Surface engineered recombinant Escherichia coli for the potential application of the cobalt contaminated wastewater treatment and the photocatalytic dye degradation.

The novel recombinant Escherichia coli strain was construct through cell surface display for the treatment of cobalt contaminated wastewater and dye contaminated wastewater. First, structural analysis of known cobalt binding peptide was conducted and core binding sites were figured out which showing better cobalt binding ability. The cobalt peptides were attached to OmpC to construct cobalt adsorbing recombinant Escherichia coli. The recombinant strain efficiently absorbed and retrieved cobalt from cobalt wastewater by adsorbing 1895 µmol/g DCW of cobalt. Following adsorption, cobalt nanoparticles were synthesized through thermal decomposition of cobalt adsorbed recombinant strain at 500˚C. The nanoparticles exhibited noteworthy photocatalytic properties, demonstrating a substantial capacity for degrading dyes when used as a catalyst at a concentration of 10 mg/dl. These results presenting potential solutions for effective and environmentally friendly approaches to address cobalt and dye contaminated wastewater treatment process.

Modulation of Singlet-Triplet Gap in Atomically Precise Silver Cluster-Assembled Material.

Silver cluster-based solids have garnered considerable attention owing to their tunable luminescence behavior. While surface modification has enabled the construction of stable silver clusters, controlling interactions among clusters at the molecular level has been challenging due to their tendency to aggregate. Judicious choice of stabilizing ligands becomes pivotal in crafting a desired assembly. However, detailed photophysical behavior as a function of their cluster packing remained unexplored. Here, we modulate the packing pattern of Ag12 clusters by varying the nitrogen-based ligand. CAM-1 formed through coordination of the tritopic linker molecule and NC-1 with monodentate pyridine ligand; established via non-covalent interactions. Both the assemblies show ligand-to-metal-metal charge transfer (LMMCT) based cluster-centered emission band(s). Temperature-dependent photoluminescence spectra exhibit blue shifts at higher temperatures, which is attributed to the extent of the thermal reverse population of the S1 state from the closely spaced T1 state. The difference in the energy gap (ΔEST ) dictated by their assemblies played a pivotal role in the way that Ag12 cluster assembly in CAM-1 manifests a wider ΔEST and thus requires higher temperatures for reverse intersystem crossing (RISC) than assembly of NC-1. Such assembly-defined photoluminescence properties underscore the potential toolkit to design new cluster- assemblies with tailored optoelectronic properties.

Effect of Ligand Attachment at Ag11 for CO Oxidation: A Computational Investigation.

Heterogeneous CO oxidation is a demanding reaction at room temperature due to the high activation energy required to break the O=O bond. While several metal clusters are reported to oxidize CO successfully, they fall short of their selectivity for the reaction and recyclability. In this regard, there is a need for economic catalysts with high catalytic activity, low activation barrier, and reusability. In this study, we have investigated the catalytic activity of the neutral pristine and ligated Ag11 cluster toward CO oxidation. We investigated the attachment effect of three organic donor ligands: trimethylphosphine, triethylphosphine, and N-ethyl pyrrolidone to the Ag11 cluster. Our results show that including donor ligands on the Ag11 cluster surface can significantly reduce the barrier heights for CO oxidation. The minimum barrier heights with the system coordinated with triethylphosphine showed the lowest activation barrier of 1.06 kcal/mol compared to the high activation barrier of 14.77 kcal/mol recorded for the pristine cluster. Exploration of the reaction mechanism and charge analysis showed that the electron donor ligands activate O2 via charge donation, thereby reducing the barrier heights of CO oxidation.

Unusually High-Spin Fe12C12- Metallo-Carbohedrene Clusters.

Ferromagnets constructed from nanometals of atomic precision are important for innovative advances in information storage, energy conversion, and spintronic microdevices. Considerable success has been achieved in designing molecular magnets, which, however, are challenging in preparation and may suffer from drawbacks on the incompatibility of high stability and strong ferromagnetism. Utilizing a state-of-the-art self-developed mass spectrometer and a homemade laser vaporization source, we have achieved a highly efficient preparation of pure iron clusters, and here, we report the finding of a strongly ferromagnetic metal-carbon cluster, Fe12C12-, simply by reacting the Fen- clusters with acetylene in proper conditions. The unique stability of this ferromagnetic Fe12C12- cluster is rooted in a plumb-bob structure pertaining to Jahn-Teller distortion. We classify Fe12C12- as a new member of metallo-carbohedrenes and elucidate its structural stability mechanism as well as its soft-landing deposition and magnetization measurements, providing promise for the exploration of potential applications.

