Removal of heavy metal ions in water by starch esters

Abstract

Corn starch has been modified with naturally occurring compounds, maleic acid (MA) and itaconic acid (IA), by esterification in an aqueous medium catalyzed by NaOH to produce adsorbents for heavy metals removal in water. The ester formation has been confirmed by wide angle x-ray scattering (WAXS), thermogravimetric analysis (TGA), Fourier Transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The effect of the mono and di-substitution with both acids, on the solubility and the swelling capacity of the modified starch have been investigated. The materials modified with maleic acid exhibited high water solubility, fact that made difficult their characterization and thus their application as adsorbents. In contrast, itaconate esters derivatives demonstrated superabsorbent characteristics and a typical polyelectrolyte behavior. Semiester derivative with greater content of carboxylic acid groups underwent the highest water uptake (H 1 ¼ 1292%). Additionally, the capability of the modified starches with itaconic acid to adsorb aqueous metal cations such as Ni 2þ , Zn 2þ , Cd 2þ , and Pb 2þ was investigated and the results were compared with the native corn starch. The modified and native starches exhibited reasonable adsorption capacity for all the cations. It was demonstrated that the native starch does not exhibit selectivity for any of the cations, whereas the itaconate starches remove higher content of Pb 2þ with the lowest hydration radius in comparison with other ions.

Influence of Chain Structures of Starch on Water Absorption and Copper Binding of Starch‐Graft‐Itaconic Acid Hydrogels

“…In general, the ability of adsorbent materials to bind metal cations depends on factors such as the ionic charge, electronegativity, and ionic radius of hydration of the metal, as well as the characteristics of the adsorbent. Unmodified starch can bind small amounts of metals by physical entrapment and weak electrostatic interactions . By grafting carboxylic groups onto the backbone of starch, it is expected to increase the strength of the attractive forces between the hydrogels and copper cations.…”

“…IA is an unsaturated dicarboxylic acid produced via the fermentation of carbohydrates with fungi . The research group of Soto et al has produced starch‐IA esters and hydrogels, and evaluated their potential for removal of metals from wastewater. However, the effect of the chains’ structure of starch has never been studied.…”

Removal of Heavy Metals from Industrial Waste Water by Biomass-Based Materials: A Review

“…The modified and native starches showed reasonable adsorption capacity for all the investigated cations. It was shown that the native starch did not exhibit selectivity for any of the cations, whereas the itaconate starches removed higher content of Pb +2 with the lowest hydration radius in comparison with other ions [64]. The structural formulae of the prepared esters are given below in Figure 9.…”

Eco‐Friendly Synthesis of Hydrogels from Starch, Citric Acid, and Itaconic Acid: Swelling Capacity and Metal Chelation Properties

“…Starch is naturally able to bind metal ions, mainly by the processes of physical entrapment along with minor electrostatic interactions . By incorporating carboxyl groups via the grafting of CA and IA, it was expected to increase the adsorption capacity.…”

“…[63][64][65] Starch is naturally able to bind metal ions, mainly by the processes of physical entrapment along with minor electrostatic interactions. [66] By incorporating carboxyl groups via the grafting of CA and IA, it was expected to increase the adsorption capacity. The grafting of carboxyl groups onto starch has been shown to increase its ion exchange capacity due to the enhanced electrostatic interactions between the adsorbent and the adsorbate.…”