Selective separation of methylene blue from aqueous solution using Mn/Pd decorated chemically modified MoS2 nanocomposites

Abstract

The presence of dyes in wastewater is posing as serious threat to human health. There are a huge number of physical, chemical, biological and hybrid methods available for the removal of colorants (dyes) from aqueous environment. In this work, we demonstrate the fabrication of new nanocomposites, MoS2-COOH/gly@M (M= Mn, Pd), with high adsorption property fabricated by chemically immobilizing manganese and palladium metallic centers onto the glycine- modified molybdenum disulfide (MoS2) material. The chemical and physical properties of adsorbents were analyzed using Fourier transform infrared spectrometer (FT-IR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) companied by energy dispersive X-ray and mapping (EDAX & MAP) analyses. Zeta potential (ξ) technique was also used to measure the surface charge of adsorbents. Performances of nanocomposites were investigated on the sewage as adsorbent for dye removal. Synthesized nanocomposites revealed selective adsorption of methylene blue (MB) dye from aqueous mixture of MB and methyl orange (MO). Results displayed the equivalent high adsorption capacity for MB and MO up to 553 and 619 mg/g, respectively (green reaction condition= 120 min contact time, ,25 °C, pH 2.0 and pH 7.0, in the presence of 2 mg adsorbent and 50 mg/L (30 mL) initial concentration of MO and MB). The remarkable adsorption capacity of dye by MoS2-COOH/gly@M (M= Mn, Pd) nanocomposites can be attributed to the intermolecular interactions due to the presence of the amine, hydroxyl, and carboxyl functionalities. To describe the adsorption mechanism of MO and MB dye by synthesized nanomaterials, the pseudo-first-order and pseudo-second-order kinetics were further studied. Isotherm models displayed that the adsorption of MB and MO onto the MoS2-COOH/gly@M (M= Mn, Pd) nanocomposites is more correspondent with the Freundlich model with high-correlation coefficients. The results showed that the electrostatic attraction and H-bonding interaction were the basic cause of the adsorption of these anionic and cationic dyes on the surface of the nanocomposites. One of the distinguished properties of adsorbents is their capability to selectively adsorb MB from an admixture of MO and MB. The adsorption selectively has expanded in the following order: MoS2 < MoS2-COOH/gly@Mn < MoS2-COOH/gly@Pd. Based on the results, this new type of nanocomposites has potential to act as an effective and affordable adsorbent material for dye removal from an industrial sewage.