Enhanced photocatalytic performance through the ferroelectric synergistic effect of p-n heterojunction BiFeO3/TiO2 under visible-light irradiation

A BiFeO₃/TiO₂ p-n heterojunction photocatalyst with ferroelectric synergistic effect under visible-light irradiation was developed through facile hydrolysis and precipitation by forming nanospheres of TiO₂ on BiFeO₃ nanocube to improve the photocatalytic efficiency. Analyses of the microstructure, optical properties, and photoelectrochemical performance indicate the formation of a core–shell heterostructure of BiFeO₃/TiO₂ with excellent energy band matching. The BiFeO₃/TiO₂ p-n heterojunction has enlarged specific surface area, higher sensitivity to visible-light, and improved separation and transfer efficiency of photoelectron-hole pairs than single TiO₂ and BiFeO₃. Moreover, the composite exhibits superior photocatalytic degradation performance for methylene blue (MB) and common antibiotic tetracycline (TC) under UV and visible-light irradiation. The MB degradation rate within 180 min reaches 78.4% and 90.4% under UV and visible-light irradiation, respectively. Furthermore, the enhanced photocatalytic mechanism of BiFeO₃/TiO₂ is explored by photoluminescence (PL), electrochemical impedance spectroscopy (EIS), transient photocurrent analysis, radical quenching, and band structure characterization.     

Synthesis and photocatalytic activity of BiFeO3 and Bi/BiFeO3 cubic microcrystals

BiFeO₃ and Bi/BiFeO₃ cubic microcrystals were synthesized in this work. The phase, microstructure, optical and photo electrochemical properties, as well as the photocatalytic activities in photocatalytic hydrogen generation were investigated. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate the successful synthesis of BiFeO₃ and Bi/BiFeO₃. The scanning electron microscope (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) results give the evidence of cubic morphology and the deposition of metal Bi on the surface of BiFeO₃. The absorption spectra show that Bi/BiFeO₃ has longer absorption edge and stronger absorption capability to visible light. The photocurrent curves, emission spectra, and electrochemical impedance spectroscopy (EIS) spectra demonstrate that Bi/BiFeO₃ has higher efficiency of electron-hole separation and charge transfer, as well as longer lifetime of the charge carriers. These benefit to the enhancement of activity in photocatalytic hydrogen generation.     

Facile Preparation of LaFeO<Subscript>3</Subscript>/rGO Nanocomposites with Enhanced Visible Light Photocatalytic Activity

The present work demonstrates a facile route for preparing LaFeO₃/rGO nanocomposites comprising of metal oxide nanoparticles and graphene. Structural, morphology, optical and photocatalytic studies of the samples were characterized using powder X-ray diffraction (XRD), FT-IR, Raman, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), thermogravimetry (TGA), X-ray photoelectron spectroscopy, UV–visible and photocatalytic. LaFeO₃/rGO nanocomposites believed as an effective photocatalyst for the degradation of methyl orange (MO) dye under visible light irradiation. The inclusion of carbon enhances the light absorption of LaFeO₃, resulting in the enhanced photocatalytic activity of the nanocomposite. The degradation of MO dye under visible light source was completely achieved using LaFeO₃/rGO as a catalyst.     

Electrospinning of magnetical bismuth ferrite nanofibers with photocatalytic activity

Bismuth ferrite (BiFeO₃) nanofibers were prepared by combining the electrospinning technique with sol–gel chemistry. The structural features of the as-prepared nanofibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained BiFeO₃ nanofibers showed a rhombohedral perovskite structure after getting annealed in an argon atmosphere. Both SEM and TEM results showed that BiFeO₃ fibers were composed of nanocrystalline particles. The photocatalytic behaviors of BiFeO₃ nanofibers were investigated by the degradation of Rhodamine B (RhB). BiFeO₃ nanofibers exhibited excellent catalytic activity under UV light irradiation, as well as under visible light irradiation in the presence of H₂O₂. The catalyst was further examined by magnetic measurement. The BiFeO₃ nanofibers exhibited a ferromagnetic behavior at room temperature, which was associated with the nanometer-size of BiFeO₃ particles. This provides an easy and efficient way to recover BiFeO₃ photocatalysts from the suspension system by applying an external magnetic field.     

