Photodegradation of organic pollutants catalyzed by iron species under visible light irradiation

The green oxidation technology is the most economically attractive and environmentally friendly oxidation technique in the treatment of organic pollutants. Photocatalytic degradation of organic pollutants by iron species is a desired green oxidation technique due to using hydrogen peroxide or ideally molecular oxygen as oxidant and water as solvent. However, the system has some disadvantages. The reaction has to be performed in acidic conditions in order to avoid Fe ion precipitation and iron sludge will be accumulated in the reaction. Moreover, the utilization of H(2)O(2) means a high cost and risks in the storage and transportation and organic pollutants can not be completely mineralized. In this perspective, we report a systematic investigation of the improvement in the Fenton system for treatment of organic pollutants in water. Several strategies have been studied on the Fenton system for overcoming the above mentioned shortcomings and enhance the efficiency. For example, in order to extend the application of the Fenton system and perform it at neutral pH, iron complexes were used to replace the Fe(2+)/Fe(3+). Moreover, iron complexes have a strong absorption in the visible region, which leads to decomposition of colorless organic pollutants under visible light irradiation. Iron complexes with special structures can activate molecular O(2) instead of H(2)O(2) under mild conditions and the supported iron species maintains a high catalytic activity after repeated use and can be reused simply by filtration. Finally, prospects for further work required to be performed for its practical application is discussed.     

Degradation of pesticide Cartap in Padan 95SP by combined advanced oxidation and electro-Fenton process

The electro-Fenton process combined with a boron-doped diamond-positive electrode in a one-compartment cell has shown efficient degradation of Cartap (95% in Padan 95SP) by hydroxyl radicals (•OH) generated in the electro-Fenton and the electrochemical oxidation processes. The influence of added NaOCl in a pretreatment step, effects of H₂O₂ concentration, Fe²⁺-ion addition, presence of further metals acting as co-catalysts, and solution pH on the efficiency of Cartap degradation were studied. The concentration of Cartap was determined by UV-vis spectroscopy according to the 5,5-dithiobis-(2-nitrobenzoic acid) procedure. The efficiency reaches approximately 80% when measured as total carbon concentration decrease, even with increased concentrations of H₂O₂, Fe²⁺, or metal ions added as co-catalyst. This limitation is presumably due to recalcitrant intermediates, which cannot be destroyed by •OH.

     

Goethite as a more effective iron dosage source for mineralization of organic pollutants by electro-Fenton process

The electro-Fenton process is an electrochemical method for wastewater treatment based on the production of hydroxyl radicals via H₂O₂ generation in the presence of ferrous ions. The aim of this work is to show the use of a new mineral iron dosage source (goethite, α-FeOOH) for electro-Fenton process that achieves a more efficient mineralization treatment. Our new proposed Goethite catalyzed electro-Fenton (GEF) process yields 95% of mineralization for an organic model pollutant such as aniline under optimum standard electro-Fenton (SEF) conditions. For that, GEF process uses only 2 ppm of soluble iron, compared with the 55 ppm of soluble iron used by SEF process. In order to show the potential scope of GEF process, the effect of goethite concentration, solution conductivity, solution pH, temperature, and applied current density are studied in detail.     

Efficient degradation of organic pollutants mediated by immobilized iron tetrasulfophthalocyanine under visible light irradiation

Supported iron tetrasulfophthalocyanine can efficiently catalyze the degradation of organic pollutants by H2O2 under visible light irradiation in an aqueous solution, and the catalyst can be easily recycled without apparent loss of activity.     

Aerobic oxidation of aldehydes by visible light photocatalysis

An efficient and environmentally benign method for the oxidation of aldehydes to carboxylic acids has been developed. Singlet oxygen, generated by visible light in the presence of a Ru or Ir photocatalyst, reacted with aldehydes to give the corresponding carboxylic acids in excellent yields. The reaction is highly chemo-selective, in which only an aldehyde moiety is reactive even in the presence of other photo-oxidation active sites. This method is an example of an ideal green chemical reaction in the sense that molecular oxygen and visible light are key sources for the transformation.     

