Evaluation of Inulin Replacing Chitosan in a Polyurethane/Polysaccharide Material for Pb2+ Removal

Abstract

Downstream waste from industry and other industrial processes could increase concentration of heavy metals in water. These pollutants are commonly removed by adsorption because it is an effective and economical method. Previously, we reported adsorption capacity of a chitosan/polyurethane/titanium dioxide (TiO₂) composite for three ions in a dynamic wastewater system. There, increasing the chitosan concentration in composite increased the cation removal as well; however, for ratios higher than 50% of chitosan/TiO₂, the manufacturing cost increased significantly. In this work, we address the manufacturing cost problem by proposing a new formulation of the composite. Our hypothesis is that inulin could replace chitosan in the composite formulation, either wholly or in part. In this exploratory research, three blends were prepared with a polyurethane matrix using inulin or/and chitosan. Adsorption was evaluated using a colorimetric method and the Langmuir and Freundlich models. Fourier-transform infrared spectroscopy (FTIR) spectra, scanning electron microscopy (SEM) micrographs, differential scanning calorimetry and thermogravimetric analysis curves were obtained to characterize blends. Results indicate that blends are suitable for toxic materials removal (specifically lead II, Pb²⁺). Material characterization indicates that polysaccharides were distributed in polyurethane's external part, thus improving adsorption. Thermal degradation of materials was found above 200 °C. Comparing the blends data, inulin could replace chitosan in part and thereby improve the cost efficiency and scalability of the production process of the polyurethane based-adsorbent. Further research with different inulin/chitosan ratios in the adsorbent and experiments with a dynamic system are justified.

Keywords: composite; heavy metals; lead pollution; polysaccharide; wastewater treatment.

Figure 1

Scanning Electron Microscopy SEM images at 50× for blends materials; (a) blend with inulin; (b) blend with chitosan and (c) blend inulin/chitosan, all samples were synthesized at 353.15 K; and (d) weight loss on mechanical stirring testaccording ASTM D-2042 norm.

Scheme 1

Reaction scheme for the polyurethane reaction. This schematic is based on reaction mechanisms descriptions for blocked mono-component polyurethane reported by Radice, et al. [30].

Figure 2

(a) Fourier Transform Infrared Spectroscopy (FTIR) spectra of the pure components used for manufacturing the materials; (b) FTIR spectra of blends components. PI = polyurethane/inulin, PC = polyurethane/chitosan, and PCI = polyurethane/chitosan/inulin.

Figure 3

On the right; TG curves of the thermal degradation and on the left; DTG curves of the thermal degradation of blends.

Figure 4

Removal conditions of Pb(II) ions by 192 mg of PC, PI or PCI material using λ = 249 nm as maximum absorbance at pH = 7.8 and 25 °C. C = ion Lead concentration; C₀ = Pb²⁺ initial concentration, 10 mg/L; C/C₀ = Pb²⁺ fractional removal; t = contact time between material and lead solution.

Figure 5

(a) Time-dependent adsorption capacity at 25 °C; (b) Adsorption capacity, varying initial concentration of lead II(Pb²⁺).

Scheme 2

Possible interaction between inulin-chitosan and Pb(II).

Figure 6

Recycling of blends; adsorption/desorption capacity for four cycles at 25 °C.

Scheme 3

Process schematic of polyurethane-based composites manufacturing.