## 1 Background  
Water decontamination is one of the most serious challenges among scientists globally due to the increasing population, pollution, and global warming [1; 2; 3; 4; 5]. Wastewater from developing industries, such as chemical manufacturing, metallurgical, battery manufacturing, papermaking, and mining industries produce a very large amount of various toxic pollutants in the form of heavy metal ions [6; 7; 8; 9]. Excess heavy metal ions concentration in wastewater is a serious risk to public health as well as to other living organisms on Earth [10; 11; 12]. These toxic heavy metal pollutants are widely found in the Earth's crust which tends to bioaccumulate in living organisms; they are non-biodegradable, which can cause various diseases, genetic disorders, and lethal ecological effects [13; 14; 12; 15]. Heavy metal ions in aqueous media pose several toxic threats to the human health as well as to the other living organisms even at low concentrations. As per the regulatory system of the WHO (World Health Organization), the permissible concentration of Pb(II) (Lead (II)) in wastewater is approximately 0.01 mg/L [16; 17; 18]. Moreover, the excess exposure of Pb(II) can lead to irreversible brain damage, cardiovascular disease, cognitive impairment, encephalopathy disease symptoms and even death [19; 20; 21; 22]. Pb(II) is also extremely toxic to the nervous system, kidneys, and may lead to a wide range of human health issues such as nausea, anemia, infertility, coma, convulsions, hemochromatosis, renal failure, cancer, adverse effects on the metabolism and intelligence, and dermatitis brass chills, and cramps in the calves [12; 14; 23; 24; 25; 26; 27]. The current tight regulatory systems do not allow the release of heavy metal ions-contaminated wastewaters into the environment and require the removal of all toxic pollutants before discharging. Therefore, the development of efficient and economical novel materials and technologies for the effective removal of metal ion pollutants are required. Several traditional techniques have been used for the removal of heavy metal ions from aqueous medium, including reverse osmosis, precipitation, biosorption, ion-exchange, electrochemical processes, membrane filtration, irradiation, coagulation, and adsorption [28; 29; 30]. Table 1 lists the techniques used for Pb(II) ions removal from the wastewaters. The main disadvantages of conventional techniques include high cost, metallic sludge generation, incomplete removal, and disposal of secondary waste. Therefore, a cost effective, potential and convenient decontamination technology for wastewater treatment is highly desirable. The high efficiency, cost-effective, and simple operation makes adsorption technology one of the most promising technology for the effective removal of the heavy metal ions from the aqueous solution which adsorb metallic ions at solid-liquid interfaces [41; 42; 43; 44; 45; 46; 47; 48; 49]. On the other hand, adsorption technology has several challenges, such as selective recovery and reuse of valuable adsorbents and pollutants in the presence of humic substances [50; 51]. Adsorbents developed with favorable structures, morphologies, superior adsorption capacities, and ease of separation are a major focus of the current research [52; 53; 54; 55; 56; 57; 58; 59; 60]. Recently, the development of nanotechnology has attracted considerable attention due to the remarkable potential of the nanoadsorbents for the selective and effective removal of ionic pollutants from aqueous solution when compared with the traditional adsorbents [61; 62; 63; 64; 65; 66; 13; 63; 62; 61; 64; 63; 65; 66]. The nanoadsorbents play a major role in the separation of heavy metal ions because they are effective sorbents due to their unique structural properties and specific adsorption tendency. Nanoadsorbents have several unique advantages over conventional adsorbents due to their large specific surface area to volume ratio, tunable pore size, regeneration, reusability etc. [67; 68; 69; 70; 33; 56; 71].