**3. Results and discussion**

#### **3.1. Test on cross-flow equipment**

**Figure 3.** Cross-flow equipment for membrane testing.

260 Desalination and Water Treatment

using the following equation:

where %*R* is salt rejection, *Cf*

of salt in the permeate.

%Conductivity rejection <sup>=</sup> Ω0 \_\_\_\_\_\_ <sup>−</sup> Ω60

%*<sup>R</sup>* <sup>=</sup> *Cf* <sup>−</sup> *<sup>C</sup>* \_\_\_\_\_*<sup>p</sup>*

flow.

where Ω0

by:

to the cross-flow cell, with an applied and stable pressure (80 psi). A 3.5 × 2 membrane piece is placed in the interior of the cell. Once feed water reaches the membrane cell, two outcomes occur: some water permeates through the membrane, leaving impurities behind and producing purified water, and the rest of the water that does not cross the membrane flows to a retentate tank. This latter effluent will have a distinctive characteristic of higher salinity than the feed

The thickness of the membranes was measured using a micrometer (Holytex paper 0.12 mm). This information can be related to the uniformity of the membrane surface. Finally, the salt rejection by the membrane is calculated considering the conductivity in the feed flow and in the permeate flow (after 60 min). For concentrations in the range of different salts used, the conductivity is proportional to solution concentration, so salt rejection can be determined

Ω0

represents the conductivity of the feed and Ω60 represents conductivity of the per-

is the concentration of salt in the feed, and *Cp*

meate after 60 min of permeation. In terms of concentration, the rejection percentage is given

*Cf*

× 100% (1)

is the concentration

× 100% (2)

The data in **Figure 4** point to a decrease in permeate flux as the salt concentration increases. This can be appreciated for the three salts tested (Na<sup>2</sup> SO4 , MgSO4, and NaCl) under constant pressure (80 psi). Comparing the control membrane A with the rest of the membranes that include capsaicin in their formulation, it is observed that capsaicin addition tends to increase permeate flux.

For the NaCl solution at 1000 ppm, membrane B presented a permeate flux increase of 9.1% compared to membrane A, whereas at 5000 ppm, the increase was 14.81%. Membrane B presented the highest permeate flux increment, with membranes C and D also having permeate flux increases compared to membrane A but not as high as those of membrane B.

Due to the hydrophilic properties of capsaicin, the flux increments observed can be attributed to the capsaicin present in the membrane elaboration process for membranes B, C, and D. The capsaicin molecule has two main functional groups: hydroxyl, a polar group which presents affinity to water, and amide, which has nitrogen and a couple of free electrons generating polarity, also resulting in affinity to water. Hence, both characteristics result in hydrophilic properties on the membrane surface.

**Figure 4.** Permeate flux results for the membranes, with Na<sup>2</sup> SO4, MgSO<sup>4</sup> and NaCl solutions at (a) 1000, (b) 3000 and (c) 5000 ppm respectively.

Even more important than its ability to permeate the main function of a membrane is to separate undesired impurities from water, that is, their salt rejection. All the membranes were tested using an NaCl solution at different concentrations (1000, 3000, and 5000 ppm) with the results shown in **Figure 5**. For each of these concentrations, the membranes show a very similar trend: membrane A (blank) has less salt removal in relation to membrane D. Membrane C shows less rejection than every other membrane (**Table 3**).

The membranes that include capsaicin extract also present a higher salt rejection than the control membrane. Membrane D presented the highest salt rejection. A possible reason of this greater NaCl rejection is the content of capsaicin placed on the support layer (polysulfone) or on the active layer (polyamide). The capsaicin functional groups having free electrons provoke major NaCl rejections. Membrane B also presented a significant increase in salt rejection compared to the control membrane A.

