# Enhanced Adsorption of Methyl Orange by Mongolian Montmorillonite after Aluminum Pillaring
## 5 Conclusions  
The pillaring modification of MMt through Al intercalation and calcination at various temperatures was successfully achieved in this study. The modified MMt reveals a higher SSA and more thermal stability than the precursor MMt, and the MO adsorption ability is consequently optimized. The increase in SSA is due to the increase in porosity, and the enlargement of interlayer space resulted from the Keggin Al\({}_{13}\) complex, together with the variation of surface properties such as structural defects generated during thermal processes. The intercalation of Keggin Al\({}_{13}\) into the interlayer of MMt not only plays an important role in supporting the structure of modified MMt against thermal decomposition but also provides more affinitive sites for MO adsorption, which are believed to be the stronger Lewis acidic surfaces to attract MO anionic dye. One of the most important findings in this study, in addition to those stated above, is that not all of the the pores developed during modification contribute to adsorb MO; only those larger than ~1.2 nm perform this function.  
The Al-pillared MMt in this study could be applied as an adsorbent in a water purification system to remove MO or other dye elements. In order to examine the practical  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Absorbent** & **Anionic Dye** & **q\({}_{\text{max}}\) (mg/g)** & **q\({}_{\text{max}}\) (mmol/g)** & **Reference** \\ \hline Al-pillared montmorillonite & Methyl Orange & 6.23 & 0.0190 & this study \\ \hline Zr-pillared bentonite (without calcination) & Methyl Orange & 44.13 & 0.1348 & [51] \\ \hline Al-pillared montmorillonite & Reactive Black 5 & 40.8 & 0.0411 & [25] \\ \hline Al-pillared bentonite (without calcination) & Acid Turquoise Blue A & 2.639 & 0.0038 & [24] \\ \hline Al-pillared montmorillonite & Orange II & 4.1 & 0.0117 & [6] \\ \hline Zr-pillared montmorillonite & Orange II & 4.3 & 0.0123 & [6] \\ \hline Cr-pillared montmorillonite & Supranol Yellow 4 GL & 58.47 & 0.0526 & [52] \\ \hline \hline \end{tabular}
\end{table}
Table 6: The maximum adsorption ability of inorganic-pillared montmorillonite towards anionic dye.  
use in water purification, the adsorption abilities of Al-pillared MMt towards different pollutants, the regeneration of Al-pillared MMt, and the adsorption abilities of Al-pillared MMt applied in the water purification will be studied in future studies.  
**Author Contributions:** Experimental design, J.C., L.S. and H.R.; methodology setup, J.C.; process of the experiment, J.C.; data acquisition, analysis, and interpretation, J.C.; technical support, J.L., Y.Z. and Z.W.; data validation, L.S. and H.R.; writing--original draft preparation, J.C.; writing--review and editing, Y.J., L.S., Z.C., J.L., Y.Z., Z.W., C.L. and H.R.; supervision, H.R.; project administration, H.R.; funding acquisition, H.R. and Y.J. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was financially supported by Guangdong Province High Education Key Platform and Research Project 2020, Project No. 2020 ZDZX1022; Guangdong High Education Youth Creation Grant, Project No. 2020 KQNCX099; and the Beijing Normal University-Hong Kong University United International College (UIC), under the Re-search Projects R5202018, R201805 and R6014.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.  
**Appendix A**