Photocatalytic Performance of Nitrogen‐Doped and Cu2+ and Ag+ Co‐Doped Sodium Trititanate

Nano‐sized (i) N‐doped sodium trititanate and (ii) N and Cu²⁺ (Ag⁺) co‐doped sodium trititanates CuTi₃NO_6?x (Ag₂Ti₃NO_6?x) were prepared by a solid‐state and ion‐exchange methods, respectively. The materials were characterized by EDS, PXRD, XPS, FESEM, TEM, UV–visible DRS, and Raman spectroscopy. All the materials were crystallized in monoclinic lattice with P21/m space group. The bandgap energy of all the samples was deduced from their UV–visible DRS profiles. Visible‐light‐induced photocatalytic oxidation of the methylene blue (MB) and methyl orange (MO), cyclohexene and phenol, was examined. The Ag⁺ co‐doped trititanate exhibited the highest photocatalytic activity among the materials investigated.     

Low‐Temperature Dielectric Relaxations Associated with Mixed‐Valent Structure in Na0.5Bi0.5Cu3Ti4O12

We, herein, present comparative investigations on the Na_0.5Bi_0.5Cu₃Ti₄O₁₂ ceramic samples with and without 10 mol% excess of Na/Bi. The samples were prepared by the standard solid‐state reaction technique. The dielectric properties of the sample were investigated in the temperature (93–320 K) and frequency (20 Hz–10 MHz) windows. Three thermally activated dielectric relaxations observed in Na_0.5Bi_0.5Cu₃Ti₄O₁₂ with the activation energies of 0.104, 0.267, and 0.365 eV for the low‐, middle‐, and high‐temperature dielectric relaxations, respectively. Only the low‐temperature relaxation was observed in both Na and Bi excessive samples. X‐ray photoemission spectroscopy results revealed the mixed‐valent structures of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in Na_0.5Bi_0.5Cu₃Ti₄O₁₂ sample, but only Ti³⁺/Ti⁴⁺ in Na and Bi excessive samples. Our results showed that the dielectric properties of the investigated samples are strongly linked with these mixed‐valent structures. The high‐ and low‐temperature relaxations were attributed to be a polaron‐type relaxation due to localized carriers hopping between Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺, respectively. The middle‐temperature relaxation is suggested to be a dipole‐type relaxation caused by the defect complex of bismuth and oxygen vacancies.     

Facile Synthesis of BiOBr/Bi2Sn2O7 Heterojunction Photocatalysts with Improved Photocatalytic Activities

BiOBr/Bi₂Sn₂O₇ heterojunction photocatalysts were successfully synthesized by treating hydrothermal as‐prepared Bi₂Sn₂O₇ nanoparticles with hydrobromic acid (HBr). Partial Bi₂Sn₂O₇ nanoparticles reacted with HBr to form the sheet‐like BiOBr, and Bi₂Sn₂O₇ nanoparticles distributed evenly on BiOBr sheets. BiOBr/Bi₂Sn₂O₇ photocatalysts treated with different concentrations of HBr solution were successfully obtained, and their structures, morphologies, optical, and visible light photocatalytic properties were characterized by XRD, DRS, PL, SEM, and TEM. The experimental results showed that the BiOBr/Bi₂Sn₂O₇ photocatalysts showed improved photocatalytic activity under visible light irradiation than pure Bi₂Sn₂O₇. The sample treated with 0.08 mol/L HBr solution shows the best visible light photodegradation performance of rhodamine B. In addition, the active species and photocatalytic mechanism were discussed in detail.     

Mn1-xCuxO2/ reduced graphene oxide nanocomposites: Synthesis,characterization, and evaluation of visible light mediated catalytic studies

The narrow optical band gap, higher electrical conductivity, and wider-absorption range are three key features that a good photocatalyst must possess. Herein, we have fabricated Cu-doped MnO₂ (Mn_1-xCu_xO₂) nanostructure by facile wet chemical approach and formed its nanocomposite with r-GO (Mn_1-xCu_xO₂/r-GO) via ultra-sonication approach. The successful replacement of host metal ions (Mn⁴⁺) with the dopant metal ions (Cu²⁺) was supported with the PXRD, FT-IR, and EDX characterizations. The effect of Cu-doping on the band gap and r-GO matrix on the conductivity of the fabricated nanocomposite was also evaluated via Tauc plots and I–V tests, respectively. The photocatalytic efficiency of the fabricated photocatalysts was tested and compared against the methylene blue (MB) under visible light irradiation. The photocatalytic experiments revealed that Mn_1-xCu_xO₂/r-GO photocatalyst exhibited superior photocatalytic aptitude than that of pristine MnO₂ and Mn_1-xCu_xO₂ photocatalysts. More precisely, the Mn_1-xCu_xO₂ photocatalysts degraded 86.89% MB dye at the rate of 0.021 min^?1 after a 90-min exposure to the visible light. Observed superior catalytic activity of the nanocomposite can be attributed to the synergistic effects between the Cu doped MnO₂ and r-GO nanosheets that resulted in its narrow band-gap (2.19 eV) and excellent conductivity (2.217 × 10^?2 Scm^?1).     

