Photocatalytic decolorization of rhodamine B by fluidized bed reactor with hollow ceramic ball photocatalyst

Photocatalytic degradation of organic contaminants in wastewater by TiO₂ has been introduced in both bench and pilot-scale applications in suspended state or immobilized state on supporting material. TiO₂ in suspended state gave less activity due to its coagency between particles. Recent advances in environmental photocatalysis have focused on enhancing the catalytic activity and improving the performance of photocatalytic reactors. This paper reports a preliminary design of a new immobilized TiO₂ photocatalyst and its photocatalytic fluidized bed reactor (PFBR) to apply photochemical degradation of a dye, Rhodamine B (RhB). But it was not easy to make a cost-effective and well activated immobilized TiO₂ particles. A kind of photocatalyst (named Photomedium), consisting of hollow ceramic balls coated with TiO₂-sol, which was capable of effective photodegradation of the dye, has been presented in this study. The photocatalytic oxidation of RhB was investigated by changing Photomedia concentrations, initial RhB concentrations, and UV intensity in PFBR This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

α-Bi2O3 nanosheets: An efficient material for sunlight-driven photocatalytic degradation of Rhodamine B

Herein, we report the sunlight driven photocatalytic degradation of toxic organic dye, Rhodamine B using α-Bi₂O₃ nanosheets as an effective photocatalyst. The α-Bi₂O₃ nanosheets were prepared by simple annealing assisted thermal decomposition method and characterized by several techniques in order to understand its morphological, compositional, structural and optical properties. Morphological, structural and compositional investigations confirmed the formation of sheet-like morphologies, high-crystalline monoclinic crystal structure, and pure α-Bi₂O₃, respectively. The synthesized α-Bi₂O₃ nanosheets exhibited a high photocatalytic degradation of a toxic organic dye, i.e. Rhodamine B (RhB). Under optimal reaction conditions, ～95% photocatalytic degradation of RhB (10 mg/L, pH 10) was observed in 180 min using 0.75 g/L catalyst dosage under sunlight irradiation. According to the findings, the synthesized catalyst had outstanding photocatalytic properties and can be used to cleanse textile wastewater under direct sunlight.     

Photocatalytic degradation of rhodamine B and phenol by solution combustion synthesized BiVO4 photocatalyst

Visible-light-induced BiVO₄ photocatalyst has been successfully synthesized via a solution combustion synthesis (SCS) method. The photocatalytic activities of the as-synthesized sample were evaluated by the photodegradation of rhodamine B (RhB) and phenol under visible-light irradiation (λ > 420 nm). The decolorization of high-concentrated RhB (10^− 4 M) and the variation of the chemical oxygen demand (COD), demonstrated that the BiVO₄ photocatalyst was efficient in aromatic organic compounds degradation. The reduction of total organic carbon (TOC) (about 22.0% after 4.5 h of irradiation) showed that the mineralization of RhB over the BiVO₄ photocatalyst is realized. Additionally, much enhanced photocatalytic performance for phenol degradation was also realized with the assistance of appropriate amount of H₂O₂.     

Surfactant-free synthesis of a novel octahedral ZnFe2O4/graphene composite with high adsorption and good photocatalytic activity for efficient treatment of dye wastewater

Recently, significant effort has been made toward the development of graphene-based visible-ligh-responsive photocatalysts and their application to dye wastewater treatment. Herein, a series of octahedral ZnFe₂O₄/graphene (ZnFe₂O₄-G) nanocomposites were synthesized using a one-pot solvothermal reaction without the need of a surfactant as novel bifunctional materials exhibiting both high adsorption and good visible-light-responsive photocatalyst properties. The crystal structure, morphology and photocatalytic degradation properties, as well as adsorption behavior, of the octahedral ZnFe₂O₄/graphene composites were investigated in detail. The adsorption capacity and UV–vis spectrometry results indicate that the dye removal efficiency over the samples followed the order of: methylene blue (MB) > rhodamine B (RhB) > methyl orange (MO). The ZnFe₂O₄-G materials exhited enhanced photocatalytic degradation properties for cationic dyes (MB and RhB) compared to those for the anionic dye (MO). In addition, the experimental results indicate that the ZnFe₂O₄-G materials can decompose H₂O₂ in the visible-light photocatalytic process to form hydroxyl radicals (•OH), which are mainly responsible for the photodegradation of the organic contaminants.     

