One-step template-free synthesis of ZnWO<Subscript>4</Subscript> hollow clusters

ZnWO₄ hollow clusters made up of nanorods were successfully prepared through a tripotassium citrate assisted hydrothermal process at 180 °C. The hollow clusters’ diameter was about 400 nm, and these clusters were made up of nanorods with a diameter of about 10 nm and a length of about 50 nm. X-ray power diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the synthesized products. Based on experiments, the growth of these hollow clusters followed an aggregation-Ostwald ripening process. The photocatalytic activities for aqueous Rhodamine B of samples were investigated, and it was seen that ZnWO₄ hollow clusters exhibited a strong photocatalytic activity.     

Sonochemical fabrication, characterization and photocatalytic properties of Ag/ZnWO4 nanorod catalyst

A ZnWO₄ nanocrystal catalyst with rod-like structure was first synthesized by powerful ultrasonic irradiation method at room temperature. Then, Ag was introduced to ZnWO₄ nanorods by a photodeposited method. The as-synthesized Ag/ZnWO₄ catalysts have been investigated by photocatalytic reaction tests and some physicochemical characterizations like XRD, BET, IR, TEM, EDX, XPS, PL, and UV–vis DRS. The results show that the prepared samples have good crystallinity and Ag addition can improve the photocatalytic performance of ZnWO₄ in degradation of rhodamine-B (RhB) under UV light irradiation. The deposition of 1 wt% Ag over ZnWO₄ leads to about a one-time increase in the photocatalytic performance with the reference of ZnWO₄. The high performance of Ag/ZnWO₄ could be attributed to the fact that the high dispersed Ag particles could act as electron traps promoting the electron–hole separation then enhancing the photocatalytic reaction.     

Template-free synthesis of ZnWO4 powders via hydrothermal process in a wide pH range

ZnWO₄ powders with different morphologies were fabricated through a template-free hydrothermal method at 180 °C for 8 h in a wide pH range. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible and luminescence spectrophotometers were applied to study the effects of pH values on crystallinity, morphology, optical and luminescence properties. The XRD results showed that the WO₃ + ZnWO₄, ZnWO₄, and ZnO phases could form after hydrothermal processing at 180 °C for 8 h with the pH values of 1, 3-11, and 13, respectively. The SEM and TEM observation revealed that the morphological transformation of ZnWO₄ powders occurred with an increase in pH values as follows: star anise-, peony-, and desert rose-like microstructures and soya bean- and rod-like nanostructures. The highest luminescence intensity was found to be in sample consisting of star anise-like crystallites among all the samples due to the presence of larger particles with high crystallinity resulted from the favorable pH under the current hydrothermal conditions.     

ZnCo2O4 nanorods as a novel class of high-performance adsorbent for removal of methyl blue

Spinel ZnCo₂O₄ nanorods were synthesized by a simple template-free hydrothermal method in the presence of zinc chloride, cobalt chloride, glucose, and urea. The phase structure, morphology and chemical composition have been characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED). The results showed that the typically porous and poly-crystalline structure was successfully grown on the surface of ZnCo₂O₄ nanorods. The ZnCo₂O₄ nanorods were further applied to remove methyl blue (MB), which was used as a model of organic pollutants in aqueous solution. In particular, the maximum equilibrium adsorption capacity of MB in ZnCo₂O₄ nanorods reaches up to 2400?mg/g, which is higher than that of most adsorbents. The adsorption isotherms and kinetics followed standard Langmuir and pseudo-second-order models, respectively. MB adsorption decreased with increasing solution pH at pH?>?7 implying that MB adsorption on ZnCo₂O₄ nanorods may via chemisorption between negatively charged MB molecular and positively charged adsorption sites on the surface of ZnCo₂O₄ nanorods. This study provides great promise of using ZnCo₂O₄ nanorods as adsorbent for removal of pollutant dyes.     

