Systematic Study of Aluminum Nanoclusters and Anion Adsorbates

Abstract

The interactions between aqueous aluminum (Al) nanoclusters and ions in solution influence the reactivity of nanomaterials in natural waters and are crucial to the targeted syntheses of aluminum oxides. To contribute to the fundamental understanding of how both anion and Al-nanocluster properties affect the interactions, we carry out systematic modeling studies that employ density functional theory calculations embedded in a continuum solvent model. Energetic and electronic structure analysis is applied toward delineating the interactions of a range of probe adsorbate anions with Al nanoclusters to elucidate how small molecules may react with naturally occurring nanomaterials. The study spans seven small molecules on three model Al nanoclusters. Using this ion set, we correlate the size, shape, and formal charge of the adsorbate to the trends in adsorption energies. A key finding is that the collective effects of exposed oxygen functional groups, i.e., the distribution of functional groups, dictates the electrostatic potential of the nanocluster surface, which, in turn, controls trends in anion adsorption. The computed adsorption and deprotonation trends are correlated to known synthetic routes of Al-nanocluster formation and subsequent crystallization to give insight into the potential optimization of synthetic conditions.

Formation of Nanoscale [Ge4O16Al48(OH)108(H2O)24]20+ from Condensation of ϵ‐GeAl128+ Keggin Polycations**

“…As done previously, we calculated changes in the Mulliken population(Dq m ) of the sulfate before and after adsorption and relate the results to deprotonation events. [20] Of the four e-Keggin interactions, only Site-1 sulfate interactions with e-GeAl 12 (Table S6 and Figure 3) result in deprotonation and an associated Dq m value greater than 0.50 e. All other interactions have Dq m values of less than 0.50 e and did not exhibit deprotonation, similar to previous observations on Keggin-anion interactions. [3c, 15, 20] To bridge the understanding between isomers and heteroatom identity for condensation reactions, we also assessed the d-isomers for GeAl 12 and Al 13 using the sulfate anion as our probe adsorbate (Table S7 and Figure S8).…”

“…When modeled as isolated clusters, the DFT calculations do not yield evidence of site‐specific acidic groups on the cluster surface. However, as done in previous studies, a strong base probe molecule can be used to elicit perturbations to cluster functional groups and ultimately identify labile protons [20] . Specifically, outer‐sphere adsorption modeled in different locations above the cluster surface can induce deprotonation of certain functional groups over the course of geometry optimization, thus identifying relatively labile protons.…”

“…In Site‐2, the sulfate anion can engage with a mixture of η 1 ‐H 2 O and μ 2 ‐OH groups on the surface of one Al 3 (OH) 6 (H 2 O) 3 trimer unit. As done previously, we calculated changes in the Mulliken population(Δ q m ) of the sulfate before and after adsorption and relate the results to deprotonation events [20] . Of the four ϵ‐Keggin interactions, only Site‐1 sulfate interactions with ϵ‐GeAl 12 (Table S6 and Figure 3) result in deprotonation and an associated Δ q m value greater than 0.50 e. All other interactions have Δ q m values of less than 0.50 e and did not exhibit deprotonation, similar to previous observations on Keggin‐anion interactions [3c, 15, 20] …”

“…However, as done in previous studies, a strong base probe molecule can be used to elicit perturbations to cluster functional groups and ultimately identify labile protons. [20] Specifically, outer-sphere adsorption modeled in different locations above the cluster surface can induce deprotonation of certain functional groups over the course of geometry optimization, thus identifying relatively labile protons. We hypothesize that if functional groups at specific locations on the cluster surface have a greater tendency to deprotonate, as revealed by the adsorbate probe modeling, then that could enable tridecamer units to connect through those sites and explain the formation of this tetramer.…”

Dissociative adsorption modes of TATB on the Al (111) surface: a DFT investigation

“…Al is also widely used in formulations of propellants and explosives; thus, it is of great importance to explore its reactions with energetic molecules. 25 Ammunition composed of TATB and aluminum powder shows excellent performance. To understand the interaction mode of TATB/Al systems, comprehensive knowledge about the interface and electronic structure of the system is necessary.…”