Matching Band Potentials Research Articles

Novel Bi2O3/NaBi(MoO4)2 heterojunction with enhanced photocatalytic activity under visible light irradiation

A novel Bi2O3/NaBi(MoO4)2 composite photocatalyst with nanostructured heterojunctions was prepared via a simple supercritical method. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–vis diffuse reflectance spectroscopy (DRS). The visible light-induced photocatalytic activities were evaluated. The activity of the composite catalyst was 5 and 13 times as much as that of pure NaBi(MoO4)2 and commercial Bi2O3, respectively. The catalyst could be reused more than five times without obvious deactivation. The enhanced photocatalytic performance was attributed to electric-field-assisted charge transfer at the heterojunction interfaces between Bi2O3 and NaBi(MoO4)2 with matching band potentials, which consequently favored an effective photoexcited electron and hole separation.

Microwave-assisted synthesis of Ag@AgBr-intercalated K4Nb6O17 composite and enhanced photocatalytic degradation of Rhodamine B under visible light

In this paper, a novel plasmonic photocatalyst, Ag@AgBr-intercalated layered niobate (denoted as K4Nb6O17/Ag@AgBr), was synthesized via a microwave-assisted ion-exchange method. The composite materials prepared were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflection spectra (UV–vis), photoluminescence (PL), X-ray fluorescence spectrometry (XRF) and X-ray photoelectron spectroscopy (XPS). The as-prepared plasmonic photocatalyst exhibited an enhanced and stable photoactivity for the degradation of Rhodamine B (RhB) under visible light irradiation. The high activity observed was attributed to the synergistic effect of surface plasmon resonance (SPR) exhibited by Ag nanoparticles on the surface of AgBr, absorption by AgBr itself, as well as the electron-hole pair separation derived from the matching band potentials between Ag@AgBr and K4Nb6O17. Photocatalytic reaction parameters, such as catalyst dosage, initial concentration of RhB, and solution pH were investigated. The mechanism of separation of the photo-generated electrons and holes at the K4Nb6O17/Ag@AgBr composite was discussed.

Effect of key operational factors on decolorization of methyl orange by multi-walled carbon nanotubes (MWCNTs)/TiO2/CdS composite under simulated solar light irradiation

Abstract To improve the photocatalytic performance of TiO2, a novel composite of TiO2/CdS nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) was prepared by a sol–gel method. This photocatalyst exhibited a strong photocatalytic activity for the decomposition of methyl orange (MO) in aqueous solution under simulated solar irradiation. The effects of key operational parameters, such as the initial MO concentration, initial pH values, catalyst dosage and the amount of additional H2O2, were systematically studied. The presence of all the anions examined (Cl−, NO 3 − , SO 4 2 − , CO 3 2 − and PO 4 3 − ) had an inhibitory effect on the decolorization of MO. The photocatalyst had good stability, as when it was used for the fifth time, the decolorization efficiency was still about 98.7% after 80 min of irradiation. The simultaneous application of simulated solar and ultrasound irradiation resulted in increased decolorization compared to that achieved by photocatalysis alone. Possible decomposition mechanisms are discussed. The enhanced photocatalytic performance might be attributable to the matched band potentials and the electron transfer between CdS and TiO2 semiconductors. These results showed that the MWCNTs/TiO2/CdS composite prepared in this study was effective and feasible for use in the decolorization of dye-containing wastewater.

Facile Synthesis of the Novel Ag3VO4/AgBr/Ag Plasmonic Photocatalyst with Enhanced Photocatalytic Activity and Stability

A novel ternary plasmonic Ag3VO4/AgBr/Ag hybrid photocatalyst was successfully fabricated via an in situ anion-exchange reaction between Ag3VO4 and KBr, followed by light reduction. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, UV–visible diffuse-reflectance spectroscopy (UV–vis DRS), and X-ray photoelectron spectroscopy. The photocatalytic activities of obtained photocatalysts were measured by the degradation of Rhodamine B and methylene blue under visible-light irradiation (λ ≥ 400 nm). As-prepared Ag3VO4/AgBr/Ag plasmonic photocatalysts exhibit wide absorption in the visible-light region and display superior visible-light-driven photocatalytic activities in degradation of organic contamination compared with pristine Ag3VO4, Ag3VO4/AgBr, and AgBr/Ag. This enhanced photocatalytic activity is attributed to the synergistic effects between Ag3VO4/AgBr-based heterostructured semiconductor photocatalysis and the surface plasmon resonance (SPR) of Ag nanoparticles (NPs). On the basis of UV–vis DRS and valence band X-ray photoelectron spectroscopy, a possible mechanism of enhanced photocatalytic activity of Ag3VO4/AgBr/Ag is proposed; the vectorial electron transfer driven by the matching band potentials of AgBr and Ag3VO4 and the SPR of Ag NPs contribute to its high photocatalytic activity and the improved stability. Therefore, the present study provides helpful insight into the design of novel and highly efficient visible-light photocatalysts in the future.

