Zn12O12 Cluster Research Articles

Low-temperature oxidation of methane mediated by Al-doped ZnO cluster and nanowire: a first-principles investigation.

First-principles calculations are performed to investigate the catalytic oxidation of methane by using N2O as an oxidizing agent over aluminum (Al)-doped Zn12O12 cluster and (Zn12O12)2 nanowire. The impact of Al impurity on the geometry, electronic structure, and surface reactivity of Zn12O12 and (Zn12O12)2 is thoroughly studied. Our study demonstrates that Al-doped ZnO systems have a better adsorption ability than the corresponding pristine counterparts. It is found that N2O molecule is initially decomposed on the Al site to provide the N2 molecule, and an Al-O intermediate which is an active species for the CH4 oxidation. The conversion of CH4 into CH3OH over AlZn11O12 and (AlZn11O12)2 requires an activation energy of 0.45 and 0.29eV, respectively, indicating it can be easily performed at normal temperatures. Besides, the overoxidation of methanol into formaldehyde cannot take place over the AlZn11O12 and (AlZn11O12)2, due to the high energy barrier needed to dissociate C-H bond of the CH3O intermediate. Dispersion-corrected density functional theory calculations were performed through GGA-PBE exchange-correlation functional combined with a numerical double-ζ plus polarization (DNP) basis set as implemented in DMol3. To include the relativistic effects of core electrons of Zn atoms, DFT-semicore pseudopotentials were adopted. The DFT + D scheme proposed by Grimme was used to involve weak dispersion interactions within the DFT calculations. The reaction energy paths were generated by the minimum energy path calculations using the NEB method.

Gas-Phase Interaction of CO, CO2, H2S, NH3, NO, NO2, and SO2 with Zn12O12 and Zn24 Atomic Clusters.

Atmospheric pollutants pose a high risk to human health, and therefore it is necessary to capture and preferably remove them from ambient air. In this work, we investigate the intermolecular interaction between the pollutants such as CO, CO2, H2S, NH3, NO, NO2, and SO2 gases with the Zn24 and Zn12O12 atomic clusters, using the density functional theory (DFT) at the meta-hybrid functional TPSSh and LANl2Dz basis set. The adsorption energy of these gas molecules on the outer surfaces of both types of clusters has been calculated and found to have a negative value, indicating a strong molecular-cluster interaction. The largest adsorption energy has been observed between SO2 and the Zn24 cluster. In general, the Zn24 cluster appears to be more effective for adsorbing SO2, NO2, and NO than Zn12O12, whereas the latter is preferable for the adsorption of CO, CO2, H2S, and NH3. Frontier molecular orbital (FMO) analysis showed that Zn24 exhibits higher stability upon adsorption of NH3, NO, NO2, and SO2, with the adsorption energy falling within the chemisorption range. The Zn12O12 cluster shows a characteristic decrease in band gap upon adsorption of CO, H2S, NO, and NO2, suggesting an increase in electrical conductivity. Natural bond orbital (NBO) analysis also suggests the presence of strong intermolecular interactions between atomic clusters and the gases. This interaction was recognized to be strong and noncovalent, as determined by noncovalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. Overall, our results suggest that both Zn24 and Zn12O12 clusters are good candidate species for promoting adsorption and, thus, can be employed in different materials and/or systems for enhancing interaction with CO, H2S, NO, or NO2.

Quantum chemical studies on chelation in nano-bio conjugate between ZnO nanoparticles and cellular energy carrier molecules

