Publications by authors named "Liang Shi-Li"

Improving the energy efficiency of electrocatalytic reduction of CO requires tuning of redox properties of electrocatalysts to match redox potentials of the substrate. Recently, we introduced nanographenes as ligands for metal complexes for such purposes by taking advantage of size-dependent properties of the conjugated systems. Here, we use computations to investigate the structure dependence of the electrocatalysis at Re(diimine)(CO)Cl complexes with nanographene ligands that contain a polycyclic aromatic hydrocarbon moiety through a pyrazinyl linkage.

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Large conjugated carbon framework has been incorporated as the diimine ligand for Re(α-diimine)(CO)Cl complexes with a pyrazinyl linkage, either to increase energy efficiency or to turn them into heterogeneous catalysts for selective electrocatalytic CO reduction. However, there exists a nonmonotonic dependence of CO reduction overpotential on the conjugation size of the ligands. Understanding its origin could facilitate heterogenization of molecular catalysts with improved energy efficiency.

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We present a novel and systematic fragmentation scheme to treat polycyclic aromatic hydrocarbons (PAHs) built off the molecules-in-molecules composite method. Our algorithm generates a set of biphenyl and naphthalene subsystems overlapping by whole sextet rings, ensuring all calculations are performed on aromatic molecules. Hence, our method is called Aromatic Fragmentation Based on a Ring Overlap Scheme (AroBOROS), and the generated fragments may be combined to form a hierarchy of subsystems to reduce errors for more complex PAHs.

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Improving energy efficiency of electrocatalytic CO conversion to useful chemicals poses a significant scientific challenge. Recently we reported on using a colloidal nanographene as the diimine ligand to form a molecular complex Re(diimine)(CO)Cl to tackle this challenge, leading to significantly improved CO reduction potential. In this work, we use theoretical computations to investigate the roles of the nanographene ligand in the reduction and the reaction pathways.

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Graphite monofluoride (GF) can undergo reductive defluorination in the presence of weak, non-nucleophilic reductants. This leads to a new approach to GF-polyaniline composites as cathode materials for significantly improving the discharge capacity of primary lithium batteries. We postulate that the reduction is mediated by residual π-bonds in GF.

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Improving energy efficiency of electrocatalytic and photocatalytic CO conversion to useful chemicals poses a significant scientific challenge. We report on using a colloidal nanographene to form a molecular complex with a metal ion to tackle this challenge. In this work, a well-defined nanographene-Re complex was synthesized, in which electron delocalization over the nanographene and the metal ion significantly decreases the electrical potential needed to drive the chemical reduction.

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Nitrogen-doped graphitic carbon materials have been extensively studied as potential replacements for Pt-based electrocatalysts for the oxygen reduction reaction (ORR). However, little is known about the catalytic mechanisms, including the parameters that determine the selectivity of the reaction. By comparing theoretical calculations of the ORR selectivity at a well-defined graphene nanostructure with experimental results, we propose a model based on interfacial solvation to explain the observed preference for the four-electron pathway in alkaline electrolytes.

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Graphene fluorination with XeF2 is an attractive method to introduce a nonzero bandgap to graphene under mild conditions for potential electro-optical applications. Herein, we use well-defined graphene nanostructures as a model system to study the reaction mechanism of graphene fluorination by XeF2. Our combined experimental and theoretical studies show that the reaction can proceed through a radical cation mechanism, leading to fluorination and sp(3)-hybridized carbon in the basal plane.

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We present transient absorption measurements and microscopic theory of biexciton binding in triangular colloidal graphene quantum dots consisting of 168 sp(2)-hybridized C atoms. We observe optical transitions from the lowest orbitally dark singlet exciton states to states below the energy of an unbound dark+bright singlet-exciton pair. Through microscopic calculations of the low-energy exciton and biexciton states via tight-binding, Hartree-Fock, and configuration interaction methods, the spectra reveal a biexciton consisting primarily of a dark-bright singlet-pair bound by ∼0.

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We measure biexciton Auger recombination (AR) in colloidal graphene quantum dots (GQDs) by transient absorption spectroscopy. AR is reflected in GQDs with 132 and 168 sp2-hybridized C atoms as a decay with a ∼0.3  ps time constant and an amplitude depending superlinearly on pump fluence.

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Nitrogen-doped graphitic carbon has been intensively studied for potential use as an electrocatalyst in fuel cells for the oxygen reduction reaction (ORR). However, the lack of a mechanistic understanding on the carbon catalysis has severely hindered the progress of the catalyst development. Herein we use a well-defined graphene nanostructure as a model system and, for the first time, reveal an oxygen activation mechanism that involves carbanion intermediates in these materials.

