Photoelectrocatalytic Degradation Of Methyl Orange Research Articles

Interface-engineered Z-scheme of BiVO4/g-C3N4 photoanode for boosted photoelectrochemical water splitting and organic contaminant elimination under solar light

Although n-type bismuth vanadate (BiVO4) is regarded as an attractive solar-light-active photoanode, its short carrier-diffusion length, sluggish oxidation kinetics, low electronic conductivity, and high recombination rate are the major intrinsic shortcomings that limit its practical application. To this end, the rational design of a solar-light-active, metal-free BiVO4-based Z-scheme heterojunction photoanode is of great significance for achieving effective charge-separation features and maximum light utilization as well as boosting redox activity for efficient environmental treatment and photoelectrochemical water splitting. Herein, we propose a facile approach for the decoration of metal-free graphitic carbon nitride (g-C3N4) nanosheets on BiVO4 to form a Z-scheme BiVO4/g-C3N4 photoanode with boosted photoelectrochemical (PEC) water splitting and rapid photoelectrocatalytic degradation of methyl orange (MO) dye under simulated solar light. The successful preparation of the Z-scheme BiVO4/g-C3N4 photoanode was confirmed by comprehensive structural, morphological, and optical analyses. Compared with the moderate photocurrent density of bare BiVO4 (0.39 mA cm−2), the Z-scheme BiVO4/g-C3N4 photoanode yields a notable photocurrent density of 1.14 mA cm−2 at 1.23 V vs. RHE (≈3-fold higher) with the promising long-term stability of 5 h without any significant photo-corrosion. Moreover, the PEC dye-degradation studies revealed that the Z-scheme BiVO4/g-C3N4 photoanode successfully degraded MO (≈90%) in 75 min, signifying a 30% improvement over bare BiVO4. This research paves the way for rational interface engineering of solar-light-active BiVO4-based noble-metal-free Z-schemes for eco-friendly PEC water splitting and water remediation.

A Simple g-C3N4/TNTs Heterojunction for Improving the Photoelectrocatalytic Degradation of Methyl Orange

In this work, highly ordered titanium dioxide nanotube arrays (TNTs) were first prepared by anodic oxidation method. Then, g-C3N4/TNTs heterojunctions were prepared by ultrasonically loading graphitic carbon nitride (g-C3N4) onto the TNTs. The morphology and crystal structure of TNTs and g-C3N4/TNTs were characterized by SEM/TEM and XRD. The photoelectrocatalytic (PEC) degradation of methyl orange (MO) by TNTs and g-C3N4/TNTs was studied in a PEC degradation system. The photocatalytic (PC), electrocatalytic (EC), and PEC degradation properties were compared, and the effect of pollutant concentration on the degradation performance of the catalysts was analyzed. According to the experimental results, the degradation rate of MO with TNTs only reaches 65.1% after 120 min, while the degradation rate of MO with g-C3N4/TNTs reaches 84.6% in the same time. Due to the synergistic effect of light and electricity, the PEC degradation efficiency of the two catalysts is greater than the sum of PC and EC degradation, proving that g-C3N4/TNTs heterojunctions provide excellent PEC performance for the degradation of MO.

Morphological and structural control of pulse electrodeposited ZnO thin films and its influence on the photoelectrocatalytic degradation of methyl orange

ZnO thin films were obtained by pulsed electrodeposition (PE). A potential of − 1.1 V is applied during the time-On (ton) period, while open-circuit potential is applied during the time-off (toff) period. The effect of the toff duration on the properties of ZnO films and their photoelectrocatalytic activity was studied in detail. Decreasing toff from 7 s to 1 s tailors the structural, morphological and optical properties of ZnO films and improves their photoelectrocatalytic activity. XRD analysis confirms a wurzite hexagonal structure along the (002) direction for all samples. The SEM images show an amelioration of ZnO morphology from nanosheets to nanorods films. The photocurrent response indicates a high value of 480 µA/cm2 for ZnO film deposited at toff = 1 s. All the electrodeposited films were tested for the photoelectrocatalytic degradation of methyl orange (MO). The ZnO film deposited at low toff (1 s) reveals a faster degradation of MO, reaching 67% after 360 min UV-irradiation. This is attributed to the nano-rod morphology that provides greater surface area and to the lower energy band-gap of the sample.

