Nanocomposites containing graphene oxide (GO), polyethyleneimine (PEI), and chitosan (CS) were synthesized for chromium(VI) and copper(II) removal from water. Response surface methodology (RSM) was used for the optimization of the synthesis of the CS-PEI-GO beads to achieve simultaneous maximum Cr(VI) and Cu(II) removals. The RSM experimental design involved investigating different concentrations of PEI (1.0-2.0%), GO (500-1500 ppm), and glutaraldehyde (GLA) (0.5-2.5%), simultaneously. Batch adsorption experiments were performed to obtain responses in terms of percent The optimum bead composition contained 2.0% PEI, 1500 ppm GO, and 2.08% GLA, and allowed Cr (VI) and Cu(II) removals of up to 91.10% and 78.18%, respectively. Finally, characterization of the structure and surface properties of the optimized CS-PEI-GO beads was carried out using X-ray diffraction (XRD), porosity and BET surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), which showed favorable adsorbent characteristics as given by a mesoporous structure with high surface area (358 m 2 g À1 ) and plenty of surface functional groups. Overall, the synthesized CS-PEI-GO beads were proven to be effective in removing both cationic and anionic heavy metal pollutants.

Selenium in water is becoming of increasing risk to human exposure because only recently serious health effects have been associated with their presence in water resources. The present study investigated the development and optimization of the composition of graphene oxide polymeric nanocomposite hydrogel beads by using response surface methodology. The use of polymers such as chitosan and polyethylenimine, which are rich in amine and alcoholic functional groups, provided enhanced removal of anionic selenium species from the water. Experimentally validated polymeric beads were used to perform batch adsorptions of selenium under different conditions such as pH, bead dosage, and diverse selenium concentrations to investigate their potential use, adsorption kinetics, and selenium removal mechanisms. Acidic conditions were found to best remove negatively charged selenium ions from aqueous solutions via −OH, −COOH, and amine functional groups present in the beads. The adsorption kinetic mechanism was better described by the pseudo-second-order adsorption kinetics, indicating that the beads remove selenium via chemisorption mechanisms. The isotherm studies showed an adsorption capacity of 1.62 mg/g based on the Langmuir isotherms at 25 °C. Regeneration studies showed loss of available adsorption sites after the first desorption treatment with different concentrations of NaOH and HCl. The mathematically optimized nanocomposite was further used to treat selenium spiked in real environmental water samples, which confirmed that the best removal of selenium occurs in acidic conditions.

Analysis of the probability distribution of induction times for acetaminophen and glycine supersaturated solutions showed that reduction in sample volume results in an exponential increase in induction times. It approximately increased by a factor of 55 when the volume was reduced from 1000 to 25 μL. To elucidate the use of confinement as an approach to nanocrystal development and polymorph access, we demonstrated the effect of volume reduction on the nucleation of two model compounds, acetaminophen and glycine. Using supersaturated solutions of both compounds at volumes ranging from 1000 to 25 μL, induction time statistics were obtained experimentally. Image analysis revealed that form I acetaminophen and β-glycine formed as the initial primary nucleation event, with β-glycine sometimes followed by a polymorph transformation to γ-glycine shortly after. Image analysis showed no variation in polymorphism occurring for acetaminophen systems across all volumes. However, it was revealed that at volume sizes below 100 μL, primary nucleation in glycine systems shifts toward γ-glycine nucleation. These results demonstrate the effects of volume reduction on nucleation induction times, its implications on polymorphism, and the extent of lessening the probability of a nucleation event.