MECHANISM OF HYDROGEN PRODUCTION IN THE PROCESSES OF RADIATION-HETEROGENEOUS SPLITTING OF WATER WITH THE PRESENCE OF NANO-METAL AND NANO-MeO 1

In the study, the optimal values of the ratio of the distance between particles to the particle size in the radiation-heterogeneous radiolysis of water in nano-Me and nano-MeO systems were determined. In those systems, the effect of water density and system temperature on the radiation-chemical release of molecular hydrogen obtained from thermal and radiation-thermal decomposition of water was considered. The article also determined the effect of particle sizes and the type of sample taken on the radiation chemical yield of molecular hydrogen. In the presented article, the change of molecular hydrogen according to adsorbed water and catalyst was studied. Thus, in the case of a suspension of nano-zirconium in water, the energy of electrons emitted from the metal is completely transferred to water molecules, which leads to an increase in the yield of hydrogen. When radiolysis of water in the presence of nano-metals, energy transfer can be carried out mainly with the participation of emitted electrons. Therefore, in the case of radiolysis of water in suspension with n-Zr, the yield of hydrogen increases by 5.4 times compared to the processes of radiolysis in an adsorbed state. However, in radiation-heterogeneous processes of obtaining hydrogen from water in contact with metal systems, it is necessary to take into account that as a result of these processes surface oxidation occurs and after a certain time the systems are converted to n-Me-MeO+H 2 O liq. systems. For nano sized oxide compounds, the mean free path of secondary electrons formed as a result of primary processes of interaction of quanta with atoms is commensurate with the particle sizes of nano-oxides ( λ ≈ R_(H-о xides)). Further, these electrons interact with the electronic subsystem of silicon. For nanocatalysts, the length of free paths of secondary and subsequent generations of electrons is greater than the size of catalyst particles (R_cat ≤ 100nm). Usually, their energy is sufficient to conduct independent radiolytic processes in the contact medium of the catalyst.


INTRODUCTION
Nanosized metal oxide photocatalyst materials for water splitting have emerged as the promising way for hydrogen generation in a low-cost and sustainable way.Various researchers have reported investigations on co-relation of crystallinity and morphology of nanomaterials to the water-splitting performance.In general, the nanomaterials with high surface-to-volume ratios are expected to promote facile charge separation/transportation of photogenerated charge carriers [1][2][3].
Overall, more work needs to be done in terms of redox material engineering, reactor technology, heliostat cost reduction and gas separation technologies before commercialization of this technology [4].
The yields of molecular hydrogen, H2, have been measured in the radiolysis of dodecane and hexane following radiolysis by γ-rays and a variety of heavy ions.Increasing the linear energy transfer (LET) from γ-rays to radiolysis with protons results in a decrease of H 2 yields by about 15% due to the increased importance of second-order H atom combination reactions.A further increase in LET results in a slight increase in H 2 yields [5].
The results suggest that the increase in H 2 production is due to the transfer of energy, possibly by an exciton, from the oxide to the water.O 2 production was at least an order of magnitude less than H 2 .The yield of H 2 in the 5 MeV helium ion radiolysis of water on CeO 2 is the same as with γ-rays, but the results with ZrO 2 are substantially lower.The H 2 yields with helium ion radiolysis may be nearly independent of the type of oxide [6][7][8][9][10].
The differences in the relative increases in molecular hydrogen with increasing LET for each of the polymers suggests that self-scavenging reactions may be important for low LET particles [11].
It has been revealed that at increase in mass of the silicon added to water the radiation-chemical yield of the molecular hydrogen received in the process of a water radiolysis grows in direct ratio (m < 0.02 g) and depending on the sizes of particles after a certain mass value (m > 0.02 g) the stationary area is observed.In the Si+H 2 O system the maximum radiation-chemical yield of molecular hydrogen is equal to 10.9; 8.07, and 5.24 molecules/100 eV at the sizes of silicon particles d = 50, 100, and 300…500 nm respectively [12].Mechanism of Hydrogen Production in the Processes of Radiation Heterogeneous...

