Oxidative decomposition of p-nitroaniline in water by solar photo-Fenton advanced oxidation process

A double-emission molecularly imprinted ratiometric fluorescent sensor based on carbon quantum dots and fluorescein isothiocyanate for visual detection of p-nitroaniline

A novel molecularly imprinted ratiometric fluorescent sensor CQDs@MIP/FITC@SiO2 for the detection of p-nitroaniline (p-NA) was constructed through the mixture of CQDs@MIP and FITC@SiO2 in the ratio of 1:1 (VCQDs@MIP:VFITC@SiO₂). The polymers of CQDs@MIP and FITC@SiO2 were prepared by sol-gel method and reversed-phase microemulsion method, respectively. CQDs@MIP was used as the auxiliary response signal and FITC@SiO2 was used as the reference enhancement signal. The signal was measured at excitation/emission wavelengths of 365/438, 512 nm. The sensor showed good linearity in the concentration range 0.14-40.00 µM (R2 = 0.998) with a detection limit of 0.042 µM for p-NA. The color change of "blue-cyan-green" could be observed by the naked eye under 365 nm UV light, thus realizing the visual detection of p-NA. The sensor presented comparable results compared with high-performance liquid chromatography (HPLC) method for the detection of p-NA in hair dye paste and aqueous samples with recoveries of 96.8-103.7% and 95.8-104.4%, respectively. It was demonstrated that the constructed sensor possesses the advantages of simplicity, excellent selectivity, superior sensitivity, and outstanding stability.

An effective magnetic nanobiocomposite: Preparation, characterization and its application for adsorption removal of P-nitroaniline from aquatic environments

In this investigation, a magnetic nanobiocomposite, denoted as CoFe2O4/Activated Carbon integrated with Chitosan (CoFe2O4/AC@Ch), was synthesized based on a microwave-assisted for the efficacious adsorption of P-nitroaniline (PNA). The physicochemical properties of the said nano biocomposite were thoroughly characterized using a suite of analytical methodologies, namely FESEM/EDS, BET, FTIR, XRD, and VSM. The results confirm the successful synthesis of the nanobiocomposite, with its point of zero charge (pHZPC) determined to be 6.4. Adsorptive performance towards PNA was systematically examined over a spectrum of conditions, encompassing variations in PNA concentration (spanning 10-40 mg/L), adsorbent concentration (10-200 mg/L), contact periods (2.5-22.5 min), and solution pH (3-11). Upon optimization, the conditions converged to an adsorbent concentration of 200 mg/L, pH 5, PNA concentration of 10 mg/L, and a contact duration of 22.5 min, under which an impressive PNA adsorption efficacy of 98.6% was attained. Kinetic and isotherm analyses insinuated the adsorption mechanism to adhere predominantly to the pseudo-second-order kinetic and Langmuir isotherm models. The magnetic nanocomposite was recovered and used in 4 cycles, and the absorption rate reached 86%, which shows the good stability of the magnetic nanocomposite in wastewater treatment. Conclusively, these empirical outcomes underscore the viability of the formulated magnetic nanobiocomposite as a potent, recyclable adsorbent for the proficient extraction of PNA from aqueous matrices.

Simultaneous elimination and detoxification of arsenite in the presence of micromolar hydrogen peroxide and ferrous and its environmental implications

Experiments for simultaneous elimination and detoxification of microgram level of As(Ⅲ) in the presence of micromolar H2O2 and Fe(Ⅱ) which are frequently encountered in natural water were conducted. The results showed that the molar ratio of oxidant to As(III) plays important role in As(III) oxidation under the experimental conditions. The extent of As(Ⅲ) oxidation with single H2O2 or Fe(Ⅱ) ranged from 7.9 % to 60.3 % and 22.2-46.6 %, respectively. Treatments with H2O2/As(Ⅲ) molar ratios in the range 150: 1-750: 1 or Fe(Ⅱ)/As(Ⅲ) molar ratios in the range 37.5: 1-375: 1 were more favor for As(Ⅲ) oxidation respectively, and increasing oxidant concentration did not result in complete As(Ⅲ) oxidation. As(Ⅲ) was completely oxidized and eliminated following the precipitation of ferric hydroxides in 5 reaction minutes when H2O2 and Fe(Ⅱ) coexisted in the reaction system. The interface characterization for the reacted precipitates after the experiment were conducted by using a high-resolution field emission scanning electron microscopy (SEM) coupled with an EX-350 energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that As(Ⅴ) was the merely arsenic species and As oxide primary situated in the subsurface layer of the reacted precipitates, whereas Fe was more concentrated in the outermost surface layer. Our research showed that H2O2 and Fe(Ⅱ) at natural level may exert significant influence on arsenic mobilization in natural water. Considering the much more toxic of As(Ⅲ) than that of As(Ⅴ), the research also provide us an environmental friendly choice in the elimination and detoxification of microgram As(Ⅲ) in drinking water.

