Degradation Of Organic Pollutants In Water Research Articles

Synergetic activation of peroxymonosulfate by MnO2-loaded β-FeOOH catalyst for enhanced degradation of organic pollutant in water

In this paper, manganese dioxide (MnO2) loaded iron oxyhydroxide (β-FeOOH) was synthesized aiming to improve the catalytic performance of β-FeOOH as peroxymonosulfate activator. The β-FeOOH@MnO2/PMS system exhibited excellent performance and its reaction rate constant of Acid Orange 7 (AO7) degradation (0.0533 min−1) was approximately 2.3 times as that in β-FeOOH/PMS system (0.0232 min−1). β-FeOOH@MnO2 possessed superior properties as catalyst than β-FeOOH, owing to the higher surface hydroxyl density with higher specific surface area, redox ability and electronic transmission rate. Moreover, on the basis of the analysis from FTIR and XPS, it was found that the redox reaction of Fe3+/Fe2+ and Mn4+/Mn3+ synergistically activated PMS as well as the generation of FeOH+ and MnOH2+ accelerated activating PMS in the β-FeOOH@MnO2/PMS system. Thus, MnO2 and FeOOH synergistically activated PMS to reactive oxygen species (ROS). And 1O2, O2− and OH were identified as predominant ROS in the β-FeOOH@MnO2/PMS system on the basis of the result from quenching experiments and ESR. As a result, TOC removal rate was increased up to 22.62%. Additionally, β-FeOOH@MnO2 exhibited good stability with low iron dissolution and manganese dissolution. Generally, this study proposed that β-FeOOH@MnO2 was an efficient and environmental catalyst as PMS activator for organic pollutant degradation in water.

Tea-phytochemicals functionalized Ag modified ZnO nanocomposites for visible light driven photocatalytic removal of organic water pollutants

Biogenic synthesis of semiconductor nanoparticles (NPs) as well as metal-semiconductor nanocomposites (NCs) has become a subject of comprehensive interest and research due to its cost-effective and eco-friendly synthesis approach. In this regard, the current work focuses on the biosynthesis of Zinc oxide (ZnO) NPs and Silver-Zinc oxide (Ag-ZnO) NCs using the leaves extract of tea plant (Camellia sinensis). The as-synthesized samples were characterized by various optical, structural and elemental characterization techniques. The successful capping of tea-phytochemicals were confirmed from the bonding information through Fourier Transform Infrared Spectroscopic analysis, while the formation of ZnO NPs and Ag-ZnO NCs were established using x-ray Diffraction, Energy Dispersive x-ray and x-ray photoelectron spectroscopic techniques. Optical absorbance of ZnO NPs revealed the formation of smaller particle size (∼5.2 nm) as compared to bulk ZnO, while the absorbance of Ag-ZnO NCs depicted the presence of metallic Ag in the sample through surface plasmon resonance. The potential of as-synthesized samples were then tested through the photocatalytic and catalytic degradation of organic water pollutants, such as Methylene blue, Paracetamol drug and para-Nitro phenol. The results indicated that Ag deposition on ZnO nanostructure was beneficial in terms of both catalytic as well as photocatalytic degradation under dark condition and visible light irradiation, respectively. A commercially available light source was used for photodegradation process instead of solar irradiation. In addition, an attempt has also been made to explain the plausible pathway of Ag-ZnO NCs formation by the functionalization of tea-phytochemicals. To the best of Authors’ understanding, this is the first attempt so-far reporting a cost-effective biosynthesis process of Ag-ZnO NCs using tea-extracts and its photocatalytic activity under visible light for the degradation of common organic pollutants.

Organic Pollutant Degradation in Water by the Vacuum-Ultraviolet/Ultraviolet/H2O2 Process: Inhibition and Enhancement Roles of H2O2.