Nano-bio complexes, made up of nanoparticle and biomolecules, have wide applications in biomedical nanotechnologies. This makes microscopic understanding of such materials important. Here, we carry out quantum chemical calculations based on DFT on nano-bio conjugate between Zn12O12 cluster (ZnONP) and energy carrier biomolecules in cellular environment, like, ATP, ADP and AMP. We focus on microscopic details of chelation by individual groups, namely, phosphate, ribose and adenine of these molecules with ZnONP. Electronic structures and bonding interactions in ground states of all the complexes are presented through the molecular orbital (MO) theory and the natural bond orbital (NBO) analyses as well as the Raman Spectra. DFT-optimized geometries and bond indices suggest presence of Zn–N(adenine) bond and multiple Zn–O(phosphate) bonds. Phosphate groups form additional O–H⋯O non-classical bonds with ZnONP. Kohn-Sham MOs and natural population analyses suggest that the adenine moiety forms a coordinate covalent bond (Zn–N) with ZnONP through adenine → ZnONP charge transfer (CT), while phosphate groups from coordinate covalent bonds (Zn–O) through ZnONP → phosphate CT in all nano-bio complexes, leading to better stability of bio-molecules-ZnONP complex with increasing of number of phosphate groups in the bio-molecules.

CO oxidation mediated by Al‐doped ZnO nanoclusters: A first‐principles investigation

AbstractUsing density functional theory the reaction pathways of CO oxidation mediated by Al‐doped Zn12O12 cluster and its assembled wire‐like (Zn12O12)n=2−4 structures were studied. It is revealed that O2 molecule is chemisorbed over the doped clusters while physisorbed over pristine (Zn12O12)n. Moreover, increasing the size of the nanocluster from AlZn11O12 to (AlZn11O12)4 enhances the O2 adsorption energy, although the amount of increase reduces as the cluster size grows. The adsorption energies of O2 over Al‐doped (Zn12O12)n clusters range from −1.83 to −2.14 eV, which are more negative than those of CO molecule (≈−0.80 eV). The Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) pathways are used to investigate the oxidation mechanisms of the CO molecule. The energy barriers for the rate limiting step in the LH mechanism (i.e., OCOO → CO2 + Oads) are around 0.30 eV, which are substantially lower than the energy barriers in the ER process.

Adsorption of syn−propanethial S−oxide on the Zn12O12 cluster: insights from ab-initio modelling

The sensitivity and reactivity of a Zn12O12 nanocluster are investigated to a syn−Propanethial−S−oxide (PSO) agent using B3LYP level of theory. In the gas phase, the Gibbs free energy change (ΔG) was calculated to be approximately −20.5 kcal/mol. We found that the Zn12O12 nanocluster is meaningfully sensitive to the PSO and it may be a possible sensor which can be used for the detection of PSO. At low PSO concentrations, the change of the HOMO–LUMO gap indicates a suitable index for the detection of PSO detection, while at high concentrations, the work function change indicates a much more appropriate index. A short recovery time of 0.10 s was predicted for the desorption of PSO from the surface of the Zn12O12 nanocluster using vacuum ultra-violet light at room temperature. The adsorption of PSO onto the Zn12O12 nanocluster is decreased after moving from the water to benzene solvent.

Solar driven CO2 hydrogenation on transition metal doped Zn12O12 cluster.

Photocatalytic hydrogenation of carbon dioxide (CO2) to produce value-added chemicals and fuel products is a critical routine to solve environmental issues. However, developing photocatalysts composed of earth-abundant, economic, and environmental-friendly elements is desired and challenging. Metal oxide clusters of subnanometer size have prominent advantages for photocatalysis due to their natural resistance to oxidation as well as tunable electronic and optical properties. Here, we exploit 3d transition metal substitutionally doped Zn12O12 clusters for CO2 hydrogenation under ultraviolet light. By comprehensive ab initio calculations, the effect of the dopant element on the catalytic behavior of Zn12O12 clusters is clearly revealed. The high activity for CO2 hydrogenation originates from the distinct electronic states and charge transfer from transition metal dopants. The key parameters governing the activity and selectivity, including the d orbital center of TM dopants and the energy level of the highest occupied molecular orbital for the doped Zn12O12 clusters, are thoroughly analyzed to establish an explicit electronic structure-activity relationship. These results provide valuable guidelines not only for tailoring the catalytic performance of subnanometer metal oxide clusters at atomic precision but also for rationally designing non-precious metal photocatalysts for CO2 hydrogenation.

