Bifunctional Surface Research Articles

Pushing the Functionality of Diamond Nanoparticles to New Horizons: Orthogonally Functionalized Nanodiamond Using Click Chemistry

AbstractClick chemistry is one of the most versatile means for the efficient grafting of larger units such as fluorescence labels or biomolecules onto the surface of nanoparticles. Here, a first study on the applicability of different strategies for the copper‐catalyzed azide–alkyne coupling of diamond nanoparticles and organic moieties is reported. Both thermally annealed nanodiamond and mechanically pretreated diamond nanoparticles of different origin can be modified with moieties carrying either azide or alkyne groups. Several organic units have been efficiently “clicked” onto these particles. The method is then applied for the bifunctional surface modification of nanodiamond leading to a material exhibiting carboxylic and alkyne groups at the same time. These can be addressed by orthogonal coupling linkers. A model material carrying two distinct fluorescent dyes is produced this way and shows the characteristic luminescence of both dyes. The findings open the way for the application of nanodiamond as multifunctional labels, drug delivery vehicles, and targeting agents in biomedical applications.

Enhanced uptake of porous silica microparticles by bifunctional surface modification with a targeting antibody and a biocompatible polymer.

Strategies were developed by which mesoporous microparticles were modified on their external surfaces with tetraethylene glycol (TEG), a protein, or both, leaving the pore surfaces available for modification with a separate moiety, such as a dye. Only particles bifunctionally modified with both TEG and a cell-specific antibody were taken up specifically by a targeted cancer cell line. In contrast to similarly functionalized nanoparticles, endocytosed microparticles were not contained within a lysosome.

Self‐Aligned Micropatterns of Bifunctional Polymer Surfaces with Independent Chemical and Topographical Contrast

Bifunctional surfaces are micropatterned using a self-aligned, dual-purpose lithographic mask and pairs of conformally deposited iCVD polymers. A first layer is deposited, then physically masked and etched in oxygen plasma. A second layer is deposited with the mask still in place. Lift-off reveals the micropatterned surface. The thicknesses of the two layers are independently controlled so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and order of deposition. We use this scheme to create surfaces that spatially confine microcondensation, as well as chemical functionality. We also demonstrate microwells whose depth can be altered in response to a water stimulus.

Multiple-structured nanocrystals towards bifunctional photoluminescent-superhydrophobic surfaces

We report a simple and efficient strategy for the preparation of diverse hierarchical structures of dithiocarbamate-functionalized CdS nanocrystals (NCs) exhibiting both photoluminescent and hydrophobic properties via a facile interfacial self-assembly technique. The ligand exchange reaction of thioglycolic acid (TGA) with dithiocarbamates at the biphase interface endowed CdS with diversiform morphologies. Simultaneously, the resulting dithiocarbamate-functionalized NCs after interfacial self-assembly exhibit good photochemical stability and enhanced photoluminescence (PL) in comparison with the parent NCs. Moreover, the introduction of dithiocarbamate ligands with long alkyl chains can significantly enhance the hydrophobic properties of NCs in this case. By simply varying the directing ligands with different intrinsic hydrophobic natures, superhydrophobic surfaces constructed from the fluorescent NCs can be fabricated.

Biomimetic bi-functional silicon nanospike-array structures prepared by using self-organized honeycomb templates and reactive ion etching

We demonstrate here a creation of a novel biomimetic bi-functional surface by using dry etching of silicon with a self-organized porous polymer. The novel silicon structures with hierarchical nanospike-array structures covered with fluorocarbons were fabricated by dry etching of silicon through the porous polymer masks. The anti-reflection and superhydrophobic properties were realized due to their large surface areas and low surface energies. These masks and silicon substrates offer great advantages and are suitable for various practical applications, including high efficiency solar cells.

Site-Specific Chemistry Directed by a Bifunctional Nanostructured Surface

Using the scanning tunneling microscope (STM), we have created a bifunctional nanostructured surface which consists of parallel stripes of gold atoms on the Au(111) substrate. Each stripe has two parallel step-edges separated by a few nanometers in distance. The two step-edges have very different binding properties to molecules, and they are able to separate C(60) molecules into two types of adsorbed structures, giving rise to a controlled formation of two-dimensional closely spaced multiple molecular nanostructures.

