Role Of Surface Functionalization Research Articles

Enhanced Electrohydrogenation of Cis,Cis-Muconic Acid to Trans-3-Hexenedioic Acid Using Hybrid Metal/Carbon Fiber Cathodes

Organic electrosynthesis is a long-known technique for diverse product development and efficient synthesis. With the recent rise of biomass as an alternative carbon and energy source, electrochemistry is further gaining popularity due to its inherently green and environmentally benign operating conditions. Electrochemical hydrogenation (ECH) reactions are particularly attractive for biomass conversion due to their ability to abstract hydrogen from water, tolerate biogenic impurities, and utilize Earth-abundant base metal electrodes. Moreover, the rate and selectivity of the reaction can be tubed by controlling the electrode material, operating potential/current density, and reactor design. However, the implementation of this decarbonized technology for chemical production is still hampered by low productivity and, as a result, unfavorable economics. cis,cis-Muconic acid (ccMA), a bioderived C6 diunsaturated diacid platform molecule, can be converted into commodity chemicals like caprolactam, adipic acid (AA), and terephthalic acid, with AA being of particular interest for the synthesis of nylon 6,6.1 Apart from various drop-in chemicals, ccMA can also be electrochemically upgraded to trans-3-hexenedioic acid (t3HDA), a potential bio-advantaged substitute for AA as the additional C=C bond in t3HDA can be leveraged to synthesize performance-advantaged polyamides.2,3 In this work, we investigated the electrohydrogenation of ccMA to t3HDA over Pb cathodes. We demonstrate that the reaction follows a radical-based pathway involving sequential electron transfer and hydrogen addition in solution to selectively produce t3HDA (100% selectivity). Next, we contacted the cathode with carbon felts (CF) to increase productivity. CF are often used in fuel cells and H2O2 electrolyzers due to their excellent conductivity, porosity for enhanced turbulence, and ability to tune the gas-liquid-solid three-phase interface. Following similar principles, we placed a CF (3mm. thickness) in contact with the Pb cathode to lower the charge transfer resistance (~3Ω) at the interface. The surface functionalities of carbon allowed us to further tune the hydrophobicity/hydrophilicity of our hybrid electrode. Molecular dynamics (MD) calculations provided critical insights into the role of surface functionalities and guided the optimal functionalization of CF’s surface. Combining reactor configuration with fine-tuning of the electrode’s microenvironment, we were able to achieve a 50x increase in t3HDA productivity reaching up to 20 g/cm2/day at a current density of 200 mA/cm2. We further replaced the kinetically sluggish oxygen-evolution reaction with the glucose oxidation reaction at the anode, allowing us to operate the electrolyzer at a lower cell potential.Overall, ECH represents a valuable alternative to thermochemical transformations for biomass upgrading. This work provides critical insights into reactor modifications for the scaled-up synthesis of bio-derived performance monomers via hybrid microbial electrosynthesis (HMES).

The role of surface functionalization in quantum dot-based photocatalytic CO2 reduction: balancing efficiency and stability.

Photocatalytic CO2 reduction offers a promising strategy to produce hydrocarbons without reliance on fossil fuels. Visible light-absorbing colloidal nanomaterials composed of earth-abundant metals suspended in aqueous media are particularly attractive owing to their low-cost, ease of separation, and highly modifiable surfaces. The current study explores such a system by employing water-soluble ZnSe quantum dots and a Co-based molecular catalyst. Water solubilization of the quantum dots is achieved with either carboxylate (3-mercaptopropionic acid) or ammonium (2-aminoethanethiol) functionalized ligands to produce nanoparticles with either negatively or positively-charged surfaces. Photocatalysis experiments are performed to compare the effectiveness of these two surface functionalization strategies on CO2 reduction and ultrafast spectroscopy is used to reveal the underlying photoexcited charge dynamics. We find that the positively-charged quantum dots can support sub-picosecond electron transfer to the carboxylate-based molecular catalyst and also produce >30% selectivity for CO and >170 mmolCO gZnSe-1. However, aggregation reduces activity in approximately one day. In contrast, the negatively-charged quantum dots exhibit >10 ps electron transfer and substantially lower CO selectivity, but they are colloidally stable for days. These results highlight the importance of the quantum dot-catalyst interaction for CO2 reduction. Furthermore, multi-dentate catalyst molecules create a trade-off between photocatalytic efficiency from strong interactions and deleterious aggregation of quantum dot-catalyst assemblies.