Converting CO2 to formic acid by tuning quantum states in metal chalcogenide clusters.

The catalytic conversion of CO2 into valuable chemicals is an effective strategy for reducing its adverse impact on the environment. In this work, the formation of formic acid via CO2 hydrogenation on bare and ligated Ti6Se8 clusters is investigated with gradient-corrected density functional theory. It is shown that attaching suitable ligands (i.e., PMe3, CO) to a metal-chalcogenide cluster transforms it into an effective donor/acceptor enabling it to serve as an efficient catalyst. Furthermore, by controlling the ratio of the attached donor/acceptor ligands, it is possible to predictably alter the barrier heights of the CO2 hydrogenation reaction and, thereby, the rate of CO2 conversion. Our calculation further reveals that by using this strategy, the barrier heights of CO2 hydrogenation can be reduced to ~0.12 eV or possibly even lower, providing unique opportunities to control the reaction rates by using different combinations of donor/acceptor ligands.

Magic Numbers in Octahedral Ligated Metal-Chalcogenide Superatoms.

The attainment of the superatomic state offers a unifying framework for the periodic classification of atomic clusters. Metallic clusters attain the superatomic state via the confined nearly free electron gas model that leads to groupings of quantum states marked by radial and angular momentum quantum numbers. We examine ligated octahedral metal-chalcogenide clusters where the nearly free electron gas model is invalid; however, the high symmetry can also lead to the bunching of electronic states. For octahedral TM6E8L6 clusters (TM = transition metal; E = chalcogen; L = ligand), the electronic shells are filled for valence electron counts of 96, 100, and 114 electrons. These magic electron counts are marked by large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, high ionization energies, and low electron affinity─all classic signatures of the superatomic state. We also find that clusters with electron counts differing from the magic counts show periodic patterns reminiscent of those observed in the periodic table of elements.

Rational Design of Bimetallic Metal Chalcogenide Clusters for CO2 Dissociation.

Thermochemical dissociation of CO2 on pure, ligated, and mixed transition metal (W, Cu) chalcogenide clusters are investigated using the first-principles gradient-corrected density functional approach. It is shown that although the pure and ligated metal chalcogenide clusters exhibit significantly high barriers for CO2 dissociation, the computed barriers for the mixed clusters are relatively lower. The lowest barrier is obtained for the Cu3W3Se8 cluster, which shows a dramatically reduced barrier height of only 0.41 eV. Detailed analysis reveals that the substitution of W by Cu sites leads to a charge transfer from Cu to W sites, resulting in locally active W sites. The lowering of the CO2 dissociation barriers can be attributed to the facile transfer of charge from the locally active W sites and also due to the alteration of the binding energy of CO2 to the charged W sites. Our studies provide an alternate strategy to design novel thermochemical catalysts for CO2 adsorption and subsequent dissociation.

Massive dipoles across the metal-semiconductor cluster interface: towards chemically controlled rectification.

An interface between a metallic cluster (MgAl12) and a semiconducting cluster (Re6Se8(PMe3)5) is shown to be marked by a massive dipole reminiscent of a dipolar layer leading to a Schottky barrier at metal-semiconductor interfaces. The metallic cluster MgAl12 with a valence electron count of 38 electrons is two electrons short of 40 electrons needed to complete its electronic shells in a superatomic model and is marked by a significant electron affinity of 2.99 eV. On the other hand, the metal-chalcogenide semiconducting cluster Re6Se8(PMe3)5, consisting of a Re6Se8 core ligated with five trimethylphosphine ligands, is highly stable in the +2 charge-state owing to its electronic shell closure, and has a low ionization energy of 3.3 eV. The composite cluster Re6Se8(PMe3)5-MgAl12 formed by combining the MgAl12 cluster through the unligated site of Re6Se8(PMe3)5 exhibits a massive dipole moment of 28.38 D resulting from a charge flow from Re6Se8(PMe3)5 to the MgAl12 cluster. The highest occupied molecular orbital (HOMO) of the composite cluster is on the MgAl12 side, which is 0.53 eV below the lowest unoccupied molecular orbital (LUMO) localized on the Re6Se8(PMe3)5 cluster, reminiscent of a Schottky barrier at metal-semiconductor interfaces. Therefore, the combination can act as a rectifier, and an application of a voltage of approximately 4.1 V via a homogeneous external electric field is needed to overcome the barrier aligning the two states: the HOMO in MgAl12 with the LUMO in Re6Se8(PMe3)5. Apart from the bias voltage, the barrier can also be reduced by attaching ligands to the metallic cluster, which provides chemical control over rectification. Finally, the fused cluster is shown to be capable of separating electron-hole pairs with minimal recombination, offering the potential for photovoltaic applications.

