P-phenylenediamine Research Articles

Lightweight and highly heat-resistant copolymerized polyimide foams for superior thermal insulation and acoustic absorption

The development of lightweight and highly heat-resistant polyimide foams (PIFs) remains a great challenge in areas of aerospace, military ships, transportation, and industries. Herein, a series of lightweight and highly thermal-resistant copolymerized PIFs are successfully fabricated by the “stepwise heating-holding” thermal foaming of the copolymerized polyester ammonium salts (C-PEAS), using 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) and 2,3,3′,4′-biphenyl tetracarboxylic acid dianhydride (α-BPDA) as codianhydride, and p-phenylenediamine (PDA) as diamine. The introduction of α-BPDA increases the rigidity of PI molecule chains and foamability of C-PEAS, and significantly improves the heat resistance of PIFs. The resultant copolymerized PIFs exhibit ultra-low densities (<10 kg m−3), excellent heat resistance (Tg ranging from 351.2 °C to 405.6 °C), and high thermal stability. Moreover, they possess high flame retardancies (LOI>44 %) and low thermal conductivities (as low as 0.0463 W m−1 K−1 at 20 °C and no more than 0.0825 W m−1 K−1 at 200 °C), demonstrating their excellent thermal insulation properties in a wide temperature range. After the continuous heating at 200 °C for 40 min, the upper surface of PIFs present low average temperatures less than 60 °C. Additionally, the copolymerized PIFs exhibit remarkable acoustic properties with average acoustic absorption coefficients above 0.6 and noise reduction coefficients (NRC) above 0.3. Therefore, the lightweight and highly heat-resistant copolymerized PIFs show great application potentials in the extreme environments of aerospace, military ships, transportation, and industries.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation.

Perylene diimides (PDIs) have garnered considerable attention due to their immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI-PDA, by linking an ortho-substituted PDI with p-phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron-transfer dynamics, leading to a ten-fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI-PDA compared to the PDI molecular counterpart, with yields exceeding 90 %. Electron property studies and density functional theory calculations show that the PDI-PDA with its well-defined crystal structure, enhances π-π stacking and lowers the electron transition barrier. Moreover, the strong electron-withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI-PDA, suppressing the rapid recombination of photogenerated electron-hole pairs and improving the charge-separation efficiency to give high photocatalytic efficiency. This study provides a brief but effective way for improving the photocatalytic efficiency of commonly used PDI-based dyes by integrating them into a framework skeleton.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation

AbstractPerylene diimides (PDIs) have garnered considerable attention due to their immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI‐PDA, by linking an ortho‐substituted PDI with p‐phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron‐transfer dynamics, leading to a ten‐fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI‐PDA compared to the PDI molecular counterpart, with yields exceeding 90 %. Electron property studies and density functional theory calculations show that the PDI‐PDA with its well‐defined crystal structure, enhances π–π stacking and lowers the electron transition barrier. Moreover, the strong electron‐withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI‐PDA, suppressing the rapid recombination of photogenerated electron‐hole pairs and improving the charge‐separation efficiency to give high photocatalytic efficiency. This study provides a brief but effective way for improving the photocatalytic efficiency of commonly used PDI‐based dyes by integrating them into a framework skeleton.

Effect of chemical structures and environmental factors on the thermal degradation mechanism of polyimide: Experiments and molecular dynamics simulations

The impact of chemical structure and environment on the thermal stability of polyimide (PI) was examined, and the degradation mechanism was determined using a combination of experiments and molecular simulations. Changes in mechanical properties and thermogravimetric analysis (TGA) were used to characterize the thermal stability of PI. Pyrolysis gas chromatography mass spectrometry (Py-GCMS) and thermogravimetric-infrared spectroscopy (TG-IR) were used to analyze the degradation products both qualitatively and quantitatively. Molecular simulation was employed to analyze the primary bond breakage and thermal degradation pathways of PI, as well as to investigate the effects of the chemical structure, atmosphere, and temperature on degradation properties. The findings indicated that p-benzene-structured 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (PDA) has the best thermal stability, whereas weak bonds like C–O–C in 4,4′-oxydianiline (ODA) and C–N in the 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) imidazole group decrease thermal stability. The formation path of low molecular weight products (CO2, CO, HCN, and NH3) and the potential degradation mechanism of PI were proposed. The process of PI thermal degradation accelerated by oxygen and high temperature was observed at the atomic level. Taken together, this work offers the possibility of monitoring the structural evolution of PI degradation process in real-time.