Enhanced Photoelectrocatalytic Activity in Ni-TiO2 Nanocomposites Fabricated By Pulse Potential Deposition

The Ni-TiO2 single layer nanocomposites were fabricated on copper substrates by the pulse plating (PP) and pulse reverse plating (PRP) techniques. Morphological studies conducted by field emission scanning electron microscopy (FESEM) revealed that pulse potentials and durations affected the microstructure of coatings. The chemical composition of coatings was studied by energy dispersive X-ray system (EDX) and it was found that by the prolongation of current-off durations in PP and anodic cycles in PRP, deposits containing 11.58 wt.% and 13.16 wt.% TiO2 were produced, respectively. The influence of heat treatment temperature on the phase structure of Ni-TiO2 nanocomposites was investigated using X-ray diffraction and it was demonstrated that the anatase to rutile transformation occurred at temperatures higher than 450°C. The hydrophilicity of Ni-TiO2 coatings was evaluated by monitoring the change of water contact angle under the UV illumination. It was observed that the nanocomposite prepared by PRP exhibited the maximum hydrophilicity after 3 hours of heat treatment at 450°C, for which the contact angel prior to UV irradiation was 78.96° and after 1h of UV irradiation it reduced to 13.65°. Surface hydroxyl groups density which account for the photo-induced hydrophilicity of the Ni-TiO2 coating was defined by X-ray photoelectron spectroscopy (XPS), before and after 1h of UV illumination. The results indicated that under the optimized condition, for the coatings prepared by PP and PRP, 12.6% and 15.3% increases were detected in the density of hydroxyl groups. To evaluate the effect of pulse plating parameters on the photocatalytic activity of the Ni-TiO2 coatings prepared by PP and PRP, photo-degradation experiments of methyl orange aqueous solution were carried out under the UV light. The results indicated that TiO2 content, irradiation duration and sintering temperature affected the photocatalytic efficiency of the coatings, and the optimized PP and PRP deposited coatings were capable of disintegrating the methyl orange up to 76.21% and 51.89% after 1 hours of UV illumination. The photoelectrocatalytic degradation of methyl orange by Ni-TiO2 coatings was studied and the effect of different applied potentials was determined. The amounts of methyl orange degraded by the PP and PRP deposited composites under the anodic potential of 600 mV along with 1 hours of simultaneous UV illumination were 75.30% and 89.61%, respectively.

Fabrication of Au nanoparticle/TiO2 hybrid films for photoelectrocatalytic degradation of methyl orange

Au nanoparticles and TiO2 nanotube hybrid materials were prepared electrochemically. The Ti wire was used to form TiO2 nanotube arrays via anodization and subsequent annealing process. The Au nanoparticles were then electrodeposited in chloroauric acid solution to form Au/TiO2 hybrid layers. These two steps were repeated to prepare Au/TiO2, TiO2/Au/TiO2 and Au/TiO2/Au/TiO2 hybrid materials, and the preparation mechanism is discussed. The Au/TiO2 hybrid materials also exhibited different photoelectrocatalytic activities for decomposing methyl orange. The application of the Au/TiO2/Au/TiO2 hybrid material as a photo-anode has been simultaneously examined toward electrochemical-oxidation, photo-oxidation, and photoelectro-oxidation of methyl orange. The photoelectrocatalytic mechanism of Au/TiO2/Au/TiO2 hybrid material and its degradation reaction mechanism for methyl orange were evaluated.

Visible light catalysis of methyl orange using nanostructured WO3 thin films

WO3 thin films have been deposited onto glass and FTO coated glass substrates using a simple chemical spray pyrolysis technique. The structural, morphological, optical and photocatalytic properties of WO3 thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc=0.38mA and Voc=0.59V) relatively higher at 300°C substrate temperature. The structure and morphology of WO3 thin films are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD study reveals that the films are polycrystalline in nature with monoclinic crystal structure. SEM images show that the substrate surface is covered with a uniform and grain like morphology. The AFM images show the rough nature of the film. The structure and local symmetry of the film are studied with the help Raman spectroscopy. The chief vibrational modes of the WO3 sample, located at 805, 715 and 269cm−1 corresponding to the stretching and the bending of O–W–O bond respectively and are consistent with a monoclinic structure and the low-frequency peaks are observed at 269 and 325cm−1 can be assigned due to the bending δ (O\\W\\O) vibrations in monoclinic structure. Photoelectrocatalytic degradation of methyl orange (MO) dye in aqueous solutions is studied. The end result shows that the degradation percentage of methyl orange (MO) using WO3 photoelectrode has reached 98% under visible light illumination after 320min. The amount of degradation is confirmed by COD and TOC analysis.

