Decomposition Of Organic Pollutants Research Articles

Photonic TiO2 photoelectrodes for environmental protections: Can color be used as a quick selection indicator for photoelectrocatalytic performance?

Colored photonic TiO2 photoelectrodes have been prepared by a simple anodizing-annealing method. Traditionally, the photoelectrocatalytic (PEC) properties of the film are obtained by measuring the actual decomposition of organic pollutants under ultraviolet or visible light, which may take tens of minutes or even hours. Here, through the combined analysis of the apparent features and PEC properties, we found that the structure would affect the color and optical performance, and the films with different colors showed different PEC performance. Interestingly, after repeated verifications, we got a rule that the PEC performance of the TiO2 films decreased in the order with typical color of yellow, blue-green, dark yellow, blue, yellow-grey, and purple. Therefore, we provide a new idea for the visualization screening of PEC performance for the film photoelectrodes, that is, color can be used as a quick selection indicator for TiO2 films.

Assessing the Role of Pt Clusters on TiO2 (P25) on the Photocatalytic Degradation of Acid Blue 9 and Rhodamine B

The role of Pt on photocatalytic substrates such as TiO2 (P25) for the decomposition of organic pollutants is still controversial in the scientific community. The well-observed behavior of an optimum catalytic activity as a function of the Pt loading is usually explained by the shift from charge separation to charge recombination behavior of Pt clusters. However, experiments supporting this explanation are still lacking to give a concise understanding of the effect of Pt on the photocatalytic activity. Here, we present an experimental study that tries to discriminate the different effects influencing the photocatalytic activity. Using atomic layer deposition in a fluidized bed reactor, we prepared TiO2 (P25) samples with Pt loadings ranging from 0.04 wt % to around 3 wt %. In order to reveal the mechanism behind the photocatalytic behavior of Pt on P25, we investigated the different aspects (i.e., surface area, reactant adsorption, light absorption, charge transfer, and reaction pathway) of heterogeneous photocatalysis individually. In contrast to the often proposed prolonged lifetime of charge carriers in Pt-loaded TiO2, we found that after collecting the excited electrons, Pt acts more as a recombination center independent of the amount of Pt deposited. Only when dissolved O2 is present in the solution, charge recombination is suppressed by the subsequential consumption of electrons at the surface of the Pt clusters with the dissolved O2 benefited by the improved O2 adsorption on the Pt surface.

Synthesis of Mn-doped ErFeO3 with enhanced photo and vibration catalytic activities

In this paper, a series of ErFe1−xMnxO3 (x = 0, 0.1, 0.3, 0.5) were readily prepared by the sol–gel method, with citric acid as the combustion agent. The powder gradually changes from the orthorhombic phase (ErFeO3, space group Pbnm) to the hexagonal phase (ErFe0.5Mn0.5O3, space group P63cm). Reduction in the optical band gap from 2.10 eV of ErFeO3 to 1.69 eV of ErFe0.5Mn0.5O3 is observed. Photocatalytic study on methylene blue (MB) by visible light irradiation showed that the photocatalytic activities are greatly enhanced for Mn-substituted ErFeO3, due to the narrower band gap and smaller particle size. Interestingly, ErFe0.5Mn0.5O3 also behaves complete degradation of MB within 120 min vibration, indicating the existence of piezo-electrochemical coupling. The possible photocatalytic and vibration catalytic mechanism of this system was also proposed. The results indicates that this system will be a good candidate for the decomposition of organic pollutant through utilizing both the natural vibration and solar energy.

