27 research outputs found
A general route via formamide condensation to prepare atomically dispersed metal-nitrogen-carbon electrocatalysts for energy technologies
Single-atom electrocatalysts (SAECs) have gained tremendous attention due to their unique active sites and strong metal–substrate interactions. However, the current synthesis of SAECs mostly relies on costly precursors and rigid synthetic conditions and often results in very low content of single-site metal atoms. Herein, we report an efficient synthesis method to prepare metal–nitrogen–carbon SAECs based on formamide condensation and carbonization, featuring a cost-effective general methodology for the mass production of SAECs with high loading of atomically dispersed metal sites. The products with metal inclusion were termed as formamide-converted metal–nitrogen–carbon (shortened as f-MNC) materials. Seven types of single-metallic f-MNC (Fe, Co, Ni, Mn, Zn, Mo and Ir), two bi-metallic (ZnFe and ZnCo) and one tri-metallic (ZnFeCo) SAECs were synthesized to demonstrate the generality of the methodology developed. Remarkably, these f-MNC SAECs can be coated onto various supports with an ultrathin layer as pyrolysis-free electrocatalysts, among which the carbon nanotube-supported f-FeNC and f-NiNC SAECs showed high performance for the O2 reduction reaction (ORR) and the CO2 reduction reaction (CO2RR), respectively. Furthermore, the pyrolysis products of supported f-MNC can still render isolated metallic sites with excellent activity, as exemplified by the bi-metallic f-FeCoNC SAEC, which exhibited outstanding ORR performance in both alkaline and acid electrolytes by delivering ∼70 and ∼20 mV higher half-wave potentials than that of commercial 20 wt% Pt/C, respectively. This work offers a feasible approach to design and manufacture SAECs with tuneable atomic metal components and high density of single-site metal loading, and thus may accelerate the deployment of SAECs for various energy technology applications
Direct Evidence for Coupled Surface and Concentration Quenching Dynamics in Lanthanide-Doped Nanocrystals
Luminescence quenching
at high dopant concentrations generally
limits the dopant concentration to less than 1–5 mol% in lanthanide-doped
materials, and this remains a major obstacle in designing materials
with enhanced efficiency/brightness. In this work, we provide direct
evidence that the major quenching process at high dopant concentrations
is the energy migration to the surface (i.e., surface quenching) as
opposed to the common misconception of cross-relaxation between dopant
ions. We show that after an inert epitaxial shell growth, erbium (Er<sup>3+</sup>) concentrations as high as 100 mol% in NaYÂ(Er)ÂF<sub>4</sub>/NaLuF<sub>4</sub> core/shell nanocrystals enhance the emission intensity
of both upconversion and downshifted luminescence across different
excitation wavelengths (980, 800, and 658 nm), with negligible concentration
quenching effects. Our results highlight the strong coupling of concentration
and surface quenching effects in colloidal lanthanide-doped nanocrystals,
and that inert epitaxial shell growth can overcome concentration quenching.
These fundamental insights into the photophysical processes in heavily
doped nanocrystals will give rise to enhanced properties not previously
thought possible with compositions optimized in bulk
In Vivo Fluorescence Imaging in the Second Near-Infrared Window with Long Circulating Carbon Nanotubes Capable of Ultrahigh Tumor Uptake
Cancer imaging requires selective high accumulation of
contrast
agents in the tumor region and correspondingly low uptake in healthy
tissues. Here, by making use of a novel synthetic polymer to solubilize
single-walled carbon nanotubes (SWNTs), we prepared a well-functionalized
SWNT formulation with long blood circulation (half-life of ∼30
h) in vivo to achieve ultrahigh accumulation of ∼30% injected
dose (ID)/g in 4T1 murine breast tumors in Balb/c mice. Functionalization
dependent blood circulation and tumor uptake were investigated through
comparisons with phospholipid-PEG solubilized SWNTs. For the first
time, we performed video-rate imaging of tumors based on the intrinsic
fluorescence of SWNTs in the second near-infrared (NIR-II, 1.1–1.4
μm) window. We carried out dynamic contrast imaging through
principal component analysis (PCA) to immediately pinpoint the tumor