Cost-effective large-scale synthesis of oxygen-defective ZnO photocatalyst with superior activities under UV and visible light

A cost-effective solution method was developed to produce ZnO photocatalyst in large quantity, through the conversion of ε-Zn(OH)₂ to ZnO in NaOH solutions. Experimental results indicated that the concentrated NaOH solution (4 mol L⁻¹) promoted the rapid formation of ZnO owing to the enhanced dissolution-precipitation reactions. The large-scale synthesis was also achieved with high-yield and solvent-recyclability. Structural analysis based on X-ray photoelectron spectroscopy, electron spin resonance and photoluminescence revealed that the as-prepared ZnO photocatalyst was rich in oxygen vacancies (V_O). The V_O-rich ZnO photocatalyst exhibited improved visible-light absorption, higher photocurrent responses and superior activities toward the degradation of rhodamine B under both UV (λ~254 nm) and visible-light illumination (λ>420 nm) compared to commercial ZnO and P25 TiO₂ powders, as well as good cycle stability. Based on the results of photoluminescence and active species detection, the V_O-enhanced photocatalytic activity was attributed to the generation of V_O-isolated level in the band structure. Under UV light, the V_O-level could promote charge separation by trapping the photoinduced electrons, while under visible-light, the V_O-level improved visible-light absorption and facilitated the charge generation. The presently developed synthesis may potentially benefit the large-scale production and low-cost application of ZnO photocatalyst for solar energy utilization.     

Synthesis of Ternary Heterostructure Semiconductor Photocatalyst and Its Photocatalytic Performance Under Visible Light Irradiation

Introducing magnetic metal onto semiconductor materials has been proven to be an attractive strategy for enhancing the photocatalytic activity in the visible region. In this work, ternary heterostructure magnetic semiconductor photocatalyst RGO/ZnFe₂O₄/Ag₂WO₄ was successfully synthesized through a simple hydrothermal method and was evaluated by photodegradation of Rhodamine B (RhB) under visible light irradiation. The composition, structure, morphology, and optical absorption properties of the as-prepared photocatalyst were investigated by XRD, FT-IR, SEM, and UV–Vis DRS, respectively. It was found that the photocatalytic activity under visible light irradiation was in the order of RGO/ZnFe₂O₄/Ag₂WO₄?>?ZnFe₂O₄?>?Ag₂WO₄?>?RGO/ZnFe₂O₄ and RGO/ZnFe₂O₄/Ag₂WO₄. The enhancement of photocatalytic performance could be attributed to the reduced graphene oxide sheets can function as an electron collector and transporter to lengthen the lifetime of the charge carriers, improving the whole photocatalytic activity. The reaction kinetics, possible degradation pathway, and catalyst stability, as well as the roles of ZnFe₂O₄ and Ag₂WO₄ in photoreaction, were comprehensively studied. The obtained results indicate that the prepared magnetic and effective catalytic materials could be potentially applied in environmental organic pollutants purification.

     

Fe2O3/TiO2/Activated Carbon Nanocomposite with Synergistic Effect of Adsorption and Photocatalysis

Fe₂O₃/TiO₂/activated carbon (FT/AC) nanocomposites supported on silica gel beads were synthesized using a sonochemical method and fully characterized. The response surface method was applied to optimize the removal of Pb(II) ions by nanocomposites under visible light. The experiments were conducted by adjusting three parameters, i.e., initial concentration of Pb(II) ions, dosage of Fe₂O₃/TiO₂ (FT) photocatalyst, and pH. The FT/AC nanocomposite showed higher efficiency for Pb(II) ion removal in comparison with FT due to the synergistic effect of activated carbon combined with Fe₂O₃/TiO₂.     

Enhancement of the visible light photocatalytic performance of C-doped TiO2 by loading with V2O5

V₂O₅ was loaded on the surface of C-doped TiO₂ (C-TiO₂) by incipient wetness impregnation in order to enhance the visible light photocatalytic performance. The physicochemical properties of the C-TiO₂/V₂O₅ composite were characterized by XRD, Raman, TEM, XPS, UV–vis diffuse reflectance spectra, and PL in detail. The result indicated that a heterojunction between C-TiO₂ and V₂O₅ was formed and the separation of excited electron–hole pairs on C-TiO₂/V₂O₅ is greatly promoted. Thus, this composite photocatalyst exhibited enhanced visible light photocatalytic activity in degradation of gas-phase toluene compared with the pristine C-TiO₂.     

Preparation of Ag@AgI-intercalated K4Nb6O17 composite and enhanced photocatalytic degradation of Rhodamine B under visible light

In this study, a novel plasmonic photocatalyst, Ag@AgI intercalated layered niobate, was synthesized via a microwave-assisted ion-exchange method. The composite materials prepared were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray fluorescence spectrometry (XRF), Brunauer–Emmett–Teller (BET) and ultraviolet–visible diffuse reflection spectra (UV–vis). The as-prepared plasmonic photocatalyst exhibited an enhanced and stable photocatalytic performance for the degradation of Rhodamine B (RhB) and up to 83% of RhB was degraded in 40 min under visible light irradiation. The mechanism of separation of the photo-generated electrons and holes at the K₄Nb₆O₁₇/Ag@AgI composite was discussed.     