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The kinetics of molecular hydrogen accumulation at a gamma radiolysis of water on n-ZrO 2 surface is investigated.Influence of gamma radiations on n-ZrO 2 +water systems is studied at various temperatures T = 300…673 K [13].
At a temperature of T = 673 K, the yield and the rate of formation of molecular hydrogen obtained in the thermal and radiation-thermal transformation of water vapor in the reaction medium increase in direct proportion to the its density at ρ < 3 mg/cm 3 , and at ρ ≥ 3 mg/cm 3 a sharp decrease in the angle slope is observed [14].
It has been established that the amount, formation rate and radiationchemical yield of molecular hydrogen defined according to both water and BeO from radiation-heterogeneous transformation of water in these systems, change depending on mass and particle size of BeO added to water [15].
Different strategies could be implemented to improve the water splitting efficiency of semiconductors.Among them, loading of catalyst onto the water splitting material is known to be one of the effective strategies to enhance the H 2 and O 2 production rates.Conclusively, to explore the efficient catalysts for photochemical water splitting require more research contribution towards the understanding of the core reaction mechanism of catalytic process with the use of sustainable and stable materials [16][17].
In the last years, the awareness of climatic change has increased leading to the temptation of exploration of alternative sources of energy.Consequently, the use of nuclear energy is increasing day by day but it is not economically and environmentally favorable [18].Transforming nuclear energy into a more affordable form of energy remains one of today's needs.Therefore, the request for green energy is the chief objective for the scientists in 21 century.The significant methods include photocatalytic, photo-electrochemical, thermal decomposition and photobiological radiolysis.Among these, photocatalytic of water is measured as the best one due to green, efficient, inexpensive with the comfort of process and with a good volume of hydrogen formed [19].
For a long time, dissimilar groups of catalysts are being developed and utilized to split water in the light but a good crop of hydrogen could not be attained at a good scale.Nanocatalysts have been produced and utilized in water splitting with good achievements [20].
Zirconium dioxide (ZrO2) has unique properties of refractoriness, low volatility, high chemical resistance, mechanical strength, wear resistance, low thermal conductivity, wide band gap, oxygen conductivity, and high refractive index.Also, zirconium dioxide has complex polymorphisms, including high-pressure phases.The unique properties have provided a wide and varied application of materials based on ZrO 2 in various fields of science and technology.Currently, the development of new technologies for the production and obtaining nanodioxide zirconium is of particular importance.Nanoscale systems differ in many respects from ordinary single-crystal systems, therefore, the study of their interaction with water under the influence of γ-radiation is of great practical and scientific interest in the field of high-energy chemistry, as well as in solving environmental problems [21].
The results showed that surface morphology is extremely important in the decomposition of liquids at solid interfaces, which may have many consequences ranging from nuclear waste storage to the H 2 economy.The presented work is devoted to the kinetics and mechanism of the formation of hydrogen as a result of the decomposition of water on the surface of nano-ZrO 2 [22].

METHOD
The experiments were performed at the static condition in specific quartz ampoules, with V = 1.0 cm 3 of volume.In order to prevent oil and lubricants from falling on the samples, three nitrogen-cooled holders are connected to the system in a vacuum-absorption device.The products of the radiolysis and thermoradiolysis of water were absent under the selected treatment modes which can be formed in the presence of organic impurities CO and CO 2 .The absorption process was the same for both methods (vapor and fluid).The gases generated were inhaled from each adsorbed ampoule to the chromatograph directly [23].
Analysis of molecular hydrogen and hydrogen-containing gases in a vacuum absorption device was carried out under static conditions.Radiation-heterogeneous processes were performed at the gamma 60 Co isotope source.The dosimetry of the source was determined by ferrosulfate, cyclohexane and methane dosimeters [24].The absorbed dose rate of the source was dDγ/dt = 0.40 Gy/s.The calculation of the absorption dose in these systems was carried out in comparison with the electron density.The absorption dose of gamma quanta was determined under the methods of ferrosulfate, cyclohexane and methane based on chemical dosimeters in the studied systems.
The ampoules were opened in a special box in which the radiolysis products entered the chromatograph column.The analysis of the products of radiation-heterogeneous processes was performed using "Gasochrome-3101", "Color-102", chromatographs.
Analysis of the number of products (H2, CO 2 ) gases released in the gas phase during the thermal and radiationthermal decomposition of water on the nano-Me and nano-MeO+H 2 O system was carried out by chromatographic method ("Gasochrome-3101", "Color-102", chromatographs).The molar density of gases in 1 mL was calculated by the following equation: where: molar density of C i -i component, molecule/ml or mol/ml; height of h i -i-th component, mm; m -sensitivity of the chromatograph; Calibration coefficient of the K i -i component, molecule/mm or mol/mm.EEJP. 1 (2024) Adil Garibov, et al.
The following formula was used to calculate the substance content of the components obtained in the gas phase during the experiment: where: molar mass, molecular or mole of N i -i component; Molar density of C i -i component, molecule/ml or mol/ml; V -a volume of the ampoule tested, ml.
The chromatographic analysis of radiation-catalytic products of water decomposition was carried out.

Obtaining molecular hydrogen during radiation-heterogeneous processes in suspensions of individual nanoelements (n-Zr and n-Si) in water.
In order to reveal the contribution of secondary electron fluxes emitted from the solid phase in the radiation-catalytic processes of hydrogen production, the kinetics of hydrogen production processes as a result of heterogeneous decomposition of water in the presence of nano-metal (n-Zr) and individual nanosemiconductor n-Si were studied (Fig. 1).
The effect of n-Zr and n-Si on the release of molecular hydrogen during radiolysis of water is investigated in their suspension in water [25].The kinetics of hydrogen production are investigated and radiation-kinetic outputs and process speeds are calculated based on them.(1) During radiation-heterogeneous radiolysis of water in a liquid state in the presence of n-Zr, the yield of molecular hydrogen is approximately 5.5 times greater than during the radiolysis of adsorbed states of water on the surface of n-Zr with a monolayer filling of the surface θ = 1.
Thus, in the case of a suspension of nano-zirconium in water, the energy of electrons emitted from the metal is completely transferred to water molecules, which leads to an increase in the yield of hydrogen.However, in radiationheterogeneous processes of obtaining hydrogen from water in contact with metal systems, it is necessary to take into account that as a result of these processes surface oxidation occurs and after a certain time the systems are converted to n-Me-MeO+H2Oliq.systems.
Under the influence of γ-quanta on n-Si, secondary electrons are generated with an energy where E g -is the band gap of the semiconductor, ∆E -k are their additional kinetic energies.Therefore, in the case of radiation-catalytic decomposition of water in the presence of a nano-semiconductor, for efficient energy transfer, it is necessary to have a condition for the interaction of energy carriers with water molecules.The effect of n-Si on the yield of molecular hydrogen during the radiolysis of water in a suspension of n-Si+H 2 O liq. was studied at various H 2 O liq. /n-Si ratios [26].To do this, we took 5 ml of bidistilled water and poured n-Si with different particle sizes into it in various amounts.Based on the weight of n-Si in the suspension and particle size, the concentrations of n-Si in V = 5 ml of water were calculated.
For this, the n-Si particles were presented as a sphere and the volume of each particle was determined by the average value of the ball radius ( ) by  =  .Taking into account the value of the specific gravity of n-Si (ρ=2.33 g), the mass of each particle m particle =V•Q was determined.
The ratio of m n-Si to the mass of each particle makes it possible to determine the total number of particles in 5 ml of suspension  = .The values of the mass and concentration of n-Si for each fraction are shown in Table 1.Mechanism of Hydrogen Production in the Processes of Radiation Heterogeneous...