The photocatalysis of BiFeO3 disks under visible light irradiation

The photocatalytic process of BiFeO₃ disks under visible light irradiation can be termed as photo-Fenton-like reaction. The active hydroxyl radicals (•OH) generated during the photocatalytic process were quantified using a terephthalic acid (TA) fluorescence probing technique, which were proved to be greatly influenced by the loading of H₂O₂ and catalyst dosage. Our results showed that the photocatalytic efficiency was enhanced with the increasing •OH concentration. There is an optimal loading of H₂O₂ (80 mM) and catalyst dosage (2.0 g/L), at which the photocatalytic degradation rate of MO was enhanced to 97% under visible light irradiation for 3 h.     

Visible light-irradiated degradation of alachlor on Fe-TiO<Subscript>2</Subscript> with assistance of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

0.1 Fe/Ti mole ratio of Fe-TiO₂ catalysts were synthesized via solvothermal method and calcined at various temperatures: 300, 400, and 500 °C. The calcined catalysts were characterized by XRD, N₂-adsorption-desorption, UV-DRS, XRF, and Zeta potential and tested for photocatalytic degradation of alachlor under visible light. The calcined catalysts consisted only of anatase phase. The BET specific surface area decreased with the calcination temperatures. The doping Fe ion induced a red shift of absorption capacity from UV to the visible region. The Fe-TiO₂ calcined at 400 °C showed the highest photocatalytic activity on degradation of alachlor with assistance of 30 mM H₂O₂ at pH 3 under visible light irradiation. The degradation fitted well with Langmuir-Hinshelwood model that gave adsorption coefficient and the reaction rate constant of 0.683 L mg⁻¹ and 0.136 mg/L·min, respectively.     

Facile Synthesis,Characterization, Catalytic and Photocatalytic Activity of Multiferroic BiFeO3 Perovskite Nanoparticles

We report the synthesis of multiferroic BiFeO₃ perovskite nanoparticles using the microwave combustion technique. Phase evolution is investigated by XRD, which confirms that the formation of a secondary α-Bi₂O₃ phase with a monoclinic structure along with the existing rhombohedral (BiFeO₃) structure. The average crystalline size has been found at 50 nm. The optical band gap was calculated from the Tauc’s plot it has been found 2.18 eV. The appearances of FT-IR spectra revealed bands at 550 and 444 cm^?1 were correlated to the rhombohedral stretching modes of BiFeO₃ nanostructure. The surface morphology showed the formation of nanosized grains with pores. The magnetization-Field (M-H) hysteresis curves revealed the appearance of ferrimagnetic behavior at room temperature. The BET surface area of BiFeO₃ perovskite nanoparticles was found 44.86 m²/g. The as-fabricated BiFeO₃ perovskite nanoparticles were investigated for their superior catalytic activity in two applications, which include (i) Glycerol to formic acid oxidation in the liquid phase with a high efficiency of over 98 percent, (ii) Under visible light, the photocatalytic breakdown of rhodamine B achieved maximal efficiency (almost 99 percent). Finally, we concluded that the BiFeO₃ perovskite nanoparticles exhibit high performance in future multifunctional devices is demonstrated by the simultaneous enhancement of catalytic and photocatalytic activities.

     

Fabrication of ternary p-n heterostructures AgCl/Ag2O/NaTaO3 photocatalysts: Enhanced charge separation and photocatalytic properties under visible light irradiation

Ternary p-n heterostructures photocatalysts of AgCl/Ag₂O/NaTaO₃ were synthesized via a simple method and the crystal structure characterized by X-ray diffraction (XRD). The morphology of the photocatalysts were characterized by scanning electron microscopy and transmission electron microscopy. The composition of the photocatalysts was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscope. The photocatalytic activity of the AgCl/Ag₂O/NaTaO₃ photocatalysts was evaluated using the degradation of Rhodamine B. The AgCl/Ag₂O/NaTaO₃ photocatalysts showed higher visible light activity than the pure NaTaO₃ and Ag₂O/NaTaO₃ photocatalysts. Additionally, the photocatalytic mechanism was that the rapidly separation of photoinduced electrons and holes resulted the enhancement of photocatalytic activity.     

