Photocatalytic Decolorization Of Methyl Orange Research Articles

TiO2-functionalized biochar from pistachio nutshells: adsorptive removal and photocatalytic decolorization of methyl orange

Pistachio nutshells-derived biochar (PNS-BC) was utilized as a cost-effective adsorbent for competently removing a model dye, methyl orange (MO) from wastewater. Three concentrations of TiO2; 1%, 2%, and 3% were used to decorate the biochar. Analysis of morphology, stability, and structure of the three adsorbents (PNS, PNS-BC, and the TiO2 functionalized biochar; TiO2@PNS-BC) was extensively explored using various characterization techniques. The synergistic photocatalytic-adsorptive efficiency of the three adsorbents was compared. In this regard, a Box-Behnken (BB) design-based multivariate scheme was inaugurated with the target of maximizing MO removal (%R) while using the minimum possible of chemicals and resources. The impact of five variables; %TiO2, dose of TiO2-PNS, reaction time, dye concentration, and pH on the magnitude of %R was investigated. Results show that 97.69% removal of MO could be recognized over 120 min using adsorption compared to 99.47% removal over 30 min using 3% TiO2@PNS-BC as a photocatalyst. A 3% TiO2@PNS-BC was the best catalyst (compared to 1% and 2%) with a decolorization rate constant of 0.12741 min−1, ~ 1.5 × faster compared to the decolorization of MO using adsorption alone. Adsorption of MO conformed well to Langmuir isotherm. A maximum adsorption capacity (qmax) of 142.38 mg/g was achieved. Adsorption kinetics fitted well with the pseudo-second order (PSO) model. Results obtained indicated that biochar of PNS is a promising, cost-effective, and economical adsorbent.

Cuprous Oxide Films Deposition by Mid-Frequency Magnetron Sputtering and Their Photocatalytic Activity under Visible Light

Cuprous oxide (Cu2O) has attracted much attention as a photocatalytic material. In this paper, the mid-frequency reactive magnetron sputtering method was used to prepare Cu2O films on glass slides, and the effects of oxygen flow and deposition time on the structures, morphologies and photocatalytic properties of the films were studied. The results show that the films prepared by this method have smooth surfaces and good absorptivity in the visible region. As the oxygen flow increases, the films transit from the mixed-phase of Cu and Cu2O to the single-phase of Cu2O. When the oxygen flow continues to increase, the films change to a mixed-phase of Cu4O3 and Cu2O. The photocatalytic decolorization of methyl orange under visible light irradiation conditions was used to assess the photocatalytic properties of the prepared films. When the oxygen flow is 6[Formula: see text]sccm and the deposition time is 15[Formula: see text]min, the film exhibits the best photocatalytic activity. Finally, the Mulliken electronegativity theory was used to explain the photocatalytic mechanism of Cu2O. This study confirmed the feasibility of preparing Cu2O photocatalytic films by magnetron sputtering, and provided the experimental basis for the subsequent study of Cu2O photocatalytic films.

Effect of charge balance vacancies on the ultraviolet photocatalytic activity of Fe3+-doped anatase

The presence of Fe3+ dopant ions rastically decreases the activity of TiO2 powders in the photocatalytic decolorization of methyl orange. A comparison of the photocatalytic activities of the 0.6 at% Fe3+: TiO2 and 0.6 at% Cr3+: TiO2 samples before and after their hydrogen annealing shows that this negative effect is mainly due to the formation of charge balance oxygen vacancies VO, and it does almost not depend on the physicochemical properties of M3+ dopants. The 57Fe Mossbauer spectrum of 2 at% Fe3+: TiO2 indicates that nearly every other Fe3+ ion introduced into TiO2 possesses a vacancy VO in its nearest surrounding.

Facile synthesis, characterization and photocatalytic activity of Ag3PO4/Ag2W2O7 heterojunction composite

