“…Furthermore, aluminum oxide is an amphoteric oxide and exists in various polymorphs such as gamma (ɣ-), delta (δ-), theta (ɵ-), rho (ρ-), eta (η-), kappa (ƙ-) and chi (χ)-alumina, in addition to its stable phase (alpha (α)-alumina, corundum) [26]. Among them, alpha-and gamma-alumina have attracted a significant attention of the research groups based on their unique characteristics; therefore, both polymorphs have various applications as mentioned previously [13][14][15][16] plasma synthesis [28], freeze-drying of sulfate solutions [29], the sol-gel method [30,31], laser ablation [32], controlled hydrolysis of metal alkoxide [33], and precipitation [34], precipitation and sol-gel process followed by calcination [35,36], sputtering [37], electrochemical [38], mechanical milling [39], pyrolysis [40], homogenous precipitation followed by calcination [41], and metal organic chemical vapor deposition [42]. However, limitations of these approaches, for both ɣ-and α-alumina nanoparticles, are of great concerns such as long reaction time, uncontrolled particle size, a high-temperature requirement, and use of expensive and toxic organic solvents.…”