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Öğe Activated carbons prepared by indirect and direct CO2 activation of lignocellulosic biomass for supercapacitor electrodes(Pergamon-Elsevier Science Ltd, 2020) Jiang, Changle; Yakaboylu, Gunes A.; Yumak, Tugrul; Zondlo, John W.; Sabolsky, Edward M.; Wang, JingxinLignocellulosic biomass was converted into hierarchical porous carbon by using a physical activation technique under a carbon dioxide environment. Both direct and indirect CO(2 )activation routes were utilized to investigate the effect of processing parameters and the kinetics of the activation. The porosity, surface chemistry, and morphology of the activated carbons were characterized in addition to their proximate and ultimate analyses. This was followed by the preparation of the activated carbon electrodes and the fabrication and electrochemical testing of these electrodes within a symmetrical supercapacitor cell. The results showed a dominant microporous structure along with the limited content of larger pores for the activated carbons prepared via both direct and indirect activation. Along with the preserved natural pore structure of the biomass, an engineered pore structure was achieved which is highly beneficial for the supercapacitors with respect to the transport and storage of ions. The morphological analysis also revealed their tortuous porous structure. The maximum specific capacitances of 80.9 and 92.7 F/g at the current density of 100 mA/g were achieved after direct and indirect activation routes, respectively. The surface functional groups were also found to play a significant role in the resultant electrochemical performance of the supercapacitors. (C) 2020 Elsevier Ltd. All rights reserved.Öğe Chemical and Combustion Characteristics of Hydrochars Obtained from Various Biomasses by Hydrothermal Carbonization(2024) Yumak, Tugrul; Sınağ, AliIn this work, various waste biomasses were subjected to hydrothermal carbonization under mild conditions. The effect of operating temperature, duration time, and biomass-to-water ratio on the chemical and combustion characteristics of the hydrochars were determined. The results were compared to MKP Alpagut lignite to understand the future of hydrochars as an effective and environmentally friendly solid fuel. It was found that the temperature dominantly affects the yield and the chemical characteristics of the hydrochars compared to the duration time and biomass-to-water ratio for real biomasses. Hydrochars obtained from real biomasses showed higher combustion temperatures and slightly higher ignition temperatures. Moreover, the HHV of hydrochar is significantly higher than the MKP lignite and raw biomass. Our results prove that the hydrothermal carbonization process can be assessed as one of the best techniques for the thermochemical conversion of waste biomass into high-value-added valuable solid fuels.Öğe Comparison of the electrochemical properties of engineered switchgrass biomass-derived activated carbon-based EDLCs(Elsevier, 2020) Yumak, Tugrul; Yakaboylu, Gunes A.; Oginni, Oluwatosin; Singh, Kaushlendra; Ciftyurek, Engin; Sabolsky, Edward M.Activated carbon-based electrodes with high surface area were synthesized by direct and indirect chemical activation of switchgrass biomass and its biochar, and decorated with MnO2 in order to enhance and compare the capacitive performance of the fabricated supercapacitors. N-2 physisorption, Raman, XPS and SEM techniques were used to examine the differences in the microstructure and surface characteristics of biomass-derived activated carbon samples and MnO2 loaded samples. All fabricated supercapacitors were highly stable and showed high-rate capacitive performance. Direct KOH and H3PO4 activation increased the specific surface area up to 1272 and 1373 m(2)/g, respectively. As a result, the capacitive performance increased from 50 to 140 F/g for directly KOH activated biomass, and from 49 to 95 F/g for directly H3PO4 activated biomass. MnO2 loading led to an increase in specific capacitance (110 F/g) for the KOH activated biochar, even though no significant effect was observed for the H3PO4 activated biochar. The effectiveness of direct chemical activation of the biomass to enhance the electrochemical performance of the fabricated supercapacitors was demonstrated by comparing it with pseudocapacitive material loading (MnO2) and indirect chemical activation of biochars.