Production of demineralised high quality hierarchical activated carbon from lignite and determination of adsorption performance using methylene blue and p-nitrophenol: The role of surface functionality, accessible pore size and surface area

In the adsorption process, the surface area, pore and particle size distribution and the chemical structure of the solid and the type of adsorbent are of vital importance. Activated carbon (AC) is a very good adsorbent material and its cost is highly dependent on the starting material and production method. The pore size and functional structure of the surface depend on the amount of activation chemical used. Hierarchical ACs were produced from lignite by loading two different amounts of KOH. The impregnation ratio (KOH/lignite) was chosen as 1/1 and 3/1 and the produced ACs were labelled as AC1 and AC3. The surface areas of AC1 and AC3 were determined as 1321.3 and 2421.3 m2/g, and the total pore volumes were 1.079 and 1.425 cm3/g. Methylene blue (MB) and p-nitrophenol (p-NP) were used to determine the adsorption performance of the produced ACs. The adsorption data were evaluated in terms of the Langmuir and Freundlich models. The amounts of MB and p-NP adsorbed on the surface were calculated in mg/g, total and accessible surface area in mg/m2. It was determined that the MB and p-NP adsorbed to the AC1 sample were higher than the AC3 sample per m2 of population. Molecular orientation is possible depending on the solid surface functionality and chemical structure of the molecule to be adsorbed. It was concluded that in addition to the large surface area, the pore width that can be entered and the functional structure of the surface are very significant factors in the adsorption processes.

Robust orientation-3D conductive network enabled high-performance flexible sensor for traffic monitoring: Role of surface functionalization on self-assembled microspheres arrays

Flexible strain sensors prepared by self-sensing nanocomposites using polydimethylsiloxane (PDMS) as the matrix material and carbon nanotubes (CNTs) as the conductive filler have received widespread attention due to their structural flexibility, outstanding weatherability and biocompatibility. Nevertheless, the high sensitivity, stable signal output, and durability are still limited by the uniform dispersion of the CNTs inside. In this paper, a novel preparation method different from direct dispersion was explored, in which CNTs were assembled on the surface of polystyrene (PS) microspheres to assist in CNT dispersion during the self-deployment of microspheres arrays. The free CNTs acted as a bridge to connect the conductive microspheres in the orientation-3D conductive network, which were essential for forming abundant conductive pathways. As numerous conductive fillers were added to the system to enhance conductivity, the self-alignment effect of the microsphere arrays was significantly inhibited, and it failed to assist well in the dispersion. Therefore, the covalent bonding strategy was employed to improve the dispersion and construct strong interfacial interaction, providing impressive electrical conductivity, structural stability, and outstanding durability and thermal stability. The PDMS/PS-C/CNT-N composites prepared with aminated CNT (CNT-N) and carboxylated PS microspheres (PS-C) showed better performance in sensitivity, achieving a gauge factor of over 70, a wide sensing range of 0–124%, and fast response of 330 ms and fast recovery of 190 ms. The developed sensory film was used as an intelligent sensor to monitor traffic flow information. It has been proved that not only the vehicle configuration can be accurately identified, but also the speed can be precisely back-calculated. It opens up new territory to develop high-performance flexible strain sensors for accurate, long-term, and stable acquisition of traffic flow information.

