Detection and mapping of the seasonal distribution of water hyacinth (Eichhornia crassipes) and valorization as a biosorbent of Pb(II) in water.

In the present research, the presence of water hyacinth (Eichhornia crassipes) on the surface of the San Jose Dam located in the city of San Luis Potosi, S.L.P, Mexico, was monitored and mapped. The monitoring was conducted for 2 years (2018-2020) with remote sensing data from OLI Landsat 8 sensors, based on the normalized difference vegetation index (NDVI). The results demonstrated the capability and accuracy of this method, where it was observed that the aboveground cover area, proliferation, and distribution of water hyacinth are influenced by climatic and anthropogenic factors during the four seasons of the year. As part of a sustainable environmental control of this invasive species, the use of water hyacinth (WH) root (RO), stem (ST), and leaf (LE) components as adsorbent material for Pb(II) present in aqueous solution was proposed. The maximum adsorption capacity was observed at pH 5 and 25 °C and was 107.3, 136.8, and 120.8 mg g-1 for RO, ST, and LE, respectively. The physicochemical characterization of WH consisted of scanning electron microscopy (SEM), N2 physisorption, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), charge distribution, and zero charge point (pHPZC). Due to the chemical nature of WH, several Pb(II) adsorption mechanisms were proposed such as electrostatic attractions, ion exchange, microprecipitation, and π-cation.

Use of bone char prepared from an invasive species, pleco fish (Pterygoplichthys spp.), to remove fluoride and Cadmium(II) in water.

In this study, bone char (BC) from pleco fish (Pterygoplichthys spp.) was synthesized, and their textural and physicochemical properties, as well as its adsorption capacity towards fluoride and Cd(II) from single and binary aqueous solutions, were determined. The results showed that the properties of the BCs were independent of the type of bone used and the surface areas were close to 110 m2 g-1. The effect of solution pH revealed that the adsorption capacity of BC towards fluoride from water raised by decreasing the solution pH. This trend was attributed to the electrostatic interaction between the positively charged surface and the fluoride in aqueous solution. On the contrary, the capacity of BC for adsorbing Cd(II) was enhanced by increasing the solution pH, indicating that electrostatic interactions were also essential but with a contrary effect in comparison with fluoride adsorption due to the negatively charged surface at pH above the point zero charge (pHPZC = 8.16). The experimental data for binary adsorption of fluoride and Cd(II) were interpreted satisfactorily using the modified Freundlich multicomponent isotherm (EFMI), and the experimental data revealed that Cd(II) have an antagonistic effect on the adsorption of fluoride, whereas the presence of fluoride does not affect the capacity of BC for adsorbing Cd(II). Thermogravimetric, XRD diffraction and IR spectroscopy analysis corroborated that the adsorption of fluoride in BC is due to electrostatic attractions, ion exchange or chemisorption and physisorption. Besides, the removal of Cd(II) occurs by physical adsorption and ion exchange. It was concluded that BC is an alternative material for the removal of fluoride and Cd(II) from aqueous solutions, and it is a possible application for using the bones of this invasive fish species.

Simultaneous removal of metronidazole and Pb(II) from aqueous solution onto bifunctional activated carbons.

In this work, it was analyzed the behavior of three commercial activated carbons with different textural and chemical properties to adsorb individually metronidazole and lead ions from aqueous solution. Afterwards, the activated carbons were modified with citric acid to remove both compounds simultaneously. Both sets of activated carbons were characterized chemically and texturally. XPS analysis was performed to corroborate the adsorption mechanism of lead on the surface of the carbons. Finally, the intraparticle diffusion of both adsorbates was elucidated by the application of diffusional model in three dimensions. The results evidenced that adsorption mechanism for MNZ and Pb(II) is independent, the adsorption for MNZ is governed by π-π dispersive interactions, whereas Pb(II) adsorption is mainly controlled by electrostatic interactions. The binary adsorption equilibrium shows that the adsorption of MNZ is independent from the concentration of Pb(II), whereas the adsorption of Pb(II) is affected by the presence of MNZ at low concentrations (0.1 mmol L-1), but it remains almost constant at concentrations of MNZ between 0.1 and 1.5 mmol L-1. Finally, the mass transport of MNZ was faster than Pb(II) from the solution to the external surface of activated carbon and the mass flux of MNZ inside the particle was superior to the mass flux of Pb(II). Lastly, there might be an obstruction phenomenon with MNZ impeding Pb(II) to reach the active sites placed into the carbon's microporosity structure. Graphical abstract.