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Under experimental conditions, the mass of  −   ≤ 0.12  is much less than the mass of water Therefore, the observed yields of molecular hydrogen were calculated both on the energy of absorbed ionizing radiation from the side of water G H2O (H 2 ) and from the side of n-Si G (n-Si) (H 2 ).Table 1 shows the values of the radiationchemical yield of hydrogen during radiation-heterogeneous radiolysis of water in the n-Si + H 2 O liq. system at various amounts, concentrations and sizes of the catalyst particle per gamma-radiation energy absorbed from the water side.With an increase in the concentration of n-Si in water under the influence of gamma rays, the yield of molecular hydrogen increases.Figure 2 (a, b, c) shows the dependences of G H2O (H 2 ) on the concentration of n-Si with different particle sizes in a suspension of n-Si+H 2 O liq.As can be seen, the addition of even the smallest amount of n-Si to water causes a sharp increase in the yield of molecular hydrogen during radiation-heterogeneous processes in the n-Si + H 2 O liq. system.EEJP. 1 (2024) Adil Garibov, et al.
Dependence  ( ) = ( ) can be conditionally divided into two sections.The first is the initial linear region, where  ( ) grows linearly with increasing  .The second region  ( ) = ( ) is characterized by a small slope of the dependence line.If radiation-heterogeneous processes would occur only on the surface of n-Si particles, then the rate and radiation-chemical yields of hydrogen would increase linearly with increasing  .The value of  , at which a transition between these regions is observed, depends on the size of the n-Si particles (Table 2.).For the convenience of calculation for the fraction d=300-500 nm, the average value d ̅ =400 nm was taken.By the value of the number of particles in the suspension and the specific surface of individual spherical particles  = 4 , the surface of the total amount of n-Si is determined in the form where  -is the total number of particles in the water.By the value of ω -the landing area of water on the surface of silica gel ω=0.453 nm 2 , the number of water molecules to fill the surface with a monolayer of water is determined Then the hypothetical value of the number of monolayers was estimated by the number of water molecules in the suspension ( = 5)  = 1.72 • 10  and ( = 1) By the value of the hypothetical value of the monolayers filling the surface of n-Si and the diameter of water molecules d(H 2 O) = 0.38 nm, one can approximately determine the distance between the particles in the suspension  −  +   .
The value of the distance between n-Si particles in the suspension was determined both in the entire region of n-Si concentration and at the transition point between the regions of dependences  ( ) = ( ).To characterize the distance of influence of individual n-Si particles on radiation-heterogeneous processes in a suspension, distances l is given per unit of particle diameter   .
As can be seen from Table 2, with an increase in the size of the n-Si particle in the H 2 O + n-Si suspension, the radiation-chemical yield of hydrogen, calculated for the energy of γ -radiation absorbed from the water side, decreases.It was found that the value of the distance, given per unit of n-Si diameter within the limits of accuracy, is constant This distance is consistent with the mean free path of secondary electrons with energy  ≈ 10 − 10 in water.
To characterize the efficiency of using the energy absorbed from the n-Si side during the radiolysis of water in the  −  +   .suspension, based on the kinetic curves of hydrogen accumulation, the values of the radiationchemical yield of hydrogen for the absorbed radiation dose from the n-Si side were calculated.Figure 3. shows the dependence of  ( ) on the concentration of n-Si in water.As can be seen, up to the value of the n-Si concentration corresponding to the transition (Table 2)  ( ), remains high.Then, a region of strong decline begins with a transition to a region of decrease with a small slope of the curves.
The n-Si particles play the role of converting the energy of primary quanta into the energy of secondary electron radiation.The energy of secondary electron radiation is in the region of  ≤ 10  eV. Figure 3 shows the dependence of the radiation-chemical yield of molecular hydrogen, calculated on the energy absorbed only from the side of  −   ( ), on the concentration of n-Si with particle sizes d=50nm in suspension.As can be seen, in the initial region Mechanism of Hydrogen Production in the Processes of Radiation Heterogeneous... EEJP. 1 (2024)  ≤ 2.5 • 10 / , the hydrogen yield in the limit of determination accuracy is stably high  ( ) ≈ 1700-1780 molecules/100 eV.At optimal concentrations of n-Si in suspension with water, the observed yields of hydrogen exceed the value of the yield during radiolysis of water under the action of γ-radiation and accelerated electrons [27].Apparently, at the initial values of the concentration  ≤  (transition), a region with a high electron density is created around the particle, and the decomposition of water molecules occurs according to the mechanism of decomposition of water in a nonequilibrium plasma [28].An increase in the concentration of  ≥ 2.5 • 10 particles/cm 3 causes a decrease in the yield of  Based on the results obtained on the effect of the n-Si concentration in water on the yield of molecular hydrogen during water radiolysis, it can be concluded that the optimal range of n-Si concentration values for efficient conversion of ionizing radiation energy into hydrogen energy.Since at values   ≥ 3 • 10 there is an efficient conversion of the energy of ionizing radiation into the energy of hydrogen.In the region   ≤ 3 • 10 , at which the distance between the particles related to the size unit n-Si decreases, the recombination of charged and intermediate decomposition products of water molecules increases.
The maximum yield of hydrogen during radiolysis of water in an n-Si suspension under the optimal regime corresponds to  ( ) = 10.9 molecules/100eV.The efficiency of converting the energy of ionizing radiation into relative conditions is And during the radiolysis of water in suspension with  −  , the yield of molecular hydrogen calculated for the energy absorbed by the total system − +   ж равно  .( ) = 13.5 /100.
The efficiency of converting the energy of ionizing radiation will be equal to Radiation-thermal processes of hydrogen production from water in the presence of nano-oxide compounds.Thermo-radiation processes for producing hydrogen are designed to convert the energy of high-temperature reactor models.As can be seen, an increase in temperature during radiation-thermal-catalytic processes stimulates the diffusion of energy carriers on the surface and secondary processes of transformation of intermediate products to final products.For nano sized oxide compounds, the mean free path of secondary electrons formed as a result of primary processes of interaction of quanta with atoms is commensurate with the particle sizes of nano-oxides ( ≈  о ).Therefore, temperature will most of all affect the secondary physicochemical and chemical processes of heterogeneous water radiolysis.Thermal and radiation heterogeneous processes were carried out under the same conditions [29].Kinetic parameters of thermocatalytic and radiation-thermocatalytic processes are determined on the basis of kinetic curves.The rate of radiation-catalytic processes of hydrogen production is determined by the difference in the values of experimentally determined radiation-thermal catalytic  РТ ( ) and  Т ( ) thermocatalytic processes.Their physicochemical properties are given in the previous sections.Figure 4 shows typical forms of kinetic curves for hydrogen production in the results of thermocatalytic (1) and radiation-thermocatalytic (2) decomposition of water at T = 673 K in the presence of  −  .
The effect of temperature on the radiation-catalytic properties of nano-oxides was studied in the temperature range T = 300÷673 K at the water vapor density in the reactor  = 5/ .
Table 3 shows the rates of radiation-thermal, thermal and radiation processes, as well as radiation-chemical yields of hydrogen, calculated for the energy absorbed by the common catalyst system+ .The corresponding methods determined the values of the rates of processes and radiation-chemical yields of hydrogen during radiation-thermal processes of water decomposition in the temperature range T = 300÷673K in the presence of, n−  and  −  .
The results obtained are shown in Tables 4 and 5.As can be seen n-ZrO 2 exhibits a relatively high radiation-thermal catalytic activity.At T = 673K, the observed value of the radiation-chemical yield of molecular hydrogen during radiolysis of water in the presence of  −  is equal to  ( ) = 25.7/100.The process of thermo-radiolysis of water occurs in the gaseous state, and therefore the efficiency of the energy conversion process in this system is Thus, radiation-thermocatalytic processes of hydrogen production from water at T ≥ 673K can compete with electrolysis processes in terms of efficiency.
Radiolytic decomposition of water molecules at T≥673K in the presence of  −  can occur both with the participation of energy carriers at the surface levels and with secondary electron radiation from  −  in the gas phase.The band gap width of  −  can be taken as  = 5.4 eV and the yield of such energy carriers as an electron and a hole will be equal to At T ≥ 673K, the intermediate H atoms are transformed into  according to reaction (11).
Therefore, the output of molecular hydrogen as a result of radiolysis of water with the participation of nonequilibrium charge carriers formed under the action of ionizing radiation will correspond to  .( ) = 9 / 100.
On the other hand, excitons are also generated in  −  under the action of γ-quanta, which can participate in the process of energy transfer.The size of the investigated samples of  −  varies in the region d = 20-30 nm, which is less than the mean free path of secondary electrons λ ≥ 2R and it can be expected that a certain part of the electrons will be emitted into the contact medium with  −  .Ultimately, these energy transfer channels from  −  in water can provide the observed value of the hydrogen yield.