Large Area Film of Highly Crystalline, Cleavable, and Transferable Semi-Conducting 2D-Imine Covalent Organic Framework on Dielectric Glass Substrate.

Two dimensional (2D) imine-based covalent organic framework (COF), 2D-COF, is a newly emerging molecular 2D polymer with potential applications in thin film electronics, sensing, and catalysis. It is considered an ideal candidate due to its robust 2D nature and precise tunability of the electronic and functional properties. Herein, we report a scalable facile synthesis of 2D imine-COF with control over film thickness (ranging from 100 nm to a few monolayers) and film dimension reaching up to 2 cm on a dielectric (glass) substrate. Highly crystalline 2D imine polymer films are formed by maintaining a quasi-equilibrium (very slow, ∼15 h) in Schiff base condensation reaction between p-phenylenediamine (PDA) and benzene-1,3,5-tricarboxaldehyde (TCA) molecules. Free-standing thin and ultrathin films of imine-COF are obtained using sonication exfoliation of 2D-COF polymer. Insights into the microstructure of thin/ultrathin imine-COF are obtained using scanning and transmission electron microscopy (SEM and TEM) and atomic force microscopy (AFM), which shows high crystallinity and 2D layered structure in both thin and ultrathin films. The chemical nature of the 2D polymer was established using X-ray photoelectron spectroscopy (XPS). Optical band gap measurements also reveal a semiconducting gap. This is further established by electronic structure calculation using density functional theory (DFT), which reveals a semiconductor-like band structure with strong dispersion in bands near conduction and valence band edges. The structural characteristics (layered morphology and microscopic structure) of 2D imine-COF show significant potential for its application in thin film device fabrication. In addition, the electronic structure shows strong dispersion in the frontier bands, making it a potential semiconducting material for charge carrier transportation in electronic devices.

Preparation of antimicrobial composite from Arabic gum-grafted-poly(p-phenylene diamine)/MOF(Fe) decorated with Cu nanoparticles as a unique nanobiosorbent for removal of cloxacillin antibiotic

The growth of the world population has led to an increase in the demand for fresh water. Water pollution is often caused by hasty urbanization without proper management of hazardous waste. Therefore, it is vital to implement new methods to remove pollutants from water. In the current study, an antimicrobial nanocomposite adsorbent composed of Arabic gum-grafted-poly(para phenylene diamine) (AG-g-PpPA) decorated with metal-organic framework and copper nanoparticles (AG-g-PpPA@MOF(Fe)/Cu) was synthesized via in-situ copolymerization. The nanocomposite was utilized for eliminating the antibiotic cloxacillin from water solutions. The effects of different factors were analyzed, including pH, the quantity of adsorbent, contact time, and preliminary cloxacillin concentrations. Ideal parameters were pH 7, 5 mg adsorbent dosage, 10 min contact time, and an initial 500 mg/L cloxacillin concentration. The adsorption process followed the Freundlich isotherm equation, with a maximum adsorption ability of 400 mg/g. The kinetics information appropriately fits a pseudo-second-order model. Thermodynamic calculation showed the adsorption occurred spontaneously. The nanocomposite also displayed antibacterial action in contradiction to Escherichia coli and Staphylococcus aureus. Additionally, the adsorbent could be recovered and reused effectively. The excellent adsorption ability highlights the potential of AG-g-PpPA@MOF(Fe)/Cu adsorbent for eliminating pharmaceutical pollutants from wastewater.

