Facile synthesis of micro and nano sized iron based metal organic frameworks for optimization of effective metronidazole removal

Belgin Gözmen | Meral Turabik

The widespread application of antibiotics has led to pollution of aquatic systems with long-lasting pharmaceutical residues that pose serious environmental hazards and encourage antibiotic resistance. Metronidazole (MNZ), which belongs to the class of nitroimidazoles used widely, can commonly be traced to occur in water bodies as it possesses high persistence in the environment. To address this issue, this study reports the synthesis of micro and nano sized MIL-101(Fe) metal-organic frameworks (MOFs), or mMIL-101(Fe) and nMIL-101(Fe), by solvothermal and ultrasonic-assisted solvothermal methods, respectively. Comprehensive physicochemical characterization confirmed the successful synthesis of highly porous materials, with mMIL-101(Fe) exhibiting octahedral crystals with average size 2.3 μm and nMIL-101(Fe) existing as nanoparticles with size around 78 nm. BET surface area measurements yielded outstanding values of 4102 m²/g for mMIL-101(Fe) and 2411 m²/g for nMIL-101(Fe). Adsorption performance against MNZ was systematically optimized using Response Surface Methodology (RSM). Adsorption isotherm experiments revealed a closer fit to the Langmuir model, reflecting monolayer adsorption. Notably, the maximum adsorption capacities were as high as 333 mg/g for mMIL-101(Fe) and a impro...

Microwave-assisted biodiesel production from waste cooking oil using pyrrolidonium ionic liquid catalyst: optimization, kinetic and thermodynamic studies

Gözmen, Belgin | Sönmez, Özgür

Biodiesel production from waste cooking oil (WCO) has been gaining popularity due to its economical and eco-friendly nature. This study aimed to produce an environmentally friendly fuel by recycling WCO. Using pyrrolidonium-based Brønsted acidic ionic liquid (IL) as a catalyst, microwave-assisted transesterification of WCO was used to produce biodiesel. Reaction conditions, including temperature, catalyst amount, methanol/oil molar ratio, and reaction time, were optimized using response surface methodology (RSM) based on Box-Behnken design (BBD). A biodiesel conversion of 97.3 % was achieved at 115 °C, for 120 min, with 10 % catalyst loading, and a 24:1 methanol/oil molar ratio. The kinetics of the transesterification reaction was investigated, with the activation energy determined to be 13.67 kJ mol−1. The thermodynamic values were also calculated, ΔH = 10.6 kJ mol−1, ΔS = − 252.53 J mol−1 K−1 and ΔG = 99.7–109.8 kJ mol−1. Thus, the microwave-assisted transesterification reaction was endothermic, endergonic, and non-spontaneous. The IL catalyst demonstrated excellent reusability, maintaining high activity for six consecutive cycles. In addition, the quality of WCO biodiesel met the ASTM D6751 standard. Pyrrolidonium-based ILs are effective catalysts for biodiesel production owin...

Heterogeneous electro-fenton treatment of clofibric acid with a Fe3O4 loaded bifunctional carbon felt cathode via different anode types

Gözmen, Belgin | Çirmi, Doğan

Pharmaceutical pollutants such as clofibric acid pose significant risks to aquatic environments and human health. In this study, a bifunctional cathode (CF@Fe3O4) was synthesized by anchoring Fe3O4 nanoparticles onto carbon felt via a solvothermal method. The material was characterized using scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The CF@Fe3O4 cathode was then evaluated in a heterogeneous electro-Fenton system for clofibric acid degradation under varying pH and current conditions using platinum and boron doped diamond anodes. Using the CF@Fe3O4/Pt pair, the highest mineralization efficiency (82%) was achieved at pH 3 and 50 mA after 5 h, whereas higher current intensities resulted in decreased mineralization. In contrast, the CF@Fe3O4/BDD system showed enhanced performance with increasing current, achieving 99% mineralization at 300 mA and pH 3. The BDD anode also enabled mineralization efficiencies above 90% across a broad pH range (3–8), along with faster reaction kinetics and improved energy efficiency. Fe3O4 loading promoted electron transfer and mitigated mass transport limitations, significantly improving degradation rates. Additionally, a small amount of Fe ion leach (1 mg L−1) at pH 3 facilitated supplementary •...

Carbon felt/CoFe2O4 cathode synthesis and use in the heterogeneous electro-Fenton process for vanillin oxidation

Gözmen, Belgin | Çirmi, Doğan

Synthetic vanillin is widely used in industries such as food and cosmetics, and it isalso produced as a by-product in various processes. This study was conductedto compare the degradation of vanillin using homogeneous and heterogeneouselectro-Fenton (EF) processes. Initially, electrocatalytic characterization was per-formed on a cathode material synthesized by solvothermal deposition of cobalt fer-rite (CoFe 2 O4 ) nanostructures onto a carbon felt (CF) substrate and compared withbare CF. Subsequently, the effectiveness of the CF@CoFe 2O 4 cathode material invanillin oxidation was compared at different pH values and currents with the hetero-geneous electro-Fenton process. The highest vanillin degradation and total organiccarbon (TOC) removal were achieved at pH 3. Following a 3 h heterogeneous EF pro-cess at 50 mA, 100% degradation, and 74% TOC removal were achieved, while theelectrode's performance remained unchanged after 5 reuses. This study reports thefirst-time use of a CF@CoFe2 O4 cathode in the electro-Fenton degradation of vanil-lin, achieving faster and more efficient removal than a conventional CF cathode whileensuring stability, low metal ion leaching, and environmental compatibility for sus-tainable treatment of persistent organic pollutants. Vanillin degradation...

Modulator-assisted solvothermal synthesis of CeO2 derived from Ce-BDC MOFs: effect on oxygen evolution reaction performance

Gözmen, Belgin | Görmez, Özkan | Çirmi, Doğan

In this study, the morphological, structural, and electrocatalytic properties of Ce-BDC-based metal–organic framework (MOF) materials synthesized under various conditions were comprehensively investigated. Four types of structures Ce-BDC, Ce-BDC-P, Ce-BDC*, and Ce-BDC*-P were prepared using a solvothermal method. The synthesis was carried out both under ambient and pressurized (P) conditions, and with or without acetic acid used as a modulator (*). To optimize the synthesis parameters, the amount of acetic acid (12.5, 25, and 50 Meq) was systematically varied, and among the samples, Ce-BDC*-50-P (synthesized under pressurized conditions with 50 Meq of acetic acid) was identified as exhibiting the highest electrocatalytic performance. Structural characterization was carried out using XRD, FT-IR, SEM–EDS, XPS, and BET analyses, which revealed the influence of synthesis parameters on crystal structure, morphology, and porosity. Electrochemical performance evaluations were conducted in 0.5 M H2SO4 solution using a standard three-electrode system. Among the synthesized samples, Ce-BDC*-50-P demonstrated the best oxygen evolution reaction (OER) activity, with a low overpotential of ~ 290 mV and a Tafel slope of 95.7 mV dec−1. Its superior catalytic activity was attributed to a high sur...