Visible light photoelectrocatalytic degradation of methyl orange using anodized nanoporous WO3

Nanoporous, monoclinic WO3 photoanodes with average pore wall thicknesses of ∼15nm were prepared by the electrochemical anodization of tungsten foil in 0.25wt% HF electrolyte at 50V and subsequent annealing at 500°C. The photoelectrocatalytic activities of the prepared photoanodes in methyl orange (MO) decoloration were assessed under visible light irradiation. Faster MO decoloration was observed in photoelectrocatalysis than in photocatalysis or electrocatalysis. The effects of various reaction parameters such as supporting electrolyte, light intensity, bias potential and initial MO concentration were examined. MO decoloration in 0.1moldm−3 NaH2PO4 electrolyte was faster than in 0.1moldm−3 Na2SO4 or NaHCO3 electrolyte. Increasing the applied bias potential or light intensity increased the decoloration rate. Increasing the MO concentration decreased the decoloration efficiency. The photoelectrocatalytic activity of a nanoporous WO3 photoanode was not reduced after recycling. The degradation under a 0.1Wcm−2 light intensity resulted in a high decoloration and mineralization efficiency and good catalyst stability. The suitable 2.77eV bandgap and efficient photogenerated charge separation were believed to contribute to the effective MO photoelectrocatalytic degradation by the WO3 photoanode.

Uniformly Dispersed and Controllable Ligand‐Free Silver‐Nanoparticle‐Decorated TiO2 Nanotube Arrays with Enhanced Photoelectrochemical Behaviors

Homogeneously dispersed silver nanoparticles (AgNPs) were successfully decorated onto the surface of TiO2 nanotube arrays (TNTA) by means of an in situ photoreduction method. TNTA films as supports exhibit excellent properties to prevent agglomeration of AgNPs, and they also avoid using polymer ligands, which is deleterious to enhancing the properties of the fabricated NPs. The silver particle size and its content could be controlled just by changing the immersion time. Detailed SEM and TEM analyses combined with energy-dispersive X-ray spectroscopy analyses with different immersion times (5, 10, 30, 60 min) have revealed the variation tendency. The prepared Ag/TNTA composite films were also characterized by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The UV/Vis diffuse reflectance spectra displayed a redshift of the absorption peak with the growth of AgNPs. The photocurrent response and the photoelectrocatalytic degradation of methyl orange (MO) were used to evaluate the photoelectrochemical properties of the fabricated samples. The results showed that the photocurrent response and photoelectrocatalytic activity largely depended on the loaded Ag particle size and content. TNTA films with a diameter of 17.92 nm and silver content of 1.15 at% showed the highest photocurrent response and degradation rate of MO. The enhanced properties could be attributed to the synergistic effect between AgNPs and TiO2. To make good use of this effect, particle size and silver content should be well controlled to develop the electron charge and discharge process during the photoelectrical process. Neither smaller nor larger AgNPs caused decreased photoelectrical properties.

Enhanced Visible‐Light‐Induced Photoelectrocatalytic Degradation of Methyl Orange by CdS Sensitized TiO2 Nanotube Arrays Electrode

AbstractIn this work, CdS sensitized TiO2 nanotube arrays (CdS/TiO2NTs) electrode was synthesized with the CdS deposition on the highly ordered titanium dioxide nanotube arrays (TiO2NTs) by sequential chemical bath deposition method (S‐CBD). The as‐prepared CdS/TiO2NTs was characterized by field‐emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD). The results indicated that the CdS nanoparticles were effectively deposited on the surface of TiO2NTs. The amperometric I‐t curve on the CdS/TiO2NTs electrode was also presented. It was found that the photocurrent density was enhanced significantly from 0.5 to 1.85 mA/cm2 upon illumination with applied potential of 0.5 V at the central wavelength of 253.7 nm. The photoelectrocatalytic (PEC) activity of the CdS/TiO2NTs electrode was investigated by degradation of methyl orange (MO) in aqueous solution. Compared with TiO2NTs electrode, the degradation efficiencies of CdS/TiO2NTs electrode increased from 78% to 99.2% under UV light in 2 h, and from 14% to 99.2% under visible light in 3 h, which was caused by effective separation of the electrons and holes due to the effect of CdS, hence inhibiting the recombination of electron/hole pairs of TiO2NTs.

Porous TiO2 Film Electrode Used for Photoelectrocatalytic Degradation of Methyl Orange in NaHCO3 Solution

PEG1000 was used as template to prepare porous TiO2 film by sol-gel method. The functions of applied potential and concentration of NaHCO3 to the photoelectrocatalytic degradation of methyl orange on porous and smooth TiO2 films were investigated. Methyl orange degradation rate has two optimal values at the applied potential of 0.8 V and 1.8 V. The addition of PEG may have negative effect on photoelectrocatalytic activity of TiO2 film. The degradation rate increases with increasing NaHCO3 concentration from 0 up to 0.05 mol/l, and then it declines after further increase of electrolyte concentration. After 100 min of reaction, the degradation rates on the films prepared without and with PEG addition are 63.78% and 65.22%, respectively.

