The new signals can be attributed to the presence of silver in the TiO 2 lattice
(Hamal and Klabunde 2007) as oxide, which cannot be seen in the XRD analysis.
Another characterization test carried out was the bandgap value measurement
by diffuse reflectance analysis and with the Kubelka–Munk function (Christy et al.
1995). According to the %w of silver aggregated to the synthesis the bandgap
value does not change between them, it only changes in comparison with the pure
TiO 2 , from 3.2 to 3.15 eV (Table 3.3), a slight change, which is attributed to the
presence of Ag and this change will lead us to propose that the material can be
activated with solar light.
Once the material was characterized, the disinfection process took place. The
treated water used contained 28/100 mL of more likely number of total fecal
coliforms. A suspension of the treated wastewater and the catalyst pH 7 was
recirculated in a tubular photoreactor and after 3 h under solar light exposure, the
samples were taken out to incubate the presumptive test of total fecal coliforms.
In Fig. 3.5 is presented the presumptive media inoculated with the disinfected
water. As can be seen, the presence of gas in tubes of the test of disinfection using
pure TiO 2 shows that in three of three tubes of the 10
-1 concentration were
positive and two tubes of three on the 10
-2 concentration also were positive. By
converting these results with a more likely number table (Ervin et al. 2010; Gilbride
2014; Scaglia et al. 2014), the final concentration of total fecal coliforms was
14/100 mL, decreasing the concentration of these microorganisms a 50 % in comparison with the treated wastewater.
For the doped Ag-TiO 2 materials, only in two of the three tubes in the concentration of 10
-1 for the 10 %w Ag were positive, meaning that with that catalyst, the more likely number of total fecal coliforms was \7.8/100 ml. The rest of
the materials remove the 100 % of the total fecal coliforms after 3 h of solar light
exposure.
To confirm the presence of fecal coliforms, especially the bacteria Escherichia
coli, the confirmative and differential medium were prepared. With the pure TiO 2 ,
the bacteria E. coli was present in a concentration \7.8/100 ml. From Fig. 3.6, it is
possible to observe that there is no presence of gas in any of the Ag-TiO 2 materials
tested, concluding that the doped material works as a disinfection agent and the
obtained water can be reused for the food production free of pathogen agents.
3.3.3 Metal Removal
From infrared analysis, it is possible to recognize in most of the samples, and blank,
representative bands detected in CTS spectrum are in agreement with other literature studies: at 3,400 cm
-1 a wide and intense band appears as a result of the
stretching vibrations of the –OH and –NH 2 groups. The double band that appears at
2,920 and 2,880 cm
-1 are due to asymmetric and symmetric stretching vibrations
of the –CH 2 groups. Bending vibrations of the –NH 2 groups and stretching vibrations of C=O groups cause the strong band at 1,657 cm
-1 with a shoulder at
90
L. Pérez-Sánchez et al.
(Hamal and Klabunde 2007) as oxide, which cannot be seen in the XRD analysis.
Another characterization test carried out was the bandgap value measurement
by diffuse reflectance analysis and with the Kubelka–Munk function (Christy et al.
1995). According to the %w of silver aggregated to the synthesis the bandgap
value does not change between them, it only changes in comparison with the pure
TiO 2 , from 3.2 to 3.15 eV (Table 3.3), a slight change, which is attributed to the
presence of Ag and this change will lead us to propose that the material can be
activated with solar light.
Once the material was characterized, the disinfection process took place. The
treated water used contained 28/100 mL of more likely number of total fecal
coliforms. A suspension of the treated wastewater and the catalyst pH 7 was
recirculated in a tubular photoreactor and after 3 h under solar light exposure, the
samples were taken out to incubate the presumptive test of total fecal coliforms.
In Fig. 3.5 is presented the presumptive media inoculated with the disinfected
water. As can be seen, the presence of gas in tubes of the test of disinfection using
pure TiO 2 shows that in three of three tubes of the 10
-1 concentration were
positive and two tubes of three on the 10
-2 concentration also were positive. By
converting these results with a more likely number table (Ervin et al. 2010; Gilbride
2014; Scaglia et al. 2014), the final concentration of total fecal coliforms was
14/100 mL, decreasing the concentration of these microorganisms a 50 % in comparison with the treated wastewater.
For the doped Ag-TiO 2 materials, only in two of the three tubes in the concentration of 10
-1 for the 10 %w Ag were positive, meaning that with that catalyst, the more likely number of total fecal coliforms was \7.8/100 ml. The rest of
the materials remove the 100 % of the total fecal coliforms after 3 h of solar light
exposure.
To confirm the presence of fecal coliforms, especially the bacteria Escherichia
coli, the confirmative and differential medium were prepared. With the pure TiO 2 ,
the bacteria E. coli was present in a concentration \7.8/100 ml. From Fig. 3.6, it is
possible to observe that there is no presence of gas in any of the Ag-TiO 2 materials
tested, concluding that the doped material works as a disinfection agent and the
obtained water can be reused for the food production free of pathogen agents.
3.3.3 Metal Removal
From infrared analysis, it is possible to recognize in most of the samples, and blank,
representative bands detected in CTS spectrum are in agreement with other literature studies: at 3,400 cm
-1 a wide and intense band appears as a result of the
stretching vibrations of the –OH and –NH 2 groups. The double band that appears at
2,920 and 2,880 cm
-1 are due to asymmetric and symmetric stretching vibrations
of the –CH 2 groups. Bending vibrations of the –NH 2 groups and stretching vibrations of C=O groups cause the strong band at 1,657 cm
-1 with a shoulder at
90
L. Pérez-Sánchez et al.