Influence of temperature on the output of molecular hydrogen during radiolysis of water in the presence of n-Zr and n-Si.
When radiolysis of water in the presence of nano-metals, energy transfer can be carried out mainly with the participation of emitted electrons.Therefore, in the case of radiolysis of water in suspension with n-Zr, the yield of hydrogen increases by 5.4 times compared to the processes of radiolysis in an adsorbed state.Based on the results of the radiation-thermocatalytic processes of hydrogen production from water presented in the previous sections, it is possible to conclude that their speed depends on the following parameters of the process regime.
where is the temperature,  -radiation, LET-linear radiation energy transfer,  is the density or pressure of water vapor in the reaction medium, S/V dispersion of microsized or particle size of nanosized solids.
In order to reveal the regularities of the effect of temperature on the yield of molecular hydrogen, the kinetics of water radiolysis in the presence of n-Zr was studied in the temperature range T = 300÷673K, at a water vapor density in the reaction medium  = 5mg/cm 3 and power exposure doses  = 0.32÷0.26Gy/s [30].The values of the rates of the processes and the radiation-chemical yield of molecular hydrogen are given in Table 6.The value of the activation energy of the processes of thermo-heterogeneous and radiation-thermal processes on the basis of the dependencies ln  ( ) ≥  was determined to be 33.8 and 22.3 kJ/mol, respectively [30].The value of  .( ) during radiation-thermal decomposition of water at T = 673K,  .( ) = 8.4 molecules/100eV does not differ much from the values of hydrogen yield during radiolysis of water in n-Zr EEJP. 1 (2024) Adil Garibov, et al.
suspension  .( ) =7.1 molecules/100eV.The observed difference in the values of the hydrogen yield can be explained by the course of process (12).The efficiency of converting the energy of ionizing radiation into the energy of hydrogen in radiation-thermal catalytic processes at T = 673K in the gaseous state in the presence of nano-zirconium is equal to The authors [31][32] studied the effect of temperature on thermal processes, radiation-thermal processes in the  −  +   contact at various temperatures T = 300÷673K and water vapor density  = 5mg/cm 3 .The effect of water vapor density on the value of kinetic parameters of heterogeneous processes of water decomposition was studied at T = 673 K,  = 0.25÷8 mg/cm 3 in the presence of n-Si with particle size d = 50 nm.The research results are shown in Table 7.
Table 7.The value of the rates of thermo-heterogeneous, radiation-thermal and radiation-chemical processes, the production of hydrogen in the n-Zr+H2O system at the size of the n-Si particle d = 50nm and at the temperature T = 673K at the density of water vapor in the reaction medium  = 0.At a constant value of water vapor density  , d_к is the catalyst particle size,  is the radiation power and LET in (14), the effect of temperature in the region T=300÷673K on the velocities and  .( ) at thermo-radiolysis of water in the  −  +   system.The observed research results are shown in Table 8.The activation energies of thermal and radiation-thermal processes of hydrogen production in the  −  +   system is determined based on the temperature dependences of the process rates in the Arrhenius coordinates ln  ( ) =  .It was found that in the temperature range T=300÷473K, the radiolysis of water in the presence of n-Si occurs only as a result of radiation-heterogeneous decomposition of water with E = 1.07 kJ/mol.As can be seen from Table 8, in the temperature range T = 573÷673K in the  −  +   system, thermo-heterogeneous and radiation-thermo-heterogeneous processes of water decomposition are observed.The activation energies of these processes are 68.60 and 53.83 kJ/mol, respectively.Comparison of the activation energies of the processes  Р ( ),  РТ ( ) and  Т ( ) shows that radiation processes in the  −  +   system cause a decrease in the activation energy of the water decomposition process [33][34][35].
After radiation-heterogeneous processes, oxide phases, hydrides (ZrH x , SiH x ), hydroxyl groups Zr-OH, Si-OH are formed on the surface.SEM and IR spectrometry methods reveal oxide phases on the surface of the initial n-Zr and n-Si samples.Therefore, radiation-heterogeneous processes of water decomposition actually occur in the contact  −  −  +  ,  −  −  +  .As can be seen from tables 7 and 8, n-ZrO 2 have a relatively high radiation-catalytic activity in the process of water decomposition.Therefore, during radiation-thermocatalytic processes of hydrogen production in the  −  −  +   system, high yields of molecular hydrogen are observed relative to  −  +   systems.The values of radiation-chemical yields of hydrogen during thermoradiolysis of water in the systems  −  +   and  −  +   in the temperature range T ≥ 573 K are comparable and vary in the range of 4.15-4.40molecules/100eV.Therefore, radiolysis and thermo-radiolysis processes in the  −  −  +   and  −  +   systems can be used as model systems for revealing the patterns of energy transfer and surface radiationchemical processes.Mechanism of Hydrogen Production in the Processes of Radiation Heterogeneous...

