A new type of continuous-flow heterogeneous electro-Fenton reactor for Tartrazine degradation

Cobalt based bimetallic catalysts for heterogeneous electro-Fenton adapting to vary pH for HEDP and MIT degradation

Most of the materials studied as catalysts in the electro-Fenton system are variants of iron oxide or iron hydroxide. However, iron-based catalysts often exhibit weak catalytic capabilities under neutral and alkaline conditions. In this work, we synthesized three cobalt based bimetallic oxides, Co2CuOx, Co2AlOx, and Co2NiOx, using hydrothermal method and evaluated them as catalysts for the heterogeneous electro-Fenton system to remove 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and Methylisothiazolinone [2-methyl-4-isothiazolin-3-one] (MIT). Co2NiOx has the highest catalytic degradation activity for HEDP, and Co2CuOx has the best catalytic degradation effect for MIT. Based on characterization results of the catalysts, the reasons for the differences in the pollutant removal efficiency were analysed, and the optimal pH for the three cobalt based oxides to remove HEDP and MIT was investigated. The results showed that the optimal pH values of the three cobalt based bimetallic oxides are not only influenced by the second metal type, but also by the properties of pollutants. Therefore, suitable cobalt based catalysts can be selected based on the different properties of pollutants, or the composition of cobalt based catalysts can be adjusted to meet the different pH requirements of target wastewater. The three cobalt based bimetallic oxides exhibited good degradation of HEDP and MIT under neutral conditions, which to some extent solved the problem of narrow pH range in the practical application of the electro-Fenton process.

Intensified degradation of tartrazine dye present in effluent using ultrasound combined with ultraviolet irradiation and oxidants

Effluent containing tartrazine can affect the environment and human health significantly prompting the current study into degradation using a sonochemical reactor operated individually and combined with advanced oxidation processes. The optimum conditions for ultrasound treatment were established as dye concentration of 10 ppm, pH of 3, temperature as 35 °C, and power as 90 W. The combination approach of H2O2/UV, H2O2/US, and H2O2/UV/US resulted in higher degradation of 25.44%, 57.4%, and 74.36% respectively. Use of ZnO/UV/US approach increased the degradation significantly to 85.31% whereas maximum degradation as 93.11% was obtained for the US/UV/Fenton combination. COD reduction was found maximum as 83.78% for the US/UV/Fenton combination. The kinetic analysis showed that tartrazine dye degradation follows pseudo first-order kinetics for all the studied processes. Combination of Fenton with UV and US was elucidated as the best approach for degradation of tartrazine.

In situ generated iron oxide nanosheet on iron foam electrode for enhanced electro-Fenton performance toward pharmaceutical wastewater treatment

Electro-Fenton (EF) is considered to be an effective technology for the purification of organic wastewater containing antibiotics, but the construction of accessible and efficient heterogeneous EF catalytic materials still faces challenges. In this study, an iron foam-derived electrode (FeOx/if-400) was prepared by a simple method (chemical oxidation combined heat treatment). The fabricated electrode presented great EF degradation efficiency under wide pH range (almost completely removing 50 mg L-1 TNZ within 60 min) and maintained great stability after consecutive operation (>95% removal after six cycles). Also, the FeOx/if-400 electrode showed good purification ability for pharmaceutical wastewater as evaluated by the quadrupole time-of-flight mass spectrometry and the three-dimensional excitation-emission matrix fluorescence spectroscopy. Based on experimental results, characterization analysis, and density functional theory (DFT) calculations, the EF reaction mechanism of FeOx/if-400 electrode and the organics degradation pathways in simulated and real matrices were proposed. Significantly, the biotoxicity assessment of the degradation intermediate products was revealed by ECOSAR software and relative inhibition of E. coli, which fully proved the environmental friendliness of the EF process by the FeOx/if-400 cathode. This work provides a green and effective EF system, showing a promising application potential in the field of organic wastewater treatment containing antibiotic contaminants.