Öğe Determination of the superior quality properties of randomly selected chestnut honey samples from the Sinop region(Taylor & Francis Inc, 2023) Avsar, Cumhur; Aslan, Hakan; Yumak, Tugrul; Tabak, Ahmet; Deniz, Nuray TurkIn this study, a total of 43 chestnut honey samples were randomly selected and collected from the Erfelek, Ayancik, and Turkeli districts of Sinop. The pollen content of all honey samples was determined, revealing that chestnut pollen accounted for over 90% in most cases. The chestnut honey from the Sinop region is considered of high quality compared to other chestnut honeys, primarily due to its low HMF (Hydroxymethylfurfural) levels, low moisture content, high proline content, and significant pollen content. The antibacterial activities of these honey samples were assessed using the agar well diffusion method, Minimal Inhibitory Concentrations (MIC), and Minimal Bactericidal Concentrations (MBC) methods. It is worth mentioning that certain samples exhibited significant activity against Staphylococcus aureus, with inhibition zones ranging from 15 to 20 mm, which is comparable to standard antibiotics. The antioxidant activities of all honey samples were evaluated using a 1,1-Diphenyl-2-picrylhydrazine assay. The results obtained indicate that the chestnut honey produced from the chestnut forests in the Sinop province meets the criteria outlined in the Turkish Food Codex Honey Communique. The high proline content exceeding 1000 mg/kg and very low hydroxymethyl furfural values below 1 mg/kg observed in certain chestnut honey samples contribute to their high quality and safety. Additionally, the average pH of 4.81 and free acidity values below 50 meq/kg recorded for the analyzed honeys further reinforce these findings.Öğe Effect of high temperature preoxidation treatment on the oxidation behavior of MoSi2 - and WSi2 -Al2O3 composites(Elsevier Science Sa, 2020) Yakaboylu, Gunes A.; Yumak, Tugrul; Sabolsky, Katarzyna; Sabolsky, Edward M.Composites of 30 vol% MoSi2 -70 vol% Al2O3 and 30 vol% WSi2-70 vol% Al2O3 were prepared via sintering at 1600 degrees C in argon. The high-temperature preoxidation treatments were applied at 1000 degrees-1200 degrees C for 10 - 120 min in air. The non-isothermal oxidation tests were conducted in air at temperatures ranging between 50 degrees and 870 degrees C to study and understand the influence of the alumina phase and preoxidation process on the low-temperature oxidation behavior. The optical and scanning electron microscopy, X-ray diffraction, X-ray photoelectron and Raman spectroscopy were used to characterize the surface layers formed. The oxidation-induced mass gains were substantially reduced by 82.1-99.8%, implying their enhanced oxidation resistance. This was due to the formation of highly dense, protective surface layers with a sufficient thickness (3.1-14.2 mu m). The structural and surface analyses revealed their complex chemistries, since the ternary (Mo-Si-Al, W-Si-Al) intermetallic, mullite, alumina and silica phases with high oxidation resistances were identified within these surface features. In addition, the high-temperature electrical properties of the composites were highly preserved after the preoxidation treatment, and their electrical conductivities were measured as 45.1-78.6 S/cm at 800 degrees C and 40.1 - 69.1 S/cm at 900 degrees C. (C) 2019 Elsevier B.V. All rights reserved.Öğe Effect of synthesis methods on the surface and electrochemical characteristics of metal oxide/activated carbon composites for supercapacitor applications(Elsevier, 2019) Yumak, Tugrul; Bragg, Dustin; Sabolsky, Edward M.MnO2/Activated Carbon (cAC) and NiO/cAC composites were synthesized by both hydrothermal and precipitation methods in order to investigate the effect of preparation methods on the surface chemistry and porous structure of composite-based electrodes and electrochemical properties. X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), N-2 physisorption, Raman spectroscopy and scanning electron microscopy (SEM) techniques were used to investigate the surface chemistry, chemical composition, pore characteristics and surface morphology of the synthesized composites. Synthesized composites were used as electrode materials within button cell supercapacitors. It was found that hydrothermal treatment to deposit the nano-oxides led to an increase in specific surface area, also this treatment resulted in oxygen-containing surface functionalities, which led to an improvement in electrochemical properties. Although the metal oxide loading caused a decrease in the specific surface area, the pseudocapacitive effect of MnO2 and NiO, and oxygen-containing surface functionalities increased the specific capacitance. MnO2 and NiO loading led to a 50% and 150% increase in specific capacitance, respectively. NiO/cAC samples obtained by precipitation method showed a higher specific capacitance compared to hydrothermally synthesized NiO/cAC. The metal oxide loading method has great influence on the surface chemistry, surface area and the resulting electrochemical performance of activated carbon-based fabricated supercapacitors.