Removal of p-arsanilic acid and phenylarsonic acid from water by Fenton coagulation process: influence of substituted amino group

Phenylarsonic acid compounds, which were widely used in poultry and swine production, are often introduced to agricultural soils with animal wastes. Fenton coagulation process is thought as an efficient method to remove them. However, the substituted amino group could apparently influence the removal efficiency in Fenton coagulation process. Herein, we investigated the optimal conditions to treat typical organoarsenic contaminants (p-arsanilic acid (p-ASA) and phenylarsonic acid (PAA)) in aqueous solution based on Fenton coagulation process for oxidizing them and capturing the released inorganic arsenic, and elucidated the influence mechanism of substituted amino group on removal. Results showed that the pH value and the dosage of H₂O₂ and Fe²⁺ significantly influenced the performance of the oxidation and coagulation processes. The optimal conditions for removing 20 mg L^-1-As in this research were 40mg L^-1 Fe²⁺ and 60mg L^-1 H₂O₂ (the mass ratio of Fe²⁺/H₂O₂ = 1.5), initial solution pH of 3.0, and final solution pH of 5.0 adjusting after 30-min Fenton oxidation reaction. Meanwhile, the substituted amino group made p-ASA much more easily be attacked by ·OH than PAA and supply one more binding sites for forming complexes with Fe³⁺ hydrolysates, resulting in 36% higher oxidation rate and 7% better coagulation performance at the optimal conditions.

Hollow-structured amorphous prussian blue decorated on graphitic carbon nitride for photo-assisted activation of peroxymonosulfate

Heterogeneous activation of peroxymonosulfate (PMS) is one of the most promising techniques for wastewater treatment. Herein, an ingenious system by coupling of photocatalysis and PMS activation was developed, using hollow-structured amorphous prussian blue (A-PB) decorated on graphitic carbon nitride (g-C₃N₄) as the catalyst. Degradation of bisphenol A (BPA) via the A-PB-g-C₃N₄ mediated PMS activation under visible light (Vis) was systematically investigated. Astonishingly, it was found that ~ 82.0%, 92.6%, 98.2% and 99.3% of BPA (40 mg/L) were removed within 2, 4, 6 and 7 min, respectively, suggesting the extremely strong oxidizing capacity of the A-PB-g-C₃N₄/PMS/Vis system. Synergistic effect between the decorated A-PB and the g-C₃N₄ substrate promoted the Fe(III)/Fe(II) redox cycling and facilitated the charge transfer at the A-PB/g-C₃N₄ heterojunction interface. As a result, both photocatalysis and heterogeneous activation of PMS were boosted in the A-PB-g-C₃N₄/PMS/Vis system, leading to the production of large amount of reactive oxygen species (ROS). The various ROS (SO₄^•-, HO•, •O₂^- and ¹O₂) was responsible for the ultrafast degradation of BPA. Moreover, the A-PB-g-C₃N₄ catalyst also exhibited outstanding reusability and stability, retaining 98.9% of the removal percentage for BPA after five consecutive reaction cycles. This study suggests that the A-PB-g-C₃N₄ can be an all-rounder to bridge photocatalysis and PMS activation, and shed a new light on the application of multiple ROS for the ultrafast elimination of micropollutants from wastewater.