Photoreduction of Carbon Dioxide Over NaNbO<Subscript>3</Subscript> Nanostructured Photocatalysts

Abstract  

NaNbO₃ had been successfully developed as a new photocatalyst for CO₂ reduction. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible spectroscopy (UV–Vis). The DFT calculations revealed that the top of VB consisted of the hybridized O 2p orbital, while the bottom of CB was constructed by Nb 3d orbital, respectively. In addition, the photocatalytic activities of the NaNbO₃ samples for reduction of CO₂ into methanol under UV light irradiation were investigated systematically. Compared with the bulk NaNbO₃ prepared by a solid state reaction method, the present NaNbO₃ nanowires exhibited a much higher photocatalytic activity for CH₄ production. This is the first example that CO₂ conversion into CH₄ proceeded on the semiconductor nanowire photocatalyst.     

Effect of metal-support interaction on the structural and enhanced photocatalytic performance of mesoporous M–TiO<Subscript>2</Subscript>/SBA-16 (M = Ag and Fe)

In this paper, a series of metal supported TiO₂/SBA-16 photocatalysts were successfully synthesized by wet impregnation method. The synthesized samples were characterized by X-ray diffraction (XRD), Raman spectra, N₂ adsorption–desorption, transmission electron microscopy (TEM), UV–visible absorption spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). It was found that SBA-16 retained the ordered mesostructure after modification. The results shown that loading different metal elements was found to have significant influences on the crystallographic structure and physical properties. Moreover, the prepared materials were evaluated on photodegradation of Rhodamine B (RhB). Experiment results showed that the degradation of RhB by these catalysts follows the pseudo-first-order kinetic model. The effect of metal element on photocatalytic activity can be attributed that the appropriate amounts of metal concentration can enhance the photocurrent due to the reduced electron–hole recombination, which can improve the efficiency of photocatalytic reactions.     

Molybdenum doped TiO2 nanocomposite coatings: Visible light driven photocatalytic self-cleaning of mineral substrates

The molybdenum doped TiO₂ nanocomposite layer double hydroxide (LDH) suspensions, Mo:TiO₂-LDHs, were synthesized by a wet impregnation method in order to enhance the pure TiO₂ (water suspension) photocatalytic activity and consequently its self-cleaning efficiency under exposure to visible light. The aim was to produce nanocomposites by a simple, energy saving and cost beneficial synthesis. The mass ratio Mo/Ti was systematically varied (0.03, 0.06, 0.09, 0.12). The obtained nanocomposite Mo:TiO₂-LDH suspensions were first characterized by UV–vis spectroscopy (band-gap energies), Zeta-sizer (particle size distribution and stability) and X-ray diffraction (XRD) (structure) and then applied onto the model mineral substrates, brick and stone. The photocatalytic activity of the obtained coating was determined based on the degradation kinetics of the Rhodamine B (RhB) under artificial visible light irradiation (white LED). The obtained results were compared to the ones of the unmodified TiO₂-LDH suspension. The obtained results also showed that all prepared nanocomposites have good photocatalytic activity, particularly the suspension Mo:TiO₂-LDH with the Mo/Ti 0.03 mass ratio which possesses the best value. In addition, as regards the visible light driven self-cleaning effect, this suspension has proven to be a good protective functional coating for porous mineral substrates (bricks and stones).     

Facile Fabrication of Pt-Doped Mesoporous ZnS as High Efficiency for Photocatalytic CO2 Conversion