Preparation of anisotropic polyimide aerogels for thermal protection with outstanding flexible resilience using the freeze-drying method.

Polyimide aerogels (PIAs) not only possess excellent thermodynamic properties but also have a high porosity structure, making them an exceptional protective and thermal insulation material, and further broadening their application scope in aerospace and other cutting-edge fields. In this work, a series of anisotropic polyimide aerogels (3,3',4,4'-biphenyltetracarboxylic dianhydride (S-BPDA), p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA)) with excellent properties were prepared. These PIAs were obtained by unidirectional freeze-drying and thermal amination of two different precursor solutions mixed in proportion. These PIAs possess an irregularly oval tubular structure, exhibiting pronounced anisotropy. (PIA-2 exhibits outstanding flexible resilience in the radial direction. It can still regain its original form after half an hour of compression by a universal testing machine, yet it cannot do so in the axial direction. The thermal diffusivity of PIA-5 in the radial direction at room temperature is as low as 0.067 mm2 s-1, and even at 200 °C, the thermal diffusivity is as low as 0.057 mm2 s-1. Meanwhile, the thermal diffusivity in the axial direction at room temperature is 0.11 mm2 s-1, surpassing the value of 0.106 mm2 s-1 of aerogels prepared from monomeric raw materials and dried under supercritical conditions). PIAs exhibit outstanding thermal stability (the axial strength and modulus retention of PIA-8 at 200 °C are as high as 52.63% and 44.82%), and its weight loss temperature of 5% is as high as 603 °C and it has a glass softening temperature of 387 °C. PIAs also demonstrate exceptional flame retardancy in imitation flame retardant experiments and exhibit outstanding thermal insulation performance when heated on a 150 °C heating plate for 10 minutes (the radial surface temperature of PIA-5 was only 49.9 °C). These anisotropic PIAs materials exhibit outstanding flexible resilience, and thermal protection performance, holding significant importance for their widespread adoption as thermal insulation materials in aerospace, high-precision electronic components, and other domains.

Construction of covalent organic frameworks membranes in situ through nonsolvent-induce phase separation for fast and accurate nanofiltration

With the development of covalent organic frameworks (COFs), their superior separation performance in membrane separation has gradually becoming apparent. The method of combining COFs with membrane materials is crucial for their applications prospect. In this study, inspired by the traditional Chinese mortise and tenon structure, we selected 1,3,5-triacetaldehyde mesityl phenol (TFP) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as the reactive building monomers. P-Phenylenediamine (PDA) was introduced into the casting solution to construct Polyether-sulfone (PES) bottom membranes with amino ligand sites, utilizing the phase transition effect generated by the non-invasive solvent-induced method (NIPS). Subsequently, COFs composite nanofiltration membranes with two-dimensional layered structures were prepared through mild interfacial polymerization (IP) under optimized reaction conditions. The synthesis of COFs composite nanofiltration membranes was demonstrated through a series of characterizations, including scanning transmission electron microscopy and infrared spectroscopy. The COFs composite nanofiltration membranes synthesized by this method exhibited better alignment, greater chemical stability, and higher separation efficiency compared to traditional interracially polymerized COFs composite nanofiltration membranes. As the method involves the addition of additives, it can be more widely applied to a broad range of organic polymer membranes. Furthermore, we demonstrated the effectiveness of the COF composite nanofiltration membranes produced using this method in the separation of molecular dyes. They exhibited rejection exceeding 99% for 0.1 g L−1 methyl blue (MB), Congo red (CR) and chrome black-T (EBT). Additionally, they achieved separation fluxes of up to 300 L m−2 h−1 bar−1 for mixed solutions (dyes/salts) and proved to be effective under extreme conditions, such as 1 M HCl/NaOH. Moreover, COFs-NH2PES composite nanofiltration membranes exhibited the ability to efficiently separate dye molecules of different sizes. This work introduces new ideas for constructing stable and durable COF functional composite membrane materials for practical applications.