Tunable surface chemistry of carbon electrodes and the role of surface functionalities towards vanadium redox reactions

The surface chemistry of carbon electrodes plays a vital role towards the kinetics of vanadium redox reactions of vanadium redox flow batteries (VRFB). In this study, O2, CO2, N2, and NH3 plasmas have been employed to modify the surface chemistry of graphite felt electrodes, and the effect of various surface functional groups on negative and positive electrode reactions of VRFB has been explored. Various analytical techniques, electrochemical characterizations and asymmetric charge–discharge experiments reveal that the surface functional groups have a specific role towards vanadium redox reactions on each side of a VRFB cell. The C=O and O-C=O groups show catalytic effects while the C-O group has an inhibiting effect on the kinetics of negative and positive electrode reactions. Pyrrolic-N shows catalytic effects on the positive electrode reactions whereas oxidized-N has catalytic effects on the negative electrode reactions. Amine groups introduced by NH3 plasma worsen the sluggish kinetics of the negative electrode reactions by boosting hydrogen evolution reaction. Based on the specific behavior, an optimal arrangement of each plasma-treated felt has also been proposed by either utilizing it as negative electrode, positive electrode or both in a VRFB cell, leading to an overall improved performance.

Role of Surface Functionalization on Cellular Uptake of AuNPs Characterized by Computational Microscopy.

A surface modification of nanoparticles (NPs) provides an effective way to control their interactions with living cells. The complete understanding of interactions between NPs and a cell membrane is a key step for the development of drug delivery. In the present work, the role of different surface charges (anionic, cationic, and zwitterionic) on the internalization through an idealized plasma membrane was investigated using a coarse-grained molecular dynamics (CGMD) technique. The decorated AuNPs used in this in silico study closely imitated those experimentally synthesized, while the idealized plasma membrane model resembled that found in living cells. The mechanism of direct translocation of a 2 nm particle by membrane was observed. The zwitterionic AuNP demonstrates a higher free-energy barrier than the positively and negatively charged AuNPs, resulting in a lack of preference for internalization across the membrane, leading to lower translocation rate and permeability of internalization. Despite the surface coverage, the agglomeration of AuNPs in a physiological condition has been observed resulting in slow unfavorable permeability. Our study highlights that in addition to surface charges, the hydrodynamic size (DH) plays an important role in the permeability of the functionalized AuNPs into the cell membrane. Through our simulations, complete understanding of interactions between ligands-coated AuNPs and the realistic plasma membrane has been established serving as a platform for the novel design of AuNPs in nanomedicine applications.

Role of surface functionalization of ZnO nanoparticles as sorbents for heavy metal ions

ABSTRACT The surface functionalization of ZnO nanoparticles (ZnO NPs) was carried out by a simple one pot co-precipitation method followed by a facile ligand introduction onto the surface. This technique allows for tailoring of the surface chemistry to impart the specificity and affinity toward the target analytes (heavy metal ions like Pb and Hg) depending on the ligand incorporated on the surface resulting in highly selective sorbents. The functionalized ZnO NPs were characterized using different techniques. Elemental, IR, and thermal analysis studies confirm the presence of functional groups. X-ray diffraction (XRD) shows functionalization does not result in change of ZnO NPs but reduces their crystallinity. The average crystallite size of the nanoparticles is not affected by functionalization indicating that the process is restricted to the surface only. Surface area measurements reveal that functionalization results in mesoporous structures as can be deduced from the average pore diameter. Functionalization resulted in enhanced uptake of Pb and Hg, and the kinetics were very fast. Different models were used to understand the sorption behavior. The Langmuir uptake capacity values for lead and mercury using the thiol-functionalized ZnO NPs were found to be 78 and 145 mg/g, respectively. The role of interfering ions on the sorption was evaluated to get an idea of the selective nature of the sorbent.

Iodine sequestration using cyclophosphazene based inorganic-organic hybrid nanoporous materials: Role of surface functionality and pore size distribution

Cyclophosphazene based inorganic-organic hybrid nanoporous materials having triazine and pyrrolic functionality named as HNM-1 and CHNM-1, respectively, with varying nitrogen content, hierarchical pore size and high specific surface area have been explored for iodine sequestration application. The presence of electron rich functionality in the HNM-1 and CHNM-1 provides a large number of active sites for the adsorption of iodine. Maximum gravimetric iodine capture capacity of 223 and 120 wt% were estimated in HNM-1 and CHNM-1 specimens, respectively, under fuel processing condition i.e. 75 °C and ambient pressure. Moreover, both the specimens have shown very good iodine release behavior in organic solvents. The recyclability of HNM-1 and CHNM-1 for iodine sorption has shown the retention of adsorption capacity by 80 and 86%, respectively, even after five cycles. The iodine sorption both in vapor as well as solution phases is greatly influenced by the nitrogen content and pore size distribution of the framework materials.