Synthesis of biomass-based BiOI@Hydrochar heterogeneous catalyst and investigation of its activity in sonocatalytic process

Gözmen, Belgin | Çomak, Gürbüz | Görmez, Özkan

Innovative studies in recent years to remove pollutants discharged into water resources through various means are critically important for protecting existing water resources. An important part of these studies is heterogeneous catalysis-based AOPs, where new generation composite materials are used and high organic pollutant degradation has been achieved. This study used the solvothermal approach to produce a BiOI@BH sonocatalyst doped with hydrochar (BH). A variety of analysis techniques, including XRD, FESEM, EDS, FTIR, DRS, and BET surface analysis, were used to assess changes in the physico-chemical properties of the BiOI@BH structure in comparison to BiOI. Both the adsorption and sonocatalytic degradation processes for the methylene blue aqueous solution were found to be more successful with the BiOI@BH structure. The following order of oxidative species activity was observed in sonocatalytic degradation: •OH > h+ > O2•–. Recovery studies showed that the decrease in the efficiency of the catalyst after 5 cycles in MB degradation was 10 %. It was determined that the MB degradation efficiency increased significantly with the use of persulfate oxidant at pH> 5. Finally, MB solution (20 mg L−1) was degraded by 99 % in the presence of 5 mM persulfate and 0.5 g L−1 BiOI@BH at 90 m...

Application and Performance Evaluation of Chemical Coagulation, Electrocoagulation, Electro-Fenton and Anodic Oxidation Processes in the Treatment of Glass Fiber Manufacturing Wastewater

Gözmen, Belgin | Görmez, Özkan

This study investigated the oxidation of wastewater generated during the production of glass fiber manufacturing material, which contains high organic carbon (18.32 g/L) and has a pH of 8.8, by chemical coagulation, electrocoagulation and electro-advanced oxidation techniques. It was determined that the total organic content (TOC) of wastewater was reduced by 53% using the chemical coagulation method. After electrocoagulation with Al/Al electrode pair for 300 minutes at 500 mA, 73% TOC removal was achieved at pH 8.8. While 50% TOC removal was completed in 2 h at 400 mA in electrocoagulation with Fe/Fe electrode pair, 71% TOC removal was obtained in the combined electrocoagulation/electro-Fenton process by adding hydrogen peroxide to the medium under the same conditions. In addition, it was also observed that the success of the anodic oxidation methods alone was lower. The electro-Fenton application after electrocoagulation was effective and provided 78% TOC but required work at pH 3 and a longer treatment time.

Esterification of oleic acid using CoFe2O4@MoS2 solid acid catalyst under microwave irradiation

Sönmez, Özgür | Gözmen, Belgin

Ensuring highly efficient biodiesel production requires catalysts. Therefore, developing heterogeneous catalysts capable of being recovered and reused without compromising effectiveness is crucial. In this context, the CoFe2O4@MoS2 heterogeneous magnetic acid catalyst was synthesized and characterized in detail by XRD, SEM-EDX, BET surface area, magnetic property and acid strength. Finally, the catalytic performance of this catalyst was evaluated for the esterification of oleic acid by microwave-assisted method. The fabricated CoFe2O4@MoS2 catalyst has a strong saturation magnetization of 15.78 emu/g, a surface area of 6.70 m2/g, and a high acid loading of 2.1 mmol H+/g, according to the characterization data. The highest oleic acid conversion of 98.2 % was achieved under the optimum conditions (7.5 wt% catalyst amount, 15:1 methanol to oleic acid molar ratio, 2 h reaction time, and 140 °C temperature). To study a comparison between heating methods, the esterification reaction was carried out under conventional heating and microwave heating was found to significantly reduce the reaction time from 4 to 2 h. The catalytic activity did not decrease considerably after eight times use, indicating that the composites exhibited strong stability and recycling capability.

Application and Performance Evaluation of Chemical Coagulation, Electrocoagulation, Electro-Fenton and Anodic Oxidation Processes in the Treatment of Glass Fiber Manufacturing Wastewater

Gözmen, Belgin | Görmez, Özkan

This study investigated the oxidation of wastewater generated during the production of glass fiber manufacturing material, which contains high organic carbon (18.32 g/L) and has a pH of 8.8, by chemical coagulation, electrocoagulation and electroadvanced oxidation techniques. It was determined that the total organic content (TOC) of wastewater was reduced by 53% using the chemical coagulation method. After electrocoagulation with Al/Al electrode pair for 300 minutes at 500 mA, 73% TOC removal was achieved at pH 8.8. While 50% TOC removal was completed in 2 h at 400 mA in electrocoagulation with Fe/Fe electrode pair, 71% TOC removal was obtained in the combined electrocoagulation/electro-Fenton process by adding hydrogen peroxide to the medium under the same conditions. In addition, it was also observed that the success of the anodic oxidation methods alone was lower. The electro-Fenton application after electrocoagulation was effective and provided 78% TOC but required work at pH 3 and a longer treatment time.

Long-life (Co, Al, Mg)-doped LiMn1.5Ni0.5O4 cathodes prepared by co-precipitation method

Görmez, Özkan | Gözmen, Belgin | Çirmi, Doğan

The spinel cathode LiMn1.5Ni0.5O4 (LMN) is garnering significant interest in the realm of lithium-ion batteries owing to its economical nature, elevated operating voltage, high theoretical energy density, and commendable thermal stability at a charged state. Various doping elements have been suggested to enhance the discharge capacity and prolong the lifetime of the LMN cathode. In this study, three doping elements (cobalt, aluminum, and magnesium) are investigated and compared using different characterization techniques. All three elements proved to be effective in extending the cycle life. Among all three elements, cobalt exhibits the highest threshold for dopant concentration beyond which performance degradation initiates. The cathode material with the highest performance, LiMn1.5Ni0.4Co0.1O4, is projected to have a cycle life of 900 cycles, contrasting with the 500 cycles of the undoped sample.

Valorization of loquat seeds by hydrothermal carbonization for the production of hydrochars and aqueous phases as added-value products

Gözmen, Belgin | Görmez, Özkan | Saçlı, Barış | Çalhan Doğan, Selda

In the framework of circular bio-economy, waste loquat seeds were utilized for the production of two addedvalue products. The seeds were hydrothermally carbonized at a temperature range of 150–250 ◦C and time range 2–6 h and the resultant hydrochars and aqueous phases were characterized using various methods. The optimum higher heating value of 30.64 MJ kg− 1 , ash content of 1.99 wt % and alkali index of 0.05 were achieved for the hydrochar prepared at 250 ◦C and 6 h, establishing its suitability for energy-related applications. The aqueous phase obtained at 250 ◦C and 6 h achieved 90% scavenging of the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical and had a IC50 value of 43.71 μg mL− 1 . Principal component analysis showed that the production of phenols, ketones, alkenes and organic acids was favored at >200 ◦C, whereas furans and aldehydes were primarily formed at 150 ◦C. Conclusively, both added-value products were obtained at the same optimum hydrothermal carbonization conditions of 250 ◦C and 6 h treatment time. In a bio-refinery context, this has the practical implication that both bio-products be obtained simultaneously, without the need to switch between different temperatures and residence times.