Degradation of tartrazine by peroxymonosulfate through magnetic Fe2O3/Mn2O3 composites activation

In this study, Fe2O3/Mn2O3 composite was synthesized by a facile two-step technique, and several methods were carried out to characterize it. Then, the decomposition experiments of tartrazine (TTZ), a kind of refractory organic pollutant, were conducted under various environmental condition to detect the catalyst performance, such as reaction system, the dosage of catalyst, peroxymonosulfate (PMS) concentration, initial pH, different natural water substances. The results exhibited that Fe2O3/Mn2O3 composite with the mole rate 2:3 had the best PMS activation performance and the removal efficiency was 97.3% within 30 min. Besides, the optimum degradation conditions of TTZ were also discussed, that is catalyst dosage (0.6 g/L), PMS concentration (0.8 g/L) and the initial pH 11. In addition, proved by the natural water substances adding experiments, HPO42−, HCO3‒, NO3‒ and NOM (nature organic matter) could slow down the experiments progressing, but Cl‒ could boost it. Then inhibitor experiments indicated both the HO and SO4‒ played a vital role in the experiments. Reusability and ions leaching experiments as well as the used catalyst physical characterization images exhibited the excellent stability and cyclicity of the Fe2O3/Mn2O3 composite. Finally, based on the XPS (X-ray photoelectron spectroscopy) and the experiments results, the possible mechanism of TTZ degradation was proposed. This system might provide a novel thought for the decomposition of refractory organic pollutant and had potential in promotion of actual sewage treatment technology.

Hydrophobizated poly(titanium oxide) containing polymeric surfaces with UV-induced reversible wettability and self-cleaning properties

The optically transparent materials based on organic-inorganic terpolymers of poly(titanium oxide) in organic copolymers of hydroxyethyl methacrylate and acrylonitrile and modified by F-content agent were demonstrated UV-induced reversible wettability. The poly(titanium oxide) inside the material had a structure close to anatase and uniformly distributed over the surface of the sample as it was determined by X-ray phase analysis and electron microscopy. The single-electron transition Ti4++ e– ⇆ Ti3+ occurred in the samples under UV-irradiation accompanied by Ti-O bond breaking and change of surface hydrophilicity with change of contact wetting angle from 77° to 5°. The transformation in the nature of the initial surface from hydrophilic to hydrophobic was provided by its treatment with poly-1,1,5-trihydroperfluoroamyl acrylate latex, the contact wetting angle increased up to 97°. The modified surface exhibited the ability to reversibly change the wettability during UV-irradiation. Light irradiation of surfaces coated with palmitic acid demonstrated the photocatalytic activity of the material in the decomposition of organic pollutants and their propensity to self-cleaning.

Enhanced the photoelectrocatalytic performance of TiO2 nanotube arrays by the synergistic sensitization of Ag-AgBr nanospheres.

Ag-AgBr nanospheres were synthesized on the tubular surface of TiO2 nanotube arrays (TiO2 NTA/Ag-AgBr) by the one-pot hydrothermal deposition strategy using cetyltrimethyl ammonium bromide (CTAB) as bromine source and morphology controlling agent. The results showed that the TiO2 NTA/Ag-AgBr (0.025) prepared with 0.025 g CTAB had the uniform particle distribution, high visible light absorption, photoelectric conversion activity and photoelectrocatalytic (PEC) removal of organic dyes and heavy metal ions. The high photocatalytic decomposition of organic pollutants in waste water was attributed to the synergistic effect of Ag-AgBr nanospheres with the strong visible light response and effective separation of electron-hole pairs. The active group and photocatalytic mechanism for the rapid pollutant removal were systematically explored. This work will open the window of TiO2 NTA based photoelectrodes for the applications in solar energy conversion and dyeing waste water purification.

Selectively Photocatalytic Activity of an Open-Framework Chalcogenide Built from Corner-Sharing T4 Supertetrahedral Clusters.

The photocatalysis process with high selectivity is a very important research forefront for the semiconductor photocatalytic decomposition of organic pollutants. However, the rational design of efficient photocatalysts with high selectivity is still a challenge. Here, we present an open-framework chalcogenide (Heta)8[In14Sn2Zn4Se33] (Heta = ethanolamine-H+) (compound 1) constructed from T4 supertetrahedral clusters [In14Sn2Zn4Se35]12- with visible-light-driven selectively photocatalytic degradation activity. Single-crystal XRD analysis shows that compound 1 crystallizes in I41/acd (no. 142) space group, with a = b = 24.3462(2) Å, c = 45.0062(9) Å, V = 26676.9(7) Å3, and Z = 8. Under visible-light irradiation, the selectively photocatalytic activities of 1 were evaluated by photodegradation of two kinds of cationic dye molecules, i.e., methylene blue (MB) and rhodamine B (RhB), against two anionic dyes, methyl orange (MO) and Kermes red (KR), with different sizes. We show that the adsorption capability and charge-matching between organic dyes and the supertetrahedral cluster together with a suitable band structure make it an excellent and selective photocatalyst. This is the first example of an open-framework chalcogenide based on supertetrahedral T4 for the selectively semiconductor photocatalytic decomposition of organic dyes.

