Modeling polydispersive ensembles of diamond nanoparticles

Surfactant-tail control of CsPbBr3 nanocrystal morphology

CsPbBr3 nanocrystals (NCs) are promising optoelectronic and catalytic materials. Manipulating their morphology can improve their properties and stability. In this work, an alkene-derived zwitterionic ligand was used to control the morphology of CsPbBr3 NCs to yield the highly unusual rhombicuboctahedron morphology, showcasing the first example of a surfactant-tail controlled growth.

Etching Kinetics of Nanodiamond Seeds in the Early Stages of CVD Diamond Growth

We present an experimental study on the etching of detonation nanodiamond (DND) seeds during typical microwave chemical vapor deposition (MWCVD) conditions leading to ultra-thin diamond film formation, which is fundamental for many technological applications. The temporal evolution of the surface density of seeds on the Si(100) substrate has been assessed by scanning electron microscopy (SEM). The resulting kinetics have been explained in the framework of a model based on the effect of the particle size, according to the Young-Laplace equation, on both chemical potential of carbon atoms in DND and activation energy of the reaction with atomic hydrogen. The model describes the experimental kinetics of seeds' disappearance by assuming that nanodiamond particles with a size smaller than a "critical radius," r*, are etched away while those greater than r* can grow. Finally, the model allows to estimate the rate coefficients for growth and etching from the experimental kinetics.

Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization

Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functionalized CNOs were exhaustively characterized by statistical Raman spectroscopy, thermogravimetric analysis coupled with gas chromatography and mass spectrometry, dynamic light scattering, UV-vis, and ATR-FTIR spectroscopies. This work provides important insights into the understanding of the basic principles of reductive CNOs functionalization and will pave the way for the use of CNOs in a wide range of potential applications, such as energy storage, photovoltaics, or molecular electronics.

Electronic g-Tensor Calculations for Dangling Bonds in Nanodiamonds

The electronic g-tensor calculations are performed for dangling bonds (DBs) introduced into nanodiamonds (NDs) with four different functional groups on their surfaces. For hydrogenated and fluorinated NDs, it is found that g-shifts of the latter vary in a much wider range, and the same is also true for the total energy differences between the highest and the lowest energy DBs. In addition, it is shown that the shape of NDs significantly impacts the energetics and g-shifts of DBs, whereas the influence of the size is much less pronounced, as is the influence of the presence of one DB in the vicinity of the other, resulting in no substantial change on their magnetic behavior. For hydroxylated and aminated NDs, it is demonstrated that the variation range of g-shifts is larger for the former, whereas the opposite is seen regarding the total energy differences. On the whole, some of the positions of DBs can be energetically very costly in these NDs; besides, the lowest energy DBs are irregular, that is, formed by OH- and NH₂-bonded C atoms, contrasting with hydrogenated and fluorinated NDs, for which irregular DBs are the most energetically unfavorable.

Electronic g-tensors of nanodiamonds: Dependence on the size, shape, and surface functionalization

The electronic g-tensor dependence on the size, shape, and surface functionalization of nanodiamonds (NDs) is theoretically investigated by selecting dangling bonds and single substitutional nitrogen atoms as a main source of the unpaired electrons. The performed g-tensor calculations reveal that aforementioned paramagnetic impurities introduced into octahedrally shaped ND of C₈₄H₆₄ size behave in a very similar manner as those embedded into a smaller octahedral model of C₃₅H₃₆ size. Since cubic and tetrahedral NDs-C₅₄H₄₈ and C₅₁H₅₂-demonstrate a wider range of g-shift values than octahedral systems, the g-tensor dependence on different shapes can be considered as more pronounced. However, a different surface functionalization scheme, namely, fluorination, results in a much larger variation of the g-shifts, pointing to a significant impact the F atoms have on the local environment of the unpaired electrons in C₃₅F₃₆. A partial surface functionalization of C₃₅H₃₆ with benzoic acid and aniline groups indicates that, in some special cases, these linkers might induce a noticeable spin density redistribution which in turn substantially modifies the g-shift values of the system. Additional infrared (IR) spectra calculations show that some of paramagnetic defects in C₃₅H₃₆ and C₃₅F₃₆ possess clearly expressed signatures which could be useful while analyzing the experimental IR spectra of NDs.

On the magnetic properties of nanodiamonds: Electronic g-tensor calculations

The electronic g-tensor calculations are carried out for various paramagnetic defects introduced into hydrogenated diamond nanocrystal C₃₅H₃₆, showing that such a system can be successfully used to model magnetic properties of nanodiamonds (NDs) with paramagnetic centers containing no vacancies. In addition, it is revealed that, depending on the geometric positions in ND, paramagnetic centers of the same type produce noticeable variations of the g-tensor values. A side-by-side comparison of the performance of effective nuclear charge and spin-orbit mean field (SOMF) approaches indicates that the latter is more sensitive to the quality of basis sets, especially concerning diffuse functions, the inclusion of which is found to be nonbeneficial. What is more, the SOMF method also exhibits a much more pronounced gauge-origin dependence. Compared to electronic charge centroid, spin centers (SCs) demonstrate a superior suitability as gauge origins, providing a better agreement with diamagnetic and paramagnetic contributions of g-tensor obtained employing gauge-including atomic orbitals (GIAOs). Therefore, SCs can be recommended for the g-tensor calculations of NDs whenever GIAOs are not available.

