N-containing Polymer Research Articles

Pyrolysis acetylation: A novel on-line Py-GC-MS derivatisation for the characterisation of nitrogen-containing polymers

Several on-line chemical reactions have been combined with Py-GC-MS to improve the chromatographic behaviour of polar pyrolysis products. Derivatisations, principally methylation and silylation, have been widely employed to the analysis of oxygenated pyrolysis products, while the conversion of nitrogen-containing compounds resulted more challenging. The present study shows that amines can be efficiently converted into the corresponding N-substituted amides (acetamides) by conducting pyrolysis in the presence of acetic anhydride (PyAc). PyAc was assessed on three common N-containing polymer families, polyethylenimine (PEI, linear and branched), polyurethane (PUR, based on the methylenediphenyl diisocianate monomer) and nylons (polyamide PA6 and PA66). Upon PyAc, PEI produced a series of N-methyl, ethyl, ethenyl acetamides indicative of the formation of several alkylated monoamines that were more difficult to detect in the free form by conventional Py-GC-MS. Acetyl derivatives of linear acyclic polyamines and piperazines were also identified confirming previous investigations. In the case of PUR, the acetylated 4,4′-diaminodiphenylmethane was generated along with the diisocyanate monomer. PyAc of PA66 produced the acetyl derivative of 1,6-hexyldiamine, while the caprolactam of PA6 was only partially acetylated. The effectiveness of acetylation was confirmed by PyAc of calibration standards for microplastic analysis. Besides the acetylated amines distinctive of PUR and PA66, the acetylated forms of 1,4-butandiol from PUR and bisphenol A from polycarbonate were detected. The results showed the potential of extension of PyAc to other polymer families and highlighted some weaknesses to be solved.

A 3D nickel(II) coordination polymer constructed by mixed- ligand strategy: synthesis, crystal structure and sensing of Hg(II) ion

A new N-containing coordination polymer, namely, [Ni(L)(dpa)·2.5H2O]n (1) (H2L = 4,4'-azanediyldibenzoic acid, dpa = 4,4’-dipyridylamine) has been constructed under hydrothermal conditions. Structural analysis reveals that complex 1 exhibits a 3D 4-connected binodal net. With functional amino group, complex 1 is developed to detect heavy metal ions by colorimetric method. Notably, 1 can selectively detect Hg2+ and it is free from the interference of other metal ions. The linear range for Hg2+ detection is 0.1 to 0.5 mL. XPS shows that the N atoms of amino groups in 1 are responsible for the Hg2+ detection.

Polymer Acceptors Containing B←N Units for Organic Photovoltaics.

ConspectusOrganic photovoltaics (OPVs), in which blend films of organic or polymer electron donor and electron acceptor are used as the active layer, are a promising photovoltaic technology with the great advantages of solution processing, low cost, and flexibility. The development of small molecular or polymer electron acceptors has boosted power conversion efficiency (PCE) of OPVs from 10% to 18%. Among them, polymer acceptors have the merits of superior morphology stability and excellent mechanical properties. However, owing to the key requirement of very low-lying LUMO/HOMO energy levels for polymer acceptors, very few conjugated polymers can work as polymer acceptors in OPVs. The majority of polymer electron acceptors are based on strong electron-withdrawing imide units or cyano substituents. Since 2015, conjugated polymers containing the boron-nitrogen coordination bond (B←N) have emerged as a new kind of polymer electron acceptor with excellent photovoltaic performance in various kinds of organic photovoltaic devices. In this Account, we summarize our research progress on polymer acceptors containing B←N units.At first, we introduce the principle of B←N to greatly down shift LUMO/HOMO energy levels, which enables B←N to be used to design polymer acceptors. Then we describe the two molecular design strategies for polymer acceptors containing B←N units. For high-efficiency OPVs, polymer acceptors should have wide absorption spectra, proper LUMO/HOMO energy levels, high electron mobility, and good donor/acceptor blend morphology. We discuss how to use molecular design to finely tune the absorption spectra, energy levels, and electron mobility of the B←N-containing polymer acceptors. We also discuss how to improve the phase separation morphology of the blends of these polymer acceptors with small molecular donors or polymer donors. These improvements lead to excellent performance of the polymer acceptors containing B←N units in three kinds of organic photovoltaic devices. The small molecular donor/polymer acceptor type organic solar cells show excellent thermal stability and PCE of 8.0%, which is the highest value reported so far. The all-polymer solar cells exhibit PCE of 10.1%. The all-polymer indoor photovoltaics show PCE as high as 27.4% under fluorescent lamp illumination at 2000 lx. This PCE is fairly comparable to those of the best organic or inorganic indoor photovoltaics. These results provide a solid foundation for future advances. Finally, we propose that great attention should be paid to further PCE enhancement of OPVs and indoor photovoltaic applications of this new emerging kind of polymer acceptor.

