Design, Synthesis, and Evaluation of Novel Magnetic Nanoparticles Combined with Thiophene Derivatives for the Removal of Cr(VI) from an Aqueous Solution

Abstract

Most heavy metals are harmful to human health and the environment, even at extremely low concentrations. In natural waters, they are usually found only in trace amounts. Researchers are paying great attention to nanotechnology and nanomaterials as viable solutions to the problem of water pollution. This research focuses on the synthesis of organic thiophene derivatives that can be used as grafted ligands on the surface of silica-coated iron oxide nanoparticles to remove Cr(VI) chromium ions from water. The Vilsmeier-Haack reaction allows the formation of aldehyde groups in thiophene derivatives, and the resulting products were characterized by the FT-IR, NMR, and GC-MS. Schiff base is used as a binder between organic compounds and nanoparticles by the reaction of aldehyde groups in thiophene derivatives and amine groups on the surface of coated iron oxide nanoparticles. Schiff base functionalized Fe₃O₄ composites (MNPs@SiO₂-SB-THCA) and (MNPs@SiO₂-SB-THCTA) were successfully synthesized by homogeneous and heterogeneous methods and characterized by a combination of FT-IR, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The adsorption studies, kinetic modeling, adsorption isotherms, and thermodynamics of the two materials, MNPs@SiO₂-SB-THCA and MNPs@SiO₂-SB-THCTA, were investigated for the removal of Cr(VI) from water at room temperature and at 50 mg/L. The high adsorption capacity at pH 6 for MNPs@SiO₂-SB-THCTA was 15.53 mg/g, and for MNPs@SiO₂-SB-THCA, it was 14.31 mg/g.

Scheme 1. Illustration of Novel Synthesized Compounds (a) 5-Formylthiophene-2-carbothioamide, (b) SB-THCA, and (c) SB-THCTA

Figure 1

FT-IR spectra of (a) Fe₃O₄, Fe₃O₄@SiO₂–NH₂, MNPs@SiO₂-SB-THCA, and MNPs@SiO₂-SB-THCTA (heterogeneous method) and (b) Fe₃O₄@SiO₂, SB-THCA, SB-THCTA, MNPs@SiO₂-SB-THCA, and MNPs@SiO₂-SB-THCTA (homogeneous method).

Figure 2

(a,b) and (c,d) ¹H NMR and ¹³C NMR spectra of 5-formylthiophene-2-carboxamide and 5-formylthiophene-2-carbothioamide, respectively.

Figure 3

XRD spectra of Fe₃O₄, Fe₃O₄@SiO₂, MNPs@SiO₂-SB-THCA, and MNPs@SiO₂-SB-THCTA.

Figure 4

TEM images with size distribution of (A) MNPs@SiO₂-SB-THCA (heterogeneous method), (B) MNPs@SiO₂-SB-THCA (homogeneous method), (C) MNPs@SiO₂-SB-THCTA (heterogeneous method), and (D) MNPs@SiO₂-SB-THCTA (homogeneous method).

Figure 5

XPS spectra of (a–d) MNPs@SiO₂-SB-THCA (heterogeneous and homogeneous methods) and (e–h) MNPs@SiO₂-SB-THCTA (heterogeneous and homogeneous methods).

Figure 6

TGA graph of the MNPs@SiO₂-SB-THCA and MNPs@SiO₂-SB-THCTA in the temperature range from 25 to 700 °C.

Figure 7

EDX spectra, mapping images of all elements, and atomic percentages of (a) SB-THCA and (b) SB-THCTA.

Figure 8

Optimization parameters for adsorption of Cr(VI) on the surface of MNPs-SiO₂-SB-THCA and MNPs-SiO₂-SB-THCTA (a) effect of the initial concentration of Cr(VI) solution, (b) effect of contact time (min), (c) effect of adsorption dosage (mg/L), and (d) effect of the initial pH of Cr(VI) solution in the range of 2–8.

Figure 9

Possible mechanism of Cr(VI) removal using MNPs@SiO₂-SB-THCA and MNPs@SiO₂-SB-THCTA.

Figure 10

Influence metal cation on (a) MNPs@SiO₂-SB-THCA and (b) MNPs@SiO₂-SB-THCTA adsorption of Cr(IV), pH 6, adsorbent dose 10 mg, contact duration 180 min, temperature 298 K, ion concentration 5 ppm, and Cr(VI) concentration 50 ppm.

Figure 11

Recyclability of the synthesized MNPs-SiO₂-SB-THCA and MNPs-SiO₂-SB-THCTA.