# Nanosponges for Water Treatment: Progress and Challenges
## 2 Nanosponges for Water Treatment
[46], Copyright 2019, American Chemical Society. ciency from effluent. Notably, a correlation between the sorption efficacy and the binding constant of micropollutants and cyclodextrin polymers was reported, revealing that complexes of pollutants with cyclodextrin polymers can play a crucial role in sorption mechanisms [50]. Superparamagnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles are decorated on the surface of \(\beta\)-cyclodextrinartin-derived carbonate nanosponges with good reusability for the elimination of dinotefuran from water (Figure 3), and the highest adsorption is \(\sim\)4.53 \(\times\) 10\({}^{-3}\) mmol g\({}^{-1}\)[51]. It appears that these magnetic nanosponges can be considered promising candidates for the removal of neonicotinoids from aqueous solutions, with high efficiency, cost-effectiveness, non-toxicity, and reusability. Poly(vinyl alcohol)-cyclodextrinrin nanosponges are synthesized via citric acid with \(\beta\)-cyclodextrinrin in the presence of poly(vinyl alcohol). These nanosponges are employed for removing paraquat from water by the adsorption process. Consequently, the maximum adsorption capacity is \(\sim\)112.2 mg g\({}^{-1}\), and the reuse of these nanosponges is \(\sim\)90.3% for paraquat remediation after five successive cycles [52]. [PERSON] et al. [53] prepared cyclodextrin-calixarene nanosponges as sorbents with high efficiency to eliminate Pb\({}^{2+}\) ions from aqueous solutions. These nanosponges can be considered promising candidates for the elimination of inorganic/organic contaminants, especially after suitable surface functionalization/modification to improve sorbent capabilities [53]. Halloysic clay (halloysic nanotubes) and organic cyclodextrin derivatives are utilized to synthesize inorganic-organic nanosponges though microwave irradiation techniques under solvent-free conditions (Figure 4) [54]. These nanosponges are deployed as nanoad-sorbents for removing Rhodamine B and some cationic/anionic dyes. Notably, the pH solution and electrostatic interactions can influence the adsorption procedure. High efficiency of adsorption can be attained for cationic dyes relative to anionic ones, offering these nanosponge hybrids for the adsorption of dyes with high selectivity [54]. Additionally, phosphorylated carbon nanotube-\(\beta\)-cyclodextrinrin nanosponges are fabricated utilizing hexamethylene diisocyanate as a cross linker. These polymers are decorated with Ag and TiO\({}_{2}\) nanoparticles via a sol-gel technique for eliminating metal ions pollutants from wastewater [55]. Nanosponges with environmentally-benign properties and higher compositions of carboxyl groups are obtained through the cross linking of \(\beta\)-cyclodextrintrin with linecaps utilizing an aqueous citric acid solution [56]. Pyromellitic nanosponges are fabricated via the reaction of \(\beta\)-cyclodextrintrin and linecaps with pyromellitic dianhydride in dimethyl sulfoxide. Consequently, pyromellitic nanosponges demonstrate better retention potentials than citrate nanosponges at a metal concentration of 500 ppm. However, these citrate and pyromellitic nanosponges exhibit higher retention potentials (\(\sim\)94%) at low metal concentrations (\(\leq\)50 ppm). The citrate nanosponge can selectively adsorb significant amounts of heavy metals in the attendance of meddlesome salts from sea water compared to the other constructed nanosponge [56]. [PERSON] et al. [57] synthesized Co\({}_{3}\)O\({}_{4}\)/NiO nanosponges through a precipitation method for the photocatalytic degradation of rhodamine B and Congo red dye, wherein they exhibited high photocatalytic efficacy, offering them as attractive candidates with superb photocatalytic performance against organic contaminants [57]. It appears that future works should be envisioned for the optimization of conditions (e.g., temperature, pH, amount of adsorbents used, contact time, competing ions, etc.) to improve the wastewater treatment processes.