Bacterial contamination is an unusual menace for human well-being. Nanotechnology proposes diverse techniques to nurture new inorganic antibacterial agents. Nano-inorganic metal oxides possess an auspicious potential to diminish bacterial effluence. Magnesium oxide (MgO) is a significant inorganic oxide and has been widely employed in numerous arenas such as catalysis, ceramics, toxic waste remediation, antibacterial activity, and as an additive in paint and superconductor products by virtue of its distinctive properties. Numerous studies have shown that magnesium oxide nanostructures possess remarkable antibacterial activity. Therefore, in this direction, few synthesis methods such as hydrothermal method, sol-gel method, etc., antibacterial activity, and antibacterial mechanisms of magnesium oxide nanostructures have been incorporated in this chapter.
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In the span of two or three decades, the distinguishing properties of nanomaterials created an enormous interest amongst the researchers to develop simple and economical procedures, technologically imperative and productive, to fabricate nanostructures with diverse morphology. Nanomaterials, metal oxide nanomaterials in particular, with high surface area to volume ratio have attracted keen interest of scientific community on account of their prospective applications in numerous areas such as nano-electronics, optoelectronics, sensing devices etc. A new class of antimicrobial agents are the metal oxide nanomaterials (Rajendra, 2010; Bindhu, 2016; Zhu, 2016). These metal oxides, such as zinc oxide (ZnO), magnesium oxide (MgO), copper oxide (CuO), calcium oxide (CaO), silver oxide (Ag2O), and titanium dioxide (TiO2) are believed to possess potential applications in food, healthcare and the environment, with the result these have been increasingly studied for their antibacterial properties. In the nanoregime, metal oxide nanomaterials display remarkable features such as antibacterial activity, large surface area to volume ration, large available surface area of interaction with cell, versatile morphology and tunable sizes, unparalleled surface properties, little chances for bacteria to develop resistance, extraordinary stability even under severe conditions, which pave the ways for abundant possibilities to develop nanomaterials as effective antimicrobial agents (He, 2016; Gold, 2018; Pugazhendhi, 2019). Among these, nanostructured MgO is particularly interesting by virtue of its strong antibacterial activity, cost effective and extraordinary thermal stability. It finds wide-range of applications in catalysis, ceramics, toxic waste remediation, antibacterial activity, paint industry and superconductor products (Yang, 2018; El-Sayyad, 2018; Sudakaran, 2017).
Magnesium oxide (MgO), a source of magnesium, is a hygroscopic solid mineral with a shiny white color, energy band gap, Eg=4.1–6.2eV, lattice parameters a=b=c=4.24nm, boiling point = 3,870 K, melting point = 3,098 K, and density = 3.6 gm/cm3. In nature, it occurs in the form of periclase from which it is extracted using different metallurgical processes. Its empirical formula is MgO. MgO is composed of lattice of Mg2+ ions and O2− ions and these constituents are held together by ionic bonding (Karthik, 2017; Fu, 2005).
Figure 1. The crystal structure of MgO showing the octahedral co-ordination of the Mg and O ions.
Figure-1 depicts the pictorial representation of MgO unit cell. The structure of MgO may be characterized as a cubic close packed arrangement of oxygen ions having magnesium ions at the octahedral sites. The Mg2+ ions as well as the O2- ions are organized in a face-centred cubic (F.C.C.) pattern with lattice parameters. Each ion in the structure is octahedrally surrounded by six similar ions of other type. A regular three-dimensional array is formed with coordination number of six for both the types of ions.
Among the family of metal oxides, magnesium oxide has a simple stoichiometry, simple crystal structure and owes good ionic character. On account of the high concentration of edge/corner sites and structural imperfections on surface, magnesium oxide nanostructures retain high specific surface and reactivity (Makhluf, 2005; Xu, 2004). For antibacterial activity, several methods have been employed to fabricate MgO nanostructures with different morphology and particle size. We have utilized two different methods namely hydrothermal method and sol-gel method for the fabrication of MgO nanoparticles.