可见光照射下取代型杂多酸盐对染料的催化降解

将杂多酸(GaWmFen)负载到阴离子交换树脂(Resin)上,得到GaWmFen/Resin(GaWmFenR)固相光催化剂,在可见光的照射下,以罗丹明B(RhB)为模型化合物,含镓的GaWmFen/Resin(GaWmFenR)催化剂可以有效地活化H2O2降解染料RhB,随着铁原子的取代数目的增多,RhB浓度比降低的趋势加快,GaW9Fe3最快,C/C0降低0.937.在光照300 min 以后,体系的总有机碳(TOC)的变化趋于平缓,减少了0.15 mg.L-1.催化剂的8次重复试验结果表明GaWmFenR固相光催化剂易于分离,并且具有良好的稳定性,可以重复利用.     

Engineering covalent organic frameworks in the modulation of photocatalytic degradation of pollutants under visible light conditions

Mixtures of triphenylamine (TPA) and phenyl phenothiazine (PTH) fragments have been incorporated into a series of extended polyimine structures that have been applied in the photodegradation of pollutants of different nature under visible light irradiation. Results obtained revealed that materials containing PTH as the sole photoactive unit resulted in the most active photocatalytic material in the degradation of polybrominated diphenyl ether-1 and Sudan Red III. In contrast, the covalent organic framework containing only TPA acted as the best photocatalyst for the degradation of Methylene Blue. These different trends are related to the versatility of PTH moiety to trigger both photoredox and energy transfer processes, while TPA is only an effective energy transfer catalyst.     

Removal of organic dye pollutants from wastewater by electrochemical oxidation

The removal of chemical oxygen demand (COD) and color from simulated dye wastewater containing organic dyes, direct yellow 4, C₂₆H₂₀N₄O₈S₂Na₂ and acid yellow 17, C₁₆H₁₀O₇N₄S₂Cl₂Na₂ experimentally investigated using an electrochemical undivided cell reactor with Pt as anode and steel as cathode. Particular attention was paid to probe the effect of supporting electrolyte (NH₄Cl), cell voltage, pH, and treatment time on the electrochemical treatment efficiency. Experiments were also carried out using 0.2?M NH₄Cl as supporting electrolyte under the condition of free pH. The experimental results showed that the process could efficiently remove the color and COD from simulated dye waste water. The overall COD removal reached at 69.9% by using supporting electrolyte and increasing voltage. The process can be described by pseudo first-order kinetics for the removal of COD.     

紫外和可见光照射下Fe-TiO2复合材料催化低浓度芳香族有机污染物降解（英文）

Fe‐TiO2 photocatalysts with different ratios of Fe to Ti were prepared by a sol‐gel process using tetra‐n‐butyl titanium and iron(III) nitrate as Ti and Fe sources, respectively. The photocatalytic function of the prepared composites was examined for the decomposition of low‐concentration(0.1 ppm) airborne benzene, toluene, ethyl benzene, and o‐xylene(BTEX). The Fe‐TiO2 composites were characterized by energy dispersive X‐ray spectroscopy, X‐ray diffraction, UV‐visible spectroscopy, and Fourier transform infrared spectroscopy. The time‐series ratios of outlet to inlet concentrations of toluene, ethyl benzene, and o‐xylene target chemicals, as determined by the Fe‐TiO2 composites under visible light exposure, were lower than or similar to those of the reference TiO2 photocatalyst. Moreover, the time‐series ratios of outlet to inlet concentrations of the three compounds, as determined for the Fe‐TiO2 composites, increased as the ratio of Fe to Ti increased from 0.001 to 0.010. In contrast, under UV exposure, the time‐series ratios of outlet to inlet concentrations of BTEX, determined for the Fe‐TiO2 composites, were similar to or higher than those obtained from the reference TiO2 photocatalyst. Fe‐TiO2 composites with an optimal Fe to Ti ratio could effectively be applied for the purification of low‐concentration aromatic organic pollutants.     

Anodic oxidation of organic pollutants: Anode fabrication,process hybrid and environmental applications

This review summarizes the recent progress in anodic oxidation of organic pollutant for water and wastewater treatment. It supplies the advances in anodes fabrication to improve the anodic performance by different modifications and preparation strategies, focusing on non-active anodes including boron-doped diamond (BDD), PbO₂, SnO₂ and Ti-based anode (e.g., Ti₄O₇, blue titanium oxide). Meanwhile, the tendency of anodic oxidation coupled or combined with other processes (adsorption, membrane separation, biological treatment and advanced oxidation process) for pretreatment or advanced treatment of organic pollutant is presented. Finally, anodic oxidation for environmental application is briefly described; several challenges need to be overcome and perspectives for future study are critically proposed.     