Role of defect structures in stabilization of ferroelectric phase in tin‐substituted lead zirconate titanate

This study reports the influence of B‐site acceptor dopants, manganese and copper, on the sequence of phase transformations in antiferroelectric (AFE) Pb(Zr_0.60Sn_0.30Ti_0.10)O₃. The sequence of phase transformations below the Curie point have been examined by dielectric, polarization‐electric field and strain‐electric field studies. The parent compound and B‐site Cu²⁺‐doped composition exhibit the same sequence, FE ← AFE ← MCC with incommensuration in the multicell cubic (MCC) state, whereas in the case of B‐site Mn³⁺‐doped system, incommensuration is found to be suppressed and only ferroelectric (FE) phase is observed below the Curie point. The underlying mechanism is related to the nature of defect complexes present in the system through detailed Electron Paramagnetic Resonance studies.     

Synthesis of novel p-n heterojunction Cu2SnS3/Ti3+-TiO2 for the complete tetracycline degradation in few minutes and photocatalytic activity under simulated solar irradiation

In this research work, p-n heterojunction Cu₂SnS₃/Ti³⁺-TiO₂ photocatalysts were synthesized by using a facile hydrothermal method to degrade tetracycline and produce hydrogen energy. The properties of Cu₂SnS₃/Ti³⁺-TiO₂ was analyzed by using XRD, SEM, TEM, HRTEM, BET, PL and UV–vis characterization. The HPLC-MS and TOC analyzer systems were used to analyze the intermediate products during the photocatalysis deprivation and total organic carbon. The characterizations showed that the addition of self-doped Ti³⁺ and Cu₂SnS₃ into TiO₂ enhanced the material's crystallinity, increased the absorption region from 450 nm to 750 nm, increased the surface area of the material from 234 to 583 m²/g and reduced the recombination of charge carriers. Under visible light irradiation, Cu₂SnS₃/Ti³⁺-TiO₂ exhibited excellent degradation performance and stability. The increase in the efficiency of the material is due to the creation of an internal electric field induced by the p-n heterojunction and reduction in the bandgap of the material, which efficiently reduced the rate of recombination, increased the surface area for light absorption and increased the transfer of charge carriers. The Cu₂SnS₃/Ti³⁺-TiO₂ photocatalyst degraded 100 % tetracycline and produced 510 μmol/hg hydrogen energy. The Cu₂SnS₃/Ti³⁺-TiO₂ composite exhibited good stability even after six cycles Cu₂SnS₃/Ti³⁺-TiO₂ degraded 98–99 % TC under visible light irridiation. The efficiency of Cu₂SnS₃/Ti³⁺-TiO₂ was also analyzed in the outdoor environment, confirming that this material can be effectively used in practical applications.     

Hydrothermal preparation of Sn3O4/TiO2 nanotube arrays as effective photocatalysts for boosting photocatalytic dye degradation and hydrogen production

The efficient TiO₂ NTs/Sn₃O₄ photocatalysts were synthesized by the hydrothermal deposition of Sn₃O₄ on TiO₂ nanotube arrays (TiO₂ NTs), and the morphology, microstructure and photocatalytic property were adjusted by changing the alkali kind. The TiO₂ NTs/Sn₃O₄ prepared with NaOH exhibited the outstanding photoelectric conversion and photocatalytic environment remediation/H₂ evolution. The methylene blue (MB) dye and Cr(VI) could be removed by the as-prepared photocatalysts under visible light irradiation, and ?O₂^?/?OH radicals were the main active species for MB photodegradation. Furthermore, the high photocatalytic H₂ evolution rate was as high as 6.49 μmol cm^?2 h^?1. The outstanding photocatalytic activity and stability of TiO₂ NTs/Sn₃O₄ photocatalysts would exhibit attractive prospect in the wastewater remediation and electric energy/hydrogen generation.     

