📄 chemistry

Enhanced removal of iodine from wastewater in the presence of two-step sulfo and amine functionalized polyvinylchloride

This study demonstrates the synthesis and characterization of a novel sulfo- and amine-functionalized polyvinyl chloride sorbent that effectively removes radioactive iodine from wastewater, achieving a maximum adsorption capacity of 705 mg/g through a process best described by Langmuir isotherm and pseudo-second-order kinetic models.

Original authors: Davronbek Bekchanov, Suyun Khushvaktov, Abdulla Saidov, Changhua An, Xintai Su, Peter Lieberzeit, Mukhtarjan Mukhamediev

Published 2026-07-30

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CC BY 4.0

Original authors: Davronbek Bekchanov, Suyun Khushvaktov, Abdulla Saidov, Changhua An, Xintai Su, Peter Lieberzeit, Mukhtarjan Mukhamediev

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the world of water treatment as a giant, bustling city where clean water is the lifeblood, but sometimes, dangerous "ghosts" sneak into the pipes. These ghosts are radioactive iodine atoms, invisible troublemakers that can slip out of hospitals and nuclear facilities, threatening to make people sick if they end up in our drinking water or the environment. To catch these ghosts, scientists act like detectives using special nets called "sorbents." Think of a sorbent not as a simple sponge, but as a high-tech Velcro strip or a magnetic trap designed to grab specific bad guys while letting the good guys swim by. The challenge is making these nets strong enough to hold onto the slippery radioactive iodine, cheap enough to use in huge quantities, and reusable so we don't just throw them away after one use. This is the corner of science where chemistry meets environmental protection, trying to build a better, smarter net to keep our water safe.

In this study, a team of researchers decided to build a brand-new kind of net using a very common material: plastic. Specifically, they took Polyvinyl Chloride (PVC)—the same tough plastic used in pipes and raincoats—and gave it a magical makeover. They didn't just coat it; they performed a two-step surgery on the plastic's molecular structure. First, they added "sulfonic acid" groups (think of these as tiny, sticky negative magnets), and then they attached "amine" groups (which act like positive hooks). The result was a new material they called PVC-(SO3H)-NH-PАМ, a "polyampholyte" that is essentially a plastic sponge with both positive and negative traps built right into its skin.

The researchers tested this new super-sponge to see how well it could catch triiodide ions (a form of iodine found in wastewater). They found that this modified plastic was an absolute champion at its job. In their experiments, it managed to grab a massive amount of iodine—up to 705 milligrams for every single gram of the plastic. That's like a tiny pebble catching a whole bucket of marbles. The study showed that the plastic worked best when the water was slightly neutral (around pH 6 to 7), acting like a perfect dance partner for the iodine ions. The scientists also discovered that the plastic didn't just sit there; it actively grabbed the iodine through a chemical handshake, a process that happened faster and more completely than simple surface sticking.

One of the coolest parts of the story is that this new net is incredibly tough and reusable. The researchers put the plastic through ten rounds of catching iodine and then washing it clean to use again. Even after ten cycles, it still caught 90% of the iodine, proving it doesn't fall apart easily. They even tested it on real wastewater from a medical clinic in Uzbekistan, where the water started with a high concentration of iodine (162 mg/L). After using the plastic, the iodine levels dropped significantly, bringing the water closer to safety standards. The study suggests that this material could be a long-term, eco-friendly solution for cleaning up toxic iodine from medical wastewater, offering a way to turn a common, cheap plastic into a powerful guardian for our water.

Technical Summary: Enhanced Removal of Iodine from Wastewater Using Two-Step Sulfo and Amine Functionalized Polyvinylchloride

Problem Statement
The release of radioactive iodine isotopes (specifically $^{129}\text{I}$ and $^{131}\text{I}$ ) from medical, disinfection, and nuclear industries poses significant environmental and health risks, including thyroid cancer and metabolic disorders. While various purification methods exist, such as ion exchange, adsorption, and membrane separation, many existing sorbents based on metal oxides or metal-organic frameworks (MOFs) are expensive, unstable, or difficult to synthesize. Although polymer-based ion exchangers offer a cost-effective alternative, the specific application of modified polyvinyl chloride (PVC) for the efficient removal of radioactive iodine from wastewater has not been extensively studied.

