N-octadecylphosphonic Acid Research Articles

Hydrophobicity modulation on a ferriporphyrin-based metal–organic framework for enhanced ambient electrocatalytic nitrogen fixation

Electrocatalytic N2 fixation represents an energy-efficient and long-term sustainable approach, which can convert N2 to NO3– or NH3 via the electrochemical N2 oxidation reaction (NOR) or N2 reduction reaction (NRR). However, the inert N2 molecule, low activity of electrocatalysts, and predisposed competitive reactions result in the poor yields and Faradaic efficiencies of N2 fixation reactions, which greatly restrict the application of such green synthesis technology. In this work, a molecular-level post-modification strategy has been explored to integrate diverse alkyl chains on a ferriporphyrin-based metal–organic framework (MOF) PCN-222(Fe), which provides adjustable hydrophobicity and highly dispersed active sites. The increased lengths of alkyl groups can gradually improve the hydrophobicity of decorated MOFs, which effectively suppress the competitive reactions and boost the electrocatalytic NOR and NRR performances. Significantly, the highest Faradaic efficiency of 70.7% so far and a state-of-the-art NO3− yield of 110.9 μg h–1 mgcat.–1 can be achieved for NOR, which are attributed to the synergistic effect of FeN4 active sites, high porosity, and strong hydrophobicity for n-octadecylphosphonic acid (OPA) decorated PCN-222(Fe).

Mechanism of selectivity control for zeolites modified with organic monolayers

The adsorptive separation of C3H6 and C3H8 gases using molecular sieves is a challenging process due to the similarity in molecular sizes for the two molecules. In this work, we report that organic phosphonic acid (PA) monolayers on zeolites significantly enhanced the ideal selectivity of C3H6/C3H8 adsorption by changing the diffusion mechanism based on the properties of the alkyl tail. With an n-octadecylphosphonic acid (ODPA) coating on zeolite 5A, the kinetic selectivity of C3H6/C3H8 was initially >8 at 25 °C, whereas for uncoated 5A, it was limited to ∼1.2. Kinetic modeling showed that in ODPA-coated 5A, the diffusion of C3H6 and C3H8 was limited by the PA monolayer at the external surface of the zeolite. In contrast, for uncoated 5A, it was controlled by the pore channels, so that the enhanced kinetic selectivity from 5A-ODPA was related to a different limiting transport mechanism. The kinetic selectivity was not temperature sensitive in the range of 25–150 °C in 5A-ODPA as the diffusion activation energies of C3H6 and C3H8 were both small. Modification of 5A with other PAs also increased the kinetic selectivity. Coating with n-butylphosphonic acid yielded lower kinetic selectivity than ODPA, ostensibly due to its shorter alkyl tail. Coating with tert-butylphosphonic acid, a sterically bulky ligand, decreased kinetic selectivity still further. However, methylphosphonic acid, which partially penetrated the near-surface region of the zeolite, severely lowered the diffusion rates. The use of organic films may enable rational design of selective adsorbents based on providing gas-specific resistance at the pore entrance.

Constructing superhydrophobic ZIF-8 layer with bud-like surface morphology on PDMS composite membrane for highly efficient ethanol/water separation

Emerging pervaporation technology is very promising to realize clean and renewable bioethanol recovery from biomass fermentation broth. The huge challenge of this technology is the need for a pervaporation membrane with high separation performance. Based on the solution-diffusion mechanism, pervaporation membrane for ethanol recovery should possess hydrophobic selective layer to improve sorption ability toward ethanol molecules, thereby enhancing the separation performance. In this study, a superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer with a nano-level bud-like surface morphology was grown on polydimethylsiloxane (PDMS) composite membrane via ZIF-8 particle dip-casting, secondary seeded growth, and hydrophobic modification by n-octadecylphosphonic acid for highly efficient ethanol/water separation. The mole ratio of 2-methylimidazole and zinc nitrate (Hmim/Zn2+) in the process of ZIF-8 secondary growth was systematically studied to construct appropriate micro-nano structure on PDMS composite membrane. The resultant optimal composite membrane exhibited a water contact angle of about 163° and an ethanol contact angle of 0°. In addition, it also displayed an outstanding separation factor of 17.4 corresponding to a total flux of 0.64 kg/m2 h with 5 wt% ethanol aqueous solution at 30 ℃, and thus the superior pervaporation performance to most other reported PDMS-based mixed matrix membranes. The strategy of constructing superhydrophobic layer on PDMS composite membrane may provide a meaningful guidance for preparing high-performance pervaporation membrane for organic recovery from aqueous solution.

