Morphology dependent in Antibacterial activities of CdSiO₃ nanopowder prepared by different Silicate precursors

 

B. M. Manohara¹, S. Thirumala², B. R. Kiran³

¹Department of Physics, Government First Grade College, Davangere-577004, India.

²Department of Environment Science, Government First Grade College, Davangere-577004, India.

³Research and Teaching Assistant in Environment Science, DDE, Kuvempu University,

Shankaraghatta-577451, India.

 

ABSTRACT:

Pure CdSiO₃ nanopowder was prepared by solution combustion (SC) technique at low temperature of at 800 ºC for 2 h by using different silicate precursors like meso-porous silica, tetraethyl ortho silicate (TEOS), fumed silica (SiO₂) and oxyledehydrazide (ODH) used as a fuel. The powder X-ray diffraction (PXRD) showed the pure monoclinic phase and the crystallite sizes were in the range of 23 - 43 nm.  The scanning electron microscope (SEM) and transition electron microscope (TEM) results reveal that the pure CdSiO₃ nanopowder were porous and agglomerated with irregular nanopowder. Fourier infrared (FTIR) and Raman spectroscopic analysis is to confirm the materials and to identify the chemical functional groups in the sample. Antibacterial studies of pure CdSiO₃ nanopowder prepared by TEOS better than the other silica precursors is a common cause of skin infections such as abscesses, respiratory infections such as sinusitis and food poisoning.

 

 

INTRODUCTION:

Phosphors with highly stable, good morphology and better yield are in great demand for energy saving applications like display, lasers, scintillators, safety indicators, dosimetry etc. In this regard, a silicate hosts found to be multi-color phosphorescence and shows inactive with alkali, oxygen and acid environment^1,2. The various silicates CdSiO₃ host exhibit a remarkable optical and luminescent property. The combined nature of ionic and covalent due to the presence of Cd²⁺ ions and strong interaction between Si-O present in the SiO₃ group. The crystal structure of CdSiO₃nanoparticles shows one dimensional chain of edge-sharing SiO₄ tetrahedron as a result dopants can be easily embedded into the host by replacing the Cd site. In order to maintain the charge neutrality, the charge compensation of Cd²⁺ and O^2- were tuned by the dopants. These dopants are responsible for the creation of deep traps at appropriate depths, which stores the excitation energy and emit the light in the visible range³.

 

 

 

Antibacterial studies to treat various bacterial infections being the living things. The toxicity to humans and other animals from antibacterial is generally considered low. However, prolonged use of certain antibacterial can decrease the number of gut flora, which may have a negative impact on health. Gram-positive bacteria are bacteria that give a positive result in the Gram stain test. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Gram-negative bacteria cannot retain the violet stain after the decolorization step, alcohol used in this stage degrades the outer membrane of gram-negative cells making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counter stain (safranin or fuchsine) and appear red or pink. Escherichia coli is a Gram-negative, rod-shaped bacterium of the genus Escherichia  that is commonly found in the lower intestine of warm-blooded organisms⁴.

 

Therefore, to improve the properties of the Antibacterial studies, the exothermic reaction based solution combustion technique was developed. The reported work in this section is the first time synthesis of CdSiO₃ Nanoparticles using ODH as a fuel and different silicate precursor like meso-porous silica, tetraethyl orthosilicate (TEOS) and fumed silica (SiO₂) by solution combustion (SC)technique. The prepared samples were characterized by PXRD, SEM, TEM, FTIR and Raman spectroscopy. The antibacterial studies were discussed in detail.

 

METHODOLOGY:

Synthesis of CdSiO₃ Nanoparticles Using Different Silicate Precursors:

The materials used for synthesis of pure CdSiO₃ nanoparticles were cadmium nitrate (Cd(NO₃)₂·4H₂O) and  freshly prepared meso-porous silica, TEOS and SiO₂was used⁵  as the source of Cd and Si respectively and pureCdSiO₃ nanoparticles prepared by solution combustion (SC)technique. The flowchart for the synthesis of pureCdSiO₃ nanoparticles prepared by different silicate precursors was shown in Fig. 1.

