Coverage Of Functional Groups Research Articles

Unveiling the influence of various vacancies on the mechanical properties of Ti4C3O2

Two-dimensional transition metal carbides and nitrides are widely recognized as potential candidates in areas such as energy storage and sensors. In this work, we explore the mechanical properties of Ti4C3O2 with a perfect cell and Ti4C3O2 with vacancies by a first-principles method. The results indicate that the loss of C in the outer layer of Ti4C3O2 is more likely to occur due to the smaller formation energy of C-vacancy. By considering the charge contribution, the removed atom changes the valence electron equilibrium concentration between that atom and its neighbors, which in turn affects the mechanical properties of Ti4C3O2. The presence of various vacancies affects the strength of the TiO bonds on the shear plane, causing Ti4C3O2 to exhibit changes towards brittleness or ductility. It is noteworthy that the elastic modulus, critical strain, and ideal stress of Ti4C3O2 with different concentrations of O vacancies are all approximately the same, suggesting that the variations in their mechanical properties are not significant for Ti4C3O2 with different degrees of O functional group coverage. Our findings offer valuable insights for the development of MXene-based nanoflexible energy storage devices, gas-sensitive sensors, high-temperature environmental applications, and beyond.

Thermal transport properties of functionalized graphene/palmitic acid phase‐change composites: A molecular dynamics study

AbstractConsidering the importance of high‐performance composite phase change materials (PCMs) for the realization of efficient thermal energy storage, molecular dynamics simulations were conducted in this study to investigate the thermal properties of graphene/palmitic acid composites and the related interfacial thermal transport. The effects of the interactions between functionalized graphene and fatty acids on the thermal transport properties needs to be investigated further. The addition of functionalized graphene (with epoxy, hydroxyl, and carboxyl groups) increased the phase transition temperature and decreased the specific heat capacity of the PCM, whereas both of these parameters increased with increasing functional group coverage (FGC). Further the effects of the FGC and functional group type on the interfacial thermal resistance (ITR) were investigated by analyzing the interaction energy and vibrational density of states, and the ITR decreased with increasing FGC. Compared to that of pure PA, the phase‐transition temperatures of the PA/pristine graphene composites were higher by ~7 K. The ability of functional groups to decrease the ITR decreased in the order of epoxy < hydroxyl < carboxyl at a constant FGC of 10.12%, with the ITR decreasing by 31.26%, 44.77%, and 56.41%, respectively. The obtained insights are expected to facilitate the design of high‐performance energy storage systems based on composites of fatty acids as PCMs.Highlights Thermal transport in functionalized graphene/palmitic acid composites is studied. Effects of functional group type/coverage on composite thermal properties are probed. Molecular dynamics simulations are used for thermal property analysis. The obtained insights promote the design of high‐performance phase‐change materials.

Step-by-step characterization of a series of polyamidoamine dendrons on carbon nanohorn surface

Polyamidoamine (PAMAM) dendrimers/dendrons chemically functionalized on carbon nanohorns (CNHs) have exhibited an excellent ability, especially for energy conversion and gene therapy applications. However, the main issue is its low functional group coverage, and the low reaction yield has been less understood. Here, we examine the surface state and functionalization efficiency of PAMAM dendrons on CNHs in each reaction step. The multifaceted measurements using Raman, ζ potential, and Fourier transform infrared spectroscopy (FT-IR) demonstrate that PAMAM dendrons are successfully synthesized on CNH surfaces. In addition, highly sensitive energy dispersive X-ray spectroscopy in the scanning electron microscope (SEM-EDS) enables precise evaluation of functional group coverage consistent with the chemical structure of each product. Furthermore, the detailed analysis of SEM-EDS imaging, morphology characterization, and FT-IR provides chemical information regarding the reactivity of PAMAM functionalization on CNHs. One important finding is that chemical interaction by hydrogen bonds among PAMAM/CNH molecules is a considerable possibility for low reactivity. Our results are widely beneficial for the realization of highly efficient grafting of PAMAM dendrons on various carbon nanomaterials.

3D-Printed Structure Boosts the Kinetics and Intrinsic Capacitance of Pseudocapacitive Graphene Aerogels.