Removal of imipramine using advanced oxidation processes: Degradation products and toxicity evolution

Doğan Çalhan, Selda | Görmez, Özkan | Gözmen, Belgin | Şüküroğlu, Ayça

Pharmaceuticals are frequently detected in natural and wastewater bodies, and are very important in environmental toxicology because of their stable nature. Advanced oxidation methods used to remove contaminants are of great benefit, especially removing pharmaceuticals unsuitable for biodegradation. In this study, imipramine was degraded by anodic oxidation and subcritical water oxidation, which are advanced oxidation methods. The determination of degradation products was performed by Q-TOF LC/MS analysis. The genotoxicity and cytotoxicity of the degradation samples were determined by the in vivo Allium Cepa method. Among the anodic oxidation samples, the lowest cytotoxicity was obtained after using 400 mA current, and 420 min of degradation time. No cytotoxic effect was observed in any subcritical water oxidation sample. However, when 10 mM hydrogen peroxide as an oxidant was used at 150 °C and the reaction time was 90 min, the subcritical water oxidation sample showed a genotoxic effect. The results of the study showed that it is crucial to evaluate the toxicity levels of the degradation products and which advanced oxidation methods are preferred for removing imipramine. The optimum conditions determined for both oxidation methods can be used as a preliminary step for biologica...

Comparative degradation of 5-fluorouracil in aqueous solution by using H2O2-modified subcritical water, photocatalytic oxidation and electro-Fenton processes

Gözmen, Belgin

This study investigated the degradation of the antineoplastic agent 5-fluorouracil (5-FU) widely applied to treat different cancers using different advanced oxidation processes such as electro-Fenton (EF), photocatalysis with TiO2, and H2O2-modified subcritical water oxidation. The treatment with the EF process was the most efficient compared to others. Interestingly, in the EF process, the oxidative degradation of 5-FU behaved differently depending on the anode used. At low currents (20 and 40 mA), Pt and DSA anodes performed better than BDD and Ti4O7 anodes. In contrast, at the higher current of 120 mA, the production of heterogeneous hydroxyl radicals (M(• OH)) became important and contributed significantly to the oxidation of 5-FU in addition to homogeneous • OH generated in the bulk solution. These latter have high O2-evolution overpotential leading to the high amount of physisorbed M(• OH) compared to Pt and DSA. The oxidative degradation of 5-FU was then performed by titanium dioxide-based photocatalytic oxidation and subcritical water oxidation processes, both of which showed a lower degradation efficiency and failed to achieve complete mineralization. Finally, a comparison was performed in laboratory-scale, taking into account the following performance indica...

A dual purpose aluminum-based metal organic framework for the removal of chloramphenicol from wastewater

Gözmen, Belgin | Geçgel, Cihan | Görmez, Özkan | Turabik, Meral

The presence of antibiotics in the aquatic environment can cause significant environmental and human health problems even at trace concentrations. Conventional treatment systems alone are ineffective in removing these resistant antibiotics. To address this problem, oxidation and adsorption techniques were used to explore the removal of recalcitrant antibiotic chloramphenicol (CAP). An aluminum-based metal-organic framework (AlMIL) with high surface area and extended porosity, was prepared and used both as adsorbent and catalyst for the oxidation of CAP. Characterization of the Al-MIL revealed a large surface area of 1137 m2 g− 1 , a homogeneous microporous structure, good crystallinity, and particle size in the range of 200–400 nm. Adsorption of CAP on AlMIL achieved equilibrium after 1 h, reaching a maximum adsorption capacity of 96.1 mg g− 1 at the optimum pH value of 5.3. The combination of adsorption and oxidation did not improve the % TOC reduction considerably, indicating an antagonistic rather than synergistic effect between the two processes. Oxidation alone in the presence of persulfate, achieved a % TOC reduction of 71% after 2 h, compared to 56% achieved by adsorption alone at the same duration. The optimum persulfate concentration was determined as 2.5 mM. T...

Degradation of isoniazid by anodic oxidation and subcritical water oxidation methods: Application of Box–Behnken design

Gözmen, Belgin | Görmez, Özkan | Doğan Çalhan, Selda

Pharmaceutical compounds released into the aquatic environment are known to cause toxic effects on the environment. Isoniazid is widely used in the treatment of tuberculosis and is, therefore, frequently encountered in environmental waters. In this study, the degradation of isoniazid was investigated by anodic oxidation and subcritical water oxidation method which are members of Advanced Oxidation Processes. The Box–Behnken Design was used to determine the effects of current, initial concentration, and electrolysis time on mineralization in the anodic oxidation process, which carried out a cell with a Pt cathode and boron-doped diamond anode. The highest mineralization value of 78.14% was achieved at optimal conditions of 300 mA, 3 h, and 100 mg/L initial concentration. The degradation of Isoniazid was also investigated under subcritical water conditions using an ecological oxidizing agent, H2O2. The maximum mineralization rate of 72.23% was obtained when 100 mM H2O2 was used for a 90 min treatment at 125 °C for 100 mg/L Isoniazid solution in the subcritical water oxidation process. The LC-MS results showed that the degradation products obtained by AO and SWO methods were different from each other. Finally, possible degradation mechanisms are proposed according to the degradation...

Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 ◦C, using 150 mM H2O2 and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H2O2 concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of p...

Degradation of phthalic acid by anodic oxidation in acidic aqueous solutions with high chromium content using boron-doped diamond anode

Gözmen, Belgin

Mineralization of phthalic acid, a highly refractory organic pollutant was studied by an anodic oxidation process with boron-doped diamond (BDD) anode in a highly acidic chromium medium. Synthetic solutions were composed of Cr(III)/Cr(VI), sulfate, sulfuric acid, and phthalic acid (initial form potassium hydrogen phthalate, KHP). Degradation/mineralization of KHP was carried out by hydroxyl radicals produced on the anode and sulfate radicals generated from the sulfate ions present in the medium. To find appropriate operating conditions, the effects of cathode type, current density, electrolysis time, and presence of Cr(VI)-Cr(III) were investigated. Thereafter, the effect of current density, amount of Cr(VI)-Cr(III) in solution, and electrolysis time on KHP mineralization was realized by using response surface methodology and central composite design. The most effective TOC removal rate was found as 94.8% in the case of 0.675% Cr(VI) and 3.825% Cr(III) content by mass at 80 mA cm−2 of current density and 360 min of electrolysis time, despite a high initial TOC content of 9400 mg L−1. As a result, the organic content of the wastewater was removed by electro-persulfate process via the catalytic effect of Cr species. Additionally, the use of BDD anode avoided metal ion pollution tha...

Hydrothermal Synthesis of Siderite and Application as Catalyst in the Electro-Fenton Oxidation of p-Benzoquinone

Görmez, Özkan | Gözmen, Belgin

A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100–500 mA), time (1–9 h), catalyst dosage (0.25–1.00 g L−1 ), and initial concentration of BQ (0.50–1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5–7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatm...

