Chitosan-Thiobarbituric Acid: A Superadsorbent for Mercury

Abstract

In the present investigation, chitosan (CH) was supramolecularly cross-linked with thiobarbituric acid to form CT. CT was well characterized by UV, scanning electron microscopy-energy-dispersive X-ray analysis, Fourier transform infrared, NMR, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction analyses, and its adsorption potential for elemental mercury (Hg⁰), inorganic mercury (Hg²⁺), and methyl mercury (CH₃Hg⁺) was investigated. Adsorption experiments were conducted to optimize the parameters for removal of the mercury species under study, and the data were analyzed using Langmuir, Freundlich, and Temkin adsorption isotherm models. CT was found to have high adsorption capacities of 1357.69, 2504.86, and 2475.38 mg/g for Hg⁰, Hg²⁺, and CH₃Hg⁺, respectively. The adsorbent CT could be reused up to three cycles by eluting elemental mercury using 0.01 N thiourea, inorganic mercury using 0.01 N perchloric acid, and methyl mercury with 0.2 N NaCl.

Scheme 1. Synthesis of CT Adsorbent

Figure 1

FTIR analysis of CH, CT, and mercury-loaded CT.

Figure 2

EDX spectra of (a) CT, (b) CT-Hg⁰, (c) CT-Hg²⁺, and (d) CT-CH₃Hg⁺.

Figure 3

NMR analysis.

Figure 4

DSC analysis.

Figure 5

XRD analysis.

Figure 6

Effect of pH variation.

Figure 7

Effect of Time Variation on the adsorption of the mercury species under study onto CT.

Figure 8

Desorption Studies of CT-Hg⁰, CT-Hg²⁺, and CT-CH₃Hg⁺.

Figure 9

Uptake of Different Metals onto CT.

Figure 10

Uptake of different metals in a synthetic mixture containing Hg²⁺, CH₃Hg⁺, Cu²⁺, Cd²⁺, Pb²⁺ and Zn²⁺.

Scheme 2. Elemental Mercury Uptake Procedure