N-containing Precursors Research Articles

Insights into the roles of DOM in humification during sludge composting: Comprehensive chemoinformatic analysis using FT-ICR mass spectrometry

Biological humification is the core process in sludge composting for organic matter stabilization. Characterizing dissolved organic matter (DOM) would be a promising way for tracking humification, but still needs fundamental understanding. This study evidenced the role of DOM in deciphering humification via comprehensive and expansive chemoinformatic analyses based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that formula-derived indices including half reaction of carbon oxidation (ΔG0Cox), oxygen to carbon ratios (O/C), double bond equivalent to carbon ratios (DBE/C) and modified aromaticity index (AImod) (except for molecular lability boundary (MLB) index) from the nitrogen (N)-containing compounds were highly correlated with the fluorescence index representing humic and fulvic acids. Besides, the identified dominant reaction types (oxidative demethylation, deamination, and desulfurization, etc.) in different stage of composting, key molecules based on paired mass distance (PMD) network, and nexus molecules (e.g., C10H14N5O7P, C9H14N3O8P, C14H18N4O3, etc.) from DOM-microbes associated network further supported the important roles of N-containing compounds in humification. Furthermore, as the precursors for humification, releasing of biogenic N-containing compounds from sludge and providing thermodynamically available CHO compounds would be important for controlling humification. The fates of N-containing precursors and stable CHO precursors in determining the degree of humification need more attentions in future research. This study provides fundamental understanding that exploring DOM composition, properties and molecular transformation is alternative to track humification in composting.

Carbon-coordinated atomic cobalt directly embedded on carbon cloth for alkaline hydrogen evolution at high current density

Electrocatalysts for high current density hydrogen evolution reaction (HER) under alkaline conditions is critical for the widespread application of water electrolysis. Carbon-supported single-atom catalysts (SACs) stabilized by N atoms have been demonstrated as efficient electrocatalysts, but mostly for acidic HER. For alkaline HER, although defective-, edge-, and dual-sites have been found to improve the adsorption pathways of the intermediates, there is still a great challenge to precisely synthesize those complex configurations in experiments to maximize the synergistic effects. Since C atom has relatively weak electronegativity than N atom, it can induce different charge redistribution of the metal atom center. However, the reported C-coordinated SACs were derived from the N-containing precursors, which could not exclude the influence of heteroatoms on the activity completely. Herein, we reported the synthesis of carbon-coordinated CoC4 sites and ultra-small Co cluster directly embedded on pure carbon cloth (Co-SA/CC) via the high temperature shockwave (HTS) method. The C atoms on the first coordination shell can tune the local electronic structure and up-shift the d-band center of the Co atom, thus strengthening H2O molecule adsorption and promoting water dissociation. The self-supporting electrode with CoC4 can lower the interfacial contact resistance, leading to higher HER performance compared with that of Pt/C at high current density (e.g. 1000 mA/cm2). These results provide a new insight into the fundamental understanding of design and synthesis of C-coordinated atomically dispersed catalytic sites.

Differentiated strategies of animal-derived and plant-derived biochar to reduce nitrogen loss during paper mill sludge composting

This work aimed to reveal the differences of nitrogen (N) transformation between animal-derived and plant-derived biochar during paper mill sludge composting. Three treatments were established, including CK (no biochar), ABC (animal-derived biochar), and PBC (plant-derived biochar). Results showed that N loss was reduced by 24.43% and 35.50% in ABC and PBC, respectively, compared with CK. Moreover, the contents of acid-insoluble N (AIN) in ABC and bioavailable organic N (BON) in PBC were 6.180 g/kg and 9.269 g/kg higher than in CK (2.602 g/kg and 8.988 g/kg). The protease activity and bacterial abundance associated with the generation of humic N-containing precursors increased in ABC. Low urease activity and a more complex bacterial N-cycling network were found in PBC. Structural equation model confirmed that AIN formation and BON retention were the dominant strategies for animal-derived and plant-derived biochar, respectively. The findings provided multiple pathways to produce N-enriched compost products.

