Sankaran Meenakshi

Enhanced fluoride sorption using La(III) incorporated carboxylated chitosan beads.

The carboxylated chitosan beads (CCB), which have a defluoridation capacity (DC) of 1385 mg F(-)/kg, have been further chemically modified by incorporating La(3+) ion (La-CCB) and its DC was found to be 4711 mg F(-)/kg whereas the raw chitosan beads (CB) possess only 52 mg F(-)/kg. The fluoride removal by La-CCB is governed by both adsorption and complexation mechanism. The functional groups present in beads were identified by FTIR analysis. The surface condition and existence of fluoride on the beads was confirmed by SEM with EDAX analysis. The experimental data have been analyzed using Freundlich and Langmuir isotherm models. Thermodynamic parameters such as DeltaG(o), DeltaH(o) and DeltaS(o) were calculated to predict the nature of sorption. The kinetic studies were investigated with reaction-based and diffusion-based models. A field trial was carried out with fluoride water collected from a nearby fluoride-endemic village.

Fluoride sorption by nano-hydroxyapatite/chitin composite

In this study the fluoride adsorption potential of novel nano-hydroxyapatite/chitin (n-HApCh) composite was explored. The sorbent was characterized using FTIR studies. The effects of pH, interfering anions and contact time were studied. The sorption data obtained under optimized conditions were subjected to Langmuir and Freundlich isotherms. Kinetic studies indicate that the rate of sorption of fluoride on n-HApCh composite follows pseudo-second-order and pore diffusion patterns. n-HApCh composite possesses higher defluoridation capacity (DC) of 2840 mg F(-)kg(-1) than nano-hydroxyapatite (n-HAp) which showed a DC of 1296 mg F(-) kg(-1). Field trials were conducted with the sample collected from a nearby fluoride endemic area.

Enriched fluoride sorption using alumina/chitosan composite.

Alumina possesses an appreciable defluoridation capacity (DC) of 1566 mg F(-)/kg. In order to improve its DC, it is aimed to prepare alumina polymeric composites using the chitosan. Alumina/chitosan (AlCs) composite was prepared by incorporating alumina particles in the chitosan polymeric matrix, which can be made into any desired form viz., beads, candles and membranes. AlCs composite displayed a maximum DC of 3809 mg F(-)/kg than the alumina and chitosan (52 mg F(-)/kg). The fluoride removal studies were carried out in batch mode to optimize the equilibrium parameters viz., contact time, pH, co-anions and temperature. The equilibrium data was fitted with Freundlich and Langmuir isotherms to find the best fit for the sorption process. The calculated values of thermodynamic parameters indicate the nature of sorption. The surface characterisation of the sorbent was performed by FTIR, AFM and SEM with EDAX analysis. A possible mechanism of fluoride sorption by AlCs composite has been proposed. Suitability of AlCs composite at field conditions was tested with a field sample taken from a nearby fluoride-endemic village. This work provides a potential platform for the development of defluoridation technology.

Development of chitosan supported zirconium(IV) tungstophosphate composite for fluoride removal.

A new biocomposite was prepared by incorporating inorganic ion exchanger namely zirconium(IV) tungstophosphate (ZrWP) into the chitosan biopolymeric matrix. The sorption behaviour of fluoride from aqueous solutions by this ZrWP/chitosan (ZrWPCs) composite has been investigated by batch technique. The fluoride sorption was studied as a function of contact time, pH, initial fluoride concentration, competing co-ions and temperature. The defluoridation capacity (DC) of the adsorbent was found to be 2025 mg F(-) kg(-1). The composite was characterized using FTIR and SEM with EDAX analysis. The equilibrium sorption data were fitted to Freundlich and Langmuir isotherms. The kinetics of sorption was found to follow pseudo-second-order and intraparticle diffusion models. The values of thermodynamic parameters indicate the nature of sorption is spontaneous and endothermic. The biocomposite was successfully used for the removal of fluoride from the field water taken in a nearby fluoride endemic village.

Removal of copper(II) using chitin/chitosan nano-hydroxyapatite composite

Polymeric composites made up of nano-hydroxyapatite (n-HAp) with chitin and chitosan have been prepared and studied for the removal of Cu(II) ions from the aqueous solution. The sorption capacity (SC) of n-HAp, n-HAp/chitin (n-HApC) composite and n-HAp/chitosan (n-HApCs) composite were found to be 4.7, 5.4 and 6.2 mg/g respectively with a minimum contact time of 30 min. Batch adsorption studies were conducted to optimize various equilibrating conditions like contact time, pH and selectivity of metal ion. The sorbents were characterized by FTIR, TEM, XRD and SEM with EDAX analysis. The sorption process was explained with Freundlich and Langmuir isotherms respectively. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated to understand the nature of sorption. A suitable mechanism for copper sorption was established and the selectivity of the metal ions for the composites was identified.