The superatomic state beyond conventional magic numbers: Ligated metal chalcogenide superatoms.

The field of cluster science is drawing increasing attention due to the strong size and composition-dependent properties of clusters and the exciting prospect of clusters serving as the building blocks for materials with tailored properties. However, identifying a unifying central paradigm that provides a framework for classifying and understanding the diverse behaviors is an outstanding challenge. One such central paradigm is the superatom concept that was developed for metallic and ligand-protected metallic clusters. The periodic electronic and geometric closed shells in clusters result in their properties being based on the stability they gain when they achieve closed shells. This stabilization results in the clusters having a well-defined valence, allowing them to be classified as superatoms-thus extending the Periodic Table to a third dimension. This Perspective focuses on extending the superatomic concept to ligated metal-chalcogen clusters that have recently been synthesized in solutions and form assemblies with counterions that have wide-ranging applications. Here, we illustrate that the periodic patterns emerge in the electronic structure of ligated metal-chalcogenide clusters. The stabilization gained by the closing of their electronic shells allows for the prediction of their redox properties. Further investigations reveal how the selection of ligands may control the redox properties of the superatoms. These ligated clusters may serve as chemical dopants for two-dimensional semiconductors to control their transport characteristics. Superatomic molecules of multiple metal-chalcogen superatoms allow for the formation of nano-p-n junctions ideal for directed transport and photon harvesting. This Perspective outlines future developments, including the synthesis of magnetic superatoms.

Interfacial magnetism in a fused superatomic cluster [Co6Se8(PEt3)5]2.

An isolated Co6Se8(PEt3)6 cluster is non-magnetic; however, we find that a magnetic unit can be formed by fusing two Co6Se8(PEt3)5 superatoms into a [Co6Se8(PEt3)5]2 dimer. Theoretical studies indicate that the dumbbell-shaped [Co6Se8(PEt3)5]2 dimer has a spin moment of 2µB, and the spin density is primarily localized at the interfacial Co-sites where two clusters are fused into a dimer. The dimer has a low ionization energy of 4.17 eV, allowing the dimer to donate charge to C70 during the formation of a cluster assembled material, as seen in recent experiments by Nuckolls and co-workers. The donation of charge causes the dimer's magnetic moment to drop from 2µB to 1µB. We hypothesize that adding electrons to the dimer, such as doping impurities to the crystal lattice, may enhance the magnetic moment by neutralizing the charged cluster. This reveals a strategy for stabilizing magnetic moments in ligated cluster assemblies.

One-Dimensional Silver-Thiolate Cluster-Assembly: Effect of Argentophilic Interactions on Excited-State Dynamics.

We report the synthesis, crystal structure, and electronic structure calculations of a one-dimensional silver-thiolate cluster-assembled and its ultrafast spectroscopic investigation. Experiments and theory find the material to have a significant gap as the HOMO-LUMO absorption corresponds to 2.69 eV, and the defect-free structure is calculated to have a gap of 2.82 eV. Cluster models demonstrate that the gap energy is length-dependent. Theoretical studies identify a nonbonding metallophilic interaction that exists between two Ag atoms in adjacent strings that helps to stabilize the chain structure. Transient absorption spectroscopy reveals that the electron dynamics is a mixture of the behavior of cluster and nanoparticle, with the material having a 346 fs ground-state relaxation like a cluster, and the electron dynamics is dominated by electron-phonon coupling with a decay time of 1.5 ps, unlike the isolated cluster whose decay is mostly radiative.

A Magnetic Superatomic Dimer with an Intense Internal Electric Dipole Moment.