Carbon nanofibers decorated with binary semiconductor (TiO2/ZnO) nanocomposites for the effective removal of organic pollutants and the enhancement of antibacterial activities

Abstract A novel photocatalytic and antibacterial carbon nanofiber decorated with TiO 2/ ZnO composite NPs was prepared by a simple electrospinning method followed by calcination and hydrothermal treatment. The loading of a small amount of ZnO NPs throughout the fibers prior to electrospinning could provide nucleation sites for the crystal growth of ZnO from its precursor during hydrothermal synthesis and could effectively hold TiO 2 /ZnO particles on the surface of the fibers for better stability. The morphology and structure of the as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, which revealed that TiO 2 /ZnO NPs were attached on the surface of the carbon nanofibers. The as-synthesized nanocomposite exhibited a strong photocatalytic activity for the decomposition of methylene blue (MB) under UV irradiation and showed good antibacterial properties as well. The enhanced photocatalytic performance of the developed nanocomposite can be attributed to the adsorption characteristic of carbon nanofiber and the matched band potentials of TiO 2 and ZnO. The perfect recovery of the catalyst after the reaction and its unchanged efficiency for cyclic use showed that it will be an economical and environmentally friendly photocatalyst.

Synthesis of Copper Hydroxide and Oxide Nanostructures via Anodization Technique for Efficient Photocatalytic Application

We have demonstrated a facile protocol for synthesizing CuO and Cu2O mixed-phase nanostructures by anodization of copper hydroxide (Cu(OH)2) nanoneedles and their heat treatment in different atmospheres, which affect photocatalytic degradation efficiency. The oxygen annealed sample had relatively small (100 nm) lamellar, spherical nanoparticulate structures on the substrate surface, which showed better photocatalytic degradation of reactive black 5 dye resulting from the appropriate morphology and phase formation, compared to the samples annealed in different atmospheres and vacuum. The pseudo first-order rate constant (k) of the oxygen annealed sample was 0.0054/min, which was relatively high due to the formation of a CuO-Cu2O heterojunction with matching band potentials. Air, nitrogen, argon and vacuum annealing resulted in bigger particles and different morphologies, which led to pseudo first-order rate constants (k) of 0.0032/min (air-annealed); 0.0021/min (N2-annealed); 0.0033/min (Ar-annealed); and 0.0027/min (vacuum-annealed), which resulted in poor photocatalytic degradation of the reactive black 5 dye.

Cadmium sulphide quantum dots sensitized hierarchical bismuth oxybromide microsphere with highly efficient photocatalytic activity

Cadmium sulphide (CdS) quantum dots (QDs) sensitized that hierarchical bismuth oxybromide (BiOBr) photocatalysts were synthesized via a facile solvothermal approach for the first time, which were characterized by XRD, XPS, SEM, TEM, PL, and UV–vis DRS spectra. The photocatalytic activities were evaluated by the decomposition of methyl orange (MO) under visible light irradiation with commercial TiO2 Degussa P25 as reference. The results revealed that CdS–BiOBr photocatalysts had strong light absorption in the visible light region compared with pure BiOBr. All CdS–BiOBr photocatalysts possessed higher photocatalytic activity than pure BiOBr and Degussa P25 under the visible light irradiation. The highest activity was obtained by 2%CdS–BiOBr. The enhanced photocatalytic performances were attributed to the matched band potentials of CdS QDs and BiOBr, which resulted in the efficient separation of photogenerated electron–hole pairs. Based on the experimental results, a reasonable photocatalytic mechanism over CdS–BiOBr photocatalysts was proposed. And the photodegradation of MO are associated with O2- radicals and the photogenerated holes on the valance bands of CdS QDs and BiOBr.