Sorption of chromium(VI) using modified forms of chitosan beads

Modified forms of chitosan beads were prepared and used for chromium removal from the aqueous solution. The prepared chitosan beads viz., protonated chitosan beads (PCB), carboxylated chitosan beads (CCB) and grafted chitosan beads (GCB) possess enhanced chromium sorption capacities (SCs) of 3239, 3647 and 4057 mg/kg respectively than the raw chitosan beads (CB) which possess the SC of 1298 mg/kg with a minimum contact time of 10min. The sorption experiments were carried out in batch mode to optimize various influencing parameters viz., contact time, pH, common ions and temperature. The sorbents were characterized by FTIR and SEM with EDAX analysis. The modified chitosan beads remove chromium by means of electrostatic adsorption coupled reduction and complexation. The adsorption data was fitted with Freundlich and Langmuir isotherms. The calculated values of thermodynamic parameters indicate the nature of chromium sorption. A field trial was carried out with water collected from a nearby industrial area.

Preparation and characterization of silica gel/chitosan composite for the removal of Cu(II) and Pb(II)

Silica gel/chitosan composite (SiCS) was prepared via., sol-gel method by mixing silica gel and chitosan and cross-linked with bifunctional cross-linker glutaraldhyde. The SiCS composite was characterized using FT-IR, SEM-EDAX, XRD and BET methods. The sorption of copper and lead ions onto SiCS has been investigated. The SiCS composite was found to have excellent metal sorption capacity than the silica gel (Si) and chitosan (CS). The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, pH, initial metal ion concentration, co-ions and temperature that influence the sorption. Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models were applied to describe isotherm constants. Equilibrium data agreed well with the Freundlich isotherm model. Thermodynamic studies revealed that the nature of sorption is spontaneous and endothermic. The SiCS removes metals by means of adsorption and complexation. Sorption capacity of SiCS is compared with other sorbents which suggest that this composite was useful for removing copper and lead from aqueous solution.

Sorption behaviour of fluoride on carboxylated cross-linked chitosan beads.

Carboxylated cross-linked chitosan beads (CCB) showed a significant defluoridation capacity (DC) of 1385 mgF(-)/kg than the raw chitosan beads (CB) which displayed only 52 mgF(-)/kg. Sorption experiments were performed by varying contact time, pH, presence of co-anions and temperature. The nature and morphology of the sorbent were discussed using FTIR and SEM with EDAX analysis. The stability of the beads in solution was explained in terms of swelling ratio of the beads. The fluoride uptake onto CCB obeys both Freundlich and Langmuir isotherms. Thermodynamic studies revealed that the nature of fluoride sorption is spontaneous and endothermic. Sorption kinetics is mainly controlled by pseudo-second-order and intraparticle diffusion models. 0.1M HCl was identified as the best eluent. The suitability of CCB at field conditions has been tested with field sample collected from a nearby fluoride-endemic area.

Preparation and application of alumina/chitosan biocomposite.

A new chitosan based biocomposite was prepared using alumina and used for the removal of chromium from the aqueous solution. The synthesized alumina/chitosan (AlCs) composite possesses an enhanced chromium sorption capacity (SC) of 8.62 mg/g than the original alumina and chitosan flakes that possess the SCs of 3.7 and 0.67 mg/g respectively, with a minimum contact period of 30 min. The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, initial chromium concentration, pH, co-ions and temperature that influence the sorption. The sorbents were characterized by FTIR, AFM, BET and SEM with EDAX analysis. The composite removes chromium by means of electrostatic adsorption coupled reduction and complexation. The adsorption data were fitted with Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. The calculated values of thermodynamic parameters indicate the nature of chromium sorption. The dynamic studies demonstrate that the sorption process follows pseudo-second-order and intraparticle diffusion models.

Role of metal ion incorporation in ion exchange resin on the selectivity of fluoride

Indion FR 10 resin has sulphonic acid functional group (H(+) form) possesses appreciable defluoridation capacity (DC) and its DC has been enhanced by chemical modification into Na(+) and Al(3+) forms by loading respective metal ions in H(+) form of resin. The DCs of Na(+) and Al(3+) forms were found to be 445 and 478 mg F(-)/kg, respectively, whereas the DC of H(+) form is 265 mg F(-)/kg at 10 mg/L initial fluoride concentration. The nature and morphology of sorbents are characterized using FTIR and SEM analysis. The fluoride sorption was explained using the Freundlich, Langmuir and Redlich-Peterson isotherms and kinetic models. The calculated thermodynamic parameters such as DeltaG degrees, DeltaH degrees, DeltaS degrees and sticking probability (S(*)) explains the nature of sorption. Comparison was also made by the elution capacity of these resins in order to select a cost effective material. A field trial was carried out to test the suitability of the resins with fluoride water collected from a nearby fluoride-endemic area.