Öğe Engineered hierarchical porous carbons for supercapacitor applications through chemical pretreatment and activation of biomass precursors(Pergamon-Elsevier Science Ltd, 2021) Yakaboylu, Gunes A.; Jiang, Changle; Yumak, Tugrul; Zondlo, John W.; Wang, Jingxin; Sabolsky, Edward M.For a better process and property control, the effect of chemical pretreatment time on the chemistry and electrochemical performance of activated carbons derived from Miscanthus grass biomass was exam-ined. The microstructure, chemistry and active functional groups were controlled by tuning the pretreatment duration, which provided the removal of certain concentrations of hemicellulose and lignin, as well as, pore development at the initial stage. The optimal KOH pretreatment (12-18 h) resulted in interconnected pore structure, rich oxygen content (18-21 at.%), significant changes in their chemistry and functional groups, and a sheet-like morphology. A high specific capacitance up to 188 F/g and a high cycling stability of 85-91% retention (after 1000-2500 cycles) at 0.1 A/g were achieved. The optimization of the pretreatment time also resulted in high specific energy (8.0 W h/kg) and specific power (377 W/ kg) at 0.5 A/g. The micro/mesopore volume, cellulose content, C/O ratio, and surface chemistry were identified to be major contributors to the electrochemical performance as a result of enhanced electroadsorption, double layer formation, and rapid ion transport. This understanding creates a simple and cost-effective route for controlling the pore network and chemistry, as well as, the resultant performance of the porous activated carbon supercapacitor electrodes. (C) 2020 Elsevier Ltd. All rights reserved.Öğe Lignin-Derived Carbonaceous Materials for Supercapacitor Applications(Springer Nature, 2023) Esakkimuthu, Esakkiammal Sudha; Ponnuchamy, Veerapandian; Yumak, Tugrul; De Vallance, DavidElectrochemical supercapacitors are energy storage systems that exhibit high-power density, high cycle stability, and fast charge–discharge capacity. Carbon-based electrodes have been extensively used for supercapacitors due to their excellent porosity, mechanical properties, and large surface areas. However, these carbons are produced from fossil-based and unsustainable resources, mainly polyacrylonitrile. In recent years, lignin has appeared as a potential alternative precursor for producing sustainable carbon materials. Specifically, lignin’s renewable nature and large content of aromatic rings with reactive functional groups make it a highly viable candidate for electrochemical supercapacitor materials. This chapter deals with the current development of carbonaceous electrodes from sustainable lignin precursors. An extensive investigation of the utilization of lignin biopolymers toward developing high-performance electrodes for supercapacitors is described. The computational modeling techniques for designing supercapacitors and investigating their properties are illustrated. In conclusion, the challenges and improvements with lignin for supercapacitors are highlighted. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Öğe On the entropic nature of unified interactions(Iop Publishing Ltd, 2019) Dil, Emre; Yumak, TugrulIn this paper, we generalize Verlinde's entropic gravity proposal on the other fundamental interactions of nature. We begin by introducing the entropic origin of the Coulomb's electrostatic force, and then the magnetic force, by assuming the holographic principle holds when a charged particle approaches a screen enclosing the emerged part of the spacetime due to a source. We assume that the entropy of the screen changes when the charge approaches as in the Verlinde's approach. Thereafter, we obtain the entropic Maxwell equations in both classical and covariant form by means of the holographic principle hold for the source. Considering the gauge covariant structure of the fundamental forces, we implicitly generalize the entropic origin of the electromagnetic force into the strong and weak nuclear forces. The possibility of the entropic origin of the all fundamental forces of nature is assumed to make a meaningful contribution to the unification scheme of the fundamental forces.