Preparation and Characterization of Multi-functional Titanium Dioxide Photocatalysts

Recent research trends of the preparation and characterization of highly efficient titanium oxide-based photocatalysts modified by different methods are reviewed on the basis of studies done in our laboratory. Special attention is focused on the preparation and characterization of TiO₂ photocatalysts prepared by the transitional metal doping and noble metal deposition method, especially combining above two methods. Fe³⁺ doped together with Au deposited TiO₂ (Au/Fe³⁺–TiO₂) was successfully prepared, which shows excellent photocatalytic activity for degradation of methyl orange (MO) under both UV and visible light (λ > 420 nm) illumination. Fe³⁺ has been confirmed by EPR to substitute for Ti⁴⁺ in the TiO₂ lattice, and Au exists as Au⁰ on the surface of the photocatalyst indicated by the results of XRD. Fe³⁺ and Au have synergistic effects on improving the photocatalytic activity of TiO₂. A proposed mechanism concerning the synergistic effects is discussed to explain the improvement of the photocatalytic activities.     

Facile preparation of flake-like blue TiO2 nanorod arrays for efficient visible light photocatalyst

Different kinds of oriented TiO₂ nanorod arrays have been actively pursuing in recent years, however, these fabrications relied on the substrates, such as fluorine-doped tin oxide glass (FTO), silicon wafer or other semiconductor precursor layer. Herein, a stable Ti³⁺ and oxygen vacancies doped blue TiO₂ flakes composed of oriented nanorod arrays were synthesized using a facile hydrothermal treatment in diluted hydrochloric acid solution. Such centimeter-scale flake-like TiO₂ product was obtained without any substrate. Since Ti³⁺ self-doped and/or oxygen vacancies TiO₂ could extend the absorption range of TiO₂ to visible light region, the blue TiO₂ sample exhibited excellent photocatalytic activity under visible light irradiation (photocatalytic degradation efficiency can nearly reach up to 100% within 60?min).     

Experimental analysis and optimization of the synthesizing property of nitrogen‐modified TiO2 visible‐light photocatalysts

BACKGROUND: The aim of this study was to investigate improvement of the photocatalytic activity of visible‐light driven nitrogen‐modified TiO₂ (N‐TiO₂) powder toward methyl blue (MB) and direct blue‐86 (DB‐86) dyes. The Taguchi method with an L₉ orthogonal array was applied to plan the synthesis parameters, i.e. nitrogen sources, nitrogen source concentrations, stirring time and calcined temperatures. 95% confirmation experiments were undertaken to verify the effectiveness of the Taguchi method. RESULTS: All N‐TiO₂ photocatalysts were shifted toward the visible light region with the optical band gap (Eg). Nitrogen source concentrations were significant parameters for the photocatalytic decolorization rate constants (k values). In comparison with pure TiO₂, the photodecolorization behavior of N‐TiO₂ toward DB‐86 was superior with a reaction rate constant of 1.68 × 10^?3 min^?1, and a 4 h photodecolorization efficiency of 34%. CONCLUSION: The Taguchi method was reported to alter the surface properties of commercial Degussa P25 TiO₂, which could then be used as a visible‐light driven photocatalyst. The visible‐light‐driven photocatalyst was investigated to determine material characteristics. Greater photodecolorization of MB and DB‐86 dye pollutants using optimally‐prepared N‐TiO₂ under visible light irradiation was successfully obtained. Copyright © 2011 Society of Chemical Industry     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Microwave dielectric properties of (Zn1/3B2/3)0.5(Ti0.8M0.2)0.5O2 (B = Nb5+, Ta5+, M = Sn4+, Ge4+) ceramics

Dielectric properties of (Zn_1/3Nb_(2?x)/3Ta_x/3)_0.5(Ti_0.8Sn_0.1Ge_0.1)_0.5O₂ (x = 0, 1, 2) and/or (Zn_1/3Nb_1/3Ta_l/3)_0.5(Ti_0.8Sn_0.2(l?y)Ge_0.2y)_0.5O₂ (y = 0, 0.5, 1) were investigated at the microwave frequencies. For the compositions with single phase of rutile structure, the dielectric constant (K) of specimens was not only dependent on the dielectric polarizabilities, but also on the bond length ratio of apical bond (d_apical) to equatorial bond (d_equatorial) of oxygen octahedron in the unit cell. Temperature coefficients of the resonant frequencies (TCF) of the specimens with B = Nb⁵⁺ and/or M = Sn⁴⁺ was larger than those with B = Ta⁵⁺ and/or M = Ge⁴⁺. These results could be attributed to the changes of the degree of oxygen octahedral distortion. Quality factors (Qf) of the specimens with B = Ta⁵⁺ and/or M = Sn⁴⁺ were larger than those with B = Nb⁵⁺ and/or M = Ge⁴⁺.     