A vacuum-ultraviolet/ultraviolet (VUV/UV) mercury lamp was found to be a highly efficient radiation source for UV-based advanced oxidation processes (AOPs). If this lamp could enhance the UV/H2O2 process, it would be very attractive. Hence, we have investigated sulfamethazine (SMN) degradation by the VUV/UV/H2O2 process based on a bench-scale mini-fluidic VUV/UV photoreaction system (MVPS), a pilot reactor, and a model analysis. At high [SMN]0 in the MVPS, the apparent SMN degradation rate constant ( k'app) increased with increasing H2O2 dose, while at low [SMN]0, k'app decreased with increasing H2O2 dose; this behavior was unexpected. Meanwhile, at low [SMN]0 in a pilot reactor, H2O2 induced just a slight enhancement in the VUV/UV/H2O process. A numerical simulation of the process suggested that for an integrated AOP (i.e., VUV/UV/H2O2) consisting of various component AOPs, H2O2 could inhibit the component AOPs with HO* that did not originate from H2O2 (e.g., VUV photolysis of water). The apparent H2O2 role in the integrated AOPs was dependent on the contribution comparison between component AOPs that involved HO* that did or did not originate from H2O2. These results revealed important information regarding the application of the VUV/UV/H2O2 process in water treatment.

Synthesis of N-F-codoped TiO2/SiO2 nanocomposites as a visible and sunlight response photocatalyst for simultaneous degradation of organic water pollutants and reduction of Cr (VI)

A new N-F-codoped TiO2/SiO2 nanocomposite was prepared by simple sol-gel method, and strongly stabilized on a substrate used in a fabricated photoreactor. The prepared photocatalysts were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, diffuse reflectance UV/Vis, photoluminescence, field emission scanning electron microscope, energy dispersive X-ray, transmission electron microscope, and N2 adsorption/desorption methods. The effective parameters of pH, flow rate of the incoming current, and the photoreactor tubes angle against sunlight were optimized. The photocatalytic performance of prepared photocatalysts was evaluated by studying the simultaneous removal of a mixture containing three azo dyes and Cr (VI) in the fabricated continuous-flow photoreactor under visible and solar irradiation. The performance of the designed system was also proved under various outdoor climate conditions. Total organic carbon and flame atomic absorption spectroscopy analysis were performed on the treated sample to confirm the decontamination of the model pollutant mixture. It was found that doping N and F in TiO2/SiO2 nanoparticles caused least agglomeration, enhanced activity under visible and solar irradiation, and fully anatase crystalline structure in the as-synthesized nanoparticles.

Iodo-Functionalized Salicylideneimine-Boron Complexes: Synthesis and Photosensitized Degradation of Organic Water Pollutants.

Boron-containing organic compounds are reported to have excellent luminescent properties, however, their ability to photosensitize singlet oxygen generation remains unexplored. The synthesis of several Schiff-base based boranils is reported, starting from commercially available salicylaldehydes and anilines. The iodo-functionalized derivatives were observed to aid in the photosensitized generation of singlet oxygen. Poly(methylmethacrylate) films incorporating these molecules were prepared and were demonstrated to be capable of serving as a reusable heterogeneous medium for the photosensitized degradation of organic water pollutants.

Comment on "Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition".

Solar-driven heterogeneous photocatalysis has been widely studied as a promising technique for degradation of organic pollutants in wastewater. Herein, we have developed a sulfite-enhanced visible-light-driven photodegradation process using BiOBr/methyl orange (MO) as the model photocatalyst/pollutant system. We found that the degradation rate of MO was greatly enhanced by sulfite, and the enhancement increased with the concentration of sulfite. The degradation rate constant was improved by 29 times in the presence of 20 mM sulfite. Studies using hole scavengers suggest that sulfite radicals generated by the reactions of sulfite (sulfite anions or bisulfite anions) with holes or hydroxyl radicals are the active species for MO photodegradation using BiOBr under visible light. In addition to the BiOBr/MO system, the sulfite-assisted photocatalysis approach has been successfully demonstrated in BiOBr/rhodamine B (RhB), BiOBr/phenol, BiOI/MO, and Bi2O3/MO systems under visible light irradiation, as well as in...

Response to Comment on "Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition".

Response to Comment on "Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition".

A new multicomponent CDs/Ag@Mg–Al–Ce-LDH nanocatalyst for highly efficient degradation of organic water pollutants

A novel type of multicomponent and recyclable nanocatalyst CDs/Ag@Mg–Al–Ce-LDH was successfully assembled by functionalizing a magnesium–aluminum layered double hydroxide support doped with Ce (denoted as Mg–Al–Ce-LDH) with carbon dots (CDs) and Ag nanoparticles.

