# Nanosponges for Water Treatment: Progress and Challenges
## 2 Nanosponges for Water Treatment
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Materials or** & & **Limitations/Challenges** & & **Advantages** & **Refs.** \\ \hline \multirow{8}{*}{(Nano) zeolites} & - & Low capacity of adsorption & - & Low cost \\  & - & Low permeability & - & High surface area \\  & - & Restrictions in the removal of organic & - & Appropriate for the elimination of \\  & - & contaminants & & various contaminants \\  & - & Complex adsorption mechanism & - & Low cost \\  & - & Low capacity of adsorption & - & Appropriate for the elimination of \\  & - & pH sensitivity & - & Appropriate for the elimination of \\  & - & pH cost & - & High efficiency for removing pollutants \\ Carbon-based & - & Low selectivity & - & Room water \\ nanomaterials & - & Poor regeneration & - & Good capacity of adsorption \\  & - & Commercialization potentials & - & Commercialization potentials \\  & - & Simplicity & - & \\  & - & pH sensitivity & - & High activity \\  & - & Needs modifications to improve & - & High efficiency \\ materials & & properties & - & Low cost and competitive tactics \\  & - & - & Biodegradability \\  & - & Low resistance towards alkaline solutions & - & High abundancy \\ Silica-based & - & Not suitable for the removal of pollution & - & Availability and low cost \\ (nano)materials & & in solutions with pH \(<\) 8 & - & Low cost \\  & - & Preparation of nanophotocatalysts & - & Stability \\  & - & Commercialization/up-scalable & - & Recyclability \\ Nanophotocatalysts & & production & - & Eco-friendliness [37; 39] \\  & - & Safety evaluations & - & High sensitivity \\  & - & - & High specific surface area \\  & - & Tunable porous structures \\  & - & Complexation behavior & - & Low cost \\ Nanosponges & - & Commercialization/up-scalable & - & Good biocompatibility \\  & - & production & - & Easy surface functionalization \\  & - & Toxicity/biosafety issues & - & Bio-absorbent properties \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Some salient advantages and limitations of materials/nanosystems applied for water treatment and pollutant removal from aqueous solutions. repulsion-ion exchange, physical adsorption, and electrostatic attraction. The maximum elimination results can be obtained for removing Co\({}^{2+}\) (-7.812 mg/g) and Pb\({}^{2+}\) (-35.86) [41]. [PERSON] et al. [42] designed glycopolymer nanosponges from monosaccharides and \(\beta\)-cyclodextrinrin by combining a Fischer glycosylation, click reaction, and cross-linking reaction for eliminating boron from water. Secondary bonding, including van der Waals forces and hydrogen bonding, among the incorporated saccharides and the adsorbates, can be accountable for vast improvements in adsorption rates and removal capabilities, providing functional candidates for water treatment and seawater desalination [42]. In addition, cyclodextrin-based nanosponges are synthesized for removing organic pollutants from water, including chlorinated disinfection by-products and 2-methylisoborneol (an odor-causing material in water). High absorption efficiency (-99%) can be attained using these polymers with excellent recyclability [43]. \(\beta\)-cyclodextrinrin-based nanosponges immobilized with magnetic nanoparticles exhibit excellent potentials for capturing and enriching organic micropollutants (the removal efficiency was -90% within -1 min), which can be further evaluated for designing sensitive sensing systems (Figure 1). These ultra-rapid and selective sensing strategies with high efficiency for molecule enrichment can be utilized to design smart nanosystems and devices with portability, flexibility, cost-effectiveness, and simplicity advantages [44]. Cyclodextrin-bas ed nanosponges are designed for the elimination of \(p\)-nitrophenol from aqueous streams through the adsorption process [45], and they are prepared via the reaction of \(\beta\)-cyclodextrinrin with hexamethylenediisocyanate as the cross-linking agent.