Showing papers on "Surface modification published in 2016"

Covalent functionalization and passivation of exfoliated black phosphorus via aryl diazonium chemistry

Abstract: Functionalization of atomically thin nanomaterials enables the tailoring of their chemical, optical and electronic properties. Exfoliated black phosphorus (BP)-a layered two-dimensional semiconductor-exhibits favourable charge-carrier mobility, tunable bandgap and highly anisotropic properties, but it is chemically reactive and degrades rapidly in ambient conditions. Here we show that covalent aryl diazonium functionalization suppresses the chemical degradation of exfoliated BP even after three weeks of ambient exposure. This chemical modification scheme spontaneously forms phosphorus-carbon bonds, has a reaction rate sensitive to the aryl diazonium substituent and alters the electronic properties of exfoliated BP, ultimately yielding a strong, tunable p-type doping that simultaneously improves the field-effect transistor mobility and on/off current ratio. This chemical functionalization pathway controllably modifies the properties of exfoliated BP, and thus improves its prospects for nanoelectronic applications.

Photoinduced charge transfer processes in solar photocatalysis based on modified TiO2

Abstract: High efficiency solar photocatalysis requires an effective separation of photogenerated charge carriers and their rapid transport to the semiconductor interface. The mechanisms and kinetics of charge separation and interfacial/interparticle charge transfers (CT) are significantly influenced by both the bulk and surface properties of the semiconductor. The surface properties are particularly important because the photocatalysis should be driven by the interfacial CT. The most popular and the most investigated semiconductor photocatalyst is based on bare and modified TiO2. This article highlights the interfacial and interparticle CTs under the bandgap excitation of TiO2 particles, visible light-induced photochemical processes via either dye-sensitization or ligand-to-metal CTs at surface modified TiO2 particles, and the applications of the photo-processes to pollutant degradation and simultaneous hydrogen production. While a variety of surface modification techniques using various nanomaterials and chemical reagents have been developed and tested so far, their effects are very diverse depending on the characteristics of the applied photocatalytic systems and even contradictory in some cases. Better understanding of how the modification influences the photoinduced CT events in semiconductors is required, particularly for designing hybrid photocatalysts with controlled CTs, which is sought-after for practical applications of photocatalysis.

Improving the functionality of carbon nanodots: doping and surface functionalization

Abstract: Distinct from conventional carbon nanostructures, such as fullerene, graphene, and carbon nanotubes, carbon nanodots (C-dots) exhibit unique properties such as strong fluorescence, high photostability, chemical inertness, low toxicity, and biocompatibility. Various synthesis routes for C-dots have been developed in the last few years, and now intense research efforts have been focused on improving their functionality. In this aspect, doping and surface functionalization are two major ways to control the chemical, optical, and electrical properties of C-dots. Doping introduces atomic impurities into C-dots to modulate their electronic structure, and surface functionalization modifies the C-dot surface with functional molecules or polymers. In this review, we summarize recent progress in doping and surface functionalization of C-dots for improving their functionality, and offer insight into controlling the properties of C-dots for a variety of applications ranging from biomedicine to optoelectronics to energy.

Improvement of Gas-Sensing Performance of Large-Area Tungsten Disulfide Nanosheets by Surface Functionalization

Abstract: Semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) are promising gas-sensing materials due to their large surface-to-volume ratio. However, their poor gas-sensing performance resulting from the low response, incomplete recovery, and insufficient selectivity hinders the realization of high-performance 2D TMDC gas sensors. Here, we demonstrate the improvement of gas-sensing performance of large-area tungsten disulfide (WS2) nanosheets through surface functionalization using Ag nanowires (NWs). Large-area WS2 nanosheets were synthesized through atomic layer deposition of WO3 followed by sulfurization. The pristine WS2 gas sensors exhibited a significant response to acetone and NO2 but an incomplete recovery in the case of NO2 sensing. After AgNW functionalization, the WS2 gas sensor showed dramatically improved response (667%) and recovery upon NO2 exposure. Our results establish that the proposed method is a promising strategy to improve 2D TMDC gas sensors.