CoFe2O4 nanoparticles decorated onto graphene oxide and graphitic carbon nitride layers as a separable catalyst for ultrasound-assisted photocatalytic degradation of Bisphenol-A

Görmez, Özkan | Gözmen, Belgin | Yakar, Ezgi

The advanced oxidation process (AOP) through ultrasound-assisted photocatalytic degradation has attracted much attention in removing emerging contaminants. Herein, CoFe2O4-GO and CoFe2O4-g-C3N4 nanocomposites were synthesized using the ultrasound-assisted co-precipitation method. TEM, XRD, XPS, EDS, SEM, and FT-IR techniques characterized the structural, morphological, and chemical properties of the synthesized nanocomposites. The analyses showed that CoFe2O4 structure was nano-sized and distributed more homogeneously in graphene oxide (GO) layers with oxygenated functional groups than graphitic carbon nitride (g-C3N4). While the efficiency of composite catalysts, as photocatalysts, for degradation of bisphenol-A (BPA) was low in the visible region in the presence of persulfate, their catalytic efficacy was higher with sonolytic activation. The addition of persulfate as an oxidant remarkably enhanced the target pollutant degradation and TOC removal of BPA solution. Both composite catalysts showed 100 % BPA removal with the synergistic effect of visible region photocatalytic oxidation and sonocatalytic oxidation in the presence of persulfate at pH 6.8. In ultrasound-assisted photocatalytic oxidation of BPA, the highest mineralization efficiencies were obtained at 2 h trea...

Evaluation of sewage sludge biochar and modified derivatives as novel SPE adsorbents for monitoring of bisphenol A

Gözmen, Belgin | Sönmez, Özgür

Sewage sludge is abundant biomass, the sustainable management of which remains a big issue worldwide. It was demonstrated that pyrolysis of sewage sludge using simple and cost-effective apparatus can produce biochars, suitable for solid-phase extraction applications of hydrophobic analytes. Detailed characterization showed that modification lead to three more hydrophobic and one more hydrophilic sample, compared to the original biochar. All samples were evaluated in the solid-phase extraction of the emerging contaminant Bisphenol A from aqueous solutions. KOH-SSB and KOH/MeOH-SSB exhibited the most promising behavior, with the latter achieving recoveries of 88.1%, at a quantity of 0.1 g at the natural pH of the BPA solution (6.5). The effect of solution pH was insignificant in the range of 4–7, whereas the initial BPA concentration had no effect in the recovery within the range of 1–100 μg L−1. The mechanism of interaction between the optimum sample and BPA was based on hydrogen bonding and π-π interactions, establishing earlier observations that the type (and not concentration) of individual surface groups and the total surface area play a significant role in the process.

Comparison of the heterogeneous GO-FePO4/electro-Fenton against the homogeneous Fe(II) ion and Fe(III)-oxalate complex/electro-Fenton for the degradation of metronidazole

Gözmen, Belgin | Görmez, Özkan

This study compared the effect of the homogeneous and the heterogeneous electro-Fenton (EF) processes on the degradation of Metronidazole (MTZ). Graphene oxide (GO)-FePO4 synthesized for use in the heterogeneous electro-Fenton process was characterized using FTIR, FE SEM-EDS and XRD analysis. The analyses showed that the amorphous composite structure formed as a result of FePO4 structures dispersed between the GO layers has an average particle size distribution of 141 nm. The activity of the GO-FePO4 catalyst was more effective at pH 3 than pH 5 which is the own pH value of metronidazole. In the heterogeneous EF process, the mineralization percentage was determined as 66% at pH 3, 0.5 g L−1 catalyst dosage after 5 h. No difference was observed in the structure of GO-FePO4, which can be used repeatedly with high performance, even after 4 cycles. In the homogeneous EF process, 0.2 mM Fe2+ ion and Fe(III)-oxalate complex containing the same amount of Fe ions were used for comparison under the same conditions. When Fe2+ ion and Fe(III)-oxalate complex were used at pH 3, 57% and 70% mineralization percentages were achieved respectively, in 5 h. However, the mineralization efficiencies of the Fe(III)-oxalate complex decreased to 47% at pH 5 and 41% at pH 7. The pseudo-first-order model...

Preparation and application of Fe-modified banana peel in the adsorption of methylene blue: Process optimization using response surface methodology

Gözmen, Belgin | Turunç, Ersan

Banana peel was used as the feedstock for the preparation of a magnetic adsorbent for the adsorption of methylene blue (MB) in aqueous solutions. The Fe-modified banana peel was characterized by surface and spectrometric methods. The Box-Behnken design (BBD) was used for determining the conditions of each experimental run and optimization of adsorption was achieved through response surface methodology. The R2, adjusted R2, and predicted R2 coefficients of the employed BBD model were determined as 0.9820, 0.9686, and 0.9182, respectively, indicating a high level of agreement between the experimental data and the proposed theoretical model. The optimum MB adsorption of 91.89% was achieved at an adsorption time of 50 min, temperature of 45 °C, adsorbent dosage of 2.5 g and MB concentration of 5 mg L−1. Equilibrium was achieved in 48 min. The most influential process parameter was the adsorbent dosage, whereas the impact of time, MB concentration and temperature was considerably smaller. The Langmuir Qmax value of 28.1 mg g−1 compared favorably to respective values from other published adsorbents.

Application of the central composite design to mineralization of olive mill wastewater by the electro/FeII/persulfate oxidation method

Gözmen, Belgin | Görmez, Özkan | Yabalak, Erdal

The olive mill wastewater is a major environmental problem, which is waiting for effective treatment. In this study, the mineralization of olive mill wastewater was investigated using the electro/FeII/persulfate process. The central composite design was utilized to examine the effect of each experimental variables (concentration of persulphate and FeII, treatment time and constant current) on the mineralization of olive mill wastewater. The optimum chemical oxygen demand removal percentage was obtained as 71.2% where the reaction conditions were 200 mA current, 250 mM persulphate, 25 mM FeII, and 6 h reaction time. In addition, the maximum percentage of total phenolic removal and the energy consumption were 88% and 4.50 kWh/kgCOD, respectively, which were obtained at the same reaction conditions mentioned above. ANOVA test was used to examine the reliability of the experimental method. The R2 and adjusted R2 coefficients were obtained as 0.9634 and 0.9305, respectively. Optimum experimental parameters were determined and theoretical equations were obtained for the degradation of olive mill wastewater. For the treatment of olive mill wastewater, an environmentally friendly oxidation process was examined and the effect of each experimental variables was clearly demonstr...

Fe‑modified hydrochar from orange peel as adsorbent of food colorant Brilliant Black: process optimization and kinetic studies

Gözmen, Belgin | Turunç, Ersan

The main aims of this work were to produce and characterize Fe-modified hydrochar from orange peel waste, optimize the adsorption through response surface methodology, investigate the role of treatment time, dye concentration, adsorbent dose and temperature, and determine the dominant mechanisms through kinetics analysis. Orange peel waste was hydrothermally carbonized at 200 °C for 8 h, and the hydrochar was embedded with magnetite nanoparticles. The composite adsorbent was characterized through spectrometric and surface analytical methods. Subsequently, analysis of variance was used to design the experimental runs, propose a polynomial equation describing the adsorption process and finally optimize the adsorption conditions. The results indicated that 99% removal can be theoretically achieved at the following conditions: dye initial concentration of 6.08 mg/L, treatment time of 26.30 min, temperature of 44.79 °C and adsorbent concentration of 2.27 g/L. The dominant factors were the dye and adsorbent concentration, whereas time and temperature variations had a much lesser impact. Among examined models, the Langmuir model showed a better match to the experimental data. The maximum monolayer adsorption capacity was determined as 10.49 mg/g. The mechanism of interaction wa...