Effect of Water Absorption on Electric Properties of Temperature-Resistant Polymers.

The effects of water absorption on the electric resistivity and dielectric constant of polyimide (PI) and poly(ethylene terephthalate) (PET) were investigated, and the mechanism of deterioration in electrical insulation properties was discussed. The polyimides are poly(oxydianiline pyromellitimide) (PMDA-ODA) and poly(para-phenylene diamine biphenyltetracarboxydiimide) (BPDA-PDA). These polymer films were immersed in pure water for various immersion times at room temperature, and the water absorption ratio was evaluated. The electric resistance for these films was measured at room temperature using a high-resistance meter, and the dielectric constant at room temperature was measured using an LCR meter in a frequency range of 200 kHz to 2 MHz. The absorption ratios at equilibrium absorption for PMDA-ODA, BPDA-PDA, and PET were 2.7, 2.5, and 0.5%, respectively. The critical volume fraction of the percolation threshold of electric conductivity due to water absorption was 0.034 for both PMDA-ODA and BPDA-PDA. On the other hand, PET did not show a significant decrease in the resistivity. For both PIs and PET, the dielectric constant observed could be explained by a series model of the respective capacitances of pure water and polymer. Actually, the resistivity of samples cut from the edges of the film after water absorption was almost the same value as that in the dry state. These results suggest that the absorbed water molecules are not uniformly dispersed in the film but are localized at the edges of the film even after the absorption equilibrium has been reached.

Exploring the surface plasmon catalytic reactions mechanism by three-phase interface modification combining with in-situ EC-SERS methods

Local surface plasmon resonance (LSPR) is a novel catalytic technique that has emerged in recent years, especially in the catalysis of aromatic amine compounds. However, the response process and mechanism are still unclear in current study. In the current field of study, the response process and mechanism are still unclear. In this work, the gas–liquid-solid three-phase interface (GLSTI) was innovatively utilized in this study to validate the reaction mechanism by surface-enhanced Raman spectroscopy. P-Aminothiophenol (PATP) and P-Phenylenediamine (PDA) underwent a surface plasmon-catalyzed reaction by using a silver nano-dendrites substrate with strong SERS activity. The GLSTI significantly facilitates the occurrence of surface plasmon catalytic reactions, which can supply enough oxygen by providing three-phase points. In situ SERS and EC-SERS technologies were combined in this study for the explorations. Therefore, this work is dedicated to deepening the exploration and expanding into new directions in plasmon-induced catalytic reactions.

Role of Patch Testing in Facial Contact Dermatitis: A Cross-Sectional Study from Central India.

Facial contact dermatitis is an emerging skin disorder due to the use of a large array of materials over the face. It leads to psychological distress in patients, impacting their quality of life. Most of the allergens applied over the face vary as per cosmetic or herbal products' availability, usage, or religious practices. Identifying and discontinuing the implicated allergens will lead to a better prognosis and reduced morbidity in clinical practice. To determine the frequency of different allergens responsible for causing facial contact dermatitis, in an urban part of central India, using patch test with the help of Indian standard and cosmetic series. All suspected patients (>18 years) of facial contact dermatitis visiting the outpatient department of dermatology were patch tested with both Indian standard and cosmetic series. Out of 38/58 patch-test-positive patients, 71.06% were females, and 28.94% were males. Most patch-test-positive females were housewives. The most common allergens implicated were thiomersal (17.24%), followed by fragrance mix (15.51%), and paraphenylene diamine (12.06%). In our study, forehead and malar areas were most commonly involved indicating fairness creams and perfumes as the important contributors to facial contact dermatitis. Antigen batteries need to be updated with changing social and cultural trends, as many with a consistent history of aggravation with some products tested negative in patch tests.

