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Streszczenie:
Abstract
In the current article, we investigated adsorption properties of Nickel (Ni), Copper (Cu), Cadmium (Cd) and silver (Ag) heavy metal atoms with zinc oxide (ZnO) nanotube and ZnO-graphene like structures sheet using Ab-initio based density functional theory (DFT) calculations. At first, both nanostructures were optimized and then most stable configuration, adsorption energy and equilibrium distance of each heavy metal with nanostructures were computed via DFT and the results were compared with each other. Our obtained results reveal that ZnO-nanotube had a better adsorbing behavior comparing to ZnO-graphene sheet case by case due to lower equilibrium distance and higher adsorption energy. This nanostructure created a strong binding with Ni, Cu and Ag but adsorption energy for Cd was clearly lower than others. Also, only Ni and Cu could have a chemisorption adsorption with the ZnO-graphene sheet and others showed a nearly weak physisorption adsorption with this nanostructure. The maximum adsorption energy for both ZnO-nanostructures occurred for nickel which were about −3.45 eV and −2.19 eV respectively. The minimum adsorption energy for ZnO nanotube occurred with Cd (−1.3 eV) while for ZnO-graphene sheet it occurred with Zn (−0.15 eV). In almost all items equilibrium distance decreased with increasing in adsorption energy. Moreover, we generated density of state (DOS) diagrams to investigate the electrical properties of studied structures.

Słowa kluczowe:
Zinc-oxideDFT dsorption Heavy metal atoms DOS

Streszczenie:
Abstract
In the present study, ab initio-based density functional theory (DFT) calculations were used to determine the effects of certain phenomena that can occur in the synthesis of Beryllium-Oxide (BeO) few-layer sheets, such as various types of defects, attaching nanocages onto the surface of graphene and attaching layers to each side of it on the mechanical and electronic properties of BeO graphene sheets. We also used the density of states (DOS) calculations to obtain a better understanding of the electronic properties of the studied nanostructures. In the first step, we calculated Young’s modulus for the pristine BeO graphene sheet that was found to be equal to 1.110 TPa. Next, the effect of small and large defects on the mechanical properties of the BeO graphene-like structure was examined, and we found that extracting one Be atom resulted in a lower Young’s modulus compared to that obtained after extracting one oxygen atom (1.087 TPa versus 1.104 TPa), demonstrating that Be had a greater effect on the stability and mechanical strength of BeO graphene than did oxygen. The same trend was found when comparing three atom vacancies with two missing Be atoms to those with two missing oxygen atoms. Furthermore, the effect of circular and rectangular shape defects was investigated, and the obtained results demonstrated that the increase in the diameter of defects with both shapes significantly decreased Young’s modulus and band gap energy values. Additionally, due to the number of detached atoms in shape defects which are more than those of small defects, this type of defect had a more destructive effect on the structure’s stability so that it decreased the Young’s modulus more than small defects. Moreover, the mechanical properties of the BeO graphene nanobud structure were determined in terms of placing different numbers of Be12O12 nanocages onto the graphene surface, and a similar decreasing trend was observed for Young’s modulus. Finally, we considered the mechanical properties of the bi- and three-layer BeO graphene-like structures and found that increasing the number of layers reduced Young’s modulus slightly. For both of the latter phenomena of attaching nanocages and layers, the band gap energy decreased.

Słowa kluczowe:
Young’s modulus

Streszczenie:
Abstract
In the current study, we Investigated the adsorption properties of zinc (Zn) and lead (Pb) atoms on the surface of carbonic and non-carbonic graphene using Density functional theory calculations. The procedure for this research can be divided into two sections. First, we calculated the adsorption value of single zinc and lead atoms with such non-carbonic graphene-like structures as Boron-Nitride (BN), Aluminum-Nitride (AlN), Gallium-Nitride (GaN), Silicon-Carbide (SiC), and Silicene. We found that the silicene was more powerful to detect the stated heavy metal atoms compared with others. The calculated adsorption values between the single zinc and lead atoms with silicene monolayer sheet were equal to −0.90 eV and −3.80 eV, respectively. We also used electron transfer calculations after adsorbing the stated heavy metal atoms and found that the calculated charge transfer was equal to 0.42 and 0.12 electrons for Silicene/Pb and Silicene/Zn complex, respectively. The density of states (DOS) results demonstrated that a strong hybridization could occur between the Pb atom and the silicene graphene. Then, we performed DFT calculations to determine the interaction energy between the mentioned metal atoms with pristine carbonic graphene. We found that the interaction in graphene/Zn (−0.09 eV) and graphene/Pb (−0.45 eV) was so weak, especially for graphene and zinc. To overcome this issue, we first activated the surface of graphene by carboxyl and hydroxide group. The interaction energy values between the zinc and lead atoms with graphene-COOH were approximately −0.18 eV and −1.01 eV, respectively, which showed improvements in the adsorption energy. Then, we approached the mentioned metal atoms on the surface of single bondOH-decorated graphene and demonstrated that the interaction energy between the single zinc and lead atoms with graphene-OH were about −0.78 eV and −3.33 eV. In other words, it improved by 755% and 623% compared with graphene/Zn and graphene/Pb, respectively. The strong adsorption between the hydroxyl group and the stated metals atom caused the OH group to be isolated from the graphene surface and become an individual molecule.

Słowa kluczowe:
DFT ,Adsorption

Streszczenie:
Abstract
In current study ab-initio based density functional theory (DFT) calculations were employed to determine the effect of different types of defect including the point (Stone-Wales (SW) and atom vacancies) and shape defects on mechanical and electronic properties of zinc oxide (ZnO) graphene-like sheet. Also, the density of states calculations (DOS) were done to give a better understanding of the electronic behavior of this structure under applied defects. With this purpose, different defects were applied to the surface of the ZnO graphene-like sheet and Young's modulus was calculated theoretically. Results showed that all applied defects had a negative effect on Young's modulus. SW defect had the lowest effect on Young's modulus among point defects. In terms of vacancy defects, increasing in the number of extracted atoms decreased modulus reversely. We also found from vacancy defects that extracting Zn atom decreased the properties more than extracting oxygen atom. So Zn atom has a higher effect on ZnO graphene-like sheet strength and stability compared to oxygen atom. The lowest obtained Young's modulus occurred in three atom vacancy with two missed Zn atoms. Furthermore, circular and square shape defects with various diameters were created on ZnO graphene-like sheet and Young's modulus was again considered.