The concentration and Brønsted acidity of surface silanol groups on mesoporous silica (SBA-15) has been studied by following the adsorption of benzylamine, BA, from water as a function of pH. The adsorbed amount of BA from water was compared to the maximum amount of BA that could be adsorbed from cyclohexane. Furthermore, the surface concentration and acidity of carboxylic acid functions on surface-functionalized SBA-15 was also studied, which allowed the relative surface concentration of remaining silanols to be obtained. Two types of silanols can be identified, where about 1/5 of the silanols have a pKa = 2 and the remaining 4/5 of the silanols have a pKa of about 8.2. According to the literature, these two types of silanols can be identified as Q3 and Q2 silanols, respectively, of which the Q3 silanols are more acidic. For the surface-functionalized materials, pKa values close to their respective intrinsic values are found for the carboxylic acid functions. However, irrespective of the method of surface functionalization, 50% or more of the accessible surface groups are silanols. The results thus suggest that the effective charge density is largely controlled by the (de)protonation of the silanol groups even for surface-functionalized mesoporous silica, which render the surface chemistry of the surface-functionalized silicas to be radically different from what simple schematic representations would suggest. The results are suggested to be of importance for reaching a predictive level of understanding for the behavior of mesoporous silica in a range of applications, as many of the foreseen applications for mesoporous silica involves water as the medium.
A simple method for surface functionalization of large-pore mesoporous silica by hyperbranching polymerization resulting in a high loading of amine groups is presented.
The ascending anxiety regarding antimicrobial resistance as well as the recalcitrant nature of biofilm-associated infections call for the development of alternative strategies to treat bacterial diseases. Nanoparticles have been considered as one of the emerging and promising platforms in this respect. Their unique physical and chemical properties may lead to fine-tuned interactions between them and bacteria. In this chapter, we aim to provide an overview on the use of nanoparticles as antimicrobial agents. Both antibacterial and anti-biofilm activities of nanoparticles and their current approaches will be reviewed. The in vitro methods that are used to evaluate the potency of nanoparticles as antimicrobial agents will be discussed in detail.
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