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    Nitrogen? and oxygen?doped carbon particles produced from almond shells by hydrothermal method for efcient Pb(II) and Cd(II) adsorption
    (Springer Science and Business Media, 2023) Saka, Cafer; Teğin, İbrahim; Kahvecioğlu, Kübra; Yavuz, Ömer
    In this study, a two-step method was applied to obtain an efective adsorbent for cadmium (Cd) (II) and lead (Pb)(II) adsorption. The frst stage includes the production of activated carbon (AC) from almond shells, which is agricultural waste, by microwave heating and potassium hydroxide (KOH) chemical agent. The second stage includes nitrogen and oxygen doping by hydrothermal heating treatment of the obtained ACs with nitric acid. The obtained materials were characterized by thermogravimetric/diferential thermal analyser (TG–DTA); Fourier transform infrared spectroscopy (FTIR); scanning electron microscope (SEM); energy-dispersive spectroscopy (EDS); C, H, N, S elemental analysis; and nitrogen adsorption analyses. The adsorption performance, mechanism, kinetics, and thermodynamics of nitrogen- and oxygen-doped activated carbons were evaluated. The obtained isotherm and kinetic results showed that the adsorption of Cd (II) and Pb (II) on nitrogen- and oxygen-doped ACs followed Langmuir isotherm and pseudo-second-order kinetics. The adsorption capacity values (Qm) obtained for Cd (II) and Pb (II) adsorption were 106.38 mg/g and 76.33 mg/g, respectively.
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    Phosphorus and oxygen co-doped carbon particles based on almond shells with hydrothermal and microwave irradiation process for adsorption of lead (II) and cadmium (II)
    (Springer Heidelberg, 2023) Kahvecioglu, Kubra; Tegin, Ibrahim; Yavuz, Omer; Saka, Cafer
    In this study, the production of activated carbon based on almond shells by microwave heating with KOH activation and then the modification of activated carbon with phosphorus and oxygen as a result of hydrothermal heating with phosphoric acid were carried out to increase the Cd(II) and Pb(II) adsorption efficiency. The resulting materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric/differential thermal analyzer (TG-DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and nitrogen adsorption. Adsorption performance, kinetics and thermodynamics of phosphorus, and oxygen-doped activated carbons were evaluated. The results showed that the adsorption of both Cd(II) and Pb(II) on phosphorus and oxygen-doped activated carbons obeyed the Langmuir isotherm and pseudo-second-order kinetics. The adsorption capacity values (Q(m)) obtained from the Langmuir isotherm for Cd(II) and Pb(II) adsorption were 185.18 mg/g and 54.64 mg/g, respectively. At the same time, the adsorption mechanism of Pb(II) and Cd(II) on the respective adsorbents was evaluated. As a result of phosphorus and oxygen atoms, Lewis base sites on carbon atoms and Lewis acid sites on phosphorus atoms are likely to form on the surface. These Lewis base sites can act as important active sites in adsorption reactions, especially of positively charged Pb(II) and Cd(II) ions.
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    Surface modification with cold plasma application on kaolin and its effects on the adsorption of methylene blue
    (Elsevier Science Bv, 2013) Yavuz, Omer; Saka, Cafer
    In this study, cold plasma treatment was applied for the surface modification of kaolin adsorbent to improve the removal of methylene blue (MB) from aqueous solution. To achieve the aim, the conditions for adsorption, including cold plasma application time, initial dye concentration, and pH were investigated with respect to the removal efficiency of MB. The changes of the surface property before and after cold plasma treatment were discussed. The maximum adsorption capacity of MB compared with untreated raw kaolin increased from 19.60 to 51.02 mg/g (up to approximately 2, 5-fold) after modification by cold plasma. The experimental data were analyzed using pseudo first-order and second-order kinetic models. The surface properties of kaolin treated with cold plasma were investigated with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and point of zero charge (pzc) measurements to understand the adsorption mechanism. (C) 2013 Elsevier B.V. All rights reserved.