Effective Photocatalytic Activity Research Articles

Crystallization-mediated amorphous CuxO (x = 1, 2)/crystalline CuI p–p type heterojunctions with visible light enhanced and ultraviolet light restrained photocatalytic dye degradation performance

We report simple and cost-effective fabrication of amorphous CuxO (x=1, 2)/crystalline CuI p–p type heterojunctions based on crystallization-mediated approaches including antisolvent crystallization and crystal reconstruction. Starting from CuI acetonitrile solution, large crystals in commercial CuI can be easily converted to aggregates consisting of small particles by the crystallization processes while the spontaneous oxidation of CuI by atmospheric/dissolved oxygen can induce the formation of trace CuxO on CuI surface. As a proof of concept, the as-fabricated CuxO/CuI heterojunctions exhibit effective photocatalytic activity towards the degradation of methyl blue and other organic pollutants under visible light irradiation, although the wide band-gap semiconductor CuI is insensible to visible light. Unexpectedly, the CuxO/CuI heterojunctions exhibit restrained photocatalytic activity when ultraviolet light is applied in addition to the visible. It is suggested that the CuxO/CuI interface can enhance the spatial separation of the electron–hole pairs with the excitation of CuxO under visible light and prolong the lifetime of photogenerated charges with high redox ability. The present work represents a critically important step in advancing the crystallization technique for potential mass production of semiconductor heterojunctions in a mild manner.

Facile green synthesis of zinc oxide nanoparticles by Eucalyptus globulus and their photocatalytic and antioxidant activity

Eucalyptus globulus leaf extract mediated synthesis of spherical zinc oxide nanoparticles (ZnO NPs) was carried out under ambient conditions. UV–Visible studies of the synthesized nanoparticles revealed the characteristic peak at 361nm indicating the formation of ZnO nanoparticles. Powder X-ray Diffractometric (XRD) study showed the strong, intense and narrow-width diffraction peaks indicating the formation of crystalline nanoparticles with most stable hexagonal phase. Field emission-scanning electron microscopy (FE-SEM) and high resolution-transmission electron microscopic (HR-TEM) results confirmed the formation of spherical ZnO NPs with mean particle size of 11.6nm which is in close agreement with XRD pattern. Further, energy dispersive X-ray diffraction analysis (EDAX) revealed the formation of highly pure ZnO NPs with the peaks of Zn and O atoms. ZnO NPs exhibited effective photocatalytic activity in degrading Methylene blue and Methyl orange with maximum degradation efficiency up to 98.3% at 30mg of catalyst doses. In addition, ZnO NPs exhibited high antioxidant activity against DPPH free radicals scavenger.

Hydrothermally grown ZnO nanoparticles for effective photocatalytic activity

ZnO nanoparticles were prepared by hydrothermal method from the source materials of zinc chloride and ammonium hydroxide. Precursor solution pH was varied to 7, 9, 11 and 13 by the addition of ammonium solution and the solution was hydrothermally treated at 150°C for 3h. Further prepared samples were annealed at 400°C for 3h. X-ray diffraction technique was employed to study the structure and crystalline nature of synthesized nanoparticles. Diffuse Reflectance Spectroscopy studies revealed that optical band gap of ZnO is slightly varied due to the effect of size of the particle. Field emission scanning electron microscope images showed that the prepared ZnO nanoparticles acquired spindle like nanorods, hexagonal disk, porous nanorods and nanoflower structures due to the effect of pH of the precursor solution. Photocatlytic activity of the prepared ZnO nanoparticles was evaluated for Rhodamine B (RhB) dye which showed 94% of degradation and good stability for five cycles.