within ∼20 s after injection. Imaging over time revealed increasing
tumor contrast up to 72 h after injection, allowing for its unambiguous
identification. The 3D reconstruction of the SWNTs distribution based
on their stable photoluminescence inside the tumor revealed a high
degree of colocalization of SWNTs and blood vessels, suggesting enhanced
permeability and retention (EPR) effect as the main cause of high
passive tumor uptake of the nanotubes
In Vivo Fluorescence Imaging in the Second Near-Infrared Window with Long Circulating Carbon Nanotubes Capable of Ultrahigh Tumor Uptake
Cancer imaging requires selective high accumulation of
contrast
agents in the tumor region and correspondingly low uptake in healthy
tissues. Here, by making use of a novel synthetic polymer to solubilize
single-walled carbon nanotubes (SWNTs), we prepared a well-functionalized
SWNT formulation with long blood circulation (half-life of ∼30
h) in vivo to achieve ultrahigh accumulation of ∼30% injected
dose (ID)/g in 4T1 murine breast tumors in Balb/c mice. Functionalization
dependent blood circulation and tumor uptake were investigated through
comparisons with phospholipid-PEG solubilized SWNTs. For the first
time, we performed video-rate imaging of tumors based on the intrinsic
fluorescence of SWNTs in the second near-infrared (NIR-II, 1.1–1.4
μm) window. We carried out dynamic contrast imaging through
principal component analysis (PCA) to immediately pinpoint the tumor
within ∼20 s after injection. Imaging over time revealed increasing
tumor contrast up to 72 h after injection, allowing for its unambiguous
identification. The 3D reconstruction of the SWNTs distribution based
on their stable photoluminescence inside the tumor revealed a high
degree of colocalization of SWNTs and blood vessels, suggesting enhanced
permeability and retention (EPR) effect as the main cause of high
passive tumor uptake of the nanotubes
In Vivo Fluorescence Imaging in the Second Near-Infrared Window with Long Circulating Carbon Nanotubes Capable of Ultrahigh Tumor Uptake
Cancer imaging requires selective high accumulation of
contrast
agents in the tumor region and correspondingly low uptake in healthy
tissues. Here, by making use of a novel synthetic polymer to solubilize
single-walled carbon nanotubes (SWNTs), we prepared a well-functionalized
SWNT formulation with long blood circulation (half-life of ∼30
h) in vivo to achieve ultrahigh accumulation of ∼30% injected
dose (ID)/g in 4T1 murine breast tumors in Balb/c mice. Functionalization
dependent blood circulation and tumor uptake were investigated through
comparisons with phospholipid-PEG solubilized SWNTs. For the first
time, we performed video-rate imaging of tumors based on the intrinsic
fluorescence of SWNTs in the second near-infrared (NIR-II, 1.1–1.4
μm) window. We carried out dynamic contrast imaging through
principal component analysis (PCA) to immediately pinpoint the tumor
within ∼20 s after injection. Imaging over time revealed increasing
tumor contrast up to 72 h after injection, allowing for its unambiguous
identification. The 3D reconstruction of the SWNTs distribution based
on their stable photoluminescence inside the tumor revealed a high
degree of colocalization of SWNTs and blood vessels, suggesting enhanced
permeability and retention (EPR) effect as the main cause of high
passive tumor uptake of the nanotubes
Covalent Hybrid of Spinel Manganese–Cobalt Oxide and Graphene as Advanced Oxygen Reduction Electrocatalysts
Through direct nanoparticle nucleation and growth on
nitrogen doped,
reduced graphene oxide sheets and cation substitution of spinel Co<sub>3</sub>O<sub>4</sub> nanoparticles, a manganese–cobalt spinel
MnCo<sub>2</sub>O<sub>4</sub>/graphene hybrid was developed as a highly
efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline
conditions. Electrochemical and X-ray near-edge structure (XANES)
investigations revealed that the nucleation and growth method for
forming inorganic–nanocarbon hybrids results in covalent coupling
between spinel oxide nanoparticles and N-doped reduced graphene oxide
(N-rmGO) sheets. Carbon K-edge and nitrogen K-edge XANES showed strongly
perturbed C–O and C–N bonding in the N-rmGO sheet, suggesting
the formation of C–O–metal and C–N–metal
bonds between N-doped graphene oxide and spinel oxide nanoparticles.
