## 6 Conclusions and Future Directions  
AC derived from waste tyres has a high potential to be used as an adsorbent and replace commercial AC due to the low cost as well as eco-friendliness of the waste tyres-based raw materials. A large number of studies on coal-based and biowaste-derived-AC are available in the literature, however, further investigation is warranted on AC that is derived from precursors such as waste tyres. This review highlights the preparation of activated carbon through pyrolysis and the activation process, the different forms of ACs that are commercially available and used by industries, and the factors affecting the adsorption. Different applications of AC derived from waste tyres were reviewed and it was observed that the AC derived from waste tyres fulfil the needs of removal of pollutants such as heavy metals and dyes from all types of wastewater, such as stormwater, wastewater treatment effluent, etc. Even though several methods for recycling waste tyres are available, there is still a significant knowledge gap or limitation, because of which a large percentage of waste tyres are still not being recycled. This could be because it has proven difficult to construct large-scale pyrolysis facilities. The extraction and disposal of harmful gases from such facilities have also been a challenge. Another possible reason could be that the necessary characterization of the rubber waste has not been undertaken, thus real-time waste tyres \begin{table}
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**Authors, Year** & **Type of Activation** & **Activation Temperature (\({}^{\circ}\)C)** & **Activation Time (h)** & **PHT** & **Surface Area (m\({}^{2}\)/g) and Pore Volume (cm\({}^{2}\)/g)** & **Type of Pollutants Removed from the Wastewater** \\ \hline [PERSON] et al., 2017 [34] & Chemical (KOH) & 750 & 2 & 7 & 265 \& 358 and 0.30 \& 0.63 & Pb\({}^{2+}\), Cd\({}^{2+}\), and Cr\({}^{3+}\) \\ \hline [PERSON] et al., 2017 [70] & Chemical (KOH) & 700 & 2 & 7 & 490 and 0.24 & Malachite green and Methyl orange \\ \hline [PERSON] et al., 2017 [71] & Chemical (ZnCl\({}_{2}\)) & 700 & 3 & 3 & 396 and 0.59 & Methylene blue dye \\ \hline [PERSON] et al., 2017 [72] & Chemical (H\({}_{3}\)PO\({}_{4}\) and H\({}_{2}\)O\({}_{2}\)) & 200 & 2 & 6.5 & 33.567 to 48.792 and 1.034 to 1.034 & Cd(II) and Pb(II) \\ \hline [PERSON] et al., 2018 [73] & Chemical (H\({}_{2}\)O\({}_{2}\)) & 200 & 2 & 6.5 & 27.44 and 0.154 & As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn \\ \hline [PERSON] et al., 2019 [74] & Chemical (KOH) & 700 and 900 & 3 & 7 & 42 to 528 and 0.31 to 0.67 & Triton X-100 (Non-ionic surfactant) \\ \hline [PERSON] et al., 2019 [75] & Physical & 719–930 & 1–3 & 2–11 & 550 and 1.223 & Manganese \\ \hline [PERSON] et al., 2019 [76] & Chemical (KOH) & 550 to 750 & 0.25 to 1.25 & 5.6 & 928 and 1.10 & Mercury \\ \hline [PERSON] et al., 2019 [77] & Chemical (KOH) & 400 & 6 & 6.5 & 2.945 & Dye removal \\ \hline [PERSON] et al., 2021 [40] & Chemical (KOH) & 750 & 1 & 7 & 82 and 0.3024 & Pb\({}^{2+}\), Zn\({}^{2+}\), and Cu\({}^{2+}\) ions \\ \hline [PERSON] et al., 2022 [78] & Chemical (KOH) & 650 and 750 & 12 & - & 150.49 and 0.034 & p-Nitrophenol \\ \hline [PERSON] et al., 2022 [79] & Chemical (ZnCl\({}_{2}\)) & 250 & 24 & 7 & - &
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Table 2: An overview of recent studies on the production of waste tyre-derived activated carbon for wastewater treatment. recycling is still lagging behind approaches developed at the laboratory scale. Moreover, the production of value-added goods may suffer without an adequate understanding of the chemical characteristics of rubber-based materials. Consequently, there is a great responsibility not just on the researchers, but also on the policymakers, government officials, and the industry to find possible ways to increase the production, quality, and yield of activated carbon from waste tyres. Conceptualization, N.M. and S.K.S. ; methodology, N.M., S.J., M.D. and S.K.S.