Abatement of Cr(VI) and As(III) by MnO2 loaded MCM-41 in wastewater treatment

One-pot hydrothermal preparation of manganese-doped carbon microspheres for effective deep removal of hexavalent chromium from wastewater

Mn-doped activated carbon microspheres (MnO_x/ACS) with super-high adsorption capacities and deep removal capability for hexavalent chromium (Cr(VI)) were successfully prepared via an ammonium persulfate-assisted hydrothermal method followed by potassium oxalate activation using KMnO₄ and sucrose as raw materials. Their -physical and chemical properties, as well as those of Mn-doped non-activated carbon spheres (MnO_x/CS), were characterized by XRD, SEM, TEM, EDS-mapping, XPS, N₂ adsorption-desorption, ICP-AES, and elemental analysis. It was found that the manganese oxide (MnO_x) particles were uniformly embedded within the carbon spheres via layer-by-layer capture, and the MnO_x/ACS exhibited strong redox activity because of the multivalent nature of MnO_x, resulting in excellent adsorption performance via reduction. In particular, MnO_x/ACS-4 with a Mn content of 1.06 wt% and a specific surface area of 1405.7 m² g^-1 achieved a maximum adsorption capacity of 660.7 mg g^-1; this can reduce Cr(VI) content to less than 0.05 mg L^-1, which meets the corresponding Chinese drinking water quality standard when the initial concentration of Cr(VI) is less than 400 mg L^-1. Furthermore, this highly efficient method can be extended to prepare V-, Mo-, or W-doped carbon microspheres with significantly enhanced adsorption performance for Cr(VI) compared to bare activated carbon sphere, indicating their good application prospect for the deep removal for heavy metal ions from wastewater.

Study on thermal, mechanical and adsorption properties of amine-functionalized MCM-41/PMMA and MCM-41/PS nanocomposites prepared by ultrasonic irradiation

In this study, two common industrial polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), were incorporated into amine-functionalized MCM-41 mesoporous silica as reinforcement agents via an ultrasonic assisted method as a facile, fast, eco-friendly, and versatile synthetic tool. Amino functionalization of MCM-41 were performed by 3-aminopropyl triethoxysilane as a coupling agent and it is denoted as APTS-MCM-41. The obtained nanocomposites (NCs), APTS-MCM-41/PMMA and APTS-MCM-41/PS, were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), and thermogravimetric analysis (TGA). Their mechanical properties were also probed via stress-strain curves and improved tensile properties were observed in the NCs relative to the neat polymers. Additionally, APTS-MCM-41/PMMA exhibited better mechanical properties than APTS-MCM-41/PS. Sorption studies were carried out on the two NCs and the effect of different process parameters, namely, pH, contact time, and initial Cd(II) concentration investigated in batch mode. Pseudo-second order and intraparticle diffusion models explain the Cd(II) kinetics more effectively for APTS-MCM-41/PMMA and APTS-MCM-41/PS, respectively. The adsorption isotherm data fitted well to Langmuir isotherm for both NCs and the maximum monolayer adsorption capacities were found to be 24.75mg/g and 10.42mg/g for APTS-MCM-41/PMMA and APTS-MCM-41/PS, respectively. The results demonstrate that the NCs show potential for use in adsorption of heavy metal ion such as Cd(II) from aqueous media.