Synthesis of Calix[4]arene‐grafted Magnetite Nanoparticles and Evaluation of Their Arsenate as Well as Dichromate Removal Efficiency

In this study, 5,17‐bis‐[(4‐benzylpiperidine)methyl]‐25,26,27,28‐tetrahydroxy‐calix[4]arene ( 3 ) has been prepared by the treatment of calix[4]arene with a secondary amine (4‐benzylpiperidine) and formaldehyde by means of Mannich reaction. The prepared Mannich base ( 3 ) has been grafted onto [3‐(2,3‐epoxypropoxy)‐propyl]‐trimethoxysilane‐modified Fe₃O₄ magnetite nanoparticles (EPPTMS‐MN) in order to obtain 5,17‐bis‐[(4‐benzylpiperidine)methyl]‐25,26,27,28‐tetrahydroxy calix[4]arene‐grafted EPPTMS‐MN (BP‐calix[4]arene‐grafted Fe₃O₄). All new compounds were characterized by a combination of FTIR and ¹H‐NMR analyses. The morphology of the magnetic nanoparticles was examined by transmission electron microscopy. Moreover, the studies regarding the removal of arsenate and dichromate ions from the aqueous solutions were also carried out by using 5,17‐bis‐[(4‐benzylpiperidine)methyl]‐25,26,27,28‐tetrahydroxy‐calix[4]arene in liquid–liquid extraction and BP‐calix[4]arene‐grafted Fe₃O₄ ( 4 ) in solid–liquid extraction experiments. The extraction results indicated that 3 is protonated at proton‐switchable binding sites in acidic conditions. Hence, facilitating binding of arsenate and dichromate is resulted from both electrostatic interactions and hydrogen bonding. To understand the selectivity of 3 , the retention of dichromate anions in the presence of Cl⁻, NO, and SO anions at pH 1.5 was also examined.     

Synthesis of Calix(aza)crown and its Oligomeric Analogue for the Extraction of Selected Metal Cations and Dichromate Anions

The present study reports the synthesis of a novel ionophore, calix[4]azacrown ( 5 ) bearing two amino groups at the lower rim along with its oligomeric analogue ( 6 ). The liquid‐liquid extraction properties of these compounds towards selected metal cations and dichromate anions have been evaluated. It is observed that ( 5 ) and ( 6 ) are good extractants for the selected metal cations. However, in the case of dichromate anion, only species ( 5 ) shows remarkable extraction properties at low pH, whereas species ( 6 ) shows poor extraction behavior. The results have importance especially in wastewater treatment to obtain environmentally safe industrial effluent and they should also assist supramolecular chemists in designing and synthesizing more sophisticated host molecules for the removal of toxic pollutants.     

Novel Calix[4]arene‐based Amberlite XAD‐4 Modified Resin for As(III) Removal from Water

The present article describes As(III) sorption behavior of novel calix[4]arene appended TS‐4 resin. The sorption ability of TS‐4 resin has been evaluated at wide range of pH, i.e., pH 2–14. The maximum As(III) sorption efficiency (95%) was achieved at pH 2, which shows that the TS‐4 resin possesses greater affinity for As(III) at this pH. Column sorption mechanism was evaluated through various operating parameters, i.e., change in concentration, flow rate, bed heights, and pH. The experimental data were also tested against bed depth service time model and from the results; it has been observed that the data is in close agreement with the theoretically calculated values. Thus, from the data it has been revealed that TS‐4 resin has maximum column efficiency of 0.13 mmol g^?1. Application of TS‐4 to real samples indicates a slight decrease (2–3%) in extraction efficiency of TS‐4 because of high concentration of total dissolved salts. Thermal behavior was tested by differential scanning calorimetry and it has been observed that TS‐4 resin is stable up to 160°C. TS‐4 resin was found to be regenerable and best regeneration was achieved by using 4% solution of NaOH. It can be deduced from the study that the resin will find its applicability in small as well as industrial scale water purification plants.