A facile route to synthesize ternary Cu2O quantum dot/graphene-TiO2 nanocomposites with an improved photocatalytic effect

A Cu₂O quantum dot/graphene-TiO₂ composite, a novel material, was successfully synthesized using a facile hydrothermal method. The hydrothermal reaction was used to load the Cu₂O and TiO₂ particles onto graphene sheets, and the resulting photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), Raman spectroscopy, and ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS). UV spectrophotometry was employed to measure the decrease in the concentration of rhodamine B (RhB), methylene blue trihydrate (MB), and reactive black B (RBB) dyes in an aqueous solution after degradation with the photocatalysts under irradiation with visible light. The results indicate that the quantum dot-sized Cu₂O is a promising material that contributes to the photocatalytic activity of Cu₂O quantum dot/graphene-TiO₂ composites.     

Synthesis, characterization and photocatalytic properties of nanosized Bi2WO6, PbWO4 and ZnWO4 catalysts

Nanosized Bi₂WO₆, PbWO₄ and ZnWO₄ photocatalysts were synthesized by a mild hydrothermal crystallization process. The physical and photophysical properties of the catalysts were characterized by X-ray diffractometry, Brunauer-Emmet-Teller surface area and porosity measurements, transmission electron microscopy, Raman spectra, and diffused reflectance spectroscopy. The rhodamine-B photodegradation in aqueous medium was employed as a probe reaction to test the photoactivities of the as-prepared samples under four irradiation wavelengths. Bi₂WO₆ not only presented the photocatalytic activity in the wide spectral scope, including UV and visible light but also exhibited the strong photosensitized capability to transform RhB under visible light irradiation (λ > 490 nm). ZnWO₄ only displayed relatively high photoactivity under UV irradiation. However, PbWO₄ showed poor photoactivity under any light irradiation. On the basis of the calculated density functional theory (DFT), the photocatalytic mechanisms were discussed.     

A new strategy for the preparation of porous zinc ferrite nanorods with subsequently light-driven photocatalytic activity

Porous zinc ferrite (ZnFe₂O₄) nanorods have been synthesized by the thermal decomposition of ZnFe₂(C₂O₄)₃ nanorods precursor, which was prepared by template-, surfactant-free solvothermal method. The morphology and structure of the obtained ZnFe₂(C₂O₄)₃ nanorods precursor and porous ZnFe₂O₄ nanorods were characterized by X-ray powder diffraction, transmission electron microscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicated that the as-synthesized ZnFe₂O₄ retained the precursor morphology of 1D nanorods with diameters of 100–200 nm and lengths of several micrometers and plenty of nanoparticles were interconnected to each other to form porous nanorods. The as-prepared ZnFe₂O₄ nanorods as a kind of subsequently light-driven photocatalyst exhibited good photocatalytic decomposition activity for methylene blue (MB).     

Three-dimensional (3D) sea-urchin-like hierarchical TiO2 microspheres: growth mechanism and highly enhanced photocatalytic activity

Three-dimensional (3D) sea-urchin-like hierarchical TiO₂ microspheres were synthesized by a template-free hydrothermal method. The effects of preparation parameters on the microstructure of 3D sea-urchin-like hierarchical TiO₂ were investigated using scanning electron microscopy (SEM), transmission electron microscopy, X-ray diffractometer, energy-dispersive X-ray spectrometer and Brunauer–Emmett–Teller technologies. The growth mechanism and photocatalytic activity of 3D sea-urchin-like TiO₂ microspheres were discussed. The results of electron microscopy characterizations SEM showed that the microspheres were consisted of numerous one-dimensional (1D) nanorods. A three-step growth model: oxygenated to be 1D nanorods, self-assembly and protonation, was proposed to illustrate the growth mechanism of sea-urchin-like structures. The synthesized 3D sea-urchin-like hierarchical TiO₂ microspheres exhibited a better photocatalytic activity for photodegradation of rhodamine B under sunlight irradiation compared to that of P25, which was attributed to the special 3D hierarchical nanostructure, the increased number of surface active sites and anatase crystal structure.     

