**2.3 Assessment of the antifungal activity of the additives**

*Aspergillus* sp., *Chaetomium globosum*, and *Cladosporium* sp. fungi were selected to evaluate the antifungal activity of the solids, based on their cellulolytic ability in agar plate assays. *Aspergillus* sp. and *Cladosporium* sp. were previously isolated from biodeteriorated fabrics by conventional microbiological techniques, whereas *C. globosum* was selected from the CIDEPINT culture collection [30]. From subcultures growing in Petri dishes, inoculums of cited fungi were obtained using a solution of 0.85% p/v NaCl and 0.005% p/v Tween 20, being the concentration of the suspension adjusted to 106 spores/mL employing a Neubauer chamber. The composition of the culture medium used was 1.5 g agar (Parafarm), 1 g dextrose (Anedra, analytical reagent), 0.5 g proteose peptone (OXOID), 0.1 g KH2PO4 (Anedra, analytical reagent), 0.05 g MgSO4.7H2O (Anedra, analytical reagent), and distilled water (Laboratory). Two different silver concentrations were selected to carry out the agar plate assays, 60 and 120 ppm. The Petri dishes were inoculated in the center with 20 mL of spore suspension of each fungus per triplicate and incubated at 28°C for 10 days. With the obtained results, the inhibition percentage (I%) was calculated according to Eq. [31]: inhibition % = [(C − E)/C] × 100, where C and E correspond to the average diameter of each fungus in the control plate and on the plate with the tested solids, respectively. Three measurements of the fungal growth diameter were made in each plate, and the standard deviation was determined.

**5**

**Figure 1.**

*Digital images of silicas.*

3473 cm<sup>−</sup><sup>1</sup>

800 cm<sup>−</sup><sup>1</sup>

*Antimicrobial Fabrics Impregnated with Ag Particles Included in Silica Matrices*

**Figure 1** shows the synthesized samples of silica with different concentrations of carbon whose images were obtained digitally. If we look at **Figure 1**, the SB sample is the one obtained with ammonium hydroxide and is taken as a control sample (it does not contain carbon), while the other images provide a light gray to dark gray coloration for higher carbon contents. For the three cases presented, the granulometry is similar when they are already dry, it is not significant compared to the SB,

The determination of the structure of the synthesized silicas was carried out by XRD. Thus the amorphous character of the synthesized materials that have only wide peaks in the 15–30° 2θ interval was confirmed and the band located around 23° 2θ was observed, which is the typical structure of this type of silica. The acid properties of the silicas measured through the potentiometric titration with *n*-butylamine were studied, which allows the evaluation of the number of acid sites and their acid strength. To interpret the results obtained, it is known that the initial electrode potential (Ei) indicates the maximum acid strength of the surface sites and the values (meq/g solid) where the plateau is reached indicate the total number of acidic sites [32]. The acid strength of surface sites can be classified according to the following ranges: very strong sites Ei > 100 mV; strong sites 0 < Ei <100 mV; weak sites −100 < Ei <0 mV, and very weak sites Ei < −100 mV, respectively [30]. It is important to clarify that this technique only indicates the trend of mass acidity of the synthesized samples. Bulk carbon has an Ei value of 37.1 mV, while silica without carbon has an Ei of 157.9 mV. It is interesting to note that the potentiometric curves have a similar shape to each other, with continuous and relatively rapid decrease in potential, which would indicate that their acidic sites are very few, regardless of the change in the amount of carbon they contain, this could that compounds that impurity carbon tend to be basic in nature. In any case, the potentiometric curves have a strong parallel with the behavior of pure silica and not of bulk carbon. The FT-IR spectrum of the SB silica shows characteristic bands at 3748 and

 assigned to the interactions between the hydroxyl groups on the silica surface and the water presented in the surrounding atmosphere. These bands can be related to the presence of isolated groups (Si▬OH) and OH stretch bands, caused by hydrogen-bound water molecules (HOH.. H) and surface silanol groups, hydrogenbound to water molecular (SiO▬H....H2O). The other characteristic bands that confirm the hydrophilic character of the silica are located at 968 and 1883 cm<sup>−</sup><sup>1</sup>

are directly related to the Si▬O interaction of the silanol groups. At 1640 cm<sup>−</sup><sup>1</sup>

intense band associated with the adsorption of water on the surface of the sample is also observed due to its hydrophilic nature. Bands in the range 1200–1000 cm<sup>−</sup><sup>1</sup>

were also detected. These interactions can be related to antisymmetric and

and

and

, an

*DOI: http://dx.doi.org/10.5772/intechopen.91631*

and only the S3B has larger granules.

**3. Results and conclusions of additives**
