Effect of the calcination process on CdO-ZnO nanocomposites by a honey-assisted combustion method for antimicrobial performance

Phase variation of manganese oxide in the MnO@ZnO nanocomposite with calcination temperature and its effect on structural and biological activities

Having powerful antibacterial and antioxidant effects, zinc oxide and manganese oxide nanomaterials are of great interest. Here we have synthesized manganese oxide decorated zinc oxide (MZO) nanocomposites by co-precipitation method, calcined at different temperatures (300-750 °C) and studied various properties. Here the crystalline structure of the nanocomposite and phase change of the manganese oxide are observed with calcination temperature. The average crystalline size increases and the dislocation density and microstrain decrease with the increase in calcined temperature for the same structural features. The formation of composites was confirmed by XRD pattern and SEM images. EDAX spectra proved the high purity of the composites. Here, different biological properties change with the calcination temperature for different shapes, sizes and structures of the nanocomposite. Nanomaterial calcined at 750 °C provides the best anti-microbial activity against Escherichia coli, Salmonella typhimurium, Shigella flexneri (gram-negative), Bacillus subtilis and Bacillus megaterium (gram-positive) bacterial strain at 300 µg/mL concentration. The nanomaterial with calcination temperatures of 300 °C and 450 °C provided better antioxidant properties.

Bioactive properties of ZnO nanoparticles synthesized using Cocos nucifera leaves

Biosynthesis of zinc oxide nanoparticles has been reported using Cocos nucifera leaf (CNL) extract along with estimation of their antimicrobial potential before and after calcination using different micro-organisms. UV-visible spectra of ZnO nanoparticles showed absorption maxima at 383 nm and 363 nm, respectively, with 3.237 eV and 3.416 eV, respectively, as the corresponding band gap energies. FESEM and TEM images showed spherical morphologies of ZnO nanoparticles within the size range 109-215 nm. XRD analysis confirmed the formation of hexagonal wurtzite structures. ATR-IR spectra revealed the presence of stretching vibrations of N-H, O-H, C=C, C=O and NH2 groups along with C-H and N-H deformation involving biomolecules from CNL extract responsible for reduction and stabilization of ZnO nanoparticles. Uncalcinated ZnO nanoparticles displayed antibacterial activities only against S. aureus and P. aeruginosa whereas calcinated ZnO nanoparticles did not show antibacterial activities against E. coli, S. aureus, P. aeruginosa and B. subtilis. ZnO nanoparticles were not active against Penicillium spp., Fusarium oxysporum, Aspergillus flavus, Rhizoctonia solani as well as HCT-116 cancer cells before as well as after calcination. Antimicrobial nature and biocompatibility of ZnO nanoparticles were influenced by different parameters of the nanoparticles along with micro-organisms and the human cells. Non-antimicrobial properties of ZnO nanoparticles can be treated as a pre-requisite for its biocompatibility due to its inert nature. These ZnO nanoparticles can serve a dual purpose by facilitating use as antibacterial agent against susceptible micro-organisms as well as a biocompatible carrier molecule in drug delivery applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03110-9.

Non-antimicrobial and Non-anticancer Properties of ZnO Nanoparticles Biosynthesized Using Different Plant Parts of Bixa orellana

As traditional cancer therapy is toxic to both normal and cancer cells, there is a need for newer approaches to specifically target cancer cells. ZnO nanoparticles can be promising due their biocompatible nature. However, ZnO nanoparticles have also shown cytotoxicity against mammalian cells in some cases, because of which there is a need for newer synthesis approaches for biocompatible ZnO nanoparticles to be used as carrier molecules in drug delivery applications. Here, we report the biosynthesis of ZnO nanoparticles using different plant parts (leaf, seed, and seed coat) of Bixa orellana followed by different characterizations. The UV-visible spectra of ZnO showed absorption maxima at 341 and 353 nm, 378 and 373 nm, and 327 and 337 nm, respectively, before and after calcination corresponding to the band gap energy of 3.636 and 3.513 eV, 3.280 and 3.324 eV, and 3.792 and 3.679 eV for L-ZnO, S-ZnO, and Sc-ZnO, respectively. X-ray diffraction analysis confirmed the formation of hexagonal wurtzite structures. Attenuated total reflectance infrared spectra revealed the presence of stretching vibrations of C-C, C=C, C=O, and NH₃ ⁺ groups along with C-H deformation involving biomolecules from extracts responsible for reduction and stabilization of nanoparticles. Field emission scanning electron microscopy and transmission electron microscopy images showed spherical and almond-like morphologies of L-ZnO and Sc-ZnO with spherical morphologies, whereas S-ZnO showed almond-like morphologies. The presence of antibacterial activity was observed in L-ZnO against Staphylococcus aureus and Bacillus subtilis, in S-ZnO nanoparticles only against Escherichia coli, and in Sc-ZnO only against Staphylococcus aureus. Uncalcinated ZnO nanoparticles showed weak antibacterial activities, whereas calcinated ZnO nanoparticles showed a non-antibacterial nature. The antifungal activity against different fungi (Penicillium sp., Aspergillus flavus, Fusarium oxysporum, and Rhizoctonia solani) and cytotoxicity against HCT-116 cancer cells were not observed before and after calcination in all three ZnO nanoparticles. The antimicrobial nature and biocompatibility of ZnO nanoparticles were influenced by different parameters of the nanoparticles along with microorganisms and the human cells. Non-antimicrobial properties of ZnO nanoparticles can be treated as a pre-requisite for its biocompatibility due to its inert nature. Thus, biosynthesized ZnO nanoparticles showed a nontoxic nature, which can be exploited as promising alternatives in biomedical applications.