Öğe Preparation of Highly Porous Carbon through Slow Oxidative Torrefaction, Pyrolysis, and Chemical Activation of Lignocellulosic Biomass for High-Performance Supercapacitors(Amer Chemical Soc, 2019) Yakaboylu, Gunes A.; Yumak, Tugrul; Jiang, Changle; Zondlo, John W.; Wang, Jingxin; Sabolsky, Edward M.Seven kinds of highly porous activated carbon were prepared from two different lignocellulosic biomass feedstocks (hybrid willow and miscanthus grass) by utilizing four different processing routes, which generally include variations of the pyrolysis, slow oxidative torrefaction, and KOH chemical activation. The activated carbons were evaluated for potential application within the electrodes of double layer supercapacitors. The synthesized activated carbons showed high specific surface area (up to 3265 m(2)/g), hierarchical pore structure composed of micro-/meso-/macropores with large pore volume (up to 1.535 cm(3)/g), and rich oxygen content (10.9-19.2 at. %). Their surface area, pore structure/volume, microstructure, and surface functional groups were highly influenced by processing routes, which in turn determined their electrochemical performance and stability. In particular, pretreating the biomass samples via slow oxidative torrefaction substantially increased their surface area, total pore volume, and meso-/micropore volume, and the surface chemistry of these materials showed a higher concentration of carboxyl groups. The performance of two-electrode symmetrical supercapacitors was evaluated in a 6 M KOH aqueous electrolyte. They exhibited relatively high specific capacitance of 70.2-162.3 F/g under constant current density of 100 mA/g, with a high cycling stability based on the capacitance retention of 95.1-99.9% after 1000 cycles. In addition, an increase of 25.0-62.2 F/g was achieved in specific capacitance by including the pyrolysis and/or slow oxidative torrefaction in the synthesis protocol. The sample (HW-D) that exhibited the best performance also maintained 94.1% of its specific capacitance after 5000 charge/discharge cycles at 100 mA/g. The synthesis strategies including the slow oxidative torrefaction pretreatment showed great promise for preparing low-cost, porous carbon materials from renewable biomass sources that are highly suitable for incorporation in supercapacitors and other electrochemical applications.Öğe Production and characterization of activated carbon foams with various activation agents for electrochemical double layer capacitors (EDLCs) applications(Elsevier, 2024) Ozcifci, Zehra; Emirik, Mustafa; Akcay, Hakki Turker; Yumak, TugrulSucrose-based activated carbons were obtained by carbon foams with sugar and cobalt (II) nitrate as precursors, followed by using different chemical activation agents. The effect of Co(NO3)2 concentration, the carbonization temperature and the activation agent on the surface chemistry, porosity were investigated. Textural characterization and electrochemical tests were performed on the activated carbon samples (CF). The results showed that the activated carbon produced by H2SO4 and KOH at 800 degrees C had a surface area of 691 m2/g and 1125 m2/g, 89% and 80% of the sample pore structure was microporous, and specific capacitance of 8.4 F/g and 162.2 F/g at a constant current density of 250 mA/g, respectively. K2CO3-activated carbon had 918 m2/g surface area and 63% of the sample pore structure with microporous and 1.4 F/g specific capacitance, H3PO4-activated carbon and ZnCl2-activated carbon had 1833 m2/g and 1597 m2/g surface area, 53% mesoporous and 50% mesoporous, 222.4 F/g and 149.9 F/g specific capacitance respectively. The most promosing result was observed in the electrochemical storage behavior of the carbon materials with hierarchical pore structure activated with H3PO4 is associated with increasing defect zones at the edges of micro- and mesoporous morphology, resulting in a higher surface area and increased conductivity of the material.