Waste iron as a robust and ecological catalyst for decomposition industrial dyes under UV irradiation

In an era of increasing environmental awareness, it is very important to work towards eliminating or at least reducing as many harmful industrial substances as possible. However, the implementation of green chemistry methods for wastewater treatment can be difficult especially due to complexity, the high cost of reagents, and the required long process time. This paper focuses on using waste iron (WI) to remove two kinds of amaranth dye commonly used in industry. To enhance the process, UV irradiation and hydrogen peroxide were used. The novelty of the research was the use of efficient and reusable WI as a heterogeneous catalyst in the process. WI material characteristics was done before and after the process using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). Zeta potential, size characterization, circularity, and direct band gap were also determined. As a result of treatment complete decolorization of both dyes was achieved, as well as 99% absorbance removal after 15-min process time. The total organic carbon (TOC) decrease after 60-min process time was in the range from 86.6 to 89.8%. Modified pseudo-second-order reaction reflects obtained results of treatment efficiency. Treatment results, confirmed by WI material characterization, indicate satisfactory stability of the catalyst and good oxidation capacity.

Highly effectual photocatalytic degradation of tartrazine by using Ag nanoparticles decorated on Zn-Cu-Cr layered double hydroxide@ 2D graphitic carbon nitride (C3N5)

Pollution of water resources is one of the main concerns of many countries. This issue originates from the entry of diverse pollutants, including dye compounds, into water sources. In this work, ternary Zn-Cu-Cr layered double hydroxides (LDH) supported on graphitic carbon nitride (g-C₃N₅) decorated by silver nanoparticles (C₃N₅-LDH-Ag) was first prepared. Application of various characterization techniques such as SEM, XRD, and FT-IR revealed that the synthesized nanocomposite was composed of Zn-Cu-Cr LDH nanoparticles, g-C₃N₅ nanosheets, and Ag nanoparticles. The prepared nanomaterials were employed for the photodegradation of tartrazine in aqueous solutions. It was found that the C₃N₅-LDH-Ag catalyst outperformed their pure g-C₃N₅, Zn-Cu-Cr LDH, and C₃N₅-LDH composite in photocatalytic degradation of tartrazine under visible light irradiation. Tartrazine (20 mg/L) can be entirely removed by 0.25 g/L C₃N₅-LDH-Ag photocatalyst under 1 h visible light irradiation (200 W) at pH 6 with a rapid degradation rate constant (k) that is 4.4, 3.9, and 2.6 times higher than that of pure C₃N₅, Zn-Cu-Cr LDH, and C₃N₅-LDH component, respectively. The formation of hydroxyl radicals on the surface of C₃N₅-LDH-Ag as the main active species was approved by the capturing experiment. The finding results approved the stability and reusability of C₃N₅-LDH-Ag in four photocatalytic degradation cycles. In general, our findings revealed that the synthesized nanocomposite could be employed as an efficient photocatalyst in environmental remediation.

Degradation of carbamazepine over MOFs derived FeMn@C bimetallic heterogeneous electro-Fenton catalyst

A highly efficient heterogeneous electro-Fenton (Hetero-EF) catalyst with core-shell structure was successfully prepared by calcination of Mn-doped Mil-53 (Fe) precursor at high temperature. FeMn@C-800/2 prepared at pyrolysis temperature of 800 °C and Fe:Mn molar doping ratio of 2:1 showed the best catalytic performance for the degradation of carbamazepine (CBZ). The characterization, properties and stability of FeMn@C-800/2 were systematically investigated, obtaining the apparent first-order reaction rate of Hetero-EF was 8.9 and 17.8 times higher than that on Fe@C-800 and Mn@C-800 at the optimized conditions of current density 10 mA cm^-2, catalyst dosage of 50 mg L^-1 and initial pH 4.0, respectively. The incorporation of Mn promoted the generation of more Fe⁰ and Fe₃C during the pyrolysis process, and enhanced the internal micro-electrolysis between Fe⁰ and carbon shell. At the same time, the presence of Mn⁰ also promoted the regeneration of Fe²⁺, and improved the activity of iron-carbon heterogeneous catalysis in the EF process, so as to degrade organic pollutants more effectively. This work would help to gain insight into the design of MOFs derived Fe-Mn bimetal catalyst and its mechanism for enhanced heterogeneous electro-Fenton.