Low temperature hydrothermal synthesis of SrTiO3 nanoparticles without alkali and their effective photocatalytic activity

SrTiO3 nanoparticle (NP) photocatalyst was synthesized with a facile and environmentalfriendly hydrothermal method using tetrabutyltitanate, strontium oxide, and ethanolamine as precursors at low temperature without alkali as mineralizer for the first time. The SrTiO3 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and N2 Brunauer–Emmett–Teller (BET) method. The SrTiO3 catalyst synthesized at 120 °C (STO-120) exhibited the highest photocurrent intensity among the samples synthesized at different hydrothermal temperatures. The high photocatalytic performance of STO-120 was mainly attributed to the more homogeneous and minimum nanoparticle size, the highest surface area, and the maximum light absorption property among the four different samples. This work presented an applicable and facile method to fabricate a highly active and stable SrTiO3 photocatalyst for organic pollutant degradation.

Influence of alkoxide structures on formation of TiO2/WO3 heterojunctions for photocatalytic decomposition of organic compounds

Reducing recombination and lowering band gap can be achieved with heterostructured photocatalysts, and the TiO2 photocatalyst film coupled with WO3 component maintains its advantageous characteristics. In order to investigate the effect of molecular structures on heterojunction formation, the three types of TiO2 precursors were used to make TiO2/WO3 heterojunction. The TiO2/WO3 composite films with high transmittance were successfully fabricated by the sol–gel spin coating method. Formation of Ti–O–W linkage was preferable from the precursor with small steric hindrance, and it was confirmed with the well scattered WO3 components in TiO2 crystal matrix and also with reduced TiO2 crystal size. High portion of Ti–O–W bond resulted in the most effective photocatalytic activity. Therefore, it is important to use a proper precursor to improve photodecomposition efficiency in manufacturing the heterostructured photocatalysts.

Protection of silica-coated ZnO nanoparticles on pre-dyed polyester fabrics against photofading

This work was designed to investigate the ability of silica-coated ZnO (ZnO&SiO2) nanoparticles (NPs) as ultraviolet (UV) absorbers for protecting pre-dyed polyester fabrics against photofading. Despite that ZnO NPs are excellent UV absorbers, their strong photocatalytic activity limits the application in UV protection. In this study, a silica layer was coated onto ZnO NPs to form a physical barrier between the ZnO and a polyester substrate, which allowed effective UV shielding while minimising the harmful effects of photocatalytic activity on the substrate. The structure and optical proprieties of ZnO&SiO2 NPs were observed. The bare ZnO and ZnO&SiO2 NPs were, respectively, applied to polyester fabrics coloured with three kinds of dyes by a dip coating method. The photofading level of treated fabrics after exposure under simulated sunlight was evaluated. The ZnO&SiO2 NPs exhibited excellent protection on pre-dyed polyester fabrics against photofading.

Hydrothermal growth of ZnO nanoflowers and their photocatalyst application

ZnO nanoflowers were prepared by the hydrothermal method and studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and photoluminescence. ZnO nanoflowers with star-like morphology were of pure wurtzite phase. The edges of the petals were composed of assemblies of smaller nanocrystallites. Green and orange emissions in photoluminescence were attributed to O vacancies and O interstitials, respectively. Furthermore, ZnO nanoflowers demonstrated the effective photocatalytic activities, and O vacancies and O interstitials were considered to be the active sites of the ZnO photocatalyst.

Enhanced visible light photocatalytic performance of ZnO nanowires integrated with CdS and Ag2S.

