## 3 Results and Discussion
### Sorbent Recyclability
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sorbent** & **Concentration** & **Loading** & **Contact Time** & **Removal** \\  & **(ppb)** & **(g.L\({}^{-1}\))** & **(min)** & **Efficiency** \\ \hline Cys-C@Fe\({}_{3}\)O\({}_{4}\) (this work) & 5–100 & 0.01 & 60 & 94–99.4\% \\  & 1000 & 0.01 & 10 & 90\% \\
2-mercapto-benzothazole & 5–200 & 1.00 & 4 & 92–99\% \\ Fe\({}_{3}\)O\({}_{4}\) composite [13] & 5–200 & 1.00 & 4 & 92–99\% \\ N(CH\({}_{2}\)COOH)\({}_{2}\) containing & 5–50 & 0.40 & 10 & \(\sim\)98\% \\ polymer/Fe\({}_{3}\)O\({}_{4}\) composite [12] & 5–50 & 0.40 & 10 & \(\sim\)98\% \\ Magnetic powdered activated carbon [14] & 100 & 1.00 & 180 & 84\% \\ Thiol-silica-coated magnetite [15] & 80 & 0.008 & 15 & 100\% \\ Acrylamide-hydroxyl-MOFs [10] & 100 & 0.05 & 60 & 80\% \\ MOF-74-Zn [16] & 20–50 & 0.10 & 120 & 54–72.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of adsorption capacities of sorbents towards Hg(II) removal from dilute aqueous metal solutions (100 ppb \(\geq\) (Hg(II)). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sorbent** & **Nmax (mg.g-1)** & **Sorbent Loading** & **Initial Hg** & **Final Hg** & **PC** \\
**Sorbent** & **(g-1-1)** & **(ppm)** & **Concentration** & **Concentration** & **(mg-1)** & **(mg-1)** \\ \hline
500 Cys-cGeFeO\({}_{4}\) (this work) & 94.33 & 0.01 & 1000 & 105 & 89.5 & 171.0 \\  & & & 100 & **0.86** & 9.9 & 2321.4 \\  & & & 50 & **0.45** & 5.0 & 2208.7 \\  & & & 20 & **0.36** & 2.0 & 1094.3 \\  & & & 10 & **0.34** & 1.0 & 569.9 \\  & & & 5 & **0.31** & 0.5 & 303.5 \\ \hline
2-mercapto-benzothiee Fe\({}_{3}\)O\({}_{4}\) composite [13] & 0.59 & 2.00 & 100 & 2.20 & 0.050 & 4.45 \\  & & & 50 & **0.70** & 0.025 & 7.1 \\  & & & 20 & **0.28** & 0.010 & 7.1 \\  & & & 10 & **0.56** & 0.005 & 1.7 \\  & & & 5 & **0.38** & 0.002 & 1.2 \\ \hline N(CH\({}_{2}\)COOH)\({}_{2}\) containing polymer/Fe\({}_{3}\)O\({}_{4}\) & 36.5 & 0.40 & 50 & 1.10 & 0.122 & 22.29 \\  & & & 20 & **0.50** & 0.049 & 19.6 \\  & & & 10 & **0.20** & 0.025 & 24.6 \\  & & & 5 & **0.10** & 0.012 & 24.6 \\ \hline Magnetic-powdered activated carbon [14] & n.d. & 1.0 & 100 & 26 & & n.d. \\ \hline Thiol-silica-coated magnetite [15] & 207.7 & 0.008 & 80 & **0.00** & n.a. & n.a. \\ \hline  & & & 100 & 20.0 & 1.6 & 16.05 \\  & & & 20 & 3.05 & 0.339 & 22.3 \\ Acrylamide-hydroxyl- MOFs [10] & 333 & 0.05 & 10 & 1.65 & 0.167 & 20.3 \\  & & & 5 & 1.45 & 0.071 & 9.8 \\  & & & 2 & **0.68** & 0.026 & 7.8 \\  & & & 1 & **0.57** & 0.009 & 3.0 \\ \hline MOF-74-Zn [16] & 63 & 0.1 & 50 & 23.9 & 0.261 & 2.19 \\  & & & 40 & 20.0 & 0.20 & 2.01 \\  & & & 20 & 13.8 & 0.062 & 0.90 \\  & & & 10 & 8.1 & 0.019 & 0.47 \\  & & & 5 & 4.5 & 0.005 & 0.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparative sorption capacities, Hg concentrations before and after treatment, Hg uptake, and partition coefficient values for various sorbents for Hg(II) removal at ultralow metal concentrations. The numbers in bold indicate the Hg(II) concentration lower than the World Health Organization (WHO) and European Union (EU) permissible limits of total mercury in drinking water. Note that n.d. is denoted as not determined as the volume of treated Hg(II) solution is unknown, while n.a is denoted as not applied due to the partition coefficient (PC) value is infinity using Equation (3).