Photoelectrocatalytic degradation of methyl orange over mesoporous film electrodes

Mesoporous TiO(2) films and ion-doped photocatalytic films, displaying a worm-like pattern, have been synthesized by dip-coating of ITO glass into an organic-inorganic sol followed by aging and calcination of the coating at different temperature. The prepared films were investigated by X-ray diffraction (XRD), UV-Vis reflectance spectra, scanning electron microscope (SEM), transmission electron microscopy (TEM) and photoelectrochemical measurement, and were confirmed to be of mesoporous characteristic. Degradation of methyl orange (MO) has been performed using the new film electrodes under UV light and artificial solar light illumination. The influence of variables, such as applied bias, pH, supporting electrolyte, MO concentration and the load of the films, on the degradation of the dye was investigated. More than 97% degradation of MO was achieved under the feasible experimental conditions in 2 h photoelectrocatalytic reaction with UV light illumination and mesoporous film TiO(2)/ITO as electrode. The activity of the mesoporous film V-TiO(2) was the highest of the newly synthesized films V-TiO(2), Ce-TiO(2), F-TiO(2) and pure TiO(2) under artificial solar light. The degradation ratio of MO was about 43% over 2 h reaction using V-TiO(2)/ITO as the electrode. The activity of the mesoporous film under artificial solar light needs to be increased further.

Facile fabrication, characterization, and enhanced photoelectrocatalytic degradation performance of highly oriented TiO2 nanotube arrays

Highly ordered TiO2 nanotube arrays were successfully fabricated using ethanol and water mixture electrolytes (40 vol% ethanol and 0.2 wt% hydrofluoric acid) by a facile electrochemical anodization method. The as-prepared nanotube arrays were grown perpendicular to the titanium substrate with about 90 nm in diameter, 20 nm in wall thickness, and around 500 nm in length. The formation mechanism of the samples is briefly discussed. A blue shift in the spectrum of UV–Vis absorption was observed with respect to a piece of the sol–gel derived TiO2 film. Moreover, photocurrent response and photoelectrocatalytic degradation of methyl orange under ultraviolet light irradiation were adopted to evaluate the photoelectrocatalytic properties of the TiO2 nanotube arrays. We demonstrate that the highly ordered TiO2 nanotube arrays possess much better photoelectrocatalytic activity than the sol–gel derived TiO2 film and good stability.

Electrochemical preparation of TiO2/SiO2 composite film and its high activity toward the photoelectrocatalytic degradation of methyl orange

Uniform TiO2/SiO2 composite films were prepared on ITO substrates by electrodeposition, and highly photoelectrocatalytic (PEC) activity of the composite films was observed toward the degradation of methyl orange (MO) in aqueous solutions. It was further found that their PEC activity was dependent on the electrodeposition parameters including deposition time, solution pH and SiO2 content. Under the optimized condition, the PEC degradation of MO on TiO2/SiO2 composite film electrode could be enhanced about 14 times relative to that on neat TiO2 film electrode. The high PEC activity of the TiO2/SiO2 composite film electrode was mainly attributed to the enhancement of the charge separation of photo-generated electron-hole pairs by the dispersion of SiO2 nanoparticles in the TiO2 matrix with the aid of the applied electric field.

Properties and Photoelectrocatalytic Behaviour of Sol-Gel Derived TiO2 Thin Films

Titanium dioxide (TiO2) thin films have been prepared on indium doped tin oxide (ITO) glass by sol-gel dip-coating method. Properties of the films were determined as a function of heat-treatment by X-ray diffraction, scanning electron microscopy and photoelectrochemical tests. The films heat-treated at higher temperatures show better crystallinity and photoresponse. The microscopic structure on the film after heat-treatment is attributed to the incorporation of organic polymer into the precursor solution. The performance of the electrodes treated at different temperature on photoelectrocatalytic degradation of methyl orange was investigated. The effect of applied potential and the ability of the electrode to be repeatedly used in photoelectrocatalytic degradation were also evaluated.

Spray pyrolysis deposited zinc oxide films for photo-electrocatalytic degradation of methyl orange: influence of the pH

Zinc oxide films were made by spray pyrolysis equipped with an optical system for in situ thickness measurement. Films were fabricated from zinc acetate water solution. The solution’s pH was modified to increase film porosity, which was subsequently analyzed using scanning electron microscopy. X-ray diffractometry revealed that resulting films were zincite-like with a preferred (0 0 2) direction depending on the temperature of deposition. Spectral optical equipment analyzed the absorption of ZnO based films in the 350–800 nm. The various zinc oxide films were brought in contact with methyl orange, whose photo-electrocatalytically induced degradation under ultraviolet irradiation was investigated in a reactor allowing optical probing of methyl orange. Results can be reconciled with the active area’s suitability for producing photoinduced holes capable of effecting oxidation of the pollutant.