Microwave-assisted d-pinitol extraction from carob: application of Box–Behnken design

Gözmen, Belgin | Sönmez, Özgür

This study investigates the effects of temperature (50–80 °C), time (10–60 min), carob-to-solvent ratio (2–8 g/40 mL), and solvent concentration (0–50 ethanol/water%, v/v) on microwave-assisted extraction of d-pinitol compound from carob fruit with optimization using Box–Behnken design. The optimal conditions for maximum d-pinitol yield (64.16 g/kg dry sample) include 50 °C temperature, 5.6 g carob/40 mL solvent, water used as a solvent, and an extraction time of 10 min. The fitness of the model was determined by ANOVA analysis with a high coefficient (R2 = 0.9057). Extraction was performed under optimum conditions for model validation, and 63.89 g/kg dry sample of d-pinitol extraction was achieved. In addition, the effects of the same variables on the total phenolic (TP) content of MEA extraction of carob were also investigated. Extraction efficiency of 426 g/kg was obtained under the optimum conditions determined for TP (80 °C, 8 g of carob, 50% ethanol, and 10 min), but it was observed that TP content decreased to 49.7 g/kg under optimum conditions determined for d-pinitol. Sucrose, glucose, and fructose sugar contents of the extract were determined only for optimum conditions for d-pinitol, and the fructose content was found to be the lowest. Determining the d-pinitol, TP, an...

Comparison of MIL-101(Fe) and amine-functionalized MIL-101(Fe) as photocatalysts for the removal of imidacloprid in aqueous solution

Gözmen, Belgin | Geçgel, Cihan | Turabik, Meral

One of the attractive iron-based metal organic framework (MOF) MIL-101(Fe) (Material Institute Lavoisier, MIL) and amine-functionalized NH2-MIL-101(Fe) materials were synthesized by conventional solvothermal method and characterized by TGA (Thermo Gravimetric Analysis), SEM (Scanning Electron Microscopy), XRD (X-Ray Diffractograms), BET (Braunner Emmet Teller) and FTIR (Fourier Transform Infrared Spectroscopy). Characterization results indicated that MIL101(Fe) materials have well defined morphology, good thermal stability, high surface area and also high porosity. These MOF materials were used as photocatalysts for photodegradation of a pesticide, imidacloprid (IMC). The response surface methodology (RSM) was applied in designing the IMC photodegradation experiments for evaluating the interactive effects of independent variables and determining the optimum condition. Central composite design as five independent variables such as initial MIL-101(Fe) concentration, initial IMC concentration, H2O2 concentration, pH and time were coded with low and high level and IMC removal percent was obtained as a response. As for the RSM results on the optimum photocatalytic condition, maximum IMC removal values were determined as 100% for the both catalysts in the end of the 30 min. The...

Degradation of chloramphenicol and metronidazole by electro-Fenton process using graphene oxide-Fe3O4 as heterogeneous catalyst

Gözmen Belgin | Görmez Özkan

This study investigates the degradation and mineralization of two widely used antibiotics, chloramphenicol and metronidazole, by an electro-Fenton process using graphene oxide-Fe3O4 as a heterogeneous catalyst. The graphene oxide-Fe3O4 composite was typically characterized through conventional spectroscopic and surface analytical methods. The effects of treatment time, pH, catalyst concentration and applied current were examined. In the absence of the graphene oxide-Fe3O4 catalyst (homogeneous environment), the optimum mineralization rates obtained were 57 and 71% at pH 3 and 300 min treatment time for metronidazole and chloramphenicol solutions, respectively. When the optimum graphene oxide-Fe3O4 concentration of 0.5 g L−1 was used, mineralization rates of 73 and 86% were achieved respectively, at the same conditions. This indicated the efficiency of the catalyst and proved that the heterogeneous electro-Fenton process was more effective compared to the homogenous electro-Fenton process. At the same conditions, degradation of chloramphenicol and metronidazole was >99%. The difference between the near-complete antibiotic degradation and the lower mineralization rates, can be justified by the presence of persistent by-products, such as oxalic and glyoxylic acid. Finally, the prepa...

Comparative mineralization of Basic Red 18 with electrochemical advanced oxidation processes

Gözmen, Belgin | Sönmez, Özgür

In this study, the role of electrochemical oxidation processes, including the electro-Fenton, the electro-persulfate (PS), and the electro/FeII /PS processes, in the removal of Basic Red 18 (BR18) from aqueous solutions was investigated. It was found that the electro-PS process successfully removes colour, but after 5 h, it produced only 75 % mineralization. In the same conditions, more effective mineralization was achieved by the electro/FeII/PS process than by the electro-Fenton method. At pH levels of 3.0 and 5.7, very effective mineralization results were produced by the electro/FeII/PS process. Moreover, the maximum mineralization current efficiency values were obtained by the electro/FeII/PS process. The mineralization efficiency of the electro/FeII/PS process was determined to be 97 % under the following conditions: BR18 initial dye concentration of 100 mg L-1, pH of 5.7, contact time of 5 h, PS concentration of 10 mM, Fe2+ concentration of 0.2 mM, and a sodium sulfate concentration of 0.05 M.

Influence of the addition of various ionic liquids on coal extraction with NMP

Sönmez, Özgür | Gözmen, Belgin

In this work, two Turkish coals were extracted with N-methyl-2-pyrrolidone (NMP) and NMP containing a small amount of ionic liquids (ILs) under reflux conditions at atmospheric pressure. The effects of coal type, ionic liquid type, ionic liquid-to-coal ratio, and ultrasonic interactions on extraction yield were investigated. The ILs used were: 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), 1-buty-4- methylpyridinium chloride ([Bmp]Cl), 1-ethyl-3-methylimidazolium chloride ([Emim]Cl), and 1-butyl-2,3-dimethylimidazolium chloride ([Bdmim]Cl). It was found that the extraction yield of coals using NMP/ILs varied with coal type, IL type and amount of IL. ILs were effective on the extraction of Afsin-Elbistan (AE) lignite, but not on the extraction of Üzülmez (UZ) coal. A significant increase in extraction yield for AE lignite was observed when a small amount of IL was added into NMP. It was determined that [Bmim]Cl was the most efficient IL used for the extraction of lignite compared to the others ILs used, and the extraction efficiency was found to increase by increasing the amount of ionic liquid added into NMP.

Adsorption of Malachite Green on Fe-modified biochar: influencing factors and process optimization

Gözmen, Belgin

Paper sludge and wheat husk biochar was converted to a Fe-composite through a simple coprecipitation process and its adsorption behavior was tested against an emerging pollutant, Malachite Green (MG). Response surface methodology was employed to determine the optimum experimental conditions and the interactions between pH, initial MG concentration, temperature and treatment time. The maximum adsorption percentage obtained experimentally was 97.1%, whereas the Box– Behnken design predicted a maximum adsorption of 98%, at pH 6.16, initial MG concentration of 6.56 ppm, temperature of 34.75°C and treatment time of 22 min. Compared with the original biochar, the Fe-modified sample improved the adsorption of MG by ~34%. The adsorption mechanism followed the Langmuir model (qmax = 172.3 mg/g, correlation coefficient 0.960) and the kinetics of the process were best described by the pseudo-second-order model (correlation coefficient 0.9818), although boundary layer effects were also observed.