The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface-functionalized 3D-printed graphene aerogel (SF-3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm-2 at a high current density of 100 mA cm-2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm-2 even at a high mass loading of 12.8 mg cm-2 . Importantly, the kinetic analysis reveals that the capacitance of SF-3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D-printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF-3D GA as anode and 3D-printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm-2 at an ultrahigh power density of 164.5 mW cm-2 , outperforming carbon-based supercapacitors operated at the same power density.

Functional Group Coverage and Conversion Quantification in Nanostructured Silica by 1H NMR

Silica nanostructured materials are important in many fields, including catalysis, imaging, and drug delivery, mainly due to the versatility of surface functionalization that can bestow a huge variety of chemical and physical properties. With most applications requiring precise control over this surface modification, characterization of surface composition and reactivity have become of extreme importance. We present a novel approach to track silica surface modification and quantify functional group coverage using only solution NMR. We test the method using different types of silica nanoparticles and surface modifications, to show that after dissolving the silica matrix, the 1H NMR spectra can be resolved for every single component of the mixture. By using an internal standard, we are able to quantify the density of ligands and follow their sequential modification. Our work presents a fast, accurate, and straightforward method for surface characterization of silica nanostructures, using widely available NMR spectroscopy and small amounts of sample.

Fire Alters Vegetation and Soil Microbial Community in Alpine Meadow

AbstractGrassland fire, as an important ecological factor, is quite influential in determining the structural and functional stability of ecosystem. In this work, the fire‐induced changes on the vegetation and soil microbial community were studied in alpine meadow. Microbial community composition was assessed by phospholipid fatty acid (PLFA) analysis, and functional diversity was determined by Biolog EcoPlate method. Our results showed that burning caused a significant increase in plant functional group coverage, biomass of grasses, soil bulk density and the ratio of roots to soils. Fire also caused an increase in soil pH and a decrease in total soil nutrient contents and soil moisture. The average well colour development of soil microorganism, the microbial functional diversity and the number of carbon source utilisation were also significantly affected by fire. Total bacteria PLFA, Gram‐positive bacteria (G+) PLFA, Gram‐negative bacteria (G−) PLFA and total PLFA of the burnt sites all increased significantly in burnt soil. The BACT/FUNG, SAT/MONO and G+/G− ratio also appeared to be higher in burnt sites. The total PLFA, G+ PLFA and G− PLFA are closely related to the plant community quantitative characteristics and soil nutrients. The total PLFA, bacteria and G+ PLFA are significantly correlated with the soil total nutrients and available nutrients. These results suggest that the ability of soil microorganisms to use a single‐carbon substrate was increased after a fire event. Grassland fire not only has direct impacts on plant community structure and function but also indirectly alters the soil microbial properties because of fire‐induced changes in plant community. Copyright © 2015 John Wiley & Sons, Ltd.

In Situ Fabrication of Low-Friction Sandwich Sheets Through Functionalized Graphene Crosslinked by Ionic Liquids

Graphene is considered a wonder material for fundamental research and industrial application, whereas its poor dispersibility and incompatibility in lubricants have impeded the application for solving lubrication problems. Here, in situ fabrication of effectively functionalized graphene sheets was developed through a moderate electrochemical method for exfoliating graphite into graphene sheets in ionic liquids solution. The as-fabricated graphene sheets with the charged groups of ionic liquids (ILs) could be self-assembled together to form the multilayer sandwich structure through the electrostatic interaction. Self-assembly multilayer graphene (MLG) exhibits so high-density coverage of functional groups that some amorphous regions are formed on the graphene basal plane, which significantly improves its dispersibility and stability in ILs lubricant. Moreover, the functionalized MLG as a novel lubricant additive greatly enhances the friction-reducing and antiwear abilities for the contact of steel/steel (friction coefficient and wear volume lubricated by ILs with MLG at applied load of 200 N and 150 °C were reduced by up to 55.9 and 84.2 %, and under high vacuum were reduced by up to 36 and 94.3 % with pure ILs as a comparison, respectively), which is attributed to the synergies of ILs and MLG because ILs with functionalized MLG can form the physical adsorptive film and tribo-chemical reaction film on the rubbing surface during friction process.