Synthesis of LaVO4/TiO2 heterojunction nanotubes by sol–gel coupled with hydrothermal method for photocatalytic air purification

With the aim of improving the effective utilization of visible light, the LaVO4/TiO2 heterojunction nanotubes were fabricated by sol–gel coupled with hydrothermal method. The photocatalytic ability was demonstrated through catalytic removal of gaseous toluene species. The nanotube samples were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), surface photovoltage (SPV), Raman spectra and N2 adsorption–desorption measurements. The characterization results showed that the samples with high specific surface areas were of typical nanotubular morphology, which would lead to the high separation and transfer efficiency of photo induced electron–hole pairs. The as-prepared nanotubes exhibited high photocatalytic activity in decomposing toluene species under visible light irradiation with fine photochemical stability. The enhanced photocatalytic performance of LaVO4/TiO2 nanotubes might be attributed to the matching band potentials, the interconnected heterojunction of LaVO4 versus TiO2, and the large specific surface areas of nanotubes.

New insights into the relationship between photocatalytic activity and photocurrent of TiO2/WO3 nanocomposite

The photocurrent has been regarded as the most efficient method to evaluate the photocatalytic activity of composite photocatalyst. A relationship is commonly recognized: the higher the photocurrent is, the higher the e−–h+ separation efficiency is, and thus the higher the photocatalytic activity is. In this paper, we use the TiO2/WO3 composite as a model heterojunction system to argue about this viewpoint, and try to explore a more comprehensive relationship. Our research reveals that there is no direct relation between photocurrent, charge separation efficiency and photocatalytic activity. It is shown that the photocurrent combined with the carrier mobility is essential in the analysis of the charge separation efficiency. In addition, the charge separation efficiency cannot be responsible for the photocatalytic activity, since it does not include the information on the redox ability of the charge carrier. It is confirmed that the photocatalytic activity which is a pluralistic concept includes three levels of degradation efficiency, initial reaction rate and mineralization ability. The difference in each level is determined by the band structures, the matched band potentials and the target pollutants. Therefore, we also propose that the introduction of pollutant ambience is needed in photocurrent test. The ratio of photocurrent in air to that in pollutant ambience can be used as an index to evaluate the initial reaction rate of photocatalytic activity.

Visible light photocatalytic activity enhancement and mechanism of AgBr/Ag3PO4 hybrids for degradation of methyl orange

Novel AgBr/Ag3PO4 hybrids were synthesized via an in situ anion-exchange method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). Under visible light (λ>420nm), AgBr/Ag3PO4 degraded methyl orange (MO) efficiently and displayed much higher photocatalytic activity than that of pure AgBr or Ag3PO4. X-ray photoelectron spectroscopy (XPS) suggests that AgBr/Ag3PO4 transformed to be Ag@AgBr/Ag3PO4@Ag system while remained good photocatalytic activity after 5 times of cycle experiments. In addition, the quenching effects of different scavengers proved that reactive OH and h+ played the major role for the MO degradation. The photocatalytic activity enhancement of AgBr/Ag3PO4 is closely related to the efficient separation of electron–hole pairs derived from the matching band potentials between AgBr and Ag3PO4, as well as the good electron trapping role of Ag nanoparticles in situ formed on the surfaces of AgBr and Ag3PO4 particles during the photocatalytic reaction.

Synthesis, characterization and photocatalytic activity of AgBr/H 2WO 4 composite photocatalyst

A new composite photocatalyst AgBr/H 2WO 4 was prepared by loading H 2WO 4 on AgBr substrate via deposition–precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). Photocatalytic degradation of methyl orange (MO) and rhodamine B (RhB) was carried out to evaluate the photocatalytic activity of AgBr/H 2WO 4 under visible-light irradiation ( λ > 420 nm). The photocatalytic results show that the AgBr/H 2WO 4 composite could degrade MO and RhB efficiently and had much higher photocatalytic activity than AgBr or H 2WO 4. X-ray photoelectron spectroscopy (XPS) suggests that AgBr/H 2WO 4 transformed to be Ag/AgBr/H 2WO 4 system while remained good photocatalytic activity after 5 times of cycle experiments. In addition, the quenching effect was examined in the photocatalytic reaction process of MO and RhB, respectively. Active h +, Br 0 and the resulting O 2 − played the major roles for the dye degradation while OH was verified to be insignificant. The high photocatalytic activity and good stability are closely related to the efficient electron–hole pairs separation derived from the matching band potentials between AgBr and H 2WO 4, as well as the surface plasmon resonance of Ag nanoparticles formed on AgBr particles during the photocatalytic reaction process.