Adsorption of 2,4-dichlorophenol on paper sludge/wheat husk biochar: Process optimization and comparison with biochars prepared from wood chips, sewage sludge and hog fuel/demolition waste

Gözmen Belgin

The adsorption of 2,4-dichlorophenol, a toxic by-product of triclosan commonly found in wastewater treatment plant effluents, was studied on paper sludge/wheat husks biochar. By using response surface methodology, the optimum conditions and effects of pH, temperature, initial 2,4-DCP concentration and time were determined. The solution pH was found to be the most influential parameter whereas the optimum adsorption conditions were predicted as: C0 = 40.28 mg L−1 , T = 326 K, pH = 2.8, t = 143 min, where a 99.95% adsorption could be achieved. Both Langmuir and Freundlich provided a good fit for the experimental data, indicating a surface and multi-layer adsorption. Kinetically, the process primarily followed the pseudo-second order model (chemisorption). By comparing the adsorption capacity at equilibrium of our main biochar (qe = 9.28 mg g−1 ) to 3 biochars prepared from different biomasses (qe values 1.57–2.96 mg g−1 ), it was concluded that pH-dependent electrostatic interactions and non-covalent π-electron donor-acceptor mechanisms play the most important role. Finally, there was indication that high concentrations of Ca and K may promote the adsorbate-adsorbent interactions and enhance adsorption

Acid Red 1 and Acid Red 114 decolorization in H2O2-modified subcritical water: process optimization and application on a textile wastewater

Gözmen, Belgin

Solutions of Acid Red 1 and Acid Red 114 were treated in H2 O2 -modified subcritical water in the temperature range of 100°C–200°C for up to 60 min. Response surface methodology based on the Box-Behnken design was used to optimize the process. For Acid Red 1, optimum decolorization of 97% can be achieved at 192°C, 181 mM H2 O2 , 51.3 min treatment time, and 121 mg/L dye concentration. For Acid Red 114, the optimum conditions were 195°C, 157 mM H2 O2 , 38 min treatment time and 110 mg/L dye concentration, where 91% decolorization could be obtained from the proposed model. It was determined that temperature is the most important factor, followed by the oxidant concentration. Degradation was less efficient for AR114 due to the double azo bonds, compared to the single azo bond of AR1. Application of the optimum treatment conditions on real reactive dye wastewater resulted in 92.7, 79.1 and 20.4% removal of BOD5 , COD and TSS, respectively.

Degradation of nitroaromatic compounds in subcritical water: application of response surface methodology

Gözmen, Belgin | Gizir, Ahmet Murat

In this study, subcritical water has been used as a medium for degradation of 2,4-dinitrotoluene (2,4-DNT), 4-nitrotoluene (4-NT) and 2-amino-4-nitrotoluene (2-A-4-NT). The effect of temperature, oxidant concentration and time were studied and the optimal combination of reaction parameters was established using response surface methodology in a Box-Behnken design. Of all the parameters examined, temperature showed the most positive effect on the degradation of the nitroaromatic compounds. Optimal reaction conditions were found to be a temperature of 240°C, 210°C and 236°C, time of 180, 178 and 172 min, oxidant concentration of 100, 99.64 and 99.61 mM for 2,4-DNT, 4-NT and 2-A-4-NT, respectively. Since high-temperature was applied, the possibility of formation of subcritical degradation products existed; therefore, total amounts of degraded nitroaromatic compounds and formed intermediate products were determined by gas chromatographic–mass spectrometric analysis

Electrocoagulation and nanofiltration integrated process application in purification of bilge water using response surface methodology

Gözmen, Belgin | Dizge, Nadir | Turabik, Meral | Gülsen, H. Elif

Marine pollution has been considered an increasing problem because of the increase in sea transportation day by day. Therefore, a large volume of bilge water which contains petroleum, oil and hydrocarbons in high concentrations is generated from all types of ships. In this study, treatment of bilge water by electrocoagulation/electroflotation and nanofiltration integrated process is investigated as a function of voltage, time, and initial pH with aluminum electrode as both anode and cathode. Moreover, a commercial NF270 flat-sheet membrane was also used for further purification. Box–Behnken design combined with response surface methodology was used to study the response pattern and determine the optimum conditions for maximum chemical oxygen demand (COD) removal and minimum metal ion contents of bilge water. Three independent variables, namely voltage (5–15 V), initial pH (4.5–8.0) and time (30–90 min) were transformed to coded values. The COD removal percent, UV absorbance at 254 nm, pH value (after treatment), and concentration of metal ions (Ti, As, Cu, Cr, Zn, Sr, Mo) were obtained as responses. Analysis of variance results showed that all the models were significant except for Zn (P > 0.05), because the calculated F values for these models were less than the critical F value...

Fe-modified sporopollenin as a composite biosorbent for the removal of Pb2+ from aqueous solutions

Gözmen, Belgin

The role of Fe-modified sporopollenin (Fe-Sp) biomass in Pb2+ removal from aqueous solutions was investigated by batch biosorption technique. The prepared biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy. The influence of pH, contact time, biosorbent dose, and initial concentration on biosorption process were optimized by using a four factor Box–Behnken design combined with response surface methodology. The results indicated a positive adsorption behavior of Fe-Sp and a strong pH dependency of the process. The optimum predicted parameters were determined as follows: biosorbent dosage 0.5 g, pH of 6.75, contact time 104 min, and initial Pb2+ concentration of 25.42 ppm. The Freundlich isotherm model provided a better fit (R2 = 0.994) for the experimental data, indicating biosorption on a heterogeneous surface. Maximum biosorption capacity (qmax) was 22.72 mg g-1 as indicated by the Langmuir isotherm. Kinetically, the adsorption process followed a pseudo- second-order model, indicating that chemisorption was the rate-limiting step.

Optimization of solvent extraction process of some Turkish coals using response surface methodology and production of ash-free coal

Gözmen, Belgin | Sönmez, Özgür

In order to produce ash-free coal (AFC) from three Turkish coals, solvent extraction of coals using 1-methylnaphthalene (1-MN) at different temperatures were conducted. The extraction yield of coals was found dependenton coal, temperature, and solvent type. When there was usage of 1-MN as solvent, the extraction yield was low. However,on addition of N-methyl-2-pyryrolidone (NMP) or quinoline (QN) into 1-MN, the extraction yield increased. Following theextractions, we obtained AFC with less than 0.65% ash content for the three coals used in this study. The response surfacemethodology (RSM) was employed to investigate the solvent extraction conditions. The factors investigated were extractiontemperature and additional polar solvent ratio. The obtained results demonstrated that either excess amount of polar solventinto 1-MN should be added at low temperatures or extraction should be done at high temperatures using less polar solvent toobtain an increase in extraction efficiency. The sensitivity and validity of results obtained by RSM were confirmed throughvalidation experiments. The results of validation experiments showed a good agreement between the experimental andpredicted values (relative error

The solubility of sebacic acid in subcritical water using the response surface methodology

Gözmen, Belgin | Görmez, Özkan | Yabalak, Erdal | Gizir, Ahmet Murat

The solubility of sebacic acid in subcritical water was investigated. Response surface methodology was used to study the combined effects of the different parameters such as temperature, static and dynamic time to optimize the process conditions for the maximum solubility of sebacic acid. Solubility results of sebacic acid were observed to be highly correlated with quadratic model according to analysis of variance. The solubility of sebacic acid was found as 500 g L-1 in the optimum conditions at 400 K temperature, 4 min dynamic time and 28 min static time. Approximation models were employed for determining solubility of sebacic acid at elevated temperatures.

