Mn3O4 nano-sized crystals: Rapid synthesis and extension to preparation of nanosized LiMn2O4 materials

Deciphering the photocatalytic degradation of polyaromatic hydrocarbons (PAHs) using hausmannite (Mn3O4) nanoparticles and their efficacy against bacterial biofilm

Polyaromatic hydrocarbons (PAHs) are life-threatening organic pollutants that severely threaten ecosystems worldwide due to their poisonous qualities, cancer-causing properties, and mutation-causing qualities. Water and soil together form a critical component of the ecosystem that supports all life. Due to the pollutants that are being disposed of in them, their characteristics have changed, and their toxicity has increased. The goal of this study was to investigate the ability of hausmannite nanoparticles to degrade fluorene from soil and water. Using the chemical method, hausmannite nanoparticles were synthesized and further characterization was performed using UV-Vis, FTIR, DLS, XRD, and SEM-EDAX. Hausmannite significantly degraded fluorene using the batch adsorption method. The degradation was also confirmed by performing reactive kinetics using Freundlich's isotherm model and Langmuir's pseudo-second-order model of soil and water. In addition to the degradation efficacy, hausmannite was also proved to inhibit biofilm formation by Pseudomonas aeruginosa. The findings of the experiments confirmed the presence of hausmannite nanoparticles, as well as their physical properties, chemical properties, degradation properties, and parameters of the kinetic study. As a result, synthesized nanoparticles have been extensively utilized as a low-cost option for removing pollutants and microbial biofilm.

Synthesis, optimization, and characterization of biogenic manganese oxide (BioMnOx) by bacterial isolates from mangrove soils with sorbents property towards different toxic metals

Manganese oxidizing bacteria, Bacillus mycoides and Bacillus subtilis were isolated from mangrove soils and optimized for the removal of Mn(II) with simultaneous production of biogenic manganese oxide (BioMnOx). The removal rate of Mn(II) was 90% in 48 h for B. mycoides and 72 h for B. subtilis under the optimized conditions at pH 7, temperature 37 °C, 120 rpm, with 1% inoculum containing 10 mM MnCl₂. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X-Ray analysis (EDAX), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize the synthesized biogenic manganese oxide. BioMnOx by Bacillus mycoides and Bacillus subtilis were identified as Bixbyite (Mn₂O₃) and Hausmannite (Mn₃O₄), respectively, with nano-sized monocrystalline nature. BioMnOx of Bacillus subtilis strain was more efficient in the removal of metals Zn and Co than BioMnOx of Bacillus mycoides except for mercury. The removal property of synthesized BioMnOx could be applied to treat multi-metal containing wastewater.

Green synthesis of single phase hausmannite Mn3O4 nanoparticles via Aspalathus linearis natural extract

Abstract

Nowadays, green synthesis of nanoparticles using plant precursors has been extensively studied. However, less attention has been given to Mn3O4. This contribution validates the synthesis of single-phase Hausmannite Mn3O4 nanoparticles by a green approach without using any standard acid/base compounds, surfactants, and organic/inorganic dissolving agents. The chemical chelation of the Mn precursor was performed via bioactive compounds of the Aspalathus Linearis’ extract, an African indigenous plant. Annealing at 400 °C for ~ 1 h was required to crystallize the small amorphous nanoparticles with an initial bimodal size distribution peaking at $$\left\langle {\phi_{1} } \right\rangle$$ ϕ 1  ~ 4.21 nm and $$\left\langle {\phi_{2} } \right\rangle$$ ϕ 2  ~ 8.51 nm respectively. Such annealing lead to increase in the diameter of the nanoparticles from 17 to 28 nm.The morphological, structural, vibrational, surface, and photoluminescence properties of the single-phase Hausmannite nanoparticles were comprehensively investigated by High Resolution Transmission Electron Microscopy(HRTEM),Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), Raman and X-rays Photoelectron Spectroscopy (XPS), spectroscopy as well as room temperature photoluminescence. Structural and morphological investigations revealed the formation of quasi-spherical nanoparticles having a single phase Hausmannite Mn3O4 crystal structure. XPS results also validated the XRD results about the formation of Hausmannite Mn3O4 nanoparticles. Raman investigations allowed a crystal-clear distinction between the Mn3O4 nature of the nanoparticles from the potential γ -Mn2O3 phase as both phases belong to the same space group and both assume tetragonally-distorted cubic lattices of nearly similar dimensions. The optical studies of the single phase Hausmannite crystalline nanoparticles exhibited a broad photoluminescence in the spectral range of 300–700 nm, which is ideal for emission devices.

Graphic abstract