A novel chalcone compound as a reagent for the validation of pharmaceutical cefotaxime sodium preparations

This paper reports the synthesis of a new heterocyclic compound, 2,7-dicloropyrido[2,3-g]quinoline-3,8-dicarbaldehyde, from p-phenylene diamine by converting p-acetanilide (1) and reacting with Vilsmeier-Haack reagent (2). Chalcone(3) is produced when two moles of 2-acetyl naphthalene respond with the two carbaldehydes in compound (2). This chalcone serves as a reagent for quantifying amino group-containing pharmaceutical compounds. At the same time, a sensitive spectrophotometric technique has been created and used in pharmaceutical preparations to measure cefotaxime sodium by diazotizing and coupling with chalcone reagent. The recommended method diazotizes the medicinal molecule with sodium nitrite in an acidic solution to form the diazonium salt. This salt is combined with Chalcone reagent in an essential medium to create a stable and colorful azo dye soluble in water. Maximum absorption of the product is shown at 406 nm. Throughout the concentration range of 0.5–30 µg/ml, Beer's law was followed. The M absorptivity was (18381.44) liters mol-1. cm-1, the average recovery rate was 100.48 percent, and the relative standard deviation was less than 0.9 %. Injection-ready pharmaceutical preparations were the focus of the methodology.

First Principles Modelling of Growth of Hybrid Organic-Inorganic Films

Hybrid organic-inorganic materials fabricated with molecular layer deposition (MLD) are a special class of materials that are attracting great interest in many economically and socially relevant technological applications due to their diphasic and tunable organic-inorganic structure. Despite the growing interest in these hybrid materials, knowledge around relevant precursor chemistries and reaction mechanisms, as well as details of many determined experimental results are unknown. Density functional theory (DFT) has proven to be a powerful tool to investigate and understand the atomic level details of the precursor chemistry and address aspects of the MLD experiments.In our work, we use first principles DFT calculations to examine key steps in the mechanism of hybrid film deposition through MLD by modelling precursor-surface and precursor-precursor reactions. We explore the growth mechanism of aluminium and titanium containing hybrid films, namely alucones and titanicones. Both materials are of high interest for passivation layers in batteries. For alucones we investigate in detail the chemistry of the MLD process between the post-trimethylaluminium (TMA) pulse methyl-terminated Al2O3 surface with aromatic compounds with hydroxy and/or amino groups as reactive groups: hydroquinone (HQ), 4-aminophenol (AP) and p-phenylenediamine (PD). Double reactions of HQ, AP and PDA with the Al2O3 surface are explored in detail to assist the interpretation of the experimental findings regarding the differences found for hybrid films grown with aromatic and aliphatic organic precursors. DFT calculations show that in contrast to aliphatic organics, an upright configuration will be present for HQ, AP and PD so that the molecules are self-assembled in an upright configuration, which leads to thicker hybrid films. We predict that aromatic molecules are the best choice for stable hybrid films and their chemistry can be manipulated without degrading stability. [1]We also investigate in detail the chemistry between the most common titanium precursors, namely titanium tetrachloride (TiCl4) and tetrakis(dimethylamido)titanium (Ti(DMA)4), and ethylene glycol (EG) and glycerol (GL) as the organic precursors for the fabrication of titanicone films. We analyse the impact of the substrate on the initial MLD reactions in titanicone film growth using three different surface models: anatase TiO2, rutile TiO2 and Al2O3. This work highlights the role of the phase of TiO2 and Ti-containing precursors in production of titanicone films and provides motivation to develop a new rutile TiO2 based hybrid film suggesting that the desired film growth, flexibility and stability can be achieved. [2][1] A. Muriqi, M. Karppinen and M. Nolan, Role of terminal groups in aromatic molecules on the growth of Al2O3-based hybrid materials, Dalton Transactions, 2021, 50, 17583-17593. doi.org/10.1039/D1DT03195C.[2] Arbresha Muriqi and Michael Nolan, “Role of Titanium and Organic Precursors in Molecular Layer Deposition of “Titanicone” Hybrid Materials”, Beilstein Journal of Nanotechnology, 2022, 13, 1240–1255. doi.org/10.3762/bjnano.13.103.