Activated peroxydisulfate by sorghum straw-based biochar for enhanced tartrazine degradation: Roles of adsorption and radical/nonradical processes

Biochar obtained from biomass waste through pyrolysis has significant potential in wastewater treatment due to its large specific surface area and multi-functional active sites. In current study, sorghum straw (SS) was pyrolyzed to prepare various biochar under nitrogen atmosphere. Adsorption kinetics of prepared biochar toward tartrazine (TTZ) was systematically investigated, and the biochar was also characterized by using multiple techniques to explore the contribution of physicochemical properties to adsorption. Then, the biochar with optimum TTZ adsorption performance, was also applied as a catalyst for peroxydisulfate (PDS) activation to degrade TTZ. Factors including PDS concentration, solution pH, and reaction temperature were examined. The optimized degradation rate constant of TTZ (1.1627 min^-1) was achieved under the conditions at 2 mM PDS, pH of 3, and 23 °C. In addition, the free radical trapping experiments and EPR spectra revealed that the reactive substances of electron (e^-), ¹O₂, SO₄^•-, O₂^•-, and •OH contributed to TTZ degradation. Density Functional Theory (DFT) also concluded that the atoms C(6), O(12), N(16), N(17), C(18) and N(22) in TTZ molecule showed larger f⁰ values which are vulnerable to radical attack. Therefore, the synergistic mechanism embodying adsorption and radical/non-radical processes were proposed. Besides, the degradation pathways of TTZ were identified with the aid of HPLC/MS technique, indicating that multiple reaction processes containing the symmetrical cleavage of azo bonds, the asymmetrical cleavage of C-N, desulfonation, and benzene-like structure cracking were involved. Therefore, this study provides a simple and effective catalytic system for TTZ degradation, and also realizes the resource utilization of solid waste.

Substantial improvement in the adsorption behavior of montmorillonite toward Tartrazine through hexadecylamine impregnation

In the present work, the surface of montmorillonite K10 was successfully modified by hexadecylamine surfactant (Mt-HDA) and its intercalation and characteristics were assessed by XRD, FTIR, SEM, EDX and BET methods. Also, its adsorption performance was systematically examined in the removal of Tartrazine (TZ), as a sulfonated azo dye model, from aqueous phase. Our results showed that the HDA modification remarkably improved the adsorption ability of montmorillonite toward TZ molecules. The highest adsorption efficiency was achieved >98% at the pH range of 4-6 within a fast process (less than 30 min). The maximum adsorption capacity Mt-HDA toward TZ molecules was found to be ~59 mg/g at 45 °C. The kinetic study indicated that the adsorption kinetic follows pseudo-second-order model, which shows the chemisorption process between Mt-HDA and TZ molecules. Besides, the adsorption isotherm showed the monolayer coverage of Mt-HDA surface adsorption sites, which was fitted with the Langmuir isotherm model in an exothermic process. The adsorption mechanism was studied.

A comprehensive study on the heterogeneous electro-Fenton degradation of tartrazine in water using CoFe2O4/carbon felt cathode

In this study, cobalt ferrite coated carbon felt (CoFe₂O₄/CF) was synthesized by solvothermal method and applied as cathode for electro-Fenton (EF) treatment of tartrazine (TTZ) in water. The materials were characterized by SEM, XRD, FTIR, CV, and EIS to explore their physical, chemical, and electrical properties. The effects of solvothermal temperature and metal content on the TTZ removal were examined, showing that 220 °C with 2 mM of Co and 4 mM of Fe precursors were the best synthesis condition. Various influencing factors such as applied current density, pH, TTZ concentration, and electrolytes were investigated, and the optimal condition was found at 8.33 mA cm^-2, pH 3, 50 mgTTZ L^-1, and 50 mM of Na₂SO₄, respectively. By radical quenching test, , ¹O₂, and HO were recognized as the key reactive oxygen species and the reaction mechanism was proposed for the EF decolorization of TTZ using CoFe₂O₄/CF cathode. The reusability and stability test showed that the highly efficient CoFe₂O₄/CF cathode is very promising for practical application in wastewater treatment, especially for dyes and other recalcitrant organic compounds to improve its biodegradability.

