Preparation of waste face masks modified with MnO2/poly(m-phenylenediamine) as a novel adsorbent for hexavalent chromium removal: Comprehensive batch and column study

Abstract

Single-use surgical face masks (SFM) have become one of the most used personal protective equipment (PPE) for preventing the transmission of diseases, especially COVID-19. However, the environment is being threatened by the huge amount of plastic waste generated by this material. In this study, a novel environmentally-friendly in-situ-surface polymerization method was employed to modify the surface of SFM with m-phenylenediamine (mPDA) for removing hexavalent chromium. The synthesized adsorbent was characterized by Field Emission-Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared Spectroscopy (FTIR). The investigations showed that the polymer and oxidant solution can be reused for several cycles, which was not possible in the conventional chemical polymerization method with ammonium persulfate (APS). The influence of various variables on the adsorption process was assessed and the optimum results was reported (adsorbent dosage: 3 g L−1, contact time: 60 min, pH: 2). The modeling investigations demonstrated that the process is followed by pseudo-second-order kinetic and University of Tehran (UT) isotherm model's assumptions, respectively. The obtained thermodynamic parameters at the investigated temperatures revealed the spontaneity and endothermic nature of Cr(VI) adsorption on the modified adsorbent. The column study was conducted and the impact of the flow rate and the feed concentration of Cr(VI) were evaluated. The experimental findings were analyzed using the Thomas model to discover how the concentration changes over time in the column operation. It was revealed that when the flow rate rose, the service volume declined.