The Role of Surface Functionalities in PtGe and PtIn Catalysts for Direct Methanol Fuel Cells

Bimetallic PtGe and PtIn catalysts were prepared over Vulcan carbon (VC) and multiwall carbon nanotubes (NT) by conventional impregnation method (CI). These supports were functionalized with citric or nitric acid. The structural and electrochemical characteristics of the different functionalized supported catalysts were analyzed in order to determine the influence of the functional groups. The methods applied were temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), cyclohexane dehydrogenation reaction (CHD), and CO stripping. The functionalization treatment with citric or nitric acid eases CO oxidation to CO2, decreasing poisoning effect of CO over Pt, due to the development of oxygenated groups on support surfaces and in the nearby Ge and In. Bimetallic catalysts supported on carbons functionalized with HNO3 present increasing electrochemical active surface values, indicating a better electrochemical behavior than the corresponding monometallic catalysts. DMFC experiments show a very good behavior of PtGe catalysts, mainly for those supported on HNO3-functionalized NT, reaching a maximum power density of 80 mW cm−2. Conversely, PtIn catalysts exhibit a very poor behavior.

Carboxyl-Functionalized Carbon Dots as Competent Visible Light Photocatalysts for Aerobic Oxygenation of Alkyl Benzenes: Role of Surface Functionality

Carbonaceous nanolights, carbon dots (CDs), are attractive alternatives to semiconducting quantum dots owing to their tunable optoelectronic properties, photostability, biocompatibility, water solu...

Role of surface functionalization on corrosion resistance and thermal stability of epoxy/glass flake composite coating on cold rolled steel

Composites of epoxy and functionalized glass flake (FGF) with enhanced corrosion protection for cold rolled steel (CRS) are developed. The influence of glass flake (GF) functionalization on their dispersion in the epoxy matrix was examined using TEM and the interface adhesion was evaluated using SEM. The coating corrosion resistance was investigated via Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization measurements and the long-term protection was measured gravimetrically by immersing bare and coated CRS specimens in 3.5 wt.% NaCl for 90 days. The study demonstrates attaching aminosilane groups to the surface of GF leads to substantial enhancement in corrosion protection and thermal stability of the epoxy-FGF (E/FGF) composite coating at small FGF loading.

Dynamics of a Water Nanodrop through a Holey Graphene Matrix: Role of Surface Functionalization, Capillarity, and Applied Forcing

Nanoporous graphene has emerged as an excellent material for desalination and water purification. Holey graphene (HG) is a special form of nanoporous graphene, where multilayers of nanoporous graphene get arranged in spatially separated stacks. In this paper, we employ molecular dynamics simulations to unravel the dynamics of a water drop in presence of an applied force F in such holey graphene architecture, which is characterized by the presence of either hydrophilic functionalization (HIF) or hydrophobic functionalization (HOF) of the edges of the holes. For realistic values of F, the consideration of water drop makes the capillary effects important, which in turn interplays with the wettability of the surface functionalization to ensure that the HG with the HOF causes both an enhanced flux and an enhanced permeated water volume. We relate these phenomena to the augmented water-hydrophilic-edge attraction that arrests the dewetting of water from the graphene stacks and slows the speed of water flowing p...

