Abstract
The availability of microbially-safe drinking water is a challenge in many developing regions. Due to the well-known antibacterial effect of silver ions, materials used for their controlled release have been widely studied for point-of-use water disinfection. However, even if it is in principle known that chloride anions can suppress the antibacterial efficiency of silver, the majority of previous studies, surprisingly, have not focused on chloride concentrations relevant for freshwaters and thus for practical applications. Here, we prepared low-cost nanocellulose-aluminium oxyhydroxide nanocomposites functionalized with silver nanoparticles. Field samples obtained from Chennai, India were used as a guideline for choosing relevant chloride concentrations for the antibacterial studies, i.e., 10, 90, and 290 ppm. The antibacterial performance of the material against Escherichia coli and Bacillus subtilis was demonstrated and the influence of chloride concentration on the antibacterial effect was studied with E. coli. A 1 h contact time led to bacterial reductions of 5.6 log10, 2.9 log10, and 2.2 log10, respectively. This indicates that an increase of chloride concentration leads to a substantial reduction of antibacterial efficiency, even within chloride concentrations found in freshwaters. This work enables further insights for designing freshwater purification systems that utilize silver-releasing materials.
Highlights
Waterborne diseases caused by micro-organisms are a major cause of death worldwide and a grand challenge remains to find sustainable solutions for their control and elimination[1]
CCNF was chosen as the starting material instead of unmodified cellulose nanofibrils (CNF) due to its inherent antibacterial properties[21,22], further promoting the intended function of the composite material
Data from the quantification of ammonium groups on the fibrils by conductometric titration was provided by the manufacturer (0.63 mmol/g). ζ-potential measurements (Supplementary Fig. S1) confirmed the positive surface charge of cationic cellulose nanofibrils (cCNF) in the whole pH range tested
Summary
Waterborne diseases caused by micro-organisms are a major cause of death worldwide and a grand challenge remains to find sustainable solutions for their control and elimination[1]. Chloride concentration ([Cl−]) has been recognized as a significant factor decreasing the antibacterial performance of silver ions due to the low solubility product of AgCl. In addition, complexation with e.g. sulfide and organic matter in freshwaters can result in decrease of free Ag+ concentration[30]. Still, this factor has not been properly considered when investigating the efficiency of silver-releasing materials for POU water purification. An objective of this study was first to screen realistic chloride concentrations relevant for applications and to explore the effect of salinity in simulated freshwaters and [Cl−], on the antibacterial effect of the composites on Escherichia coli, a bacterium typically used as a biological indicator of drinking water safety[31]. The fact that [Cl−] can vary significantly in freshwater sources and that this can affect silver-based water disinfection is the main issue we highlight in this work
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