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Controlled multistep synthesis in a three-phase droplet reactor.

ABSTRACT: Channel-fouling is a pervasive problem in continuous flow chemistry, causing poor product control and reactor failure. Droplet chemistry, in which the reaction mixture flows as discrete droplets inside an immiscible carrier liquid, prevents fouling by isolating the reaction from the channel walls. Unfortunately, the difficulty of controllably adding new reagents to an existing droplet stream has largely restricted droplet chemistry to simple reactions in which all reagents are supplied at the time of droplet formation. Here we describe an effective method for repeatedly adding controlled quantities of reagents to droplets. The reagents are injected into a multiphase fluid stream, comprising the carrier liquid, droplets of the reaction mixture and an inert gas that maintains a uniform droplet spacing and suppresses new droplet formation. The method, which is suited to many multistep reactions, is applied to a five-stage quantum dot synthesis wherein particle growth is sustained by repeatedly adding fresh feedstock.

SUBMITTER: Nightingale AM

PROVIDER: S-EPMC4024758 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Controlled multistep synthesis in a three-phase droplet reactor.

Nightingale Adrian M AM Phillips Thomas W TW Bannock James H JH de Mello John C JC

Nature communications 20140506

Channel-fouling is a pervasive problem in continuous flow chemistry, causing poor product control and reactor failure. Droplet chemistry, in which the reaction mixture flows as discrete droplets inside an immiscible carrier liquid, prevents fouling by isolating the reaction from the channel walls. Unfortunately, the difficulty of controllably adding new reagents to an existing droplet stream has largely restricted droplet chemistry to simple reactions in which all reagents are supplied at the ti ...[more]

PMID: 24797034

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Project description:Despite its complex structure, coal has shown to be a promising precursor for graphene synthesis by chemical vapor deposition (CVD). However, the presence of heteroatoms and aliphatic chains in coal can lead to defects in the graphene lattice, preventing the formation of pristine graphene layers. Therefore, the goal of this study was to formulate a multistep coal fractionation scheme to extract and characterize the most aromatic fractions and explore their potential as graphene precursors. The scheme consisted of direct coal liquefaction under different conditions, Soxhlet extraction with heptane then toluene, and preparative liquid chromatography on silica gel using heptol solutions with different heptane/toluene ratios. The fractions obtained by this process were analyzed by proton nuclear magnetic resonance, thermogravimetric and elemental analyses, and automated SAR-AD (saturates, aromatics, resins-asphaltene determinator) separations. This characterization allowed the identification of two aromatic fractions with and without heteroatoms, which were subsequently used for graphene synthesis by CVD on nickel and copper foils. Raman spectrometry revealed that both fractions primarily formed defect-free multilayered graphene with approximately 11 layers on nickel due to the high solubility of carbon and the defect-healing effect of nickel. On the other hand, these fractions generated amorphous carbon on copper due to the high solubility of hydrogen in copper, which competed with carbon. Molecules in the more aromatic heteroatom-free fraction still contained alkyl pendant substituents and did not share the same planarity and symmetry to form defect-free graphene on copper. Thus, the quality of graphene was governed by the substrate on nickel and by the precursor quality on copper. When deposited directly on lacey carbon-coated copper grids of a transmission electron microscope, the heteroatom-free fraction gave rise to much larger graphene domains. The presence of heteroatoms promoted the formation of small self-assembled agglomerates of amorphous carbon.

Dataset Information

Controlled multistep synthesis in a three-phase droplet reactor.

Publications

Controlled multistep synthesis in a three-phase droplet reactor.

Similar Datasets

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