Manipulation of Amorphous-to-Crystalline Transformation: Towards the Construction of Covalent Organic Framework Hybrid Microspheres with NIR Photothermal Conversion Ability

Abstract: An approach to transforming amorphous organic networks into crystalline covalent organic frameworks (COFs) with retention of the colloidal nanosize and uniform morphology is presented. Specifically, Fe3O4 nanoclusters are encapsulated by a disordering polyimine network via the Schiff-base reaction. The formed imine bonds could be reconstructed under thermodynamic control to reform the polyimine networks into imine-linked COFs in situ. Such a core–shell microsphere exhibits the uniform size and spherical shape, controllable COF shell thickness, accessible surface modification, and improved solution dispersibility as well as maintenance of high surface area, periodic micropores, and superior magnetic responsiveness. Additionally, the photothermal conversion effect is demonstrated for the first time on the nanoCOF layers upon exposure to near infrared light, providing convincing evidence for potential use in phototherapy.

Carbon dots: surface engineering and applications

Abstract: Carbon dots have attracted a great deal of attention because of their high performance, cheap and facile preparation, and potential applications in a wide area. In order to broaden their applications, especially to meet specific requirements, surface engineering, including tailoring surface functional group coating and subsequent chemical modification as required, is an effective strategy for further functionalization of carbon dots. In this article, representative approaches to coating the surface with various functional groups, and strategies for conjugating specific materials onto the surface of carbon dots for functional modification via covalent bonds, electrostatic interactions and hydrogen bonds are highlighted, as well as the results from explorations of their various applications in target modulated sensing, accurate drug delivery and bioimaging at high resolution.

Void Engineering in Metal-Organic Frameworks via Synergistic Etching and Surface Functionalization

Abstract: The rational design and engineering of metal–organic framework (MOF) crystals with hollow features has been used for various applications. Here, a top-down strategy is established to construct hollow MOFs via synergistic etching and surface functionalization by using phenolic acid. The macrosized cavities are created inside various types of MOFs without destroying the parent crystalline framework, as evidenced by electron microscopy and X-ray diffraction. The modified MOFs are simultaneously coated by metal–phenolic films. This coating endows the MOFs with the additional functionality of responding to near infrared irradiation to produce heat for potential photothermal therapy applications.

Comparative tribological and corrosion resistance properties of epoxy composite coatings reinforced with functionalized fullerene C60 and graphene

Abstract: This study investigated the effects of incorporation of two different shapes functionalization fullerene C60 (FC60) and functionalization graphene (FG), into the polymer matrix on the tribological and anti-corrosion performances of epoxy coating. The structural and morphological characterization was examined using Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. It was found that the functional groups had been grafted on the surface of C60 and G. The tribological and anti-corrosion results indicated that composite coatings showed a lower friction coefficient, wear traces area and higher anti-corrosion in comparison with neat epoxy, owing to the balance of reinforcement, lubrication and barrier properties of nanofillers and cracks generated by them, and optimal additive concentration of FC60 and FG both were 0.5 wt.%. Furthermore, this work opens up that FC60/EP coatings exhibited better tribological performance but worse corrosion resistance ability compared with FG/EP coatings due to the different shapes of nanofillers. Different tribological and anti-corrosion mechanisms were analyzed in details.

Molecular surface functionalization to enhance the power output of triboelectric nanogenerators

Abstract: Triboelectric nanogenerators (TENGs) have been invented as a new technology for harvesting mechanical energy, with enormous advantages. One of the major themes in their development is the improvement of the power output, which is fundamentally determined by the triboelectric charge density. Besides the demonstrated physical surface engineering methods to enhance this density, chemical surface functionalization to modify the surface potential could be a more effective and direct approach. In this paper, we introduced the method of using self-assembled monolayers (SAMs) to functionalize surfaces for the enhancement of TENGs' output. By using thiol molecules with different head groups to functionalize Au surfaces, the influence of head groups on both the surface potential and the triboelectric charge density was systematically studied, which reveals their direct correlation. With amine as the head group, the TENG's output power is enhanced by ∼4 times. By using silane-SAMs with an amine head group to modify the silica surface, this approach is also demonstrated for insulating triboelectric layers in TENGs. This research provides an important route for the future research on improving TENGs' output through materials optimization.

Surface functionalization of carbon nanotubes: fabrication and applications

Abstract: Carbon nanotubes (CNT)s show exceptional one-dimensional π-electron conjugation, mechanical strength, high chemical and thermal stability, which make them very attractive for use in many applications. CNTs intrinsically tend to hold together as ropes and bundles due to van der Waals interactions. The prevention of such behavior has been investigated by testing a variety of surface modification methods. The functionalized CNTs present enhanced properties enabling facile production of novel nanomaterials and nanodevices. The functionalization of CNTs could improve their chemical compatibility and dissolution properties, which would enable both a wider characterization and consequent chemical reactivity. This review aims to provide a brief synopsis of CNT functionalization and highlights recent developments in the functionalization of CNTs and their applications.