High performance n-type organic field-effect transistors based on halogenated derivatives of naphthalene tetracarboxylic diimides

We synthesized three kinds of naphthalene tetracarboxylic diimides (NDIs) containing halogenated phenyl groups by one-step reaction, and they were used as organic semiconductor layers in top-contact Organic field-effect transistors (OFETs). Besides, we adopted SiO2/Si substrates that treated by N-octadecylphosphonic acid (ODPA). In addition, a layer of 4, 4′, 4″-triphenylamine (n-3-methylphenyl-n-phenylamine) triphenylamine (m-MTDATA) was deposited by vacuum between the organic semiconductor layer and the gold electrode as the modification material. It was found through experiments that all the organic materials synthesized by us showed n-type organic semiconductor characteristics. Happily, the device made of NDI-FAN attained the highest electron mobility of 2.2 × 10−1 cm2v−1s−1 at room temperature and in air. The crystallinity and morphology of the films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM). The results expose that introducing electron withdrawing substituents into naphthalene tetracarboxylic diimides besides inserting ODPA and m-MTDATA are effective ways to achieve high electron mobility.

Molecular Coverage Determines Sliding Wear Behavior of n-Octadecylphosphonic Acid Functionalized Cu-O Coated Steel Disks against Aluminum.

The sliding wear behavior of Cu–O coated steel disks functionalized with n-octadecyl-phosphonic acids was evaluated against aluminum in ball-on-disk tribometer experiments. After 5 m of sliding the friction coefficient of the functionalized sample with maximum molecular coverage is ≤0.3 ± 0.1. Surfaces with lower coverage mitigate friction and wear as well exhibiting initially similar low friction coefficients but reveal the breakdown of lubrication for sliding distances <5 m. The length of the low friction sliding distance before breakdown scales with the coverage of n-octadecylphosphonic acids on the Cu–O surface. Coverage hence determines the tribological behavior of the functionalized surface against sliding aluminum. As the coverage is increased, detrimental asperity contacts between the rubbing surfaces are reduced.

Synthesis of Phosphonic Acid Ligands for Nanocrystal Surface Functionalization and Solution Processed Memristors

Here, we synthesized 2-ethylhexyl, 2-hexyldecyl, 2-[2-(2-methoxyethoxy)ethoxy]ethyl, oleyl, and n-octadecyl phosphonic acid and used them to functionalize CdSe and HfO2 nanocrystals. In contrast to branched carboxylic acids, postsynthetic surface functionalization of CdSe and HfO2 nanocrystals was readily achieved with branched phosphonic acids. Phosphonic acid capped HfO2 nanocrystals were subsequently evaluated as memristors using conductive atomic force microscopy. We found that 2-ethylhexyl phosphonic acid is a superior ligand, combining a high colloidal stability with a compact ligand shell that results in a record-low operating voltage that is promising for application in flexible electronics.

Flexible, Low-Voltage, and n-Type Infrared Organic Phototransistors with Enhanced Photosensitivity via Interface Trapping Effect

Flexible and low-voltage near-infrared organic phototransistors (NIR OPTs) were prepared with a low-band gap donor-acceptor conjugated polymer as the semiconductor layer and n-octadecyl phosphonic acid modified anodic alumina (AlO x/ODPA) as the insulating layer. The phototransistors exhibit the typical n-type transistor characteristics at a voltage below 5 V. The photosensitivity of phototransistors can be enhanced by regulating the packing densities of the ODPA self-assembled monolayers and forming different trap states. The enhanced OPTs exhibit good photosensitivity to 808-980 nm NIR with the photocurrent/dark current ratio and photoresponsivity as high as 5 × 103 and 20 mA W-1, respectively, benefiting from the charge-trapping effect at the AlO x/ODPA interface. The OPTs also present a fast optical switching speed of 20/30 ms and an excellent mechanical flexibility. The outstanding performance of the NIR OPTs indicates that the development of wearable electronics is, indeed, possible.

