A polydimethylsiloxane/montmorillonite/filter paper composite as a self-standing and easily separable adsorbent for methylene blue removal from aqueous solutions

Abstract

Here, a catalyst-free route is reported for fabricating self-standing and robust paper-based adsorbents for methylene blue (MB) removal from aqueous solutions through the attachment of montmorillonite (MMT) to filter paper (FP) substrate surfaces using polydimethylsiloxane (PDMS) chains. Characterization results showed that the thickness of the combined PDMS and MMT layer was 4.0 +/- 0.7 g m-2, with MMT accounting for 2.2 +/- 0.3 wt% of the composite. The specific surface area of MMT, FP, and PDMS/MMT/FP composite was 203.4, 1.3, and 1.8 m2 g-1, respectively. A point of zero charge of 3.84 was measured for PDMS/MMT/FP. Spectroscopic analysis suggested interactions among MMT, PDMS, and FP, including the possible formation of Si-O-C bonds between PDMS and cellulose, the principal component of FP. Scanning electron microscopy (SEM) images revealed clay particles distributed uniformly across the fibers. MB adsorption tests conducted under identical conditions (100 mL, 5 mg L-1; 6 cm x 6 cm sheets) showed that the PDMS/MMT/FP composite removed 90.0% of the dye (corresponding to a qe of 1.4 mg g-1), almost doubling the 51.3% removal performance of pristine FP, despite the low MMT loading of only 2.2 wt% in the composite. The PDMS/MMT/FP composite closely followed the pseudo-second-order kinetic model and showed a better fit to the Langmuir isotherm. Even after 15 days of continuous shaking in MB solution at 150 rpm, the PDMS/MMT/FP composite retained its integrity, still exhibiting MMT particles across its surface and similar Al contents before and after the MB adsorption test, as evidenced by SEM and spectroscopic studies. These findings demonstrate that our simple and environmentally benign route can produce low-cost, self-standing paper-based adsorbents with clear promise for wastewater-treatment applications.