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The Mechanism of Radiation-Catalytic Processes for Hydrogen Production from Water When ionizing radiation interacts with nano-catalysts, primary processes generate free secondary electron radiation, electrons in the conduction band, holes in the valence band, and excitons: In the scheme ( 15), e v -are secondary electrons, e pr -are electrons in the conduction band, p-holes in the valence band, ex-excitons, which are formed as the end product of a cascade of processes of interaction of secondary elements with catalyst atoms.As an example, let's look at the physical stage of processes occurring in the  −  +   system under the action of gamma -quanta with energy  = 1.25 MeV [12][13][14][15].
It is revealed that the interaction of gamma-quanta with the atoms of the systems occurs mainly according to the mechanism of Compton scattering.With Compton scattering of gamma-quanta from silicon atoms, depending on the scattering angle, the kinetic energy of Compton electrons varies in the range of 0 ... 1.02 MeV.For nanocatalysts, the length of free paths of secondary and subsequent generations of electrons is greater than the size of catalyst particles (R_cat ≤ 100nm).Therefore, in scheme (1), secondary electrons for radiation-heterogeneous processes involving nanoscale catalysts are also indicated as end products.
Water on the surface of oxide systems creates electron-donor complexes H 2 Os, which capture holes formed under the action of ionizing radiation (16).Many radiation catalytic active oxide compounds have broad valence levels, and therefore the holes in them are highly mobile.In the presence of levels of water molecules on the surface, they interact according to the reaction: Electrons formed in radiation-catalytically active oxides under the action of ionizing radiation can have energies in a wide range and enter into multiple interactions with the electronic structures of oxides.As a result, they go through approximately the following energy stages.
1.The electron energy becomes less than the ionization energy of the medium  ≤ (), where W(I) is the threshold energy, of the formation of ion vapors in the medium.The value of  is the dependence of the band gap for radiation-catalytically active catalysts and is equal to  ≈ 2÷3 E g [20].Taking into account the values of the water ionization potential for W(I) ≈ 30 eV, these electrons can be characterized as underionization electrons.Electrons with energy  ≤ () in a medium can enter into an electron-electron interaction and generate an excited state of excitons.After certain energies, the electrons are localized in the structural centers and eventually thermolyzed.Exciton levels of radiation catalytic active oxides  ≈  − .2. The value of E g in radiation catalytic active catalysts varies in the range of 5÷10 eV [21].And therefore, the localized exciton levels of these oxides are smaller than the values of the band gap and vary in the range  ~5 − 8 eV [22].For example, in SiO 2 the energy of underexcitation electrons is equal to E ~ 7.4 eV. 3.After the generation of excitons in oxide systems, underexcitation electrons appear, which have a lower  ( ≤ 10 ).These electrons first interact with LO photons and then with acoustic phonons.In oxide systems, electrons with energies below the ionization threshold  can create excitons and enter into an electron-phonon interaction.The electron-phonon interaction is more probable in the electron energy range 4÷20 eV [66].The electron-phonon interaction occurs first with LO photons and then with acoustic phonons.After numerous collisions, thermalization of electrons occurs.For example, in SiO 2 electrons with an energy of 1÷8 eV, the thermalization time varies in the range  ≤ 1 [28].On average, electrons with energy  э ≤ W (I) are thermalized in time τ = 250÷350 fs.The thermalization time of electrons with energy  э ≤ W (I) in water is comparable to the thermalization time in SiO 2 , which approximately vary in the range τ = 250÷350fs.During thermalization, electrons in both phases in  −   systems can move at a distance of several nanometers.For example, for pure SiO 2 , electrons with an energy of 3 eV during thermalization can migrate from 8 to 30 nm distances.Table 9 shows the values of relative permittivity ( ), onsager radius ( =  /(4  )), diffusion constant  =  / and recombination constant of electron with cations (holes)  =  /(4) : where, q -charge, k B -Boltzmann constant, T -temperature, μ -particle mobility, t -time [25].As can be seen, the values of the electron-hole recombination constants in SiO 2 are 4 times greater than in water.The on sager radius is about 20 times smaller than in SiO 2 .And therefore, in water, secondary electrons can propagate a large distance from the parent ion.EEJP. 1 (2024) Adil Garibov, et al.
Thus, by analyzing the processes occurring in  э ≤ W radiation-catalytic active oxides, one can imagine the mechanism of radiation-heterogeneous processes of water decomposition with the participation of energy carriers according to scheme (15).
Formed according to the scheme   * interacts with electrons from the conduction band: * singlet-excited water molecules in the   state (E=8.4eV)undergo decay [13]: However, during the recombination of   ions with quasi-free electrons, the energy corresponding to dissociative recombination with E ≈ 11 eV is released: During the radiation-catalytic decomposition of water in the presence of nanocatalysts at T ≥ 673K, the transformation of H atoms into H 2 can occur according to the reaction [15]: The radiolysis of water on the surface of oxide systems can involve subexcited electrons formed in the oxide phase [16][17][18]: The course of these reactions was confirmed by the authors as a result of a study of the dissociative capture of electrons with energy E e ≤ 12 eV [12].According to reaction ( 17) -( 22), the maximum yield is observed at the electron energy E e = 7.4 eV.
As is known, during the radiation-catalytic decomposition of water into a surface-adsorbed state, the maximum yield of hydrogen is limited by the total yields of nonequilibrium charge carriers and excitons and is equal to G(H 2 )~8-9 molecules/100eV.A particularly high yield of molecular hydrogen is observed during the radiolysis of water in suspension with nano-oxides [24][25][26] and nanosized individual elements Ze, Si [27].The observed yield of hydrogen in these processes cannot be explained within the framework of the existing theoretical concepts of energy transfer in radiation-heterogeneous processes.