Pickering Emulsion Stabilized by Commercial Titanium Dioxide Nanoparticles in the Form of Rutile and Anatase

The possibility of obtaining direct Pickering emulsions by means of self-organization on the oil/water interface of commercial titanium dioxide by the structure modification of rutile and anatase is studied. The stability of emulsion to coalescence is estimated microscopically. The surface properties of hydrophilic anatase nanoparticles are investigated to develop a way to partially hydrophobize their surface with molecules of n-octadecylphosphonic acid. The conditions of modifying titanium dioxide nanoparticles are chosen for the formation of stable Pickering emulsion.

N-type organic field effect transistors based on naphthalene tetracarboxylic diimides derivatives containing halogen elements

Naphthalene tetracarboxylic diimides (NDIs) derivatives, functionalized with p-fluorophenyl (NDI-FAN), p-chlorophenyl (NDI-ClAN), p-fluorobenzyl (NDI-FBN), were synthesized and used to fabricated organic field effect transistors (OFETs) through vacuum evaporation. All materials display high decomposition temperature and low LUMO energy level facilitating air stable electron transport. OFETs devices based on N-octadecylphosphonic acid (ODPA) treated SiO2/Si substrate affords electron mobility up to 1.8 × 10−1 cm2v−1s−1 with high on/off ratio of 6.7 × 103 in air. Replaced the p-fluorophenyl by p-fluorobenzyl also leads to a comparable mobility reaching 1.1 × 10−1 cm2v−1s−1 with a low threshold voltage of 1.8 V. Microstructure and morphology of thin films were investigated to shed light on the reason for distinct electrical performance. These results demonstrate that fluorinated N-substituent is an alternative method to optimize molecular arrangement and device performance.

On Stabilization of Colloidal Quantum Dots of Cadmium Selenide in the Presence of Octadecylphosphonic Acid

Classical molecular dynamics has been used to study the stabilization of colloidal quantum dots of CdSe with n-octadecylphosphonic acid molecules in combination with different auxiliary ligands, such as trioctylphosphine, trioctylphosphine oxide, and hexadecylamine. The effects of different ligands that may be formed due to interactions of n-octadecylphosphonic acid with CdO and Se in an initial mixture have been considered. It has been shown that, among these ligands, the stabilizing effect increases with a rise in the charge of a ligand per n-octadecyl chain. The role of the auxiliary ligands, e.g. octadecene that devoid of functional groups, has been studied.