Improved ultrasonic degradation of hydrophilic and hydrophobic aldehydes in water by combined use of atomization and UV irradiation onto the mist surface.

Ultrasonic irradiation of 430 kHz, which induces both the chemical effect of pyrolysis and the physical effect of atomization, was carried out to achieve highly effective decomposition of organic substances in water with UV254 irradiation and H2O2 addition. To investigate the influence of physicochemical properties of the substrate on the degradation rate, three different aldehydes, namely, formaldehyde, acetaldehyde, and benzaldehyde, were selected as model substrates. Upon ultrasonic irradiation alone, the removal ratio of the hydrophobic substrate benzaldehyde reached 100% after 120 min, whereas the removal ratios of the hydrophilic substrates formaldehyde and acetaldehyde were only 21.1% and 53.0%, respectively. By combining ultrasonic atomization and UV254 irradiation, formaldehyde and acetaldehyde underwent effective gas-phase decomposition on the surfaces of the mist particles. Photolysis by UV254 irradiation mainly affected for the decomposition of aldehydes on the mist surface rather than the reaction of hydroxyl radicals derived from H2O2 made by water sonolysis. However, the addition of H2O2 effectively improved the decomposition and mineralization rates for both hydrophilic and hydrophobic aldehydes owing to the generation of hydroxyl radicals on the surfaces of the mist particles, which greatly contributed to the gas-phase decomposition. Consequently, the effective decomposition of organic pollutants was achieved regardless of their physicochemical properties in aqueous media.

Buoyancy Assisted Janus Membrane Preparation by ZnO Interfacial Deposition for Water Pollution Treatment and Self‐cleaning

AbstractWater pollution, such as marine oil spill and organic chemicals pollution, is a worldwide challenge. To advance this emerging field, Janus membranes with asymmetric wettability, for oil–water separation, similitude of diode in electrocircuit, are fabricated by leveraging the buoyancy of poly(vinylidene fluoride) nanofiber on water/air interface. ZnO nanowires are in situ grown on the surface of nanofibers immersed in the solution, mimicking a nanoscale Setaria viridis structure. Such Janus membrane shows a good hydrophilicity/underwater oleophobicity on ZnO nanowires modified side and exhibits opposite hydrophobicity on the other side. Due to the side‐specific morphologies, this membrane can work either as “water‐removing” type or “oil‐removing” type filter as a diode in fluid. The membrane shows excellent permeability with the water and oil flux up to 1210 and 7653 L m−2 h−1, respectively, only driven by gravity. The durability of functional membrane is excellent and separation efficiency is higher than 97.24% after ten cycling tests. Furthermore, the hydrophilic side demonstrates an excellent photocatalytic performance over the degradation of rhodamine B dye, as self‐cleaning properties. This Janus membrane is to be an excellent candidate for wastewater remediation, both oil/water separation and organic pollutant decomposition.

Controlled synthesis and exceptional photoelectrocatalytic properties of Bi2S3/MoS2/Bi2MoO6 ternary hetero-structured porous film

