# Nanosponges for Water Treatment: Progress and Challenges
## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Strategies** & \multicolumn{2}{c}{**Limitations/Challenges**} & \multicolumn{2}{c}{**Advantages**} & **Refs.** \\ \hline Reverse osmosis & - & Not suitable for small organic pollutants & - & Seawater desalination & \\ technique & - & High cost, energy, and pressure & - & Organic/inorganic pollutant removal of bacteria from wastewater & [5,6] \\  & - & Possibility of toxicity and hazardous & & \\  & effects caused by inorganic coagulants & & & \\ Flocculation/ & - & Formation of large amounts of toxic & - & Improvements in water clarity to & \\ coagulation & - & Not suitable for removing heavy metals & & decrease turbidity & [7,8] \\  & - & \multicolumn{1}{c}{Not suitable for removing heavy metals} & & \\  & & or emerging contaminants & & \\  & - & Not suitable for the purification of water & & \\  & & with dilution of heavy metals at a & & \\ Chemical & low level & - & Low cost & \\ precipitation & - & Sludge production & - & Simplicity & [9] \\  & - & Additional operative cost for the removal & & \\  & & of sludge & - & Case of processes & \\  & - & Low selectivity & - & High capacities for binding to metals & \\ Adsorption & - & High cost of adsorbents & - & Reusability & [10] \\  & - & Hard separation/isolation & - & High efficiency/efficacy & \\  & & - & Scalability & \\ Electrochemical & - & High cost & - & Flexible operations & \\ techniques & - & High energy consumption & - & High separation & [11,12] \\  & - & Long duration time & - & Less harmful/toxic by-products & \\ Photocatalysis & - & Restricted appliances & - & Concurrent elimination of organics & [13] \\  & - & Preparative process of photocatalysts & and metals & & \\  & - & Formation of concentrated sludge & - & Higher discernment & \\  & - & High cost of operation and maintenance & - & Minimal period of detention & [14] \\ Flotation & - & High cost of initial capital & - & Higher proficiency & \\  & - & Empirical process & - & Higher rate of overflow & \\  & - & Complicated processes & & \\  & - & Low permeate flux & - & Requirement of small spaces & \\ Membrane & - & High cost of membranes & - & High selectivity & \\ filtration & - & High costs of operation and maintenance & - & Requirement of low pressure & \\ techniques & - & Deterioration of productivity & - & Requirement of low pressure & \\  & - & Frequency of membrane regeneration & & \\  & - & High cost & - & High efficiency of removal & \\  & - & Renewal of resins & - & Fast kinetics & \\ Ion exchange & - & Secondary pollution toxicity/organic & - & High capacity of treatment processes & \\ method & - & contamination from resins & - & Suitability for removing nitrates and & [17,18] \\  & - & Organic matter adsorption & arsenic from water & \\  & - & Possibility of bacterial or chlorine & - & Up-scalability & \\  & & contaminations & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Some salient advantages and limitations of water treatment strategies. rescence and electric charge nanosponges based on specific properties), stimuli-responsive (with the ability of behavior modulation by external environmental changes, such as temperature/pH and reducing/oxidative circumstances), and molecularly-imprinted (with high selectivity/specificity toward molecules) nanosponges [21]. These polymers with unique properties, architectures, and high cross-linked three-dimensional networks are broadly studied in the field of pharmaceutics and biomedicine [22]. Additionally, nanosponges with suitable modifications or functionalities using carbon nanotubes, TiO\({}_{2}\), Ag, etc., have been scrutinized for removing or capturing organic/inorganic pollutants from water and wastewater [23; 24]. For instance, cyclodextrin-based nanosponges exhibit promising capacities for removing dissolved organic carbon from water (\(\sim\)84%) [25]. Surfactant-modified zeolite nanosponges are designed for removing nitrate in contaminated water, with the highest nitrate elimination capability (1338 mmol Kg\({}^{-1}\)/83 mg g\({}^{-1}\)) [26].