Removal of the Water‐Soluble Plastic Pollutant Poly(vinyl alcohol) Using Kaolinite: Physicochemical Effects and Adsorption Mechanisms

The adsorption behavior of poly(vinyl alcohol) (PVOH), a representative water‐soluble plastic, onto kaolinite clay was systematically investigated under varying physicochemical conditions. Four PVOH fractions with molecular masses ranging from 49 to 125 × 10 ³  g mol ^–1 were evaluated to determine the effects of pH, electrolyte concentration, thermal treatment, homogenization, and ultrasonication on adsorption performance. Adsorption equilibrium and kinetic analyses showed that the Langmuir isotherm ( R ²  > 0.99) and pseudo‐second‐order kinetic model ( R ²  > 0.99584) best described the adsorption process. Adsorption capacity increased with polymer molecular mass and decreased by approximately 18% as pH increased from 2 to 10 due to increasing negative surface charge and electrostatic repulsion. Elevated electrolyte concentrations reduced adsorption through ionic competition and active‐site blockage. In contrast, ultrasonication and thermal pretreatment significantly enhanced adsorption by increasing surface area and surface charge density. Spectroscopic and physicochemical analyses confirmed that hydrogen bonding between PVOH hydroxyl groups and kaolinite silanol/aluminol groups, together with van der Waals interactions, dominated the adsorption mechanism. These findings demonstrate the potential of modified kaolinite as a sustainable and low‐cost adsorbent for mitigating soluble plastic pollution.