A novel approach for the oxidative degradation of organic pollutants in aqueous solutions mediated by iron tetrasulfophthalocyanine under visible light radiation

An efficient approach has been developed to decompose toxic organic pollutants. The photodegradation of Rhodamine B (RhB), salicylic acid, and Orange II was examined in the presence of iron tetrasulfophthalocyanine ([Fe(PcS)]) and H(2)O(2) under visible irradiation. It was found that under visible light irradiation, organic pollutants in the [Fe(PcS)]/H(2)O(2) system can be rapidly degraded, but the concentration of [Fe(PcS)] remains nearly unchanged, and this indicates that [Fe(PcS)] has a good catalytic character. EPR results and other experimental results suggest that the light-activated reaction process involves the formation and reaction of HO(.) radicals. On the basis of the experimental results, a possible reaction mechanism for the degradation of organic pollutants under visible light illumination in the aqueous [Fe(PcS)]/H(2)O(2) solutions is proposed.     

Electrochemical oxidation of organic pollutants for wastewater treatment

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Metal-free activation of H2O2 by g-C3N4 under visible light irradiation for the degradation of organic pollutants

Semiconducting carbon nitride materials were successfully prepared via a thermal poly-condensation of dicyandiamide as a precursor at >500 °C. The resulting materials were investigated as metal-free catalysts for the activation of H(2)O(2) with visible light under mild conditions, using the decomposition of Rhodamine B (RhB) in aqueous solution as a model reaction. Results revealed that carbon nitride catalysts can activate H(2)O(2) to generate reactive oxy-radicals under visible light irradiation without employment of any metal additives, leading to the mineralization of the dye. Factors affecting the degradation of organic compounds are pH values and the concentration of H(2)O(2). Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, indicating good (photo)chemical stability of metal-free polymeric carbon nitride photocatalysts for environmental purification. This study demonstrated a promising approach for the activation of green oxidant, hydrogen peroxide, by the newly-developed polymer photocatalysts for environmental remediation and oxidation catalysis.     

Advanced oxidation process by electron-beam-irradiation-induced decomposition of pollutants in industrial effluents

Electron-beam irradiation considered on advanced oxidation process induces the decomposition of pollutants in industrial effluent. Experiments were conducted using a radiation dynamics electron beam accelerator with 1.5 MeV energy and 37 kW power. The effluent samples from an industrial complex were irradiated using the IPEN's liquid effluent irradiation pilot plant. The experiments were conducted using one sample from each of eight separate industrial units and five samples of a mixture of these units. The physical–chemical characterization of these samples is presented. The electron beam irradiation was efficient in destroying the organic compounds delivered in these effluents, mainly, chloroform, dichloroethane, methyl isobutyl ketone, toluene, xylene and phenol. The necessary dose to remove 90% of the most organic compounds from industry effluent was 20 kGy. The removal of organic compounds from this complex mixture was explained by the destruction G value (Gd) that was obtained for those compounds with different initial concentrations and was compared with literature.     

Heterogeneous degradation of toxic organic pollutants by hydrophobic copper Schiff-base complex under visible irradiation

A hydrophobic complex of Cu2+[bis-salicylic aldehyde-o-phenylenediamine],Cu-SPA,was prepared and used as a heterogeneous photocatalyst to degrade organic pollutants in water under visible irradiation(420 nm)at neutral pH.The structure of complex was characterized by using nuclear magnetic resonance(NMR),elemental analysis,IR and UV-vis spectrometries.Degradation of Rhodamine B(RhB),Sulforhodamine B(SRB)and Benzoic acid(BA)in water were used as model reactions to evaluate the photocatalytic activities of Cu-SPA.The results indicated that RhB and SRB were easily adsorbed on the hydrophobic surface of Cu-SPA from aqueous solution(the maximum adsorption amount:Qmax=11.09 and 8.05μmol/g,respectively).Under visible irradiation,RhB and SRB were decolorized completely after 210 and 240 min,respectively,and BA was removed completely after 5 h.The efficiency of H2O2was>95%,in contrast to that of the reaction without catalyst or light(<20%).In water soluble medium,the hydrophobic Cu-SPA can be used more than 6 cycles.ESR results and the behavior of cyclic voltammetry showed that,in the reaction process,Cu2+-SPA was reduced to intermediate state Cu+-SPA firstly,which was extremely unstable and reacted rapidly with H2O2,leading to high reactive oxygen species(·OH radical)to degrade the substrate.     