In this work, Bi2S3/MoS2/Bi2MoO6 hetero-structured porous films were fabricated via a facile anion exchange process using the as-prepared Bi2MoO6 nanoflake array film as substrate material. The formation of Bi2S3/MoS2/Bi2MoO6 ternary hetero-structured porous film is both thermodynamically controllable and reaction time dependent. Systematic experiments were done to investigate the products at each reaction stage and disclose the relationships between the composite components and reaction temperature and time. The study showed that the energy barrier need to be overpassed when MoS2 and Bi2S3 were simultaneously produced. The optimized Bi2S3/MoS2/Bi2MoO6 photoelectrode exhibited significantly higher photoelectrocatalytic efficiency than Bi2MoO6, binary Bi2S3/Bi2MoO6 and Bi2S3/MoS2 photoelectrodes. The remarkable degradation efficiency of the Bi2S3/MoS2/Bi2MoO6 photoelectrode comes from the synergy of high quality assembly and heterostructure interfaces between the three components. The optimized film assembly and stepwise band alignment in the ternary heterostructure composite contribute to visible light utilization, transport and separation of charge carriers, mass transport, and accessibility of active sites. The generated active species such as superoxide anions (O2−) and holes were detected to promote the decomposition of organic pollutants. The reasonable photoeletrocatalytic degradation mechanism was also proposed.

Template‐Free Macro‐Mesoporous TiO2/Carbon Nitride Interface for Visible‐Light‐Driven Photocatalysis

Porous titanium dioxide (TiO2) materials are pivotal in broad catalytic applications. However, design and development of macro‐mesoporous TiO2 involve a hard or soft templating method, which impedes the additional cost and complexity. Herein, a simple, scalable, and template‐free synthesis route to ordered uniform macro‐mesoporous TiO2 (mTiO2) layers is presented. The controlled aging of titanium tetraisopropoxide precipitates self‐assemble into an extended macroporous TiO2 network. As proved by X‐ray diffraction, the prepared materials are of anatase TiO2. Morphological analysis of mTiO2 displays a uniform macroporous network. To delight, the obtained mTiO2 possesses an extensive specific surface area of 257 m2 g−1, with an average pore size of ≈2 nm. This simplistic method provides a high yield of mTiO2 products. To find the practical utility of mTiO2, visible light active graphitic carbon nitride (g‐C3N4) is combined with mTiO2 and examined for photo fixation of dinitrogen (N2) and decomposition of organic pollutants. Remarkably, the mTiO2/g‐C3N4 interface shows drastically enhanced NH4+ production and dye degradation photocatalytic activity as compared with g‐C3N4 and commercial TiO2. This versatile and eco‐friendly preparation process of surface‐rich mTiO2 is scalable and may find widespread potential in large‐scale photocatalytic applications.

Ultrathin structural BiOI with surface oxygen vacancies for improved photocatalytic degradation of organic pollutants

Ultrathin BiOI nanosheets with surface oxygen vacancies have been synthesized in situ and evaluated as improved bismuth oxyhalide photocatalysts for the degradation of organic pollutants. Environmental remediation, in particular the degradation of phenol and bisphenol A is of interest due to the toxicity and persistent nature of these compounds. The efficient photocatalytic activity of ultrathin structural BiOI is the result of enhanced carrier photocatalysis. This has been determined by several experiments, such as trapping experiments, electron spin resonance and reactive oxygen species quantification experiments. The durability and stability of the catalysts has also been verified by cyclic experiments. These bismuth oxyhalide photocatalysts shows promise for the efficient and sustainable decomposition of persistent organic pollutants.

Ni/ZnO heterostructured microspheres: electronic structure engineering for enhanced photocatalytic activity

Wurtzite ZnO is one of benchmark photocatalysts for the decomposition of organic pollutants. The wide band gap of about 3.4 eV, however, hinders its application in photocatalysis, which requires the electronic structure engineering to reduce the band gap for the enhancement of its optical absorption. Herein, a sodium citrate-assisted hydrothermal route is reported to prepare uniform Ni/ZnO heterostructured microspheres. The ZnO microspheres with the size of about 2.5 μm are assembled by ZnO nanosheets decorated by Ni nanoparticles of about 3 nm. The Ni/ZnO heterostructures provide enhanced surface activity, which is not only resulted from the larger surface area, but also caused by the formation of mid-gap-like electronic states in the heterostructures. Besides, it can promote the separation of the excited charges. Therefore, the Ni/ZnO microspheres deliver a significantly enhanced photodegradation ratio of 93% towards the probe organic pollutant of rhodamine B in comparison with that of bare wurtzite ZnO samples (degradation ratio of 72%). Density functional theory studies reveal that the Ni/ZnO heterostructures can improve the optical absorption of ZnO by forming mid-gap-like electronic states.

