## 4 Conclusions  
In this study, magnetic nanocomposites have been successfully prepared by a simple combustion method, confirmed by XRD, FT-IR spectroscopy, magnetic properties, N\({}_{2}\) adsorption-desorption, TG/DSC and SEM analyses, and applied as an adsorbent for the removal of two anionic dyes (AY 42 and AR 213) from aqueous solutions. The removal efficiency of the investigated dyes decreased with an increase in the pH and increased with increasing adsorbent doses, initial dye concentrations and temperatures. The adsorption process can be performed under normal conditions (room temperature (25 \({}^{\circ}\)C) and natural  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Dye** & **Temp.** & \(\Delta G^{\circ}\) & \(\Delta H^{\circ}\) & \(\Delta S^{\circ}\) \\  & **(\({}^{\circ}\)C)** & **(J/mol)** & **(J/mol)** & **(J/mol\(\cdot\)K)** \\ \hline \multirow{4}{*}{AY42} & 25 & \(-\)5969.99 & \multirow{4}{*}{AY42} & \multirow{4}{*}{45} \\  & 45 & \(-\)6370.66 & & \\ \cline{1-1} \cline{3-4}  & 65 & \(-\)6771.33 & & \\ \cline{1-1} \cline{3-4}  & 25 & \(-\)6765.64 & & \\ \cline{1-1} \cline{3-4}  & 45 & \(-\)7219.71 & & \\ \cline{1-1} \cline{3-4}  & 65 & \(-\)7673.78 & & \\ \hline \hline \end{tabular}
\end{table}
Table 11: Thermodynamic parameters for the adsorption of the investigated dyes on PM4.  
solution pH (6.8 for AY 42 and 6.9 for AR 213)), which is important for possible large-scale applications. Kinetic studies revealed that the pseudo second-order model can better fit the experimental data, and the Langmuir isotherm model describes the adsorption process. The maximum adsorption capacity determined by the Langmuir model was 62.36 mg/g for AY 42 and 77.99 mg/g for AR 213, and the maximum removal efficiencies obtained under the optimum working conditions were 98.54% for AY 42 and 97.58% for AR 213. The thermodynamic parameters indicate that the adsorption of the anionic investigated dyes was a spontaneous and endothermic process, due to the positive \(\Delta H^{\circ}\) values and negative \(\Delta G^{\circ}\) values at the various temperatures investigated. The facile and economic synthesis method for adsorbents, which has a high adsorption capacity and magnetic separation efficiency, indicates that the as-prepared magnetic nanocomposites are promising adsorbent materials for the removal of dyes from aqueous solutions.  
Conceptualization, S.G.M. and L.C.; synthesis: M.-A.N. and R.I.; structural characterization: M.-A.N.; XRD: R.I.; FT-IR: R.R.; nitrogen adsorption-desorption: C.I.; adsorption studies: M.-A.N. and S.G.M.; supervision: S.G.M. and L.C.; writing--original draft preparation, M.-A.N., and R.R.; writing--review and editing, R.I. and S.G.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
All the data is available within this manuscript.  
This work was supported by Program No. 2 of \"[PERSON]\" Institute of Chemistry. The authors would like to thank [PERSON] from West University of Timisoara, Romania for magnetic measurements, [PERSON] from Politehnica University Timisoara for TG/DSC analysis, and [PERSON] from National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara for the SEM analyses for investigated magnetic nanocomposite.  
The authors declare no conflict of interest.