حذف فلزات سنگین و آلوده کننده ارگانیک از آب با استفاده از جاذب های پلیمر های دندریت Removal of heavy metals and organic pollutants from water using dendritic polymers based adsorbents: A critical review

1. Introduction Fresh water is a basic requirement for the sustainability of human and wild life on the earth. The availability of clean drinking water is paramount to maintain a healthier life. Intensive industrialization and urbanization have resulted in pollution of the natural water resources with inorganic and organic pollutants [1–2]. These pollutants include but not limited to heavy metals, polyaromatic hydrocarbons, and dyes. The toxicity and health risks of these pollutants are well-understood, and their presence in drinking water above a certain limit can pose serious health risks to the human body. This is the reason that removal of these pollutants from water is a great subject of research nowadays [3]. Among different removal technologies, adsorption has been widely adopted [4]. In this regard, a wide range of adsorbents has been studied that include materials based on carbon [5], silica [6], polymers [7], natural adsorbents [8–9], and others. The development of new adsorbents that are cost-effective, efficient, and non-toxic in nature is a hot topic of research in the area of water treatment and purification. Dendritic polymers are highly branched polymers that contain three-dimensional architectures. They can be classified at least into the following six subclasses based on some structural differences; dendrimers, hyperbranched polymers, multi-arm star polymers, dendronized or dendrigrafts polymers, hypergrafts or hypergrafted polymers, dendritic-linear block polymers [10–12]. Schematic diagram of different classes of dendritic polymers is given in Fig. 1. Among these classes, dendrimers are most widely used for water purification applications. Although other dendritic polymers have also been employed in some reports, most of the authors used term “dendrimer” even for other subclasses of dendritic polymers. Dendrimers are novel nanostructured synthetic polymers that possess a highly branched structure with a unique three-dimensional molecular configuration and a large number of (reactive) end groups [13–15]. They are complex monodisperse macromolecules with a regular and well-defined chemical structure, and are excellent structurally ordered systems. Their functional groups can react with different functional moieties of other molecules at the nanoscale. This reactivity comes from multifunctional architecture and empty internal cavities. Dendrimers have received special attention for functionalization over various substrates as they possess many superior properties compared to linear polymers. They are unique in their viscosity, density distribution, and flexibility [16]. Exploration of different applications of dendrimers is still a growing field of research in supramolecular chemistry. They exhibited promising potential to be used in drug delivery [17], tissue engineering [18], bio-imaging [19], catalysis [20], cancer therapy [21], and in many other areas. They have been anticipated as promising adsorbents for the removal and analytical extraction of different pollutants from water. It is their ease of functionalization with different chemical groups and presence of numerous internal cavities that enable them to selectively adsorb the target pollutants. They have a wide range of applications in water treatment particularly as an adsorbent for the removal and extraction of different heavy metals, dyes, and organic pollutants. As analytical extractions and removal rely on the same concept [22], dendrimers have shown some exciting applications in analytical extractions [23–32], but the core of this article is to focus and highlight their applications in the adsorption based removal of pollutants.