First, it is necessary to analyze the processes of the physical and physical-chemical stages in individual components of H 2 O+nanocatalysts.Under the influence of gamma-quanta and electrons on water, the yield of electronion pairs is 3.4 vapor/100 eV [32].Radiation-catalytically active catalysts in terms of electrical properties can be attributed to insulators Eg~4÷9 eV (nZrO 2 , nSiO 2 , nAl 2 O 3 ) and n-Si semiconductors with Eg ≈ 1.5 eV.The threshold energies of the formation of electron-hole pairs in them are equal to En (dielectric)=2.0Eg; En (semiconductor) = 3.0 Eg and the yields of electron-hole pairs when exposed to quanta are 12.5-5.5 vapor/100eV for dielectrics, 22vapor/100eV for semiconductors.On the other hand, the density of solids is greater than that of water.For these reasons, when γ-quanta are exposed to the system of nanocatalysts +H 2 O, the concentration of secondary electrons in the solid phase will be much higher than in water.For example, in the n-Si+H 2 O system, the number of electron-hole pairs inside a silicon particle is about 18 times greater than in pure water [30].
Individual particles of nanocatalysts can be represented as a sphere with radius R. The mean free path of energy carriers inside this sphere is .Effective energy transfer to the surface of the contacting medium can occur if ≥R.
Therefore, with a decrease in the particle size of nanocatalysts, the yield of molecular hydrogen during the radiationcatalytic decomposition of water increases [31].
As the energy of secondary electrons increases, the mean free path in dielectrics and semiconductors decreases [56].Therefore, in the field of action of  radiation on nanocatalysts, the energy of electrons emitted from them is low and usually lies in the range ≤10 2 eV.The maximum free path of electrons with an energy of 100 eV in water corresponds to 20 nm [33].Therefore, it can be imagined that during radiation-catalytic processes with the participation of nanocatalysts, a spherical shell with a radius of 20 nm with a high concentration of electrons with energy E≪10 2 eV is formed around a spherical particle of catalysts with a radius R.
In the reactor of radiation-catalytic processes, nano-particles are in the form of densely packed spheres.Many physical properties of adsorbed water molecules, such as ionization potential, ion formation energy, excited states, and dissociation energy, differ greatly from those of pure water [35].Therefore, the yields of target products in the radiation-catalytic decomposition of water, depending on the layer of adsorbed states, differ greatly [21][22][23][24].Secondary electron radiation emitted from nanocatalysts after a multiple cascade of processes of electron-electron interactions cause ionization, excitation in the water phase in the volume between nanoparticles and finally become underexcitation electrons ( < 7.
The resulting   ions can recombine with electrons, forming   * : +  →   * (25) Excited water molecules can decompose according to the reaction: After multiple electron-electron, electron-phonon interactions during the time  = 10 − 10 s, electrons can be solvated: With the participation of  -in an aqueous medium, the formation of hydrogen can occur according to the following reactions [25][26][27][28][29][30]: However, as a result of these processes, the yield of molecular hydrogen does not exceed the yield of molecular hydrogen during the radiolysis of water under the action of electrons [60-65].Radiation-catalytic processes of water decomposition in the presence of nano-semiconductor and nano-metal cannot be explained by the above mechanisms of energy transfer in adsorbed water molecules.During the radiolysis of water in contact with metals, the observed high yields of molecular hydrogen are explained by the decomposition of water with the participation of secondary electron radiation emitted from the metal [66].
In the volume between the grains of nanocatalysts during the radiation-catalytic decomposition of water, electrons enter from all sides, forming a volume with a high concentration of electrons ( ).Approximately, this volume of water can be represented as a sphere with a radius of 20 nm.In this volume =  = 3.35 • 10  under normal conditions there will be  ~ 10 water molecules.If we take into account that the number of gamma quanta falling per unit time and the number of secondary electrons formed as a result of scattering of primary quanta and secondary electrons, we can be sure that in the volume between nanoparticles without a concentration of secondary electrons there will be a high value of the ratios  /   will be quite high.Therefore, the mechanism of one-stage nonequilibrium discharges can be applied [67].
Under excited electrons can expend their energy on vibrational excitation of water molecules and enter into a dissociative attachment reaction with a water molecule.Under excitation electrons lose their excess energy in ~10 s and then thermalize or solvate [56].
The maximum of the dissociative attachment cross section occurs at the electron energy E e ≈ 6 eV: In the electron energy range Ee ~ 1-30 eV, multiple dissociative attachment of electrons can occur: Multiple use of the electron is possible due to the high-rate K e = 10  / of the destruction of the negative ion  by electron impact according to reaction (23)(24)(25)(26)(27)(28)(29)(30)(31)(32).
It has been established that at low electron energies (Te ≈ 1eV), the electron energy is spent on vibrational excitation of water molecules.The characteristic vibrational quantum of water molecules is equal to hω = 0.2 eV.Sequential vibrational excitation of water molecules occurs in the reaction medium, as a result of which highly excited states are populated into vibrational V-V relaxation, and at the end, a reaction occurs with the participation of   * [57]:   * +   →  +  +   (33) The rate of this process is expressed with the formula: Radiation-catalytic processes can be on technological radiation installations (isotope, accelerators and sources of bremsstrahlung).
Radiation-thermal catalytic processes can be implemented by a combination of radiation installations and hightemperature modular nuclear reactors.The schematic diagram of these complexes is shown in Figure 5.
At a temperature of T ≥6 73K, a high efficiency occurs during the radiation-thermocatalytic decomposition of water.The hydrogen obtained by the membrane separation from oxygen can be further used for various purposes or for the production of electricity.