A novel membrane-aerated biofilter for the enhanced treatment of nitroaniline wastewater: Nitroaniline biodegradation performance and its influencing factors

Nitroaniline (NA) wastewater is known to be highly toxic and biodegradation-resistant. Based on the principles of molecular oxygen supply and biofilm formation, a novel membrane-aerated biofilter (MABF) combining membrane aeration with a biofilter was established for the first time to treat NA wastewater containing the same concentrations of p-nitroaniline (PNA) and o-nitroaniline (ONA). The NA wastewater treatment performance of the MABF was investigated, and the NA biodegradation characteristics were evaluated. When the influent NA concentration was 120 mg/L, the PNA and ONA removal rates reached 100% and 86.56%, respectively. The NA removal loading reached 111.62 g/m³·d, and the total nitrogen (TN) removal rate reached 82.97%. The synergistic effects of the diverse microorganisms in the membrane-aerated and nonaerated zones of the MABF enhanced the removal of NA and nitrogen. This MABF is an economically efficient and environmentally friendly technology for treating wastewater containing toxic and hazardous organic compounds.

Facile and large-scale fabrication of (Mg,Ni)(Fe,Al)2O4 heterogeneous photo-Fenton-like catalyst from saprolite laterite ore for effective removal of organic contaminants

A facile and cost effective acid leaching-coprecipitation method was developed to prepare spinel-type (Mg,Ni)(Fe,Al)₂O₄ from saprolite laterite ore in large scale. The as-prepared (Mg,Ni)(Fe,Al)₂O₄ exhibited excellent photo-Fenton-like catalytic activity in decomposing different kinds of organic dyes and antibiotic tetracycline in the present of oxalic acid (H₂C₂O₄). The influential factors of RhB degradation efficiency were investigated, including the (Mg,Ni)(Fe,Al)₂O₄ dosage, H₂C₂O₄ concentration and the intensity of simulated sunlight. Meanwhile, the reaction mechanism of (Mg,Ni)(Fe,Al)₂O₄/H₂C₂O₄/simulated sunlight system was also proposed. As the formation of highly photochemical [≡Fe(C₂O₄)₃]^3- complex ions on the surface of the (Mg,Ni)(Fe,Al)₂O₄, the obtained (Mg,Ni)(Fe,Al)₂O₄ showed degradation efficiency (η) over 90.0 % for common organic dyes and antibiotic tetracycline within 180 min under the optimum conditions. The η and TOC removal for RhB were still over 98.0 % and 46.0 % after five reuse cycles, respectively. The excellent catalytic performance and recyclability make the (Mg,Ni)(Fe,Al)₂O₄ fabricated from natural saprolite laterite ore more competitive in dealing with wastewaters contaminated by organic pollutants.

Critical review on the chemical reduction of nitroaniline

Conversion of nitroaniline (NA), a highly toxic pollutant that has been released into aquatic systems due to unmanaged industrial development in recent years, into the less harmful or a useful counterpart is the need of the hour. Various methods for its conversion and removal have been explored. Owing to its nominal features of advanced effectiveness, the chemical reduction of 4-NA using various different nanocatalytic systems is one such approach that has attracted tremendous interest over the past few years. The academic literature has been confined to case studies involving silver (Ag) and gold (Au) nanoparticles, as these are the two most widely used materials for the synthesis of nanocatalytic assemblies. Focus has also been given to sodium borohydride (NaBH₄), which is used as a reductant during the chemical reduction of NA. This systematic review summarizes the fundamentals associated with the catalytic degradation of 4-NA, and presents a comprehensive and critical study of the latest modifications used in the synthesis of these catalytic systems. In addition, the kinetics, mechanisms, thermodynamics, as well as the future directions required for understanding this model reaction, have been provided in this particular study.

Schematic illustration of catalytic reduction of 4-NA in the presence of nanocatalysts and a reducing agent.

Remedial Technologies for Aniline and Aniline Derivatives Elimination from Wastewater

BACKGROUND

Aniline and its derivatives are widely used as intermediate chemicals in the pharmaceutical and dye industries and are present in their wastewaters. These chemicals are of concern due to their potential detrimental effects on public health and aquatic species in the environment.

OBJECTIVES

Various available remedial technologies presented in the literature were investigated to determine the most suitable technology for the elimination of aniline and aniline derivatives from waste streams.

METHODS

The related literature was collected electronically from ScienceDirect, Google Scholar, the International Agency for Research on Cancer (IARC), ResearchGate and Wiley Online Library for systematic review. The search terms included 'aniline', 'aniline degradation', 'advanced oxidation processes (AOPs)', 'aniline derivatives' and 'Fenton's reagent'.

DISCUSSION

Aniline and its derivatives are a serious issue in the effluents of dye and pharmaceutical industries, but a number of efficient treatment methods using biological, physical and AOPs have been presented in the literature.

