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 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...

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...

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...

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...

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...

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...

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.