A novel high rotation bubble reactor for the treatment of a model pollutant in ozone/goethite/H2O2 and UV/goethite coupled processes

This work proposes a novel approach for the coupling of ozonation and Fenton processes using a new prototype of a high rotation bubble reactor (HRBR), which improves utilization of the ozone and hydrogen peroxide through bubble generation and axial and radial dispersion of the flow. The HRBR integrates the rotor and the diffuser in the same device facilitating the generation and dispersion of the ozone bubbles inside the reaction tank. Thus, the mass transfer to the liquid phase is enhanced. Most of the experiments were carried out under neutral pH and 1580 rpm of agitation during the 20 min of reaction. Total ibuprofen degradation was achieved within 20 min of operation for most of the couplings and individual processes evaluated. It was successfully demonstrated that the HRBR can be used as a reactive system for heterogeneous Fenton and ozonation coupling because it presents a high synergy. For the ozonation process, the reactor also displayed a good performance because the residual ozone in the gas is lower than 0.4 mg/L, which indicates that there is a suitable ozone utilization. Ibuprofen degradation by other processes like oxidation direct by H₂O₂ and heterogeneous Fenton was 28.0% and 73.1%, respectively. It was determined that the reaction rate, synergy, OUI (ozone utilized index), and consumption of electrical energy (EE/O) of the coupled processes could be improved by using the HRBR depending on the experimental conditions.

Significant improvement in biodegradability of a real Optical Brightening Agent (OBA) wastewater using small doses of Fenton's reagent

Optical Brightening Agent (OBA) wastewater (OBAW) has been reported to be highly resistant to biodegradation. In this study, a real OBAW from an industry which was already treated using primary and secondary treatments (residual COD of secondary clarifier overflow (SCO): 3400-3700 mgL^-1) was further treated by Fenton's treatment (FT). Zahn-Wellens biodegradability test revealed that using small doses of H₂O₂ and Fe⁺², the biodegradability of SCO improved to 90% as compared to ∼18% without FT. UV-Vis analysis revealed that ca. 80% of initially present OBAs were removed by treatment sequence outlined in this study. Biodegradability study on individual raw wastewaters from four types of OBAs (designated OBA-TS, OBA-DS-U, OBA-HS, and OBA-DS-D) being manufactured at the time of this study, revealed that OBA-TS wastewater was the most biodegradable (>95% biodegradability) followed by OBA-DS-U (∼60%), OBA-HS (∼20%), and OBA-DS-D (<5%). Application of FT improved the biodegradability of these streams as: OBA-DS-U (∼70%), OBA-HS (∼60%), and OBA-DS-D (∼50%). A treatment sequence consisting of waste coal dust (WCD) pretreatment-FT-biodegradation is a novel, economical, and sustainable approach to treating highly recalcitrant OBA wastewater.

Simultaneous persulfate activation by electrogenerated H2O2 and anodic oxidation at a boron-doped diamond anode for the treatment of dye solutions