The role of surface functionalities in fabricating supported Pd-P nanoparticles for efficient formic acid oxidation

In the present work, O–functionalized carbon nanotubes (OCNTs) supported Pd–P nanoparticles (Pd–P/OCNTs) were prepared by using sodium hypophosphite (NaH2PO2) as the P source and the reducing agent. The presence of O-functionalities on the carbon surface provide a microenvironment of the reaction system which favors the anchorage of P precursors and Pd salt ions through the electrostatic interaction and the formation of chemical bonds on the carbon support. Thus, Pd nanoparticles supported on the OCNTs could be efficiently incorporated with P. Pd with the modified outer electron structure enhanced the electrocatalytic performance for formic acid oxidation (FAO).

Controlling Oriented Attachment and in Situ Functionalization of TiO2 Nanoparticles During Hydrothermal Synthesis with APTES

Understanding growth mechanisms and the role of surface functionalization is of key importance to control shape and morphology of nanoparticles and their properties. Here, we describe the growth mechanism and the effect of hydrothermal synthesis parameters (pH, time, and precursor/functionalization agent ratio) during in situ functionalization of anatase TiO2 nanoparticles with 3-aminopropyltriethoxysilane. Elongated crystallographically oriented TiO2 nanoparticles were formed by oriented attachment mechanism in addition to spherical nanoparticles. The growth mechanism is determined by a combination of ex situ techniques such as high-resolution transmission electron microscopy combined with in situ synchrotron X-ray diffraction and density functional theory calculations. Oriented attachment induced by the functionalization agent is shown to be the origin of the elongation of the nanoparticles, as only spherical nanoparticles were formed in the absence of surface functionalization. Finally, it was shown th...

Modular assembly of superstructures from polyphenol-functionalized building blocks.

The organized assembly of particles into superstructures is typically governed by specific molecular interactions or external directing factors associated with the particle building blocks, both of which are particle-dependent. These superstructures are of interest to a variety of fields because of their distinct mechanical, electronic, magnetic and optical properties. Here, we establish a facile route to a diverse range of superstructures based on the polyphenol surface-functionalization of micro- and nanoparticles, nanowires, nanosheets, nanocubes and even cells. This strategy can be used to access a large number of modularly assembled superstructures, including core-satellite, hollow and hierarchically organized supraparticles. Colloidal-probe atomic force microscopy and molecular dynamics simulations provide detailed insights into the role of surface functionalization and how this facilitates superstructure construction. Our work provides a platform for the rapid generation of superstructured assemblies across a wide range of length scales, from nanometres to centimetres.

Seeded precipitation polymerization for the synthesis of gold-hydrogel core-shell particles: the role of surface functionalization and seed concentration

Polymer encapsulation is an important pathway to stabilize inorganic nanoparticles, allow their phase transfer to different media, and access inter-particle distance control in particle assembly. In the past, hydrogels were shown to be a versatile encapsulation material offering rather thick polymeric shells through free radical precipitation polymerization. In this work, we systematically investigate the influence of nanoparticle surface functionalization and concentration on the formation of core-shell microgels. Spherical gold nanoparticles are used as seeds in the radical polymerization of N-isopropylacrylamide and N,N′-methylenebisacrylamide. We find that the encapsulation occurs via precipitation of oligomers/polymers onto the seed particle surface, independent of the presence of polymerizable groups. Furthermore, we identify the seed concentration regime where almost exclusively core-shell particles are formed. In this concentration range, the hydrogel thickness is precisely controllable by the amount of seeds. Monitoring the polymerizations in situ by dynamic light scattering and absorbance spectroscopy provides first insights into the encapsulation mechanism and its time dependence.

Role of surface functionality on the formation of raspberry-like polymer/silica composite particles: Weak acid–base interaction and steric effect