CONCLUSIONS

Comparison of the available technologies showed that AOPs were the most cost effective and efficient technologies for eliminating aniline and its derivatives from wastewater.

COMPETING INTERESTS

The authors declare no competing financial interests.

Investigating the photo-Fenton process for treating soil washing wastewater

PURPOSE

Petroleum hydrocarbons have created numerous problems for water resources. The main objective of this study was focused on the application of advanced oxidation processes (AOPs) in treatment of effluent of petroleum contaminated soil washing operation.

METHODS

The AOP process in the present study was run with Fe²⁺/H₂O₂ (Fenton's reagent), Fe²⁺/H₂O₂/UV (photo-Fenton's reagent) and UV lamp (medium pressure mercury lamp, 400 W) in the batch-mode reactor at laboratory-scale.

RESULTS

Various parameters and optimized values which could maximize the removal efficiency of COD were: Fe²⁺ = 0.1 g/L, H₂O₂ = 1 g/L, pH = 3 and irradiation time of 120 min. Under the optimal conditions, the removal efficiency of COD and TOC were achieved 86.3% and 68% respectively. The results showed that the reaction of the oxidation of diesel fuel by Fenton and photo-Fenton systems followed second-order kinetic model with reaction rate constants (k) of 7 × 10^-6 and 3 × 10^-6 l/mg min^-1 respectively.

CONCLUSIONS

The photo-Fenton process can be used as an effective and environmental friendly method in the degradation of petroleum organic compounds.

Tetracycline Removal Under Solar Illumination Over Ag3 VO4 /mpg-C3 N4 Heterojunction Photocatalysts

Ag₃ VO₄ /mpg-C₃ N₄ (mesoporous graphitic carbon nitride) heterojunction photocatalysts were prepared by anchoring tiny Ag₃ VO₄ particles on the nanosheet of mpg-C₃ N₄ . The prepared Ag₃ VO₄ /mpg-C₃ N₄ heterojunctions were used to remove tetracycline (TC), a kind of antibiotics widely released into the aquatic environment under solar irradiation. Compared with pure mpg-C₃ N₄ and Ag₃ VO₄ , Ag₃ VO₄ /mpg-C₃ N₄ displayed much higher photocatalytic activity (83.2% removal rate within 90 min under visible-light irradiation). Importantly, no apparent deactivation was observed for Ag₃ VO₄ /mpg-C₃ N₄ -40 after five cycles, inferring a good reusability. As confirmed by photocurrent measurement and photoluminescence spectra, the excellent photocatalytic property of Ag₃ VO₄ /mpg-C₃ N₄ was credit to the electron-hole separation enhancement at the formed heterojunction of two semiconductors. In addition, a possible mechanism and intermediate products for the Ag₃ VO₄ /mpg-C₃ N₄ photocatalysts toward the photodegradation of TC in aqueous solution under artificial sunlight radiation were proposed based on the scavengers trapping test, ESR spectra and a high-performance liquid chromatography (HPLC) coupled with mass spectrometer (MS) analysis. This investigation provides a low cost, green and easily practical approach to remove the antibiotics in the aquatic environment.

Supercritical water oxidation of 2-, 3- and 4-nitroaniline: A study on nitrogen transformation mechanism

Supercritical water oxidation (SCWO) of 2-, 3- and 4-nitroaniline (NA) was investigated under residence time of 1-6 min, pressure of 18-26 MPa, temperature of 350-500 °C, with initial concentration of 1 mM and 300% excess oxygen. Among these operating conditions, temperature and residence time played a more significant role in decomposing TOC and TN than pressure. Moreover, the products of N-containing species were mainly N₂, ammonia and nitrate. When temperature, pressure and retention time enhanced, the yields of NO₃^- and org-N were reduced, the amount of N₂ was increasing, the proportion of NH₄⁺, however, presented a general trend from rise to decline in general. The experiment of aniline/nitrobenzene indicated that TN removal behavior between amino and nitro groups would prefer to happen in the molecule rather than between the molecules, therefore, the smaller interval between the amino and nitro group was the more easily to interreact. This might explain the reason why TN removal efficiency was in an order that 2-NA > 3-NA > 4-NA. The NH₄⁺/NO₃^- experiment result demonstrated that ammonia and nitrate did convert into N₂ during SCWO, however, the formation of N₂ was little without auxiliary fuel. Density functional theory (DFT) method was used to calculate the molecular structures of 2-, 3- and 4-NA to further explore reaction mechanism, which verified that amino group was more easily to be attacked than nitro group. Based on these results, the conceivable reaction pathways of 2-, 3- and 4-NA were proposed, which contained three parts, namely denitrification, ring-open and mineralization.

