Solvents prepared from natural terpenes (menthol and thymol), as H-bond acceptors, and a series of organic acids (chain lengths of 8, 10, and 14 C atoms), as H-bond donors, were characterized and tested as reaction media for liquid–liquid extraction purposes. Due to their high hydrophobicity, they seem to be promising alternatives to conventional (nonpolar and toxic) solvents, since they possess relatively less toxic, less volatile, and consequently, more environmentally friendly characteristics. Assuming that the equilibrium is established between solvent and analyte during a ligandless procedure, it can be concluded that those nonpolar solvents can efficiently extract nonpolar analytes from the aqueous environment. Previous investigations showed a wide range of applications, including their use as solvents in extractions of metal cations, small molecules, and bioactive compounds for food and pharmaceutical applications. In this work, hydrophobic solvents based on natural terpenes, which showed chemical stability and desirable physicochemical and thermal properties, were chosen as potential reaction media in the liquid–liquid extraction (LLE) procedure for Pb(II) removal from aqueous solutions. Low viscosities and high hydrophobicities of prepared solvents were confirmed as desirable properties for their application. Extraction parameters were optimized, and chosen solvents were applied. The results showed satisfactory extraction efficiencies in simple and fast procedures, followed by low solvent consumption. The best results (98%) were obtained by the thymol-based solvent, thymol–decanoic acid (Thy-DecA) 1:1, followed by L-menthol-based solvents: menthol–octanoic acid (Men-OctA) 1:1 with 97% and menthol–decanoic acid (Men-DecA) 1:1 with 94.3% efficiency.

Selective separation and removal of a metal species from complex matrices of other species is of critical importance in separation sciences and especially in industrial processes. The selectivity and efficiency of Pb(II) ion removal from an aqueous solution in the presence of Ni(II), Zn(II), Co(II), Cu(II), and Cd(II) ions as competing ions in a multi-component aqueous source phase through bulk liquid membrane system were investigated. The influence of the palmitic and oleic acid as supporting surfactants in the membrane phase on the removal of Pb(II) ions was also analyzed. Dicyclohexano-18-crown-6 dissolved in chloroform, proved to be a selective and efficient carrier for Pb(II) ions. In the optimized procedure, 3 hours of equilibrium time was required to achieve the maximum removal efficiency. It was found, that removal of Pb(II) ions was achieved without significant reduction in the efficiency compared to the liquid membrane transport of a single-component system. None of these cations interfered with Pb(II) removal. The presence of the oleic and palmitic acid in the membrane phase increase the content of Pb(II) removed to the receiving phase. In optimal transport conditions, more than 97% efficiencies for the removal of Pb(II) were obtained for a system supported by oleic acid. The excellent efficiency and high degree of selectivity for the Pb(II) ion removal by the proposed BLM system, reveals its potential application for the selective removal, concentration, and purification of lead ions from its different mixtures.

In this study, the efficacy of different extraction techniques (maceration, ultrasound-assisted and Soxhlet extraction) on the content of biologically active components in extracts from fresh and dried nettle leaves, and their antioxidant activity were analyzed. Methanol was used as the solvent. Total phenolic content and antioxidant capacity were determined by Folin-Ciocalteu, DPPH and FRAP methods, respectively. High content of total phenolic compounds and high antioxidant activity were recorded in extracts of dried nettle. Extracts obtained from fresh nettle samples showed significantly lower content of analyzed bioactive components and lower antioxidant activity. In the case of all extracts, Soxhlet extraction proved to be the most efficient, and maceration the least efficient extraction technique for isolation of bioactive components from nettle leaves.

The conductometric study of ligand structure influence on the Pb(II) complexation with crown ethers in different solvents has been investigated. In this paper, the complexation reaction of macrocyclic ligand, 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and Pb(II) cation was studied in different solvents: dichloromethane (DCM) and 1,2- dichloroethane (1,2-DCE). The effects of surfactant structure (Triton X-100 and Triton X-45) on the conductivity of the Pb(II) complex with 18-crown-6 and dibenzo-18-crown-6 ether have been investigated. The conductance data showed that the stoichiometry of the complexes in most cases is 1:1(ML). It is also demonstrated that the influence of crown ethers is deeply affected by the organic solvent used. In the solvents studied, the stability of the resulting complexes showed higher stability in dichloromethane comparing with 1,2- dichloroethane. Macrocyclic ligand 18-crown-6 showed more suitable for complexation of Pb(II) ions compared to dibenzo-18-crown-6. Adding a surfactant affected the higher absolute values of the conductivity of systems, but not the change in the stoichiometric ratio between a metal ion and macrocyclic ligand.

Among numerous techniques for successful separation and removal of metal cations, transport through bulk liquid membranes attracts special attention of researchers. In this paper, different ligands were applied as possible carriers for Cd(II) ions. Influence of substituents in macrocyclic ligands derived from 18-crown-6 reflected in decreased amount of transported Cd(II) ions, compared to 18-crown-6 (61,26%), in all used solvents, following the order: DCH18C6<DB18C6<B18C6<18C6. Addition of nonionic surfactants as possible carriers for Cd(II) ions within the liquid membranes also resulted with decreased transport rates, due to additional interactions of Cd(II) ions and carriers within the membrane.