No abstract

Formation of functional monolayers on surfaces of carbon materials is inherently difficult because of the high bond strength of carbon and because common pathways such as SN2 mechanisms cannot take place at surfaces of solid materials. Here, we show that the radical initiators can selectively abstract H atoms from H-terminated carbon surfaces, initiating regioselective grafting of terminal alkenes to surfaces of diamond, glassy carbon, and polymeric carbon dots. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) demonstrate formation of self-terminating organic monolayers linked via the terminal C atom of 1-alkenes. Density functional theory (DFT) calculations suggest that this selectivity is at least partially thermodynamic in origin, as significantly less energy is needed to abstract H atoms from carbon surfaces as compared to typical aliphatic compounds. The regioselectivity favoring binding to the terminal C atom of the reactant alkenes arises from steric hindrance encountered in bond formation at the adjacent carbon atom. Our results demonstrate that carbon surface radical chemistry yields a versatile, selective, and scalable approach to monolayer formation on H-terminated carbon surfaces and provide mechanistic insights into the surface selectivity and regioselectivity of molecular grafting.

Weakly bound noble gases (Ne, Ar, Kr, and Xe) are being utilized as probes to monitor the photocatalytic activity of the TiO 2 (110) surface. In this work, this adsorption problem is examined using different van der Waals-corrected DFT-based treatments on periodic systems. The assessment of their performance is assisted by the application of nonperiodic DFT-based symmetry adapted perturbation theory [SAPT(DFT)]. It is further verified by comparing with experimentally based determinations of the adsorption energies at one-monolayer surface coverage. Besides being dispersion-dominated adsorbate/surface interactions, the SAPT(DFT)based decomposition reveals that the electrostatic and induction energy contributions become highly relevant for the heaviest noble-gas atoms (krypton and xenon). The most reliable results are provided by the revPBE-D3 approach: it predicts adsorption energies of −118.4, −165.8, and −2231.7 meV for argon, krypton, and xenon, which are within 6% of the experimental values, and attractive long-range tails which are consistent with our ab initio benchmarking. Moreover, the revPBE density functional describes the short-range part of the potential energy curve more precisely, avoiding the exchange-only binding effects of the PBE functional. The nonlocal vdW-DF2 density functional performs well at the long-range potential region but largely overestimates the adsorption energies of noble gas atoms as light as argon. The Tkatchenko−Scheffler dispersion correction combined with the revPBE functional produces accurate estimations of the adsorption energies (to within 10%) but long-range attractive tails that decay too slowly as in first-generation nonlocal vdW-DF density functional. Lateral interactions between coadsorbate atoms contribute up to about 15−20%, being key in achieving good agreement with experimental measurements. The interaction with the noble-gas atoms reduces the work function of the TiO 2 (110) surface, agreeing to the experimental observation of an inhibited photodesorption of coadsorbed molecular oxygen.

Nickel-enriched lithium nickel manganese cobalt oxide, an increasingly used complex metal oxide, has unexpected dissolution behavior and impacts on two model environmental organisms.