Mineralization of pyrrole, a recalcitrant heterocyclic compound, by electrochemical method: Multi-response optimization and degradation mechanism

In this study, the electrochemical (EC) oxidation of a recalcitrant heterocyclic compound namely pyrrole has been reported using platinum coated titanium (Pt/Ti) electrodes. Response surface methodology (RSM) comprising of full factorial central composite design (CCD) with four factors and five levels has been used to examine the effects of different operating parameters such as current density (j), aqueous solution pH, conductivity (k) and treatment time (t) in an EC batch reactor. Pyrrole mineralization in aqueous solution was examined with multiple responses such as chemical oxygen demand (COD) (response, Y₁) and specific energy consumption (SEC) in kWh/kg of COD removed (response, Y₂). During multiple response optimization, the desirability function approach was employed to concurrently maximize Y₁ and minimize Y₂. At the optimum condition, 82.9% COD removal and 7.7 kWh/kg of COD removed were observed. Degradation mechanism of pyrrole in wastewater was elucidated at the optimum condition of treatment by using UV-visible spectroscopy, Fourier transformed infra-red spectroscopy (FTIR), cyclic voltammetry (CV), ion chromatography (IC), higher performance liquid chromatography (HPLC) and gas chromatography-mass spectroscopy (GC-MS). The degradation pathway of pyrrole was proposed on the basis of the various analysis.

Low cost Fenton's oxidative degradation of 4-nitroaniline using iron from laterite

The present study aims to establish the use of iron (Fe) from larerite in the case of Fenton's oxidation process which is a simple and cost-effective method for degradation of nitro compounds in effluents and in surface or ground water. 4-nitroaniline (4-NA) degradation by Fenton's oxidation method is the subject of the present study so as to optimize pH, hydrogen peroxide/iron (H/F) ratio at different initial concentrations of 4-NA. The optimum pH obtained was 3. The present study has also established optimum H/F ratio for the different initial concentrations of 4-NA for both conventional and use of Fe from laterite. The maximum removal efficiency of 99.84% was obtained for an H/F ratio of 100 for 0.5 mM initial concentration of 4-NA. The study establishes the use of Fe extracted from locally available laterite soil (LS) as a replacement of Fe salts so as to reduce the cost of the process.

Rapid degradation of p-arsanilic acid with simultaneous arsenic removal from aqueous solution using Fenton process

Although banned in some developed countries, p-arsanilic acid (p-ASA) is still used widely as a feed additive for swine production in many countries. With little uptake and transformation in animal bodies, nearly all the p-ASA administered to animals is excreted chemically unchanged in animal wastes, which can subsequently release the more toxic inorganic arsenic species upon degradation in the environment. For safe disposal of the animal wastes laden with p-ASA, we proposed a method of leaching the highly water-soluble p-ASA out of the manure first, followed by treatment of the leachate using the Fenton process to achieve fast oxidation of p-ASA and removal of the inorganic arsenic species released (predominantly arsenate) from solution simultaneously. The effects of solution pH, dosages of H2O2 and Fe(2+), and the presence of dissolved organic matter (DOM) on the treatment efficiency were systematically investigated. Under the optimum treatment conditions (0.53 mmol L(-1) Fe(2+), 2.12 mmol L(-1) H2O2, and initial pH of 3.0), p-ASA (10 mg-As L(-1)) could be completely oxidized to As(V) within 30 min in pure water and 4 natural water samples, and at the final pH of 4.0, the residual arsenic levels in solution phase were as low as 1.1 and 20.1-43.4 μg L(-1) in the two types of water matrixes, respectively. The presence of humic acid significantly retarded the oxidation of p-ASA by scavenging HO, and inhibited the As(V) removal through competitive adsorption on ferric hydroxide. Due to the high contents of DOM in the swine manure leachate samples (TOC at ∼500 mg L(-1)), much higher dosages of Fe(2+) (10.0 mmol L(-1)) and H2O2 (40.0 mmol L(-1)) and a longer treatment time (120 min) were required to achieve near complete oxidation of p-ASA (98.0%), while maintaining the levels of residual arsenic in the solution at <70.0 μg L(-1). The degradation pathway of p-ASA in the Fenton process was proposed based on the major degradation products detected. Together, the results demonstrate that the Fenton process is promising as an efficient, robust, and low-cost treatment method for controlling the risk of p-ASA in the animal wastes generated at factory farms.

