Clean water is essential for human survival, yet wastewater often contains hazardous contaminants such as heavy metals and synthetic dyes, which pose significant risks to both environmental and public health. In response to the urgent need for effective water purification technologies, this study explores the development and application of functionalized variants of the prototypical polymer of intrinsic microporosity (PIM-1) for the removal of cationic species from aqueous media. Specifically, this work focuses on the synthesis, characterisation, and adsorption performance of hydrolysed PIM-1 (cPIM-1) and its novel alkylsulfonic acid derivatives, PS-cPIM-1 and BS-cPIM-1, for the removal of copper ions (Cu²⁺), Methylene Blue (MB⁺), and Safranin O (SO⁺).
PIM-1 was synthesised via aromatic nucleophilic substitution between 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane and 2,3,5,6-tetrafluoroterephthalonitrile. The resulting polymer was chemically modified through acid hydrolysis of the nitrile (-CN) groups to introduce carboxylic acid groups, yielding cPIM-1. Further functionalization was achieved through O-alkylation with either 1,3-propanesultone (PS) or 1,4-butanesultone (BS), introducing strong cation-exchange sulfonic acid groups to produce PS-cPIM-1/BS-cPIM-1. These modifications were confirmed using FT-IR, ¹H NMR, TGA, elemental analysis, and GPC for PIM-1 molecular weight distribution.
The adsorption performance of cPIM-1, PS-cPIM-1, and BS-cPIM-1 for Cu²⁺ was evaluated using UV-Vis spectroscopy with polyethyleneimine (PEI) as an indicator under conditions of pH 5.5–6.5 and 293 K. All materials followed the nonlinear Langmuir isotherm and pseudo-second-order kinetic (PSO) models. cPIM-1 exhibited a maximum adsorption capacity (qₘ) of 17 mg g⁻¹ and reached equilibrium within 15 minutes. In comparison, PS-cPIM-1 and BS-cPIM-1 achieved substantially higher capacities of 39 mg g⁻¹ and 43 mg g⁻¹, respectively, and reached equilibrium in 20 minutes. These results demonstrate the enhanced performance of the alkylsulfonic acid variants, particularly BS-cPIM-1, which combines high capacity, strong acidic functionality and rapid uptake, making it an excellent candidate for cationic metal ion removal.
In dye adsorption studies, cPIM-1 and BS-cPIM-1 were tested for MB⁺ and SO⁺ removal. For MB⁺, cPIM-1 slightly outperformed BS-cPIM-1, with capacities of 475 mg g⁻¹ and 466 mg g⁻¹, respectively, due to its less bulky structure allowing better accessibility to binding sites. Adsorption followed PSO kinetics for cPIM-1 (equilibrium in 40 minutes), and pseudo-first order (PFO) kinetics for BS-cPIM-1 (equilibrium in 250 minutes). For SO⁺, BS-cPIM-1 exhibited significantly higher uptake (336 mg g⁻¹) compared to cPIM-1 (263 mg g⁻¹). Interestingly, BS-cPIM-1 showed continuous adsorption without a clear equilibrium point, suggesting its potential for long-term or high-throughput applications.
Overall, this study successfully developed a series of modified PIM-1-based adsorbents tailored for effective cationic contaminant removal. The novel sulfonated derivatives, especially BS-cPIM-1, exhibited superior adsorption capacity, strong affinity for bulky dye molecules, and rapid uptake of metal ions. These results underscore the importance of functional group chemistry and steric design in adsorbent development. Importantly, these polymers also remain soluble in common organic solvents, which enhances their processability and adaptability for membrane fabrication or further chemical modification. The combination of high performance, structural tunability, solution processability, scalability and excellent data reproducibility makes them highly promising for future applications in advanced water treatment and environmental remediation technologies.
| Date of Award | 23 Sept 2025 |
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| Original language | English |
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| Awarding Institution | - The University of Manchester
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| Supervisor | Peter Budd (Main Supervisor) & Michael Turner (Co Supervisor) |
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