Bifunctional Heterogeneous Catalysis of Silica–Alumina‐Supported Tertiary Amines with Controlled Acid–Base Interactions for Efficient 1,4‐Addition Reactions

We report the first tunable bifunctional surface of silica-alumina-supported tertiary amines (SA-NEt(2)) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon-carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA-NEt(2)) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA-NEt(2) catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA-NEt(2) catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time (13)C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid-base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid-base interactions.

Bridge polysilsesquioxane xerogels with a bifunctional surface layer of the ≡Si(CH2)3NH2/≡Si(CH2)3SH composition

Xerogels with a bifunctional surface layer of the ≡ Si ( CH 2 ) 3 NH 2 / ≡ Si ( CH 2 ) 3 SH composition are syn- thesized by hydrolytic co-polycondensation of bis(triethoxy)silane ( C 2 H 5 O ) 3 Si ( CH 2 ) 2 Si ( OC 2 H 5 ) 3 and two tri- functional silanes, namely, 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Using IR, 1 H MAS NMR, and 13 C CP/MAS NMR spectroscopic techniques, it is shown that in addition to complexing groups, the surface layer also contains water, silanol groups that are involved in the hydrogen bond formation and also residual ethoxysilyl groups. According to 29 SiCP/MAS NMR spectroscopic data, the degree of poly- condensation of synthesized xerogels exceeds 80%. It is found that the use of 1,2-bis(triethoxysilyl)ethane as the structuring agent in place of tetraethoxysilane allows one to synthesize bifunctional xerogels with the highly developed biporous structure ( S sp = 607-680 m 2 /g, V c = 1.38-1.47 cm 3 /g, d = 2.9-3.1 and 18.3 nm). Changing the ratio structuring-silane/functionalizing-silane-mixture from 2 : 1 to 4 : 1 in the reaction system has virtually no effect on the porous structure parameters of final xerogels.

Bifunctional superparamagnetic surface molecularly imprinted polymer core-shell nanoparticles

Superparamagnetic surface molecularly imprinted polymer core-shell nanoparticles were prepared via surface atom transfer radical polymerization (ATRP) using the ATRP agent functionalized Fe3O4 support as the chain transfer agent.

Bifunctional microstructured films and surfaces obtained by soft lithography from breath figure arrays

Breath figure films of polystyrene and polyalkylthiophene presenting regular patterns of 600 nm and 5 µm are used as templates to prepare negative polydimethylsiloxane stamps containing an entrapped quantity of the primary polymer. These breath figure replica are used to generate single or double layers of the entrapped conjugated polymer in the form of networks on any substrates. Besides this, polystyrene printed in this way can be used as a resist mask that allows the polymerization of aniline in a regular micrometric arrangement on a platinum electrode or to generate a regular acid/base patterning on a plain polyaniline film.

Concomitant Crystallization of ROY on Patterned Substrates: Using a High Throughput Method to Improve the Chances of Crystallization of Different Polymorphs

In this study, we demonstrate how increasing the number of crystallization trials can help crystallize polymorphs which may not be obtained in a fewer number of trials due to statistical reasons. Crystallization experiments were conducted using patterned substrates of self-assembled monolayers (SAMs) with solutions of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (known as ROY for its red, orange, and yellow crystals) in dimethylsulfoxide (DMSO). The patterned bifunctional surface was immersed and slowly withdrawn from undersaturated solutions. The solution preferentially wetted the metallic islands, and as the solvent evaporated, ROY crystals exclusively nucleated on the lyophilic metallic islands. Raman microscopy was utilized to characterize the crystalline form on each metallic island. In one of the experiments, over 10 000 islands were analyzed, and we calculated the probability of crystallizing a particular polymorph on an island. We were able to crystallize six of the seven stable polym...

Novel Magnetically Separable Mesoporous Fe2O3@SBA-15 Nanocomposite with Fully Open Mesochannels for Protein Immobilization

Magnetically separable Fe2O3@SBA-15 nanocomposite with fully open mesochannels and bifunctional surface properties was prepared by selective deposition of iron oxide nanoparticles in the micropores of mesoporous SBA-15 silica with hydrophobic mesopore surface. The iron oxide nanoparticles embedded in the micropores were estimated to be composed of 67% α-Fe2O3 and 33% γ-Fe2O3, and the nanocomposite was found to exhibit superparamagnetic properties. With the bifunctional surface properties, the Fe2O3@SBA-15 nanocomposite showed enhanced adsorption capacity for cytochrome c and a maximum saturated uptake at neutral solution pH.

