A systematic review on iron-based nanoparticle-mediated clean-up of textile dyes: challenges and prospects of scale-up technologies

Ferrous sulfide nanoparticles can be biosynthesized by sulfate-reducing bacteria: Synthesis, characterization and removal of heavy metals from acid mine drainage

Ferrous sulfide nanoparticles (nFeS) have proven to be effective in removing heavy metals (HMs) from wastewater. One such approach, which has garnered much attention as a sustainable technology, is via the in situ microbial synthesis of nFeS. Here, a sulfate-reducing bacteria (SRB) strain, Geobacter sulfurreducens, was used to initially biosynthesize ferrous sulfide nanoparticles (SRB-nFeS) and thereafter remove HMs from acid mine drainage (AMD). SRB-nFeS was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) coupled to an energy dispersive spectrometer (EDS), three-dimensional excitation-emission matrix (3D-EEM) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Such characterization showed that SRB mediated the reduction of SO42- to S2- to form nFeS, where the metabolized substances functioned as complexing agents which coordinated with nFeS to form biofunctional SRB-nFeS with improved stability. One advantage of this synthetic route was that the attachment of nFeS to the bacterial surface protected SRB cells from HM toxicity. Furthermore, due to a synergistic effect between nFeS and SRB, HM removal from both solution and AMD by SRB-nFeS was enhanced relative to the constituent components. Thus, after 5 consecutive cycles of HM removal, SRB-nFeS removed, Pb(Ⅱ) (92.6%), Cd(Ⅱ) (78.7%), Cu(Ⅱ) (76.0%), Ni(Ⅱ) (62.5%), Mn(Ⅱ) (62.2%), and Zn(Ⅱ) (88.5%) from AMD This study thus provides new insights into the biosynthesis of SRB-nFeS and its subsequent practical application in the removal of HMs from AMD.

Assessment on the photocatalytic and phytotoxic activities using ecobenevolently synthesized iron oxide nanoparticles from the root extracts of Glycyrrhiza glabra

The present study is the first attempt to utilize the root extracts of Glycyrrhiza glabra as a novel biological route for the synthesis of iron oxide nanoparticles (Fe2O3NPs) under optimized conditions. The process variables namely concentration of ferric chloride, root extract of G. glabra and temperature were optimized using Response Surface Methodology (RSM) to obtain high yield. Phytochemicals mediated the reduction process and served as capping and stabilizing agent. The biosynthesized Fe2O3NPs characterized using UV-Vis spectroscopy exhibited a prominent peak at 350 nm. The crystallinity and valence state of Fe2O3NPs was confirmed by XRD and XPS. The surface functionalization of the nanoparticles was confirmed from the presence of functional groups in the FT-IR spectrum. The FESEM analysis revealed the biosynthesized Fe2O3NPs are irregular and the EDX spectrum recorded the presence of iron and oxygen in the synthesized nanoparticles. The biosynthesized Fe2O3NPs exhibited an appreciable photocatalytic activity against methylene blue under sunlight with a maximum decolorisation efficiency of 92% within 180 min of reaction time. The experimental data of adsorption studies well fitted with Langmuir isotherm and pseudo-second order kinetic model. The thermodynamic study proved to be spontaneous, feasible and endothermic in nature. The phytotoxicity study revealed 92% germination and increased seedling growth in the green gram seeds exposed to Fe2O3NPs. Hence the study established the efficiency of biosynthesized of Fe2O3NPs in photocatalytic and phytotoxic activities.

Outstanding adsorption capacity of iron oxide synthesized with extract of açaí berry residue: kinetic, isotherm, and thermodynamic study for dye removal

Contamination of water by toxic dyes is a serious environmental problem. Adsorbents prepared by an environmentally safe route have stood out for application in pollutant removal. Herein, iron oxide-based nanomaterial composed of Fe(III)-OOH and Fe(II/III) bound to proanthocyanidins, with particles in the order of 20 nm, was prepared by green synthesis assisted by extract of açaí (Euterpe oleracea Mart.) berry seeds from an agro-industrial residue. The nanomaterial was applied in the adsorption of cationic dyes. Screening tests were carried out for methylene blue (MB), resulting in an outstanding maximum adsorption capacity of 531.8 mg g-1 at 343 K, pH 10, 180 min. The kinetics followed a pseudo-second-order model and the isotherm of Fritz-Schülnder provided the best fit. Thermodynamic data show an endothermic process with entropy increase, typical of chemisorption. The proposed mechanism is based on the multilayer formation over a heterogeneous adsorbent surface, with chemical and electrostatic interactions of MB with the iron oxide nanoparticles and with the proanthocyanidins. The high adsorption efficiency was attributed to the network formed by the polymeric proanthocyanidins that entangled and protected the iron oxide nanoparticles, which allowed the reuse of the nanomaterial for seven cycles without loss of adsorption efficiency.