The electronic and magnetic properties of the ligand-decorated Fe6S8 cluster and fused superatomic dimer are investigated using first-principles density functional theory. It is shown that the redox properties of the Fe6S8 cluster can be effectively controlled by altering the nature of the attached ligands. Donor ligands such as phosphines reduce the ionization energy of the Fe6S8 cluster, whereas the acceptor ligands such as CO increase the electron affinity. Such variation in the redox properties of the Fe6S8 cluster is the result of the ligand-induced shift in the cluster's electronic levels, so the occupation number remains mostly unaffected, leading to a marginal change in the spin magnetic moment of the cluster. A combination of two identical Fe6S8 clusters decorated by unbalanced ligands results in a superatomic dimer with a massive dipole moment and a large spin magnetic moment. Donor ligands on one side of the superatomic dimer with acceptor ligands on the other cause significant intercluster charge transfer. The resulting superatomic dimer offers an interesting motif for spintronics-related applications.

Electron transport properties of PAl12-based cluster complexes.

The electronic transport properties of PAl12-based cluster complexes are investigated by density functional theory (DFT) in combination with the non-equilibrium Green's function (NEGF) method. Joining two PAl12 clusters via a germanium linker creates a stable semiconducting complex with a large HOMO-LUMO gap. Sequential attachment of an electron-donating ligand, N-ethyl-2-pyrrolidone, to one of the two linked clusters results in the shifting of the electronic spectrum of the ligated cluster while the energy levels of the unligated cluster are mostly unchanged. Using this approach, one can eventually align the HOMO of the ligated cluster to the LUMO of the non-ligated cluster, thereby significantly reducing the HOMO-LUMO gap of the complex. As a result, the transport properties of the complex are highly dependent on the number of attached ligands. Although a single ligand is observed to generally decrease the current, the inclusion of two or more ligands shows a significant increase in the amount of current at most voltages. The resulting increase of the current can be attributed to two factors, first the reduction in the HOMO-LUMO gap due to ligand attachment which has moved the transmission orbitals into the bias window. Secondly, when two or more ligands are attached to the complex, the HOMOs become delocalized across the scattering region, and this significantly enhances the currents.

A ligand-induced homojunction between aluminum-based superatomic clusters.

A superatomic molecule formed by joining two metallic clusters linked by an organometallic bridge can behave like a semiconductor and the addition of ligands can induce a significant energy level shift across an inter-cluster homojunction. This shift is induced by the N-ethyl-2-pyrrolidone ligands, and the placement of the ligands strongly affects the direction of the dipole moment, including the case where the dipole moment is parallel to the cluster interface. This computational study provides an alternative strategy for constructing nanometer-scale electronic interfaces between clusters mimicking semiconductor motifs. The semiconducting features in the PAl12 clusters emerge from the grouping of the quantum states in a confined nearly free electron gas that creates a substantial energy gap. An organometallic Ge(CH3)2(CH2)2 bridge links the clusters while maintaining the cluster's electronic shell structure. The amount of level shifting between the bridged clusters can be changed by controlling the number of ligands. Attaching multiple ligands can result in a broken gap energy alignment in which the HOMO level of one cluster is aligned with the LUMO level of the other bridged cluster. Furthermore, the singly ligated bridged superatomic molecule is found to exhibit promising features to separate the electron-hole pairs for photovoltaic applications.

A mechanistic insight into rhodium-doped gold clusters as a better hydrogenation catalyst.

The reaction mechanism of the hydrogenation of ethylene on pristine (Aun, n = 8 and 20) and rhodium-doped (AunRh) gold clusters was unveiled by theoretical calculations. All reaction pathways are predicted and the thermodynamic and kinetic parameters are computed and compared. Doping a rhodium atom on the magic gold cluster surface is effective in reducing the activation barriers for hydrogenation and in creating two competitive pathways with significantly higher turnover frequencies. The lower barriers of hydrogenation on the AunRh clusters were analyzed and explained based on distortion/interaction activation strain (DIAS) analysis. Further insights into the reaction mechanism on both types of clusters are provided by intrinsic bond orbital (IBO) calculations. This theoretical study provides an idea to elucidate the hydrogenation mechanism on Au clusters and the effect of the rhodium dopant on the catalytic process.

Account of chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C-H activation: a DFT investigation.

