Waste Fiber-Based Poly(hydroxamic acid) Ligand for Toxic Metals Removal from Industrial Wastewater

Abstract

Toxic metals in the industrial wastewaters have been liable for drastic pollution hence a powerful and economical treatment technology is needed for water purification. For this reason, some pure cellulosic materials were derived from waste fiber to obtain an economical adsorbent for wastewater treatment. Conversion of cellulose into grafting materials such as poly(methyl acrylate)-grafted cellulose was performed by free radical grafting process. Consequently, poly(hydroxamic acid) ligand was produced from the grafted cellulose. The intermediate products and poly(hydroxamic acid) ligand were analyzed by FT-IR, FE-SEM, TEM, EDX, and XPS spectroscopy. The adsorption capacity (q_e) of some toxic metals ions by the polymer ligand was found to be excellent, e.g., copper capacity (q_e) was 346.7 mg·g^-1 at pH 6. On the other hand, several metal ions such as cobalt chromium and nickel also demonstrated noteworthy sorption capacity at pH 6. The adsorption mechanism obeyed the pseudo second-order rate kinetic model due to the satisfactory correlated experimental sorption values (q_e). Langmuir model isotherm study showed the significant correlation coefficient with all metal ions (R² > 0.99), indicating that the single or monolayer adsorption was the dominant mode on the surface of the adsorbent. This polymer ligand showed good properties on reusability. The result shows that the adsorbent may be recycled for 6 cycles without any dropping of starting sorption capabilities. This polymeric ligand showed outstanding toxic metals removal magnitude, up to 90-99% of toxic metal ions can be removed from industrial wastewater.

Keywords: adsorption; heavy metals; poly(hydroxamic acid); waste fiber; wastewater.

Figure 1

Poly(hydroxamic acid) with metal complex as the ligand-Cu (left), ligand-Co (second left), ligand-Cr (third from left), and ligand-Ni (utmost right).

Scheme 1

Poly(methyl acrylate)-grafted cellulose and poly(hydroxamic acid)-metal complex (CL indicated an anhydroglucose unit).

Figure 2

FT-IR spectra of (a) waste cellulose, (b) poly(methyl acrylate)-grafted cellulose (c) poly(hydroxamic acid), and (d) poly(hydroxamic acid)-copper complex.

Figure 3

FE-SEM micrograph of (a) pure cellulose, (b) poly(methyl acrylate)-grafted cellulose, (c) poly(hydroxamic acid), and (d) poly(hydroxamic acid) ligand-copper complex.

Figure 4

(a) TEM micrograph and (b) energy-dispersive X-ray (EDX) spectra of poly(hydroxamic acid)-Cu(II) complex.

Figure 5

XPS spectra of (a) poly(hydroxamic acid) ligand and (b) poly(hydroxamic acid)-Cu(II).

Figure 6

O1s core-level XPS spectra of (a) poly(hydroxamic acid) ligand and (b) poly(hydroxamic acid)-Cu(II) complex.

Figure 7

N1s core-level XPS spectra of (a) poly(hydroxamic acid) ligand and (b) poly(hydroxamic acid)-Cu(II) complex.

Figure 8

The plot of sorption capacity versus various pH by poly(hydroxamic acid); experimental conditions: 100 mg of dried poly(hydroxamic acid), 10 mL of 0.1 M CH₃COONa buffer solution at pH 3–6, and 5 mL of 0.1 M heavy metal ion solutions agitated for 2 h.

Figure 9

The effect of different binding contact time of selected metal ions by poly(hydroxamic acid); experimental conditions: 100 mg of dried poly(hydroxamic acid), 10 mL of 0.1 M CH₃COONa buffer solution at pH 6, and 5 mL of 0.1 M heavy metal solutions agitated for 5, 15, 30, 60, and 120 min.

Figure 10

Pseudo-first-order kinetic plots of metal adsorption by polymer ligand; experimental conditions: 100 mg of poly(hydroxamic acid), 10 mL of 0.1 M CH₃COONa buffer solution, and 5 mL of 0.1 M heavy metal solution at pH 6 agitated for 2 h.

Figure 11

Pseudo-second-order kinetic plots of adsorption by polymer ligand; experimental conditions: 100 mg of poly(hydroxamic acid), 10 mL of 0.1 M CH₃COONa buffer solution, and 5 mL of 0.1 M heavy metal at pH 6 agitated for 2 h.

Figure 12

The effect of different initial heavy metals concentrations on adsorption by poly(hydroxamic acid) ligand; experimental conditions: 100 mg of dried poly(hydroxamic acid), 5 mL of 0.1 M CH₃COONa buffer solution, and 5 mL of 0.1 M heavy metal solutions (10, 300, 600, 1200 and 2400 ppm) at pH 6 agitated for 2 h.

Figure 13

Linear plots of Langmuir adsorption isotherm by poly(hydroxamic acid) ligand; experimental conditions: 100 mg of poly(hydroxamic acid), 5 mL of 0.1 M CH₃COONa buffer solution, and 5 mL of 0.1 M heavy metal solutions (10, 300, 600, 1200 and 2400 ppm) at pH 6 agitated for 2 h.

Figure 14

Linear plots of Freundlich adsorption isotherm by poly(hydroxamic acid) ligand; experimental conditions: 100 mg of poly(hydroxamic acid), 5 mL of 0.1 M CH₃COONa buffer solution, and 5 mL of 0.1 M heavy metal solutions (10, 300, 600, 1200, and 2400 ppm) at pH 6 agitated for 2 h.

Figure 15

Reusability study of poly(hydroxamic acid) ligand in 6 cycles of adsorption-desorption of cobalt ions.

Figure 16

Removal of metal ions in industrial wastewater samples by poly(hydroxamic acid) ligand.