Heavily-Doped SOI with SAM-Based Gate Dielectrics in Application to TMDC FETs

Semiconducting transition metal dichalcogenides (TMDC) have been growing interest for both scientific interest and practical applications because of their various material properties. Potential applications and fundamental understanding in new classes of semiconductor materials motivates the fabrication of field-effect transistors (FETs) that are indispensable for probing of carrier transport properties, accumulation of charge and interfacial phenomena. This paper reports a fabrication and characterization of TMDC FETs with heavily-doped silicon-on-insulator substrate. The silicon processing is sophisticated technology that can be extended to the reliable operation of TMDC FETs with high reproducibility. In this presented approach, the heavily-doped SOI can work as a gate electrode in FETs, while the carrier injection into TMDC layer is possible by preparing overlap structure between gate electrode and source/drain contacts. The effectiveness of our approach was demonstrated through the fabrication and characterization of FETs.P-type SOI(88 nm)/BOX(145 nm) wafer was cleaned with SPM and HF solutions. For heavily-doped n-type SOI (n+ SOI), phosphorus-doped spin-on-glass (SOG) was deposited with spin coating and baked on a hot plate at 180 oC. The substrate was annealed at 1000 oC in N2 for 30 min to perform solid phase diffusion. Then, SOG was removed by 1 % HF for 30min. For heavily-doped p-type SOI (p+ SOI), B+ ions were implanted into SOI layer. Activation was performed at 1000 oC in Ar for 30 min. SOI layer was patterned by chemical dry etching with CF4/O2. Thermal SiO2 was grown by dry oxidation at 900 oC for 10 min. Next, AlOx was deposited by RF sputtering. After contact opening with 1 % HF, Al (20 nm)/TiN (20 nm) were deposited by RF sputtering and lift-off for electrical contact to SOI. The substrates were subjected to annealing in forming gas at 420 oC for 30 min to improve the quality of gate dielectrics and electrical contact of gate pad. Al (10 nm)/Au (40nm) was deposited by thermal evaporation and lift-off for contact electrodes. Subsequently, the substrate was exposed to oxygen plasma to form hydroxyl groups on the surface of AlOx. Then, the substrate was immersed into 2-propanol containing 5 mM n-octadecylphosphonic acid (ODPA) for 6 hours at room temperature. Annealing was conducted at 100 oC in N2 for 30 min to stabilize ODPA. The gate dielectrics consists of hybrid ODPA/AlOx/SiO2. Mechanically exfoliated WS2 was transferred to the substrate with the PDMS elastomer. Finally, devices were annealed in N2 at 150 oC for 30 min to improve source/drain contact.The FET operation was observed for both n+ and p+ SOI gate. The threshold voltage (Vth) was evaluated by linear extrapolation method with the drain current measured as a function of gate voltage at a low drain voltage of 0.05 V. In the case of n+ SOI gate electrode, the Vth of -0.71 V, On/Off ratio of 103～104 and subthreshold slope (SS) of 150 mV/dec were evaluated. On the other hand, the Vth of -0.13 V, On/Off ratio of 103～104 and subthreshold slope (SS) of 107 mV/dec were obtained for p+ SOI gate electrode. The difference in Vth between n+ and p+ SOI gate electrodes is derived from the difference in the Fermi level of SOI. The proposed method is suited for research in electrical characteristics of various TMDC semiconductors.

High performance n-channel organic field-effect transistors based on halogenated derivatives of 1,2,4,5-benzenetetracarboxylic diimides

Three kind of 1,2,4,5-benzenetetracarboxylic diimides (BTDs) with halogenated phenyl groups were synthesized through one-step reaction with high yields. Top-contact organic field-effect transistors (OFETs) were fabricated via vacuum deposition of BTDs as the semiconducting channel materials on N-octadecylphosphonic acid (ODPA) treated SiO2/Si substrates. The electronic characterization was measured in ambient condition. All these derivatives exhibit excellent n-channel OFET transport with the highest mobility up to 9.2×10−2cm2v−1s−1 for BTD-ClAN deposited at room temperature. The crystallinity and morphology of film were improved by modified the substrate and demonstrated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Our results indicates that introducing electron-withdrawing substituents into 1,2,4,5-benzenetetracarboxylic diimides is an effective way to achieve high OFETs performance.

Tight Binding of Carboxylate, Phosphonate, and Carbamate Anions to Stoichiometric CdSe Nanocrystals.

To completely displace the carboxylate surface ligands from cadmium selenide nanocrystals, oleic acid impurities are first removed using dimethylcadmium or diethylzinc. In addition to metal carboxylate and methane coproducts, reactions with CdMe2 produce surface bound methyl groups (δ = 0.4 ppm, 0.04-0.22 nm-2) that photolytically dissociate to methyl radicals and n-doped nanocrystals. Without oleic acid impurities, cadmium carboxylate can be completely displaced from the surface using n-alkylamines (NH2R', R' = n-butyl, n-hexyl, n-octyl) (≤0.01 carboxylates nm-2). Colloidal dispersions of amine bound nanocrystals (CdSe-NH2R') are indefinitely stable at amine concentrations of 0.1 M or higher and slowly aggregate at lower concentrations. Dissociation and evaporation of the amine ligands in 4-ethylpyridine, tri-n-butylphosphine, or molten tri-n-octylphosphine oxide solution results in nanocrystal aggregation. CdSe-NH2R' reacts with oleic acid, n-octadecylphosphonic acid, or carbon dioxide to form surface bound n-alkylammonium oleate, phosphonate, and carbamate ion pairs that bind with greater affinity than primary n-alkylamines. The results indicate that nanocrystal dispersions solely stabilized by neutral donor ligands are relatively unstable compared to those stabilized by adsorbed metal carboxylate or phosphonate complexes or by ion pairs. The challenge of differentiating between the neutral ligand bound form and adsorbed ion pairs is discussed.

