Effect of Preparation Methods on the Adsorption of Glyphosate by Calcined Ca-Al Hydrotalcite

Isolation of aqueous pesticides on surface-functionalized SBA-15: glyphosate kinetics and detailed empirical insights for atrazine

Atrazine and glyphosate are two of the most used pesticides around the world causing serious water contamination. In this study, amine-functionalized Santa Barbara Amorphous-15 silica (SBA-15-NH2) was synthesized and employed for the aqueous adsorption of atrazine and glyphosate. The adsorbent was mesoporous post-functionalization with lower surface area, pore volume, size, and stability when compared to the SBA-15. The pesticides adsorption rates were high with over 85% of potential adsorption having occurred within the initial 180 min. The equilibria for atrazine and glyphosate adsorption were 60 and 360 min, respectively, and the rate data fit the fractal pseudo-second-order and pseudo-second-order models, respectively. Atrazine adsorption was higher at lower solution pH with reduced adsorption as the pH value increased. There was enhanced atrazine adsorption as temperature increased from 22 to 32 °C, but further temperature rise resulted in lower adsorption compared to that recorded at 22 °C. The processes comprise electrostatic interaction, trapping of atrazine within mesopores, and multi-layer adsorption of atrazine on surface-adsorbed atrazine. The equilibrium data fitted the Langmuir adsorption isotherm model better than the Freundlich. The SBA-15-NH2 adsorption capacity for atrazine and glyphosate was better than many adsorbents reported in literature, the adsorbent is reusable, and exhibited sustained efficiencies for atrazine that was ≥82% even after 3-cycles, an indication of chemical stability and renewability.

Calcined Bean Dregs-Hydrocalumite Composites as Efficient Adsorbents for the Removal of Ofloxacin

Calcined bean dregs-hydrocalumite composites were prepared through in situ self-assembly of hydrocalumite on the surface of bean dregs and used for the adsorption of ofloxacin from water. The adsorbents were characterized by scanning electron microscopy, X-ray powder diffraction, and N2 physical adsorption. The results showed that the adsorption performance of calcined bean dregs-hydrocalumite composites for ofloxacin was much better than that of a single bean dreg carbon or calcined hydrocalumite. The effects of preparation and adsorption conditions on the adsorption property of calcined bean dregs-hydrocalumite for ofloxacin were also investigated. The adsorption ratio of ofloxacin reached up to 99.93% using 4 g·L-1 adsorbent dosage with 20 mg·L-1 initial concentration of ofloxacin at 30 °C in 2 h. The adsorption process mainly occurred in the first 5 min. In addition, the adsorption of ofloxacin by calcined bean dregs-hydrocalumite was more in line with pseudo-second-order dynamics and the Langmuir isotherm model.

Zinc oxide nanoparticles adsorb emerging pollutants (glyphosate pesticide) from aqueous solutions

The present study captures the precipitation synthesis of zinc nanoparticles and modification with alumina and oleic acid. The crystalline size evaluated from the XRD profile of the zinc oxide nanoparticles was 18.05 nm but was reduced to 14.20 and 14.50 nm upon modification with oleic acid and alumina. The XRD spectra also showed evidence of the amorphous nature of zinc oxide nanoparticles and subsequent enhancement upon modification. A porous appearance was observed in the SEM instrumentation but seems to be enhanced by modification. The FTIR absorption spectra of the nanoparticles showed a peak associated with ZnO vibration around 449 cm, but the enhanced intensity was observed due to modification. The prepared ZnO-NPs and the modified samples were good materials for the adsorption removal of glyphosate from water, recording efficiencies above 94% at neutral pH and showing a possible incremental trend with an enhanced period of contact and adsorbent dosage. The adsorbents showed maximum capacity that ranged from 82.85 to 82. 97 mg/g. The adsorption models of Freundlich, Temkin, Dubinin-Radushkevich and BET showed excellent fitness. Results from computational results complemented experimental data and were used to identify the sites for adsorption and characteristics of molecular descriptors for the systems.

Efficient removal of glyphosate from aqueous solutions by adsorption on Mg-Al-layered double oxides: thermodynamic, kinetic, and mechanistic investigation

Up to 90% of glyphosate was removed in 40 min by a 2:1 Mg2Al-layered double oxide (LDO) at pH 10, and the adsorption kinetics fitted a pseudo-second-order law. The adsorption isotherms were type L, and the Langmuir model best fitted the experimental data, with qmax of 158.22 μg/mg at 25 °C. The intraparticle diffusion model suggested that the adsorption process is dependent on the thickness and formation of the film at the solution/solid interface. The XRD results excluded the intercalation of glyphosate anions, and FTIR along with solid-state 13C and 31P MAS NMR confirmed that the glyphosate anions interact through the carboxylate and/or phosphonate moieties, both in end-on and side-on modes to the LDO surface. Glyphosate removal was also investigated in the presence of different anionic species, and simultaneous adsorption showed that carbonate and phosphate ions strongly influence glyphosate removal.