The Interaction of Adenine with Zn12O12 Cluster from Density Functional Theory

Geometries associated energy gap and electronic properties of adenine, DNA base interaction on the ZnO model cluster have been investigated by using density functional theory with the B3LYP exchange-correlation potential and effective core potential (ECP) LanL2DZ basis sets. The most stable interaction characteristics were analysed with respect to the binding energy, frontier orbital, elemental positions. Natural population analysis charge is also examined to understand the associated charge transfer in structures of cluster and complex. In the Zn-N bonding, combination coefficient from atom orbitals of nitrogen is much higher than that of zinc. The corresponding weight for this coefficient is 94.80%. The results of this study can serve as an orientation for the design of composite material in biomedical nanotechnology.

Density Functional Theory Studies of Zn12O12 Clusters Doped with Mg/Eu and Defect Complexes

We report a density functional theory study of ZnO cluster doped with Eu and Mg along with native point defects using the generalized gradient approximation including the Hubbard parameter. The Zn atomic positions are found to be energetically more favorable doping sites than O. The Eu has a lower formation energy than Zn and O vacancies, helps in lowering the formation energy of point defects and induces spin polarization. Mg is less favorable dopant energetically and is not inducing any magnetism in the cluster. Presence of Eu and point defects along with Mg can help in sustaining spin polarization, implying that transition metal and rare earth dopant is a favorable combination to invoke desirable properties in ZnO based materials. Eu–Eu doping pair prefers ferromagnetic orientation and a spin flip is induced by Eu in the Eu–Mg configuration. Further, Eu doping increases the value of static refractive index and optical absorption in the UV region compared to the undoped ZnO cluster.

Doping superalkali on Zn12O12 nanocage constitutes a superior approach to fabricate stable and high-performance nonlinear optical materials

Fabrication of stable nonlinear optical materials is highly demanding due to their widespread applications in optical and optoelectronic devices. Novel inorganic complexes are theoretically designed and investigated by doping superalkalis on Zn12O12 cluster. The results reveal that doping causes shifting of excess electrons from superalkalis towards Zn12O12 cluster and enhances the NLO properties of these isomers. Moreover, the effect of doping different superalkalis (Li3O, Na3O and K3O) over Zn12O12 nanocages is also studied. All the isomers have shown excellent NLO response and are transparent under ultraviolet region of workable laser conditions. Comparative analysis reveals that hyperpolarizability shows monotonic dependence on atomic number of metal atom in the superalkalis. K3O@Zn12O12 exhibits the highest first hyperpolarizability (βo) value of 394,217 au. The band gap is reduced up to 70% as compared to pristine nanocage, making them n-type semiconductors. This study provides a pathway for designing thermally stable inorganic complexes as potential precursors for high-performance NLO materials.

Rare earth functionalization effect in optical response of ZnO nano clusters

The electronic structure of rare earth (RE) doped Zn12O12 clusters – namely, REZn11O12 and RE2Zn10O12 with RE = Nd, Eu and Gd have been investigated within the framework of density functional theory formalism. Doping of a RE atom is found to be energetically favorable in this zinc oxide cluster. We have found that the cage structure of the host cluster Zn12O12 does not change significantly by the substitutional doping of a RE atom on Zn sites. The magnetic coupling between RE ions in the host cluster is found to be ferromagnetic. The static polarizabilities and optical properties of the RE doped Zn12O12 clusters have been studied based on the time dependent density functional theory. With RE doping, the polarizability increases as compared to that of the host cluster. The analysis of the optical absorption spectra indicate that the f electrons in RE doped clusters are significantly more involved in low-energy transitions. For Eu doped clusters give rise to more quenched oscillator strengths as compared to that of Nd and Gd doped zinc oxide clusters. With the increase in number of RE atoms, the red shift is observed in the optical spectrum of the zinc oxide cluster.

