# Iron–Carbonate (Bi, Cu, Li) Composites with Antimicrobial Activity After Silver(I) Ion Adsorption

## TL;DR

This study creates iron-carbonate composites that can capture silver ions and show strong antimicrobial effects, especially against fungi.

## Contribution

The novelty lies in developing iron-carbonate composites with tailored adsorption properties and demonstrating their antimicrobial activity after silver ion adsorption.

## Key findings

- The composites SFC, SFB, and SFL showed comparable maximum silver ion adsorption capacities of around 19.3-19.9 mg/g.
- SFC-Ag exhibited 100% inhibition against tested microorganisms, including bacteria and fungi.
- The adsorption process is physical, endothermic, and spontaneous, occurring at the adsorbent-adsorbate interface.

## Abstract

In the present study three composite materials based on iron in combination with bismuth, copper or lithium carbonates FeNO3@Li2CO3 (SFL), FeNO3@CuCO3 (SFC), and FeNO3@(BiO)2CO3 (SFB) were synthesized by coprecipitation. The purpose was to obtain materials that possess targeted adsorbent properties for the recovery of silver ions from aqueous solutions. After synthesis, to emphasize the adsorptive qualities of materials for the recovery of silver ions, the synthesized composite materials, as well as those doped with silver ions following the adsorption process (SFL-Ag, SFC-Ag, and SFB-Ag), were characterized and several adsorption-specific parameters were examined, including temperature, contact time, pH, adsorbent dose, and the initial concentration of silver ions in solution. Subsequently, the ideal adsorption conditions were determined to be as follows: pH > 4, contact time 60 min, temperature 298 K, and solid–liquid ratio (S–L) of 0.1 g of adsorbent to 25 mL of Ag (I) solution for all three materials. The Langmuir model properly fits the experimental equilibrium data of the adsorption process; however, the Ho–McKay model closely represents the adsorption kinetics. The maximum adsorption capacities of the materials, 19.7 mg Ag(I)/g for SFC, 19.3 mg Ag(I)/g for SFB, and 19.9 mg Ag(I)/g for SFL, are comparable. The adsorption mechanism is physical in nature, as evidenced by the activation energies of 1.6 kJ/mol for SFC, 4.15 kJ/mol for SFB, and 1.32 kJ/mol for SFL. The highest Ag(I) concentration used for doping all three materials in the study was 150 mg Ag(I)/L. The process is endothermic, spontaneous, and takes place at the interface between the adsorbent and the adsorbate, according to thermodynamic theory. Subsequently, the antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans microorganisms was evaluated by rate of inhibition assessment. The SFC-Ag material showed a percentage of 100% inhibition with respect to the positive control for each microorganism. All synthetized materials have better efficiency as antifungal agents.