Fast and effective recovery of Au(III) from aqueous solution by a N-containing polymer

In this work, a N-containing polymer was successfully synthesized by one-step treatment with 3-amine-1,2,4-triazole ligands and Zn(II) using the thermal solvent method, and employed to recover Au(III) from water. The adsorption kinetics was comprehensively studied through kinetics models including pseudo-first-order model, pseudo-second-order model, moving boundary model and Weber-Morris model. It is found that the overall adsorption rate was determined by chemical adsorption, and the rate-limiting step of diffusion steps is film diffusion. Rising temperature can improve the adsorption rate significantly, making the adsorption equilibrium time be reduced from 6 h at 298 K to 2 h at 318 K. The adsorption isotherm can be described well by Sips model, indicating it is a heterogeneous adsorption. The material shows high adsorption capacity towards Au(III) up to 1073 mg/g. It shows strong affinity towards Au(III) in the mixture solutions containing Au(III), Cu(II), Zn(II), Co(II), Cd(II), Pb(II) and Ni(II) ions. The material can be easily and completely desorbed by thiourea solution and still maintains its adsorption performance only with a slight decrease after three cycles. Combined with studies on pH influence, adsorption kinetics, adsorption isotherm and XPS analysis, it can be concluded that the adsorption mechanism could be attributed to electrostatic interaction, the coordination of the Zn–OH and -C-N/-CN- with Au(III), and partial reduction of Au(III) to Au(I) by –NH group on the polymer. The N-containing polymer is an excellent candidate for Au(III) recovery efficiently and selectively from aqueous solution.

Solvent-free synthesis of N-containing polymers with high cross-linking degree to generate N-doped porous carbons for high-efficiency CO2 capture

Nitrogen-containing polymers with high cross-linking degrees are attractive precursors for the preparation of N-doped porous carbons (NDPCs), while their synthesis in liquid phases is difficult. Moreover, the difference between liquid-phase synthesis and solvent-free synthesis has not been well clarified. Herein, a solvent-free strategy was employed for the synthesis of an N-containing polymer from 1,3,5-tris(chloromethyl)-2,4,6-trimethylbenzene and p-phenylenediamine (producing NUT-71-F) and compared thoroughly with the liquid-phase method. NUT-71-F exhibited obviously higher yield than the counterpart NUT-71-S produced in the solvent (70.8% vs. 49.8%) due to the greater crosslinking degree and different linkage ways. The NDPCs based on NUT-71-F presented higher yields, more developed porosities, and better CO2 adsorption capacities in contrast to their analogues from NUT-71-S. The NUT-71-F-700 obtained from carbonization at 700 °C showed an excellent CO2 uptake of 8.1 mmol/g at 273 K and 1 bar, which is apparently higher than NUT-71-S-700 (5.4 mmol/g) and various benchmarks.

Nitrogen and sulfur dual-doped high-surface-area hollow carbon nanospheres for efficient CO2 reduction

The electrochemical reduction of CO2 (CO2RR) can substantially contribute to the production of useful chemicals and reduction of global CO2 emissions. Herein, we presented N and S dual-doped high-surface-area carbon materials (SZ-HCN) as CO2RR catalysts. N and S were doped by one-step pyrolysis of a N-containing polymer and S powder. ZnCl2 was applied as a volatile porogen to prepare porous SZ-HCN. SZ-HCN with a high specific surface area (1510 m2 g−g1) exhibited efficient electrocatalytic activity and selectivity for CO2RR. Electrochemical measurements demonstrated that SZ-HCN showed excellent catalytic performance for CO2-to-CO reduction with a high CO Faradaic efficiency (~93%) at −0.6 V. Furthermore, SZ-HCN offered a stable current density and high CO selectivity over at least 20 h continuous operation, revealing remarkable electrocatalytic durability. The experimental results and density functional theory calculations indicated that N and S dual-doped carbon materials required lower Gibbs free energy to form the COOH* intermediate than that for single-N-doped carbon for CO2-to-CO reduction, thereby enhancing CO2RR activity.

N-Doped Carbon As Peroxidase-Like Nanozymes for Total Antioxidant Capacity Assay.