Visible-Light-Driven Photocatalytic Degradation of Organic Water Pollutants Promoted by Sulfite Addition.

Solar-driven heterogeneous photocatalysis has been widely studied as a promising technique for degradation of organic pollutants in wastewater. Herein, we have developed a sulfite-enhanced visible-light-driven photodegradation process using BiOBr/methyl orange (MO) as the model photocatalyst/pollutant system. We found that the degradation rate of MO was greatly enhanced by sulfite, and the enhancement increased with the concentration of sulfite. The degradation rate constant was improved by 29 times in the presence of 20 mM sulfite. Studies using hole scavengers suggest that sulfite radicals generated by the reactions of sulfite (sulfite anions or bisulfite anions) with holes or hydroxyl radicals are the active species for MO photodegradation using BiOBr under visible light. In addition to the BiOBr/MO system, the sulfite-assisted photocatalysis approach has been successfully demonstrated in BiOBr/rhodamine B (RhB), BiOBr/phenol, BiOI/MO, and Bi2O3/MO systems under visible light irradiation, as well as in TiO2/MO system under simulated sunlight irradiation. The developed method implies the potential of introducing external active species to improve photodegradation of organic pollutants and the beneficial use of air pollutants for the removal of water pollutants since sulfite is a waste from flue gas desulfurization process.

Contaminant salts as enhancers of sonocatalytic degradation of organic water pollutants: Effect of concentration, reaction time and adsorption on the efficiency of enhancement and the fate of concurrently formed H2O2

The effect of salts/anions on ZnO-mediated sonocatalytic degradation of phenol in water is investigated. Anions such as CH3COO−, SO42−, CO32−, HCO3−, NO3−, F−, Cl− and PO43− enhance the degradation. However, the effect is dependent on concentration of the anion and duration of reaction. The enhancing effect in sonocatalysis is different from and contradictory to the inhibiting effect of anions in photo- and sonophoto- catalysis. The enhancement is maximum in the presence of F−, SO42− and CH3COO− and the least in the presence of HCO3− and PO43− though minor exceptions are there depending on the experimental conditions. The basic mechanism of enhancement involves the formation of reactive radical anions by interaction of the anions with the highly reactive .OH radicals and their reaction with phenol. The lower reactivity of the radical anions compared to OH is compensated by the relatively higher concentration. Moreover, they interact exclusively with the substrate whereas the .OH participates in many reactions simultaneously including recombination and self- deactivation. Other effects of dissolved salts/anions such as increasing the ionic strength of the medium, modification in the partition coefficient, decreasing vapor pressure, increase in hydrophilicity etc. also favor sonocatalytic degradation of phenol. The concentration of concurrently formed H2O2 does not increase corresponding to the degradation of phenol and varies in a wave-like fashion (oscillation) due to the simultaneous formation and decomposition with either of them dominating periodically. The anions also influence the nature of the oscillation curve. Possible reasons for the anion effect and potential practical application are discussed.

Effective degradation of organic water pollutants by atmospheric non-thermal plasma torch and analysis of degradation process

The paper reports the use of atmospheric non-thermal plasma torch as a catalyst for degradation of various organic pollutants dissolved in water. A flow of He mixed with air was used to produce the dielectric barrier discharge (DBD), at the tip of the torch, using pulsed electric excitation at 12 kV. The torch, operated at a power of 750 mW/mm2, was seen to completely degrade the aqueous solutions of the pollutants namely methylene blue (MB), methyl orange (MO) and rhodamine-B (RB), at around 10−4 M concentrations, the concentration of polluants is one order higher than of routinely used heterogeneous photocatalytic reactions, within 10 min of irradiation time at room temperature. UV Visible spectra of the organic dye molecules, monitored after different intervals of plasma-irradiation, ranging between 1 and 10 min, have been used as tools to quantify their sequential degradation. Further, instead of using He, only air was used to form plasma plume and used for degradation of organic dye which follow similar trend as that of He plasma. Further, Liquid Chromatography Mass Spectroscopy (LCMS) technique has been used to understand degradation pathway of methylene blue (MB) as a representative case. Total organic carbon (TOC) measurements indicates significant decrease in its content as a function of duration of plasma exposure onto methylene blue as a representative case. Toxicity studies were carried out onto Gram negative Escherichia coli. This indicated that methylene blue, without plasma treatment, shows growth inhibition, whereas with plasma treatment no inhibition was observed.