DFT calculations reveal pronounced HOMO-LUMO spatial separation in polypyrrole-nanodiamond systems

The low-cost efficient generation of renewable energy and its blending with societal lifestyle is becoming increasingly pervasive. Diamond-based inorganic-organic hybrid systems may have an immense, yet still mostly unexplored, potential in photovoltaic solar cells applications. In this work, we study the interactions of polypyrrole (PPy) with diamond nanoparticles (so-called nanodiamonds, NDs) by computational density functional theory (DFT) methods. We compute the structural and electronic properties of such hybrid organic-inorganic systems. During modeling, PPy is chemisorbed and physisorbed on (111) and (100) ND edge-like surface slabs terminated with oxygen, hydroxyl, carboxyl, and anhydride functional groups, i.e., in the arrangements most commonly found in real NDs. Moreover, NDs terminated with an amorphous surface layer (a-C:H, a-C:O) are considered to approach realistic conditions even further. In a predominant number of cases, we obtain the spatial separation of HOMO and LUMO at the interface, facilitating exciton dissociation. Further, there is a favorable energy level alignment for charge transport. The theoretical results, therefore, show the promising potential of PPy-ND composites in photovoltaic applications.

Predicting the impact of structural diversity on the performance of nanodiamond drug carriers

Diamond nanoparticles (nanodiamonds) are unique among carbon nanomaterials, and are quickly establishing a niché in the biomedical application domain. Nanodiamonds are non-toxic, amenable to economically viable mass production, and can be interfaced with a variety of functional moieties. However, developmental challenges arise due to the chemical complexity and structural diversity inherent in nanodiamond samples. Nanodiamonds present a narrow, but significant, distribution of sizes, a dizzying array of possible shapes, and a complicated surface containing aliphatic and aromatic carbon. In the past these facts have been cast as hindrances, stalling development until perfectly monodispersed samples could be achieved. Current research has moved in a different direction, exploring ways that the polydispersivity of nanodiamond samples can be used as a new degree of engineering freedom, and understanding the impact our limited synthetic control really has upon structure/property relationships. In this review a series of computational and statistical studies will be summarised and reviewed, to characterise the relationship between chemical complexity, structural diversity and the reactive performance of nanodiamond drug carriers.

Impact of speciation on the electron charge transfer properties of nanodiamond drug carriers

Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove useful in designing drug delivery systems where the release of (selected) drugs needs to be sensitive to specific conditions at the point of delivery.

Challenges in modelling nanoparticles for drug delivery

Although there have been significant advances in the fields of theoretical condensed matter and computational physics, when confronted with the complexity and diversity of nanoparticles available in conventional laboratories a number of modeling challenges remain. These challenges are generally shared among application domains, but the impacts of the limitations and approximations we make to overcome them (or circumvent them) can be more significant one area than another. In the case of nanoparticles for drug delivery applications some immediate challenges include the incompatibility of length-scales, our ability to model weak interactions and solvation, the complexity of the thermochemical environment surrounding the nanoparticles, and the role of polydispersivity in determining properties and performance. Some of these challenges can be met with existing technologies, others with emerging technologies including the data-driven sciences; some others require new methods to be developed. In this article we will briefly review some simple methods and techniques that can be applied to these (and other) challenges, and demonstrate some results using nanodiamond-based drug delivery platforms as an exemplar.

Size and shape dependent deprotonation potential and proton affinity of nanodiamond

Many important reactions in biology and medicine involve proton abstraction and transfer, and it is integral to applications such as drug delivery. Unlike electrons, which are quantum mechanically delocalized, protons are instantaneously localized on specific residues in these reactions, which can be a distinct advantage. However, the introduction of nanoparticles, such as non-toxic nanodiamonds, to this field complicates matters, as the number of possible sites increases as the inverse radius of the particle. In this paper we present > 10(4) simulations that map the size- and shape-dependence of the deprotonation potential and proton affinity of nanodiamonds in the range 1.8-2.7 nm in average diameter. We find that while the average deprotonation potential and proton affinities decrease with size, the site-specific values are inhomogeneous over the surface of the particles, exhibiting strong shape-dependence. The proton affinity is strongly facet-dependent, whereas the deprotonation potential is edge/corner-dependent, which creates a type of spatial hysteresis in the transfer of protons to and from the nanodiamond, and provides new opportunities for selective functionalization.

The impact of structural polydispersivity on the surface electrostatic potential of nanodiamond

The discovery of the multipolar surface electrostatic potential on faceted diamond nanoparticles explained numerous observations over the past decades, but also raised questions as to how it could be reconciled with seemingly contradictory observations of micron sized diamond and bulk diamond surfaces. It was also unclear how surface electrostatic potential would vary for more quasi-spherical shapes, and derivatives of the ideal truncated octahedron. Here we present new results examining the size-dependence of the multi-polar surface electrostatic potential up to experimentally relevant sizes, and explore the impact of {110} facets which have been shown to present in reasonable quantities (experimentally). We have used computational methods that are consistent with previous work to allow for a direct comparison, and show that both particle size and the fraction of {110} facets on nanodiamond play a critical role in the surface charge. When the particle size is below ~2.5 nm multipoles are likely to dominate, but over ~3.0 nm the {110} facets efficiently neutralize the charges leading to a practically monopolar distribution, consistent with observations at other length scales.