On the Fragmentation of Ni(II) β-Diketonate-Diamine Complexes as Molecular Precursors for NiO Films: A Theoretical and Experimental Investigation

NiO-based nanomaterials have attracted considerable interest for different applications, which have stimulated the implementation of various synthetic approaches aimed at modulating their chemico-physical properties. In this regard, their bottom-up preparation starting from suitable precursors plays an important role, although a molecular-level insight into their reactivity remains an open issue to be properly tackled. In the present study, we focused on the fragmentation of Ni(II) diketonate-diamine adducts, of interest as vapor-phase precursors for Ni(II) oxide systems, by combining electrospray ionization mass spectrometry (ESI-MS) with multiple collisional experiments (ESI-MSn) and theoretical calculations. The outcomes of this investigation revealed common features in the fragmentation pattern of the target compounds: (i) in the first fragmentation, the three complexes yield analogous base-peak cations by losing a negatively charged diketonate moiety; in these cations, Ni-O and Ni-N interactions are stronger and the Ni positive charge is lower than in the parent neutral complexes; (ii) the tendency of ligand electronic charge to migrate towards Ni further increases in the subsequent fragmentation, leading to the formation of a tetracoordinated Ni environment featuring an interesting cation-π intramolecular interaction.

Metal Oxide-Related Dendritic Structures: Self-Assembly and Applications for Sensor, Catalysis, Energy Conversion and Beyond

In the past two decades, we have learned a great deal about self-assembly of dendritic metal oxide structures, partially inspired by the nanostructures mimicking the aesthetic hierarchical structures of ferns and corals. The self-assembly process involves either anisotropic polycondensation or molecular recognition mechanisms. The major driving force for research in this field is due to the wide variety of applications in addition to the unique structures and properties of these dendritic nanostructures. Our purpose of this minireview is twofold: (1) to showcase what we have learned so far about how the self-assembly process occurs; and (2) to encourage people to use this type of material for drug delivery, renewable energy conversion and storage, biomaterials, and electronic noses.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

The Early Steps of Molecule-to-Material Conversion in Chemical Vapor Deposition (CVD): A Case Study

Transition metal complexes with β-diketonate and diamine ligands are valuable precursors for chemical vapor deposition (CVD) of metal oxide nanomaterials, but the metal-ligand bond dissociation mechanism on the growth surface is not yet clarified in detail. We address this question by density functional theory (DFT) and ab initio molecular dynamics (AIMD) in combination with the Blue Moon (BM) statistical sampling approach. AIMD simulations of the Zn β-diketonate-diamine complex Zn(hfa)₂TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), an amenable precursor for the CVD of ZnO nanosystems, show that rolling diffusion of this precursor at 500 K on a hydroxylated silica slab leads to an octahedral-to-square pyramidal rearrangement of its molecular geometry. The free energy profile of the octahedral-to-square pyramidal conversion indicates that the process barrier (5.8 kcal/mol) is of the order of magnitude of the thermal energy at the operating temperature. The formation of hydrogen bonds with surface hydroxyl groups plays a key role in aiding the dissociation of a Zn-O bond. In the square-pyramidal complex, the Zn center has a free coordination position, which might promote the interaction with incoming reagents on the deposition surface. These results provide a valuable atomistic insight on the molecule-to-material conversion process which, in perspective, might help to tailor by design the first nucleation stages of the target ZnO-based nanostructures.

Growth of WOx from Tungsten(VI) Oxo-Fluoroalkoxide Complexes with Partially Fluorinated β-Diketonate/β-Ketoesterate Ligands: Comparison of Chemical Vapor Deposition to Aerosol-Assisted CVD

Tungsten(VI) oxo complexes of the type WO(OR)₃L [R = C(CH₃)₂CF₃, C(CF₃)₂CH₃, CH(CF₃)₂, L = hexafluoroacetylacetonate (hfac), ethyl trifluoroacetoacetonate (etfac), acetylacetonate (acac)] bearing partially fluorinated alkoxide and/or chelating ligands were synthesized. Thermal decomposition behavior and mass spectrometry (MS) fragmentation patterns of selected examples were studied. The thermolysis products of WO(OC(CF₃)₂CH₃)₃(hfac) were characterized by nuclear magnetic resonance and gas chromatography-MS. Studies of the sublimation behavior of the complexes demonstrated that their volatility depends on the degree of fluorination. Comparative studies of the deposition of tungsten oxide by chemical vapor deposition (CVD) and aerosol-assisted CVD were carried out using WO(OC(CF₃)₂CH₃)₃(hfac) as a single-source precursor. WO_x materials were successfully deposited by both deposition methods, but the deposits differed in morphology, structure, and crystallinity.

The deposition of cadmium selenide and cadmium phosphide thin films from cadmium thioselenoimidodiphosphinate by AACVD and the formation of an aromatic species

Aerosol-assisted chemical vapour deposition (AACVD) of Cd[(SPiPr2)(SePiPr2)N]2 yields hexagonal cadmium selenide and monoclinic cadmium phosphide films on glass substrates between 475 and 525 °C at different argon flow rates. The films were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). All the results of XRD, EDAX and XPS are in agreement with our previous investigations on Cd[(SePiPr2)2N]2. A breakdown mechanism is proposed based on mass spectra and density functional theory calculations. A large peak at m/z 207 in the mass spectra, previously assigned by us as a new aromatic species, is also observed for this complex.

