Imam Bakhsh Solangi

Removal of fluoride from aqueous environment by modified Amberlite resin

Fluoride in drinking water above permissible level is responsible for human being affected by skeletal fluorosis. In this study, Amberlite XAD-4 has been modified by introducing amino group onto the aromatic ring for its application in fluoride remediation. Characterization of the modified resin was made by, FT-IR and elemental analysis (CHNS) techniques. The pH 9 was optimum value for quantitative sorption of fluoride in both batch and column experiments. The desorption of fluoride was achieved by using 10% HCl. The batch and column sorption studies of fluoride with modified resin were carried out to evaluate sorption isotherms too. Thus equation isotherms such as Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) were successfully used to model the experimental data. The sorption capacity of modified Amberlite XAD-4 resin was found as 5.04 x 10(-3) mol g(-1). From the D-R isotherm parameters, it has been evaluated that the uptake of fluoride by modified resin occurs through ion exchange adsorption mechanism. The study will contribute toward the removal of fluoride from the aqueous environment as well as in the field of analytical and environmental chemistry.

Synthesis and application of a highly efficient tetraester calix[4]arene based resin for the removal of Pb2+ from aqueous environment

The present study describes the Pb(2+) sorption potential of newly synthesized tetraester calix[4]arene (TC4) based resin from aqueous media. The TC4 resin was synthesized through diazotization reaction of TC4 with Amberlite XAD-4 in the presence of sodium nitrite in acidic medium. The TC4 resin was characterized by using different analytical techniques such as FT-IR, elemental analysis and scanning electron microscopy (SEM). The Pb(2+) removal ability of the resin from the aqueous environment has been evaluated by both batch adsorption as well as column studies. The experiments have been conducted involving the determination of effect of pH, adsorbate concentration, adsorbent dosage, contact time and temperature. Moreover, on the basis of kinetic studies, the pseudo-first-order and pseudo-second-order adsorption kinetics were calculated. The thermodynamic parameters of lead adsorption were also calculated. Equation isotherms such as Langmuir (L), Freundlich (F), and Dubinin-Radushkevich (D-R) were successfully used to model the experimental data. From the D-R isotherm parameters, it was considered that the uptake of Pb(2+) by TC4 resin is ion exchange mechanism. From the results it has been found that the TC4 resin is a versatile adsorbent for the removal of Pb(2+) from the aqueous environment. The study also confers its impact on human health, reinstate of polluted sites and other fields of material science.

Synthesis and application of p-tert-butylcalix[8]arene immobilized material for the removal of azo dyes

The present study describes synthesis of a new resin through immobilization of p-tert-butylcalix[8]arene onto silica and its application for the removal of azo dyes from aqueous media as well as from textile effluents. The newly synthesized material 4 is characterized by FT-IR spectroscopy, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). Reactive Black-5 (RB-5) and Reactive Red-45 (RR-45) azo dyes were used as sorbate. Batch wise sorption experiments were conducted to optimize various experimental parameters such as the effect of sorbent dosage, electrolyte, pH, dye concentration, and contact time. The optimized pH for the effective removal of RB-5 and RR-45 dyes was 9 and 3, respectively. The increase in material 4 dosage increased the percent sorption. Both Langmuir and Freundlich isotherm models were applied to experimental data and Langmuir isotherm model found to be best fit. The results revealed that material 4 was potentially more effective sorbent for the sorption of selected azo dyes as compared to pure silica and p-tert-butylcalix[8]arene. The field studies also supported the effectiveness of material 4, which could be useful for the removal of both the dyes and also for the normalization of pH, TDS, conductivity and salinity near to the drinking water.

An excellent fluoride sorption behavior of modified amberlite resin

The article describes a convenient method for the modification of Amberlite XAD-4 resin by introducing thio-urea binding sites onto the aromatic rings. The modified (ATU) resin has been employed for the quantitative sorption of fluoride ions in batch as well as column experiments. The parameters (i.e. pH, contact time, etc.) were optimized and desorption of fluoride ions was fulfilled by using 0.01 M HCl solution. The equation isotherms such as Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin were also successfully applied to model the experimental data. The sorption capacity of the ATU resin was found as 3.286 mmol g(-1). From the D-R isotherm parameters, it has been calculated that the uptake of fluoride ion by ATU resin occurs through ion exchange sorption mechanism. The study will contribute toward the remediation of fluoride polluted areas as well as in the various fields of materials science.

Synthesis and application of calix[4]arene based resin for the removal of azo dyes

The present study describes a novel synthetic method for the immobilization of calix[4]arene (II) onto the surface of modified Amberlite XAD-4 resin (4), which does not require the derivatization of calixarene moiety. The novel calix[4]arene based resin (C4 resin) 5 was used as sorbent for the removal of azo dyes. Batch-wise sorption study was carried out and observed that the C4 resin (5) is more effective as compared to compound II as well as pure Amberlite XAD-4 resin (1) to remove the selected dyes [i.e. Reactive Black-5 (RB-5), Reactive Red-45 (RR-45) and Congo Red (CR)]. The effect of sorbent dosage and pH on % sorption was studied. During the extraction process, various kinds of interactions such as electrostatic repulsion, deprotonation of the hydroxyl groups of C4 resin, dissociation of reactive dyes into anions/cations and structural variations were monitored and found that they are highly pH dependent.