Optical biosensors based on ZnO nanostructures: advantages and perspectives. A review

Abstract: This review article highlights the application of beneficial physico-chemical properties of ZnO nanostructures for the detection of wide range of biological compounds. As the medical diagnostics require accurate, fast and inexpensive biosensors, the advantages inherent optical methods of detection are considered. The crucial points of the immobilization process, responsible for biosensor performance (biomolecule adsorption, surface properties, surface defects role, surface functionalization etc.) along with the interaction mechanism between biomolecules and ZnO are disclosed. The latest achievements in surface plasmon resonance (SPR), surface enhanced Raman spectroscopy (SERS) and photoluminescence based biosensors along with novel trends in the development of ZnO biosensor platform are presented.

Enhancing the Hydrophilicity and Cell Attachment of 3D Printed PCL/Graphene Scaffolds for Bone Tissue Engineering

Abstract: Scaffolds are physical substrates for cell attachment, proliferation, and differentiation, ultimately leading to the regeneration of tissues. They must be designed according to specific biomechanical requirements, i.e., certain standards in terms of mechanical properties, surface characteristics, porosity, degradability, and biocompatibility. The optimal design of a scaffold for a specific tissue strongly depends on both materials and manufacturing processes, as well as surface treatment. Polymeric scaffolds reinforced with electro-active particles could play a key role in tissue engineering by modulating cell proliferation and differentiation. This paper investigates the use of an extrusion-based additive manufacturing system to produce poly(e-caprolactone) (PCL)/pristine graphene scaffolds for bone tissue applications and the influence of chemical surface modification on their biological behaviour. Scaffolds with the same architecture but different concentrations of pristine graphene were evaluated from surface property and biological points of view. Results show that the addition of pristine graphene had a positive impact on cell viability and proliferation, and that surface modification leads to improved cell response.

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry

Abstract: Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti(4+) to form planar p-type [Ti(4+)n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B(3+), Al(3+) and Sn(4+)) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Impact of Gold Nanoparticle Stabilizing Ligands on the Colloidal Catalytic Reduction of 4-Nitrophenol

Abstract: Gold nanoparticles (AuNPs) have received considerable interest owing to their unique properties and applications in catalysis. One of the major challenges for colloidal nanoparticles in catalysis is the limited stability and resulting aggregation. Nanoparticle functionalization with ligands or polymers is a common strategy to improve the colloidal stability, which in turn blocks the reactive surface sites and eliminates catalytic activity. Here, we investigate thiolated polyethylene glycol (HS-PEG) as a stabilizing ligand during AuNP catalytic reduction of 4-nitrophenol. We show a direct relationship between the chain length and packing density of HS-PEG with respect to AuNP catalytic activity. High surface coverage of low molecular weight HS-PEG (1 kDa) completely inhibited the catalytic activity of AuNPs. Increasing HS-PEG molecular weight and decreasing surface coverage was found to correlate directly with increasing rate constants and decreasing induction time. Time-resolved UV–vis absorbance spectros...

Optical properties of functionalized Ti3C2T2 (T = F, O, OH) MXene: First-principles calculations

Abstract: Role of surface termination on the dielectric and optical properties of Ti3C2T2 (T = F, O, OH) MXene is studied using first-principles density functional theory. The results show that the surface functionalization has a significant impact on the optical properties of the MXene. For example, in the visible range of the spectrum, the oxidized sample shows larger absorption, whereas surface fluorination results in weaker absorption as compared to pristine MXene. In the ultraviolet energy range, all functional groups lead to the enhancement of both absorption and reflectivity of the material. Dielectric properties of MXene are also sensitive to the surface functionalization. Our findings demonstrate the importance of surface termination on the optical properties of the MXene.

Imparting Functionality to MOF Nanoparticles by External Surface Selective Covalent Attachment of Polymers

Abstract: Selective functionalization of the external surface of porous nanoparticles is of great interest for numerous potential applications in the field of nanotechnology. Regarding metal–organic frameworks (MOFs), few methods for such modifications have been reported in the literature. Herein, we focus on the covalent attachment of functional polymers on the external surface of MIL-100(Fe) nanoparticles in order to implement properties such as increased chemical and colloidal stability or dye-labeling for the investigation of the particles by fluorescence based techniques. We prove covalent nanoparticles-polymer bond formation by liquid NMR after dissolution of the functionalized MOF under mild conditions and estimate the amount of covalently attached polymer by UV–vis spectroscopy. The functionalization of the MOF nanoparticles with fluorescently labeled polymers enables the investigation of nanoparticle uptake into tumor cells by fluorescence microscopy. Furthermore, the influence of the polymer shell on the ...

