Abstract
Owing to their high surface area and superior adsorption properties, spirobifluorene polymers of intrinsic microporosity (PIMs), namely PIM-SBF-Me (methyl) and PIM-SBF-tBu (tert-butyl), were used for the first time, to our knowledge, for the removal of methylene blue (MB) dye from wastewater. Spirobifluorene PIMs are known to have large surface area (can be up to 1100 m2 g−1) and have been previously used mainly for gas storage applications. Dispersion of the polymers in aqueous solution was challenging owing to their extreme hydrophobic nature leading to poor adsorption efficiency of MB. For this reason, cationic (cetyl-pyridinium chloride), anionic (sodium dodecyl sulfate; SDS) and non-ionic (Brij-35) surfactants were used and tested with the aim of enhancing the dispersion of the hydrophobic polymers in water and hence improving the adsorption efficiencies of the polymers. The effect of surfactant type and concentration were investigated. All surfactants offered a homogeneous dispersion of the polymers in the aqueous dye solution; however, the highest adsorption efficiency was obtained using an anionic surfactant (SDS) and this seems owing to the predominance of electrostatic interaction between its molecules and the positively charges dye molecules. Furthermore, the effect of polymer dosage and initial dye concentration on MB adsorption were also considered. The kinetic data for both polymers were well described by a pseudo-second-order model, while the Langmuir model better simulated the adsorption process of MB dye on PIM-SBF-Me and the Freundlich model was more suitable for PIM-SBF-tBu. Moreover, the maximum adsorption capacities recorded were 84.0 and 101.0 mg g−1 for PIM-SBF-Me and PIM-SBF-tBu, respectively. Reusability of both polymers was tested by performing three adsorption cycles and the results substantiate that both polymers can be effectively re-used with insignificant loss of their adsorption efficiency (%AE). These preliminary results suggested that incorporation of a surfactant to enhance the dispersion of hydrophobic polymers and adsorption of organic contaminants from wastewater is a simple and cost-effective approach that can be adapted for many other environmental applications.
Highlights
Water is the most important compound for living organisms to carry out their day-to-day vital activities
The recorded adsorption efficiencies (AEs) were 68.1% and 9.6% for Polymers of intrinsic microporosity (PIMs)-SBF-Me and PIM-SBF-tBu, respectively. This poor performance was related to the hydrophobic nature of the polymers, which limited their dispersion in the aqueous solution and, subsequently, the adsorption of the dye
It was noted that, when Methylene blue (MB) was mixed with sodium dodecyl sulfate (SDS) at concentration lower than SDS critical micelle concentration (CMC), the solution changed in colour and the absorbance performance changed [30]
Summary
Water is the most important compound for living organisms to carry out their day-to-day vital activities. Textile pollution is a serious growing issue that is threatening all living creatures, public health, agricultural, fishing and other activities causing toxic, carcinogenic and mutagenic effects. Continuing efforts from both academia and the industry have been dedicated to minimize these ongoing threats such as physical adsorption [3], oxidation [4], biological treatment [5], photocatalysis [6] and others. To achieve maximum removal of contaminants from wastewater, optimization of adsorption is important to achieve maximum elimination rate, a series of parameters such as the adsorbent dosage, contaminant concentration, and in some cases temperature and pH control are crucial [10]. The preparation of efficient porous materials for this application is in great demand, and several adsorbents have been reported including nanoparticles [11], carbonaceous matter [12], composites [8] and bioadsorbents [13]
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