Atomic force microscopy was performed (**Figure 6**) in order to characterize the surface of the

**C (%)**

Development, Characterization, and Applications of Capsaicin Composite Nanofiltration…

**D (%)**

http://dx.doi.org/10.5772/intechopen.76846

membrane. Each membrane was measured at five different points. The RMS roughness measurements for each membrane, as well as the average measurements, are presented in **Table 4**. From **Table 4**, it is evident that adding capsaicin extract to the active layer reduces the average roughness from 334.08 (membrane A) to 129.4 nm (membrane B). Similarly, when capsaicin was added to both the active layer and the porous support, the average roughness decreased from 334.08 (membrane A) to 221.26 nm (membrane D). On the other hand, the membrane with capsaicin only in the porous support (membrane C) presented the smallest reduction in average roughness, from 334.08 (membrane A) to 276.66 nm (membrane C). This suggests that including capsaicin on the polyamide active layer reduces the surface roughness the

The contact angle measurement calculates the angle formed between the surface of a water droplet and a solid surface (see **Figure 7**). This measurement is related to the wettability. In

for each

263

membranes. A scale of 50 μm was used, such that the scanned area was 2500 μm<sup>2</sup>

**B (%)**

1000 52.5 67.22 58.41 70.06 3000 53.05 63.09 55.00 67.62 5000 49.59 59.30 50.98 63.92

membranes.

**NaCl (ppm)** **A (%)**

**3.3. Characterization by contact angle measurement**

**Figure 6.** Atomic force microscope images and measurements for membranes A, B, C and D.

**Table 3.** NaCl rejection percentage for membranes A, B, C, and D.

#### **3.2. Characterization by atomic force microscopy**

Atomic force microscopy allows us to zoom into a small area of the membrane surface. Using this technique, the roughness of the membrane can be visualized, providing measurement data in the scale of microns. Membrane roughness affects both the permeate flux and the salt rejection. Furthermore, roughness provides spaces for marine bacteria to settle, initiating biofilm formation, which later leads to membrane biofouling. For these reasons, smooth surfaces are most desirable on membranes.

**Figure 5.** Salt rejection results for the membranes, with NaCl solutions at (a) 1000, (b) 3000 and (c) 5000 ppm respectively.


**Table 3.** NaCl rejection percentage for membranes A, B, C, and D.

Even more important than its ability to permeate the main function of a membrane is to separate undesired impurities from water, that is, their salt rejection. All the membranes were tested using an NaCl solution at different concentrations (1000, 3000, and 5000 ppm) with the results shown in **Figure 5**. For each of these concentrations, the membranes show a very similar trend: membrane A (blank) has less salt removal in relation to membrane D. Membrane C

The membranes that include capsaicin extract also present a higher salt rejection than the control membrane. Membrane D presented the highest salt rejection. A possible reason of this greater NaCl rejection is the content of capsaicin placed on the support layer (polysulfone) or on the active layer (polyamide). The capsaicin functional groups having free electrons provoke major NaCl rejections. Membrane B also presented a significant increase in salt rejection

Atomic force microscopy allows us to zoom into a small area of the membrane surface. Using this technique, the roughness of the membrane can be visualized, providing measurement data in the scale of microns. Membrane roughness affects both the permeate flux and the salt rejection. Furthermore, roughness provides spaces for marine bacteria to settle, initiating biofilm formation, which later leads to membrane biofouling. For these reasons, smooth surfaces

**Figure 5.** Salt rejection results for the membranes, with NaCl solutions at (a) 1000, (b) 3000 and (c) 5000 ppm respectively.

shows less rejection than every other membrane (**Table 3**).

compared to the control membrane A.

262 Desalination and Water Treatment

are most desirable on membranes.

**3.2. Characterization by atomic force microscopy**

Atomic force microscopy was performed (**Figure 6**) in order to characterize the surface of the membranes. A scale of 50 μm was used, such that the scanned area was 2500 μm<sup>2</sup> for each membrane. Each membrane was measured at five different points. The RMS roughness measurements for each membrane, as well as the average measurements, are presented in **Table 4**.

From **Table 4**, it is evident that adding capsaicin extract to the active layer reduces the average roughness from 334.08 (membrane A) to 129.4 nm (membrane B). Similarly, when capsaicin was added to both the active layer and the porous support, the average roughness decreased from 334.08 (membrane A) to 221.26 nm (membrane D). On the other hand, the membrane with capsaicin only in the porous support (membrane C) presented the smallest reduction in average roughness, from 334.08 (membrane A) to 276.66 nm (membrane C). This suggests that including capsaicin on the polyamide active layer reduces the surface roughness the membranes.

