Polysaccharides like starch, chitosan, and pectin are attractive for removing heavy metal ions from water. Chitosan (n+) is mixed with pectin (n−) to enhance ion adsorption from aqueous media. This study involves two parts. First, 1 g/L stock solutions of pectin and chitosan at pH 5 are prepared and used to create polyelectrolyte complexes (PECs) with varying molar charge ratios (n−/n+). Pectin is added to stirred chitosan solutions to form PECs, relying on ionic interactions between chitosan's amino groups and pectin's carboxyl groups. However, the resultant PEC concentration is insufficient for effective heavy metal ion removal. In response, the second part of the study focuses on a specific PEC with n−/n+ of 0.84. The stock solution concentration is increased to 5 and 10 g/L at pH 5, enhancing efficiency and forming a gel. The gel dispersion is freeze‐dried, and the resultant PECs are used for adsorption experiments with Cd²⁺, Ni²⁺, Fe^2+/3+, Mn²⁺, and Cu²⁺ sulfate solutions. Adsorption rates are in the order Cu²⁺ > Fe^2+/3+ > Cd²⁺ > Ni²⁺ > Mn²⁺ for a 20 mg/L salt concentration, indicating high PEC affinity for heavy metal ions.

The separation of toxic pollutants such as Pb²⁺, Cd²⁺, and Al³⁺ from water is a constant challenge as contamination of natural water bodies is increasing. Al³⁺ and especially Pb²⁺ and Cd²⁺ are ecotoxic and highly toxic for humans, even in ppb concentrations, and therefore removal below a dangerous level is demanding. Herein, the potential adsorber material starch, being ecofriendly, cheap, and abundantly available, was investigated. Thus, four different native starch samples (potato, corn, waxy corn, and wheat starch) and two oxidized starches (oxidized potato and corn starch) were comprehensively analyzed with streaming potential and charge density measurements, SEM-EDX, ATR-FTIR, ¹H-NMR, and TGA. Subsequently, the starch samples were tested for the adsorption of Pb²⁺, Cd²⁺, and Al³⁺ from the respective sulfate salt solution. The adsorption process was analyzed by ICP-OES and SEM-EDX, and the adsorption isotherms were fitted comparing Langmuir, Sips, and Dubinin-Radushkevich models. Oxidized starch, for which chemical modification is one of the simplest, and also native potato starch were excellent natural adsorber materials for Al³⁺, Cd²⁺, and especially Pb²⁺ in the low concentration range, exhibiting maximum adsorption capacities of 84, 71, and 104 µmol/g for oxidized potato starch, respectively.

Polyelectrolyte complexes (PECs) have gained increasing attention in recent decades due to their importance in various applications, such as water treatment and paper processing. These complexes are formed by mixtures of polycations (n+) and polyanions (n−), known as polyelectrolytes (PEs). In this study, a series of PECs were prepared with different molar charge ratios (n−/n+) using biopolymers such as chitosan (lch) and pectin (p) at pH 5, in addition to the synthetic polymer poly(ethylene alt maleic acid) (PEMA) at the same pH. Two types of chitosan—low molecular weight chitosan (lch) and high molecular weight chitosan (hch)—were used as polycations, and these were mixed with two types of pectin with either a high esterification degree (hp) or a low esterification degree (lp), as well as PEMA as polyanions. These components interacted via electrostatic forces to form the following PEC combinations: (lch&lp), (lch&hp), (hch&hp), and (lch&PEMA). The charge density, turbidity, and particle size of the formed PECs were examined to evaluate the influence of molecular weight and mixing speed on the formation process.

The adsorption of heavy metal ions from surface water with ecologically safe and biodegradable biopolymers is increasingly becoming an appealing research challenge. Starch as a biopolymer is exceptionally attractive to solve this problem for its low cost and abundant availability in nature. To expel Ni²⁺, Fe^2+/3+, and Mn²⁺ from water, we analyzed two native and two oxidized starches, namely potato and corn starch, as bio-adsorbers. The morphology and the surface property of the different starches were studied using SEM. To assess the effectiveness of adsorption onto the starches, we tested three realistic concentrations based on German drinking water ordinance values that were 10-fold, 100-fold, and 1000-fold the limits for Mn²⁺, Fe²⁺, and Ni²⁺, respectively. The concentration of the different ions was measured using the ICP-OES. Furthermore, from subsequent investigations of the adsorption isotherms, we evaluated the adsorption capacities and mechanisms. The adsorption isotherms were fitted using the Langmuir, Sips, and Dubinin–Radushkevich models, whereby Sips showed the highest correlation. Oxidized potato starch achieved viable adsorption capacities of 77 µmol Fe²⁺/g, 84 µmol Mn^2+/g, and 118 µmol Ni^2+/g. Investigating the influence of initial swelling in water on the adsorption performance, we found that especially the percentage removal with oxidized starches decreased significantly due to the formation of hydrogen bonds with water molecules at their binding sites with prior swelling.

Providing safe drinking water free of heavy metal ions like iron and oxyanions like sulfate has become a worldwide issue. Starch, as one of the widely cheapest and available biomaterials, has demonstrated its capability to adsorb heavy metal ions from water in various scientific research, but in low adsorption rates. Therefore, this paper aims to prepare a biopolymer based on a starch–chitosan blend to raise the adsorption efficiency of starch. Two types of chitosan were used to modify potato starch (ps): low molecular chitosan (ch60) and high molecular chitosan (ch4000). Nano potato starch (n.ps) was prepared from potato starch and was also modified with both chitosans. The surface property, the morphology, the particle size, and the structure of the samples were analyzed. Moreover, the investigation of the samples by the zeta potential and charge density were evaluated to determine the charge of the adsorbents’ surface. Furthermore, the pseudo first order (PFO) and pseudo second order (PSO) were employed to examine the adsorption kinetic. The adsorption isotherms of Fe^2+/3+ and SO₄²⁻ were fitted employing Langmuir, Sips, and Dubinin-Radushkevich adsorption models. The maximum achieved sorption capacities from the FeSO₄ solution for Fe^2+/3+ were as follows: 115 mg/g for n.ps & ch4000, 90 mg/g for ps & ch4000, 80 mg/g for n.ps & ch60, and 61 mg/g for ps & ch60. Similarly, for SO₄²⁻, it was 192 mg/g for n.ps & ch4000, 155 mg/g for n.ps & ch60, 137 mg/g for ps & ch4000, and 97 mg/g for ps & ch60.