Features of the influence of stabilizing ligands on luminescence properties of cadmium selenide colloidal quantum dots

It has been shown that immediately after the synthesis, the luminescence efficiency of CdSe quantum dots stabilized by n-octadecylphosphonic acid together with one of the auxiliary ligands decreases in the order: oleylamine, hexadecylamine, trioctylphosphine oxide, 1-octadecene, and stearic acid, which is due to combination of the energy of their binding with surface atoms of the nanoparticles and the packing density of the ligands in the shell. In the course of post-synthetic ripening of the quantum dots in a solution, changes in their luminescence quantum yield occur, depending on the solvent polarity and due to rearrangement of the ligands in the shells. The effect of dark recovery of trap luminescence from UV-irradiated quantum dots stabilized by octadecylphosphonic acid and a long-chain amine has been found.

Luminescent properties of CdSe quantum dots in dispersion media with different polarity

It has been found that the luminescence quantum yield of CdSe colloidal quantum dots (QD) synthesized in the presence of n-octadecylphosphonic acid and trioctylphosphine oxide significantly depends on the polarity of the medium in which they are dispersed and increases with decreasing the polarity of the medium. Different methods of increasing the quantum yield have been studied; the conditions have been found under which its value reaches 0.9, which is comparable to record values currently known for core@shell QD and is maximum for QD without an additional semiconductor shell. The effect of precipitating solvents on the luminescence efficiency of QD has been studied.

Preparation of mesoporous ZrO2-coated magnetic microsphere and its application in the multi-residue analysis of pesticides and PCBs in fish by GC–MS/MS

A novel mesoporous ZrO2 immobilized magnetic Fe3O4 microsphere (m-ZrO2@Fe3O4) was successfully synthesized and characterized by transmission electron microscope (TEM), X-ray diffractometer (XRD), nitrogen adsorption measurement (NAM), energy-dispersive X-ray analysis (EDX), vibrating sample magnetometer (VSM). Then the resultant m-ZrO2@Fe3O4 and an n-octadecylphosphonic acid modified magnetic microsphere (Fe3O4-OPA) were employed as clean-up co-adsorbents of QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method for the analysis of 42 pesticides and 7 polychlorinated biphenyls (PCBs) in fish samples. Lipid co-extractives such as fatty acids in QuEChERS extracts could be efficiently removed through the Lewis acid–Lewis base interaction between m-ZrO2@Fe3O4 and carboxylic groups, while some other apolar interferents could be adsorbed through hydrophobic interaction by Fe3O4-OPA. Meanwhile, the magnetic property of adsorbents endows the clean-up procedure with manipulative convenience. Several parameters affecting the clean-up performance were investigated. Under the optimal conditions, the modified QuEChERS method combined with gas chromatography–tandem mass spectrometry (GC–MS/MS) for the multi-class, multi-residue analysis of pesticides and PCBs in fish samples was validated according to linearility, recovery and precision. Good linearities were obtained for all analytes with R2 larger than 0.9903. Limits of detection (LODs) were found to be in the range of 0.02–4.40ng/g. The method recoveries of all analytes spiked at three concentration levels in blank fish samples were from 69.8% to 117.1%, with the intra-day and inter-day relative standard deviations (RSDs) less than 13.4% and 16.5%, respectively.