#### **3.3. Characterization by contact angle measurement**

The contact angle measurement calculates the angle formed between the surface of a water droplet and a solid surface (see **Figure 7**). This measurement is related to the wettability. In

**Figure 6.** Atomic force microscope images and measurements for membranes A, B, C and D.


**3.4. Characterization by ATR-IR** 

**Table 5.** Contact angle measurements for membranes.

**Figure 8.** Infrared spectra for membranes A, B, C and D.

**Membrane Description Measurement**

The infrared spectra for the four membranes are shown in **Figure 8**. The spectra for membranes A and C do not show vibration through stretching on C=O of the amide group at 1652.78 cm−1. This is due to the absence of capsaicin in membrane A, while membrane C only included capsaicin in the porous support layer and, therefore, the infrared spectrum is not able to detect it. On membrane B, the signal is found at 1605.97 cm−1 and for membrane D at 1619.90 cm−1.

A PS-TMC 56.8 57.5 59.5 58.6 57.0 57.88 B PS-TMCCAP 34.9 42.3 40.7 38.1 34.4 38.08 C PSCAP-TMC 55.0 55.6 52.1 53.5 54.9 54.22 D PSCAP-TMCCAP 48.1 47.3 49.8 47.2 49.1 48.30

**1 2 3 4 5 Average**

http://dx.doi.org/10.5772/intechopen.76846

265

Development, Characterization, and Applications of Capsaicin Composite Nanofiltration…

It is possible that the signal at 1652.78 cm−1 was not seen due to a new link formed between capsaicin and the acyl on TMC, developing a new covalent link between a carbonyl group and

**Table 4.** Membrane roughness values from AFM measurements.

**Figure 7.** Contact angle measurements for membranes A, B, C and D.

the case of membranes, it can also be related to the permeability of the membrane, as a smaller angle means that water can dissolve more readily in the membrane matrix. Every liquid, at a given temperature, will show a unique equilibrium contact angle.

**Table 5** shows contact angle measurements for the membranes tested, at an ambient temperature of 22°C. The control membrane A had the largest contact angle and membrane B presented the smallest. The lower contact angles exhibited by membranes B and D may be attributed to the presence of capsaicin on the surface of those membranes. This is also supported by the permeate flux results, as membranes B and D resulted in the highest values for flux. Moreover, it was also found that the inclusion of capsaicin in the porous support layer of the membrane (membrane C) also leads to a smaller contact angle than the control membrane A, albeit to a lesser degree than when capsaicin is included in the active layer.


**Table 5.** Contact angle measurements for membranes.

#### **3.4. Characterization by ATR-IR**

The infrared spectra for the four membranes are shown in **Figure 8**. The spectra for membranes A and C do not show vibration through stretching on C=O of the amide group at 1652.78 cm−1. This is due to the absence of capsaicin in membrane A, while membrane C only included capsaicin in the porous support layer and, therefore, the infrared spectrum is not able to detect it. On membrane B, the signal is found at 1605.97 cm−1 and for membrane D at 1619.90 cm−1.

It is possible that the signal at 1652.78 cm−1 was not seen due to a new link formed between capsaicin and the acyl on TMC, developing a new covalent link between a carbonyl group and

**Figure 8.** Infrared spectra for membranes A, B, C and D.

the case of membranes, it can also be related to the permeability of the membrane, as a smaller angle means that water can dissolve more readily in the membrane matrix. Every liquid, at a

**Membrane AFM Measurement of RMS roughness (nm) Average RMS roughness (nm)**

A 306.2 325.5 357.8 318.8 362.1 334.08 B 97.4 108.8 176.6 100.0 164.2 129.39 C 294.2 305.1 264.9 245.7 273.4 276.66 D 266.2 203.7 185.5 199.1 251.8 221.26

**Table 4.** Membrane roughness values from AFM measurements.

264 Desalination and Water Treatment

**Table 5** shows contact angle measurements for the membranes tested, at an ambient temperature of 22°C. The control membrane A had the largest contact angle and membrane B presented the smallest. The lower contact angles exhibited by membranes B and D may be attributed to the presence of capsaicin on the surface of those membranes. This is also supported by the permeate flux results, as membranes B and D resulted in the highest values for flux. Moreover, it was also found that the inclusion of capsaicin in the porous support layer of the membrane (membrane C) also leads to a smaller contact angle than the control membrane

given temperature, will show a unique equilibrium contact angle.

