Nanodiamond‐Palladium Core–Shell Organohybrid Synthesis: A Mild Vapor‐Phase Procedure Enabling Nanolayering Metal onto Functionalized sp³‐Carbon

Abstract

We report a novel approach for the bottom-up construction of hybrid organic-inorganic nanocomposites with an intimate arrangement between sp 3 -carbon three-dimensional (3D) molecular-size nanodiamonds (diamondoids) and a coated palladium surface as nanolayers. The construction process is conducted stepwisely from the gas phase, using first controlled vapor-phase self-assembly of taylor-made functionalized diamantane derivatives, followed by low-temperature (45 °C) chemical vapor deposition of an organometallic complex (CVD) in a reducing H 2 atmosphere over the self-assembled diamondoid scaffold. The use of self-assemblies of primary diamantane phosphine and phosphine oxide, which are produced with high structural uniformity and reproducibility, yields new hybrid diamondoid-palladium materials incorporating Pd-O-PHdiamantane bonding motifs. Additional investigations provide evidence for a very challenging issue in the intimate construction of sp 3 -C/metal scaffolds. SEM and TEM microscopies combined with XPS surface analysis and EDX bulk analysis confirm the formation of diamondoid-palladium organohybrid with unique surface layering. The vapor phase-controlled mild synthetic process allows excellent control over nanocomposite formation and morphology from molecular-level modifications. As such, this bottom-up composite building process bridges scales from the molecular (functionalized diamondoids) over nanoscopic (self-assemblies) to microscopic regime (hybrid), in the challenging association of transition metals with an electronically saturated sp 3 -carbon organic host material.

Diamondoid Nanostructures as sp3‐Carbon‐Based Gas Sensors

“…Diamondoids are promising for nanoelectronics, since they exhibit unique effects such as quantum confinement, hence offering possibilities for band gap tuning . Diamondoid derivatives serve as building blocks in “bottom‐up” strategies to build unique sp 3 ‐carbon‐based nanocomposites …”

“…This band‐structure doping inspired approach would combine sp 3 ‐C nanodiamond semiconductors with transition metals. Accordingly, we recently reported robust self‐assemblies of volatile P‐functionalized diamondoids into nanocrystals by mild vapor deposition, followed by Pd nanolayer coating under mild CVD conditions …”

“…The primary phosphine 9‐(hydroxydiamant‐4‐yl)phosphine (H 2 P‐DiamOH, 1 ) and its oxide (H 2 (O)P‐DiamOH, 2 ) were synthesized from diamantane (Figure ; Supporting Information, Figure S1,S2). These diamondoid derivatives were used in powder form, first for their vapor‐phase self‐assembly, then for generating the metal composites Pd@PH 2 ‐DiamOH ( 3 ) and Pd@P(O)H 2 ‐DiamOH ( 4 ), respectively . This was achieved by low‐temperature chemical vapor deposition of a Pd nanolayer over the crystal self‐assembly .…”

“…The nanolayering of palladium over self‐assembled 1 and 2 led to nanocomposites 3 and 4 , respectively, for which scanning electron microscopy views are given in Figure . The self‐assemblies of 1 – 4 were produced with high structural uniformity and reproducibility . The surfaces composition of these materials has been characterized by XPS, showing covalently built robust Pd@diamondoid hybrids that incorporate Pd−O−P(H) n –diamantane binding motifs.…”

“…Consistently, we found that uptake of H 2 was also possible with nanomaterials 1 – 4 , inducing resistance increase (Supporting Information, Figure S12) that confirms the p‐type character of these gas sensors. Using the diamondoid phosphine 5 Cl 2 (O)P–DiamOH, we checked that efficient gas sensing properties were related to the primary phosphine‐based diamantanol compounds. We observed for Cl 2 (O)P–DiamOH‐based materials much lower H 2 uptake (if any) compared to 1 (Supporting Information, Figure S12a).…”