Co L-edge and Mn L-edge XANES suggested substitution of Co<sup>3+</sup> sites by Mn<sup>3+</sup>, which increased the activity of the catalytic
sites in the hybrid materials, further boosting the ORR activity compared
with the pure cobalt oxide hybrid. The covalently bonded hybrid afforded
much greater activity and durability than the physical mixture of
nanoparticles and carbon materials including N-rmGO. At the same mass
loading, the MnCo<sub>2</sub>O<sub>4</sub>/N-graphene hybrid can outperform
Pt/C in ORR current density at medium overpotentials with stability
superior to Pt/C in alkaline solutions
Ag<sub>2</sub>S Quantum Dot: A Bright and Biocompatible Fluorescent Nanoprobe in the Second Near-Infrared Window
Ag<sub>2</sub>S quantum dots (QDs) emitting in the second near-infrared region (NIR-II, 1.0–1.4 μm) are demonstrated as a promising fluorescent probe with both bright photoluminescence and high biocompatibility for the first time. Highly selective <i>in vitro</i> targeting and imaging of different cell lines are achieved using biocompatible NIR-II Ag<sub>2</sub>S QDs with different targeting ligands. The cytotoxicity study illustrates the Ag<sub>2</sub>S QDs with negligible effects in altering cell proliferation, triggering apoptosis and necrosis, generating reactive oxygen species, and causing DNA damage. Our results have opened up the possibilities of using these biocompatible Ag<sub>2</sub>S QDs for <i>in vivo</i> anatomical imaging and early stage tumor diagnosis with deep tissue penetration, high sensitivity, and elevated spatial and temporal resolution owing to their high emission efficiency in the unique NIR-II imaging window
Ultra-Low Doses of Chirality Sorted (6,5) Carbon Nanotubes for Simultaneous Tumor Imaging and Photothermal Therapy
Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic fluorescence and strong optical absorption in the near-infrared (NIR) biological window (0.7–1.4 μm), rendering them ideal for <i>in vivo</i> imaging and photothermal therapy. Advances in SWCNT sorting have led to improved nanoelectronics and are promising for nanomedicine. To date, SWCNTs used <i>in vivo</i> consist of heterogeneous mixtures of nanotubes and only a small subset of chirality nanotubes fluoresces or heats under a NIR laser. Here, we demonstrate that separated (6,5) SWCNTs exchanged into a biocompatible surfactant, C<sub>18</sub>-PMH-mPEG, are more than 6-fold brighter in photoluminescence on the per mass basis, afford clear tumor imaging, and reach requisite photothermal tumor ablation temperatures with a >10-fold lower injected dose than as-synthesized SWCNT mixtures while exhibiting relatively low (6,5) accumulation in the reticuloendothelial system. The intravenous injection of ∼4 μg of (6,5) SWCNTs per mouse (0.254 mg/kg) for dual imaging/photothermal therapy is, by far, the lowest reported dose for nanoparticle-based <i>in vivo</i> therapeutics
Chirality Enriched (12,1) and (11,3) Single-Walled Carbon Nanotubes for Biological Imaging
The intrinsic band gap photoluminescence of semiconducting
single-walled
carbon nanotubes (SWNTs) makes them promising biological imaging probes
in the second near-infrared (NIR-II, 1.0–1.4 μm) window.
Thus far, SWNTs used for biological applications have been a complex
mixture of metallic and semiconducting species with random chiralities,
preventing simultaneous resonant excitation of all semiconducting
nanotubes and emission at a single well-defined wavelength. Here,
we developed a simple gel filtration method to enrich semiconducting
(12,1) and (11,3) SWNTs with identical resonance absorption at ∼808
nm and emission near ∼1200 nm. The chirality sorted SWNTs showed
∼5-fold higher photoluminescence intensity under resonant excitation
of 808 nm than unsorted SWNTs on a per-mass basis. Real-time <i>in vivo</i> video imaging of whole mouse body and tumor vessels
was achieved using a ∼6-fold lower injected dose of (12,1)
and (11,3) SWNTs (∼3 μg per mouse or ∼0.16 mg/kg
of body weight vs 1.0 mg/kg for unsorted SWNTs) than a previous heterogeneous
mixture, demonstrating the first resonantly excited and chirality
separated SWNTs for biological imaging
Historical Essay on Agriculture and Rural Life -Michigan
Historical essay describing Michigan's agriculture and rural life. Provided by Michigan State University as part of “Preserving the History of United States Agriculture and Rural Life: State and Local Literature, 1820-1945, a proposal submitted to the National Endowment for the Humanities, Division of Preservation and Access on behalf of the United States Agricultural Information Network (USAIN)National Endowment for the Humanities (NEH), Division of Preservation and Acces