2D Protein Supramolecular Nanofilm with Exceptionally Large Area and Emergent Functions.

Abstract: 2D nanofilms assembled by pure protein with a macroscopic area and multiple functions can be directly formed at the air/water interface or at the solid surface at a timescale of several minutes. The multifunctionality of the nanofilm coating is demonstrated by both top-down and bottom-up micro-/nanoscale interfacial engineering, including surface modification, all-water-based photo/electron-beam lithography, and electroless deposition.

Phosphonic Acids for Interfacial Engineering of Transparent Conductive Oxides

Abstract: Transparent conducting oxides (TCOs), such as indium tin oxide and zinc oxide, play an important role as electrode materials in organic-semiconductor devices. The properties of the inorganic–organic interface—the offset between the TCO Fermi level and the relevant transport level, the extent to which the organic semiconductor can wet the oxide surface, and the influence of the surface on semiconductor morphology—significantly affect device performance. This review surveys the literature on TCO modification with phosphonic acids (PAs), which has increasingly been used to engineer these interfacial properties. The first part outlines the relevance of TCO surface modification to organic electronics, surveys methods for the synthesis of PAs, discusses the modes by which they can bind to TCO surfaces, and compares PAs to alternative organic surface modifiers. The next section discusses methods of PA monolayer deposition, the kinetics of monolayer formation, and structural evidence regarding molecular orientati...

Understanding Pt Nanoparticle Anchoring on Graphene Supports through Surface Functionalization

Abstract: The enhancement of Pt nanoparticle anchoring strength and dispersion on carbon supports is highly desirable in polymer electrolyte membrane fuel cells (PEMFCs) as well as in other catalysis processes. Presented here is a comprehensive study of the interaction between catalyst nanoparticles and carbon supports in terms of the electronic structure change and its effects on the electrocatalytic performance of supported catalysts. Graphene was chosen as an ideal model support because the unique 2-D structure allows the direct investigation of the interaction with supported metal nanoparticles at their interface. We developed a facile strategy to covalently graft p-phenyl SO3H—or p-phenyl NH2—groups onto the graphene surface. The functional groups were found to not only facilitate the homogeneous distribution of Pt nanoparticles on the surface of graphene supports and reduce the Pt average particle size but also strengthen the interaction of the Pt atoms with the functional groups and, consequently, minimize t...

Graphene-Gold Nanoparticles Hybrid-Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor.

Abstract: Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene-AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene-Au nanocomposites. The paper highlights the graphene-gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.

Fluorine-Free Oil Absorbents Made from Cellulose Nanofibril Aerogels

Abstract: Aerogels based on cellulose nanofibrils (CNFs) have been of great interest as absorbents due to their high absorption capacity, low density, biodegradability, and large surface area. Hydrophobic aerogels have been designed to give excellent oil absorption tendency from water. Herein, we present an in situ method for CNF surface modification and hydrophobic aerogel preparation. Neither solvent exchange nor fluorine chemical is used in aerogel preparations. The as-prepared hydrophobic aerogels exhibit low density (23.2 mg/cm–3), high porosity (98.5%), good flexibility, and solvent-induced shape recovery property. Successful surface modification was confirmed through field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and water contact angle measurements. The hydrophobic aerogels show high absorption capacities for various oils, depending on liquid density, up to 47× their original weight but with low water uptake (<0.5 g/g a...

Enhancement of CO2 Capture on Biomass-Based Carbon from Black Locust by KOH Activation and Ammonia Modification

Abstract: A novel biomass-based carbon material was successfully prepared from black locust by KOH chemical activation in combination with surface modification by heat treatment with ammonia solution for enhancing CO2 adsorption. The textural and surface characteristics of the prepared activated carbons were analyzed with N2 adsorption isotherms, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and X-ray photoelectron spectroscopy (XPS). The results show that the modified activated carbon possesses a high surface area of 2511 m2/g, a large micropore volume of 1.16 cm3/g, and a high nitrogen content of 7.21 wt %. The adsorption behavior of CO2 onto all activated carbon samples was experimentally evaluated by a volumetric method at three different adsorption temperatures of 0, 25, and 50 °C under atmospheric pressure (1 bar). High CO2 uptakes of 7.19 and 5.05 mmol/g at 0 and 25 °C were achieved for the sample AC-KOH-N due to its well-developed micropore structur...