Porous Graphitic Carbon Nitride Synthesized via Using Carbon Nanotube as a Novel Recyclable Hard Template for Efficient Visible Light Photocatalytic Organic Pollutant Degradation

AbstractTwo‐dimensional (2D) graphitic carbon nitride (g‐C3N4) has attracted considerable attention due to its many intriguing properties in visible light photocatalysis. However, the photocatalytic performance of g‐C3N4 is far from satisfaction partly because standard synthesis methods prepare rather dense materials with low specific surface area. Herein, we report a facile approach to prepare porous g‐C3N4 via using carbon nanotubes (CNT) as a novel hard template for the first time. Unlike other hard templates, CNT can be easily removed by ultrasonic method and recycled to produce porous g‐C3N4. The as‐prepared porous g‐C3N4 has a much higher specific surface area of 103.3 m2 g−1 than the bulk g‐C3N4 of 10.5 m2 g−1. The photocatalytic organic pollutant decomposition rate of porous g‐C3N4 is nearly 4.4 times as high as that of bulk g‐C3N4 under visible light (λ > 400 nm) irradiation. This work opens a new way to explore the sustainable, environment‐friendly preparation of high‐performance g‐C3N4 for solar energy conversion and environmental remediation, especially for large‐scale applications in industry.

Single-step aerosol synthesis of oxygen-deficient blue titania

We present a novel approach for the single-step, continuous aerosol synthesis of blue, oxygen-deficient titania in a hot-wall reactor operated under reducing conditions by adding hydrogen. The precursor titanium(IV) tetraisopropoxide is evaporated in a bubbler and consecutively carried into the reactor by a nitrogen stream where it undergoes thermal decomposition. According to X-ray diffraction analysis, several reduced titania states, among them the Magnéli phases Ti4O7 and Ti5O9, are formed via the intermediates anatase and rutile. By slight modifications in the reactor setup both nanoparticles in the size range from 20 to 50 nm with high surface area and well-defined spherical submicron particles of 100 to 160 nm diameter can be produced. In particular, crystallographically phase-pure Ti4O7 is formed at high reactor temperatures. The presented synthesis process is scalable and poses an attractive alternative for the multi-step synthesis of oxygen deficient titania nanoparticles that is currently done via batch-wise annealing. Such nanoparticles are attractive material in the field of photocatalysis. They can be used for both water splitting to produce hydrogen and the decomposition of organic pollutants.

High Defect Nanoscale ZnO Films with Polar Facets for Enhanced Photocatalytic Performance

The fabrication of highly efficient photocatalytic thin films has important consequences for self-cleaning, organic pollutant decomposition, and antimicrobial coatings for a variety of applications. Here, we developed a simple synthesis method to produce efficient, high-surface-area zinc oxide (ZnO) photocatalytic films using aerosol-assisted chemical vapor deposition. This approach used mixtures of methanol and acetic acid to promote preferential growth and exposure of polar facets, which favor photocatalytic activity. Interestingly, the initial enhanced efficiency of the films was correlated to structural defects, likely oxygen vacancies, as supported by photoluminescence spectroscopy results. Discussion over the influence of such defects on photocatalytic performance is described, and the need for strategies to develop high-surface-area materials containing stable defects is highlighted.

Ag Loading Enhanced Photocatalytic Activity of g-C3N4 Porous Nanosheets for Decomposition of Organic Pollutants.