Magnetic mediation effect of a C impurity in a Mn-doped Zn12O12 nanocluster: a case of multiple exchange interactions

The stability and exchange interaction mechanism of a doped Zn12O12 cluster with Mn and C atoms were investigated by first-principles calculations. For the Mn-doped Zn12O12 cluster, it is identified that a superexchange interaction deriving the hybridization between the Mn and O 2pxy orbitals dominates the Mn(↑)–Mn(↓) antiferromagnetic coupling, although a direct exchange interaction deriving the Mn–Mn bonding is also found. In order to turn the Mn spin state in the Mn-doped Zn12O12 cluster, C doping is undertaken to change the magnetic interactions of these impurities. It is proved that the C incorporation into the Mn-doped Zn12O12 cluster destroys the short-ranged antiferromagnetic coupling, where multiple exchange interactions take over, including the direct exchange interaction and the kinetic p-d exchange interaction partially due to the geometric distortion and surface effect with dangling bonds (sp2-like hybrids). It is concluded that the kinetic p-d exchange interaction plays a dominant role in Mn/C-doped Zn12O12 clusters.

Density functional studies of small gases adsorbed on the ZnO sodalite-like cage and its adsorption abilities

The geometry optimizations of ZnO sodalite-like cage (ZnOSL), Zn12O12 cluster and its adsorption configuration with diatomic (H2, N2, O2, CO, NO), triatomic (CO2, N2O, NO2, H2O, SO2) and tetraatomic (NH3) gases were carried out using density functional theory method. Adsorption energies of these gases on ZnOSL were obtained at the B3LYP/Lanl2DZ level of theory. The strongest adsorption energies of diatomic and triatomic gases on ZnOSL at ML=0.082 are ΔEads(O2)=−14.09 and ΔEads(SO2)=−35.06kcal/mol, respectively. The adsorption energy of ammonia adsorbed on ZnOSL at ML=0.082 is ΔEads(NH3)=−25.41kcal/mol. Energy gaps and density of states plots for ZnOSL and their gases adsorption configurations are reported. All the adsorption results computed by the B3LYP/Lanl2DZ method were validated by comparison with their corresponding results computed by the B97D/Lanl2DZ method.

Covalent Functionalization of Zn12O12 Nanocluster with Thiophene

Covalent functionalization of a ZnO nanocluster with thiophene molecule was studied by means of density functional theory calculations. The obtained results show that the molecule is physically adsorbed on the surface of nanocluster with adsorption energies in the range of −0.33 to −0.42 eV. In this study, 2η-C4H4S–Zn12O12 cluster is the most stable adsorption among all thiophene adsorption configurations. Accordingly, HOMO–LUMO energy gap of the nano-cluster is changed about 0.24 to 0.72 % using the DFT calculations. The values of charge transfer shows that π-back bonding exists for 2η and 5η bonding modes. Present results might be helpful to provide an effective way to modify the Zn12O12 properties for further applications such as generation of the new hybrid compounds.

First Principles Study on Encapsulation of Alkali Metals into ZnO Nanocage

Encapsulation of alkali metals (Li, Na, K, and Rb) into Zn12O12 nanocage has been investigated using density functional theory. Encapsulation of Li and Na atoms is found to be thermodynamically favorable at 298 K and 100 kPa, with negative Gibbs free energy change ΔG of about −130.12 and −68.43 kJ/mol, respectively. By increasing the size of encapsulated atom the process become less favorable so that in the cases of K and Rb encapsulations the ΔG values are positive. The results indicate that the LUMO, Fermi level, and specially HOMO of the cluster are shifted to higher energies so that the HOMO-LUMO gap of the cluster is significantly narrowed in all the cases. After encapsulation of the alkali metals the work function of cluster is decreased due to the shift of the Fermi level to higher energies. Therefore, the emitted electron current density from the Zn12O12 cluster will be increased.

