Rhamnolipids as Green Stabilizers of nZVI and Application in the Removal of Nitrate From Simulated Groundwater.

Environmental contamination caused by inorganic compounds is a major problem affecting soils and surface water. Most remediation techniques are costly and generally lead to incomplete removal and production of secondary waste. Nanotechnology, in this scenario with the zero-valent iron nanoparticle, represents a new generation of environmental remediation technologies. It is non-toxic, abundant, cheap, easy to produce, and its production process is simple. However, in order to decrease the aggregation tendency, the zero-iron nanoparticle is frequently coated with chemical surfactants synthesized from petrochemical sources, which are persistent or partially biodegradable. Biosurfactants (rhamnolipids), extracellular compounds produced by microorganisms from hydrophilic and hydrophobic substrates can replace synthetic surfactants. This study investigated the efficiency of a rhamnolipid biosurfactant on the aggregation of nanoscale zer-valent iron (nZVI) and its efficiency in reducing nitrate in simulated groundwater at pH 4.0. Two methods were tested: 1) adding the rhamnolipid during chemical synthesis and 2) adding the rhamnolipid after chemical synthesis of nZVI. Scanning electron microscopy field emission, X-ray diffractometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, Dynamic Light Scattering, and zeta potential measurements were used to characterize bare nZVI and rhamnolipid-coated nZVI. The effects of the type of nZVI and initial NO3 concentration were examined. Nanoscale zer-valent iron with the addition of the rhamnolipid after synthesis achieved the best removal rate of nitrate (about 78%), with an initial nitrate concentration of 25 mg L-1. The results suggest that nZVI functionalized with rhamnolipids is a promising strategy for the in situ remediations of groundwater contaminated by NO3, heavy metal, and inorganic carbon.

Silver nanoparticles stabilized by ramnolipids: Effect of pH.

Rhamnolipids are glycolipid biosurfactants that have remarkable physicochemical characteristics, such as the capacity for self-assembly, which makes these biomolecules a promising option for application in nanobiotechnology. Rhamnolipids produced from a low-cost carbon source (glycerol) were used to stabilize silver nanoparticles. Silver nanoparticles (AgNPs) have been the subject of studies due to their physical chemical as well as biological properties, which corroborate their catalytic and antimicrobial activity. We compared nanoparticles obtained with three different pH values during synthesis (5, 7 and 9) in the presence of rhamnolipids. Dynamic light scattering showed that larger particles were formed at pH 5 (78-190 nm) compared to pH 7 (6.5-43 nm) and 9 (5.6-28.1 nm). Moreover, nanoparticle stability (analyzed based on the zeta potential) was enhanced with the increase in pH from 5 to 9 (-29.86 ± 1.04, -37.83 ± 0.90 and -40.33 ± 0.57 mV, respectively). Field emission gun scanning electron microscopy confirmed the round morphology of the silver nanoparticles. The LSPR spectra of AgNP for the pHs studied are conserved. In conclusion, different pH values in the presence of rhamnolipids used in the synthesis of silver nanoparticles directly affect nanoparticle size and stability.