Öğe Removal of Cefdinir from Water Using Waste Material-Derived Activated Biochar as a Rapid, Effective, and Sustainable Adsorbent(Wiley, 2021) Gumus, Dilek; Yumak, Tugrul; Gumus, FatihCefdinir adsorption onto non-activated biochar (WL-BC) and activated biochars (WL-BC-H, WL-BC-OH) prepared from waste biomass (WL) is comparatively investigated in view of adsorption factors, adsorption isotherms and adsorption kinetics. Batch experiments are conducted to assess the effects of pH, adsorption time and initial antibiotic concentration. Various advanced techniques are applied to characterize the prepared biochars (BCs). Characterization of the new BCs reveal that the activation process do not have a significant effect on the chemical structure of activated carbons, but it increases the surface area up to eight times. The equilibrium data are simulated with the Langmuir adsorption model indicating monolayer adsorption for both activated biochars WL-BC and WL-BC-H. However, the adsorption isotherm for WL-BC-OH is represented well by the Freundlich model, which shows that multilayer adsorption took place. The kinetic data are analyzed using various kinetic models. The maximum adsorption capacity of the activated biochar is approximately tenfold in comparison to the non-activated biochar. Additionally, the real wastewater experiments with treated campus wastewater show that the adsorptive performance of the activated biochar is not affected by other ions. Consequently, BCs derived from defatted laurel leaves could be effective and eco-friendly adsorbents for removing cefdinir from wastewater.Öğe Some physicochemical properties of pure and pollution-free Sinop chestnut honey(Taylor & Francis Inc, 2024) Tabak, Ahmet; Deniz, Nuray Turk; Avsar, Cumhur; Aslan, Hakan; Yumak, TugrulThis study was designed to investigate some physicochemical properties (color, electrical conductivity, ash, water-insoluble and mineral matter contents) of chestnut honey produced in the Ayanc & imath;k, T & uuml;rkeli and Erfelek regions of Sinop province, where chestnut forests are dense. The experimental data showed that most of the honey samples had different amber color tones. The electrical conductivity values and the amounts of water-insoluble matter for all chestnut honeys were determined above 0.8 mS/cm and below 0.1 g per 100 g, respectively. In addition, honey samples contained mainly potassium and calcium and other minerals such as magnesium, sodium, aluminum and iron. It has been demonstrated that these chestnut honeys are registered with Geographical Indication and meet the criteria required in the Turkish Food Codex Honey Communiqu & eacute; of the Ministry of Agriculture and Forestry. These honeys have not been exposed to any external processing (heat treatment, etc.), have not been adulterated, do not contain impurities, and are pure and high quality.Öğe Sucrose-based activated carbon foams as an electrode active material for supercapacitors(Springer, 2023) Ozcifci, Zehra; Ozsanli, Mehmet Ali; Akcay, Hakki Turker; Yumak, TugrulActivated carbon foams (ACFs) have been successfully prepared by foaming sucrose with Zn nitrate and further chemical activation with H3PO4. The effect of the foaming agent (Zn) concentration and the activation temperature on the surface chemistry, porosity, and morphology were investigated. The ACFs reveal high specific surface area, non-uniform variable porous structure, and high oxygen content. The ACFs represent high specific capacitance and very low equivalent serial resistance (ESR) values as electrode material. The ACF obtained at 600 degrees C has a specific capacitance of 205.4 F/g at 1 A/g constant current density. The pseudocapacitive contribution of oxygen-containing surface functional groups was proved by CV curves at slow scan rates. The high performance of the ACFs may be attributed not only to the high surface area, and hetero-atom-containing SGFs but also to the unique surface morphology which originated from the release of gaseous products during the foaming process.