In Vivo Synthesis of Nanocomposites Using the Recombinant Escherichia coli

Biogenic gold nanorod (AuNR)-Ag core-shell nanocomposites (NCs) are synthesized by using recombinant Escherichia coli to demonstrate in vivo synthesis of biogenic NCs for the first time. The chemically synthesized AuNRs are internalized into the E. coli, and Ag ions are reduced and grown on the surface of the AuNRs with the assistance of metal-binding proteins, producing biogenic core-shell AuNR-Ag NCs. The core-shell structure of the biogenic AuNR-Ag NC is confirmed by transmission electron microscopy and energy-dispersive X-ray analysis. The biogenic AuNR-Ag NCs exhibit good plasmonic effects. While the core-shell morphology of the AuNR and Ag NCs is due to the similar lattice of Au and Ag, the shape of the biogenic NCs composed of gold nanoparticles and Fe is aciniform, and that of Fe₃ O₄ NPs and Au/Ag is a network structure, demonstrating the controllability of biogenic nanosynthesis using diverse metal combinations with different NC morphologies.

Recombinant Escherichia coli as a biofactory for various single- and multi-element nanomaterials

Nanomaterials (NMs) are mostly synthesized by chemical and physical methods, but biological synthesis is also receiving great attention. However, the mechanisms for biological producibility of NMs, crystalline versus amorphous, are not yet understood. Here we report biosynthesis of 60 different NMs by employing a recombinant Escherichia coli strain coexpressing metallothionein, a metal-binding protein, and phytochelatin synthase that synthesizes a metal-binding peptide phytochelatin. Both an in vivo method employing live cells and an in vitro method employing the cell extract are used to synthesize NMs. The periodic table is scanned to select 35 suitable elements, followed by biosynthesis of their NMs. Nine crystalline single-elements of Mn3O4, Fe3O4, Cu2O, Mo, Ag, In(OH)3, SnO2, Te, and Au are synthesized, while the other 16 elements result in biosynthesis of amorphous NMs or no NM synthesis. Producibility and crystallinity of the NMs are analyzed using a Pourbaix diagram that predicts the stable chemical species of each element for NM biosynthesis by varying reduction potential and pH. Based on the analyses, the initial pH of reactions is changed from 6.5 to 7.5, resulting in biosynthesis of various crystalline NMs of those previously amorphous or not-synthesized ones. This strategy is extended to biosynthesize multi-element NMs including CoFe2O4, NiFe2O4, ZnMn2O4, ZnFe2O4, Ag2S, Ag2TeO3, Ag2WO4, Hg3TeO6, PbMoO4, PbWO4, and Pb5(VO4)3OH NMs. The strategy described here allows biosynthesis of NMs with various properties, providing a platform for manufacturing various NMs in an environmentally friendly manner.

Solution combustion synthesis of metal oxide nanomaterials for energy storage and conversion

The design and synthesis of metal oxide nanomaterials is one of the key steps for achieving highly efficient energy conversion and storage on an industrial scale. Solution combustion synthesis (SCS) is a time- and energy-saving method as compared with other routes, especially for the preparation of complex oxides which can be easily adapted for scale-up applications. This review summarizes the synthesis of various metal oxide nanomaterials and their applications for energy conversion and storage, including lithium-ion batteries, supercapacitors, hydrogen and methane production, fuel cells and solar cells. In particular, some novel concepts such as reverse support combustion, self-combustion of ionic liquids, and creation of oxygen vacancies are presented. SCS has some unique advantages such as its capability for in situ doping of oxides and construction of heterojunctions. The well-developed porosity and large specific surface area caused by gas evolution during the combustion process endow the resulting materials with exceptional properties. The relationship between the structural properties of the metal oxides studied and their performance is discussed. Finally, the conclusions and perspectives are briefly presented.

Solution based CVD of main group materials

This critical review focuses on the solution based chemical vapour deposition (CVD) of main group materials with particular emphasis on their current and potential applications. Deposition of thin films of main group materials, such as metal oxides, sulfides and arsenides, have been researched owing to the array of applications which utilise them including solar cells, transparent conducting oxides (TCOs) and window coatings. Solution based CVD processes, such as aerosol-assisted (AA)CVD have been developed due to their scalability and to overcome the requirement of suitably volatile precursors as the technique relies on the solubility rather than volatility of precursors which vastly extends the range of potentially applicable compounds. An introduction into the applications and precursor requirements of main group materials will be presented first followed by a detailed discussion of their deposition reviewed according to this application. The challenges and prospects for further enabling research in terms of emerging main group materials will be discussed.

Synthesis and characterization of Pt magnetic nanocatalysts with a TiO2 or CeO2 layer

The Pt magnetic nanocatalysts with a TiO₂ or CeO₂ layer have been fabricated successfully.

A plasma-assisted approach for the controlled dispersion of CuO aggregates into β iron(iii) oxide matrices

High-purity supported β-Fe₂O₃/CuO nanosystems with tailored morphology and tuneable copper content were fabricated by a two-step plasma-assisted process.

Ruthenium complexes as precursors for chemical vapor-deposition (CVD)

The progress in precursor chemistry for the chemical vapor deposition of ruthenium containing thin films is reviewed.