Herein, the chemical bonding of both pristine rhodium (Rhn, 2 ≤ n ≤ 9) and mono-vanadium-doped rhodium (RhmV, 1 ≤ m ≤ 8) clusters was understood by density functional theory. The calculated results provided conclusive evidence that a single vanadium dopant thermodynamically stabilized the rhodium clusters by increasing the interatomic bond orders and henceforth the binding energy. Moreover, an in-depth account of the high bond order of RhmV clusters was presented by analyzing the intracluster bonding orbitals and the orbital composition. In addition, the reaction mechanism and thermodynamic parameters of C-H activation processes on both types of clusters were thoroughly investigated, and the results were compared. This comparison revealed that in addition to thermodynamic stabilization, the vanadium dopant enhanced the reactivity of the cluster toward C-H activation by reducing the activation barrier and endothermicity to a reasonable extent. Thus, the obtained results provide an insight into the structure and bonding of both types of inorganic clusters (Rhn and RhmV) and reveal the potential application of vanadium as a dopant for the enhancement of both stability and catalytic properties of rhodium clusters.

Aluminum cluster for CO and O2 adsorption.

Low temperature oxidation of CO to CO2 is an important process for the environment. Similarly adsorption of CO from the releasing sources is also of major concern today. Whereas the potential of gold and silver clusters is well proven for the catalysis of the above mentioned reaction, the potential of aluminum (Al) clusters remains unexplored. The present study proves that, similar to the transition metals, Al clusters can also be used for adsorption of gases. We first tested the potential of Al cluster as adsorbents for CO. The high binding energy (BE) values prove that Al clusters can be used for adsorbing both CO and O2. Since oxygen binding is more facile, we adsorbed oxygen on Al and then checked the effect of this O2 on the BE of CO. The results were obtained by DFT calculations at M062X/TZVP level of theory. Graphical abstract Activation of carbon monoxide (CO) on oxygen-adsorbed aluminum (Al) cluster.

Mechanistic Investigation of the Carbon-Iodine Bond Activation on the Niobium-Carbon Cluster.

The activation process of carbon-iodine (C-I) bond on neutral and cationic niobium metcars (Nb8C12) is investigated using density functional theory and related computational techniques. Metallocarbohedrenes or metcars are a class of stable metal-carbide clusters of specific stoichiometry and of great interest to cluster chemists since their first discovery. The detailed reaction mechanism along with the overall energy profile of the C-I dissociation reaction on niobium metcar and its cations is presented in this paper. The tunneling-corrected rate constants and their related reaction parameters such as the pre-exponential factor are also included alongside. The major differences between the reaction mechanism of the neutral and cationic metcars are also highlighted as well. Despite the available experimental results, the C-I bond dissociation on metcars has remained an unexplored problem in the theoretical and computational domains. Thus, the present investigation can fill in the gap and may also provide new insights provoking further developments in cluster and materials chemistry in future.

Radical attached aluminum nanoclusters: an alternative way of cluster stabilization.

The stability and electronic structure of radical attached aluminum nanoclusters are investigated using density functional theory (DFT). A detailed investigation shows good correlation between the thermodynamic stability of radical attached clusters and the stability of the attached radical anions. All other calculated parameters like HOMO-LUMO gap and charge transfer are also found to be consistent with the observed thermodynamic stabilities of the complexes. Investigation of the electronic structure of radical attached complexes further shows the presence of jellium structures within the core similar to the ligated clusters. Comparison with available experimental and theoretical data also proves the validity of superatomic complex theory for the radical attached clusters as well. Based on the evaluated thermodynamic parameters, selected radical attached clusters are observed to be more thermodynamically stable in comparison with experimentally synthesized ligated clusters. Stabilization of small metal clusters is one of the greatest challenges in current cluster science and the present investigation confirms the fact that radical attached clusters can provide a viable alternative to ligated clusters in the future.

Electron Detachment and Subsequent Structural Changes of Water Clusters.

A cost-effective equation of motion coupled cluster method, EOMIP-CCSD(2), is used to investigate vertical and adiabatic ionization potential as well as ionization-induced structural changes of water clusters and compared with CCSD(T), CASPT2, and MP2 methods. The moderate N(5) scaling and low storage requirement yields EOMIP-CCSD(2) calculation feasible even for reasonably large molecules and clusters with accuracy comparable to CCSD(T) method at much cheaper computational cost. Our calculations shed light on the authenticity of EOMIP-CCSD(2) results and establish a reliable method to study of ionization energy of molecular clusters. We have further investigated the performance of several classes of DFT functionals for ionization energies of water clusters to benchmark the results and to get a reliable functionals for the same.