# A Review of Adsorbents for Heavy Metal Decontamination: Growing Approach to Wastewater Treatment
## 6 Factors Affecting the Adsorption Process
### Synthetic Polymer Adsorbents
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**S. No.** & **Adsorbent** & **Metal Ion** & **Adsorption Capacity** & **References** \\ \hline \multirow{2}{*}{1} & \multicolumn{2}{c}{Amine-mercaptan modified poly} & \multirow{2}{*}{Hg(II)} & \multirow{2}{*}{621.8 mg/g} & [29] \\  & (GMA-DVB) & & & \\ \hline \multirow{2}{*}{2} & \multicolumn{2}{c}{(GMA-MMA-DVB) having pendant urea} & \multirow{2}{*}{Hg(II)} & \multirow{2}{*}{7.8 mmol/g} & [205] \\  & & group & & \\ \hline \multirow{2}{*}{3} & \multicolumn{2}{c}{Dibutylamine and chloroacetamide} & \multirow{2}{*}{Hg(II)} & \multirow{2}{*}{2.5 mmol/g} & [206] \\  & & modified poly (GMA-EGDMA) & & \\ \hline \multirow{2}{*}{4} & \multirow{2}{*}{Cross-linked Poly (GMA-aspartic acid)} & Cu(II) & 1.40 mmol/g & [207] \\  & & Cd(II) & 1.28 mmol/g & \\ \hline \multirow{2}{*}{5} & \multicolumn{2}{c}{Ethylenediamine modified} & \multirow{2}{*}{Pt(IV)} & \multirow{2}{*}{1.3 mmol/g} & [208] \\  & & poly(GMA-co-EGDMA) & & \\ \hline \multirow{2}{*}{6} & \multicolumn{2}{c}{Ferric oxide containing poly} & \multirow{2}{*}{Hg(II)} & \multirow{2}{*}{124.8 mg/g} & [29] \\  & & & & \\ \hline \multirow{2}{*}{7} & \multicolumn{2}{c}{PGMA–EDA} & \multirow{2}{*}{Hg (II)} & \multirow{2}{*}{4.76 mmol/g} & \multirow{2}{*}{[209]} \\  & & PGMA–DETA & & 4.80 mmol/g & \\ \cline{1-1}  & & PGMA–TEPA & & 4.21 mmol/g & \\ \hline \multirow{2}{*}{8} & \multicolumn{2}{c}{PGMA–EDA} & \multirow{2}{*}{Pb(II)} & \multirow{2}{*}{4.74 mmol/g} & \multirow{2}{*}{[209]} \\  & & PGMA–DETA & & 4.73 mmol/g & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Adsorption capacities of functionalised glycidyl methacrylate for removal of toxic metal ions. 555.55 mg/g. The sorption rate of hexavalent chromium ions onto amine-functionalised glycidyl methacrylate copolymer was studied by [PERSON] et al. [217]. Two samples of macroporous crosslinked poly(GMA-EGDMA) functionalised with ethylenediamine and diethylene triamine moieties having different pore sizes of the polymers were prepared through the suspension copolymerisation method. The rate of sorption of chromium by amino-functionalised poly (GMA-EGDMA) was studied individually for each ion as well in a mixture of solutions. Kinetic models were used to explain the phenomena of metal sorption. [PERSON] et al. reported cross-linked poly(glycidyl methacrylate-aspartic acid) was used for the recovery of Cu and Cd ions from aqueous solution by using chelating resin [207]. Equilibrium sorption values were found to be 1.40 and 1.28 mmol/g for Cu and Cd ions, respectively in non-competitive conditions. However, under competitive conditions, adsorption selectivity for Cu ions was observed in the presence of Cd at pH 2-2.5. Grafting of glycidyl methacrylate with dimethylamine and HCl leads to the formation of an anion exchanger bearing N\({}^{+}\)HR\({}_{2}\) Cl\({}^{-}\) functional group [218]. The resin was found to remove 99.6% vanadium metal ion in the pH range of 4-6. [PERSON] and co-workers prepared chitosan and alginate nanocomposites for the extraction of chromium (VI) from wastewater [219]. Chitosan and alginate nanoparticles were synthesised separately by an ionic crosslinking process by using sodium tripolyphosphate, calcium chloride, and its nanocomposites of ratio 1:1 were synthesised in the presence of glutaraldehyde as a crosslinker. An adsorption study has been done by the batch method and various factors have been studied such as the effect of rate of adsorption, the effect of initial concentration, adsorbent dose, pH, and stirring time. On studying the effect of time on adsorption phenomena, it was found that CS-AL nanocomposites with glutaraldehyde showed maximum adsorption within 300 min. [PERSON] et al. synthesised layer-by-layer (LbL) assembled forward osmosis (FO) membranes by accumulating several polyethyleneinimes (PEI) and sodium alginate (SA) bilayers on polydopamine-functionalised polyvinylidene fluoride (PVDF) supportive membrane [220].