Adsorption and dissociation of Cl2 molecule on ZnO nanocluster

Adsorption of chlorine molecule (Cl2) on the Zn12O12 nano-cage has been analyzed using density functional theory. It has been shown that the Cl2 molecule is strongly adsorbed on the cluster via two mechanisms including chemisorption and dissociation with Gibbs free energy changes in the range of −0.36 to −0.92eV at 298K and 1atm. These processes also significantly change the electronic properties of cluster by decreasing its HOMO/LUMO energy gap and increasing the work function. The Fermi level shifts towards lower energies upon the interactions between Cl2 and the cluster, resulting in raised potential barrier of the electron emission for the cluster and hence avoiding the field emission. The Zn12O12 cluster is transformed to a p-type semiconductor substance upon the Cl2 dissociation. We believe that the obtained results may be helpful in several fields of study such as sensors, catalysts, and field emission investigations.

Structures, stabilities, and magnetic properties of Cu-doped ZnnOn (n = 3, 9, 12) clusters: A theoretical study

The structural, electronic, and magnetic properties of Cu-doped ZnnOn (n=3,9,12) clusters have been studied using spin-polarized density functional theory. We firstly investigate the lowest-energy structures of pure ZnnOn (n=1–13) clusters based on the extensive searching, and identify that the Zn3O3, Zn9O9 and Zn12O12 clusters possess relatively higher stability. Then, these stable clusters are taken as candidates for investigating the effect of Cu-atom doping. Three doping modes, that is, substitutional, exohedral, and endohedral doping, are considered. It is found that the substitutional mono- and bi-doped clusters are the most stable among doped clusters. The HOMO–LUMO gaps of the doped clusters are all reduced due to the p–d hybridization caused by the Cu-atom doping. For the monodoped clusters, all isomers have a magnetic moment of 1μB, which is mainly contributed by the Cu 3d and Cu-surrounding O 2p states. However, for the bidoped clusters, the ground states have zero magnetic moment with the spins on the Cu atoms being either antiferromagnetically coupled or completely quenched, except for Cu2ZnO3 cluster.

Electronic structure and magnetism of transition metal doped Zn12O12 clusters: Role of defects

We present a comprehensive study of the energetics and magnetic properties of ZnO clusters doped with 3d transition metals (TMs) using ab initio density functional calculations in the framework of generalized gradient approximation+Hubbard U (GGA+U) method. Our results within GGA+U for all 3d dopants except Ti indicate that antiferromagnetic interaction dominates in a neutral, defect-free cluster. Formation energies are calculated to identify the stable defects in the ZnO cluster. We have analyzed in details the role of these defects to stabilize ferromagnetism when the cluster is doped with Mn, Fe, and Co. Our calculations reveal that in the presence of charged defects the TM atoms residing at the surface of the cluster may have an unusual oxidation state, that plays an important role to render the cluster ferromagnetic. Defect induced magnetism in ZnO clusters without any TM dopants is also analyzed. These results on ZnO clusters may have significant contributions in the nanoengineering of defects to achieve desired ferromagnetic properties for spintronic applications.

Structural, electronic, and magnetic properties of manganese-doped Zn12O12 clusters: A first-principles study

A first-principles study has been performed to evaluate the structural, electronic, and magnetic properties of Zn(12)O(12) clusters doped with one or two Mn atoms. The substitutional, exohedral, and endohedral dopings are taken into account. For the monodoped clusters, the substitutional isomer is most energetically favorable, and an exohedral isomer may appear as a low-lying metastable state. All isomers present 5 mu(B) magnetic moment that is mainly contributed by the Mn-3d component. For the bidoped clusters, the antiferromagnetic state is degenerate with the ferromagnetic state at larger Mn-Mn distance (>5 A), while it is more energetically favorable at smaller Mn-Mn distance. Thus, the cohesion of bidoped isomer is sensitive to the magnetic coupling or chemical bonding. The endohedral bidoped isomer is found to be a stable local minimum, and the direct Mn-Mn interaction causes the reduction of local magnetic moment of Mn to about 4 mu(B).