Homogeneous and heterogeneous degradation of caffeic acid using photocatalysis driven by UVA and solar light

Waste water from the wine industry is characterized by a high concentration of dissolved organic matter and the presence of natural phenolic compounds with low biodegradability. High concentrations of phenolic compounds may cause environmental pollution and risks to human health. In this article caffeic acid (CA) was used as a model compound of wine effluent because it is refractory to the conventional wastewater treatments. The oxidation of caffeic acid in water solution (0.01 g L(-1)) by heterogeneous photocatalysis and photo-Fenton reaction was studied using UVA. The optimal conditions for each treatment were performed by multivariate experimental design. The optimal conditions for heterogeneous photocatalysis were pH 5.3 and 0.9 g L(-1) TiO2. In the case of photo-Fenton treatment, optimized variable were 82.4 μmol L(-1) of Fe(2+) and 558.6 μmol L(-1) of H2O2. The degradation profiles of CA were monitored by UV-Vis, HPLC, TOC and COD. To reach 90% of CA removal, 40 and 2 min of reaction, respectively, were required by heterogeneous and photo-Fenton processes, respectively. For comparison purposes, the reactions were also performed under solar light. The use of solar light does not change the efficiency of the photo-Fenton reaction, yet the performance of the heterogeneous process was significantly improved, reaching 90% of degradation in 15 min.

Recent developments in heterogeneous photocatalytic water treatment using visible light-responsive photocatalysts: a review

This review summarizes the recent progress in the design, fabrication, and application of visible light-responsive photocatalysts.

Effects of the steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent on the adsorption of p-nitroaniline in aqueous solution

A hyper-cross-linked polymeric adsorbent with "--CH2--phenol--CH2--" as the cross-linked bridge (denoted GQ-05), and another hyper-cross-linked polymeric adsorbent with "--CH2--p-cresol--CH2--" as the cross-linked bridge (denoted GQ-03) were synthesized to reveal the effect of the steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent on adsorption capacity and adsorption rate of p-nitroaniline (PNA) from aqueous solution. The results of adsorption kinetics indicated the order of the adsorption rate GQ-05>GQ-03. The pseudo-first-order rate equation could describe the entire adsorption process of PNA onto GQ-05 while the equation characterized the adsorption process of GQ-03 in two stages. The order of the adsorption capacity GQ-05>GQ-03 was demonstrated by thermodynamic analysis and dynamic adsorption. The steric hindrance of micropores in the hyper-cross-linked polymeric adsorbent was a crucial factor for the order of the adsorption capacity and adsorption rate.

Oxidative degradation of sulfathiazole by Fenton and photo-Fenton reactions

This article presents experimental results on 47 μmol L(-1) sulfathiazole (STZ) degradation by Fenton and photo-Fenton reactions using multivariate analysis. The optimal experimental conditions for reactions were obtained by Response Surface Methodology (RSM). In the case of the Fenton reactions there were 192 μmol L(-1) ferrous ions (Fe(II)) and 1856 μmol L(-1) hydrogen peroxide (H2O2), as compared with 157 μmol L(-1) (Fe(II)) and 1219 μmol L(-1) (H2O2) for photo-Fenton reactions. Under these conditions, around 90% of STZ degradation were achieved after 8 minutes treatment by Fenton and photo-Fenton reactions, respectively. Moreover, a marked difference was observed in the total organic carbon (TOC) removal after 60-min treatment, achieving 30% and 75% for the Fenton and photo-Fenton reactions, respectively. Acetic, maleic, succinic and oxamic acids could be identified as main Fenton oxidation intermediates. A similar pattern was found in the case of photo-Fenton reaction, including the presence of oxalic acid and ammonia at short periods of irradiation with UV-A. The calculated values of Average Oxidation State (AOS) corroborate the formation of oxidized products from the initial steps of the reaction.

