Background Juglans regia L. shells as agricultural wastes can be considered as alternative sorbents to minimize the problems associated with heavy metal pollution. Objective In this study Juglans regia L. shells and Juglans regia L. shells modified with hydrazine hydrate were used as sorbents and compared for the preconcentration of Cd(II) ions from aqueous solution. Methods For the characterization of sorbents, the scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analysis and fourier transform infrared spectroscopy (FTIR) were used. For preconcentration, solid phase extraction (SPE) technique was used. Preconcentration studies were performed with column method and pH, eluent type and concentration, sample volume, flow rate and interfering ions effect were studied to determine the optimum column parameters. Results The limit of detection (LOD) of the sorbents are 0.31 µg/L and 0.18 µg/L, respectively. According to the Langmuir isotherm model for both sorbents KL=0.030 L/mg, R2=0.994, 0.016 L/mg, R2=0.991 and maximum adsorption capacities of the sorbents were found to be as 29.6 mg/g and 65.7 mg/g, respectively. The mean recoveries and RSD values at 95% confidence level (N = 6) for Cd(II) were 100.9% and 3.42; 100.6% and 3.79 for the JRS and JRS-HH sorbents, respectively. Conclusions In this method good results obtained when compared with the literature and the proposed method was successfully applied to the certificated reference material (NIST 1640) analysis. Highlights: Juglans Regia L. shells are an effective and inexpensive sorbent for preconcentration metal ions when modified. Thus, low-cost agricultural wastes are both recovered and have an economic value.

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In this study, a new sorbent is synthesized using surface imprinting technique. Cu(II)-imprinted multiwalled carbon nanotube sorbent (Cu(II)-IMWCNT) is used as the solid phase in the solid-phase extraction method. After the preconcentration procedure, Cu(II) ions are determined by high-resolution continuum source atomic absorption spectrometry. A total of 0.1 mol L À1 ethylenediaminetetraacetic acid (EDTA) is used to remove Cu(II) ions from the sorbent surface. The optimum experimental conditions for effective preconcentration of Cu(II), parameters such as pH, eluent type and concentration, flow rate, sample volume, sorbent capacity, and selectivity are investigated. The synthesized solid phase is characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The maximum adsorption capacities of Cu(II)-IMWCNT and non-imprinted solid phases are 270.3 and 14.3 mg g À1 at pH 5, respectively. Under optimum experimental conditions for Cu(II) ions, the limit of detection is 0.07 μg L À1 and preconcentration factor is 40. In addition, it is determined to be reusable without significant decrease in recovery values up to 100 adsorption-desorption cycles. Cu(II)-IMWCNT have a high stability. To check the accuracy of the developed method, certified reference materials, and water samples are analyzed with satisfactory analytical results.

Four novel hetero dimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid       (H2dipic), [Ni(H2O)5Co(dipic)2] (1), [Co(H2O)5Co(dipic)2][Ni(H2O)5Ni(dipic)2][Co(dipic)(H2O)3] (2), [Cu(H2O)5Ni(dipic)2]2[Co(dipic)(H2O)] (3) and [Ni(H2O)5Cu(dipic)2]2[Co(dipic)(H2O)] (4) have been prepared and characterized by elemental, AAS, spectral (IR and UV-Vis), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques. The results indicate that metal ions coordinate with 2,6-pyridinedicarboxylate ions (dipic2-) nitrogen atoms and carboxylate oxygen atoms of ligands. The mole ratio of dipic2- and metal ions in the complexes have been determined to be 2:2 (Co, Ni) for 1, 5:5 (3Co, 2Ni) for 2, 5:5 (Co, 2Ni and 2Cu) for 3 and 5:5 (Co, 2Ni and 2Cu) for 4 according to the results of elemental analysis. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H2O)] unit for 2 square plane) according to results of spectroscopic analysis. The TG and DTA properties of compounds have been studied.                     KEY WORDS: 2,6-Pyridinedicarboxylic acid, Mixed metal, Metal complex   Bull. Chem. Soc. Ethiop. 2020, 34(2), 313-321 DOI: https://dx.doi.org/10.4314/bcse.v34i2.9

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