N-doping strategy has been explored to enhance the activity of carbon nanozymes because the reconstructed electronic structures in N-doped carbon nanozymes are advantageous for the catalytic process. However, carbon nanozymes with high N content are still difficult to obtain due to the instability of N element under high calcination temperatures. To address this challenge, here we proposed a new N-doping strategy to fabricate highly active and specific peroxidase-like carbon nanozymes by using a high N-containing polymer (i.e., polyethylenimine (PEI)) as the N source and a natural clay mineral (i.e., montmorillonite (MMT)) as a template, respectively. We showed that the assembly of MMT with PEI protected N loss under high calcination temperatures and thus retained more catalytically active N sites. The mechanism study showed that the hydroxyl radical could be the key intermediate involved in the peroxidase-like catalysis. We then used the optimized carbon nanozyme with high and specific peroxidase-like activity (i.e., CP600-6) to detect H2O2, glucose, and ascorbic acid. Moreover, we successfully determined the total antioxidant capacity (TAC) in real samples including four commercial beverages, fresh orange juice, and three kinds of vitamin C tablets. The current study not only provides a new strategy for fabricating peroxidase-like nanozymes but also develops a facile TAC assay for future use in evaluation of antioxidant food quality and oxidative stress in healthcare.

NIR-responsive carbon dots for efficient photothermal cancer therapy at low power densities

Carbon dots (CDs) with unique optical properties are a stable and highly biocompatible fluorescent material offering enormous application potential in optical imaging and photothermal cancer therapy (PTT). However, the low photothermal conversion efficiency and the high power density still impede the development of CDs in PTT. Herein, the nitrogen and oxygen co-doped CDs (N-O-CDs) with strong absorbance in the near infrared (NIR) region were prepared from 1,3,6-trinitropyrene (TNP) and N-containing polymer of branched polyethylenimine (BPEI) via a one-step molecular fusion route. The as-prepared black N-O-CDs with high photostability and superb biocompatibility can be utilized not only as a new fluorescence imaging agent but also as an excellent PTT agent in vivo. The structure, optical properties, bioimaging, photothermal effect in vitro, and therapeutic efficiency in vivo of the N-O-CDs are investigated. The low power density (0.8 W cm−2) and high photothermal conversion efficiency (η = 38.3%) facilitate N-O-CDs to act as an ideal theranostic agent for fluorescence imaging and photothermal therapy in vitro and in vivo. This work highlights CDs as an excellent candidate for efficient cancer therapy.

Design of Organic-Inorganic Hybrid Nanocatalysts to Enhance Catalytic Activity and Durability for Oxygen Reduction Reaction

In Pt-transition metal (TM) alloy nanoparticles for proton exchange membrane fuel cells (PEMFCs), the TM surface can be easily oxidized by air, water, and acidic electrolytes. Accordingly, the electron transfer from the TM to Pt is retarded owing to the electronegative O species on the TM surface, and the dissolution of the surface TM oxide is accelerated during the fuel cell operation, which results in catalyst degradation. Therefore, we propose a novel hybrid catalyst concept that selectively modifies the surface Co atoms with N-containing polymers, resulting in highly active and durable PtCo nanoparticles useful for the oxygen reduction reaction (ORR). The N-containing polymer functionalized on carbon black selectively interacts with the Co precursor, resulting in Co-N bond formation on the PtCo nanoparticle surface. Electron transfer from Co to Pt in the PtCo nanoparticles is therefore enhanced by the increase in the difference in electronegativity between Pt and Co. In addition, the dissolution of Co and Pt is prevented by the selective passivation of surface Co atoms and the decrease in the O binding energy of surface Pt atoms, respectively. As a result, the activity and durability of organic-inorganic hybrid PtCo nanocatalysts for the ORR are significantly enhanced by the electronic ensemble effects.

Kinetics and Electrocatalytic Activity of Co(Aminopyrine)-Derived Nitrogen-Doped Porous Nanocomposite for Oxygen Reduction Reaction in Alkaline Electrolyte

Non precious metal (NPM) catalysts are considered as promising candidates ofreplacing Pt for the oxygen reduction reaction (ORR) inpolymer electrolyte membrane fuel cells for its low cost and rich resource. It has been reported that the substitution of some carbon atoms withheteroatoms, such as N, S, P, I and B, is an effective way totailor NPM catalysts’ electron-donor properties thus effectively weakening the O−O bonding1 and leading to a high ORR catalytic activity. Up to now, extensive research efforts have been made to explore the N doped non-noble metal oxygen reduction catalysts2 since nitrogen has electronegativity higher than other elements3. In our recent work, we found that sulfur-doping could lead to increased catalyst porosity and therefore promote mass transport4.5. As yet, the S doped ones, in particular the S and N co-doped carbon materials are less reported6-8. On the other hand, the specific surface area and porous structure, which determine the accessible part of active sites and the transport properties of ORR-relevant species (H+, e−, O2, H2O), are believed to play the important role in the performance of NPM catalysts.In this regard, template method has drawn great attention to obtain the specified morphologyand predetermined microstructure9,10. Based on the above conceptions, in this work, we report a novel kind of heteroatom-doped carbon catalyst from N-containing polymer and sulfate by template method and acid leaching.Poly(diallyldimethylammonium chloride)(abbreviate as PDDA) was employed as sources of nitrogen and carbon, ferrous sulfate as precursor of sulfur and metal, while the nanoscale silica as sacrificial supports to create pores.

