Bioactive glasses (BGs) are attractive materials for tissue regeneration because of their biocompatibility, angiogenic and osteogenic characteristics . Nanoscale BGs, are particularly attractive material in biomedical applications. For example, it can be used in coating , scaffolds , and hydrogels  as advanced bioactive filler to improve the matrices functionalities (e.g. mechanical properties, biominerlization ability, and osteogenesis), because of their morphological benefits (e.g., low dimension, uniform size, controllable shape) . Mesoporous bioactive glass nanoparticles (MBGN), among many nanoscale BGs, are gaining popularity in tissue regeneration, or nanomedical application as bioactive fillers or drug carriers due to their large surface to volume ratio, wide specific surface area, and customizable size/pore structure . The application field of MBGs has moved a big step forward by including a controllable amount of different ions in their composition . The chemical composition of BGs, in addition to their morphology, can be modified for specific uses . Silver (Ag), for example, can be added to BGs to boost their antibacterial activity . Infections caused by bacteria continue to be a significant clinical obstacle for repairing and regenerating efficient tissue [9-11]. Alternatively, using antibacterial materials may reduce the infection risk without the bacterial resistance problem [10-12]. There is a high need for antibacterial formulations employed in tissue regeneration therapies. Antibacterial metal ions have been around for a long time , and Ag has been shown to have good broad-spectrum bactericidal activity . Adding Ag to BGs may enhance their antibacterial properties . It is possible to produce mesoporous bioactive glass nanoparticles (MBGN) containing silver metal in two ways: one-step and post-modification. Firstly, Ag precursors (typically soluble silver salts) are introduced to create and for BGN [16, 17]. In the second method, Different metal ions (such Ca and Ag) have been inserted after BGN formation while maintaining the produced nanoparticles' form, size, and porosity .
In this research, Ag-doped MBGs were synthesized using the spray pyrolysis method with different deposition time at 400 ﹾC and studied the optical and structural properties
Materials and methods
Synthesis of Ag-MBG Nanoparticles
The preparation of Ag-MBG nanoparticles by chemical spray pyrolysis method was illustrated in Figure 1.
Formation of Ag-MBG nanoparticle sample
The Ag-doped MBG nanoparticle is formed on a hot glass sheet substrate by the chemical spray pyrolysis system shown in Figure 2. The glass sheets were distributed on the hot plate, and the preparing solution was sprayed when the temperature of the heater reached 400 °C. The spraying operation continued fifteen times with 2 s spraying time, and the time interval between two spry processes was equal to 2, 4, and 6 min. Then, the layer appeared on the surface of the substrate, and nanostructure Ag-doped MBG particles were formed.
The Absorption measurement was tested using UV-VIS spectrophotometer type (Lambda 365, USA).
Field emission scanning electron microscopy (FE-SEM, model TESCAN MIRA3, French) with a 10-mm squared active area was used to assess the surface morphology of produced powders.
Fourier transformer infrared spectrophotometer (FTIR, model Perkilin Elmer Frontier) was used to obtain the infrared spectra of the produced glasses. The spectra were recorded using Fourier transform spectrometer near, mid, and far-infrared ranges.
Results and discussion
Temperature is one of the critical parameters in preparing nanoparticles. It has a significant effect on the homogeneity of the prepared nanoparticle because it is responsible for the varying crystal structure of the material. The temperature of 400 ﹾC shows the best results because the particles return to aggregate by increasing it. The structure and composition of Ag-MBG were evaluated using the SEM and EDX analysis, as shown in Figure 3. Figure 3 reveals Ag-MBG particles' surface at 400 °C with a different time interval between two spray processes (2, 4, and 6 min).
At 2 min of spray deposition, SEM shows that their surfaces were heterogeneous agglomerates (nanoparticles) with different sizes (16-22 nm) were observed in the structure, which is an expected case since the spray precipitation technique relies on the nucleation-aggregation-agglomeration-growth mechanism. Their EDX spectra show a significant amount of Si and a small amount of O, Ca, C and Ag.
As for the time of 4 min, SEM showed aggregation of spherical particles on sample surfaces with the increase in the size of the nanoparticles (13-24 nm). Their EDX spectrum of the new surface layer showed higher concentrations of Si with a slight increase of O, Ca, C and Ag.
At 6 min, the surface was almost homogeneous, covered by a layer of Ag-nanoparticles that diameters range from (24 to 33 nm), with a slight increase of O, Ca, C, and Ag.
The FTIR spectrum observed the chemical structure and the bond between MBG and Ag nanoparticles. Figure 4 demonstrates the FTIR spectrum for the sample Ag-MBG with a time interval between two spray processes (2, 4, and 6 min) respectively at 400 °C. The band type extracted from these spectrums was listed in the table behind it.
The optical properties were examined by measuring the transmittance of the film in the visible region of the electromagnetic spectrum Ag-MBG thin film is not very transparent. The maximum transmittance is about (2%, 15%, 53%) recorded for the time of spray pyrolysis 2, 4, and 6 min, as shown in Figure 5.
The surface plasmon resonance of the samples was reported in the wavelength range of 200-1000 nm using a UV-VIS spectrophotometer in addition to the substance structure and chemical characterization. As the time interval increased (2, 4, and 6 min), the absorption increased due to the thickness increasing (Figure 6).
Figure 7 shows the absorption coefficient (α) variation with wavelength variation for Ag-MBG thin film. The relation shows that the absorption coefficient increases with increasing the time interval from (2, 4, and 6 min) min, respectively.
From these results, one can calculate the energy band gap. Figure (8) shows that the absorption coefficient (α) for examined thin film increases as photon energy increases. The absorption coefficient has values (which increases the possibility of a direct transition occurring). Also, the extinction coefficient as a function of λ exhibits the same behavior of α as a function of hυ (eV). Figure (8) shows the direct energy gap for Ag-MBG thin films.
The Urbach energy, which values are reported in Table 1, provides information about the localized state in the band gap. This effect can be explained by rising packing density as the degree of amorphousness of the films decreases, resulting in decreasing in localized state.
The SEM images of the Ag-doped MBG particles revealed that the particles were spherical at all periods investigated. At 6 min. The surface was almost homogeneous, covered by a layer of Ag-nanoparticles with diameters ranging from (24 to 33 nm). The variation of the absorption coefficient (α) with wavelength variation for Ag-MBG thin film shows that the absorption coefficient increases with increasing the time interval (2, 4, and 6 min), respectively. In addition, the absorption coefficient as a function of hυ (eV) and the extinction coefficient as a function of λ take the same behavior.
Institute of laser for postgragute studies, University of Baghdad, supported this work.
How to cite this article: Tayseer A. Kareem*, Dunia K. Mahdi. Synthesis and characterization of silver nanoparticles-doped mesoporous bioactive glass prepared by spray pyrolysis. Eurasian Chemical Communications, 2022, 4(4), 330-337. Link: http://www.echemcom.com/article_145019.html
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