Polymeric Nanocomposite Materials for the Removal of Hexavalent Chromium

Sahu, Sumanta (2021) Polymeric Nanocomposite Materials for the Removal of Hexavalent Chromium. PhD thesis.

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Abstract

Water pollution due to heavy metals is a global concern in degrading nature’s resources and is causing serious threat to living organisms. Hexavalent chromium (Cr(VI)) is a highly toxic heavy metal contaminant to which millions of people are exposed all over the world. Even short-term exposures to Cr(VI) can lead to DNA mutation and damages genetic information causing cancerous tumours. Therefore, Cr(VI) remediation is one among the major concerns for researcher. In this thesis, the synthesis and application of polymeric nanocomposite based novel materials has been described for sequestration of hexavalent chromium by adsorptive route. Initially, the polymeric nanocomposite of thorium oxide polyaniline and lanthanum phosphate polyaniline are synthesised by taking aniline as organic component and thorium oxide and lanthanum phosphate nanoparticles as inorganic constituents. Later, the polymeric nanocomposite of polypyrrole layered double hydroxide and cerium phosphate polypyrrole nanocomposite are developed by pyrrole as organic component and layered double hydroxide and cerium phosphate nanoparticles as inorganic components. The structural, functional, morphological, textural and thermal stability of the as-prepared materials are evaluated by XRD, FESEM, EDX, TEM, TGA- DTA, FTIR, Raman, XPS, Zeta potential, N2 sorption isotherm and other instrumental analysis. The core shell thorium oxide polyaniline nanocomposite is synthesized using aniline as a favourable conducting polymer by situ polymerization method and used for the removal of Cr(VI) from water. The thorium oxide polyaniline nanocomposite effectively adsorb Cr(VI) ions through electrostatic attractions, which are partially reduced to Cr(III) during the adsorption experiment. The synthesized nanocomposite material exhibits high uptake capacity towards Cr(VI) as compared to other reported materials. The Langmuir isotherm model follows the adsorption process better than the Freundlich isotherm with maximum adsorption capacity of 141 mg g-1. Thermodynamic parameters are also computed which indicated the spontaneous and the endothermic nature of the adsorption process. A novel lanthanum phosphate polyaniline nanocomposite is synthesised by the simple sol-gel technique and used for selective adsorption of Cr(VI). The selectivity is estimated by evaluating the distribution coefficient, electrical double layer theory as well as valency and Pauling’s ionic radii of interfering ions (phosphate, iodide, sulfate, chloride, sulfide). The high tolerance capability of lanthanum phosphate polyaniline against the interfering ions make it appropriate for efficient removal of Cr(VI) ions. The nanocomposite shows the highest removal percentage of 98.6% towards Cr(VI) at room temperature. The XPS analysis reveals the adsorption mechanism due to the combined effect of both adsorption and reduction. Cr(VI) is adsorbed through electrostatic interactions while the =N-/-NH- group facilitated the in situ chemical reduction. Polypyrrole modified Mg-Al layer double hydroxides material is synthesized via in-situ oxidative polymerization method followed by microwave irradiation. The material is then used as an adsorbent for Cr(VI) removal at varying temperatures. The maximum Langmuir adsorption capacity of PPY-LDHs is calculated as 76.21 mg g-1. The high distribution coefficient value (> 104 mL g−1) reveals the great affinity for Cr(VI). The adsorption mechanism is proposed which asserts that the removal of Cr(VI) onto the adsorbent is a combine effect of reduction of Cr(VI) to Cr(III) and chemical sorption which takes place through ion-exchange in the interlayer regions and over the surface through electrostatic attractions and hydrogen bonding. Flower like cerium phosphate polypyrrole nanocomposite material is synthesized by in situ oxidative polymerization method and used for sequestration for Cr(VI). Field emission scanning electron microscopy and transmission electron microscopy images reveal the flower-like morphology of the synthesized nanocomposite. Meanwhile, the fabrication of polypyrrole on cerium phosphate nanoparticles provides a plentiful of active adsorption sites to interact with hexavalent chromium ions. The Cr(VI) adsorption follows Langmuir isotherm model showing a high adsorption capacity of 117.78 mg g-1 at room temperature at low pH. The adsorption dynamic study demonstrates that the rate- determining step of adsorption is controlled by surface diffusion, pore diffusion and film diffusion. XPS spectra confirmed the simultaneous adsorption of Cr(VI) and in situ chemical reduction to Cr(III). Regeneration studies illustrate the efficiency of more than 80%, even after five cycles. All the above synthesized materials are effectively adsorbed Cr(VI) ions from water. Therefore, these materials could be a unique alternative to act as an ideal adsorbent for the effective treatment of Cr(VI) containing wastewater.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Nanocomposite; Polymer nanocomposite; Heavy metals; Cr(VI); Adsorption; reduction; Distribution coefficient; Kinetic study; Isotherm study; Thermodynamic study.
Subjects:Chemistry > Environmental Chemistry
Chemistry > Physical Chemistry > Nanoparticle Synthesis
Chemistry > Polymer Chemistry
Divisions: Sciences > Department of Chemistry
ID Code:10477
Deposited By:IR Staff BPCL
Deposited On:06 Oct 2025 12:45
Last Modified:06 Oct 2025 12:45
Supervisor(s):Patel, Raj Kishore

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