**Figure 7.** Contact angle measurements for membranes A, B, C and D.

A, albeit to a lesser degree than when capsaicin is included in the active layer.

**Author details**

**References**

Jesús Álvarez-Sánchez1

German Eduardo Devora-Isiordia1

Gustavo Adolfo Fimbres-Weihs3

Cd. Obregón, Sonora, México

susmat.2016.02.001

10.1021/acs.iecr.6b04016

2012;**2**:804-840. DOI: 10.3390/membranes2040804

2017;**33**(5):397-409. DOI: 10.1080/08927014.2017.1318382

, Griselda Evelia Romero-López1

1 Departamento de Ciencias del Agua y Medio Ambiente, Instituto Tecnológico de Sonora,

3 CONACYT-ITSON, Departamento de Ciencias del Agua y Medio Ambiente, Instituto

[1] Le NL, Nunes SP. Materials and membrane technologies for water and energy sustainability. Sustainable Materials and Technologies. 2016;**7**:1-28. http://dx.doi.org/10.1016/j.

[2] Ray C, Jain R. Drinking Water Treatment Technology—Comparative Analysis. Dordrecht: Springer ; 2011. DOI: 10.1007/978-94-007-1104-4\_2. ISBN: 978-94-007-1103-7

[3] Llenas L, Martinez-Llado X, Yaroshchuk A, Rovira M, de Pablo J. Nanofiltration as pretreatment for scale prevention in seawater reverse osmosis desalination. Desalination and Water Treatment. 2012;**36**:310-318. DOI: https://doi.org/10.5004/dwt.2011.2767

[4] Carrero-Parreño A, Onishi VC, Salcedo-Díaz R, Ruiz-Femenia R, Fraga RE, Caballero JA, Reyes-Labarta JA. Optimal pretreatment system of flowback water from shale gas production. Industrial and Engineering Chemistry Research. 2017;**56**:4386-4398. DOI:

[5] Nguyen T, Roddick FA, Fan L. Biofouling of water treatment membranes: A review of the underlying causes. Monitoring Techniques and Control Measures. Membranes.

[6] Suwarno SR, Hanada S, Chong TH, Goto S, Henmi M, Fane AG. The effect of different surface conditioning layers on bacterial adhesion on reverse osmosis membranes.

[7] Al Ashhab A, Sweity A, Bayramoglu B, Herzberg M, Gillor O. Biofouling of reverse osmosis membranes: Effects of cleaning on biofilm microbial communities, membrane performance, and adherence of extracellular polymeric substances. Biofouling.

Desalination. 2016;**387**:1-13. http://dx.doi.org/10.1016/j.desal.2016.02.029

\* \*Address all correspondence to: gustavo.fimbres@itson.edu.mx

2 Instituto Tecnológico de Tijuana, Tijuana B.C., Mexico

Tecnológico de Sonora, Cd. Obregón, Sonora, México

, Reyna Guadalupe Sánchez-Duarte1

Development, Characterization, and Applications of Capsaicin Composite Nanofiltration…

, Sergio Pérez-Sicairos<sup>2</sup>

,

267

and

http://dx.doi.org/10.5772/intechopen.76846

**Figure 9.** Piperazine – 1,3,5 Benzenetricarbonyl trichloride – capsaicin reaction.

nitrogen on the amide of capsaicin. Then, a new functional group is formed: Ar–C=O–N–C=O (**Figure 9**). The wavelength for this new link would be lower, because of the resonance effect of the free electrons of nitrogen, generating a simple C-O link, as Pavian et al. [16] had expressed.
