Polyethyleneimine (PEI) has a wide range of applications in the water treatment industry. Its core value lies in its unique molecular structure: as a water-soluble cationic polymer, it carries a high density of positive charges, enabling it to efficiently neutralize, adsorb, or chelate various negatively charged pollutants in water. It is often used as a raw material for chemical modification or combined with other materials to improve treatment efficiency and reduce costs.
Ⅰ. Heavy Metal Ion Removal: Efficient Capture via Multiple Mechanisms
The abundant amine groups (-NH₂) on the PEI molecular chain can efficiently capture heavy metal ions through chelation, forming stable flocculent precipitates for removal. Common applications include:
1. Chemical Modification
Reacting PEI with carbon disulfide (CS₂) produces sodium polyethyleneimine xanthate (PEX), a polymeric flocculant that can simultaneously remove multiple heavy metal ions and turbidity. For example, studies have shown its effectiveness in treating copper-containing wastewater, demonstrating excellent dual functions of copper and turbidity removal.
2. Material Composites
Loading PEI onto alginate gel beads achieves an adsorption capacity of 565.0 mg/g for Pb²⁺. Furthermore, ultraporous cryogels prepared from PEI can simultaneously adsorb and remove multiple heavy metal ions such as Cd(II) and Co(II) from wastewater.
Ⅱ. Dye Wastewater Treatment
The Main Force of Electrostatic Adsorption Dyes in dyeing and printing wastewater are mostly negatively charged. PEI, as a cationic adsorbent, achieves efficient adsorption through electrostatic attraction.
1. PEI-Modified Materials
Adsorbents prepared by grafting PEI onto styrene-maleic anhydride copolymer (SMA) exhibit good adsorption performance for anionic dyes.
2. Bio-Based Composite Materials
PEI, obtained by grafting PEI onto zein, achieves an adsorption capacity of 631.0 mg/g for Reactive Black 5 (RB5) dye. In addition, novel materials such as PEI-modified pectin magnetic microspheres also demonstrate excellent dye adsorption performance.
Ⅲ. Membrane Separation Technology
From Basic Materials to Functional Coatings
Polyethyleneimine PEI is a key material for preparing high-performance water treatment membranes. It can be used as a coating, additive, or reactive monomer to significantly improve membrane separation efficiency and antifouling capabilities.
1. As a functional coating
A positively charged separation layer can be constructed on the membrane surface to create a positively charged nanofiltration membrane, which can effectively retain positively charged pollutants in water, such as certain dyes and polyvalent cations, and improve antifouling performance.
2. For interfacial polymerization
As a reactive monomer, it can undergo interfacial polymerization with pyromellitic chloroformyl chloride, forming a dense separation layer on the base membrane to create a composite nanofiltration membrane for water filtration and purification.
3. As a hydrophilic modification additive
Grafting PEI onto nanoparticles and then mixing it into the casting solution can prepare nanocomposite membranes with stronger hydrophilicity and better antifouling capabilities.
Ⅳ. Flocculation and Coagulation
Enhancing Coagulation: PEI neutralizes the negative charge of suspended particles in water, destabilizing them and causing them to aggregate into large flocs, accelerating sedimentation. It is often used as a coagulant or coagulant aid in the pretreatment stage of water supply and wastewater treatment.
Ⅴ. Challenges and Solutions in Application
Despite the powerful functions of PEI, some challenges exist in practical applications, requiring targeted solutions:
Technical Challenges: When used as a membrane material, the high charge density of PEI can lead to an overly dense selective layer, reducing permeability.
Cost Control: Direct use of pure PEI is costly; therefore, chemical modification or composite treatment is key to its economical and efficient application.
Usage Conditions: Application effectiveness is easily affected by the pH value of the water and coexisting substances (such as humic acid), requiring optimization of process parameters for specific water quality.
