*4.1.1 UV-Vis spectrometry analysis*

In this study, green synthesis of AgNP has been demonstrated from a filamentous marine *P. tenue*. It is well known that AgNPs exhibit a yellow-brown color in aqueous solution due to excitation of surface layer oscillations in AgNP. The reduction of silver ions of Silver sulfhate to AgNPs upon exposure to *P. tenue* ultrasonic biomass was followed by changing the color of the culture medium. As shown in **Figure 4A–D**, the changing color of the reaction mixture from green to yellow and then dark brown, followed by precipitation of grayish-black particles, proved the bioconversion of silver ions and the formation of AgNPs in an aqueous medium. The silver sulfate solution with washed *P. tenue* biomass turned yellow indicating the formation of silver nanoparticles.

**Figure 5** shows the UV-Vis spectrum of the synthesized nanoparticle from *P. tenue*. A clear peak was observed with a maximum absorbance at 380–420 nm with

#### **Figure 4.**

*(A) P. tenue culture (ASN-III medium),(B) Silver sulfate solution as the negative control, (C) Adding (1 g) ultrasonication wet biomass and Ag2SO4(1 Mm), the picture show the color change of silver sulfate solution by P. tenue in biomass and (D) The complete reduction of ionic silver (Ag+) and grayish black precipitation of AgNPs.*

*Green Synthesis of Silver Nano-Particle from Cyanobacteria and Effect on Microalgal Growth… DOI: http://dx.doi.org/10.5772/intechopen.106039*

**Figure 5.**

*UV-Vis spectrum was recorded after the reaction of 1Mm silver sulfhate solution with (1 g) P.tenue ultrasonication wet biomass at PH 7 and 25 °C and formation of AgNPs.*

an absorbance of 1 mM of the silver sulfate solution. The occurrence of the peaks within shows the presence of silver nanoparticles in the solution. Agreeing Grayblack silver nanoparticle precipitation on *P. tenue* is observed in an experiment. They observed a characteristic protein coat at 270–275 nm in the ultraviolet spectrum. Ahmed et al. [22] shows that increasing the concentration of silver sulfate solution with 1 g of *Phormidium tenue* ultrasonic wet biomass causes the bioconversion of silver ions to silver nanoparticles. Furthermore, increasing the concentration of Silver sulfate solution with 1 g of *P. tenue* caused the ultrasonic wet biomass to induce the bioconversion of silver ions to silver to decrease, and the subsequent formation of SNPs in an aqueous medium. Regarding this concern, [18] observed a characteristic peak at 380–420 nm at 12 h. In principle, the wide plasma bonds with absorption at the longest wavelengths could be due to the size distribution of the nanoparticles. Silver ion reduction occurs either by an electron shuttle or by a reducing agent released by ultrasonicated *P. tenue* biomass into solution.

#### *4.1.2 Fourier transformers infra-red spectrometry (FT-IR)*

FTIR is used to identify the biomolecules in *P. tenue* responsible for the silver ions reduction and stabilization of reduced silver ions [22]. The FTIR spectrum of the AgNPs obtained from *P. tenue*, shows strong absorption peaks at 3390.90, 1634.19, 1419.41, 1111.25, 614.429, and 477.719 cm−1 representing different functional groups such as fragments The stretching OH of the alcohol or phenol, the N-H (amino acid), the C-O carboxylic anion, the saturated C-O group, and the stretching N-O, respectively (**Figure 6**).

The absorption peak at 3390 cm−1 indicates the presence of the N-H (amino acid). In agreement with this study [12] confirmed the presence of a protein coat responsible for the biosynthesis of nanoparticles. The presence of protein as a stabilizer surrounds silver nanoparticles. Protein molecule consisting of different functional groups in the amino acid chain such as amino group, carboxyl group, and sulfate group present in cyanobacterial protein promotes the formation of microscopic silver nanoparticles with narrow particle size distribution, and hydroxyl groups and sulfonic acid are beneficial for the synthesis of silver nanoparticles with slightly larger particle size in weakly reduced media.

#### **Figure 6.**

*FTIR analysis of Phormidium tenue show the presence of protein shell for the reduction of silver ions.*

In the presence of Silver nanoparticles inside the cytoplasm, silver ions are reduced to AgNP, since Ag2SO4, a toxic reactant, is used in metabolism, it eventually kills the cells. When the cyanobacteria died, the silver nanoparticles produced inside the cell were released across the cell membrane into solution, as indicated by the precipitation of silver nanoparticles around the cell. The dead *P. tenue* also releases organic matter (proteins and other biochemicals), which causes silver to continue to precipitate from solution outside the cell. The protein molecules act as a reducing agent for the silver nanoparticles. Protein molecule consisting of different functional groups in the amino acid chain such as amino group, carboxyl group, and sulfate group present in cyanobacterial protein promotes the formation of silver nanoparticles. Silver ions are reduced in the presence of sulfate reductase, resulting in the formation of a stable silver hydrosol (1111.25 in cm−1) and stabilized by a capping peptide [13].

#### *4.1.3 XRD- size determination analysis*

X-ray diffraction patterns have been widely used in nanoparticle research as the main characterization tool to obtain essential characteristics such as crystal structure, crystal size, and strain of nanoparticles. Randomly oriented crystals in nanocrystalline materials cause the widening of the diffraction peaks. In addition, homogeneous lattice distortion and structural defects lead to widening of peaks in diffraction patterns [23].

**Figure 7** illustrates the XRD pattern of silver nanoparticles. The device apex width is obtained with standard silver powder-free from dimensional expansion, defects, and distortion. Using the Williamson and hall method and a Gaussian profile for the peak form, the average crystal sizes obtained at 60 nm and 88.18 nm for the peaks were 2θ = 32.40 and 2θ = 46.40, respectively.

#### *4.1.4 Scanning electron microscopy (SEM) analysis*

The size and structure of nanoparticles were further characterized using SEM analysis. SEM image of obtained nanoparticles clearly distinguishes the difference *Green Synthesis of Silver Nano-Particle from Cyanobacteria and Effect on Microalgal Growth… DOI: http://dx.doi.org/10.5772/intechopen.106039*

#### **Figure 7.** *The XRD pattern of silver nanoparticle.*

#### **Figure 8.** *SEM image of the silver nanoparticle produced by P. tenue.*

between shape and size. The surface deposited silver nanoparticles are clearly seen at high magnification in the micrograph (**Figure 8**).