Novel Bi4O5Br2/MnxZn1-xFe2O4 magnetic composite with an enhanced photodegradation activity and excellent recyclability

Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ nanocomposites with impressive photocatalytic and recyclability properties were synthesised using a microemulsion method. In addition to the photocatalytic effect, the crystal structure and morphology, photoelectrochemical characteristics, magnetic effect and photocatalytic mechanism of Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ were also investigated. As the best sample, the removal rate of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst with 7.5 wt% Mn_xZn_1-xFe₂O₄ to rhodamine B (RhB) reached up to 99.4% within 60 min. The enhanced photocatalyst activity was mainly attributed to the type-II heterojunction formed between Bi₄O₅Br₂ and Mn_xZn_1-xFe₂O₄, which not only optimised the energy band structure, but also led to the building of an interior electromagnetic field within the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ heterojunction. Meanwhile, the constantly producing and migrating h⁺ and ·O₂^? were the main active components. In particular, the results of the saturation magnetization tests and magnetic recovery experiments revealed that the magnetic composite photocatalyst can be recovered effectively. The results of the removal rate of RhB remaining at 85.2% after five uses reflected the advantages of the stability of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst. In brief, this paper presented an original idea to develop a novel composite magnetic photocatalyst and research the enhancement mechanism of photocatalysis.     

Facile synthesis of ZnBi<Subscript>2</Subscript>O<Subscript>4</Subscript>-graphite composites as highly active visible-light photocatalyst for the mineralization of rhodamine B

Novel highly active visible-light photocatalysts in the form of zinc bismuth oxide (ZnBi₂O₄) and graphite hybrid composites were prepared by coupling via a co-precipitation method followed by calcination at 450 °C. The as-prepared ZnBi₂O₄-graphite hybrid composites were tested for the degradation of rhodamine B (RhB) solutions under visible-light irradiation. The existence of strong electronic coupling between the two components within the ZnBi₂O₄-graphite heterostructure suppressed the photogenerated recombination of electrons and holes to a remarkable extent. The prepared composite exhibited excellent photocatalytic activity, leading to more than 93% of RhB degradation at an initial concentration of 50mg·L^-1 with 1.0 g catalyst per liter in 150min. The excellent visible-light photocatalytic mineralization of ZnBi₂O₄-1.0graphite in comparison with pristine ZnBi₂O₄ could be attributed to synergetic effects, charge transfer between ZnBi₂O₄ and graphite, and the separation efficiency of the photogenerated electrons and holes. The photo-induced h+ and the superoxide anion were the major active species responsible for the photodegradation process. The results demonstrate the feasibility of ZnBi₂O₄-1.0graphite as a potential heterogeneous photocatalyst for environmental remediation.     

The synthesis and characterization of a new butterfly-like polyoxometalate: K5Na2[Mo9V3O38]·9H2O

A new butterfly-like compound K₅Na₂[Mo9V₃O₃₈]·9H₂O 1 has been synthesized in aqueous solution and characterized by elemental analysis, IR spectroscopy, TG analysis, UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammogram and single-crystal X-ray diffraction analysis. Compound 1 is a new butterfly-like molybdodivanadate composed by Mo (VI) and V (V) with the Mo/V ratio 3:1, the polyoxoanion [Mo₉V₃O₃₈ ]^7? can be described as two {MMo₄O₁₈} (M = Mo/V) units connected by one {V₂O₈} core. The photocatalyst property of compound 1 has been investigated, which shows a good photocatalyst for degradation of RhB.     

Novel in-situ synthesis of Au/SnO2 quantum dots for enhanced visible-light-driven photocatalytic applications

In recent years, visible-light-driven metal–semiconductor nanocomposites have emerged as a suitable material for the decomposition of various water and air pollutants. In this work, a novel plasmonic Au nanoparticle (NP)/SnO₂ quantum dot (SQD) nanocomposite photocatalysts were prepared via a one-step solvothermal technique. The as-prepared plasmonic photocatalysts were characterized by various techniques, and the results established the formation of Au/SQD nanocomposites. The photocatalytic activity of the as-prepared plasmonic Au/SQD nanocomposites was examined by the degradation of Rhodamine B (RhB) at room temperature under visible light, and the Au/SQD photocatalyst, prepared using 1.0?g of tin chloride, exhibited a higher rate constant of RhB degradation than pristine SQDs. This exceptional improvement in catalytic performance under visible light is ascribed to a shift of the band gap from the ultraviolet to the visible region. The surface plasmon resonance effect of Au NPs and the synergistic coupling of the metal and the semiconductor QDs also played a vital role in enhancing the catalytic performance. The process of the photocatalytic degradation of RhB by the Au/SQD nanocomposites under visible light is described.     