Au nanoparticle decorated N-containing polymer spheres: additive-free synthesis and remarkable catalytic behavior for reduction of 4-nitrophenol

We demonstrated a simple, one-step route for assembling Au nanoparticles (NPs) on N-containing polymer nanospheres through in situ reductive growth process.Using resorcinol–melamine–formaldehyde resin nanospheres (RMF NSs) as a functional platform, neither a surfactant/ligand nor pretreatment is needed in the synthetic process of Au@RMF NSs hybrid nanostructure. When used as a catalytic media for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol, the Au@RMF NSs hybrid nanostructures show significantly enhanced catalytic performance than the ever reported Au-based catalyst. The absorption modal of 4-NP on this nanostructure is also discussed by theoretical calculations using density functional theory. The calculated results verify the preferential capture of 4-NP by the N-containing functionalities of RMF NSs, which is critical step for the acceleration of Au-based catalytic reaction kinetics, leading to the remarkable improved catalytic behavior. The superior features of RMF NSs as well as minimal economical cost compared with other polymer and non-polymer will promote further interest in the field of N-containing catalysis.

N-functionalized carbon nanotubes as a source and precursor of N-nitrosodimethylamine: implications for environmental fate, transport, and toxicity.

Hazardous byproducts may be generated during the environmental processing of engineered nanomaterials. Here, we explore the ability of carbon nanotubes with nitrogen-containing surface groups (N-CNTs) to generate N-nitrosodimethylamine (NDMA) during chemical disinfection. Unexpectedly, we observed that commercial N-CNTs with amine, amide, or N-containing polymer (PABS) surface groups are a source of NDMA. As-received powders can leach up to 50 ng of NDMA per mg of N-CNT in aqueous suspension; presumably NDMA originates as a residue from N-CNT manufacturing. Furthermore, reaction of N-CNTs with free chlorine, monochloramine, and ozone generated byproduct NDMA at yields comparable to those reported for natural organic matter. Chlorination also altered N-CNT surface chemistry, with X-ray photoelectron spectroscopy indicating addition of Cl, loss of N, and an increase in surface O. Although these changes can increase N-CNT suspension stability, they do not enhance their acute toxicity in E. coli bioassays above that observed for as-received powders. Notably, however, dechlorination of reacted N-CNTs with sulfite completely suppresses N-CNT toxicity. Collectively, our work demonstrates that N-CNTs are both a source and precursor of NDMA, a probable human carcinogen, while chemical disinfection can produce CNTs exhibiting surface chemistry and environmental behavior distinct from that of native (i.e., as-received) materials.

Iron Complex-Catalyzed Ammonia–Borane Dehydrogenation. A Potential Route toward B–N-Containing Polymer Motifs Using Earth-Abundant Metal Catalysts

Ammonia-borane (NH(3)BH(3), AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H(2) release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy(3))[N(SiMe(3))(2)](2) (1) and four-coordinate Fe(DEPE)[N(SiMe(3))(2)](2) (2) yield a mixture of (NH(2)BH(2))(n) and (NHBH)(n) products with up to 1.7 equiv of H(2) released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH(2)BH(2))(n) and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).

Measuring synthesis rates of nitrogen-containing polymers by using stable isotope tracers1,2

The major N-containing polymer compounds in the body include protein, RNA, and DNA. The endogenous gastrointestinal secretions as well as the portal-drained visceral and peripheral immune responses are basic physiological functions. Elevated endogenous secretions and immune activities, as affected by developmental stages, diets, and management factors, decrease the availability of dietary nutrients for peripheral muscle synthesis and deposition. Measurements of in vivo protein, RNA, and DNA synthesis rates associated with the viscera, peripheral immune cells, and skeletal muscles should, in principle, be the sensitive biochemical and cellular endpoints for studying factors affecting nonruminant nutrition, metabolism, and growth. The selection of stable isotope tracers for precursors, routes of tracer delivery, and mass spectrometric analyses of tracer enrichments are the major methodological considerations. To measure in vivo protein, RNA, and DNA synthesis rates, oral feeding with heavy water (2H2O), and continuous infusion of [U-13C]glucose and [15N]Gly intravenously for labeling the sugar moieties ribose and deoxyribose and de novo purine base synthesis have been established. Flooding doses of tracer Phe, for example, L-[ring-2H5]Phe, via the i.p. route are reliable and cost-effective for measuring in vivo protein synthesis rates, especially for the viscera in small nonruminants. Therefore, measurements of the major N-containing polymer synthesis rates in the viscera, the peripheral immune cells, and muscles through oral feeding with 2H2O and/or i.p. flooding doses of Phe tracers are the emerging tools for studying nonruminant nutrition, metabolism, and growth under research and field test conditions.