A series of Ag3PO4/Ag2W2O7 heterojunction composite photocatalyst with ascending Ag2W2O7 content (W loading 0–30%) were synthesized through one-shot coprecipitation technique and characterized by XRD, SEM, Raman and DR UV–Vis spectroscopy. The photocatalytic activity of the synthesized samples was evaluated by the photocatalytic decolorization of methyl orange (MO) dye under visible light illumination and compared with that of neat Ag3PO4. Ag3PO4/Ag2W2O7 heterojunction composite with W loading 10% exhibited the highest photocatalytic activity, in which 65% of MO was decolorized after 10 min, versus 9% in the case of neat Ag3PO4. Moreover, the apparent rate constant of MO decolorization in the case of Ag3PO4/Ag2W2O7 composite was 7.2 times higher than neat Ag3PO4. However, Ag3PO4/Ag2W2O7 heterojunctions with W loadings exceeding 10% showed lower photocatalytic efficiency, most likely, due to increasing Ag2W2O7 content in the composite which shields Ag3PO4 surface and restricts the photocatalytic process. The enhancement in the photocatalytic activity of the prepared samples was attributed to the effective separation of photogenerated electron-hole pairs as a result of the formed heterojunction between Ag3PO4 and Ag2W2O7 in the composite. The formed Ag3PO4/Ag2W2O7 heterojunction showed a shift of the optical absorption edge of Ag3PO4 to longer wavelengths. Thus, it can be concluded that Ag3PO4/Ag2W2O7 heterojunction composite with W loading of 10% is a promising photocatalyst in visible light illumination for industrial wastewater treatment.

Photoluminescence and photocatalytic activities of Ag/ZnO metal-semiconductor heterostructure

Present article focuses on the photocatalytic activities of ZnO nanorods and Ag/ZnO heterostructure deposited on polyethylene terephthalate (PET) substrate. ZnO nanorods are synthesized by thermal decomposition technique and Ag nanoparticles deposition is done by photo-deposition technique using UV light. X-ray diffraction studies reveal that the ZnO nanorods are of hexagonal wurtzite structure. Further, as-prepared samples are characterized by Scanning Electron Microscopy (SEM), Photoluminescence (PL) spectroscopy and UV-Vis spectroscopy. The surface plasmon resonance response of Ag/ZnO is found at 420 nm. The photocatalytic activities of the samples are evaluated by photocatalytic decolorization of methyl orange (MO) dye with UV irradiation. The degradation rate of MO increases with increase in irradiation time. The degradation of MO follows the first order kinetics. The photocatalytic activity of Ag/ZnO heterostructure is found to be more than that of ZnO nanorods. The PL intensity of ZnO nanorods is stronger than that of the Ag/ZnO heterostructure. The strong PL intensity indicates high recombination rate of photoinduced charge carriers which lowers the photocatalytic activity of ZnO nanorods. The charge carrier recombination is effectively suppressed by introducing Ag nanoparticles on the surface of the ZnO nanorods. This study demonstrates a strong relationship between PL intensity and photocatalytic activity.

Preparation of ZnO nanoparticles using a rotating packed bed

Zinc oxide (ZnO) nanoparticles can be prepared by the precipitation method in a rotating packed bed (RPB). In this work, precursors were firstly prepared in a continuous mode using the liquid-liquid reaction of zinc chloride (ZnCl2) and sodium hydroxide (NaOH). The effects of the molar ratio of ZnCl2 to NaOH, the flow rates of aqueous ZnCl2 and NaOH, the rotational speed, and the concentrations of ZnCl2 and NaOH on the size of the precursors were examined. Experimental results demonstrate that larger flow rates of the reactant and precipitant, a higher rotational speed, and higher concentrations of ZnCl2 and NaOH were associated with smaller precursors. The smallest precursors were obtained at a ZnCl2 concentration of 0.8mol/L, an NaOH concentration of 1.6mol/L, a rotational speed of 2000rpm, and flow rates of 0.5L/min. Then, the aforementioned precursors were calcined at 450°C for 1h to yield ZnO nanoparticles with a mean size of 68nm and a rather narrow size distribution. The photocatalytic activity of ZnO nanoparticles was evaluated by the photocatalytic decolorization of methyl orange. After 3L of aqueous methyl orange had been photodegraded by ZnO nanoparticles for 200min, the decolorization efficiency of methyl orange was found to be 84%.

One-pot template-free synthesis of porous CdMoO4 microspheres and their enhanced photocatalytic activity

The optical and catalytic performances of materials strongly depend on their size, morphology, dimensionality and structure. Herein, we demonstrate a facile one-pot template free synthesis of hierarchical CdMoO4 porous microspheres via a simple low temperature oil bath method. The photoactivity of the as-prepared samples was evaluated by photocatalytic decolorization of Methyl Orange (MO) and Methylene Blue (MB) mixed dye aqueous solutions at ambient temperature under full solar spectrum. The results indicated that the concentration of ammonium molybdate and reaction time greatly influence the diameter, average crystallite size, specific surface area, pore structure and photocatalytic activity of the prepared samples. Especially, under the suitable conditions the prepared hierarchical CdMoO porous microspheres exhibited enhanced photocatalytic activity and high stability. Furthermore, it is found that the photocatalytic activity and formation rate of hydroxyl radicals greatly depend on the particle sizes and morphology of as-prepared samples. This work not only demonstrates a simple way to fabricate the hierarchical CdMoO4 porous microspheres but also shows a possibility for utilization of CdMoO4 porous microspheres for the photocatalytic treatment of waste water pollutants.