Photocatalytic degradation of azo dye using TiO2 supported on spherical activated carbon

TiO₂ supported on spherical activated carbon (TiO₂/SAC) was prepared through an ion-exchange method followed by a heat-treatment process. The adsorption characteristic of TiO₂/SAC was evaluated using azo dye methyl orange (MO) as a target substance, and the photocatalytic degradation of MO under UV irradiation was also discussed. A synergistic effect of both the adsorption capacity of activated carbon and the photoactivity of TiO₂ on the removal of MO from aqueous solution was observed. Experimental results revealed that the photocatalytic degradation of MO improved with increasing photocatalyst dosage and followed a pseudo-first order kinetic. After five-cycle runs, TiO₂/SAC still exhibited relatively high photocatalytic characteristic for the degradation of MO. Besides, the prepared TiO₂/SAC can be helpful in the easy separation of photocatalyst from solution after photocatalysis of MO. Furthermore, the use of liquid chromatography/mass spectrometry (LC/MS) technique, identified three intermediates as degradation products during the photocatalytic reaction of MO with TiO₂/SAC.     

Preparation and characterization of a novel activated carbon‐supported N‐doped visible light response photocatalyst (TiO2−xNy/AC)

A photocatalyst, TiO_2?xN_y/AC (activated carbon (AC) supported N‐doped TiO₂), highly active in both the Vis and UV range, was prepared by calcination of the TiO₂ precursor prepared by acid‐catalyzed hydrolysis in an ammonia atmosphere. The powders were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X‐ray diffraction, N₂ adsorption, Fourier transform infrared spectroscopy and phenol degradation. The doped N in the TiO₂ crystal lattice creates an electron‐occupied intra‐band gap allowing electron‐hole pair generation under Vis irradiation (500–560 nm). The TiO_2?xN_y/AC exhibited high levels of activity and the same activity trends for phenol degradation under both Vis and UV irradiation: TiO_2?xN_y/AC calcined at 500 °C for 4 h exhibited the highest activity. The band‐gap level newly formed by doped N can act as a center for the photo‐generated holes and is beneficial for the UV activity enhancement. The performance of the prepared TiO_2?xN_y/AC photocatalyst revealed its practical potential in the field of solar photocatalytic degradation of aqueous contaminants. Copyright © 2007 Society of Chemical Industry     

Hydrothermal synthesis and visible-light photocatalytic activity of porous peanut-like BiVO4 and BiVO4/Fe3O4 submicron structures

Porous peanut-like BiVO₄ and BiVO₄/Fe₃O₄ submicron structures were synthesized by a template-free hydrothermal process at 160 °C for 24 h. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM) and UV–vis spectroscopy. The photocatalytic activity of BiVO₄ and BiVO₄/Fe₃O₄ submicron structures were evaluated for the degradation of Rhodamine B (RhB) and methylene blue (MB) under visible light irradiation with and without the assistance of H₂O₂. According to the experimental results obtained, porous peanut-like BiVO₄/Fe₃O₄ composite photocatalyst shows higher photocatalytic activity in the H₂O₂-assisted system under visible light irradiation compared to BiVO₄. Recycling test on the BiVO₄/Fe₃O₄ composite photocatalyst for the degradation of RhB under visible light irradiation indicates that the composite photocatalyst is stable in the H₂O₂-assisted system in five cycles. Therefore, this composite photocatalyst will be beneficial for efficient degradation of organic pollutants present in water and air under solar light.     