Electrochemical oxidation of carbendazim on boron-doped diamond anode

Gözmen, Belgin

Biological and physical-chemical factors may play a role in the degradation to variable extent. Therefore, but our study focused on revealing the influence of operating factors on the reaction of electro-oxidation of pesticide by boron-doped diamond anode (BDD) electrode, The influence current density, sodium chloride concentration and pesticide concentrations were critically examined. Further the pesticide investigated in our work named carbendazim. The toxicity of the examined pesticide is well known; however, little information is available regarding his natural degradation process. The degradation processes as current density were followed by high-performance liquid chromatography (HPLC) technique. The results of these influences are expressed in terms of the Chemical Oxygen Demand (COD removal). In this manuscript we report that, the highest electro degradation activity was achieved in the presence of NaCl (0.1g/l), 80 mA/cm2, 30 ppm carbendazim concentration and temperature of 25 C.

Efficient removal of insecticide “imidacloprid” from water by electrochemical advanced oxidation processes

Turabik, Meral | Gözmen, Belgin

The oxidative degradation of imidacloprid (ICP) has been carried out by electrochemical advanced oxidation processes (EAOPs), anodic oxidation, and electro-Fenton, in which hydroxyl radicals are generated electrocatalytically. Carbon-felt cathode and platinum or boron-doped diamond (BDD) anodes were used in electrolysis cell. To determine optimum operating conditions, the effects of applied current and catalyst concentration were investigated. The decay of ICP during the oxidative degradation was well fitted to pseudo-first-order reaction kinetics and absolute rate constant of the oxidation of ICP by hydroxyl radicals was found to be kabs(ICP)=1.23×109 L mol−1 s −1 . The results showed that both anodic oxidation and electro-Fenton process with BDD anode exhibited high mineralization efficiency reaching 91 and 94 % total organic carbon (TOC) removal at 2 h, respectively. For Pt-EF process, mineralization efficiency was also obtained as 71 %. The degradation products of ICP were identified and a plausible general oxidation mechanism was proposed. Some of the main reaction intermediates such as 6-chloronicotinic acid, 6-chloronicotinaldehyde, and 6-hydroxynicotinic acid were determined by GC-MS analysis. Before complete mineralization, formic, acetic, oxalic, a...

Removal of Basic Textile Dyes in Single and Multi-Dye Solutions by Adsorption: Statistical Optimization and Equilibrium Isotherm Studies

Gözmen, Belgin | Turabik, Meral

The removal of three basic dyes by adsorption onto bentonite was investigated forsingle, binary, and ternary solutions in a batch system. Before and after dye adsorption,bentonite samples were analyzed by using X-ray fluorescence spectrometer, SEM,and Fourier transform IR spectrometry. The D-optimal design and response surfacemethodology were applied in designing the experiments for evaluating the interactiveeffects of each initial concentrations variable of the dyes in binary systems. Predictedvalues were found to be in good agreement with experimental values, which definedpropriety of the model and the achievement of D-optimal in optimization of adsorptionof binary dye systems. The competitive adsorption results showed that the adsorptionamount of a dye was suppressed in the presence and increasing concentrationsof second or third dye. For mono-component isotherm modeling, Langmuir andFreundlich models were applied to equilibrium data of single, binary, and ternarydye solutions, while modified Langmuir, Sheindrof–Rebhun–Sheintuch and modifiedextended Freundlich models were also applied to equilibrium data of binary dyesolutions for multi-component isotherm modeling. The results showed that theLangmuir was the more suitable model for single dye systems while extendedFreundlich model...

Electrolysis of coal slurries to produce hydrogen gas: Relationship between CO2 and H2 formation

Gözmen, Belgin

The purpose of this study was to produce hydrogen gas by electrolysis of coal slurries and to investigate the relation between hydrogen (H2) and carbon dioxide (CO2) formation. Electrolysis of coal slurries was evaluated at 40 °C and 1.0 V cell potential to examine H2 and CO2relationship. When electrolysis was performed after the coal slurry was mixed with Fe(II)/Fe(III) ions and stirred overnight (>12 h), no CO2 gas was observed at the anode compartment. The results of total organic carbon (TOC) indicated that after electrolysis, few organic compounds were transformed into the solution and these organic compounds did not convert into CO2. GC analysis, on the other hand, revealed that the H2 collected at the cathode was pure and did not require any further purification process. Hydrogen generation or electrolysis efficiency of coal slurries cannot be calculated or estimated by examining CO2 generation as reported in the literature. Low temperature and low cell potential were not sufficient to oxidize coal quantitatively.

Degradations of model compounds representing some phenolics in olive mill wastewater via electro‐Fenton and photoelectro‐Fenton treatments

Gözmen, Belgin

The electrochemical oxidation of vanillic acid, o‐coumaric acid and protocatechuic acid, three representative toxic phenolics in olive mill wastewater, was studied using carbon felt cathode in the electro‐Fenton system. Results obtained, in the presence or absence of UV support, were compared throughout the degradation processes up to mineralization. It was demonstrated that all three phenolic compounds reacted completely with hydroxyl radicals and degraded efficiently. It was shown in the photoelectro‐Fenton process that the degradation and mineralization efficiency of the phenolic compounds were enhanced by the effect of UV light, especially at the later stages of the degradation processes.

Degradation of Acid Red 274 using H2O2 in subcritical water: Application of response surface methodology

Gözmen Belgin

In this research, the degradation of Acid Red 274 (AR 274) was investigated under subcritical water conditions using H2O2, which led to the oxidative degradation of Acid Red 274 up to its 80% of mineralization. The Box–Behnken design matrix and response surface methodology (RSM) were applied in designing the experiments for evaluating the interactive effects of the three most important operating variables. Thus, the interactive effects of temperature (100–250 °C), oxidant (H2O2) concentration (50–250 mM), and time (30–60 min.) on the degradation of AR 274 were investigated. A total of 17 experiments were conducted in this research, and the analysis of variance (ANOVA) indicated that the proposed quadratic model could be used for navigating the design space. The proposed model was essentially in accordance with the experimental case with correlation coefficient R2 = 0.9930 and Adj-R2 = 0.9839, respectively. The results confirmed that RSM based on the Box–Behnken design was a compatible method for optimizing the operating conditions of AR 274 degradation.