A molecular dynamics simulation study on thermal conductivity of functionalized bilayer graphene sheet

We investigate the thermal conductivity of chemically functionalized bilayer graphene sheet by using molecular dynamics simulations, focusing on the effects of different functional groups and tensile strain. Our simulation results show that chemical functionalization leads to the reduction in the thermal conductivity of bilayer graphene sheet and the reduction is proportional to the coverage of functional groups. Unlike the pristine graphene sheet, the tensile strain can enhance the thermal conductivity of functionalized bilayer graphene sheet. The underlying mechanisms for the thermal conductivity change are elaborated via the vibrational density of states of the graphene sheets.

Electrical control of nanoscale functionalization in graphene by the scanning probe technique

Functionalized graphene is a versatile material that has well-known physical and chemical properties depending on functional groups and their coverage. However, selective control of functional groups on the nanoscale is hardly achievable by conventional methods utilizing chemical modifications. We demonstrate electrical control of nanoscale functionalization of graphene with the desired chemical coverage of a selective functional group by atomic force microscopy (AFM) lithography and their full recovery through moderate thermal treatments. Surprisingly, our controlled coverage of functional groups can reach 94.9% for oxygen and 49.0% for hydrogen, respectively, well beyond those achieved by conventional methods. This coverage is almost at the theoretical maximum, which is verified through scanning photoelectron microscope measurements as well as first-principles calculations. We believe that the present method is now ready to realize ‘chemical pencil drawing’ of atomically defined circuit devices on top of a monolayer of graphene.

UV activation of polymeric high aspect ratio microstructures: ramifications in antibody surface loading for circulating tumor cell selection

The need to activate thermoplastic surfaces using robust and efficient methods has been driven by the fact that replication techniques can be used to produce microfluidic devices in a high production mode and at low cost, making polymer microfluidics invaluable for in vitro diagnostics, such as circulating tumor cell (CTC) analysis, where device disposability is critical to mitigate artifacts associated with sample carryover. Modifying the surface chemistry of thermoplastic devices through activation techniques can be used to increase the wettability of the surface or to produce functional scaffolds to allow for the covalent attachment of biologics, such as antibodies for CTC recognition. Extensive surface characterization tools were used to investigate UV activation of various surfaces to produce uniform and high surface coverage of functional groups, such as carboxylic acids in microchannels of different aspect ratios. We found that the efficiency of the UV activation process is highly dependent on the microchannel aspect ratio and the identity of the thermoplastic substrate. Colorimetric assays and fluorescence imaging of UV-activated microchannels following EDC/NHS coupling of Cy3-labeled oligonucleotides indicated that UV-activation of a PMMA microchannel with an aspect ratio of ~3 was significantly less efficient toward the bottom of the channel compared to the upper sections. This effect was a consequence of the bulk polymer's damping of the modifying UV radiation due to absorption artifacts. In contrast, this effect was less pronounced for COC. Moreover, we observed that after thermal fusion bonding of the device's cover plate to the substrate, many of the generated functional groups buried into the bulk rendering them inaccessible. The propensity of this surface reorganization was found to be higher for PMMA compared to COC. As an example of the effects of material and microchannel aspect ratios on device functionality, thermoplastic devices for the selection of CTCs from whole blood were evaluated, which required the immobilization of monoclonal antibodies to channel walls. From our results, we concluded the CTC yield and purity of isolated CTCs were dependent on the substrate material with COC producing the highest clinical yields for CTCs as well as better purities compared to PMMA.

Electronic Transport Properties of Chemically Modified Double-Walled Carbon Nanotubes

We present a study on the quantum transport properties of chemically functionalized metallic double-walled carbon nanotubes (DWNTs) with lengths reaching the micrometer scale. First-principles calculations evidence that, for coaxial tubes separated by the typical graphitic van der Waals bond distance, the chemical modification of the outer wall with sp3-type defects affects the electronic structure of both the outer and the inner tube, which reduces significantly the charge transport capability of the DWNTs. For larger spacing between sidewalls, the conductivity of the outer wall decreases with increasing functional group coverage density, while charge transport in the inner tube is equivalent to that of a pristine nanotube. Additionally, [2 + 1] cycloaddition of CCl2 onto the outer DWNT sidewall barely affects the hyperconjugated π-network of the double wall, and charge transport remains in the quasi-ballistic regime. These results indicate an efficient route for tailoring electronic transport in DWNTs provided inner shell geometry and grafted functional groups are properly chosen.