 

 

Fig.1: Flow chart for the synthesis of pure CdSiO₃ nanopowders prepared by different silicate precursor

 

PXRD analysis was performed using Shimadzu X-ray diffractometer with CuK_a radiation (l=1.5405Å) along with a nickel filter.  The data was collected in 2q ranges from 10-60 degree. Morphology of the sample was analyzed by using Hitachi table top SEM. TEM, SAED pattern and HRTEM measurements were done using JEOL 2100 HRTEM. FTIR spectrum was recorded along with KBr pellets. Raman studies were carried out on a Raman system. The clinical isolations of pathogenic bacterial strains Such as Gram+ve S. aureus (NCIM-5022), Gram-ve E.coli (NCIM-5051were purchased from NCL, Pune. These strains were maintained on nutrient agar slant at 4^◦C

 

RESULTS AND DISCUSSION:

Investigations from PXRD:

Fig. 2 shows the PXRD of pure CdSiO₃nanoparticles (a) As-formed, calcined samples for 2h at (b) 600 (c) 700 (d) 800 (e) 900⁰C prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂. The diffraction peaks of pure CdSiO₃ nanoparticleswere well matched with the JCPDS card No. 35-0810 confirms the formation of CdSiO₃ nanoparticles. Among all the prepared silica, the sample calcined at 800^oC for 2 h shows better crystallanity and monoclinic phase.

 

 

Fig. 2: PXRD of pure CdSiO₃ nanopowders (a) As Formed, Calcined for 2h at (b) 600 ⁰C (c) 700 ⁰C (d) 800 ⁰C (e) 900 ⁰C prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂

The average particle size ‘D’ was calculated by employing the Debye- Scherrer’s formula,

 

where, ‘β’ is the full width at half maximum of the diffraction peak, ‘λ’ is the wavelength of X-ray (1.5418 A), ‘θ’ is the Bragg’s angle, ‘k’ is the Scherrer’s constant The average crystallite size ‘D’ of the pure CdSiO₃ samples was found to be ~ 23 - 43 nm for the samples calcined at 800^oC for 2 h.

 

Further, strain⁶ present in the CdSiO₃ nanoparticles synthesised was estimated using the W-H equation. It is known that the FWHM can be expressed as a linear combination of the contribution from the lattice strain and crystalline size.

 

where ‘ε’ is the strain associated with the nanoparticles ⁷. From the W-H plots the lattice strain is extracted from the slope and the crystalline size was extracted from the y-intercept of the linear fit. The actual particle size for which the strain has been taken into account can be evaluated from extrapolation of the plot as shown in Fig.3 (a). The ‘D’ was calculated from Scherrer’s method and Williamson–Hall plots were in good agreement. Also, observed that the crystallite size is least in TEOS as a silica source shown in the Table 1.

 

Fig. 3: (a). W-H plots of pure CdSiO₃ nanopowders prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂

 

Table.1: Average particle size of pure CdSiO₃ nanopowders prepared by different silicate precursor

Sl. No	Silica Source	Scherer’s equation (nm)	W-H Plot (nm)	Lattice strain € x10-3
01	Meso-porous silica	30	34	1.41
02	TEOS	23	32	2.16
03	Fumed Silica	32	43	1.07

Morphological analysis:

TEM and SEM collectively provide significant tool for the characterization of nanoparticles. SEM pictures of pure CdSiO₃ nanoparticles prepared by different silicate precursors shown in Fig.4 reveal the morphologies of CdSiO₃ nanoparticles are highly porous and agglomerated with poly crystalline nature. The pores and voids can be attributed to the large amount of gases escaping out of the reaction mixture during combustion.