Developing high efficiency, environmentally friendly, and low-cost mesoporous Pt/ZnS photocatalyst for CO₂ conversion to CH₃OH is significant for clean energy conversion. Herein, we described a facile synthesis of mesoporous ZnS framework decorated Pt NPs as high efficiency for CO₂ conversion through visible light illumination. The results indicated that Pt/ZnS nanocomposites showed that the structural and crystallinity integrity of polyhedral heterojunction obviously maintain after incorporating Pt NPs, and they are well-distributed on the ZnS surface with particles size about 3–5 nm. The optimized photocatalyst 1.5% Pt/ZnS nanocomposite could prominently exhibit a high photocatalytic efficiency compared to undoped ZnS. Remarkably, the yield of CH₃OH of 400 µmolg^??1 in 9 h over 1.5% Pt/ZnS nanocomposite indicated a significantly promoted CH₃OH formation, nearly 22-fold greater than that of the undoped ZnS NPs, which substantially verified the great promoting potential for conversion of clean energy. The CH₃OH formation rate over mesoporous 1.5% Pt/ZnS nanocomposite (44.5 µmolg^?1 h^?1) is larger 24 times than that of undoped ZnS NPs (1.86 µmolg^?1 h^?1). The recycled Pt/ZnS photocatalyst does not alter the CH₃OH formation remarkably after five repeating cycles with excellent durability. Electrochemical impedance spectroscopy, photocurrent response, and photoluminescence analyses were investigated to support our results and suggested mechanism for enhancement of CO₂ conversion to CH₃OH.

     

Facile green synthesis of ytrium-doped BiFeO3 with highly efficient photocatalytic degradation towards methylene blue

Bismuth ferrite (BiFeO₃) is considered as one of the most promising materials in the field of multiferroics with great potentials in photocatalysis due to their excellent properties of relatively small band gap, stable structures, and low cost. In this work, a facile green route was successfully used for the fabrication of high-purity yttrium-doped and undoped bismuth ferrite (BiFeO₃) nanoparticles. κ-carrageenan seaweed was used as a biotemplate for the construction of the material. The obtained products were characterized and the photocatalytic effect of doped and undoped BiFeO₃ were evaluated on the degradation of methylene blue (MB) under direct sunlight. The formed particles are in the range of 80–90 nm that exhibited morphology of rhombohedral perovskite structure as confirmed by FESEM and HRTEM analysis. Decreasing of band gap energy from 2.07 eV to 2.05 eV as the concentration of yttrium dopant increased significantly affected their photocatalytic behaviour. There was a remarkable improvement in the photocatalytic activity of 1% of yttrium-doped BiFeO₃ towards the decomposition of methylene blue (MB) under direct sunlight irradiation. This was attributed to the strong absorption of visible light and the effective separation of photoinduced e− and h + pair, as compared to the pristine BiFeO₃. In addition, the influence of operational parameters on the removal efficiency of MB, such as catalyst dosage and initial dye concentrations, was optimized as a function of time. The kinetics of the photocatalytic MB removal was later found to follow Langmuir Hinshelwood model.     

Property Characterization and Photocatalytic Activity Evaluation of BiGdO3 Nanoparticles under Visible Light Irradiation

BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min⁻¹ with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment.     

Synthesized Hollow TiO<Subscript>2</Subscript>@g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> Composites for Carbon dioxide Reduction Under Visible Light

The hollow TiO₂@g-C₃N₄ composites were synthesized by a facile stirring method. The phase compositions, optical properties, and morphologies of the samples were characterized via X-ray diffraction, scanning electron microscope, transmission electron microscopy, high resolution transmission electron microscopy, fourier transform infrared spectroscopy, N₂ adsorption–desorption, UV–Vis diffuse reflectance spectroscopy and Photoluminescence. The photocatalyitc performance was evaluated by reduction carbon dioxide under visible light irradiation. The results indicated that TiO₂@g-C₃N₄ nanocomposites displayed higher photocatalytic activity compared with pure g-C₃N₄. The increased photocatalytic activity of TiO₂@g-C₃N₄ nanocomposites can be attributed to facilitating the photo-induced electron–hole separation efficiency and enhancing the photo-induced electron migration.

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Effect of Thermal Treatment on the Photocatalytic Activity in Visible Light of TiO<Subscript>2</Subscript>-W Flame Spray Synthesised Nanopowders

Effect of W doping as well as a thermal treatment on the structural and photocatalytic properties of TiO₂ produced by flame spray synthesis (FSS) were the subject of investigation. Structural properties were studied by means of X-ray diffraction (XRD), BET adsorption isotherm and transmission electron microscopy (TEM). The surface condition was investigated by X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) and differential thermal and thermogravimetric analysis (DTA-TGA). The photocatalytic properties were studied by optical measurements and photodecomposition of methylene blue under visible irradiation. It was found that the photoactivity in the visible region was enhanced significantly by the W-doping as well as by additional thermal treatment of those nanopowders. The obtained TiO₂-W nanopowders exhibited higher performance under visible light than P25.     