Synthesis, characterization and photocatalytic performance of VDyO x composite under visible light irradiation

A VDyO x (V 2O 5/DyVO 4) composite photocatalyst was prepared using a simple solution method. The powders were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Visible light-induced photocatalytic activities of the powders were evaluated by the degradation of acetone. Results generally show that the binary semiconductors V 2O 5/DyVO 4 with matching band potentials exhibit better photocatalytic properties compared with those of the single phase V 2O 5 or DyVO 4. An acetone conversion of 91.6% was achieved over V 1.5Dy 1O x composite photocatalyst under visible light irradiation. Effective electron–hole separation in the two semiconductors is believed to be mainly responsible for the increased photocatalytic performance of composites. The performance of the VDyO x composite catalyst can be further improved by loading a small amount of Pt. In addition, the Pt doped V 1.5Dy 1O x catalyst was also proven to be efficient in the photodegradation of 2-propanol and benzene.

Preparation and photocatalytic properties of CdS/La 2Ti 2O 7 nanocomposites under visible light

A novel CdS/La 2Ti 2O 7 nanocomposite photocatalyst working under visible light was prepared by a simple sonochemical coupled method. The catalyst was characterized by powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy. The nanocomposite exhibited a strong photocatalytic activity for decomposition of methyl orange (MO) under UV and visible light irradiation. Moreover, the nanocomposite with La/Cd = 1:3 shows the highest photocatalytic activity. The enhanced photocatalytic performance might be attributed to the layered structure of CdS/La 2Ti 2O 7 nanocomposites and the matched band potentials of the two semiconductors.

Efficient Degradation of Benzene over LaVO4/TiO2 Nanocrystalline Heterojunction Photocatalyst under Visible Light Irradiation

A nanocrystal heterojunction LaVO4TiO2 visible light photocatalyst has been successfully prepared by a simple coupled method. The catalyst was characterized by powder X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectra, photoluminescence, and electrochemistry technology.The results showed that the prepared nanocomposite catalysts exhibited strong photocatalytic activity for decomposition of benzene under visible light irradiation with high photochemical stability. The enhanced photocatalytic performance of LaVO4/TiO2 may be attributed to not only the matched band potentials but also interconnected heterojunction of LaVO4 and TiO2 nanoparticles.

Preparation and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst SnS x/TiO 2

Visible-light-responsive composite photocatalysts SnS 2/TiO 2 and SnS/TiO 2 with different mass ratios were prepared by in-situ synthesis technology in solution with commercial TiO 2. The junction-based materials SnS x ( x=1, 2)/TiO 2 were found to have high visible-light photocatalytic performance and possess much better activity than the single-phase SnS x or TiO 2. The greatly enhanced photocatalytic activity of the SnS x /TiO 2 composites was mainly attributed to the matching band potentials and efficient charge transfer and separation at the tight-bonding interface between SnS x and TiO 2. The fact was confirmed by the comparison of photocatalytic activities of the SnS 2/TiO 2 samples prepared by physical mixing method and in-situ synthesis technique.

Heterojunction semiconductor SnO 2/SrNb 2O 6 with an enhanced photocatalytic activity: The significance of chemically bonded interface

Heterojunction photocatalysts SnO 2/SrNb 2O 6 were synthesized by a milling–annealing technique. The powders were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflection spectroscopy (DRS). Their UV-induced photocatalytic activities were evaluated by the degradation of methyl orange and methylene blue. The results generally show that the binary semiconductors SnO 2/SrNb 2O 6, with matching band potentials, exhibit better photocatalytic properties than the single phase SrNb 2O 6 or SnO 2. The effective electron–hole separation both at the chemically bonded interface and in the two semiconductors is believed to be mainly responsible for the increased photocatalytic performance of composites. The formation of chemically bonded interfaces between SnO 2 and SrNb 2O 6 particles makes the interparticle charge transfer more spatially available and smoother, which is significant to enhance the photocatalytic activity.

Photocatalytic Activities of Heterojunction Semiconductors Bi2O3/BaTiO3: A Strategy for the Design of Efficient Combined Photocatalysts

The heterojunction semiconductors Bi2O3/BaTiO3 were prepared by a milling-annealing method. The powders were characterized by X-ray diffraction (XRD), the Brunauer−Emmett−Teller (BET) method, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and UV−vis diffuse reflection spectroscopy (DRS). Their UV-induced photocatalytic activities were evaluated by the degradations of methyl orange and methylene blue. The results generally show that the heterojunction semiconductors Bi2O3/BaTiO3 exhibit better photocatalytic properties than the single-phase BaTiO3 or Bi2O3. The obviously increased performance of Bi2O3/BaTiO3 is ascribed mainly to the electric-field-driven electron−hole separations both at the interface and in the semiconductors. A strategy for the design of efficient heterojunction photocatalysts was proposed. That is, an electron-accepting semiconductor and a hole-accepting semiconductor with matching band potentials, which respectively possess high electron and hole c...