Bifunctional calix[4]arene sensor for Pb(II) and Cr2O7(2-) ions.

A readily available chromionophore 5,11,17,23-tetra-tert-butyl-25,27-bis(hydrazidecarbonylmethoxy)-26,28-dihydroxycalix[4]arene (HCC4) was employed as a chromogenic sensing probe selective for Pb(II) and Cr2O72− ions among a series of various ions such as Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II), Al(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II) as well as Cr2O72−, CH3CO2−, Br−, Cl−, F−, I−, ClO4− and NO3− that have been examined by UV-visible and fluorescence spectroscopic techniques. The HCC4 in DCM-MeCN system forms 2:1 (ligand-metal) complex with Pb(II). It also shows 2:1 stoichiometry with Cr2O72−. The complexation phenomenon has been confirmed by FTIR spectroscopy that favors the selective nature of HCC4 with Pb(II) and Cr2O72−. Thermal gravimetric analysis (TGA) also supports its utility in drastic conditions.

Kinetic Study of an Effective Pb(II) Transport through a Bulk Liquid Membrane Containing Calix[6]arene Hexaester Derivative as a Carrier

The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol−1 and 14.79 kJ mol−1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k1, k2) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k1 and k2 was found to be in the order of CH2Cl2 > CHCl3 > CCl4.

SORPTION OF CONGO RED ONTO P-TERT-BUTYLCALIX[4]ARENE BASED SILICA RESIN

The present study deals with the application of p-tert-butylcalix[4]arene based silica resin (4) for the removal of Congo Red (CR) from aqueous solution through batch-wise sorption. Different parameters such as pH, temperature, sorbent dosage and contact time were optimized to achieve better sorption results. It has been found that the sorption of CR dye on resin 4 was highly pH dependent and significant percent sorption (80%) was achieved at its original pH (i.e. 5.8 pH). The equation isotherms and the thermodynamic parameters such as Gibbs free energy ΔG, enthalpy ΔH and entropy ΔS were also applied to evaluate experimental data. The positive and negative value of ΔH and ΔG demonstrates that sorption process is endothermic and spontaneous in nature. It has also been noticed that the Freundlich isotherm model could provide the best fit to describe the sorption equilibrium.

Immobilization of α-amylase onto a calix[4]arene derivative: Evaluation of its enzymatic activity

In order to enhance the cost-effectiveness practicability of enzymes in many industries such as pharmaceutical, food, medical and some other technological processes, there is great need to immobilize them onto a solid supports. In this study, a new and efficient immobilization of α-amylase from Saccharomyces cerevisiae has been developed by using the surface functionalization of calix[4]arene as support. A glutaraldehyde-containing amino group functionalized calix[4]arene was used to immobilize α-amylase covalently. In this procedure, imide bonds are formed between amino groups on the protein and aldehyde groups on the calix[4]arene surface. The surface modified support was characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM). The effect of various preparation conditions on the immobilized α-amylase process such as immobilization time, enzyme concentration, temperature and pH were investigated. The influence of pH and temperature on the activity of free and immobilized α-amylase was also studied using starch as substrate. The optimum reaction temperature and pH value for the enzymatic conversion catalyzed by the immobilized α-amylase were 25°C and 7, respectively. Compared to the free enzyme, the immobilized α-amylase retained 85% of its original activity and exhibited significant thermal stability than the free one and excellent durability.

A Convenient Approach Toward Fluoride Sorption by Calix[4]arene Based Sorbent

The present study describes the sorption of fluoride on a potential and newly synthesized p-tetraaminocalix[4]arene based resin (p-TAC4 resin). The p-TAC4 resin was synthesized via immobilization of p-tetranitrocalix[4]arene (p-TNC4) onto the Merrifield resin followed by catalytic reduction with SnCl2/EtOH/HCl. The p-TNC4 and p-TAC4 resins were characterized using FT-IR, elemental analysis, and scanning electron microscopy (SEM). Fluoride removal capability from the aqueous media of the p-TAC4 resin has been evaluated through batch sorption study. The effect of pH, sorbate concentration, sorbent dosage, and contact time on fluoride removal was evaluated. The Langmuir (L), Freundlich (F), and Dubinin–Radushkevich (D-R) isotherms revealed that the fluoride on p-TAC4 resin follows physiosorption mechanism. All the results support and emphasize that the p-TAC4 resin is an effective sorbent for the removal of fluoride from the aqueous environment at a wide range of pH. The study may confer its impact on human health, reinstate polluted sites and other fields such as analytical, clinical, as well as material sciences.