Atomically dispersed Fe sites on hierarchically porous carbon nanoplates for oxygen reduction reaction

Developing cost-effective, robust and stable non-precious metal catalysts for oxygen reduction reaction (ORR) is of paramount importance for electrochemical energy conversion devices such as fuel cells and metal-air batteries. Although Fe-N-C single atom catalysts (SACs) have been hailed as the most promising candidate due to the optimal binding strength of ORR intermediates on the Fe-N4 sites, they suffer from serious mass transport limitations as microporous templates/substrates, i.e., zeolitic imidazolate frameworks (ZIFs), are usually employed to host the active sites. Motivated by this challenge, we herein develop a hydrogen-bonded organic framework (HOF)-assisted pyrolysis strategy to construct hierarchical micro/mesoporous carbon nanoplates for the deposition of atomically dispersed Fe-N4 sites. Such a design is accomplished by employing HOF nanoplates assembled from 2-aminoterephthalic acid (NH2-BDC) and p-phenylenediamine (PDA) as both soft templates and C, N precursors. Benefitting from the structural merits inherited from HOF templates, the optimized catalyst (denoted as Fe-N-C SAC-950) displays outstanding ORR activity with a high half-wave potential of 0.895 V (vs. reversible hydrogen electrode (RHE)) and a small overpotential of 356 mV at 10 mA cm−2 for the oxygen evolution reaction (OER). More excitingly, its application potential is further verified by delivering superb rechargeability and cycling stability with a nearly unfading charge–discharge gap of 0.72 V after 160 h. Molecular dynamics (MD) simulations reveal that micro/mesoporous structure is conducive to the rapid mass transfer of O2, thus enhancing the ORR performance. In situ Raman results further indicate that the conversion of O2 to *O2− the rate-determining step (RDS) for Fe-N-C SAC-950. This work will provide a versatile strategy to construct single atom catalysts with desirable catalytic properties.

Ingestion of car tire crumb rubber and uptake of associated chemicals by lumpfish (Cyclopterus lumpus)

Car tire rubber constitutes one of the largest fractions of microplastics emissions to the environment. The two main emission sources are tire wear particles (TWPs) formed through abrasion during driving and runoff of crumb rubber (CR) granulate produced from end-of-life tires that is used as infill on artificial sports fields. Both tire wear particles and crumb rubber contain a complex mixture of metal and organic chemical additives, and exposure to both the particulate forms and their leachates can cause adverse effects in aquatic species. An understanding of the exposure pathways and mechanisms of toxicity are, however, scarce. While the most abundant metals and organic chemicals in car tire rubber have multiple other applications, para-phenylenediamines (PDs) are primarily used as rubber antioxidants and were recently shown to cause negative effects in aquatic organisms. The present study investigated the responses of the marine lumpfish (Cyclopterus lumpus) to crumb rubber exposure in a controlled feeding experiment. Juvenile fish were offered crumb rubber particles with their feed for 1 week, followed by 2 weeks of depuration. Crumb rubber particle ingestion occurred in &amp;gt;75% of exposed individuals, with a maximum of 84 particles observed in one specimen. Gastrointestinal tract retention times varied, with some organisms having no crumb rubber particles and others still containing up to 33 crumb rubber particles at the end of the experiment. Blood samples were analyzed for metals and organic chemicals, with ICP-MS analysis revealing there was no uptake of metals by the exposed fish. Interestingly, high resolution GC-MS analysis indicated that uptake of PDs into lumpfish blood was proportionate to the number of ingested CR particles. Three of the PDs found in blood were the same as those identified in the additive mixture Vulkanox3100. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) was the most concentrated PD in both the crumb rubber and lumpfish blood. The transformation product 6PPD-quinone was detected in the rubber material, but not in the blood. This study demonstrates that PDs are specific and bioavailable chemicals in car tire rubber that have the potential to serve as biomarkers of recent exposure to tire chemicals, where simple blood samples could be used to assess recent tire chemical exposure in vertebrates, including humans.