Optimization of a heterogeneous catalytic hydrodynamic cavitation reactor performance in decolorization of Rhodamine B: application of scrap iron sheets

A low pressure pilot scale hydrodynamic cavitation (HC) reactor with 30 L volume, using fixed scrap iron sheets, as the heterogeneous catalyst, with no external source of H2O2 was devised to investigate the effects of operating parameters of the HC reactor performance. In situ generation of Fenton reagents suggested an induced advanced Fenton process (IAFP) to explain the enhancing effect of the used catalyst in the HC process. The reactor optimization was done based upon the extent of decolorization (ED) of aqueous solution of Rhodamine B (RhB). To have a perfect study on the pertinent parameters of the heterogeneous catalyzed HC reactor, the following cases as, the effects of scrap iron sheets, inlet pressure (2.4-5.8 bar), the distance between orifice plates and catalyst sheets (submerged and inline located orifice plates), back-pressure (2-6 bar), orifice plates type (4 various orifice plates), pH (2-10) and initial RhB concentration (2-14 mg L(-1)) have been investigated. The results showed that the highest cavitational yield can be obtained at pH 3 and initial dye concentration of 10 mg L(-1). Also, an increase in the inlet pressure would lead to an increase in the ED. In addition, it was found that using the deeper holes (thicker orifice plates) would lead to lower ED, and holes with larger diameter would lead to the higher ED in the same cross-sectional area, but in the same holes' diameters, higher cross-sectional area leads to the lower ED. The submerged operation mode showed a greater cavitational effects rather than the inline mode. Also, for the inline mode, the optimum value of 3 bar was obtained for the back-pressure condition in the system. Moreover, according to the analysis of changes in the UV-Vis spectra of RhB, both degradation of RhB chromophore structure and N-deethylation were occurred during the catalyzed HC process.

Photocatalytic Degradation of p-Nitroaniline with Composite Photocatalyst H3P12W40/TiO 2

The prepared composite photocatalyst H3PW12O40/TiO2 was synthesized by sol-gel impregnation method and characterized by scanning electron microscope(SEM), energy-dispersive X-ray spectroscopy(EDS), Fourier transform infrared(FT-IR), X-ray diffraction(XRD), UV-vis diffuse reflectance spectrum(DRS) to investigate its optical, physical and chemical properties. The results indicated that the modified catalyst was coated with P and W element, still have uniform anatase structure. Meanwhile, there is a chemical interaction exists between the Keggin unit and the surface of the titania matrix. Compared with original H4PW12O40 or TiO2 matrix, the adsorption threshold onset of the composite extended to the visible region. Effects of H3PW12O40/TiO2 dosage, pH value, initial p-NA concentration on the photocatalytic degradation of p-NA under 250W UV irradiation were investigated. The optimal H3PW12O40/TiO2 dosage and pH value for degradation of 10mg/L p-NA were o.6g/L and 3.0, respectively. The degradation rate of p-NA by H3PW12O40/TiO2 process could be fitted pseudo-first-order kinetics. Moreover, 66% degradation of p-NA was still observed in the 5th recycle experiment. Futhermore, 4-Aminophenol, Phenol, Hydroquinone, 4-Benzoquinone and other intermediate products were indentifieded by GC/MS and a possible reaction mechanism is proposed on the basis of all the information obtained from the analysis of FT-IR and the above intermediates.

Hydroxyl radical concentration profile in photo-Fenton oxidation process: generation and consumption of hydroxyl radicals during the discoloration of azo-dye Orange II

Dynamic behaviors of hydroxyl (OH) radical generation and consumption in photo-Fenton oxidation process were investigated by measuring OH radical concentration during the discoloration of azo-dye Orange II. The effects of operating parameters for photo-Fenton discoloration, i.e. dosages of H(2)O(2) and Fe, initial dye concentration, solution pH and UV irradiation, on the generation and consumption of OH radicals playing the main role in advanced oxidation processes were extensively studied. The scavenger probe or trapping technique in which coumarin is scavenger of OH radical was applied to estimate OH radical concentration in the photoreactor during the photo-Fenton discoloration process. The OH radical generation was enhanced with increasing the dosages of Fenton regents, H(2)O(2) and Fe. At the initial stage of photo-Fenton discoloration of Orange II, the OH radical concentration rapidly increased (Phase-I) and the OH radical concentration decreased after reaching of OH radical concentration at maximum value (Phase-II). The decrease in OH radical concentration started when the complete discoloration of Orange II was nearly achieved and the H(2)O(2) concentration became rather low. The dynamic behavior of OH radical concentration during the discoloration of Orange II was found to be strongly linked with the change in H(2)O(2) concentration. The generation of OH radical was maximum at solution pH of 3.0 and decreased with an increase of solution pH. The OH radical generation rate in the Fenton Process was rather slower than that in the photo-Fenton process.