Acid–Base Bifunctional Catalytic Surfaces for Nucleophilic Addition Reactions

This article illustrates the modification of oxide surfaces with organic amine functional groups to create acid-base bifunctional catalysts, summarizing our previous reports and also presenting new data. Immobilization of organic amines as bases on inorganic solid-acid surfaces afforded highly active acid-base bifunctional catalysts, which enabled various organic transformations including C--C coupling reactions, though these reactions did not proceed with either the homogeneous amine precursors or the acidic supports alone. Spectroscopic characterization, such as by solid-state MAS NMR and FTIR, revealed not only the interactions between acidic and basic sites but also bifunctional catalytic reaction mechanisms.

Hydrodechlorination of 1,2-dichloroethane catalyzed by dendrimer-derived Pt–Cu/SiO 2 catalysts

Dendrimer-metal-nanocomposites (DMNs) were used as precursors to prepare SiO 2-supported monometallic Pt, Cu, and bimetallic Pt–Cu catalysts with Pt/Cu atomic ratios of 1:1 (Pt 50Cu 50) and 1:3 (Pt 25Cu 75). After impregnation of these DMNs onto the support, the catalysts were thermally treated and activated following an optimized protocol. Scanning transmission electron microscopy (STEM) showed that the metal nanoparticles in the dendrimer-derived SiO 2-supported catalysts were smaller and had a narrower size distribution compared with those in conventional catalysts prepared using corresponding metal salts via the wet-impregnation method. Slow deactivation was observed for hydrodechlorination of 1,2-dichloroethane over monometallic Cu catalysts, which showed an activity about one to two orders of magnitude lower than that of the Pt-containing catalysts. Hydrodechlorination of 1,2-dichloroethane over the Pt and Pt 50Cu 50 catalysts produced mainly ethane, and the selectivity toward ethane increased with temperature. For the Pt 25Cu 75 catalyst, the selectivity toward ethane decreased in favor of that of ethylene. The overall activity decreased with increasing Cu loading in the catalysts. Activity based on surface Pt sites suggests the formation of bifunctional surfaces in Pt 25Cu 75 catalyst favoring C Cl bond scission on Cu sites and hydrogenation of intermediate ⋅CH 2CH 2⋅ on Pt sites. In addition, kinetic analyses suggest different reaction mechanisms for hydrodechlorination of 1,2-dichloroethane over Pt and Cu-enriched surfaces in the Pt–Cu bimetallic catalysts.

Reactivity descriptors for direct methanol fuel cell anode catalysts

We have investigated the anode reaction in direct methanol fuel cells using a database of adsorption free energies for 16 intermediates on 12 close-packed transition metal surfaces calculated with periodic, self-consistent, density functional theory (DFT–GGA). This database, combined with a simple electrokinetic model of the methanol electrooxidation reaction, yields mechanistic insights that are consistent with previous experimental and theoretical studies on Pt, and extends these insights to a broad spectrum of other transition metals. In addition, by using linear scaling relations between the adsorption free energies of various intermediates in the reaction network, we find that the results determined with the full database of adsorption energies can be estimated by knowing only two key descriptors for each metal surface: the free energies of OH and CO on the surface. Two mechanisms for methanol oxidation to CO 2 are investigated: an indirect mechanism that goes through a CO intermediate and a direct mechanism where methanol is oxidized to CO 2 without the formation of a CO intermediate. For the direct mechanism, we find that, because of CO poisoning, only a small current will result on all non-group 11 transition metals; of these metals, Pt is predicted to be the most active. For methanol decomposition via the indirect mechanism, we find that the onset potential is limited either by the ability to activate methanol, by the ability to activate water, or by surface poisoning by CO ∗ or OH ∗/O ∗. Among pure metals, there is no obvious candidate for a good anode catalyst, and in order to design a better catalyst, one has to look for bi-functional surfaces such as the well-studied PtRu alloy.