Synthesis of Fe-doped octahedral Pt3Ni nanocrystals with high electro-catalytic activity and stability towards oxygen reduction reaction

Octahedral Pt3Ni nanocrystals doped with Fe (Pt3Ni-Fe) are synthesized through solvothermal methods in N,N-dimethylformamide solvent at 210 °C. By manipulating the amount of combinational capping agents, the size of the octahedral Pt3Ni-Fe nanocrystals can be controlled between 7 and 19 nm. It is found that one of the capping agents, n-octadecylphosphonic acid, is critical in obtaining the octahedral morphology. A volcano-shaped relation between oxygen reduction reaction (ORR) activity and nanocrystal size is determined for the carbon-supported octahedral Pt3Ni-Fe, with the highest ORR activity observed from the 13 nm nanocrystal. It is also found that Pt3Ni-Fe electro-catalysts show enhanced stability. This work demonstrates that Fe-doping can enhance the electro-catalytic performance of octahedral Pt3Ni.

X-ray and neutron investigation of self-assembled lipid layers on a titanium surface

Titanium is the most widely preferred metal material for bone reconstruction in orthopedics and dentistry. To improve its biological performance, various coatings can be applied. In this investigation, a biomimetic coating on a model implant surface was studied in X-ray and neutron reflectivity experiments to probe the quality of this coating, which is only few nanometers thick. Titanium was deposited on polished silicon surfaces using a magnetron sputtering technique. To improve the lipid coating's stability, a stronger van der Waals interaction was first created between the implant surface and the biomimetic coating by adding a phosphonic acid (n-octadecylphosphonic acid - OPA) monolayer onto the surfaces. Then, three monolayers of POPE (phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-ethanolamine) were transferred using the Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques. The analysis of X-ray and neutron specular reflectivity data shows that OPA molecules cover the model implant surface completely and that approximately 50% coverage of POPE can be achieved by LB and LS transfer.

Application of phosphonic acid self-assembled monolayer in organic field-effect transistors

This study explores a strategy of using phosphonic acid derivative as self-assembled monolayer (SAMs) on Si/SiO2 surface and using 6,13-pentacenequinone (PQ) as the template layer to induce the crystallization of 6,13-diphenylpentacene (DPP) in vacuum deposited thin film transistors, which showed the field-effect mobility as high as 8.3×10−3cm2/Vs. It is found that n-Octadecylphosphonic acid (ODPA) SAMs plays a unique role in modulating the morphology of PQ to form flat layer, which is helpful for crystallization of DPP. This indicated that ODPA bilayer-step surface play important roles in controlling the growth of both PQ and DPP by vacuum thermal deposition.

Tribological and stability investigations of alkylphosphonic acids on alumina surface

Alumina substrates are commonly used for various micro-/nanoelectromechanical systems (MEMS/NEMS). For efficient and lifetime longevity of these devices, lubricant films of self-assembled monolayers (SAMs) with nanometer thickness are increasingly being employed. In the present paper, we report preparation, tribological and stability investigations of alkylphosphonic acids on the alumina surface.The alkylphosphonic acids were prepared on the alumina surface using the liquid phase deposition method. The effectiveness of modification of the alumina surface by alkylphosphonic acids was investigated using water contact angle measurements, secondary ion mass spectrometry, X-ray photoelectron and infrared spectroscopy.Frictional behavior in milinewton load range was studied by microtribometry. It is shown that surface modification of the alumina surface by alkylphosphonic acids reduces the coefficient of friction values compared to the unmodified alumina. In comparison to the non-modified alumina surface, all tested alkylphosphonic acids cause a decrease in the friction coefficients in friction tests for counterparts made from different materials, such as steel, zirconia and silicon nitride. It is also found that the alumina surface modified by alkylphosphonic acids with longer chain has a higher degree of hydrophobicity and lower coefficient of friction. The best frictional properties are obtained for the system consisting of the alumina surface modified by n-octadecylphosphonic acid and silicon nitride counterpart.Stability tests in different environmental conditions: laboratory, acidic and alkaline solutions were also monitored.