## 5 Conclusions  
In this work, activated carbon from paper waste was successfully used for the uptake of Cr(VI) and MB from water by batch adsorption experiments. The FTIR results showed changes in the spectra after activation. SEM images showed that the surface morphology of the adsorbents consisted of amorphous particles. EDX showed that all activated samples had a higher content of (O) compared to CPW. Raman spectra showed characteristic peaks assigned to the disordered (D) and graphitic (G) bands around 1350 and 1600 cm\({}^{-1}\). BET showed that the activated samples had a larger surface area than CPW. Batch adsorption studies showed that the initial concentration of contaminants in the water influenced the extent of uptake. At a higher initial concentration (200 mg/L), there was a stronger interaction between the contaminant and the adsorbent than at the lower initial concentrations (20, 40, 60, 80 mg/L). These data are consistent with the Freundlich isotherm. The data obtained from the effect of time showed that the rate and the interval of contact time are crucial. This study showed that the uptake increased when the interaction time between the pollutant and the adsorbent was increased. The rate data were consistent with the PSO model. The study of the pH of the solution showed that the adsorption of Cr(VI) decreased when the pH was gradually increased; on the other hand, MB showed increased adsorption with increasing solution pH. The temperature studies show that the enthalpy was positive, indicating that the uptake process is endothermic. The Gibbs free energy values were all negative, indicating that adsorption between the adsorbents and the contaminants was favored. Entropy, on the other hand, showed positive values, indicating an increase in freedom during uptake. After four consecutive cycles, all the samples retained more than 60% of their uptake capability. Future research for carbon derived from paper waste \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Precursor** & **Activator** & **qe (mg/g)** & **Pollutant** & **Reference** \\ \hline Carbon from hemp roots & H\({}_{3}\)PO\({}_{4}\) & 43.60 & Cr(VI) & [39] \\ Carbon from paper & HNO\({}_{3}\) & 36.93 & & This study \\ Carbon from pine corn & H\({}_{3}\)PO\({}_{4}\) & 29.60 & & [40] \\ Coal reject & H\({}_{3}\)PO\({}_{4}\) & 29.90 & & [41] \\ Coconut shell carbon & HNO\({}_{3}\) & 10.88 & & [42] \\ Carbon from mango kernels & H\({}_{3}\)PO\({}_{4}\) & 7.800 & & [13] \\ Waste carbon & H\({}_{2}\)SO\({}_{4}\) & 7.485 & & [43] \\ Commercial carbon & HCl & 4.350 & & [44] \\ Coconut shell carbon & H\({}_{2}\)SO\({}_{4}\) & 4.040 & & [43] \\ \hline Montmorillonite@MgAl LDH nanocomposite & - & 815.9 & MB & [45] \\ Magnetic asphalt-based activated carbon & KOH & 710.0 & & [46] \\ Carbon from pine corn & ZnCl\({}_{2}\) & 60.97 & & [47] \\ Acid geopolymer-based clays & H\({}_{3}\)PO\({}_{4}\) & 49.00 & & [48] \\ Carbon from paper & HNO\({}_{3}\) & 35.25 & & This study \\ Commercial carbon & KOH & 20.88 & & [49] \\ Carbon from acorn peels & KOH & 17.54 & & [50] \\ Black cumin seeds & H\({}_{2}\)SO\({}_{4}\) & 16.42 & & [51] \\ Carbon from stems of _Lantana camera_ L. & - & 15.39 & & [52] \\ Spent rice biomass & - & 8.130 & & [53] \\ Carbon from rice husks & KOH & 7.110 & & [54] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparative adsorption studies with similar biochar and hydrochar materials. includes testing the modification and activation using green solvents and nanoparticles. It is also necessary to investigate the adsorptive feasibility of other metal ions and dyes, anions, pharmaceuticals, and organics. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14114585/s1](https://www.mdpi.com/article/10.3390/app14114585/s1)]([https://www.mdpi.com/article/10.3390/app14114585/s1](https://www.mdpi.com/article/10.3390/app14114585/s1)). Conceptualization, N.D.S. ; Methodology, K.M., P.M.T. and N.D.S. ; Software, P.M.T. ; Validation, P.M.T. ; Formal analysis, K.M. ; Investigation, K.M.