A fluorescence based method for the quantification of surface functional groups in closed micro- and nanofluidic channels

Surface analysis is critical for the validation of microfluidic surface modifications for biology, chemistry, and physics applications. However, until now quantitative analytical methods have mostly been focused on open surfaces. Here, we present a new fluorescence imaging method to directly measure the surface coverage of functional groups inside assembled microchannels over a wide dynamic range. A key advance of our work is the elimination of self-quenching to obtain a linear signal even with a high density of functional groups. This method is applied to image the density and monitor the stability of vapor deposited silane layers in bonded silicon/glass micro- and nanochannels.

Modification of multiwall carbon nanotubes with ruthenium(II) terpyridine complex

Multiwall carbon nanotubes (MWCNTs, 1–3 μM in length and 20–25 nm in diameter) were initially functionalized with a 2,2′:6′2″-terpyridine-chelated ruthenium(II) complex by covalent amidation. The resulting functionalized ruthenium MWCNTs (RuMWCNTs, 1–2 μM in length and 10–20 nm in diameter) were characterized by thermogravimetric analysis, X-ray photoelectronic spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM). Thermogravimetric experiments of RuMWCNTs show that the functional group coverage of terpyridine–rutheniun–terpyridine (tpy–Ru–tpy) is 0.7036 mmol/1.0 g carbon. The XPS results show N1s and Ru3d5/5 signals, confirming the presence of tpy–Ru–tpy groups on the surface of MWCNTs. The FTIR spectra of the RuMWCNTs display the typical stretching mode of the carboxyl group (amide I) and a combination of amide N–H and C–N stretching mode (amide II). The Raman D- and G-line peak intensity ratio of RuMWCNTs (ID/IG 2.21) exceeds that of pristine MWCNTs (ID/IG 1.93), suggesting covalent bonding of tpy–Ru–tpy to MWCNTs and supporting the disruption of the graphitic integrity due to the proposed covalent functionalization. High-resolution SEM images confirm that tpy–Ru–tpy moieties are interconnected or attached as aggregated structures (100–200-nm range) on the surfaces of the carbon nanotubes after functionalization. The electrical property of RuMWCNTs depicts higher resistance (10.10 M Ω) than that of OX-MWCNTs (15.38 kΩ).

Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-ray Absorption, Emission, and Photoelectron Spectroscopies

Electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra are compared with the density of states calculated in the frame of the density functional theory. The carbon shell of Ni nanoparticles has been found to be multilayer graphene with significant (about 6%) amount of Stone--Wales defects. Results of the experiments evidence protection of the metallic nanoparticles from the environmental degradation by providing a barrier against oxidation at least for two years. Exposure in air for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles with coverage of functional groups.

Influence of chemisorption on the thermal conductivity of graphene nanoribbons

The thermal conductivity of graphene nanoribbons (GNRs) functionalized by the chemical attachment of methyl and phenyl groups at random positions is calculated using reverse nonequilibrium molecular dynamics. The GNRs exhibit a rapid drop in thermal conductivity with increasing degree of functionalization; a functional group coverage regime of as little as 1.25% of GNR atoms reduces the thermal conductivity by about 50%. The thermal conductivity of nanoribbons with zigzag edges is more sensitive in the degree of functionalization than nanoribbons with armchair edges. The simulation results indicate that the rapid drop in thermal conductivity is a consequence of the higher angular momentum of functional groups, which rotate the unsupported sp 3 bonds and thus reduce the phonon mean free paths.

Uniform and monodisperse polysilsesquioxane hollow spheres: synthesis from aqueous solution and use in pollutant removal

A series of organofunctional polysilsesquioxane hollow spheres were prepared by an environment-friendly method. The use of this simple and reproducible synthetic approach resulted in highly uniform and monodisperse hollow spheres with high coverage of functional groups, namely, fluoroalkyl, phenyl, vinyl and methyl groups. By adjusting the precursor concentration, the particle size and shell thickness could be precisely controlled. The structure and functionality of these hollow spheres were characterized by field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, solid-state NMR spectroscopy, X-ray diffraction and nitrogen adsorption–desorption studies. These materials were used as adsorbents to treat the benzophenone-containing wastewater, and it was found that the hydrophobic contaminants could be effectively removed. The hydrophobic surface property of the polysilsesquioxane hollow spheres was found to be an important factor that influences the adsorption capacity.