Preparation of α-SnWO4 hierarchical spheres by Bi3+-doping and their enhanced photocatalytic activity under visible light

Bi-doped α-SnWO4 porous spheres assembled by thin plates were prepared by a simple hydrothermal process without any template. The effects of Bi3+ ions on the microstructure and photocatalytic activity of α-SnWO4 were investigated. The doping of Bi can induce a shape transformation from nanoplates of pure α-SnWO4 to hierarchical spheres of Bi-doped samples. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic de-colorization of methyl orange (MO) under visible light irradiation. Bi-doped α-SnWO4 samples exhibit better photocatalytic property than pure α-SnWO4, and the optimal Bi-doping concentration is around 0.5at%. The enhanced photocatalytic properties of Bi-doped α-SnWO4 spheres can be ascribed to the porous hierarchical structure and the introduction of defects induced by Bi-doping, which improve visible-light absorption and allow the efficient charge separation of the photogenerated electron-hole pairs. Bi-doped α-SnWO4 has a great potential in industrial water treatment due to its satisfactory recyclability and stability.

Enhanced photocatalytic activity of calcined natural sphalerite under visible light irradiation

The photocatalytic activity of natural sphalerite (the main mineral ore of ZnS) is relatively low in the absence of sacrificial donors. Present work focuses on the improvement of the photocatalytic activity of a natural sphalerite obtained from Abuni deposit, Nigeria, via calcination at 600°C, 700°C and 800°C. The raw and calcined natural sphalerite samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and specific surface area analysis. The activity of the raw and calcined samples was evaluated using photocatalytic decolorization of methyl orange (MO) as the model reaction. The kinetics of photocatalytic decolorization of MO on the raw and calcined natural sphalerite samples was fitted to the pseudo-first order approximation of the Langmuir–Hinshelwood model. The photocatalytic activity of the natural sphalerite was doubled upon calcination at 700°C. The natural sphalerite calcined at 700°C is also more active than the ones calcined at 600°C and 800°C due to the combined effects of chemical composition, crystallite size, specific surface area and oxygen vacancies.

A novel fabrication of Cu2O@Cu7S4 core-shell micro/nanocrystals from Cu2O temples and enhanced photocatalytic activities

Uniform and monodispersed Cu2O@Cu7S4 core-shell micro/nanocrystals have been synthesized successfully at room temperature via a simple chemical etching reaction, using Cu2O as sacrificial template. The structure and properties of the crystals were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS). The photocatalytic activity of the Cu2O@Cu7S4 crystals was evaluated by photocatalytic decolorization of MeO (methyl orange) aqueous solution at ambient temperature under visible-light irradiation. The results show that the as-prepared Cu2O@Cu7S4 crystals revealed core-shell structure, which maintained the same morphology with corresponding template and were composed of cuboctahedron Cu7S4 shell and active Cu2O core. Due to the unique Cu2O@Cu7S4 core-shell structure, the crystals exhibit enhanced photocatalytic activity than that of the pure Cu2O crystals, and the photocatalytic activity of different R crystals is diverse from each other. A possible formation mechanism has been proposed.

Novel porous Ag2S/ZnS composite nanospheres: Fabrication and enhanced visible-light photocatalytic activities

Elimination of toxic organic compounds from wastewater is a longstanding challenge in the fields of environmental science, especially, under the visible-light irradiation. Here we present a facile design to fabricate novel porous Ag2S/ZnS composite nanospheres via a hydrothermal procedure followed by a cation exchange method. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray energy-dispersive spectroscopy (EDS), and UV–vis spectroscopy were used to characterize the crystallinity, morphology, structure and properties of the composite nanospheres. The photocatalytic performance was evaluated by the photocatalytic decolorization of methyl orange in aqueous solution under visible light irradiation. Results show that the composite nanospheres exhibited enhanced visible light photocatalytic activity compared with the initial porous ZnS nanospheres. Among them, sample of Ag0.4Zn0.8S gave the highest degradation rate of about 96% under visible-light irradiation within 15 min. The enhanced photocatalytic activity was presumed to result from the direct photoinduced interfacial charge transfer (IFCT) from the valence band (VB) of ZnS to Ag2S, due to the intimate contact between ZnS and Ag2S, the porous structure, and the appropriate composition ratio of porous Ag2S/ZnS composite. The present method could be extended to fabricate a large number of semiconductor composites for catalysis and solar cells based on the difference of the solubility products.