A series of ZnO-CdS-Ag2S ternary nanostructures with different amounts of Ag2S were prepared using simple and low-cost successive ionic layer adsorption and reaction (SILAR) and a chemical precipitation method. The ZnO nanowires, with a diameter of ∼ 100 nm and a length of ∼ 1 μm, were modified by coating CdS and Ag2S. CdS has a high absorption coefficient and can efficiently match with the energy levels of ZnO, which can enhance the light absorption ability of the nanostructures. In addition, Ag2S with a narrow band gap was used as the main light absorber and played an important role in increasing the light absorption in the visible light region. The photocatalytic activity of the ZnO-CdS-Ag2S ternary nanostructures was investigated using the degradation of methyl orange (MO) in an aqueous solution under visible light. The ZnO-CdS-Ag2S ternary nanostructures were found to be more efficient than ZnO nanowires, ZnO-CdS nanowires, and ZnO-Ag2S nanowires. There is 7.68 times more photocatalytic activity for MO degradation in terms of the rate constant for ZnO-CdS-Ag2S 15-cycle ternary nanostructure compared to the as-grown ZnO. Furthermore, the effect of the amount of Ag2S and CdS on the ZnO surface on the photocatalytic activity was analyzed. The superior photo-absorption properties and photocatalytic performance of the ZnO-CdS-Ag2S ternary nanostructures can be ascribed to the heterostructure, which enhanced the separation of the photo-induced electron-hole pairs. In addition, visible light could be absorbed by ZnO-CdS-Ag2S ternary nanostructures rather than by ZnO.

Structure and effective visible-light-driven photocatalytic activity of α-NiMoO4 for degradation of methylene blue dye

α-NiMoO4 powders were prepared by the Pechini method. The sample was investigated by X-ray powder diffraction (XRD) measurement, structural refinement, scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). The average size of α-NiMoO4 powders was measured to be 250 nm. The optical absorption spectrum of α-NiMoO4 confirmed an efficient absorption in the UV–visible light wavelength region. The sample presents a narrowed band-gap energy of 2.23 eV, and the effective photocatalytic activity was evaluated by the photodegradation of methylene blue (MB). The effective photocatalytic activity was discussed on the base of the crystal structure characteristics such as heavily distorted NiO6, activated optical centers and good electric conductivity. These results indicate that the hexagonal tunnel-structure alternately connected by MoO4 and the heavily distorted NiO6 is the dominated superiority for high photocatalytic capacity.

Synthesis, optical properties and photodegradation for methylene blue of Ni-vanadate K2Ni(VO3)4 nanoparticles

A Ni2+-containing vanadate, K2Ni(VO3)4 was developed as a new visible-light-driven photocatalyst. The nanoparticles were prepared by the modified Pechini method. The sample was characterized by the measurements such as X-ray powder diffraction, scanning electron microscope, and UV–Vis absorption spectrum. The photocatalytic activity of K2Ni(VO3)4 nanoparticles was evaluated by the photodegradation of methylene blue under visible-light irradiation in air. K2Ni(VO3)4 shows a photocatalytic activity due to the efficient absorption in the UV–Visible-light wavelength region with a narrowed band-gap energy of 2.08 eV and an indirectly allowed electronic transition. These results indicate that this vanadate garnet could be a potential photocatalyst driven by visible light. The effective photocatalytic activity was discussed on the basis of the special structural characteristic such as heavily distorted NiO6, rich, activated optical centers with tunnel structure for high photocatalytic capacity, and discussed on the basis of the photoluminescence and the decay lifetime.

Improved liquid phase deposition of anatase TiO2 hollow microspheres with exposed {0 0 1} facets and their photocatalytic activity

An improved liquid phase deposition (LPD) method was developed to prepare the TiO2 microspheres with enhanced crystallinity in this study. The as-prepared samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), nitrogen adsorption and desorption instrument, as well as the UV-Vis absorption spectroscopy. The results showed that the samples prepared at various precursor concentrations were identified as the well-crystalline anatase TiO2 exposed with reactive {001} facets, which was caused by the introduction of fluorine during the hydrolysis process of (NH4)2TiF6 precursor solution. Moreover, with increased concentration of precursor solution, the dissolution of {001} facets occurred and the typical hollow spherical structure was also found. The photocatalytic experiments revealed that the as-prepared anatase TiO2 microspheres exhibited an effective photocatalytic activity during the process of Rhodamine B (RhB) degradation.