Community structure and composition in response to climate change in a temperate steppe

Climate change would have profound influences on community structure and composition, and subsequently has impacts on ecosystem functioning and feedback to climate change. A field experiment with increased temperature and precipitation was conducted to examine effects of experimental warming, increased precipitation and their interactions on community structure and composition in a temperate steppe in northern China since April 2005. Increased precipitation significantly stimulated species richness and coverage of plant community. In contrast, experimental warming markedly reduced species richness of grasses and community coverage. Species richness was positively dependent upon soil moisture (SM) across all treatments and years. Redundancy analysis (RDA) illustrated that SM dominated the response of community composition to climate change at the individual level, suggesting indirect effects of climate change on plant community composition via altering water availability. In addition, species interaction also mediated the responses of functional group coverage to increased precipitation and temperature. Our observations revealed that both abiotic (soil water availability) and biotic (interspecific interactions) factors play important roles in regulating plant community structure and composition in response to climate change in the semiarid steppe. Therefore these factors should be incorporated in model predicting terrestrial vegetation dynamics under climate change.

Different factors’ effect on the SWNT-fluorocarbon resin interaction: A MD simulation study

Molecular mechanics (MM) and molecular dynamics (MD) simulations are conducted to investigate the influence of four different factors, namely temperature, chirality, radius and surface chemical modification, on the interaction between single-walled carbon nanotubes (SWNTs) and three fluorocarbon resins: PVF, PVDF, and PTFE. The results show that the interactions between the SWNTs and fluorocarbon resins are not influenced by temperature and chirality but strongly depend on the radius of SWNTs with the interactions increasing monotonously with the radius. Also the surface chemical modification on the SWNTs has a great effect on the interaction between the nanotubes and the fluorocarbon resins. Among five kinds of functional groups: methyl, amidogen, hydroxyl, –F and carboxyl, the three fluorocarbon resins can only adhere onto the SWNTs modified by methyl. The interactions between the SWNTs and the fluorocarbon resins are observed to increase with increasing functional group coverage. However, in the case for PTFE, an optimum functional group coverage is found beyond which the interactions decrease again. In addition, the ability of the PTFE to adsorb onto the methylic SWNTs is weaker than that of the other two resins due to its non-adhesive nature.

Modification of MCM-41 by Surface Silylation with Trimethylchlorosilane and Adsorption Study

Siliceous MCM-41 samples were modified by silylation using trimethylchlorosilane (TMCS). The surface coverage of functional groups was studied systematically in this work. The role of surface silanol groups during modification was evaluated using techniques of FTIR and 29Si CP/MAS NMR. Adsorption of water and benzene on samples of various hydrophobicities was measured and compared. It was found that the maximum degree of surface attachments of trimethylsilyl (TMS) groups was about 85%, corresponding to the density of TMS groups of 1.9 per nm2. The degree of silylation is found to linearly increase with increasing pre-outgassing temperature prior to silylation. A few types of silanol groups exist on MCM-41 surfaces, among which both free and geminal ones are responsible for active silylation. Results of water adsorption show that aluminosilicate MCM-41 materials are more or less hydrophilic, giving a type IV isotherm, similar to that of nitrogen adsorption, whereas siliceous MCM-41 are hydrophobic, exhibiting a type V adsorption isotherm. The fully silylated Si−MCM-41 samples are more hydrophobic, giving a type III adsorption isotherm. Benzene adsorption on all MCM-41 samples shows type IV isotherms regardless of the surface chemistry. Capillary condensation occurs at a higher relative pressure for the silylated MCM-41 than that for the unsilylated sample, though the pore diameter was found reduced markedly by silylation. This is thought attributed to the diffusion constriction posed by the attached TMS groups. The results show that the surface chemistry plays an important role in water adsorption, whereas benzene adsorption is predominantly determined by the pore geometry of MCM-41.