Synthesis of Cu2O nanocrystallites and their adsorption and photocatalysis behavior

Cuprous oxide (Cu₂O) nano-crystallites have been prepared via an electrochemical method by the anodic dissolution of copper in an alkaline solution of concentrated sodium chloride in a simple electrochemical cell. The effect of addition of glucose on the crystal size, structure and photocatalytic activity of Cu₂O particles was studied. Photocatalytic decolorization of MeO in aqueous Cu₂O suspensions was investigated. X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transformation infrared spectroscopy (FTIR) were used to characterize the samples. UV–vis Spectroscopy was employed to investigate the photocatalysis behavior of the Cu₂O samples. The adsorption performance of the Cu₂O samples showed that after adsorption of 2 h, the decolorization efficiencies of MO reached 11.81%, 95.24% and 56.53% for samples 1, 2 and 3, respectively, which proves that sample 2 has the highest adsorption capacity. The photocatalytic results showed that the as prepared Cu₂O on the addition of 5 g/L glucose was the best sample since it was photostable and decolorized 98.7% of MeO solution in 30 min without any further decrease in the photocatalytic efficiency with increase in the irradiation time for 120 min. Higher concentrations of glucose lead to the decrease of photocatalytic efficiencies of the Cu₂O particles.     

Electrochemical synthesis and photocatalytic property of cuprous oxide nanoparticles

Cuprous oxide (Cu₂O) nanoparticles of 35 nm in crystal size have been successfully synthesized via electrochemical method in alkali NaCl solutions with copper as electrodes and K₂Cr₂O₇ as additive. Photocatalytic degradation of methyl orange (MeO) in aqueous Cu₂O solution was investigated under either ultraviolet (UV) light or sunlight. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformation infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS) were introduced to characterize the samples. The results indicate that electric current shows no obvious effect on the growth of Cu₂O nanocrystals and that 97% of MeO can be decolorized under UV irradiation for 2 h or under sunlight for 3 h when amount of Cu₂O is 2 g/L. Recycling use of the catalyst revealed that Cu₂O still has a high photocatalytic efficiency when repeatedly used for four times. Cu₂O nanoparticles still kept its cubic crystal phase, but fractionally oxidized to be CuO after the photocatalysis. Compared with the original Cu₂O nanoparticles, there has 1 eV shift of Cu 2p electron and 1.6 eV shift of Cu Auger signals for the Cu₂O powders after four times photocatalysis. Some new peaks can also be observed at 401.1, 237.4 and 170.2 eV in the Cu₂O powders after photocatalysis.     

Morphology and phase selective synthesis of CuxO (x = 1, 2) nanostructures and their catalytic degradation activity

Cu_xO (x = 1, 2) nanocrystals have been synthesized by the composite-hydroxide-mediated approach. The obtained nanocrystals were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrum. The morphology of the nanocrystals changed from sphere-shaped nanostructures to flower-shaped nanostructures, and finally to nanowires associated with phase transformation from CuO to Cu₂O by increasing the temperature. The possible phase transformation mechanism was discussed. The catalytic degradation activity of the Cu_xO (x = 1, 2) nanocrystals to methyl orange was also investigated. The photocatalytic ability of the sphere-shaped nanostructures is much higher than that of the nanowires, owing to its absorption of wider range of light energy. This work provides a new facile synthesis route of Cu_xO (x = 1, 2) nanocrystals and suggests their possible application in organic pollutants removal.     

Preparation,characterization and photocatalytic properties of terbium orthoferrite nanopowder

Perovskite-type terbium orthoferrite (TbFeO₃) nanopowder was synthesized through a polyacrylamide gel route. The as-synthesized particles were characterized by XRD, TEM, BET surface area, UV–visible absorption spectroscopy, and XPS. It is shown that the particles are uniformly and regularly shaped like spheres with an average size of ～50 nm, and have a BET specific surface area of 15.4 m² g^?1. The optical energy bandgap of the nanosized TbFeO₃ is obtained to be 1.98 eV. The photocatalytic activity of the TbFeO₃ particles was evaluated by the photodegradation of various organic dyes including methyl orange (MO), rhodamine B (RhB), methylene blue (MB), acid fuchsine (AF), and congo red (CR). It is demonstrated that the product exhibits a pronounced photocatalytic degradation of the dyes under visible-light irradiation. The photocatalytic efficiency is observed to depend on the dye type, and under the present experimental conditions it follows the sequence: CR > AF > MB > RhB > MO.     

