Applied sciences  
Article Synthesis and Characterization of Cerium Oxide Nanoparticles: Effect of Cerium Precursor to Gelatin Ratio  
[PERSON], [PERSON]. Pouroutzidou1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,19,17,18,  
from the atomic scale. Top-down processes use mechanical means to break down or crush bulk material into smaller pieces to create nanoparticles [5]. The sol-gel technique is the most widely preferred of the rest of the bottom-up synthesis methods due to its simplicity as well as it is a cost-effective and low-temperature synthesis technique friendly to the environment [6; 7]. Cerium (Ce) is the most prevalent among rare earth elements. It is the most active member of the lanthanide series with an electronic configuration [Xe]4f15d16s2 [8]. Cerium is a block F, group 3, period 6 element with the atomic number 58 [9]. Cerium has two typical oxidation states, Ce (III) and Ce (IV), although most rare earths exist in trivalent. This facilitates the formation of CeO\({}_{2}\) and Ce\({}_{2}\)O\({}_{3}\) and thus it possesses antioxidant and catalytic properties due to its redox behavior [5]. Due to the electrical arrangement of Ce\({}^{3+}\)-[Xe]4f1 being less resilient than Ce\({}^{4+}\)-[Xe]4f0, the oxidation state of Ce\({}^{3+}\) is thought to be unstable in relation to Ce\({}^{4+}\)[10]. Ceria is a whitish and crystalline substance that turns yellowish when it is impure. Cerium is found in the core of a tetrahedron, with oxygen atoms occupying the four corners. A face-centered cubic (f.c.c.) unit cell with the space group Fm3m and a lattice constant of 0.541134 nm is how it is characterized [10]. The ceria structure is known to create distinct, oxygen-deficient, nonstoichiometric CeO\({}_{(2-x)}\) oxide structures (with \(0\leq x\leq 0.5\)) under reducing circumstances and at high temperatures. Ceria does, however, have the propensity to form distinct compositions at lower temperatures. Ceria's capacity to deliver oxygen and thus create a significant number of vacancies, which accounts for its reductive qualities, which make it easy to construct oxygen-deficient nonstoichiometric phases. The \"reduced\" structures may easily be changed back to CeO\({}_{2}\) by being exposed to an oxidizing atmosphere while still maintaining their fluorite structure [8; 11]. The idea of oxygen vacancy in the lattice structure is the lack of single or numerous oxygen atoms in the unit cell of ceria [12]. The enhanced surface activity is related to cerium's oxygen storage capacity (OSC), which is directly connected to how quickly cerium can alter its oxidation state. Cerium oxide has a dynamic valence and defect structure that may vary suddenly or in reaction to environmental factors including temperature, the existence of other ions, and the partial pressure of oxygen [13]. The ratio of Ce\({}^{3+}\)/Ce\({}^{4+}\) and the amount of oxygen vacancies have significant impacts on the nanoceria's capacity to switch between different oxidation states. According to studies, the number of oxygen vacancies increases as cerium oxide nanoparticles decrease in size [14]. Many studies have revealed that cerium oxide nanoparticles, which have a distinctive electron structure, may function as biological antioxidants. It has been suggested that oxygen vacancies at the surface mediate this antioxidant action. Additionally, the ceria nanoparticles' electron defects might not be eliminated following their initial interaction with reactive oxygen species, making them potentially powerful catalysts in a live cell [15]. More oxygen vacancies ensure that oxygen atoms may move around inside the crystal more easily, which encourages redox reactions on the surface and results in great catalytic activity [10]. Due to the ability of nanoceria to interchange between two oxidation states Ce\({}^{3+}\) and Ce\({}^{4+}\), it appears to have a strong antioxidant activity by scavenging ROS.