# Biochars as a Solution for Silver Removal and Antimicrobial Activity in Aqueous Systems
## 4 Conclusions  
This study evaluated the efficiency of biochars derived from plant biomass, specifically rice husks and cotton fabric, for silver ion removal. Among them, activated rice husk biochar (ARHB) exhibited the highest adsorption capacity (23.11 mg/g), attributed to its superior structural properties, including a high specific surface area (844 m\({}^{2}\)/g) and total pore volume (0.42 cm\({}^{3}\)/g).  
The adsorption mechanism was a multi-step process involving physisorption, chemisorption, cation exchange, and reduction, as also confirmed by thermodynamic and XPS analyses. Physisorption played a dominant role, while metallic silver (Ag\({}^{0}\)) formation on RHB and ARHB indicated partial chemical transformation during adsorption.  
Beyond adsorption, ARHB exhibited significant antibacterial properties, reducing _E. coli_ colonies by 83% within 30 min, demonstrating its potential as a dual-function material for wastewater treatment.  
These findings highlight the potential of biochars derived from renewable agricultural waste as sustainable and efficient adsorbents for silver ion removal and recovery, contributing to waste vaporization, water purification, and circular economy principles.  
\begin{table}
\begin{tabular}{l c c c} \hline \multirow{2}{*}{**Antimicrobial Mean**} & \multicolumn{2}{c}{**Growth of _E. coli_ (Number of Colonies) After Different**} \\ \cline{2-4}  & **Intervals of Exposure to Materials with Ag\({}^{+}\)** & **60 min** \\ \hline Silver-loaded ARHB & 100\% & 83\% & 81\% \\ \hline Control (saline solution) & 0 & 0 & 0 \\ \hline \end{tabular}
\end{table}
Table 7: Investigation of the action of plant material with Ag\({}^{+}\) on _E. coli_ in a suspension with a concentration of 10\({}^{6}\) cells mL\({}^{-1}\).  
\begin{table}
\begin{tabular}{l c} \hline
**Antimicrobial Mean** & **Inhibitory Zones, mm** \\ \hline Sample ARHB with Ag\({}^{+}\) & 13.25 \(\pm\) 1.3 \\ \hline Control thiamphenicol & 18.80 \(\pm\) 0.4 \\ \hline Control (saline solution) & 9.00 \(\pm\) 0.0 \\ \hline \end{tabular}
\end{table}
Table 8: In vitro antimicrobial action of plant material with Ag\({}^{+}\) on _E. coli_.  
**Author Contributions:** Conceptualization, I.U., P.V., T.P. and D.M.; methodology, I.U., P.V. and T.P.; formal analysis, I.U., D.V., T.P. and I.A.; investigation, I.U., P.V. and T.P.; data curation, I.U., P.V., T.P. and I.A.; writing--original draft preparation, I.U., P.V. and T.P.; writing--review and editing, I.U., P.V. and T.P.; visualization, I.U. and P.V.; project administration, P.V. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is contained within the article.  
**Acknowledgments:** Research equipment of the Distributed Research Infrastructure INFRAMAT, part of the Bulgarian National Roadmap for Research Infrastructures, supported by the Bulgarian Ministry of Education and Science, was used in this investigation.  
**Conflicts of Interest:** The authors declare no conflicts of interest.