Chemical vapour deposition in narrow capillaries: Electro-osmotic flow control in capillary electrophoresis

BackgroundIn capillary electrophoresis (CE), the inner surface of fused-silica capillaries is commonly covalently modified with liquid silanes to control electroosmotic flow (EOF). This liquid phase deposition (LPD) approach is challenging for long and narrow-diameter capillaries (≥1 m, ≤25 μm ID) inhibiting commercial production. Here, we use chemical vapour deposition (CVD) to covalently modify capillaries with different silanes. Using a home-built CVD device, capillaries were modified with neutral (3-glycidyloxypropyl) trimethoxysilane (GPTMS), the weak base (3-aminopropyl) trimethoxysilane (APTMS), the weak acid 3-mercaptopropyltrimethoxysilane (MPTMS) and the neutral hydrophobic trichloro(1H,1H,2H,2H-perfluorooctyl) silane (PFOCTS). Gas-phase modification of GPTMS with acid and ammonia allowed further modification of the surface prior to molecular layer deposition (MLD) of poly(p-phenylene terephthalamide) (PPTA) using the self-limiting sequential reaction between terephthalaldehyde (TA) and p-phenylenediamine (PD) vapours. ResultsCapillaries coated with GPTMS by CVD showed a greater reduction in EOF at all pH values than the conventional LPD. APTMS showed a reduction of the EOF at pH 9, with EOF reversal observed below pH 6. MPTMS provided a slightly lower EOF than an unmodified capillary at high pH, and a slightly higher EOF at lower pH. PFOCTS provided the most consistent EOF as a function of pH. The deposition of successive layers of PPTA resulted in increased surface coverage of the polymer and a greater reduction in EOF at pH higher than 5. The stability of a 10 μm ID GPTMS coated capillary was tested at pH 8.8 in a 200 mM CHES/Tris BGE for the separation of inorganic anions. Over 1.5 months of continuous operation (≈4130 runs), the reproducibility of the apparent mobilities for chloride, nitrite, nitrate and sulfate were 2.43%, 2.56%, 2.63% and 3.05%, respectively. The intra-day and inter-day column-to-column reproducibility and batch-to-batch reproducibility for all the coated capillaries ranged between 0.34% and 3.95%. SignificanceThe study demonstrates the superior performance of CVD coating for suppressing the EOF compared to LPD allowing the easy modification of long lengths of narrow capillary. The variation in silane, and the ability of MLD to modify and control the surface chemistry, provides a simple and facile method for surface modification. The stability of these coatings will allow long-term capillary electrophoresis monitoring of water chemistry, such as for monitoring fertiliser run-off in natural waters.

Thermally degraded polyurea as cathode catalyst of an anion exchange membrane fuel cell

Cobalt-doped, MDI (methylene diphenyl diisocyanate)-based polyurea (Co-MPUr) is prepared from the condensation polymerization between p-phenylene diamine (PDA) and MDI in the presence of cobalt ions (Co(II)), which is calcined to become the Co, N–co-doped carbonaceous cathode catalysts (Co–N–Cs). Fourier Transform Infrared Spectrometer (FT-IR) is used to prove the successful synthesis of the MDI-based polyurea (MPUr) structure. The porous and coral-like morphologies of the calcined Co-MPUr are characterized by transmission electron microscope (cryo-TEM) and high-resolution transmission electron microscope (HR-TEM), and field-emission scanning electron microscope (FE-SEM). The extremely high specific surface area (> 900 m2 g–1) and porosity are analyzed by BET analyzer. Sharp graphite diffraction peaks are found in the x-ray diffraction (XRD) patterns, resulting from the high crystallinity, and Raman spectra demonstrate higher G-band intensity than D-band. The cathode catalyst performance (ORR: oxygen reduction reaction) of the Co–N–Cs compared with commercial Pt/C catalysts are characterized by current-voltage (CV) and linear sweeping voltage (LSV) curves. The single cell using Co–N–C catalyst as cathode catalyst (CC) demonstrates a high maximum power density (Pmax) of 327.6, compared to 286.4 mW cm−2 of Pt/C.

