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    Activated carbon derived from tea waste: A promising supporting material for metal nanoparticles used as catalysts in hydrolysis of ammonia borane
    (Pergamon-Elsevier Science Ltd, 2020) Akbayrak, Serdar; Ozcifci, Zehra; Tabak, Ahmet
    Activated carbons with high porosity and high surface area are promising materials to be used in wide-range applications. They can easily be prepared from various biomass source following by simple and reproducible activation and carbonization steps. In this study, the woody part of tea which is highly available tea waste after the harvesting of tea leaves is considered as the precursor of highly porous activated carbon. In fact, activated carbon with well-ordered porous structure (micropore area = 1614.3 m(2) g(-1), micropore volume = 1.13 cm(3) g(-1)) and high surface area (2559 m(2) g(-1)) was achieved using this tea waste. The obtained activated carbon was used to support cobalt, nickel and copper nanoparticles which were used as catalysts in H-2 generation from aqueous ammonia borane. The results reveal that Co nanoparticles with an average particle size of 3.18 nm on activated carbon provide higher activity (TOF = 7.5 min(-1)) as compared to nickel (TOF = 4.8 min(-1)) and copper nanoparticles in this reaction. Herein, we report also the kinetic studies including the effect of temperature, metal concentration and metal loading on the catalytic activity in hydrolysis of ammonia borane.
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    Noble metal nanoparticles supported on activated carbon: Highly recyclable catalysts in hydrogen generation from the hydrolysis of ammonia borane
    (Academic Press Inc Elsevier Science, 2019) Akbayrak, Serdar; Ozcifci, Zehra; Tabak, Ahmet
    Noble metal nanoparticles including rhodium, ruthenium and palladium have been extensively used in catalysis field. Since their limited abundance and high cost, many methods have been developed to obtain highly active and recyclable catalysts. In this work, Rh3+, Ru3+, Pd2+ ions were impregnated on activated carbon derived from pumpkin stalk in distilled water and then reduced with sodium borohydride to form Rh-0, Ru-0, Pd-0 nanoparticles on the surface of carbon. The analyses show that these nanoparticles were successfully dispersed on the activated carbon. Rh-0, Ru-0, Pd-0 nanoparticles on activated carbon provide a turnover frequency value of 188 min(-1), 235 min(-1) and 40 min(-1), respectively, at 25.0 +/- 0.1 degrees C. They preserve their activity even after multiple use in H-2 generation from the hydrolysis of ammonia borane. (C) 2019 Elsevier Inc. All rights reserved.
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    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, Tugrul
    Sucrose-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.
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    Sucrose-based activated carbon foams as an electrode active material for supercapacitors
    (Springer, 2023) Ozcifci, Zehra; Ozsanli, Mehmet Ali; Akcay, Hakki Turker; Yumak, Tugrul
    Activated 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.
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    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, Turgut
    The 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] .