Fabrication and photocatalysis of mesoporous ZnWO4 with PAMAM as a template

Mesoporous ZnWO₄ was prepared with the template of PAMAM. The as-formed samples were characterized by X-ray diffraction (XRD), nitrogen absorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy (DRS). It is found that the size of pore is in the range of 5-22 nm and that the porosity of ZnWO₄ is composed of aggregated ZnWO₄ nanoparticles. The photocatalytic activities towards degradation of rhodamine B (RhB) and malachite green (MG) under UV light has been investigated. The formation mechanism of mesoporous structures is proposed.     

Hydrothermal synthesis and characterization of CePO4/C core-shell nanorods

The CePO₄/C nanocomposite with core-shell nanostructure has been successfully synthesized using glucose and CePO₄ by a facile and simple hydrothermal method at 160 °C for 24 h. The new material consists of a monoclinic CePO₄ core and an amorphous-C shell. The TEM micrograph indicated that the CePO₄/C nanocomposite was core-shell nanorods. The effects of glucose concentration on the C shells and luminescent intensity of CePO₄/C nanocomposite were investigated. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). This method is simple, low-cost and does not need any surfactant.     

Hydrothermal synthesis,characterisation and photocatalytic properties of BiOIO3 nanoplatelets

In this work, BiOIO₃ nanoplatelets were successfully prepared by a simple hydrothermal method. The as-prepared samples were characterised by energy-dispersive spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction and ultraviolet visible diffuse reflectance spectroscopy. The photocatalytic activities of the as-prepared BiOIO₃ nanoplatelets were evaluated by photodegradation of rhodamine B (RhB) under simulated solar light. The results showed that the change of temperature within a certain range has almost no influence on the morphology and size of BiOIO₃ nanoplatelets. However, it had an obvious effect on the photocatalytic performance of BiOIO₃ nanoplatelets. The results showed that the BiOIO₃ sample synthesised at 130 °C exhibited the highest photocatalytic activities compared to others, with RhB completely decomposed in 80 min. The products with proper crystallinity formed at 130 °C have the optimal rate of RhB photodegradation. It indicated that the most favourable crystallinity made it beneficial to improve the photocatalytic activity. The possible mechanism of the photocatalytic reaction based on deep analysis and the experimental results was discussed in detail.     

Construction of one dimensional ZnWO4@SnWO4 core-shell heterostructure for boosted photocatalytic performance

The one-dimensional ZnWO₄@SnWO₄ photocatalyst with a core-shell heterostructure was successfully constructed by a simple two-step method. It is interesting to note that ZnWO₄@SnWO₄ composite photocatalyst owns a higher photocatalytic activity for RhB degradation under visible light irradiation. The introduction of SnWO₄ shell layer, which forms a clear heterogenous interface between ZnWO₄ and SnWO₄, increases the photo-absorption efficiency of ZnWO₄ nanorods. In addition, its band-edge absorption evidently shifts toward the visible region. Based on the photoelectrochemical (PEC) and electron spin resonance (ESR) measurements, it is found that the photocatalytic activity was attributed to the efficient separation and transfer of photo-generated charge carriers. Hence, they can produced more hydroxyl radical (OH) as the main active species in the photocatalytic reaction process.     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Synthesis of ZnWO4 nano-particles by a molten salt method

ZnWO₄ nano-particles were successfully synthesized by a molten salt method at 300 °C. The as-prepared powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL), respectively. The size and morphology of ZnWO₄ nano-particles were affected by such conditions as the calcining time and the weight ratio of the salt to the ZnWO₄ precursor. The resultant sample is a pure phase of ZnWO₄ without any impurities. The PL spectra results showed that the optical property of ZnWO₄ crystallites obviously relied on their particle sizes.     

Microwave-assisted hydrothermal synthesis and optical property of Co3O4 nanorods

Single crystalline Co₃O₄ nanorods have been successfully synthesized through thermal decomposition of the precursor, which was obtained by the microwave-assisted hydrothermal route. The obtained sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results confirm that the resulting oxide was pure single-crystalline Co₃O₄ nanorods. The optical property test indicates that the absorption peak of the nanorods shifts towards short wavelength. And the blue shift phenomenon might be ascribed to the quantum effect.     