Synthesis of sea urchin-like cuprous oxide with hollow glass microspheres as cores and its preliminary application as a photocatalyst

Cuprous oxide (Cu₂O) microcrystals with sea urchin-like morphologies were successfully prepared on the surface of hollow glass microspheres (HGMs) using sodium sulfite (Na₂SO₃) as the reducing agent and sodium acetate–acetic acid (NaAc–HAc) as buffer solution in copper sulfate (CuSO₄) solution. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal-thermogravimetry (DTA-TG), and visible spectrophotometer. Based on the SEM images of the as-obtained samples, it was found that the HGMs played a crucial role in the formation of sea urchin-like Cu₂O. Meanwhile, the stirring time was also important for coating process. The as-prepared sea urchin-like microcrystals are cubic phase Cu₂O. The as-prepared products can be oxidized at 240 °C. The preliminary study on the photocatalytic behavior of the sea urchin-like Cu₂O showed that the photodegradation efficiency of 40 mg/L methyl orange (MO) reached 95.15% within 30 min.     

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (～7 nm) single-phase Cu₂ZnSnS₄ nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu₂ZnSnS₄ nanoparticles with the growth along (1 1 2) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu₂ZnSnS₄ nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ～1.72 eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu₂ZnSnS₄ nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu₂ZnSnS₄ nanoparticles is found to be 0.0144 min^?1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu₂ZnSnS₄ nanoparticles for the dye degradation is also demonstrated.     

Synthesis and characterization of novel magnetically separable NiFe2O4@AlMCM-41-Cu2O core-shell and its performance in removal of dye

The synthesis of magnetic NiFe₂O₄@AlMCM-41-Cu₂O core-shell as a new class of visible light driven photocatalyst was suggested. The magnetic NiFe₂O₄ core was prepared by solvothermal method. The intermediate AlMCM-41 shell was prepared by the method of liquid crystal templating mechanism and subsequently cuprous oxide (Cu₂O) nanoparticles (NPs) were synthesized in NiFe₂O₄@AlMCM-41core-shell via colloidal chemistry approach. The properties of prepared magnetic core-shell were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption–desorption measurement and vibration sample magnetometer (VSM). Based on EDX results, the weight percentage (wt%) of NiFe₂O₄ core, MCM-41 shell and Cu₂O NPs were calculated to be 68.89, 30.55 and 0.56%, respectively. It consisted of mesoporous structure with a surface area of 687.00 m² g^?1, an average pore size of 2.95 nm and possessed excellent magnetic properties of 4.74 emu g^?1. The TEM results indicated that the NiFe₂O₄ as core were regular spheres with diameter of 68 nm, and the average thickness of AlMCM-41 shells was ～35 nm. The particles size of Cu₂O incorporated in core-shell was less than 5 nm. The photocatalytic activity was evaluated under visible light irradiation using the removal of methylene blue (MB) dye as a model reaction. The removal rate of MB achieved up to 90% after 60 min under visible light irradiation, and the NiFe₂O₄@AlMCM-41-Cu₂O can be recycled and reused.     

Sol-gel synthesis,structural and enhanced photocatalytic performance of Al doped ZnO nanoparticles

In this research ZnO and Zn_1?x Al_xO (x = 1, 3, 5, 7% mol) nanoparticles were synthesized by sol-gel method. The effect of Al concentration on the structure, morphology, absorption spectra and photocatalytic properties investigated by using X-ray, TEM, EDS and UV–Vis spectrophotometer approaches. Hexagonal, spherical and rod-like structure was achieved as the dominant structure for undoped nanoparticles, low and high concentrations of doped Al, respectively. Photocatalytic activity of nanoparticles was measured by degradation of methyl orange as a pollutant under radiation of ultraviolet (UV). The experimental test results indicate that the best photocatalytic performance is at of 5% of Al. Furthermore, the doped ZnO nanoparticles have more activity in visible area compared with undoped nanoparticles. The absorption amount in this area increases by raising the Al concentrations. Furthermore, the band gap of the particles decreases from 3.22 eV to 2.93 eV by increasing Al percentage.     

Photocatalytic behavior of TiO2 nanoparticles supported on porous aluminosilicate surface modified by cationic surfactant

In order to utilize the photocatalytic function of TiO₂ nanoparticles in materials manufactured from organic polymeric compounds, such as paper, resins, and textiles, TiO₂ nanoparticles supported on aluminosilicate, which contained 1, 5, and 10 wt% of TiO₂ were prepared by mixing commercial TiO₂ nanoparticles and porous aluminosilicate at pH 7 in a cationic surfactant aqueous solution. Most of the supported TiO₂ nanoparticles on the aluminosilicate surface were observed by TEM–EDS (energy depressive X-ray spectroscopy) analysis. TiO₂ nanoparticles supported on aluminosilicate reduced the formaldehyde concentration from 20 to 0 ppm after UV irradiation for 20 h; the reduction of formaldehyde concentration under UV irradiation was obviously different from that in the dark. Moreover, a paper mixed with 20 wt% of TiO₂ nanoparticles supported on aluminosilicate bleached the stains colored with cigarette tar after UV irradiation for 6 h. However, the paper maintained its initial tensile strength even after UV irradiation for 1 year; in contrast, the paper mixed with a simple dry mixture of TiO₂ powder and aluminosilicate lost approximately half of its initial tensile strength after a year. TiO₂ nanoparticles supported on aluminosilicate could exhibit photocatalytic activity without decomposing the organic polymeric compounds.     

