# Wastewater Treatment by Polymeric Microspheres: A Review
## 2 Synthetic Polymer
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**S. No** & **Polymer** & **Adsorbate** & **Result** & **Kinetic** & **Isotherm** & **Model** & **Reference** \\ \hline
1 & PVA & CODMn removal rate & 16.99\% & - & - & [33] \\ \hline
2 & poly(EGMDA-VIM) & phenol & 34.7441 mg/g & PSO & Freundlich & [34] \\ \hline
3 & PAN, phenolic resin & oil removal efficiency & 93.6\% & - & - & [35] \\ \hline
4 & P(St-DVB)/CuNi & Pb(II), Cd(II), Mn(II), & 15.60, 5.28, 22.42, & & & \\  & Zn(II) & 20.57 mg/g & & & & \\ \hline
5 & St-DBV-SH & Cu(II), Zn(II), Cd(II), & 45.26, 32.42, 62.77, 135.85, & & & \\  & Pb(II), Ni(II) & 49.88 mg/g & & & & \\ \hline
6 & SPS & Pb(II), Zn(II), Cu(II) & 49.16, 15.38, 13.89 mg/g & PSO & Langmuir & [38] \\ \hline
7 & DVB, TEVS &
\begin{tabular}{c} nitrobenzene, \\ 4-nitrophenol, phenol \\ \end{tabular} & - & - & - & [39] \\ \hline
8 & P(VP-DVB)-6 & SY, BPB dye & 261.78, 277.01 mg/g & PSO & Langmuir & [40] \\ \hline  & PVA: polyvinyl alcohol, CODMn: chemical oxygen demand using KMnO\({}_{\text{A}}\), EDDMA-VIM: ethylene glycol methacrylate\({}_{\text{n}}\)-vinyl imidazole, PAN: polyacrylamide\({}_{\text{St-DVB}}\): styrene-divinylbenzene, SPS: sulphonated polystyrene, TEVS: trichotyvinylsilane, VI: vinyl pyridine, SY: sunstely yellow, BPB: bromophenol blue. \\ \end{tabular}
\end{table} 
Table 2: Summary efficiency of vinylic polymer as adsorbent. but decreased as initial metal concentration increased. Adsorption differed for each metal, and P(St-DVB)/CuNi BNC showed the highest adsorption efficiency for Mn\({}^{2+}\) and Zn\({}^{2+}\). It also differed regarding the pH range. While lead showed the best adsorption at pH 5-7, Cd, Mn, and Zn were optimal at pH 7. The maximum adsorption capacity for each metal was 15.60 mg for Pb(II)/g, 5.28 mg for Cd(II)/g, 22.42 mg for Mn(II)/g, and 20.57 mg for Zn(II)/g, respectively. The adsorption process followed the PFO kinetic model and the Langmuir adsorption isotherm model. Another microsphere using St-DVB was modified by introducing attractive thiol (SH) groups on the surface of polymeric matrices for the removal of heavy metal ions in wastewater [37]. The obtained St-DBV-SH microsphere was fabricated using a four-step modification. First, parent St-DVB microspheres were treated by H\({}_{2}\)SO\({}_{4}\) to obtain thiol derivatives. The ileum was then added, and sulfonic groups were converted to chloride acylsulfonic groups while PCL\({}_{5}\) and POCl\({}_{3}\) existed. Lastly, the microsphere was reduced by using SnCl\({}_{2}\cdot\)2H\({}_{2}\)O. The modification allowed a thiol group with 12.94% of sulfur on the surface of microsphere, and it had low swelling tendency in organic solvents of 8% (at maximum). The presence of thiol groups was confirmed via elemental analysis. DSC analysis showed lowered thermal resistance after modification, but it was sufficient for sorption process. The batch method was conducted to evaluate the removal of Cu(II), Zn(II), Cd(II), Pb(II), and Ni(II). For all adsorption studies, pH 5 was the optimal condition. The adsorption followed the PSO kinetic model and the Langmuir isotherm model, which was confirmed by high values of determination coefficients. Similarly, a monodisperse sulphonated polystyrene (SPS) microsphere was prepared to check the effect of the sulfonic group for the sustainable elimination of heavy metals in wastewater [38]. It also followed the PSO kinetic model and the Langmuir isotherm model. The SPS microsphere was fabricated using a scalable method by sulphonated modification, having a considerable number of sulphonic groups on the surface of the microsphere (which provided efficient binding sites for metal ions). The abundant sulphonic acid groups and their superior monodisperse properties increased the adsorption ability in both quantity and speed. The theoretical maximum capacities at pH 3.5 and 30 \({}^{\circ}\)C were 49.16 mg/g for Pb\({}^{2+}\), 15.38 mg/g for Zn\({}^{2+}\), and 13.89 mg/g for Cu\({}^{2+}\), respectively. The adsorption equilibrium for Pb\({}^{2+}\) was reached within 1 min.