## 2 Neutralization Technologies Based on Nanocrystalline Metal Oxides  
Neutralization technology is not only limited to acid-base chemical neutralization, but also includes the elimination or minimizing of hazardous properties of a substance that undergoes uncontrolled release. Such a broad approach imposed the necessity of finding a universal solution that would concurrently be easy to use. The current neutralization technologies use decontamination solutions based on various types of oxidants (such as: hydrogen peroxide, ozone, chloramine, peracetic acid, salts of dichloroisocyanuric acid, persulphates, urea, percarbonates, magnesium perphthalate, etc.) [4; 5; 6; 7; 8; 9; 10; 11]. However, this technology is not universal and it mainly comprises the removal of threats related to toxic compounds of organic origin. In the most common neutralization technologies use is made of mixtures that consist of nanoparticles of such metal oxides as MgO, CaO, ZnO, SrO, TiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), CuO, Fe\({}_{2}\)O\({}_{3}\) with grain diameters ranging from a few nanometers to several dozen micrometers [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. The nanocrystalline MgO with grains of a 4 \(\upmu\)m diameter and a specific surface exceeding 500 m\({}^{2}\)/g is characterized by a particularly large surface and activity [14; 15; 16; 17; 18; 30; 34]. Reducing the size of nanocrystallites causes a significant increase in the share of surface atoms, including those occupying edge and corner places, particularly as their network defects comprise the active sites of the oxide neutralizer [34]. Consequently, the material that contains crystallites with a diameter of 2 \(\upmu\)m has more than half of the atoms/ions located on the surface and a specific surface close to 1000 m\({}^{2}\)/g. It should be borne in mind that 10% of the locations are occupied by edge atoms/ions and 1% by corner ones [45]. An important feature of nanocrystallites is also the size of inter-crystalline pores. Given that their size is close to the size of the nanocrystals themselves, this significantly affects the diffusion characteristics of gases. At a diameter below 10 \(\upmu\)m the Knudsen diffusion area is entered where collisions between gas molecules occur less frequently than collisions between pore walls. This is the cause of a smaller mass transfer through the nanocrystalline material by three to four orders of magnitude and promotes the phenomenon of capillary condensation that allows the effective capture of air vapors. Besides the typical acid-base neutralization, nanooxide-based specimens lead to dissociative adsorption on the surface of nanocrystals. As a consequence, in addition to chemisorption, the molecule breaks down into less toxic elements by hydrolysis of PO, P-CN, PS bonds [35; 37; 34], CX (X = F, Cl, Br, I) [21; 22; 29]. Such processes take place in a wide range of toxic industrial agents (TSP), halogenated organic warfare agents, as well as paralytic-convulsive (sarin, tabun, soman, VX), stinging (luisite, HD), asphyxiant (COCl\({}_{2}\)), and general toxic ones (AsH\({}_{3}\), HCN). The dissociative chemisorption process is known in literature for polar water molecules and alcohols on the surface of MgO (100) [42; 46]. Dissociative chemisorption does not occur on sorbents based on activated carbon [41]. As has been mentioned earlier, nanotechnologies based on oxide mixtures also have the ability of absorbing vapors of hazardous substances from the atmosphere. For the MgO-TiO\({}_{2}\) mixture, after 2 min, a concentration reduction of over 95% is observed for such vapors and gases as NH\({}_{3}\), Cl\({}_{2}\), CH\({}_{2}\)OCH\({}_{2}\), HCl, NO\({}_{2}\), SO\({}_{2}\), CH\({}_{3}\)SH [3]. As regards toxic warfare agents, MgO, CaO, SrO, Al\({}_{2}\)O\({}_{3}\) and mixed MgO-Al\({}_{2}\)O\({}_{3}\) and SrO-Al\({}_{2}\)O\({}_{3}\) oxides are particularly active when prepared in the form of a modified airgel [29; 36; 37; 39].