Cd2+, Cu2+, Pb2+, Sr2+, and Y3+ binding characteristics of 17β‐estradiol molecularly imprinted polymer particles incorporated with dicyclohexano‐18‐crown‐6 for urine bioassay

The metal ion binding characteristics of molecularly imprinted polymer (MIP) submicron particles prepared using 17β‐estradiol (E2) as a template, and incorporated with dicyclohexano‐18‐crown‐6 (DCH18C6), were studied using differential pulse anodic stripping voltammetry. When Sr²⁺ was added to DCH18C6‐E2‐MIP particles already occupied by Cd²⁺, Cu²⁺, and Pb²⁺ inside the binding sites, a displacement reaction was observed: Cd²⁺/Cu²⁺/Pb²⁺‐DCH18C6‐E2‐MIP + Sr²⁺ = Sr²⁺‐DCH18C6‐E2‐MIP + Cd²⁺/Cu²⁺/Pb²⁺. This demonstrated that DCH18C6 had stronger binding affinity for Sr²⁺ than Cd²⁺ Cu²⁺ or Pb²⁺. Strong DCH18C6 binding affinity was also observed for Y³⁺. Atomic emission spectrometry showed that DCH18C6‐E2‐MIP particles (150 mg/mL) resulted in 52% binding of Sr²⁺ (2000 ppm, at pH 6.3 ± 0.1 and ionic strength of 0.1M NaNO₂). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photoluminescence Properties of Er/Pr‐Doped K0.5Na0.5NbO3 Ferroelectric Ceramics

Er/Pr‐doped K_0.5Na_0.5NbO₃ ceramics have been fabricated and the effects of Pr³⁺ on their photoluminescence properties have been investigated systematically. The visible upconversion emissions, near‐infrared and mid‐infrared downconversion emissions of Er³⁺ ions under the excitation of 980 nm have been studied in detail. The effects of Pr³⁺ on PL properties and energy‐transfer processes have also been elucidated. By selecting an appropriate excitation source, simultaneous visible downconversion emissions of Er³⁺ and Pr³⁺ ions can be realized, and the emission colors of the ceramics can be tuned via the concentration of Pr³⁺ ions in a wide range from yellowish green to yellow. Our results also reveal that the photoluminescence emissions of the ceramics can be enhanced by the alignment of polarization of the ferroelectric host.     

Enhanced visible‐light‐driven photocatalytic activities of LiInO2 by Mo6+‐doping strategy

A novel visible‐light‐driven photocatalyst of Mo‐doped LiInO₂ nanocomposite was successfully synthesized through a sol‐gel method. The effect of Mo‐doping concentrations on the microstructures and properties of LiInO₂ was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy, photoluminescence, and ultraviolet‐visible absorption spectra. The photocatalytic properties of the as‐prepared samples were evaluated by the photocatalytic degradation of methylene blue (MB) dye under visible‐light irradiation. The results demonstrated that the photocatalytic activity of 6% Mo‐LiInO₂ reached to 98.6%, which was much higher than that of the undoped photocatalyst LiInO₂ (only 46.8%). The enhanced photocatalytic activity is ascribed to Mo‐doping strategy. The holes play an important role in the process of the photodegradation of MB. The superior photocatalytic activity of the as‐prepared Mo‐LiInO₂ nanocomposites suggests a potential application for organic dye degradation of wastewater remediation. This work provides a further understanding on tailoring the band structure of semiconductor photocatalyst for enhancing visible‐light absorption and promoting electron‐hole separation by Mo‐doping strategy.     

Photocatalytic Decomposition of Synthetic Alizarin Red S by Nickel Doped TiO2

The photocatalytic degradation in aqueous medium of the Alizarin Red S (ARS) dye using UV blacklight irradiation (?? = 365 nm) over sol?Cgel nickel-titania doped photocatalyst (0.5?C6 wt% Ni) was investigated. The doped semiconductors were characterized by XRD, nitrogen physisorption and UV?CVis diffuse reflectance spectroscopy. High specific surface areas (90 m²/g) and small crystallite sizes, which varied with the Ni content, were obtained. No evidence concerning the formation of NiO was observed by XRD, which suggested the deposition of small NiO composites onto the TiO₂ surface. A shift to the visible region of the Eg band gap was obtained by increasing the nickel content in the semiconductors. The substitution of some Ti⁴⁺ by Ni²⁺ cations during the preparation of the photocatalysts was proposed. It was found that the synthesis of the catalysts with 0.5, 1.5, 3 and 6 wt% of Ni resulted in semiconductors that were more active than P25 commercial titania in the photodegradation of ARS.     