Visualization of the Formation and 3D Porous Structure of Ag Doped MnO2 Aerogel Monoliths with High Photocatalytic Activity

Owing to their intriguing properties, aerogels with rich and hierarchical pore systems are best appreciated in catalysis, sensing, and separation technologies. Herein, a comprehensive study is presented for inorganic monolithic aerogel of Ag doped MnO2 (Ag-MnO2), synthesized solely out of nanowires of diameter ∼10 nm. We demonstrated a 3D image of the full bulk structure of the aerogel using X-ray computed tomography (μCT), providing a concise and statistical description of its porous structure for the first time. Interestingly, a flow-through supermacroporous system was observed as a result of freeze-drying. Owing to the rich pore system, the Ag-MnO2 aerogel monolith exhibited photocatalytic degradation of organic water pollutants, which was superior in performance as compared to that of the MnO2 powder and compressed Ag-MnO2 pellet. A detailed study of photocatalytic mechanism was also carried out, indicating that Ag can simultaneously modulate the physical and chemical properties of MnO2. This work hig...

Adsorption and Photocatalytic Degradation of Methylene Blue Using Potassium Polytitanate and Solar Simulator.

Solar photocatalytic degradation of organic water pollutants can be used to degrade toxic organic pollutants in water. In this study, potassium titanate nanofibres were synthesized by an aqueous peroxide route at high pH and examined as photocatalysts for photodegradation of methylene blue (MB) using a solar simulator. Initially, MB was adsorbed on the surface of potassium polytitanates to achieve adsorption equilibrium before the photocatalysts were illuminated using solar simulator. The results showed that potassium polytitanate nanofibres were effective adsorbents of MB and also facilitated its photocatalytic degradation. Sulphate ion evolution during photocatalysis confirmed that some mineralisation occurred and hence photo-oxidative degradation of MB took place. The optimum operational conditions for the photocatalytic degradation of MB were found at 0.05 g/L of photocatalyst load, 10 mg/L MB and pH 7. The stability and regeneration of the photocatalyst specimen was also studied for 3 degradation cycles using adsorption/photocatalysis model. Morphological structure analysis of potassium titanate showed nanocrystallines structure of longitudinally-oriented isolated fibre with a length up to several micrometres with diameters ranging from 10 to 20 nanometres.

Porous CuO nanostructure as a reusable catalyst for oxidative degradation of organic water pollutants

Porous CuO nanostructure exhibits high catalytic activity for the degradation of methylene blue and methyl orange in the presence of H2O2.

Visible light-active sub-5 nm anatase TiO2 for photocatalytic organic pollutant degradation in water and air, and for bacterial disinfection

Visible-light-sensitive sub-5nm anatase titanium dioxide (TiO2) nanoparticles (NPs) were fabricated without any doping and calcination treatments. The energy band gap was effectively narrowed to ~2.98eV. The surface and subsurface hydroxyl defects were ascertained as the origin for the band gap narrowing and for the efficient azo-based dye degradation in water and formaldehyde decomposition in air, as well as disinfection of Staphylococcus aureus bacteria, under visible light irradiation.

Nitride-based materials SHS-produced from ferroalloys: I. potential application as catalysts, abrasives, and in film heaters

Products of SHS nitriding of ferroboron and ferrosilicon are analyzed for their potential use as catalysts for deep degradation of organic water pollutants (oxalic acid, phenol), grinding grains, and in film heaters.