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The Shockley-Queisser limit is the maximum power conversion efficiency of a conventional solar cell based on a single semiconductor junction. One approach to exceed this limit is to harvest hot electrons/holes that have achieved quasi-equilibrium in the light absorbing material with electronic temperatures higher than the phonon temperature. We argue that graphene based materials are viable candidates for hot carrier chromophores.

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When the size of a semiconductor crystal is reduced to the nanometer scale, the crystal boundary significantly modifies electron distribution, making properties such as bandgap and energy relaxation dynamics size dependent. This phenomenon, known as quantum confinement, has been demonstrated in many semiconductor materials, leading to practical applications in areas such as bioimaging, photovoltaics, and light-emitting diodes. Graphene, a unique type of semiconductor, is a two-dimensional crystal with a zero bandgap and a zero effective mass of charge carriers.

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Nitrogen doping has been a powerful way to modify the properties of carbon materials ranging from activated carbon to graphene. Here we report on a solution chemistry approach to nitrogen-doped colloidal graphene quantum dots with well-defined structures. N-doping was demonstrated to significantly affect the properties of the quantum dots, including the emergence of size-dependent electrocatalytic activity for the oxygen reduction reaction.

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Metal particles supported by carbon materials are important for various technologies yet not well understood. Here, we report on the use of well-defined colloidal graphene quantum dots as a model system for the carbon materials to study metal-carbon interaction. In the case of palladium, our studies show high affinity between the metal nanoparticles with the graphene.

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Article Synopsis
  • The study aimed to assess the impact of a comprehensive control program for clonorchiasis in Yangshan County to promote effective practices.
  • Five areas within the county were randomly chosen for the investigation and implemented health education and infection control measures.
  • Results showed a significant reduction in the infection rate of Clonorchis sinensis from 14.01% in 2006 to 6.87% in 2009, surpassing the national goal of a 40% decrease.
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The band gap and redox potential of semiconductor nanocrystals are two quantities of primary importance for their applications in energy conversion devices. Herein, we report on covalent functionalization of colloidal graphene quantum dots through a solution-chemistry approach and studies of their band gaps and redox potentials. We show that their band gaps and redox potentials can be independently controlled, the former by size and the latter by functionalization.

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Controlling the orientation of nanostructures with anisotropic shapes is essential for taking advantage of their anisotropic electrical, optical, and transport properties in electro-optical devices. For large-area alignment of nanocrystals, so far orientations are mostly induced and controlled by external physical parameters, such as applied fields or changes in concentration. Herein we report on assemblies of colloidal graphene quantum dots, a new type of disk-shaped nanostructures, on polar surfaces and the control of their orientations.

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Reducing hot-carrier relaxation rates is of great significance in overcoming energy loss that fundamentally limits the efficiency of solar energy utilization. Semiconductor quantum dots are expected to have much slower carrier cooling because the spacing between their discrete electronic levels is much larger than phonon energy. However, the slower carrier cooling is difficult to observe due to the existence of many competing relaxation pathways.

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Electronic relaxation in photoexcited graphenes is central to their photoreactivity and their optoelectrical applications such as photodetectors and solar cells. Herein we report on the first ensemble studies of electronic energy relaxation pathways in colloidal graphene quantum dots with uniform size. We show that the photoexcited graphene quantum dots have a significant probability of relaxing into triplet states and emit both phosphorescence and fluorescence at room temperature, with relative intensities depending on the excitation energy.

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We report a solution-chemistry-based approach to large, stable colloidal graphene quantum dots with uniform size and shape. The versatility of solution chemistry allows us to tune the structures of the graphenes and thus their properties.

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Graphenes have very attractive properties for photovoltaics. Their tunable bandgap and large optical absorptivity are desirable for efficient light harvesting. Their electronic levels and interfacing with other materials for charge transfer processes can both be tuned with well-developed carbon chemistry.

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A new type of voltage-sensitive dye is proposed based on the electric-field dependence of electron transfer. These dyes contain an electron donor-acceptor pair in which intramolecular electron transfer competes with fluorescence emission, converting changes in electric field to those in fluorescence intensity. With electron-transfer distance of nanometers, theoretical analysis shows that these dyes can have high sensitivity to neuron action potentials with high fluorescence quantum yield, allowing for fast optical neuroimaging with large signal-to-noise ratio.

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Novel hybrid materials containing silicate and charged oligo(p-phenylene vinylene) (OPV) amphiphiles were fabricated in one step by spin casting using evaporation-induced self assembly. The conjugated segments were substituted with trimethylammonium bromide groups at both termini, and tetraethyl orthosilicate served as the silicate precursor. X-ray diffraction scans of the hybrid films revealed Bragg diffraction peaks with d-spacings of 2.

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