Sunlight driven high photocatalytic activity of Sn doped N-TiO2 nanoparticles synthesized by a microwave assisted method

Environment-friendly photocatalysts under sunlight with wide spectral responses for wastewater treatment are currently an exciting area of research. Herein, we report the synthesis of Sn doped N-TiO₂ nanoparticles with different contents of Sn by a greener microwave assisted method. The phase purity, morphology, particle size, optical properties, and elemental composition were systematically analyzed by various sophisticated analytical techniques. The X-ray diffraction (XRD) patterns revealed Sn doped N-TiO₂ nanoparticles in the anatase phase. The shift of XRD peaks observed at lower angle and the XPS results indicate the successful doping of Sn⁴⁺ in the lattice of N-TiO₂. The optical absorption edges of Sn-doped N-TiO₂ showed an obvious red shift that plays a crucial role in the photocatalytic activity under abundant sunlight. We further explored Sn doped N-TiO₂ for photodegradation of methyl orange (MO) and Zopiclone (Z-class drug) under sunlight irradiation. A maximum of 95% and 91% of MO and Zopiclone were photodegraded over 0.25% Sn doped N-TiO₂ under sunlight within 80 and 120 min, respectively, which is ∼7-fold higher than bare N-TiO₂. The enhanced photocatalytic activity could be attributed to combined effects of reduced crystallite size, suppressed recombination rate of photogenerated electron-hole pairs, and increased optical absorption towards visible light that establish their impending use to treat polluted water. The possible mechanism for high photocatalytic activity of Sn doped N-TiO₂ has also been discussed.     

Generation of hydrogen under visible light irradiation with enhanced photocatalytic activity of Bi2WO6/Cu1.8Se for organic pollutants under Vis‐NIR light reign

To make better use of solar light, a new Bi₂WO₆/Cu_1.8Se photocatalyst active to visible and near‐infrared light has been synthesized by a facile hydrothermal method. The composites were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), UV‐vis diffuse reflectance spectroscopy (DRS), and photoluminescene (PL). The photocatalytic activities of Bi₂WO₆/Cu_1.8Se are evaluated by degrading Congo red solution and hydrogen generation from water. It was found that the molar percentage of Cu_1.8Se had great effects on the morphology and photocatalytic property of the Bi₂WO₆/Cu_1.8Se heterojunctions, and the composite with suitable molar amount of Cu_1.8Se exhibits much enhanced photocatalytic activity for Congo red degradation under visible and near‐infrared light irradiation and for hydrogen generation under visible light compared to Bi₂WO₆. The significant improvement photocatalytic activity of the composite could be attributed to its good light absorption, suitable band gap structure, and effective separation of photogenerated electron‐hole pairs of Bi₂WO₆/Cu_1.8Se heterojunction. This work presents an efficient multifunction photocatalyst owning the activity both for water splitting under visible light and for organic contaminants decomposition under visible‐near‐infrared light.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Effects of Nonstoichiometry and Cocatalyst Loading on the Photocatalytic Hydrogen Production with (Y1.5Bi0.5)1−xTi2O7−3x and (YBi)1−xTi2O7−3x Pyrochlores

By adjusting the Ti/(Y+Bi) ratios during synthesis, nonstoichiometric pyrochlores of (Y_1.5Bi_0.5)_{1 ? x}Ti₂O_{7 ? 3x} and (YBi)_{1 ? x}Ti₂O_{7 ? 3x} were prepared by an aqueous sol–gel method and annealed at different temperatures. The materials were characterized by X‐ray diffraction and UV–vis reflectance spectroscopy. The samples were tested for photocatalytic hydrogen production in the presence of methanol as sacrificial agent after being loaded with nanoparticles of rhodium or platinum acting as cocatalysts. It was found that materials being completely inactive in a stoichiometric composition can be tuned to good photocatalysts by optimizing the Ti/(Y+Bi) ratio. The increase in activity is supposed to derive from an optimization of the TiO₆‐octahedral geometry due to the generation of vacancies inside the structure. Increasing the Bi loading shifts the absorption edge into the visible, but unfortunately, an increase of the bismuth content in the structure also leads to stability issues during photocatalysis, which can be suppressed or at least weakened by a higher cocatalyst loading.