Fabrication of porous silver/titania composite hollow spheres with enhanced photocatalytic performance

Silver/titania composite hollow spheres were first synthesized through an in-situ chemical reaction using functional-grouped carbon spheres as the template in this study. The prepared samples were characterized through an X-ray diffraction, N2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy and UV–Vis spectrophotometer. The photocatalytic activity of as-prepared samples was evaluated by photocatalytic decolorization of Methyl orange (MO) aqueous solution at ambient temperature under UV light. We found a structure with an optimal Ag:TiO2 composition that exhibited a photodecomposition rate constant more than twice as high as titania hollow spheres lacking silver, and over three times higher than a commercial photocatalyst.

Synthesis of nanocrystalline Ga–TiO2 powders by mild hydrothermal method and their visible light photoactivity

In this work, nano-sized gallium doped titanium dioxide (Ga–TiO2) powders with different dopant concentrations (0.1, 0.6 and 1.2mol%) were synthesized by a mild hydrothermal method dwelling at 150°C for 10h without any post heat treatment. The synthesized samples were characterized by X-ray diffraction (XRD), Brunauer–Emment–Teller (BET) specific surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–visible light diffuse-reflection spectra (DRS). The photocatalytic activities were evaluated via photocatalytic decolorization of methyl orange under 420–780nm visible light irradiation. Due to the small particle size, large specific surface area, improved visible light response and enhanced separation of photo-excited carriers, Ga–TiO2 photocatalysts exhibit better photocatalytic activity than that of Degussa P25 or un-doped TiO2, which prepared under the same processing conditions. Among all the Ga doped TiO2 photocatalysts, 0.6mol% Ga–TiO2 shows the best photo-decolorization efficiency reaching up to 82%.

Photocatalytic Decolorization Study of Methyl Orange by TiO<sub>2</sub>–Chitosan Nanocomposites

The photocatalytic decolorization of methyl orange (MO) by TiO2-chitosan nanocomposite has been studied. This study was started by synthesizing TiO2-chitosan nanocomposites using sol-gel method with various concentrations of Titanium(IV) isopropoxide (TTIP) as the TiO2 precursor. The structure, surface morphology, thermal and optical property of TiO2-chitosan nanocomposite were characterized by X-ray diffraction (XRD), fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and diffuse reflectance ultra violet (DRUV) spectroscopy. The photocatalytic activity of TiO2-chitosan nanocomposite was evaluated by photocatalytic decolorization of methyl orange as a model pollutant. The results indicate that the particle size of TiO2 increases with increasing ofthe concentration of TTIP, in which TiO2 with smallest particle size exhibit the highest photocatalytic activity. The highest photocatalytic decolorization was obtained at 5 h of contact time, initial concentration of MO at 20 ppm and at solution pH of 4. Using these conditions, over 90% of MO was able to be decolorized using 0.02 g of TiO2-chitosan nanocomposite under UV light irradiation. The TiO2-chitosan nanocomposite could be reused, which meant that the TiO2-chitosan nanocomposites can be developed as an effective and economical photocatalyst to decolorize or treat dye in wastewater.

A facile preparation of nanosized ZnO and its use in photocatalytic decolorization of methyl orange

Nanoparticles zinc metal was prepared by a simple electrochemical method of a N,N-dimethylformamide solution containing 0.1M tetraethylammoniumperchlorate in the presence of naphthalene as a mediator in a one-compartment cell fitted with a platinum plate cathode and a zinc plate anode at 60mA/cm2 of constant current under a nitrogen atmosphere. The prepared zinc oxide (ZnOelec) was characterized by FE-SEM, TEM, XRD, nitrogensorptionand DRUV spectrophotometer, which confirmed that the particles of ZnOelec are composed of pure nanosized ZnO with a large surface area andmajority of particle size was less than 20 nm. The particles size of the ZnOelec affected its photoactivity, which clearly observed when it was tested on adecolorization of methyl orange under UV illumination. By using ZnOelec, 50% of higher removal percentage of MO was achieved compared tocommercial zinc, which only gave 30% after 30 min of contact time. These result shows that ZnOelec has a great potential to be used as a catalyst for thephotocatalytic decolorization of industrial dyes wastewater.