The development of new or upgraded electrochemical water treatment technologies is considered a topic of great interest. Here, Tartrazine azo dye solutions were treated by means of a quite innovative dual electrochemical persulfate (S₂O₈^2-, PS) activation that combines H₂O₂ generation at an air-diffusion cathode and anodic oxidation (AO) at a boron-doped diamond (BDD) anode using a stirred tank reactor. This so-called AO-H₂O₂/PS process was compared to AO with stainless steel cathode, both in 50 mM Na₂SO₄ medium, finding the oxidation power increasing as: AO < AO-H₂O₂ < AO/PS < AO-H₂O₂/PS. In the latter, the dye and its products were mainly destroyed by: (i) hydroxyl radicals, formed either from water oxidation at BDD surface or via reaction between H₂O₂ and S₂O₈^2-, and (ii) sulfate radical anion, formed from the latter reaction, thermal PS activation and cathodic S₂O₈^2- reduction. Hydroxyl radicals prevailed as oxidizing agents, as deduced from trials with tert-butanol and methanol. The reaction between S₂O₈^2- and accumulated H₂O₂ was favored as temperature increased from 25 to 45 °C. The effect of PS content up to 36 mM, dye concentration within the range 0.22-0.88 mM, current density (j) between 8.3 and 33.3 mA cm^-2 and pH between 3.0 and 9.0 on the process performance was examined. All decolorization profiles agreed with a pseudo-first-order kinetics. The best results for treating 0.44 mM dye were attained with 36 mM PS at pH 3.0, j = 16.7 mA cm^-2 and 45 °C, yielding total loss of color, 62% TOC removal and 50% mineralization current efficiency after 360 min. The slow mineralization was attributed to the persistence of recalcitrant byproducts like maleic, acetic, oxalic, formic and oxamic acids. It is concluded that the novel AO-H₂O₂/PS process is more effective than AO/PS to treat Tartrazine solutions, being advisable to extend the study to other organic pollutants.

Improving Fe-based heterogeneous Electro-Fenton nano catalyst using transition metals in a novel orbiting electrodes reactor

In recent decades the electro-Fenton process has widely been utilized for removing recalcitrant compounds. However, this process is accompanied by several problems such as limited working pH range, production of significant amount of iron sludge, and incapability in reusing used iron ions. Hence, the heterogeneous electro-Fenton process is a convenient way to address these problems. One of the shortcomings of this method, in comparison with the homogeneous electro-Fenton process, is its lower reaction rate. In the first phase of this study, a heterogeneous Fe-based nanocatalyst was prepared. After optimizing the affecting parameters, three transition metals (M: Cu, Co and, Cr) were used in the second phase of the study to improve the performance of this nanocatalyst in removing the indicator pollutant (acid blue 25). The characteristics of nanocatalysts were determined via FESEM, XRD, FTIR, and N₂ adsorption-desorption techniques. The results indicated an enhancement in dye removal efficiency (nearly 8 percent), and the reaction rate (nearly 64 percent) due to the nanocatalysts improved by the presence of transition metals. The reactions with Fe-based nanocatalyst containing copper ions in pH = 3, initial dye concentration = 200 mg L^-1, I = 3.57 mA cm^-2, nanocatalyst concentration = 100 mg L^-1, electrodes angular velocity = 50 rpm, Na₂SO₄ concentration = 0.01 M were capable of removing 97% of dye, 79% of COD and, 65% of TOC. The nanocatalysts were used in 5 cycles, and the dye removal efficiency did not drop considerably, a feature that adds to their importance from an economic point of view. The concentration of leached transition metals into the solution was measured using the ICP-AES technique, which was less than the allowable Iranian standard concentration of discharge into the surface water bodies, thus no need for secondary treatment of wastewater.

The reverse electrodialysis driven electrochemical process assisted by anodic photocatalysis for hydrogen peroxide production

A novel system combined with photocatalytic fuel cell and electrochemical system assisted by reverse electrodialysis (PREC) is proposed for H₂O₂ production and electricity generation. Results demonstrated the H₂O₂ concentration increased gradually with time and reached around 940 mg/L at 24 h. The optimum air flow rate was 15 L/min. The current efficiency was 31.3%. The maximum short-circuit current density, maximum open-circuit voltage and maximum power density were 0.95 mA/cm², 1.52 V and 68 W/m². The salinity-driven potential, created with the five pairs of the HC and LC cells in the PREC, was calculated to be 0.72 V. Additionally, the energy efficiency (η_E) was 40.5%. The integrated system is confirmed to be serviced as an efficient technology for H₂O₂ electro-genneration and salinity-gradient energy utilization simultaneously.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.