A hybrid compound containing polyoxoanions and organic dye cations with visible-light photocatalytic H2 evolution activity

A hybrid polyoxometalate-aminoazobenzene dye compound, (C12H12N3)3PW12O40 2CH3CN (1) has been synthesized in CH3CN/H2O solution under conventional reaction conditions. The structure of 1 was determined by single-crystal X-ray diffraction, and further characterized by IR spectroscopy, UV–vis spectra and diffuse reflectance spectra. The absorption edge of 1 is largely red-shifted compared to the pure polyoxoanions, due to the introduction of the dye cations. Photocatalytic studies indicated that compound 1 exhibits effective photocatalytic H2 evolution activity under visible-light.

A visible-light-driven photocatalytic activity of vanadate garnet AgCa2Ni2V3O12 nanoparticles

A visible-light-driven photocatalyst of nanosized vanadate garnet AgCa2Ni2V3O12 was prepared by a modified Pechini method. The nanoparticles were characterized with the measurements such as X-ray powder diffraction (XRD) and structural refinements, scanning electron microscope (SEM), and UV–visible (UV–Vis) absorption spectrum. The sample has an efficient absorption in the UV–Vis light region with a narrow band-gap energy of 2.16 eV and an indirect allowed electronic transition. Besides, the photocatalysis of AgCa2Ni2V3O12 nanoparticles was evaluated by photo-degradation of methylene blue under visible-light irradiation, which shows excellent photocatalytic activity. The effective photocatalytic activity was discussed on the base of the garnet crystal structure such as the activated optical centers of Ni–O octahedron and V–O tetrahedral, highly distorted Ag–O dodecahedra, and long V–V distance in the lattices.

Photocatalytic ability of vanadate garnet Ca5Ni4(VO4)6 under visible-light irradiation

A new visible-light-driven photocatalyst was developed in a vanadate garnet Ca5Ni4(VO4)6. The particles were prepared by a modified Pechini method. The sample was characterized with measurements such as x-ray powder diffraction, scanning electron microscope, and UV–vis absorption spectrum. The photocatalytic activities of Ca5Ni4(VO4)6 particles were evaluated by photodegradation of methylene blue under visible-light irradiation in air. Ca5Ni4(VO4)6 shows photocatalytic activity due to an efficient absorption in the UV–visible light wavelength region with a narrowed band gap energy of 2.13 eV and an indirectly allowed electronic transition. These results indicate that this vanadate garnet could be a potential photocatalyst driven by visible-light. The effective photocatalytic activity was discussed on the base of the crystal structure, the photoluminescence and the decay lifetime. The photocatalytic ability of Ca5Ni4(VO4)6 is related to structure characteristics such as the regular and isolated VO4 tetrahedron, the optical centers of Ni–O octahedron, the low opportunity for the recombination of electron–hole pairs in the lattices.

Ultrasonic synthesis of high fluorescent C-dots and modified with CuWO4 nanocomposite for effective photocatalytic activity

High fluorescent C-dots were synthesized from dextrose via facile ultrasonic wave assisted reaction. Carbon dots (C-dots)/Copper tungstate (CuWO4) heterostructure has been prepared via a facile reflux approach. The novel C-dots/CuWO4 photocatalyst were characterized by using transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV–vis, photoluminescence and X-ray photoelectron spectroscopy. The photocatalytic property of heterostructure nanocomposite has also been investigated by using rhodamine B as a model organic pollutant. The obtained results revealed that as prepared C-dots are predominately multilayer graphene oxide with luminance properties. After incorporation of C-dots onto the CuWO4, it contributes to the improvement of charge separation and reduction of charge recombination and thereby enhancing the photocatalytic property, respectively. The C-dots in the nanocomposites can efficiently trap electrons, thus hindering the recombination of photogenerated electrons and holes. The heterostructure nanocomposite with 5.0 wt% C-dots shows the highest photocatalytic activity, which is about three times as that of pure CuWO4.