Synthesis of α-β Bi2O3 heterojunction photocatalyst and evaluation of reaction mechanism for degradation of RhB dye under natural sunlight

A few biphasic nano composites containing α and β Bi₂O₃ of varying composition were synthesized by facile solvothermal method without using any capping agent and further calcination. X-ray diffraction, microscopic and spectroscopic techniques were employed for characterization of the as synthesized catalysts which are used as photocatalysts in degradation of pollutant, Rhodamine B (RhB) dye. The band gap of the nanocatalysts as calculated from tauc plot varies within 2.35–2.58 eV for β-form and 2.85–3.19 eV for α-form in the α-β Bi₂O₃ hetrojunctions. The operational parameters that influence the degradation process were optimized. The best catalyst dosage and pH are 0.5 gL^-1 and 4 respectively and the best concentration of H₂O₂ when added is 2 mM for 10 ppm aqueous solution of dye. Among different heterojunctions, the best catalyst which is produced from bismuth nitrate concentration of 0.05 M, degrades RhB up to 99.6% at pH 4 under 120 min sunlight irradiation. The effects of addition inorganic salts in RhB dye solution were also examined. The radical trapping experiments have been applied to explore the involved and main species responsible for degradation. The identification of degradation products of RhB was analyzed and the plausible mechanistic pathway is drawn from HPLC and HRMS. It shows that the degradation of RhB proceeds via initial generation of N-deethylated products followed by ring opening ones, which indicates the photosensitization induced photocatalytic mechanism of the reaction.     

Selective adsorption and degradation of rhodamine B with modified titanium dioxide photocatalyst

A new highly selective photocatalyst (RhB‐MIP/TiO₂) was successfully prepared by surface molecular imprinting technique using rhodamine B (RhB) as template molecule. The adsorption kinetics show RhB‐MIP/TiO₂ possessed fast adsorption rate, and adsorption behavior followed the pseudo‐second‐order kinetics. The static binding experiments revealed RhB‐MIP/TiO₂ displayed strong affinity and high adsorption capacity for RhB. Moreover, the equilibrium adsorption rate of RhB‐MIP/TiO₂ for RhB can be well fitted by the Langmuir isotherm model. The thermodynamics parameters indicated that the binding system of RhB‐MIP/TiO₂ was endothermic and spontaneous. Compared with non‐imprinted photocatalyst (NIP/TiO₂), RhB‐MIP/TiO₂ exhibited excellent selectivity toward RhB, whose selectivity coefficient for RhB relative to rhodamine 6G (Rh6G) was 2.99. Selective photocatalytic degradation experiments indicated that the apparent rate constant for the photodegradation of RhB over RhB‐MIP/TiO₂ is 0.0212 min^?1, being 216% of that over NIP/TiO₂ (0.0098 min^?1). Therefore, RhB‐MIP/TiO₂ exhibited higher photocatalytic selectivity toward RhB. The prepared photocatalyst RhB‐MIP/TiO₂ has a promising perspective in industrial wastewater treatment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40890.     

Synthesis of magnetically separable core–shell structured Ni<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanoparticles photocatalysts for the degradation of organic dyes

In this paper, the core–shell structured NiFe₂O₄@TiO₂ nanoparticles and nanochains as photocatalysts were successfully prepared through hydrothermal and hydrolysis method. The as-prepared core–shell structure was composed of a magnetic NiFe₂O₄ core and photocatalytic titanium oxide coating shell. SEM and TEM images characterized the morphology of NiFe₂O₄@TiO₂ nanoparticles. Moreover, the results of XRD patterns proved that the TiO₂ coating shell consisted of anatase. The VSM measurements showed that the saturation magnetization values of NiFe₂O₄ and NiFe₂O₄@TiO₂ nanoparticles was 65 and 53 emu/g, respectively. The photocatalyst of NiFe₂O₄@TiO₂ nanoparticles exhibited the outstanding recyclable performance for RhB. And, the photo_degradation ration of maintained 69 % after the photocatalyst experienced ten photocatalysis experiments, which is better than that of Fe₃O₄@TiO₂ photocatalysts.     

Synthesis and characterization of α/β-Bi2O3 with enhanced photocatalytic activity for 17α-ethynylestradiol

The α/β-Bi₂O₃ photocatalyst was successfully synthesized by a novel solvothermal-calcination method. The physical and chemical properties of as-prepared samples were characterized based on XRD, XPS, SEM, TEM, EDS, BET, UV–vis DRS and PL techniques. The synthesized α/β-Bi₂O₃ photocatalyst exhibited enhanced photocatalytic activity for 17α-ethinylestradiol (EE2), and 96.9% of EE2 was degraded after only 24 min of visible-light irradiation using α/β-Bi₂O₃ as photocatalyst. The reaction rate constant over α/β-Bi₂O₃ photocatalyst was 1.42, 2.23, 9.22 and 54.1 times higher than pure β-Bi₂O₃, α-Bi₂O₃+β-Bi₂O₃, α-Bi₂O₃ and P25 respectively. Effect of catalyst dosage and pH value was investigated. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. α/β-Bi₂O₃ was a fairly stable and efficient photocatalyst under the studied experimental conditions, proving that the α/β-Bi₂O₃ photocatalyst was a promising photocatalyst for the practical application.