A polymeric complex method to nanocrystalline BiCu2VO6 with visible light photocatalytic activity

Nanocrystalline BiCu₂VO₆ was successfully synthesized by a facile polymeric citrate complex method. The samples were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectra (DRS), thermogravimetric analyses (TG) and differential thermal analyses (DTA). BiCu₂VO₆ showed photocatalytic activity for the degradation of RhB under visible light irradiations with the coexistence of H₂O₂. As compared to BiCu₂VO₆ prepared via a solid state reaction, BiCu₂VO₆ prepared via a polymeric citrate complex method showed higher photocatalytic activity. The visible light photocatalytic activity of BiCu₂VO₆ was also proposed.     

Synthesis of manganese vanadate nanobelts and their visible light photocatalytic activity for methylene blue

Manganese vanadate nanobelts have been synthesised by a simple hydrothermal process using polymer polyvinyl pyrrolidone as the surfactant by adjusting the pH value. The X-ray diffraction, selected area electron diffraction and the high-resolution transmission electron microscopy (TEM) show that the manganese vanadate nanobelts are composed of a single crystalline monoclinic Mn₂V₂O₇ phase. Scanning electron microscopy and TEM observations show that the thickness, width and length of the nanobelts are 20 nm, 350 nm–1 μm and several dozens to several hundreds of micrometres, respectively. The photocatalytic activities of the manganese vanadate nanobelts have been evaluated by the photocatalytic degradation of methylene blue (MB) in an aqueous solution as a model pollutant under the solar light irradiation. After 4 h of the irradiation by the solar light, the MB solution with the volume of 10 mL and the concentration of 10 mg·mL^?1 can be totally degraded using 10 mg manganese vanadate nanobelts.     

Hydrothermal synthesis of hemisphere-like F-doped anatase TiO<Subscript>2</Subscript> with visible light photocatalytic activity

Hemisphere-like F-doped anatase TiO₂ has been synthesized by hydrothermal treatment of TiF₄ aqueous solution in the presence of starch at 130 °C for 10 h, and then calcined at 450 °C for 2.5 h in air. The as-synthesized product has been investigated by photocatalytic reaction test and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–Vis diffuse reflectance spectra (DRS). The results showed that fluorine was successfully doped into the TiO₂ hemispheres. The F-doped TiO₂ hemispheres showed high visible light activity in degradation of acid orange II, which could be attributed to the creation of oxygen vacancies and good crystallinity.     

Facile synthesis of MnV2O6 nanostructures with controlled morphologies

MnV₂O₆ nanostructures including nanorods, nanobelts, and nanosheets, have been synthesized by a facile hydrothermal reaction between Mn(CH₃COO)₂·4H₂O and commercial V₂O₅. The synthesized products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The influences of synthetic parameters, such as, reaction time, temperature and medium, on the morphologies of the resulting products have been investigated. As the reaction temperatures increase from 120 °C to 180 °C, MnV₂O₆ nanorods and nanobelts are obtained, respectively. The time-dependent experimental results at 180 °C reveal that the sizes of MnV₂O₆ nanobelts increase gradually with the reaction proceeding. Interestingly, as the reaction is carried out with the aid of H₂O₂ solution, flower-like MnV₂O₆ nanosheets are formed.     

Hydrothermal synthesis and characterization of TiO2 nanorod arrays on glass substrates

Large-scale, well-aligned single crystalline TiO₂ nanorod arrays were prepared on the pre-treated glass substrate by a hydrothermal approach. The as-prepared TiO₂ nanorod arrays were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. X-ray diffraction results show that the main phase of TiO₂ is rutile. Scanning electron microscopy and transmission electron microscopy results demonstrate that the large-scale TiO₂ nanorod arrays grown on the pre-treated glass substrate are well-aligned single crystal and grow along [0 0 1] direction. The average diameter and length of the nanorods are approximately 21 and 400 nm, respectively. The photocatalytic activity of TiO₂ nanorod arrays was investigated by measuring the photodegradation rate of methyl blue aqueous solution under UV irradiation (254 nm). And the results indicate that TiO₂ nanorod arrays exhibit relatively higher photocatalytic activity.