Lifeng Cui

Revealing the Cell–Material Interface with Nanometer Resolution by Focused Ion Beam/Scanning Electron Microscopy

The interface between cells and nonbiological surfaces regulates cell attachment, chronic tissue responses, and ultimately the success of medical implants or biosensors. Clinical and laboratory studies show that topological features of the surface profoundly influence cellular responses; for example, titanium surfaces with nano- and microtopographical structures enhance osteoblast attachment and host-implant integration as compared to a smooth surface. To understand how cells and tissues respond to different topographical features, it is of critical importance to directly visualize the cell-material interface at the relevant nanometer length scale. Here, we present a method for in situ examination of the cell-to-material interface at any desired location, based on focused ion beam milling and scanning electron microscopy imaging to resolve the cell membrane-to-material interface with 10 nm resolution. By examining how cell membranes interact with topographical features such as nanoscale protrusions or invaginations, we discovered that the cell membrane readily deforms inward and wraps around protruding structures, but hardly deforms outward to contour invaginating structures. This asymmetric membrane response (inward vs outward deformation) causes the cleft width between the cell membrane and the nanostructure surface to vary by more than an order of magnitude. Our results suggest that surface topology is a crucial consideration for the development of medical implants or biosensors whose performances are strongly influenced by the cell-to-material interface. We anticipate that the method can be used to explore the direct interaction of cells/tissue with medical devices such as metal implants in the future.

A microfluidic positioning chamber for long-term live-cell imaging.

We report a microfluidic positioning chamber (MPC) that can rapidly and repeatedly relocate the same imaging area on a microscope stage. The “roof” of the microfluidic chamber was printed with serials of coordinate numbers that act as positioning marks for mammalian cells that grow attached to the “floor” of the microfluidic chamber. MPC cell culture chamber provided a simple solution for tracking the same cell or groups of cells over days or weeks. The positioning marks were used to register time‐lapse images of the same imaging area to single‐pixel accuracy. Using MPC cell culture chamber, we tracked the migration, division, and differentiation of individual PC12 cells for over a week using bright field and fluorescence imaging. Microsc. Res. Tech., 2010.

A High-Performance, Low-Tortuosity Wood-Carbon Monolith Reactor

A highly efficient 3D wood-derived carbon monolith reactor with a low tortuosity is demonstrated for high-temperature reaction applications, using catalytic steam reforming of biomass tar as the model system. Outstanding catalytic activity is achieved as the reactant gases flow through this 3D natural wood-derived catalyst, where over 99% toluene conversion and good stability at 700 °C are observed.

Effect of support calcination temperature on Ag structure and catalytic activity for CO oxidation

SiO2 with different nanostructures, namely hexagonal mesoporous silica(HMS), and three unordered commercial silica, were used as supports to fabricate silver catalysts using an incipient wetness impregnation method. It was found that Ag/HMS catalyst showed a high catalytic activity. Next, the HMS support was calcined at different temperatures before impregnation of AgNO3. The effect of calcination temperature of HMS support was investigated in terms of structure and catalytic activity of Ag catalysts. The support and catalysts were characterized by N2 adsorption-desorption isotherms, Thermogravimetric-differential thermal analyzer, X-ray diffraction, H2-temperature program reduction and transmission electron microscopy. The results showed that calcination of HMS at an appropriate temperature(750 °C) before catalyst preparation would benefit the formation of highly dispersive small sized Ag particles on the HMS support and markedly enhance the catalytic activity of Ag/HMS catalyst toward CO oxidation.

Hierarchically mesostructured TiO2/graphitic carbon composite as a new efficient photocatalyst for the reduction of CO2 under simulated solar irradiation

A hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high content of nanocrystalline TiO2 was prepared using a simple one-step nanocasting route. X-ray diffraction, thermogravimetric analysis, nitrogen adsorption–desorption, transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize this photocatalyst. It was observed that the coexistence of silica and graphitic carbon during the high temperature treatment stabilized the crystalline phase and the size of the anatase TiO2 nanocrystals (5–7 nm in diameter), which were uniformly dispersed in the graphitic carbon matrix after silica removal. The obtained hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high specific surface area and a high surface concentration of hydroxyl groups exhibited considerably higher activity in the photocatalytic reduction of CO2 with H2O under simulated solar irradiation compared to mesostructured anatase TiO2 prepared using a sol–gel method.

Efficient Photocatalytic Bilirubin Removal over the Biocompatible Core/Shell P25/g-C 3 N 4 Heterojunctions with Metal-free Exposed Surfaces under Moderate Green Light Irradiation

Highly-monodispersed g-C3N4/TiO2 hybrids with a core/shell structure were synthesized from a simple room temperature impregnation method, in which g-C3N4 was coated through self-assembly on the commercially available Degussa P25 TiO2 nanoparticles. Structural and surface characterizations showed that the presence of g-C3N4 notably affected the light absorption characteristics of TiO2. The g-C3N4/TiO2 heterojunctions with metal-free exposed surfaces were directly used as biocompatible photocatalysts for simulated jaundice phototherapy under low-power green-light irradiation. The photocatalytic activity and stability of g-C3N4/TiO2 were enhanced relative to pure P25 or g-C3N4, which could be ascribed to the effective Z-scheme separation of photo-induced charge carriers in g-C3N4/TiO2 heterojunction. The photoactivity was maximized in the 4 wt.% g-C3N4-coated P25, as the bilirubin removal rate under green light irradiation was more than 5-fold higher than that under the clinically-used blue light without any photocatalyst. This study approves the future applications of the photocatalyst-assisted bilirubin removal in jaundice treatment under moderate green light which is more tolerable by humans.