CONCLUSION
Based on the results obtained on the effect of the n-Si concentration in water on the yield of molecular hydrogen during water radiolysis, it can be concluded that the optimal range of n-Si concentration values for efficient conversion of ionizing radiation energy into hydrogen energy.Since at values   ≥ 3 • 10 there is an efficient conversion of the energy of ionizing radiation into the energy of hydrogen.In order to reveal the contribution of secondary electron fluxes emitted from the solid phase in the radiation-catalytic processes of hydrogen production, the kinetics of hydrogen production processes as a result of heterogeneous decomposition of water in the presence of nano-metal (n-Zr) and individual nano-semiconductor n-Si were studied.Thus, in the case of a suspension of nano-zirconium in water, the energy of electrons emitted from the metal is completely transferred to water molecules, which leads to an increase in the yield of hydrogen.When radiolysis of water in the presence of nano-metals, energy transfer can be carried out mainly with the participation of emitted electrons.Therefore, in the case of radiolysis of water in suspension with n-Zr, the yield of hydrogen increases by 5.4 times compared to the processes of radiolysis in an adsorbed state.However, in radiation-heterogeneous processes of obtaining hydrogen from water in contact with metal systems, it is necessary to take into account that as a result of these processes surface oxidation occurs and after a certain time the systems are converted to n-Me-MeO+H2Oliq.systems.For nano sized oxide compounds, the mean free path of secondary electrons formed as a result of primary processes of interaction of quanta with atoms is commensurate with the particle sizes of nano-oxides (λ ≈ R_(H-оxides)).Further, these electrons interact with the electronic subsystem of silicon.For nanocatalysts, the length of free paths of secondary and subsequent generations of electrons is greater than the size of catalyst particles (R_cat≤100nm).Usually, their energy is sufficient to conduct independent radiolytic processes in the contact medium of the catalyst.ORCID Gunel T. Imanova, https://orcid.org/0000-0003-3275-300X