Conceptual Integration of Homogeneous and Heterogeneous Catalyses

This article illustrates how bifunctional catalyst surfaces are created by modifying oxide surfaces with organic functional groups and/or with metal complexes, summarizing our previous reports and also presenting new data, which provide a new class of catalytic materials with a high complexity for selective catalysis including C–C coupling, hydroformylation, and asymmetric reactions. The catalyst surfaces are characterized by in situ physical analysis techniques such as time-resolved XAFS, FT-IR, solid-state MAS NMR and so on.

Sorption of Hg2+, Nd3+, Dy3+, and Uo 2 2+ ions at polysiloxane xerogels functionalized with phosphonic acid derivatives

The sorption properties of silicas with mono- and bifunctional surface layers containing the complexing fragment ≡Si(CH2)3NHP(S)(OC2H5)2 were studied. It was found that xerogels synthesized by the solgel method (like mesoporous silicas obtained by the template method) can extract mercury(II) ions from acidified solutions (SSC up to 450 mg/g). In a nonporous xerogel with a bifunctional surface layer (≡P=S/-SH), thiol groups proved to be primary sorption sites for Hg2+ ions; part of the ligand groups were inaccessible to metal ions. Xerogels containing the phosphonic acid residues ≡Si(CH2)2P(O)(OH)2 sorbed uranyl and lanthanide ions from their nitrate solutions. The resulting surface complexes contained two (for the UO22+ ion) or three innersphere ligand groups (for the Nd3+ and Dy3+ ions). The maximum SSCs were 340 mg/g for the uranyl ion and 120 mg/g for the lanthanide ions.

Structural Features of Surface Layers of Bifunctional Polysiloxane Xerogels Containing 3-Aminopropyl Groups and 3-Mercaptopropyl Groups

Polysiloxane xerogels containing both -SH and -NH2 functions have been prepared using the sol-gel method with alkoxysilane precursors [such as Si(OEt)4, (MeO)3Si(CH2)3SH and (EtO)3Si(CH2)3NH2]. Molar ratios of 3.2:1, 1.1:1 and 0.4:1 for the two functions -SH and -NH2 were employed. Xerogels which contain only one of the two functions were also synthesized for comparative purposes.It was shown that the use of stannic compounds as catalysts for xerogels with 3-mercaptopropyl groups resulted in a product which possessed a non-porous structure, while the use of fluoride ions allowed the synthesis of a sample with a porous structure (Ssp = 216 m2/g, Vs = 0.152 cm3/g, d = 3.5 nm). Xerogels with a bifunctional surface layer possess a bimodal structure. Infrared, Raman and multinuclear solid-state NMR (1H, 13C, 29Si) spectroscopy data showed: (i) the absence of deprotonation for the 3-mercaptopropyl groups in the bifunctional surface layer of the xerogels; and (ii) that 3-aminopropyl groups form hydrogen bonds in...

Liquid nanoparticle masterbatches for the deposition of solid inorganic materials

Deposition of materials by digital fabrication methods demands a high degree of homogeneity of the formulation. At the same time, viscosity control is highly important for the processability of the ink. This is especially challenging when it comes to depositing solid high-surface area particles. As well, the particle size and the particle size distribution of the particles in the ink is crucial, especially if ink jet techniques are applied.We present a process to manufacture liquid nanoparticle-masterbatches from commercially available agglomerated nanopowders. The process thus enables the use of inorganic solids in digital fabrication techniques. Each masterbatch contains specifically surface-modified inorganic nanoparticles dispersed in a low-viscosity solvent, like water, alcohol, acetate, ketone, or hydrocarbon solvents. The powders are deagglomerated using agitator bead mills. The particle-medium interface is chemically tailored with respect to the solvent and to further components of the formulation by use of bifunctional surface modifiers.

Polysiloxane xerogels with a bifunctional surface layer containing O/N, O/S, S/N, and S/S donor centers

Formation of bifunctional xerogels containing -NH2, -SH, -P(O)(OEt)2, and -NHP(O,S)(OEt)2 complexing groups in the surface layer was studied using sol-gel method (fluoride ion catalyst, ethanol solvent) and three-component systems.