Degradation of acid red 97 dye in aqueous medium using wet oxidation and electro-Fenton techniques

Gözmen Belgin | Gizir, Ahmet Murat

Degradation of the acid red 97 dye using wet oxidation, by different oxidants, and electro-Fenton systems was investigated in this study. The oxidation effect of different oxidants such as molecular oxygen, periodate, persulfate, bromate, and hydrogen peroxide in wet oxidation system was compared. Mineralization of AR97 with periodate appeared more effective when compared with that of the other oxidants at equal initial concentration. When 5 mM of periodate was used, at the first minute of the oxidative treatment, the decolorization percentage of AR97 solution at 150 and 200 °C reached 88 and 98%, respectively. The total organic carbon removal efficiency at these temperatures also reached 60 and 80%. The degradation of AR97 was also studied by electro-Fenton process. The optimal current value and Fe2+ concentration were found to be 300 mA and 0.2 mM, respectively. The results showed that electro-Fenton process can lead to 70 and 95% mineralization of the dye solution after 3 and 5 h giving carboxylic acids and inorganic ions as final end-products before mineralization. The products obtained from degradation were identified by GC/MS as 1,2-naphthalenediol, 1,1′-biphenyl-4-amino-4-ol, 2-naphthalenol diazonium, 2-naphthalenol, 2,3-dihydroxy-1,4-naphthalenedion, phthalic anhydride, 1...

Photocatalytic degradation of Basic Red 46 and Basic Yellow 28 in single and binary mixture by UV/TiO2/periodate system

Gözmen Belgin | Turabik, Meral

The present study deals with the investigation of photocatalytic degradation and mineralization of C.I. Basic Red 46 (BR46) and C.I. Basic Yellow 28 (BY28) dyes in single and binary solutions as a function of periodate ion concentration (IO4−), irradiation time, initial pH and initial dye concentrations. First order derivative spectrophotometric method was used for to simultaneous analysis of BY28 and BR46 in binary mixtures. Langmuir–Hinshelwood kinetic model was applied to experimental data and apparent reaction rate constant values were calculated. The apparent degradation rate constant values of BR46 were higher than those of BY28 for all experiments in single dye solutions. On the other hand, the significant reductions were observed for the apparent degradation rate constant values of the BR46 in the presence of BY28 in binary solutions whereas TOC removal efficiency slightly enhanced in binary system. The highest TOC removal efficiency was obtained at pH 3.0 by adding 5 mM periodate ion in to the solution in the presence of 1 g/L TiO2 for both dye solutions. After 3 h illumination, 68, 76 and 75% mineralization were found for 100 mg/L BY28, 100 mg/L BR46 and 50 + 50 mg/L mixed solutions, respectively.

Oxidative degradations of reactive blue 4 dye by different advanced oxidation methods

Gözmen Belgin | Gizir Ahmet Murat

The degradations of an anthraquinone dye, the reactive blue 4 (RB4), were studied by wet air oxidation (WAO), wet peroxide oxidation (WPO), photocatalytic oxidation, and electro-Fenton (EF) advanced oxidation. The RB4 oxidation was evaluated by the decrease in total organic carbon (TOC) content and concentration. The most efficient method for mineralization of RB4 was WPO, but in all methods TOC removal efficiency was above 75% after 60 min of treatment.

Indirect Electrochemical Treatment of Bisphenol A in Water via Electrochemically Generated Fenton's Reagent

Gözmen, Belgin

Bisphenol A (BPA) has been treated with electrochemically generated Fenton's reagent in aqueous medium. Hydroxyl radicals that were formed in Fenton's reagent reacted with the organic substrate producing two different isomers of monohydroxylated product and, upon successive hydroxylation, mainly one dihydroxylated product. Further hydroxylation first degraded one of the aromatic rings, and the side chain thus formed was then cleaved off the other aromatic ring. The second aromatic ring was also degraded upon successive hydroxylations. Small saturated and unsaturated aliphatic acids were the last products prior to mineralization. It was found that use of cuprous/cupric ion pair resulted a faster conversion of BPA and faster mineralization when compared using ferrous/ferric ions, but this happened at the expence of excess electrical charge utilized for an equivalent conversion or mineralization. Degradation by using ferrous/ferric ions was more efficient than cuprous/cupric ions case in terms of total mineralization versus charge utilized, and a mineralization of 82% had been achieved by applying 107.8 mF of charge to a 0.7 mM BPA solution of 0.200 dm3. The rate constant of the monohydroxylation of BPA in the presence of ferrous/ferric ions had been determined as 1.0 × 10...

Indirect electrochemical treatment of bisphenol A in water via electrochemically generated Fenton's reagent
ndirect Electrochemical Treatment of Bisphenol A in Water via Electrochemically Generated Fenton's Reagent

Gözmen Belgin

Bisphenol A (BPA) has been treated with electrochemically generated Fenton's reagent in aqueous medium. Hydroxyl radicals that were formed in Fenton's reagent reacted with the organic substrate producing two different isomers of monohydroxylated product and, upon successive hydroxylation, mainly one dihydroxylated product. Further hydroxylation first degraded one of the aromatic rings, and the side chain thus formed was then cleaved off the other aromatic ring. The second aromatic ring was also degraded upon successive hydroxylations. Small saturated and unsaturated aliphatic acids were the last products prior to mineralization. It was found that use of cuprous/cupric ion pair resulted a faster conversion of BPA and faster mineralization when compared using ferrous/ferric ions, but this happened at the expence of excess electrical charge utilized for an equivalent conversion or mineralization. Degradation by using ferrous/ferric ions was more efficient than cuprous/cupric ions case in terms of total mineralization versus charge utilized, and a mineralization of 82% had been achieved by applying 107.8 mF of charge to a 0.7 mM BPA solution of 0.200 dm3. The rate constant of the monohydroxylation of BPA in the presence of ferrous/ferric ions had been determined as 1.0 × 10...

Direct Liquefaction of High-Sulfur Coals:  Effects of the Catalyst, the Solvent, and the Mineral Matter

Gözmen, Belgin

Two low-rank coals with high sulfur contents (Gediz subbituminous coal:  7.6 wt % S:dry basis. Çayirhan lignite:  5.7 wt% S:dry basis.) were subjected to hydroliquefaction. Liquefaction conditions included dry or solvent mediated runs under pressurized hydrogen without added catalyst or with the impregnated catalyst precursor ammonium heptamolybdate (AHM). Gediz coal having higher sulfur content gave 90% conversion in the absence of catalyst and solvent. Maximum conversion (98%) and maximum oil + gas yield (70%) from this coal were obtained by impregnating AHM onto coal and carrying out liquefaction in H2/tetralin system at 450 °C for 30 min. Under the same conditions, Çayirhan lignite gave 85% conversion and 70.5% oil + gas yield. The superior hydrodesulfurization effect of impregnated AHM on the oil fraction when used in the absence of solvent (less than 0.1% S in lignite's oil and less than 1% S in subbituminous coal's oil following one-stage hydrogenation) is a promising finding of this work. AHM was found to be much more effective in liquefaction of Çayirhan lignite and this has been ascribed to the well-dispersion of AHM throughout this lignite's structure via a cation-exchange mechanism through oxygen functionalities. Strong evidence for the catalytic effect...