Degradation of the antibiotics amoxicillin, ampicillin and cloxacillin in aqueous solution by the photo-Fenton process

The study examined degradation of the antibiotics amoxicillin, ampicillin and cloxacillin in aqueous solution by the photo-Fenton process. The optimum operating conditions for treatment of an aqueous solution containing 104, 105 and 103 mg/L amoxicillin, ampicillin, and cloxacillin, respectively was observed to be H(2)O(2)/COD molar ratio 1.5, H(2)O(2)/Fe(2+) molar ratio 20 and pH 3. Under optimum operating conditions, complete degradation of amoxicillin, ampicillin and cloxacillin occurred in 2 min. Biodegradability (BOD(5)/COD ratio) improved from approximately 0 to 0.4, and COD and DOC degradation were 80.8 and 58.4%, respectively in 50 min. Photo-Fenton treatment resulted in the release and mineralization of organic carbon and nitrogen in the antibiotic molecule. Increase in ammonia and nitrate concentration, and DOC degradation were observed as a result of organic carbon and nitrogen mineralization. DOC degradation increased to 58.4% and ammonia increased from 8 to 13.5mg/L, and nitrate increased from 0.3 to 14.2mg/L in 50 min.

Heterogeneous photo-Fenton photodegradation of reactive brilliant orange X-GN over iron-pillared montmorillonite under visible irradiation

Decolorization and mineralization of reactive brilliant orange X-GN was investigated under visible light irradiation (lambda>or=420 nm) by using Fe-Mt/H(2)O(2) as the heterogeneous photo-Fenton reagent. The characterization results (XRD, FTIR, XRF, BET, XPS, UV-vis diffuse spectra) of Fe-Mt suggested that small-sized hydrolyzed iron successfully intercalated into the interlayer spaces of the clay via pillaring. The stability of the Fe-Mt catalyst was evaluated according to the decolorization efficiency for X-GN with used catalyst from previous runs and the concentration of iron ions leached from the solid structure into the reaction solution. The catalytic results showed that at a reaction temperature of 30 degrees C, pH 3.0, 4.9 mmol/L H(2)O(2) and 0.6g/L catalyst dosage, 98.6% discoloration and 52.9% TOC removal of X-GN were achieved under visible irradiation after 140 min treatment. Furthermore, the maximum concentration of dissolved iron ions was 1.26% of the total iron content in the Fe-Mt catalyst after photocatalysis. A halogen lamp as light source has demonstrated that visible radiation can be successfully used for a heterogeneous photo-Fenton process.

Fenton degradation of 4,6-dinitro-o-cresol with Fe(2+)-substituted ion-exchange resin

The Fenton degradation of 4,6-dinitro-o-cresol (DNOC) was studied under different experimental conditions using Amberlyst 15 ion-exchange resin containing ferrous ion. DNOC was found to be effectively degraded under most conditions, and it was observed that, with the addition of HCl, the desorption of ferrous ion from the resin into the solution played a major role in this degradation. The total iron concentration in the reaction solution was found to increase with the addition of HCl, and a pseudo-first-order kinetic model was applied to the desorption of ferrous ion from the resin on the basis of the assumption of a first-order ion-exchange process. The degradation rate of DNOC also increased as a function of HCl. A kinetic model was developed to simulate the degradation of DNOC under different operating conditions, assuming the first-order desorption of ferrous ion. Different cations were compared with H(+), and H(+) was found to be the most efficient at facilitating the degradation reaction at low concentrations, whereas Ca(2+) was found to be most efficient at high concentrations. pH was measured during the reaction, and its effect on degradation was explored. It was found that a lower pH could lead to faster degradation of the target compound. Degradation of DNOC under different delivery rates of H(2)O(2) was studied, and optimal conditions were determined. The results also showed that the delivery rate of H(2)O(2) did not affect the ion-exchange process of the resin.