 

Fig. 4: SEM micrographs of pure CdSiO₃ nanopowders (a) as formed, calcined at (b) 600 ⁰C (c) 700 ⁰C (d) 800 ⁰C and 900 ⁰C for 2 h prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂

 

TEM and HRTM images of pure CdSiO₃ nanoparticle scalcined at 800 ⁰C for 2 h prepared by different silicate precursor (A) meso-porous silicate (B) TEOS and (C) SiO₂are shown in Fig 5(a) and (b) respectively.  The sample consists of irregular shaped particles with an‘D’ was found to be ~ 30 nm. Fig. 5(c) shows the SAED pattern of pure CdSiO₃ NPs having polycrystalline nature. The possible elements present were studies by EDAX shown in Fig.5 (d) and Fig.5 (e) table shows quantity of element present in the sample confirms the presence of only Cd, Cu, Si and O elements. The Cu element identified was due to copper grid used as a base material ⁸.

 

Fig.5: (a) TEM (b) HRTEM images of pure CdSiO₃ nanopowders (c) SAED (d) EDAX (e) atomic weight % calcined at 800⁰C for 2h prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂

 

FT-IR spectral analysis:

FTIR spectra were recorded in the range 4000-400 cm^-1 using Perkin Elmer Spectrum 65 with KBr pellets was shown in Fig.6. The spectra showed the band in the range 875–1114 cm^-1 was owing to unequal stretching vibration of Si–O–Si bond and stretching vibrations of edge Si–O bonds. The peaks at 468 cm^-1 were the characteristic stretching vibrations of Si–O–Si bridges. A weak absorption peak at 2397 cm^-1 specifies the existence of C=O bond, may be due to adsorbed CO₂ in the sample⁹. The sharp peak corresponding to ~ 680 cm^-1 can be ascribed to Si–O bond, which exists in the form of SiO_3. The absorption at around 3490 cm^-1 indicates the presence of hydroxyl groups.

 

Fig. 6: FTIR Spectra of pure CdSiO₃ nanopowder As-formed and calcined for 2 h prepared by (A) meso-porous silicate (B) TEOS and (C) SiO₂

Raman Spectroscopy:

The Raman spectrum for the sample indicates the presence of prominent and highest vibrational band at 856.38 cm^-1 along with two anti-symmetric stretching modes appear at 966.7 and 1006.21 cm^-1 (Fig.7). The peak at 1006.21 cm^-1 is due to the symmetric stretching mode of the Si0₆ octahedral group, the two lower frequency modes 633.02 and 703.33 cm^-1 are likely to be associated with motion of the Cadmium ion. Bands below 350 cm^-1 are due to external modes and are difficult to be assigned because of mixing¹⁰. At 487 cm^-1, the Ag mode corresponds to the scissors movement of Si-O-Si group’s along the c axis, while the peak at 322.81 and 107.77 cm^-1 are due to an A_u and B_3g mode relates with the bending of O-Si-O groups within the ab plane and the simultaneous movement of Cd ions along the b axis.

 

Fig.7: Raman Spectraof pure CdSiO₃ nanopowders calcined at 800 ⁰C for 2 h prepare by (A) meso-porous silicate (B) TEOS and (C) SiO₂

 

Antibacterial Studies:

In vitro antibacterial activities were carried out by the using of Agar well diffusion method¹¹. In this method followed had the following procedure: First of all, Nutrient Medium (Peptone 5g/l, Beef extract 3g/l. agar–agar 15g/l, pH 7.2) was poured into sterilized Petri dishes (90 mm diameter). Nutrient broth containing 100 ml of 24-h incubated cultures of the respective strains such as S. aureus and E.coli was spread separately on the agar medium using with the help of Sterile L-shaped glass rod. Wells were created using a sterilized cork borer under aseptic conditions. Previously, prepared (250, 500, 750, 1000µg/µL) of different nanoparticle such as pure CdSiO₃Nps prepared by meso-porous silica, TEOS and SiO₂ as silica source nanoparticles is dispersed in sterile distillled water at different concentration was loaded to each wells by using sterile micropipettes. Simultaneously the standard antibiotics (as positive control) were tested against the pathogens. Negative control was prepared using respective the sterile distilled water. Ciprofloxacin (Hi Media, Mumbai, India) as positive control. Nutrient agar Plates were then incubated at 37^◦C for 36h. At the end of the incubation period, inhibition zones formed on the medium were evaluated in millimeters. Triplicates were maintained in each of the compound and the average values are calculated for the ultimate antibacterial activity.