Öğe Surface and chemical characteristics of platinum modified activated carbon electrodes and their electrochemical performance(Tubitak Scientific & Technological Research Council Turkey, 2021) Yumak, Tugrul; Yumak, Serap; Karabulut, AbdulkerimPlatinum (Pt) loaded activated carbons (ACs) were synthesized by the thermal decomposition of platinum (II) acetylaceton ate (Pt(acac)(2)) over chemically activated glucose-based biochar. The effect of Pt loading on surface area, pore characteristics, surface chemistry, chemical structure, and surface morphology were determined by various techniques. XPS studies proved the presence of metallic Pt-0 on the AC surface. The graphitization degree of Pt loaded ACs were increased with the loaded Pt-0 amount. The electrochemical performance of the Pt-loaded ACs (Pt@AC) was determined not only by the conventional three-electrode system but also by packaged supercapacitors in CR2032 casings. The capacitive performance of Pt@AC electrodes was investigated via cyclic voltammetry (CV), galvanostatic charge-discharge curves (GCD), and impedance spectroscopy (EIS). It was found that the Pt loading increased the specific capacitance from 51 F/g to 100 F/g. The ESR drop of the packaged cell decreased with the Pt loading due to the fast flow of charge through the conductive pathways. The results showed that the surface chemistry is more dominant than the surface area for determining the capacitive performance of Pt loaded AC-based packaged supercapacitors.Öğe Surface characteristics and electrochemical properties of activated carbon obtained from different parts of Pinus pinaster(Elsevier, 2021) Yumak, TugrulDifferent parts (needle and cone) of the same biomass (pine, Pinus pinaster) were used as carbon source for activated carbon production. Biomass-derived activated carbons (ACs) were produced by the chemical activation of pyrolytic char. Dependence of the surface characteristics to the biomass type and activation agent were discussed by N2 Physisorption, Raman, and X-ray photoelectron spectroscopy (XPS) techniques. Pine-cone-derived ACs exhibit higher BET surface area and mesopore volume to micropore volume ratio compared to needlederived ACs. Regardless of the biomass type, higher BET surface area and Vmes/Vmic ratio were obtained by KOH activation. XPS results proved that the KOH dominantly reacts with the aliphatic groups while H3PO4 reacts with aromatic groups during the activation. Hence, KOH activation led to the higher relative amounts of surface aromatic groups which will contribute to the total specific capacitance by creating pseudocapacitance. The electrochemical performance of the synthesized ACs was determined in packaged supercapacitors in CR2032 casings. Galvanostatic charge-discharge and self-discharge tests proved that all packaged supercapacitors displayed a repeatable cycle behavior and were highly stable. Cone-derived AC-based supercapacitors displayed higher specific capacitance than those of needle-derived ACs at all current densities (0.25-1 A/g). However, higher ESR values were observed for cone-derived AC based electrodes. The cone-derived AC (by KOH activation) based supercapacitor displayed 99% capacitance retention over 5000 cycles at 500 mA/g current density. It is found that the biomass type primarily affects the surface and electrochemical properties of ACs.Öğe Treatment of wastewater containing organic pollutants in the presence of N-doped graphitic carbon and Co3O4/peroxymonosulfate(Springer Japan Kk, 2023) Akcay, Hakki Turker; Demir, Adem; Ozcifci, Zehra; Yumak, Tugrul; Keles, TurgutThe disposal of organic pollutants is one of the important research topics. Some of the studies in this field are based on the degradation of organic pollutants with a catalytic agent. The cobalt tetraoxide/peroxymonosulfate system is an important catalytic system used for the radical degradation of organic pollutants. To increase the catalytic efficiency of such reactions, graphitization of activated carbon used as a support solid and nitrogen doping to the carbon structure are commonly used methods. In this study, cobalt tetraoxide production, N-doping and graphitization were carried out in a single step by heat treatment of activated carbon doped with the phthlocyanine cobalt (II) complex. The catalytic performance of the catalyst/peroxymonosulfate system was investigated by changing the pH, catalyst, and PMS concentration parameters on rhodamine B and 1,3,5 trichlorophenol, which were used as models. It was seen that the catalysts had 97% activity on rhodamine B in 16 min and 100% on 1,3,5 trichlorophenol in 6 min. It was observed that the catalysts continued to show high catalytic activity for five cycles in reusability studies and had a very low cobalt leaching rate. These results are in good agreement with previously published studies. In line with these results, the synthesized N-doped graphitic carbon/Co3O4 catalyst can be used as an effective catalyst for wastewater treatments. [GRAPHICS] .
