Selçuk Şimşek

In this study, the adsorption properties of a composite material consisting of polyacrylamide, an inert polymer, and an extract obtained from the water-soluble part of a green walnut shell were investigated for Hg(II) ions. SEM, EDX, FTIR, and PZC analyses were performed to characterize the newly synthesized material. SEM and EDX analyses confirmed that the surface of the synthesized adsorbent became softer and smoother after adsorption, indicating the presence of Hg in its elemental composition. FTIR analysis showed that mercury enters the structure through chemical interactions, and there are changes in bond vibration frequencies in the presence of Hg(II). According to the PZC point analysis, the point at which the surface charge was zero was found to be pH 4. The Langmuir model was used to calculate the adsorption capacity after investigating the effect of concentration on adsorption. The adsorption capacity was found to be 1.808 molkg⁻¹ (362,67 mgg⁻¹) from the Langmuir model, which is very high compared to similar adsorbents. PFO model was used to explain the adsorption kinetics and very fast adsorption kinetics were observed. The adsorption entropy increased, free enthalpy of adsorption was negative, and heat of adsorption was in the energy-consuming direction.

In this study, we investigated whether the corm tunic structure, which is the underground part of the Crocus (Iridaceae) plant, can be used for adsorption and recovery/removal of uranium from an aqueous solution. The characterization of this structure, which has not been studied for its interaction with metals before, has been elucidated by point zero charge (PZC), FTIR, and SEM analyses. Extensive investigations were conducted on the adsorption properties of the biomass used and the pH, temperature, time, adsorbent dosage, and uranyl ion concentration variables were optimized. The experimental data were interpreted using theoretical adsorption models. The Langmuir model revealed a maximum adsorption capacity of the material to be 0.286 mol kg⁻¹. Adsorption kinetics were also described using pseudo-first order, pseudo-second order, Elovich, and intra-particular diffusion models. It is shown that the adsorption pH reaches the highest adsorption at the natural pH of the uranium solution. Experimental studies showed that the adsorption was endothermic and spontaneous. It has been shown that this biomaterial can be used as an adsorbent for the removal of uranium as well as a biomarker for determining the environmental uranium concentration.

In this study, the biosorption properties of fast green FCF (FG) dye in an aqueous solution were investigated using cranberry (Cornus mas L.) kernel (CK) as lignocellulosic biowaste. The biosorbent performance of the cranberry (Cornus mas L.) kernel biomass for FG dye molecules was optimized: 500 mg L⁻¹ at natural pH: 6.0 at 25°C. The maximum biosorption capacity for CK biomass was found to be 21.6 mg g⁻¹ from the Langmuir isotherm model. Biosorption thermodynamics showed that FG dye biosorption to CK biomass was spontaneous, entropy-increasing, and endothermic. The kinetic data were described by the PSO and IPD kinetic models. Thermodynamic parameters were calculated, and it was seen that the biosorption process is spontaneous and endothermic. FT-IR spectrum after biosorption provided data supporting the formation of electrostatic interactions, n-π interactions, and H-bonds between anionic FG dye molecules and CK biomass. When the results of this study were evaluated as a whole, it was concluded that CK biosorbent is a natural, abundant, low-cost, effective, and potential biosorbent for the removal of FG dye molecules from wastewater.

Adsorption is a widely used method for pollution removal and for the recovery of valuable species. In recent years, the use of metal-organic compounds among the adsorbents used in adsorption studies has increased. In this study, the performance of the water-insoluble Fe complex as a metal organic framework (MOF-Fe-Ta) of water-soluble tannic acid, which is not used as an adsorbent in uranium recovery and removal, was investigated. For the characterization of the new synthesized material, Fourier transform infrared, scanning electron microscopy, and X-ray diffraction analyses were performed. The changes in the adsorption process based on various parameters were investigated and discussed. The point of zero charges value of the adsorbent was found as 5.52. It was noticed that the adsorption increases as the pH increases. Analyzing the effect of concentration on adsorption, we determined which model explained the adsorption better. The monolayer capacity of the adsorbent determined in light of the Langmuir model was reported as 0.347 mol kg^-1. The Freundlich constant, namely the β value obtained in the Freundlich model, which is a measure of surface heterogeneity, was found to be 0.434, and the E_DR value, which was found from the Dubinin-Raduskevich model and accepted as a measure of adsorption energy, was 10.3 kJ mol^-1. The adsorption was kinetically explained by the pseudo-second-order model and the adsorption rate constant was reported as 0.15 mol^-1 kg min^-1. The effect of temperature on adsorption was studied; it was emphasized that adsorption was energy consuming, that is, endothermic and ΔH was found as 7.56 kJ mol^-1. The entropy of adsorption was positive as 69.3 J mol^-1 K^-1. As expected, the Gibbs energy of adsorption was negative (-13.1 kJ mol^-1 at 25 °C), so adsorption was considered as a spontaneous process. Additionally, the power and mechanism of the interaction between studied adsorbent and adsorbate are explained through density functional theory computations. Computationally obtained data supported the experimental studies.