## 4 Factors that Affect the Adsorption Process  
### Effect of pH  
The extraction of the ions can be altered through the pH of the solution. The desired pH can be obtained through a suitable buffer. Buffer affects the process of ion formation during the interaction of metal ions and adsorbent. A discussion in an article explained the impact of pH on the adsorption of mercury ions by polyacrylamide-amino-1,3,4-thiadiazole (PAN-ATD) in the pH range 2.5-6.5 at 298 K. It was found that adsorption value of chelating  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**S. No.**} & \multicolumn{1}{c}{**Adsorbent**} & \multicolumn{1}{c}{**Maximum Adsorption**} & \multicolumn{1}{c}{**Initial**} & \multicolumn{1}{c}{**Optimum pH**} & \multicolumn{1}{c}{**Reference**} \\ \hline
7. & Dendrimer-grafted polyacrylamidefliribers & Hg\({}^{2+}\): 227.64 mg /g/180 min & 1–500 ppm & [86] \\ \hline
8. & Thio-functionalized polyacrylamidefliribers & Hg\({}^{2+}\): 322.8 mg /g/200 min & 30–500 ppm & [32] \\ \hline
9. & Maghemite- and graphene-oxide-embedded Polyacrylonitrile & As\({}^{5+}\): 36.1 mg/g/90 min & 1–50 ppm & [124] \\ \hline
10. & Fe\({}_{2}\)O\({}_{3}\)/polyacrylonitrile & Pb\({}^{2+}\): 70.34 mg/g/120 min & 100 ppm & [87] \\  & nanofiber & Pb\({}^{2+}\): 49.57 mg/g/120 min & 50 ppm & [87] \\ \hline
11. & Alkylated polyacrylamideflirible-PEI anion exchange fiber & NO\({}_{3}\)’: 31.32 mg/g/10 min & 10–100 ppm & [92] \\ \hline
12. & Polyacrylonitrile @NC fibers & Cr\({}^{6+}\): 290.70 mg/g/2880 min & 20–300 ppm & [93] \\  & & 2,4-dichlorophenoxyacyacetic acid: & 20–300 ppm & [93] \\  & & 164.47 mg/g/2160 min & 20–300 ppm & \\ \hline
13. & Amine-modified polyacrylamideflirible & Cu\({}^{2+}\): 150.6 mg/g/600 min & 200 ppm & \\  & & Ag\({}^{+}\): 155.5 mg/g/300 min & 200 ppm & [125] \\  & nanofiber mats & Fe\({}^{2+}\): 116.5 mg/g/300 min & 200 ppm & \\  & & Pb\({}^{2+}\): 60.6 mg/g/300 min & 200 ppm & \\ \hline
14. & PAA/dextran/aniline nanofibers & Pb\({}^{2+}\): 951.1 mg/g/5 min & 200 ppm & [98] \\  & & Cu\({}^{2+}\): 832.7 mg/g/5 min & & \\ \hline
15. & Amino-functionalized polyacrylamidefliribers & Hg\({}^{2+}\): 1116 mg /g/120 min & 850 ppm & [99] \\ \hline
16. & Polyacrylonitrile/cyclodextrinurin/graphene oxide nanofibers & Crystal violet: 16.47 mg/g/10 min & 25–100 ppm & [101] \\ \hline
17. & Polyacrylonitrile/ polyacrylamidefliribers & Direct red 80: 999 mg/g/5 min & & \\  & & Direct red 23: 942 mg/g/5 min & 40 ppm & [76] \\ \hline
18. & Aminated PAN/PVDF composite nanofibers & Direct red 23: 573.3 mg/g/ & 50 ppm & [96] \\ \hline
19. & Carbon-dot-modified Polyacrylonitrile fiber & Methyl orange: 422 mg/g & 65 ug/mL & [126] \\ \hline
20. & Fe/Ag bimetallic nanoparticles immobilized on EDTA-EDA-modified polyacrylonitrile nanofibers & Methyl orange: 96\% & 100 ppm & [127] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Cont.  
resin rises with pH from 2.5 to 6.5 and attained the highest value 456.1 mg/g at pH 6.5. The adsorption was decreased at low pH value of solution due to the competitive adsorption effect of H\({}^{+}\) ions with mercury ions. As the value of pH reached 4.0, mercuric hydroxide (Hg(OH)\({}_{2}\)) was the main compound to be formed. The amine group was deprotonated as the pH was increased as shown in Figure 8[45].