The g-C3N4 porous nanosheets with different loading amount of Ag nanoparticles (NPs) are successfully prepared by a simple liquid-phase reduction method. These Ag/g-C3N4 composites have an improved photocatalytic performance for decomposing organic pollutants compared with that of pure g-C3N4 nanosheets. Many measurements have been used for characterizing the samples, such as XRD, FTIR, UV-Vis DRS, PL, XPS, EDS, SEM, and TEM. In Ag/g-C3N4, the Ag NPs are uniformly coated on the g-C3N4 surface, the diameter is mainly in the range of 8~18 nanometers. Loading of Ag NPs expand the response to the visible light for g-C3N4 and increasing the producing rate of photogenerated e−-h+ pairs. The loading of silver NPs obviously enhances the photocatalytic activity of C3N4 nanosheets toward the Rhodamine B (RhB) decomposition under the simulated sunlight irradiation. With different loading amounts of Ag NPs, Ag/g-C3N4 (3 wt% of Ag) showed the highest photocatalytic activity for RhB decomposition among these as-prepared samples, which is 10 times of the rate of pure C3N4. Based on the experimental results, a possible photocatalytic mechanism for Ag/g-C3N4 is proposed.

Near-infrared-light-induced decomposition of Rhodamine B triggered by localized surface plasmon at gold square dimers with well-defined separation distance

Localized surface plasmon-induced photoreactions at metal nanostructures have become central research topics in biology, catalysis, and analytical chemistry. In particular, the decomposition of organic pollutants is a popular topic. Rhodamine B is useful in the dye industry and biology; however, it is harmful to humans and the environment. In this study, we investigated the decomposition of the Rhodamine B molecule with a structurally well-defined array of gold square dimers. The array of gold square dimers was fabricated by electron beam lithography, which provided a homogenous well-defined reaction field. Continuous Raman spectral measurements using a near-infrared laser clearly showed that while the Rhodamine B molecules were stable in the absence of the gold square dimers, they were decomposed under near-infrared-light irradiation.

Multipurpose Usage of Magnetic Proppantsduring Shale Gas Exploitation

Abstract Magnetic material may be added to proppant, as the magnetic marker allows to determine the range and efficiency of hydraulic fracturing. However, magnetic proppant may be also used in flowback fluid treatment and monitoring of environmental pollution. As a result of shale gas hydraulic fracturing, large volume of flowback fluid is created. Flow back fluid have similar properties to fracturing fluid, but it is potentially enriched with large amount of salts and organic compounds leached from shale. Magnetic proppant may serve as a heterogeneous catalyst during organic pollutants decomposition. Additionally, in case of leakage and consequently the fracturing fluid pollution, magnetic proppant is placed into the soil environment. It can be detected using magnetometric methods. This article discusses the above-mentioned issues based on the knowledge and experience of the authors and the literature review.

Photodecomposition and adsorption of hazardous organic pollutants by Ce-doped ZnO@Ce-doped TiO2-N/S-dual doped RGO ternary nano-composites photocatalyst for water remediation

In this research, I found that the doping of ZnO@TiO2 core−shell and reduced graphene oxide (RGO) by rare earth cerium ion (Ce4+/Ce3+) and nitrogen (N) and sulfur (S) dual heteroatom is effective way to improve the photocatalytic decomposition of hazardous organic pollutants (phenol, bisphenol and methylene blue (MB)) in the water under visible light irradiation. The 0.1 mol% Ce/ZnO@0.1 mol% Ce/TiO2-N/S/5 wt% RGO, 0.1 mol% Ce/ZnO@0.1 mol% Ce/TiO2-5 wt% RGO, 0.1 mol% Ce/TiO2-N/S/5 wt% RGO, TiO2-N/S/5 wt% RGO and0.1 mol% Ce/ZnO@0.1 mol% Ce/TiO2 ternary and binary nano-composites photocatalyst were synthesised via a simple sol–gel route. Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy (DRS), and Brunauer−Emmett−Teller (BET) analysis were used to characterize the fabricated nano-photocatalyst samples. The N/S/dual-doped RGO nano-sheets were fabrication by a facile hydrothermal route using cysteine as precursor for both N and S heteroatoms. Furthermore, cysteine can simultaneously act as a reducing agent of GO. The 0.1 mol% Ce/ZnO@0.1 mol% Ce/TiO2-N/S/5 wt% RGO exhibited high photodegradation of various hazardous organic pollutants under visible light irradiation.