obtained at 180 °C. Transmission electron microscopy images showed particles that are almost spherical in shapes with average crystallite sizes of 21–38 nm for CuS1 prepared at 180 °C and 3–7 nm for CuS2 prepared at 120 °C and confirms that the chosen reaction temperature determine the crystallite sizes of the nanoparticles.     

Photocatalytic degradation of reactive black 5 azo dye by zinc sulfide quantum dots prepared by a sonochemical method

Zinc sulfide (ZnS) nanoparticles (NPs) with an average particle size of 2 nm were successfully synthesized under ultrasonic irradiation without any surfactant and high temperature treatment. Prepared NPs were characterized by powder X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, dynamic light scattering analysis, and UV–vis absorption spectroscopy. The energy band gap of ZnS NPs was measured by UV–vis absorption spectroscopy. The photocatalytic activity of semiconducting sulfide quantum dots for degradation of an azo dye called reactive black 5 (RB5) was investigated. Results showed that the dye can be photocatalytically degraded with high rate by ZnS NPs under UV light irradiation. The kinetics of removal of RB5 in aqueous solutions was studied in a series of experiments which were varied in the amount of ZnS NPs, contact time, pH, dye concentration, and temperature. The experimental data were fitted very well in the pseudo-second order kinetic model. 95% of dye was successfully removed in 10 min using 0.2 g ZnS NPs in a neutral pH. A possible molecular mechanism for photocatalytic degradation of dye by ZnS NPs was also given.     

WO3/TiO2 nanocomposites: Salt–ultrasonic assisted hydrothermal synthesis and enhanced photocatalytic activity

A series of WO₃/TiO₂ composite photocatalysts were fabricated via a facile salt–ultrasonic assisted hydrothermal process. The obtained samples were characterized by X-ray diffraction, scanning eletron microscopy, energy dispersive X-ray spectroscopy and UV–vis diffused reflectance spectroscopy. It was confirmed that anatase TiO₂ and monoclinic WO₃ coexisted in the composites. The photocatalytic activity of as-prepared WO₃/TiO₂ composites for degradation of Rhodamin B (RhB) under visible light irradiation was investigated. The results showed that WO₃/TiO₂ composites have a higher photocatalytic activity than those of pure TiO₂ and pure WO₃. First-principle calculations based on density functional theory were performed to explore the electronic structure and illustrate the photocatalytic mechanism of WO₃/TiO₂. The calculated energy gap was 2.53 eV, which was close to the experimental observation (2.58 eV). Due to the combination of WO₃/TiO₂, the photoinduced electrons and holes transfer between the WO₃ and TiO₂ in opposite directions, thus providing sufficient charge separation, which contributed to the photocatalytic activity enhancement.     

Effects of calcination temperatures and additives on the photodegradation of methylene blue by tin dioxide nanocrystals

The tin dioxide (SnO₂) nanocrystals were synthesized by direct precipitation method and a series of SnO₂ samples were obtained via calcining SnO₂ at different temperatures. The characteristics of SnO₂ samples were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), Brunauer Emmett Teller (BET), photoluminescence spectroscopy (PL), and UV–vis diffuse reflectance spectroscopy (DRS). The effects of calcination temperatures and additives on the photodegradation of methylene blue (MB) on SnO₂ samples under UV-light irradiation have been researched. The results showed that the SnO₂ sample with low temperature-treated (T≤200 °C) exhibits the highest degradation efficiency, while with increasing temperature-treated (from 400 °C to 1000 °C) SnO₂ samples show decreasing degradation activities. The additives, such as methanol, sodium fluoride, Fe(III), Ag⁺, and terephthalic acid showed different influences on MB degradation in UV/SnO₂ systems. It has been demonstrated that in SnO₂-MB systems both hydroxy radicals (OH) generated on the surface of SnO₂ and photogenerated holes (h⁺_vb) in the valence band (VB) of SnO₂ jointly control the photo-oxidation process of MB. In SnO₂ system with increasing temperature-treated (T≥400 °C) the contribution of OH to MB degradation gradually decreased due to the diminution of surface-bonding hydroxyl groups (–OH) and chemisorbed water (H₂O) molecules on the surface of SnO₂, by comparison, the contribution of h⁺_vb increased. The effects of Ag⁺ and Fe(III) species on MB degradation and the formation of OH were investigated in detail and the mechanisms have been discussed. The presence of Ag⁺ ion at low concentration promotes the degradation of MB by capturing the photogenerated electrons (e_cb⁻) on the surface of SnO₂ catalyst, suppressing the recombination of photogenerated electrons and holes. The presence of Ag⁺ ion at high concentration observably reduces the degradation in catalyst system which the photodegradation process is controlled by OH, conversely, it intensively promotes the degradation in which the photodegradation process is controlled by h⁺_vb. The effects of Fe(III) species on the degradation are similar to those of Ag⁺ ions.     

g-C3N4/Ag3PO4 composites with synergistic effect for increased photocatalytic activity under the visible light irradiation

The g-C₃N₄ was synthesized by a hydrothermal method and the g-C₃N₄/Ag₃PO₄ composites were prepared by a ordinary precipitation method. Microstructures, morphologies and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the Ag₃PO₄ nanoparticles were dispersed on the surface of the flake-like g-C₃N₄, and the heterojunction was formed on the interface. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst presented the highest photocatalytic activity for organic dye methylene blue (MB) degradation, and its photocurrent intensity was approximately 2 times than that of the pure Ag₃PO₄. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst also exhibited photocatalytic performance in the decomposition of colorless antibiotic ciprofloxacin (CIP). The capture experiment confirmed that holes acted as the main active species during the photocatalytic reaction.     

Solvothermal synthesis and characterization of quaternary Cu2ZnSnSe4 particles

Quaternary chalcogenide Cu₂ZnSnSe₄ (CZTSe) particles for low cost thin film solar cells were synthesized utilizing a facile solvothermal method. Depending upon different solvents and temperatures, different morphologies and desired chemical composition of CZTSe particles were obtained. The as-obtained particles were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction pattern, energy dispersive X-ray spectrometry and UV–visible (UV–vis) absorption spectra. XRD results revealed that the temperature of 250 °C is suitable for the solvothermal synthesis of CZTSe. UV–vis absorption spectra showed the as-obtained CZTSe particles had strong absorption of visible light and their energy band gaps were tunable; these findings are relevant to the size and morphology of CZTSe particles and are of interest for solar cells.     

Preparation and characterization of conductive polypyrrole/kaolinite composites

Conductive polypyrrole (PPy)/kaolinite clay composites were prepared by in situ chemical polymerization of pyrrole in the presence of kaolinite using FeCl₃ as oxidant. The PPy content and conductivity of the composites reached 32.8% and 8.3×10^?2 S/cm at HCl concentrations of 1.5 M and 0.5 M, respectively. The microhardness of the composites containing different amounts of PPy was higher than that of the PPy and kaolinite components. The highest microhardness observed was 30.17 kg/mm² for the composite containing 9.6% PPy. The electrical resistance of the composites was monitored during heating–cooling cycles over the range 5–120 °C. The change in resistance with temperature was more repeatable for the composite than for PPy. The composites were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The humidity-sensing properties were also examined.