Influence of crosslinker chemistry on the adsorption performance of vinyl carbazole-derived hyper-crosslinked polymers

Developing effective adsorbents for dye-polluted wastewater remains an important environmental challenge. In this work, two hyper-crosslinked polymers (HCPs), Cz–CH and Cz–CY, were synthesized via Friedel–Crafts polymerization of vinyl carbazole (Cz) with chloranil (CH) and cyanuric chloride (CY) as crosslinkers, respectively. The obtained polymers exhibit high surface areas (453.6 and 388.1 m² g⁻¹) and mesoporous structures with pore widths of 4.49 and 3.50 nm. Morphological analysis reveals distinct structural features, with Cz–CH forming spherical particles, while Cz–CY displays sheet-like and tubular morphologies. The adsorption performance toward Rhodamine B (RhB) was systematically evaluated using kinetic, isotherm, and diffusion models. Cz–CH HCP demonstrates rapid adsorption equilibrium within 5 min and a high maximum capacity of 1339 mg g⁻¹, whereas Cz–CY HCP shows a lower capacity of 797 mg g⁻¹ with a slower, diffusion-influenced uptake process. Kinetic analysis reveals distinct behaviors for the two materials: Cz–CH predominantly follows a pseudo-first-order model, associated with fast diffusion and surface adsorption, while Cz–CY shows a better fit to the pseudo-second-order model, indicating a stronger contribution from chemisorption alongside diffusion limitations. In both cases, intraparticle diffusion is not the sole rate-limiting step. The equilibrium data for both polymers are well described by the Langmuir isotherm, suggesting monolayer adsorption on relatively uniform active sites. These findings highlight the critical role of crosslinker chemistry in tuning pore structure, adsorption kinetics, and interaction mechanisms, offering valuable insights for the design of efficient porous polymer adsorbents for dye removal under model conditions.