Exfoliation-free solvothermal synthesis of ink-like MoS2 gel for printable water purification filters

Abstract

A novel screen-printing approach was employed to fabricate molybdenum disulfide (MoS₂) based membranes using exfoliation-free solvothermally synthesized ink-like MoS₂ gel and Whatman filter paper (WFP). Three membranes, MoS₂-WFP-1, MoS₂-WFP-2, and MoS₂-WFP-3, were fabricated by varying the number of print coatings to tailor the hydrophobicity and mechanical integrity. Structural and morphological investigations were performed by X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (FE-SEM) analysis. The XPS results confirmed a well-adhered MoS₂ layer with mixed 1T/2H phases that enhanced mechanical and thermal stability. The MoS₂ incorporated membranes exhibited increased tensile strain, moderate water uptake (53–55%), and contact angles (104–118°) which increased with increasing coat number, demonstrating tunable surface wettability. In spite of reduced pure water flux, compared to bare filter paper, each coated membrane exhibited stable flux over a 60 min filtration period. The membranes efficiently removed the Congo red (∼90%), methylene blue (∼55%) and Cr(VI) (∼72%) under pH-dependent conditions. The pH-dependent removal arises from electrostatic interactions between the MoS₂ surface and charged species, where protonation of the negatively charged MoS₂ surface at acidic pH enhances the attraction of anionic contaminants (Congo red and Cr anions such as such as HCrO₄⁻ and Cr₂O₇²⁻), while deprotonation at basic pH favors adsorption of cationic MB. The investigations confirm a simple, scalable and low-cost route for the fabrication of printable MoS₂ membrane filters suitable for wastewater purification.