Figure 1 .
Figure 1.Kinetics of obtaining molecular hydrogen during radiolysis of water in n-Zr+H2O suspension, at T = 300K, D = 0.15 Gy/s On the basis of the kinetic curve, the kinetic parameters of hydrogen production are determined   = 6.67 • 10  •  •  ;   = 7.1 /100(1) and based on them the concentration is estimated n-Si with different particle sizes  = ( ) .

Figure 3 .
Figure 3. Dependence of  ( ) during radiolysis of water in n-Si suspension with d = 50 nm in water on n-Si concentration, T = 300K,  = 22 /.
( ) from 1780 to 430 molecules/100 eV at  = 15.8 • 10 particles/cm 3 .The observed dependences of  ( ) and  ( ) on  in suspension show that after certain values of  radiation processes occur, which cause a decrease in the conversion efficiency energy of ionizing radiation into the energy of hydrogen.Therefore, after  (transition), the growth rate of  ( ) decreases, and  ( ) sharply decreases.

Figure 5 .
Figure 5. Scheme of the technological complex for obtaining molecular hydrogen by radiation-thermal catalytic decomposition of water with a combination of high-temperature nuclear reactors 1 -high-temperature module reactor (SMR); 2 -sources of ionizing radiation; 3 -reactor for carrying out radiation-thermal processes of hydrogen production in the presence of catalysts  −  ,  −   и  − ); 4 -system for igniting the mixture and generating steam for the turbogenerator; 5 -turbogenerator for generating electricity; 6 -column for membrane separation of a mixture of  +  .

Table 1 .
Effect of n-Si Concentration during Heterogeneous Radiolysis of Water in the Presence of n-Si (in Suspension)

Table 2 .
Influence of n-Si concentration and distance between particles during water radiolysis in the  −  +   system (in suspension)

Table 3 .
The value of the rates of processes and radiation-chemical yields of hydrogen during thermal and radiation-thermal catalytic processes of water decomposition in the presence of n-ZrO2 at different temperatures № T, K  ( ) • 10 / •   ( ), /100  ( )  ( )  ( )

Table 4 .
Influence of temperature on thermo-and radiation-thermal catalytic processes of obtaining molecular hydrogen in the system n−  +  ,

Table 5 .
Influence of temperature on thermo-and radiation-thermal catalytic processes of obtaining molecular hydrogen in the system n− +  ,  Mechanism of Hydrogen Production in the Processes of Radiation Heterogeneous...

Table 6 .
The value of the rates of thermo-, radiation-thermal and radiation-catalytic processes in the n-Zr+H2O contact and the radiation-chemical release of hydrogen in the temperature range, T= 300 ÷ 673,

Table 8 .
Effect of temperature on the kinetic parameters of hydrogen production during thermo-radiolysis of water in the presence of n-Si with d = 50nm,  =8 mg/cm 3 under the action of gamma radiation with  = 0.18 Gy/s

Table 9 .
The value of the parameters of processes involving nonequilibrium carriers in SiO2 and H2O charges