Preparation and photocatalytic properties of Bi2Zr2O7 photocatalyst

Bismuth zirconate complex oxides (Bi2Zr2O7) with various novel morphologies were successfully prepared via a facile sedimentation–calcination method. The structure, morphology, composition and light absorption properties were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance. The photocatalytic activity of Bi2Zr2O7 photocatalyst was tested in the reduction of methyl orange under solar light irradiation. The results showed that the prepared sample exhibited irregular morphology with features ranging from 20 to 50nm in size, had a direct band gap of 2.59eV and displayed effective photocatalytic activity under simulated solar irradiation.

Effect of processing variables on the photocatalytic properties of ZnO thin films prepared using the polymeric precursor method

The preparation of ZnO thin films using the polymeric precursor method is reported, and the influence of the thickness and calcination temperature on their effective photocatalytic activity was analyzed. The ZnO thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV–vis spectroscopy (UV-DRS), and atomic force microscopy (AFM). Thicker films with a lower calcination temperature exhibited better photoactivity for RhB photodegradation under UV irradiation. The average particle size increased from 14 to 45nm as the calcination temperature increased from 400 to 600°C. In addition, the stability results indicated no significant deactivation even after four successive re-uses in RhB photodegradation.

Optical properties and visible-light-driven photocatalytic activity of Bi8V2O17 nanoparticles

Bi8V2O17 (4Bi2O3·V2O5) nanoparticles with the uniform size of about 50 nm were fabricated through the Pechini method. The crystal structure was investigated by X-ray powder diffraction and the structural refinement. The surface of the as-synthesized samples was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy, and X-ray photoelectron spectroscopy. The optical properties, band structure, and the degradation mechanisms were discussed. The experimental results demonstrate that Bi8V2O17 nanoparticles have an efficient visible-light absorption with band-gap energy of 1.85 eV and a direct allowed electronic transition. The photocatalytic activity was evaluated by the photodegradation of the methylene blue (MB) under visible-light irradiation (λ > 420 nm) as a function of time. These results indicate that Bi8V2O17 could be a potential photocatalyst driven by visible light. The effective photocatalytic activity was discussed on the base of the crystal structure characteristic.

On structure and methylene blue degradation activity of an Aurivillius-type photocatalyst of Bi4V2O11 nanoparticles

Aurivillius-type photocatalyst of Bi4V2O11 nanoparticles with an average particle size of 45nm was prepared by the modified Pechini method. The sample was investigated by X-ray powder diffraction (XRD) and the structural refinement. The nanoparticles were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopic (XPS) and UV–vis absorption spectrum. Bi4V2O11 nanoparticles show an efficient absorption in the UV–vis light wavelength region with a narrowed band gap energy of 2.08eV and an indirect allowed electronic transition. The photocatalytic activities of Bi4V2O11 nanoparticles were evaluated by photodegradation of methylene blue (MB) under visible-light irradiation in air atmosphere. These results indicate that Bi4V2O11 could be a potential photocatalyst driven by visible-light. Hybridization of the 6s and 6p orbitals of Bi3+ and the resulting lone electron pair yields interesting properties. The effective photocatalytic activity was discussed on the base of the crystal structure characteristic such as polar (VO3.5□0.5)2− anionic groups, Aurivillius-type (Bi2O2)2+ layers and long distance of the nearest V–V in the lattices, etc.

Optical properties and visible light-driven photocatalytic activity of Bi11VO19 nanoparticles with δ-Bi2O3-structure

The δ-Bi2O3-structural Bi11VO19 nanoparticles with the average size of ∼70nm were fabricated through the Pechini method for a possible photocatalytic application. The crystal structure was investigated by X-ray powder diffraction (XRD) and the structural refinement. The as-synthesized sample was also characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), UV–vis spectroscopy and photoluminescence measurements. The experimental results demonstrate that Bi11VO19 nanoparticles have an efficient visible light absorption with band-gap energy of 2.23eV. The photocatalytic activity was evaluated by the photodegradation of the methylene blue (MB) under visible light irradiation (λ>420nm) as a function of time. All the results indicate that Bi11VO19 could be a potential photocatalyst driven by visible-light. The effective photocatalytic activity was discussed on the base of the crystal structure characteristic.