Methodology
The study focuses on the synthesis and characterization of a novel polyampholyte sorbent, designated as PVC-(SO $_3$ H)-NH-PАМ, derived from a two-step modification of commercial PVC (brand I40-13A).

Synthesis:
- Step 1 (Sulfonation): PVC was modified with sulfur powder (2:1 mass ratio) at 433 K for 6 hours to introduce sulfide and hydrosulfide groups. These were subsequently oxidized using nitric acid to form a sulfocation exchanger (PVC-SO $_3$ H).
- Step 2 (Amination): The PVC-SO $_3$ H was reacted with polyethylenepolyamine (PEPA) in a 70–80% solution at 423–433 K for 5–6 hours to introduce amine groups, resulting in the final polyampholyte.
Characterization: The material was analyzed using FTIR, SEM-EDX, TGA, DSC, BET, and BJH surface analysis to determine structural, morphological, and physicochemical properties.
Adsorption Studies: Experiments were conducted using artificial triiodide ( $\text{I}_3^-$ ) solutions. Kinetics were evaluated using pseudo-first-order and pseudo-second-order models. Equilibrium data were fitted to Langmuir and Freundlich isotherm models. Thermodynamic parameters ( $\Delta G$ , $\Delta H$ , $\Delta S$ ) were calculated at temperatures of 293 K, 303 K, and 313 K.
Practical Application: The sorbent was tested in a column for dynamic sorption and subjected to 10 cycles of sorption-desorption using NaOH and HCl. Finally, it was applied to real wastewater from a medical clinic in Uzbekistan containing 162 mg L $^{-1}$ of iodine.

Key Results

Reaction Kinetics and Activation Energy: The amination reaction of the sulfocation exchanger was determined to follow a reaction order of 1.1 with respect to PEPA concentration. The activation energy for this modification was calculated at approximately 70 kJ/mol, which is lower than the 138.5 kJ/mol reported for direct PVC modification with PEPA, suggesting that sulfo groups facilitate the reaction.
Material Properties: The synthesized polyampholyte possesses a mesoporous structure with a BET surface area of 5.50 m $^2$ g $^{-1}$ and a pore diameter of 14.58 nm. FTIR confirmed the presence of sulfo (-SO $_3$ H) and secondary/tertiary amine groups. Thermal analysis indicated the material is stable for industrial use, with decomposition beginning around 224°C.
Adsorption Performance:
- Capacity: The maximum adsorption capacity ( $q_{max}$ ) for $\text{I}_3^-$ ions was 705 mg g $^{-1}$ at 303 K.
- Isotherms: The adsorption data fit the Langmuir model best ( $R^2 = 0.9987$ ), indicating monolayer adsorption on a homogeneous surface. The separation factor ( $R_L$ ) indicated favorable adsorption.
- Kinetics: The process followed a pseudo-second-order kinetic model ( $R^2 > 0.999$ ), suggesting chemisorption involving valence forces through sharing or exchange of electrons between sorbent and sorbate.
- Thermodynamics: The positive enthalpy ( $\Delta H = 56.4$ kJ mol $^{-1}$ ) confirmed the endothermic nature of the process, while the negative Gibbs free energy ( $\Delta G$ ) indicated spontaneity.
pH Dependence: Maximum sorption efficiency (>80%) occurred in the pH range of 6–7. At low pH, sorption was negligible; at high pH, efficiency dropped due to the deprotonation of amino groups.
Reusability and Real-World Application: The sorbent maintained high efficiency over 10 sorption-desorption cycles. In real wastewater treatment, the material reduced iodine concentration from 162 mg L $^{-1}$ to below 42 mg L $^{-1}$ after 10 cycles, meeting World Health Organization standards (40–50 mg L $^{-1}$ ).

Significance and Claims
The paper claims that the synthesized PVC-(SO $_3$ H)-NH-PАМ represents a sustainable, environmentally friendly, and cost-effective solution for removing toxic iodine from medical wastewater. By utilizing a two-step modification of a widely available industrial polymer (PVC), the authors demonstrate a method that yields a high-capacity sorbent (705 mg g $^{-1}$ ) with excellent reusability. The study highlights that the bifunctional nature of the polyampholyte (containing both cationic and anionic groups) facilitates effective ion exchange and coordination bonding with iodine species. The authors conclude that this material is suitable for the long-term, effective purification of radioactive iodine from medical clinic wastewater, offering a practical alternative to more expensive or complex metal-based sorbents.

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