Adsorption of Paraquat by Poly(Vinyl Alcohol)-Cyclodextrin Nanosponges

Abstract

The contamination of hydrosoluble pesticides in water could generate a serious problem for biotic and abiotic components. The removal of a hazardous agrochemical (paraquat) from water was achieved by adsorption processes using poly(vinyl alcohol)-cyclodextrin nanosponges, which were prepared with various formulations via the crosslinking between citric acid and β-cyclodextrin in the presence of poly(vinyl alcohol). The physicochemical properties of nanosponges were also characterized by different techniques, such as gravimetry, thermogravimetry, microscopy (SEM and Stereo), spectroscopy (UV-visible, NMR, ATR-FTIR, and Raman), acid-base titration, BET surface area analysis, X-ray diffraction, and ion exchange capacity. The C10D-P2 nanosponges displayed 60.2% yield, 3.14 mmol/g COOH groups, 0.335 mmol/g β-CD content, 96.4% swelling, 94.5% paraquat removal, 0.1766 m2 g−1 specific surface area, and 5.2 × 10−4 cm3 g−1 pore volume. The presence of particular peaks referring to specific functional groups on spectroscopic spectra confirmed the successful polycondensation on the reticulated nanosponges. The pseudo second-order model (with R2 = 0.9998) and Langmuir isotherm (with R2 = 0.9979) was suitable for kinetics and isotherm using 180 min of contact time and a pH of 6.5. The maximum adsorption capacity was calculated at 112.2 mg/g. Finally, the recyclability of these nanosponges was 90.3% of paraquat removal after five regeneration times.

Adsorption of Cationic Contaminants by Cyclodextrin Nanosponges Cross-Linked with 1,2,3,4-Butanetetracarboxylic Acid and Poly(vinyl alcohol)

“…Hence, the presence of PVOH in nanosponges is indispensable for the improvement of adsorption capacity towards cationic pollutants, the BP5 nanosponges were selected for the next study. nanosponges using citric acid as a cross-linking agent which had displayed the lower adsorption of PQ for all nanosponges without β-CD, comparing with the system containing β-CD [120]. The physical properties of BP5 nanosponges before and after PQ, SO, and MG, respectively, adsorption was observed is monitored in Figure 9.…”

“…Polymers 2021, 13, x FOR PEER REVIEW 13 of 23 nanosponges using citric acid as a cross-linking agent which had displayed the lower adsorption of PQ for all nanosponges without β-CD, comparing with the system containing β-CD [120]. The physical properties of BP5 nanosponges before and after PQ, SO, and MG, respectively, adsorption was observed is monitored in Figure 9.…”

“…An amount of 10 mL of contaminant solution with a 25 mg/L initial concentration and optimal pH was poured into a test tube containing 20 mg of nanosponges under agitation of 150 rpm at different times (15,30,45,60,120,180, and 300 min) at 30 • C. The measurement of contaminants was described in the previous section. Experimental data were then fitted with two kinetics models:…”

“…Thus, a contact time of 180 min was selected for the next study. In this work, the system without β-CD was not been studied to compare the efficiency of cationic contaminant removal because we reported in the previous work for similar nanosponges using citric acid as a cross-linking agent which had displayed the lower adsorption of PQ for all nanosponges without β-CD, comparing with the system containing β-CD [120].…”

“…Cyclodextrin polymers have widely been developed by different types of polymerization to enhance the solubility for both the guest molecule and the cyclodextrin polymer and improve the adsorption capacity towards organic molecules. Adsorbents based on cyclodextrin and its derivatives have been widely used for environmental applications [20, and other fields [115][116][117][118][119][120]. Moreover, insoluble cyclodextrin polymers are also named "cyclodextrin nanosponges" because these nanomaterials exhibit a hyperbranched framework with a three-dimensional structure, a sponge-like pattern, and a specific mission to react with a functional cross-linker or other chemical reactants [95].…”