Purification of textile wastewater by using coated Sr/S/N doped TiO<Subscript>2</Subscript> nanolayers on glass orbs

Simultaneous doping of TiO₂ nanoparticles with three elements including Sr, S, and N is reported. The resulting material shows superior photocatalytic performance toward degradation of textile waste under visible and sunlight. The pure and doped TiO₂ nanolayers were prepared by sol-gel method and were fixed on a bed of glass orbs. The immobilized TiO₂ were characterized by a variety of techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), spectroscopy diffusion reflection (DRS), energy dispersive X-ray spectrometry (EDS) and elemental analysis (CHNS). The photocatalytic activity of the prepared fixed-bed materials toward degradation of the textile wastes was determined by using ultraviolet-visible spectroscopy (UV-Vis) and measurement of the chemical oxygen demand testing (COD). The best photocatalytic activity was observed with the use of Sr/S/N-TiO₂ nano-layers. Afterwards, the experimental conditions were optimized by tuning reaction parameters, including amount of doped metal ion on photocatalyst structure, sample solution pH and photoreactor output flow rate. The results confirmed that at natural pH 5.9 of sample solution, maximum decomposition of 91-99% of azo dyes was obtained in 8 h under visible irradiation. Finally, the experiments were repeated under 1.5 AM sunlight with high volume of reactants in order to confirm the cost-effectiveness of the designed photocatalyst.     

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.     

Photocatalytic removal of NOx over immobilized BiFeO<Subscript>3</Subscript> nanoparticles and effect of operational parameters

Perovskite type BiFeO₃ (BFO) was synthesized by sol-gel auto-combustion method. Synthesized BFO was immobilized on the micro slides glass plates by sol-gel dip-coating method. The sample was characterized by XRD, FESEM, UV-Vis DRS, and BET techniques. The XRD pattern confirmed the perovskite structure, and from the Debye-Scherrer equation the average crystalline size was calculated as 19 nm. The FE-SEM images of prepared BFO showed porous structure with low agglomeration. The band gap energy was calculated about 2.13 eV, and the specific surface area (SSA) of prepared BFO nanostructure was obtained 55.1m² g^?1. The photocatalytic activity of prepared pure and immobilized BFO was investigated in the removal of NOx under UV irradiation, in the batch photoreactor. The effects of operational parameters such as initial concentration of NOx, light intensity and amount of coated photocatalyst, under identical conditions, were investigated. The results showed that the highest conversion of NOx was obtained as 35.83% in the 5 ppm of NOx with 1.2 g immobilized BFO and under 15 W illumination lamp.     

Intensifying the photocatalytic degradation of methylene blue by the formation of BiFeO3/Fe3O4 nanointerfaces

A novel highly efficient photocatalyst composite BiFeO₃/Fe₃O₄ has been synthesized by mechanosynthesis and applied to the degradation of Methylene Blue under visible light. Structural, optical and photocatalytic properties of the proposed photocatalyst composites are carefully investigated. The nanointerfaces, associated to ferrous Fe²⁺ ions of the Fe₃O₄ nanoparticles, improve the photocatalytic efficiency when compared with pure BiFeO₃ or Fe₃O₄. The time required to the complete degradation of Methylene Blue solution is 40 min for the sample with 20% of Fe₃O₄ which is more than 7 times faster than the time required using BiFeO₃ alone. Moreover, with the addition of H₂O₂ a complete degradation is achieved just after 10 min, which is faster than any other photocatalytic reaction reported for BiFeO₃-based materials. This enhancement is assumed to be related to an electron drain process due to the difference between energy levels of the conduction bands of BiFeO₃ and Fe₃O₄ combined with the direct Fenton-like process associated with the Fe²⁺ ions of the composites.