Cu(II) as a General Cocatalyst for Improved Visible-Light Photocatalytic Performance of Photosensitive Ag-Based Compounds

Usually, cocatalyst modification of photocatalysts is an efficient approach to enhance the photocatalytic performance by promoting effective separation of photogenerated electrons and holes. It is highly required to explore new and effective cocatalysts to further enhance the photocatalytic performance of photocatalytic materials. In the present work, Cu(II) cocatalyst was successfully loaded on the surface of various Ag-based compounds (such as AgCl, Ag3PO4, AgBr, AgI, Ag2CO3, and Ag2O) by a simple impregnation route, and their photocatalytic activity of Cu(II)/Ag-based photocatalysts was evaluated by the photocatalytic decolorization of methyl orange and photocatalytic decomposition of phenol solution under visible-light illumination. As one of the typical photosensitive Ag-based compounds, the photocatalytic activity of AgCl could be greatly improved by optimizing the amount of Cu(II) cocatalyst, and the highest photocatalytic performance of the resulted Cu(II)/AgCl was higher than that of the unmodifi...

Enhanced photocatalytic decolorization of methyl orange by gallium-doped α-Fe2O3

Gallium (Ga)-doped hematite (α-Fe2O3) with different molar ratios of Ga/Fe (1%, 2%, 3% and 4%) was prepared by a facile parallel flow co-precipitation method. The photocatalysts prepared were characterized by the Brunauer–Emmett–Teller method, X-ray diffraction, UV/vis diffuse reflectance spectroscopy, and scanning electron microscope. The photo-generated charges separation efficiency of different photocatalysts was investigated using benzoquinone as scavenger. The formation rate of OH radicals produced during the photocatalytic reaction process was studied by a terephthalic acid photoluminescence probing technique. Doping Ga3+ into α-Fe2O3 increases the specific surface area and the separation efficiency of photo-induced charges. The catalytic activity of the photocatalysts for decolorization of methyl orange aqueous solution was investigated. The results show that α-Fe2O3 doped with 3% Ga possesses the best photocatalytic activity. The underlying mechanism is suggested.

Photocatalytic decolorization of methyl orange solution with KIO3

The use of azo dyes must be controlled and the sewage must be properly treated before being released into the environment. Thus, it is crucial to develop processes that can destroy these azo dyes completely. It has been reported that a methyl orange (MO) aqueous solution can be effectively decolorized in KIO3 homogeneous system under UV light irradiation. In this study, the kinetics and effects of KIO4, H2O2, K2S2O8, and KBrO3 on the decolorization of MO with KIO3 under UV light irradiation were investigated in detail. The results show the decolorization reaction is a zero-order reaction when the concentration of MO is above 25 mg/L. IO4-, S2O82-, BrO3-, and H2O2 can greatly inhibit the photocatalytic decolorization reaction of MO. Several observations indicate the photocatalytic decolorization of MO with KIO3 under UV irradiation occurs by ⋅O2- attack only. A more detailed mechanism of KIO3 photocatalysis will be further investigated in the near future.

Preparation and Characterization of HAp/TiO<sub>2</sub> Nanocomposite for Photocatalytic Degradation of Methyl Orange under UV-Irradiation

A new in-situ precipitation technique is introduced in this study to prepare hydroxyapatite/titania nanocomposites. This technique provides a better control over the microstructures and phase compositions of nanocomposites. The structure and surface morphology of hydroxyapatite/titania nanocomposite were characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy and scanning electron microscopes. The photocatalytic activity of hydroxyapatite/titania nanocomposite was evaluated by photocatalytic decolorization of methyl orange in aqueous solution as a model pollutant under UV-irradiation. X-ray diffraction and Fourier transform infrared results indicated that hydroxyapatite and anatase (TiO2) were the major crystalline phases. There had been no reaction between hydroxyapatite and titania compounds. Based on the SEM images, the overall morphology of the samples indicates that there exists a distribution of small particles and large agglomerates.The hydroxyapatite/titania nanocomposite exhibited high photocatalytic activity hydroxyapatite/titania nanocomposite under UV-irradiation. After 8 h of irradiation by UV-irradiation, over 80% of methyl orange solution (5 mg L-1) was decolorized with 1 gL-1 of the photocatalyst. Since this process does not require the addition of hydrogen peroxide and uses UV-irradiation in this study are environmentally friendly method to decolorize azo dye.

Kinetic Study on Photocatalytic Decolorization of Methyl Orange Aqueous Solution with KIO<sub>4</sub> under UV Irradiation

It has been generally agreed that methyl orange (MO) can be effectively decolorized in KIO4 homogeneous reaction system under UV irradiation. The knowledge on the kinetics of the system possesses both practical and theoretical values. Decolorization efficiency of MO increases as the loading of KIO4 increases and has no an optimal amount of KIO4 in this case. The decolorization reaction manifests the first order with lower concentration and the zero order with higher concentration. As the initial concentration goes up, the order of the reaction is reduced from 1 to 0.