Lin Lai

Modeling the thermostability of surface functionalisation by oxygen, hydroxyl, and water on nanodiamonds

Understanding nanodiamond functionalisation is of great importance for biological and medical applications. Here we examine the stabilities of oxygen, hydroxyl, and water functionalisation of the nanodiamonds using the self-consistent charge density functional tight-binding simulations. We find that the oxygen and hydroxyl termination are thermodynamically favourable and form strong C–O covalent bonds on the nanodiamond surface in an O2 and H2 gas reservoir, which confirms previous experiments. Yet, the thermodynamic stabilities of oxygen and hydroxyl functionalisation decrease dramatically in a water vapour reservoir. In contrast, H2O molecules are found to be physically adsorbed on the nanodiamond surface, and forced chemical adsorption results in decomposition of H2O. Moreover, the functionalisation efficiency is found to be facet dependent. The oxygen functionalisation prefers the {100} facets as opposed to alternative facets in an O2 and H2 gas reservoir. The hydroxyl functionalisation favors the {111} surfaces in an O2 and H2 reservoir and the {100} facets in a water vapour reservoir, respectively. This facet selectivity is found to be largely dependent upon the environmental temperature, chemical reservoir, and morphology of the nanodiamonds.

Interparticle Interactions and Self-Assembly of Functionalized Nanodiamonds.

Although unpassivated detonation nanodiamonds are known to form tightly bound (and sometimes ordered) superstructures, in most high performance applications the surface are deliberately functionalized, and this can profoundly alter the aggregation behavior. In the present study, we model the aggregation of functionalized nanodiamonds and show that functionalization greatly reduces the Coulombic interactions characteristic of unsaturated particles. Our results provide new insights into the interactions of functionalized nanoparticles.

Surface phase diagram and thermodynamic stability of functionalisation of nanodiamonds

Surface functionalisation has been widely applied to nanodiamonds, as well as other nanomaterials, with the aim of promoting stability (saturation of dangling bonds) and expanding applications. Since nanodiamonds are a promising candidate for applications in biology and nanomedicine, careful control of the stability and homogeneity of the surface functionalisation is crucial. Here, the facet-dependent thermodynamic stabilities of individual diamond nanoparticles functionalised with hydrogen, oxygen, and hydroxyl have been systematically examined using electronic structure computer simulations. Based on these results, phase diagrams for the functionalised nanodiamonds have been established, mapping the stability as a function of the partial pressures of the participating species.

Diamond nanoparticles as a new platform for the sequestration of waste carbon

The use of carbon nanostructures to capture and store waste carbon, such as methane and carbon dioxide, is intrinsically attractive, particularly if the same molecules can be subsequently used as synthetic precursors. However, to facilitate adsorption of these highly stable species high pressures are required, and fragile carbon-based nanostructures may not survive. By combining electronic structure simulations and ab initio thermodynamics, we have investigated the thermochemical conditions required to adsorb CH, CH2, CO and CO2 on diamond nanoparticles, which can withstand higher temperatures and pressures than alternative carbon-based nanostructures. We find that, while CO2 must be over-saturated to facilitate stable adsorption (with high efficiency), the strength of the resultant C-O bonds means that desorption will not occur spontaneously when atmospheric pressure is resumed.

Charge-induced restructuring and decomposition of bucky-diamonds

Due to the small number of atoms in nanostructures, additional charge is likely to cause significant changes in their structure and properties. Here, we examine the charge-dependent structural evolution of individual bucky-diamonds, which have been proposed as a promising candidate for biological and medical applications, using self-consistent charge density functional based tight-binding simulations. We find that there exists a threshold of excess charge for each model bucky-diamond, above which destruction of the structures ensues. Our results also reveal the existence of a phase transition between bucky-diamonds and onion-like carbon below the failure threshold.