Photocatalytic degradation of reactive brilliant blue X-BR in aqueous solution using quantum-sized ZnO

Quantum-sized ZnO was prepared using sol–gel method with zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O) and lithium hydroxide monohydrate (LiOH·H₂O) as raw material. The ZnO particles annealed at different temperature were characterized by means of X-ray diffraction (XRD), Infrared absorption spectroscopy (IR) and UV–vis spectroscopy. The degradation rate of reactive brilliant blue X-BR in aqueous solution was used to evaluate the photocatalytic performance of the quantum-sized ZnO. The experimental results indicated that the photocatalytic property of the ZnO was excellent. The photocatalytic efficiency of quantum-sized ZnO was significantly influenced by the calcining heat. When calcined at 300 °C, its size is 6.78 nm and the photocatalytic performance is the best. The degradation rate of reactive brilliant blue X-BR could exceed 90% in 15 min at 35 °C, when the concentration of the quantum-sized ZnO was 0.35 mg/L.     

Effects of aluminum substitution on photocatalytic property of BiVO4 under visible light irradiation

Novel visible-light-driven Al/BiVO₄ photocatalysts were synthesized via a facile hydrothermal method for the first time. The samples were characterized by X-ray diffraction, N₂-sorption, UV–vis diffuse reflectance spectra, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transformed infrared spectra and X-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of methylene blue under visible light irradiation (400 nm < λ <580 nm) and was compared with that of single-phase BiVO₄. The results revealed that the introduction of Al can improve photocatalytic performance greatly and different concentration of Al resulted in different photocatalytic activity. The highest activity is obtained by the sample with a doping concentration of 12 at%. The reason for the enhanced photocatalytic activities of Al/BiVO₄ samples was also discussed in this paper.     

Preparation and properties of ce-doped TiO2 photocatalyst

TiO₂ nanoparticles doped with different content of Ce ion were prepared by sol–gel method. The samples were characterized by XRD, XPS, TEM, UV–Vis, and PL, the photocatalytic activity was evaluated by photocatalytic degradation of methylene blue (MB) under the irradiation of fluorescent lamp. The results indicate that Ce ion is incorporated into the lattice of TiO₂, which can restrain the increase of grain size, broaden the absorption region to visible light, and inhibit the recombination of the photo-generated electron and hole pairs. Moreover, the photocatalytic activity of Ce-TiO₂ in MB degradation is evidently enhanced. The MB degradation rate of the sample with Ce:Ti = 0.33% (molar ratio) in 8 h is 90.03%, which is much higher than that of P25 (68.19%).     

Synthesis of heterostructured In2O3/BiOCl powders and their visible-light-driven photocatalytic activity for the degradation of Rhodamine B

Heterostructured In₂O₃/BiOCl powders were synthesized by chemical coprecipitation method at room temperature followed by thermal treatment at 400 °C for 2 h. The TEM results confirmed the formation of sheet-like BiOCl nanostructures with the thickness of ca. 5–7 nm. In order to investigate the effect of In₂O₃ on the photocatalytic activity of heterostructured powders, the amount of In₂O₃ was varied from 0 wt% to 14 wt%. Adsorption and photocatalytic activity of the samples were evaluated for the degradation of Rhodamine B (RhB) in the dark and under visible light irradiation, respectively. The heterostructured In₂O₃/BiOCl powders showed high adsorption capacity and enhanced photocatalytic activity compared to P25 and pure BiOCl. Based on the results obtained in this study, the mechanism for the enhancement of photocatalytic activity of heterostructured In₂O₃/BiOCl powders is discussed. 10 wt% In₂O₃/BiOCl composite also exhibited good cycle performance for the degradation of RhB under visible light irradiation.     

Solvent-free synthesis of Cu-Cu2O nanocomposites via green thermal decomposition route using novel precursor and investigation of its photocatalytic activity

In the present study, Cu-Cu₂O binary nanocomposites were successfully synthesized through a one-pot, cost-effective and green thermal decomposition route using PMP-Cu(II), extracted from pomegranate marc peels (PMP) by Cu(II), as a novel starting reagent for the first time. The morphology, crystalline structure, and composition of as-prepared Cu-Cu₂O nanocomposites were extensively characterized by SEM, XRD, EDS and HRTEM. Effect of reaction parameters such as time, temperature and precursor type on product composition and morphology was evaluated. Moreover, methylene blue (MB) was used as a model of organic dye pollutant and photodegradation experiments were conducted by UV-vis spectrophotometry. The as-synthesized Cu-Cu₂O binary nanocomposites demonstrated their potential as an excellent photocatalyst for degradation of MB under visible-light irradiation and Cu-Cu₂O photocatalyst with higher content of Cu₂O (prepared in air) exhibits the highest photocatalytic efficiency (～99% degradation of MB in <150 min).     

Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst

TiO₂ photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO₂ in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO₂ = 0.05 at%, N:TiO₂ = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%).     

BiOBr photocatalyst with high activity for NOx elimination

Bismuth oxybromide (BiOBr) was synthesized in aqueous medium in presence of EDTA as structure-directing agent following a simple coprecipitation method at 23 °C and by microwave irradiation at 110 °C. The physicochemical properties of BiOBr (morphology, specific surface area, energy band gap and photocatalytic activity) were modified using different EDTA concentrations. Nanoparticles of BiOBr with {1 1 0} crystallographic exposed facets were obtained as a peculiar feature of the synthesis followed. The photocatalytic activity of BiOBr was evaluated in the oxidation reaction of nitric oxide (NO) in gaseous phase under UV–Vis and visible irradiation. An enhancement in the NO conversion degree was reached for BiOBr synthesized by coprecipitation with an EDTA/Bi molar ratio of 0.6. This sample showed a NO conversion degree of 94%, a selectivity to nitrate ions of 98%, a good stability after four cycles of irradiation and sample was able to retain its high photocatalytic activity under humidity conditions (70% RH). The use of different chemical scavengers revealed that superoxide radical (O₂^•-) was the main reactive specie in the mechanism of the photocatalytic reaction. BiOBr photocatalyst was successfully incorporated in two formulations of ceramic coatings to develop prototypes of building materials with active surface for the photocatalytic elimination of NO_x gases from the air.     

Microwave-assisted synthesis and highly photocatalytic activity of MWCNT/ZnSe heterostructures

The multi-walled carbon nanotubes (MWCNTs) coated with the face-center cubic ZnSe nanoparticles with a uniform and small diameter have been prepared to form MWCNT/ZnSe heterostructures by microwave irradiation. The morphology, loading quantity and size of the ZnSe nanoparticles in the range of 15–50 nm can be controlled easily by adjusting the microwave power, pH value of the initial solution, the molar ratios of the Zn(AC)₂/MWCNTs and the appropriate complexing agent. The photoluminescence measurement indicates that the MWCNT/ZnSe heterostructures are blue-shifted compared to reported bulk ZnSe. The UV–vis absorption spectra of the heterostructures appears two sharp absorption peaks at 336 and 344 nm, respectively. It was demonstrated that the heterostructures could photodegrade the fuchsine acid in the solution with highly photocatalytic activity.     

Photocatalytic degradation of an azo dye using Bi3.25M0.75Ti3O12 nanowires (M = La,Sm, Nd,and Eu)

Bi_3.25M_0.75Ti₃O₁₂ (BMT, M = La, Sm, Nd, and Eu) nanowires were synthesized through simple hydrothermal route and their structural and photocatalytic properties were investigated. XRD results indicated that these compounds are of layered perovskites structure. In addition, the band gaps of Bi_3.25La_0.75Ti₃O₁₂ (BLT), Bi_3.25Sm_0.75Ti₃O₁₂ (BST), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT), and Bi_3.25Eu_0.75Ti₃O₁₂ (BET) were estimated to be about 2.403, 2.594, 2.525, and 2.335 eV, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Bi_3.25M_0.75Ti₃O₁₂ (M = La, Sm, Nd, and Eu) showed markedly higher catalytic activity compared to traditional N doped TiO₂ (N-TiO₂) and pure bismuth titanate (Bi₄Ti₃O₁₂, BIT) for MO photocatalytic degradation under visible light irradiation. The high photocatalytic performance of Bi_3.25M_0.75Ti₃O₁₂ photocatalysts could be attributed to the strong visible light absorption and the recombination restraint of the e^?/h⁺ pairs resulting from doping of rare earth metal ions. Furthermore, BET nanowires exhibited the highest photocatalytic activity.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Preparation and visible-light photocatalytic activity of Au-supported porous CeO2 spherical particles using templating

Porous spherical CeO₂ particles were prepared by impregnation of a cerium precursor solution into organic monolith sphere particles, with subsequent firing at 500 °C in air. The single-phase CeO₂ powder had specific surface area of greater than 140 m²/g. Photodeposition with UV illumination loaded Au onto the CeO₂ particle surface, which changed from yellowish to purple because of localized surface plasmon resonance (LSPR). The Au-loading increased photocatalytic decomposition activity of the CeO₂ powder for gaseous 2-propanol (IPA) under visible light. Thermal desorption of IPA, which was adsorbed to all porous spheres, provided flux to the photocatalytic reaction field of the sphere outer surface.