Efficient photocatalytic degradation of organic water pollutants using V–N-codoped TiO2 thin films

TiO2, N-doped TiO2, V-doped TiO2, and V–N-codoped TiO2 thin films have been prepared using RF-magnetron sputtering and their photocatalytic activities have been investigated. The codoping strategy was adopted to decrease both the band gap of TiO2 and the recombination rate of the photo-generated electron–hole pairs. Low concentration doping with single element (V or N) preserves the anatase dominated phase in TiO2 film while codoping with V and N produces a mixed phase of nearly equal amount of rutile and anatase as inferred from the XRD and Raman spectroscopy studies. XPS studies reveal that, for N-doped TiO2 elemental N resides at interstitial lattice positions but codoping with V permits N to reside in both substitutional and interstitial sites in TiO2 lattice. UV–vis studies indicate that the band gap of TiO2 (3.2eV) reduced to 3.0eV, 2.8eV and 2.5eV, by N-doping, V-doping and V–N codoping, respectively. The photocatalytic activity of pure, N-doped, V-doped, and V–N codoped TiO2 thin films were tested by examining the degradation of methylene blue, chlorophenol and nitrophenol as a function of time. It was observed that the codoped TiO2 gave the highest photocatalytic activity in comparison to the mono-doped and undoped TiO2 because of high visible light absorption and possible reduction in the recombination of photo-generated charges. Density of states calculated using density functional theory (DFT) showed that the narrowing of band-gap for the codoped TiO2 is obtained by the formation of isolated energy levels of V 3d and N 2p states below the conduction band and above the valence band of pure TiO2, respectively. While for the mono-doped TiO2 the narrowing of the band gap is only contributed by impurity levels formed near any one of the band edges. It is concluded that for the codoped TiO2, high visible light absorption is caused by the formation of impurity energy states near both the band edges which also act as the trapping sites for both the photo-generated charges to reduce the recombination process.

Synthesis and characterization of Fe,S-codoped TiO2 nanoparticles: Application in degradation of organic water pollutants

A novel iron and sulfur co-doped TiO2 photocatalyst was synthesized by modified sol–gel method using titanium (IV) isopropoxide, Fe(NO3)3.9H2O and thiourea as precursors. The samples were characterized by XRD, SEM, TEM, DRS and FT-IR analysis. XRD results showed that Titania and Fe,S-codoped TiO2 nanoparticles calcined at 500°C only contained anatase phase. Fe2O3 crystallites appear as the doping content with 5.0mol%. SEM analysis revealed the doping of Fe and S does not leave any change in the morphology of the catalyst surface. DRS data showed a red shift in absorption edge of samples and with increasing Fe content, absorption increases in visible region. The photocatalytic activity was evaluated by photocatalytic oxidation of methyl orange (MO) and methylene blue (MB) solutions under the UV and visible irradiation. The results show 2% Fe,S-codoped TiO2 nanoparticles have higher activity than other samples under visible light. Under the UV light, undoped and 5% Fe,S-codoped TiO2 are the best catalysts for MB and MO solutions, respectively. Because of synergetic effect of S and Fe, Fe,S-codoped TiO2 catalyst has higher activity than undoped TiO2 and Fe or S doped TiO2.

Study on the mechanism of organic pollutant degradation in water by hybrid gas-liquid discharge

Study on the mechanism of organic pollutant degradation in water by hybrid gas-liquid discharge

Degradation of organic water pollutants through sonophotocatalysis in the presence of TiO 2

The degradation of 2-chlorophenol and of the two azo dyes acid orange 8 and acid red 1 in aqueous solution was investigated kinetically under sonolysis at 20 kHz and under photocatalysis in the presence of titanium dioxide particles, as well as under simultaneous sonolysis and photocatalysis, i.e. sonophotocatalysis. The influence on the degradation and mineralisation rates of the initial substrate concentration and of the photocatalyst amount was systematically investigated to ascertain the origin of the synergistic effect observed between the two degradation techniques. The evolution of hydrogen peroxide during kinetic runs was also monitored. Small amounts of Fe(III) were found to affect both the adsorption equilibria on the semiconductor and the degradation paths. Ultrasound may modify the rate of photocatalytic degradation by promoting the deaggregation of the photocatalyst, by inducing the desorption of organic substrates and degradation intermediates from the photocatalyst surface and, mainly, by favouring the scission of the photocatalytically and sonolytically produced H 2O 2, with a consequent increase of oxidising species in the aqueous phase.