The surface functionality of polymer microspheres is the crucial factor to determine the nucleation and growth of silica particles and to construct the organic/inorganic hierarchical structures. The objective of this work was to evaluate the surface functionality and hierarchical morphology relationship via in situ sol–gel reaction. Carboxylic-functionalized poly (styrene-co-maleic anhydride) [P(S-co-MA)], poly(ethylene glycol)-functionalized poly(styrene-co-poly(ethylene glycol) methacrylate) [P(S-co-PEGMA)], and hybrid functionalized poly(styrene-co-maleic anhydride-co-poly(ethylene glycol) methacrylate) [P(S-co-MA-co-PEGMA)] microspheres were synthesized by emulsifier-free polymerization and used as templates. The morphologies of the composite particles were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results showed that core–shell structure was obtained with P(S-co-MA) as templates; raspberry-like structure was observed by using P(S-co-MA-co-PEGMA) as templates; and no silica particles were attached onto the surface of P(S-co-PEGMA) microspheres. These results indicated that the carboxylic groups on the surface formed by hydrolysis of anhydride groups were the determinate factor to control the nucleation of silica nanoparticles, and the PEG chains on the surface can affect the growth of silica particles. In addition, the particulate films were constructed by assembling these composite particles on glass substrates and modified with dodecyltrichlorosilane, the contact angles of water on the dual-sized structured surface were up to 160°.

Activated carbon fibers for efficient VOC removal from diluted streams: the role of surface functionalities

The effect of surface functionalities, specific surface area and pore size of activated carbon fibers (ACFs) on the adsorption of toluene and acetaldehyde, two volatile organic compounds (VOC), at low concentrations (~80 ppmv) and short contact time (20 ms) has been studied. Two different types of ACFs characterized by low temperature N2 adsorption: ultramicroporous (d pore < 1 nm) and supermicroporous (d pore ~ 1–2 nm) were tested. Both ACFs were effective for the removal of toluene attaining the adsorption capacity as large as 51 wt%. The surface chemistry of ACFs (O-containing functional groups) was characterized by temperature-programmed desorption monitoring the CO/CO2 evolved. Oxidative treatment of ACFs by nitric acid increased the surface concentration of O-groups. This resulted in lower adsorption capacity towards toluene but higher one towards acetaldehyde. This result was rationalized based on different type of VOC interactions with the carbon surface.

On the hydration of subnanometric antifouling organosilane adlayers: A molecular dynamics simulation

The connection between antifouling and surface hydration is a fascinating but daunting question to answer. Herein, we use molecular dynamics (MD) computer simulations to gain further insight into the role of surface functionalities in the molecular-level structuration of water (surface kosmotropicity) – within and atop subnanometric organosilane adlayers that were shown in previous experimental work to display varied antifouling behavior. Our simulations support the hypothesized intimate link between surface hydration and antifouling, in particular the importance of both internal and interfacial hydrophilicity and kosmotropicity. The antifouling mechanism is also discussed in terms of surface dehydration energy and water dynamicity (lability and mobility), notably the crucial requirement for clustered water molecules to remain tightly bound for extensive periods of time – i.e. exhibit slow exchange dynamics. A substrate effect on surface hydration, which would also participate in endowing antifouling adlayers with hydrogel-like characteristics, is also proposed. In contrast, the role of adlayer flexibility, if any, is assigned a secondary role in these ultrathin structures made of short building blocks. The conclusions from this work are well in line with those previously drawn in the literature.

Interaction between Palladium Nanoparticles and Surface‐Modified Carbon Nanotubes: Role of Surface Functionalities

AbstractIt is crucial to accurately describe the interaction between the surface functionality and the supported metal catalyst because it directly determines the activity and selectivity of a catalytic reaction. It is, however, challenging with a metal–carbon catalytic system owing to the ultrafine feature, instability, and subtle response of the components upon application of an external field. Herein, we use in situ TEM, electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy techniques to record the interaction in palladium on carbon nanotubes (CNTs) from room temperature to 600 °C. We focus on probing the effects of oxygen and nitrogen‐containing functional groups on supported palladium nanoparticles (NPs) in the model catalytic system. The stability of palladium NPs supported on CNTs depends strongly on the surface properties of CNTs. Moreover, the oxygen‐containing functional groups on the CNT surfaces, such as carboxylic acids and anhydrides, have an even stronger interaction with palladium NPs than the nitrogen‐containing counterparts. Our work contributes to elucidation of the complex metal–carbon interaction and unlocks potential in activity and selectivity control of these catalytic systems.