Surfactant-assisted Nanocasting Route for Synthesis of Highly Ordered Mesoporous Graphitic Carbon and Its Application in CO2 Adsorption

Highly ordered mesoporous graphitic carbon was synthesized from a simple surfactant-assisted nanocasting route, in which ordered mesoporous silica SBA-15 maintaining its triblock copolymer surfactant was used as a hard template and natural soybean oil (SBO) as a carbon precursor. The hydrophobic domain of the surfactant assisted SBO in infiltration into the template’s mesoporous channels. After the silica template was carbonized and removed, a higher yield of highly-ordered graphitic mesoporous carbon with rod-like morphology was obtained. Because of the improved structural ordering, the mesoporous carbon after amine modification could adsorb more CO2 compared with the amine-functionalized carbon prepared without the assistance of surfactant.

Scalable and clean exfoliation of graphitic carbon nitride in NaClO solution: enriched surface active sites for enhanced photocatalytic H2 evolution

Graphitic carbon nitride (g-C3N4) has attracted wide attention as a promising visible-light-driven metal-free semiconductor photocatalyst. The transportation and transformation of photogenerated carriers during the photocatalytic process of g-C3N4 are restricted by the insufficient surface active sites and low charge separation efficiency. As a top-down strategy, the exfoliation of layer-stacked bulk g-C3N4 into nanosheets is widely recognized as an applicable route, yet still challenging in terms of scalable and clean synthesis. Herein, this challenge was tackled via a simple hydrothermal method in NaClO solution, in which the synergetic effect of alkaline metal ion intercalation and the oxidative exfoliation of bulk g-C3N4 was involved. Highly active g-C3N4 nanosheets were easily made in the laboratory in tens of grams and this simple process could readily be extended to the scale of kilograms. The hydrothermal treatment created vertical channels for directional electron transfer and obtained ultrathin holey g-C3N4 nanosheets with remarkable hierarchical porosity and good hydrophilicity. The holey g-C3N4 nanosheets exhibit a high specific surface area (170.7 m2 g−1), a narrow band gap (2.55 eV), a large number of exposed edges, and superior electron transport ability. These holey g-C3N4 nanosheets have an average H2 evolution rate 9 times that of bulk g-C3N4. This green, facile and scalable method to synthesize few-layer g-C3N4 nanosheets affords a new strategy to design and fabricate other functional 2D materials.

Constructing Highly Uniform Onion-Ring-like Graphitic Carbon Nitride for Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution

The introduction of microstructure to the metal-free graphitic carbon nitride (g-C3N4) photocatalyst holds promise in enhancing its catalytic performance. However, producing such microstructured g-C3N4 remains technically challenging due to a complicated synthetic process and high cost. In this study, we develop a facile and in-air chemical vapor deposition (CVD) method that produces onion-ring-like g-C3N4 microstructures in a simple, reliable, and economical manner. This method involves the use of randomly packed 350 nm SiO2 microspheres as a hard template and melamine as a CVD precursor for the deposition of a thin layer of g-C3N4 in the narrow space between the SiO2 microspheres. After dissolution of the microsphere template, the resultant g-C3N4 exhibits uniquely uniform onion-ring-like microstructures. Unlike previously reported g-C3N4 powder morphologies that show various degrees of agglomeration and irregularity, the onion-ring-like g-C3N4 is highly dispersed and uniform. The calculated band gap for onion-ring-like g-C3N4 is 2.58 eV, which is significantly narrower than that of bulk g-C3N4 at 2.70 eV. Experimental characterization and testing suggest that, in comparison with bulk g-C3N4, onion-ring-like g-C3N4 facilitates charge separation, extends the lifetime of photoinduced carriers, exhibits 5-fold higher photocatalytic hydrogen evolution, and shows great potential for photocatalytic applications.

Heterogeneous catalysis of CO 2 -diethanolamine absorption with MgCO 3 and CaCO 3 and comparing to non-catalytic CO 2 -monoethanolamine interactions

The solid catalysts, CaCO3 and MgCO3, were adopted to accelerate CO2 absorption with diethanolamine (DEA) solvent. It turned out that these solid alkaline earth metal carbonates can accelerate CO2 absorption, with overall time reduction up to 14–28% for CaCO3, and 11–28% for MgCO3. After comparing CO2 loadings and time resolved amine concentrations, the solid chemicals can enhance the CO2 absorption of DEA and became compatible with the monoethanolamine (MEA) solution at the same CO2 loading without catalysts. The Lewis base can serve as heterogeneous catalysts for the amine scrubbing process and then facilitate CO2 absorption. These results indicated the heterogeneous catalysts can partly cover the shortage of DEA with CO2 absorption, and facilitate the amine scrubbing process with shorter column with ease.