Synthesis, Characterization and Conductivity Studies of Poly(p-phenylenediazomethine)/Polyethylene blends

The structural requirement for a conducting polymer is a conjugated π electron system. It can be easily oxidised or reduced by charge -transfer agents which are called dopants. In the present study, a new conducting polymer based on glyoxal and p-phenylene diamine was synthesized in DMF and was characterized by IR spectra, GPC and TGA. In-situ polymerization of glyoxal and p-phenylenediamine was done in DMF containing different amounts of PE. The D.C. conductivity and the effect of dopants like HC1O4, HCl and 12 on conductivity of each sample was studied. The D.C. conductivity of the samples increased on doping with HCI, HC1O4 and iodine while the D.C. conductivity of all blends decreased with increase in the amount of polyethylene.

Design and synthesis of dual functional porphyrin-based COFs as highly selective adsorbent and photocatalyst

In this work, amide bonds linked 2D porphyrin-based covalent organic framework (Por-PD-COF) was designed and synthesized through condensation reaction between meso-tetrakis (p-carboxyphenyl) porphyrin (TCPP) and para-phenylenediamine (PD). Large surface area, abundant active sites and good stability of Por-PD-COF made it can quickly and efficiently absorb methylene blue (MB) selectively and remove it from aqueous solution. More importantly, in different mixture of organic dyes including RhB and MB, MB and MO, Por-PD-COF can selectively adsorb MB with a large adsorption capacity (328.57 mg·g−1), while a little MO and hardly RhB because of the unique charge selectivity and specific pore size. Especially in the mixture solution of MO and MB, compatitive adsorption appeared, MB can substitute the adsorbed MO on the active sites in the channel of Por-PD-COF. Furthermore, with the band gap narrow to 1.02 eV, Por-PD-COF could be used as efficient photocatalyst to degrade MB (99%, 180 min) directly under visible light irradiation, and can be reused for four times with almost no absorptive and photocatalytic capacity losing. The possible adsorption and photocatalytic mechanisms of Por-PD-COF were also proposed. As a result, with the uncomplicated preparation, effective and selective adsorption and reusability, Por-PD-COF was a promising specific adsorbent and photocatalyst for further application in specific organic molecules separation and organic waste removal from aqueous solution.

Detection of trimethylamine (TMA) gas using mixed shape cobalt doped ZnO nanostructure

Mixed shape cobalt (Co) doped ZnO nanostructures was synthesize using hydrothermal method with variable amount (0, 5 and 15%). The synthesized nanostructures were found to be selective towards trimethyl amine (TMA) sensing. The impact of doping on structural, optical, thermal stability, morphology and shape of Co doped ZnO nanostructures were studied using XRD, FT-IR, XPS, UV–Visible, HR-TEM, SAED, FESEM and EDS. The doping concentration was optimized for maximal gas response. ZnO and Co doped ZnO nanostructures were used to study TMA sensing at various temperatures (RT, 50, 75, 100, 125 °C) and found to be optimal at 100 °C for maximal gas response of TMA gas (50 ppm). ZnO and Co doped ZnO nanostructures were exposed to various amines and found to be more selective towards sensing of TMA. Moreover, the gas sensing study was carried out at different humidity rates (11, 32, 51, 63 and 84%) using variable saturated solutions. Co doped ZnO (15%) shows maximum response (86.1%) as compared to undoped (ZnO NPs) and doped (5%). The response and recovery time was recorded to be 19.4 and 15.5 s for 50 ppm of TMA gas. As the concentration of TMA gas increases from 10 to 100 ppm the gas sensing response increases. TMA gas shows enhanced selectivity towards mixed shape Co doped ZnO as compared to the other gases (benzyl amine, diphenyl amine, dimethyl amine, n-butyl amine, aniline, p-phenylene diamines, o-phenylene diamines, m-phenylene diamines and allyl amine gas). The reproducibility study of Co doped ZnO was performed for 70 days.