Fabrication of nanoporous polymeric crystalline TiO2 composite for photocatalytic degradation of aqueous organic pollutants under visible light irradiation

A nanoporous polymeric crystalline TiO₂ composite (TiO₂/PDVB‐MA) has been successfully synthesized through an in situ synthesis method using divinylbenzene (DVB), methacrylic acid (MA) and tetrabutyl titanate. The experimental results showed that TiO₂ nanoparticles composed of the mixture phases of anatase and rutile were homogeneously dispersed into the PDVB‐MA support. The TiO₂/PDVB‐MA composite was used as photocatalyst for Rhodamine B (RhB), bisphenol A and 2,4,6‐trichlorophenol degradation under visible light irradiation. More interestingly, the excellent photocatalytic performance of the composite was observed with regard to RhB and bisphenol A, which might be ascribed to the synergistic effect between TiO₂ nanoparticles and PDVB‐MA. Moreover, TiO₂/PDVB‐MA composite could be recycled at least four times in the removal of RhB, suggesting that it is a promising photocatalyst to catalyze the degradation of organic pollutants under visible light irradiation.     

Electrochemical oxidation of organic pollutants in low conductive solutions

This mini-review supplies current opinion about the most recent works, which have been carried out toward the electrochemical treatment of organic compounds spike in low conductive solution. In particular, the first section is focused on the use of a solid polymer electrolyte in order to allow current flux with a low cell voltage even in a solution without supporting electrolyte. Meanwhile, the second section describes the microfluidic cells that are characterized by very small distances between electrodes (tens or few hundreds μm) that reduce the ohmic resistances and increase the mass transport of the pollutants to electrodes’ surfaces.     

Degradation of hazardous organic dyes with solar‐driven advanced oxidation process catalyzed by the mixed metal–organic frameworks

phosphonate‐based bimetallic metal‐ organic frameworks, namely STA‐12(M₁, M₂) (M₁, M₂ = Mn, Fe, Co), show photocatalytic activity for the degradation of Rhodamine B (RhB) and Methylene blue (MB) from aqueous solution under natural sunlight irradiation. The degradation of the dyes, appears to be faster with STA‐12(Fe, Mn) than other synthesized MOFs. Thus, photo‐Fenton oxidative discoloration of dyes has been studied by H₂O₂ catalyzed with the STA‐12(Fe, Mn). The process is first order with respect to dyes and the synergistic index in the STA‐12(Fe, Mn)/sunlight/H₂O₂system reached as high as 472%. Mineralization of dyes was discussed by spectroscopic and TOC measurement. Besides, the efficiency of STA‐12(Fe, Mn) used in photocatalytic process was attentively investigated through the characterization of reactive radicals, the stability and reusability of the photocatalyst, also the effect of operational parameters such as H₂O₂ dosage, solution pH and initial dye concentration. This work demonstrates the first example of facilitating photo‐Fenton‐like excitation of H₂O₂ via phosphonate based mixed metal organic frameworks as photocatalysts and explained a new opportunity for solar‐induced AOP environmental remediation and protection.     

氮缺陷石墨相氮化碳的制备及其光催化降解环境有机污染物性能

通过在三聚氰胺热分解过程中加入NaHCO₃制备出具有氮缺陷的石墨相氮化碳（g-C₃N₄）,利用X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）、N₂吸附-脱附、X射线光电子能谱（XPS）、紫外-可见漫反射光谱（UV-vis DRS）和固体荧光光谱（PL）等方法对其进行表征,并在可见光（λ> 420nm）照射下,以水相中罗丹明B（RhB）的降解为模型反应,研究了该氮缺陷g-C₃N₄对有机污染物降解的光催化活性。结果表明,引入氮缺陷可以提高g-C₃N₄对可见光的吸收以及电子-空穴对的分离效率,进而提高g-C₃N₄的可见光催化活性。催化剂CNK0.005、CNK0.01和CNK0.05在30min内对RhB的降解率分别为79.8%、100.0%和87.6%;而在相同条件下,没有氮缺陷的g-C₃N₄对RhB的降解率仅为59.8%。