# Metachrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions
## 3 Natural Polymers, Inorganic Materials, and Polymer/Inorganic Composite as Metal Ions Sorbents
Chitosan-poly(maleic acid) nanomaterial, obtained by grafting poly(maleic acid) onto chitosan and crosslinked with glutaraldehyde, was used for mercury, lead, copper, cadmium, cobalt, and zinc (Hg(II), Pb(II), Cu(II), Cd(II), Co(II), and Zn(II)) ions adsorption [46]. The obtained material was selective for Hg(II) ions, with a maximum sorption capacity of 1044 mg/g at pH 6.0. The increasing interest in mesoporous silica originates from its favorable porous characteristics, i.e., large surface area in the range 600-1000 m\({}^{2}\)/g, narrow pore-size distributions, and large and controlled pore size (5-30 nm), which results in fast kinetics of metal ions adsorption [34]. The sorption performances could be improved by co-condensation and post-synthesis grafting functionalization. [PERSON] et al. tested mesoporous silica materials functionalized with amino and mercapto groups (fiber-like, rod-like, and platelets) as Cu(II) and Pb(II) adsorbents [47]. It was concluded that thiol-functionalized mesoporous silica adsorbents have a better affinity for Pb(II) compared to amino-mesoporous silica. On the other hand, amino-mesoporous silica has a stronger affinity for Cu(II) ions. However, grafting could reduce the pore size of the modified mesoporous materials, particularly when grafting is performed with bulky functional groups. This might cause a decrease in diffusion to the adsorption sites and, consequently, reduce adsorption capacity. [PERSON] et al. [48] observed a sharp decrease in silica pore volume and surface area after grafting. For example, a surface area decrease of 53% was observed for aminopropyl functionalized mesoporous silica compared to an initial mesoporous silica support. [PERSON] et al. studied the adsorption of Cu(II) on various inorganic adsorbents (silica gel, aluminum oxide, etc. ), functionalized with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) [49]. The Cu(II) removal capacity of DTPA-modified silica was considerably lower compared to EDTA-modified silica, suggesting that the adsorption was restricted due to the decrease in pore sizes and pore blockage when the bulkier DTPA was attached to the material. The composite of mesoporous silica functionalized with (3-chloropropyl) triethoxysilane with incorporated tetrakis(4-hydroxyphenyl) porphyrin was used as Pb(II) ions adsorbent [50]. The optimal pH values for Pb(II) and for Cu(II) ions sorption were 2-6 and 5, respectively. The maximum Pb(II) adsorption capacity of the composite was 134 mg/g. It was observed that the presence of porphyrin in silica causes a significant increase in heavy metal ion adsorption. The adsorption process is well fitted with Langmuir isotherm, while the kinetics obeys the pseudo-second-order kinetics. [PERSON] et al. used magnetic multiwall magnetic carbon nanotubes (6O-MWCNTs@Fe\({}_{3}\)O\({}_{4}\)) as Cd(II), Ni(II), Zn(II), Cu(II), and Pb(II) sorbent. The rapid sorption was observed, with 30 min needed to attain equilibrium [51]. It was shown that 6O-MWCNTs@Fe\({}_{3}\)O\({}_{4}\) exhibits good selective Pb(II) adsorption performances, with a high Pb(II) maximum adsorption capacity of 215.05 mg/g, much higher than the existing adsorption capacity of this type of adsorbent. The adsorption capacities for Cu(II) and Cd(II) were 87.1 mg/g and 57.3 mg/g, respectively.