 

Antibacterial activity of pure CdSiO₃ nanoparticles prepared by meso-porous silica, TEOS and SiO₂ as silica source against pathogenic bacterial strains such as S. aureus and E.coli in agar well diffusion method¹¹. The highly significant antibacterial activity in S. aureus when compare to E.coli of pathogenic bacterial strains Mechanism of the bactericidal effect of nanoparticles was generally was been attributed to the decomposed of bacterial outer membranes by (ROS), primarily ^_HO which lead to phospholipid peroxidation and ultimately cell death. The pathogenic bacterial strains of Gram +ve bacteria S. aureus and Gram-ve bacteria, E.coli, with various concentration (250, 500, 750, 1000µg/µL) of different nanoparticle such as pure CdSiO₃Nps prepared by meso-porous silica, TEOS and SiO₂ as silica source showed the zone of inhibition shown in Fig.8 (A, B and C) and data was shown in Table.2. Most E.coli strains are harmless, but some serotypes can cause serious food poisoning in their hosts, and are  occasionally responsible for product recalls due to food contamination. Staphylococcus aureus is a gram-positive bacteria and is frequently found in the nose, respiratory tract and on the skin.

 

 

Fig. 8: Antibacterial activity of pure CdSiO₃nanopowders against a) E.coli (b) S.aureus prepared by (A) Meso-porous silica (B) TEOS and (C) SiO₂

Table.2. Data of Antibacterial activity of pure CdSiO₃nanopowders against a) E. coli (b) S.aureus prepared by different silicate precursor

Sample Pure CdSiO3 Nps	Concentration	E.coli (a)	S.aureus (b)
Standard Ciprofloxacin	5 µg/µl	11.18±0.03	10.45±0.03
(A)    Perpared by Meso-porous silica	250 µg/µl 500 µg/µl 750 µg/µl 1000 µg/µl	0.35±0.03 0.45 ±0.03 1.05±0.03 2.00±0.00	--------- --------- 0.75 ±0.03 1.32 ±0.16
(B)     Prepared by TEOS	250 µg/µl 500 µg/µl 750 µg/µl 1000 µg/µl	-------- 0.50 ±0.00 1.42±0.06 2.40±0.06	-------- -------- 0.48±0.04 1.25±0.03
(C)     Prepared by SiO2	250 µg/µl 500 µg/µl 750 µg/µl 1000 µg/µl	-------- -------- 0.30±0.03 1.10±0.06	-------- -------- -------- --------

 

CONCLUSION:

Pure CdSiO₃ nanoparticles was successfully synthesized by self-sustainable propellant wet chemical technique using different silicate precrusor. PXRD analysis confirms the monoclinic phase was formed at low calcined temperature of 800 ⁰C for 2 h compared to high temperature conventional methods.  SEM, HRTEM and TEM picture show that the powder was highly porous, foamy and agglomeration. Hence, pure CdSiO₃ nanoparticles prepared by simple SC method, TEOS as silica source gives the high intensity and gives better results. Antibacterial studies of pure CdSiO₃ nanoparticles prepared by TEOS better than the other silica precursors is often positive for catalase and nitrate reduction.

 

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Received on 15.04.2019           Modified on 23.05.2019

Accepted on 28.06.2019         © RJPT All right reserved