Effect of UV/Chlorine Oxidation on Disinfection Byproduct Formation from Diverse Model Compounds

Disinfection byproduct (DBP) formation is a potential concern for the UV/chlorine advanced oxidation process (AOP) in water treatment. In this study, 11 model compounds were selected as natural organic matter (NOM) surrogates, including seven active DBP precursors and four poor precursors. The effect of UV/chlorine on their DBP formation in the UV reactor and during 24 h postchlorination was investigated in comparison to dark chlorination. DBPs evaluated included adsorbable organic halides (AOX), trihalomethanes, haloacetic acids (HAAs), haloacetaldehydes (HALs), trichloronitromethane (TCNM), and dichloroacetonitrile (DCAN). UV/chlorine AOP was conducted at a typical UV dose adopted in drinking water treatment and at both pH 6.0 and 7.8 with postchlorination pH kept at pH 7.8. For most of the active DBP precursors, UV/chlorine either decreased their AOX formation potential (FP) and DBPFP by <25% or showed an insignificant impact. Three poor DBP precursors were activated by UV/chlorine oxidation, especially at pH 6.0, with a significant increase of AOXFP and DBPFP percentage-wise, but the absolute increase was low (less than 186 μg-Cl/mg-C and 50 μg DBP/mg-C). UV/chlorine converted some chloroform precursors to HAA or HAL precusors. For N-containing precursors, UV/chlorine increased TCNM formation and decreased DCAN formation, especially at pH 6.

Structure-controllable growth of nitrogenated graphene quantum dots via solvent catalysis for selective C-N bond activation

Photophysical and photochemical properties of graphene quantum dots (GQDs) strongly depend on their morphological and chemical features. However, systematic and uniform manipulation of the chemical structures of GQDs remains challenging due to the difficulty in simultaneous control of competitive reactions, i.e., growth and doping, and the complicated post-purification processes. Here, we report an efficient and scalable production of chemically tailored N-doped GQDs (NGs) with high uniformity and crystallinity via a simple one-step solvent catalytic reaction for the thermolytic self-assembly of molecular precursors. We find that the graphitization of N-containing precursors during the formation of NGs can be modulated by intermolecular interaction with solvent molecules, the mechanism of wh\tich is evidenced by theoretical calculations and various spectroscopic analyses. Given with the excellent visible-light photoresponse and photocatalytic activity of NGs, it is expected that the proposed approach will promote the practical utilization of GQDs for various applications in the near future.

Changes and release risk of typical pharmaceuticals and personal care products in sewage sludge during hydrothermal carbonization process

Hydrochars were obtained by hydrothermal carbonization treatment of municipal sewage sludge. Effects of reaction temperature (180–300 °C) and reaction time (2–15 h) on structural characteristics of the hydrochars, and changes and release risk of typical pharmaceuticals and personal care products (PPCPs) in the hydrochars were investigated. Reaction temperature played a more important role than reaction time on hydrochar properties and decarboxylation reaction was the primary process during the converting of sludge to hydrochars. The sludge hydrochars had higher yields, carbon recovery rates, polarity and less aromaticity than biochars. Hydrothermal process reduced PPCPs’ load in sludge hydrochars effectively except caffeine and acetaminophen. The hydrochars prepared at intermediate and high temperatures (240 and 300 °C) had higher caffeine concentrations than the original sludge, which can be ascribed to the transformation of N-containing precursors. The highest CaCl2 extracted caffeine concentration occurred at intermediate temperature of 240 °C (48.1 μg/kg) due to the stronger affinity of caffeine in the high-temperature hydrochars. Caffeine was not detected in hydroxypropyl-β-cyclodextrin (HPCD) extract. Hydrochars prepared at low temperature (180 °C) had a higher acetaminophen concentration than the original sludge, which was attributed to the high thermal stability temperature of acetaminophen. Low- and intermediate-temperature hydrochars had higher CaCl2 extracted acetaminophen concentrations. The HPCD extracted acetaminophen was low with a range of nd to 6.72 μg/kg. In conclusion, PPCPs are less likely to constitute a limiting factor on the farm application of sludge hydrochar. This study provides theoretical support for the safe application of sludge hydrochar in the farmland.

Nitrogen-doped microporous carbon materials with uniform pore diameters: Design and applications in CO2 and H2 adsorption

Abstract Nitrogen-doped microporous carbon materials (N-MCs) with uniform pore diameters have promising applications in gas absorption, however their fabrication is challenging. Herein, we report a new approach to prepare N-MCs with uniform pore size using azo-linked organic polymers (AOPs) as the N-containing precursors. The AOPs were synthesized via the reactions of 1,3,5-tris(4-nitrophenyl)benzene (TNPB) and melamine (MA), and their N contents were tuned by changing the molar ratios of MA to TNPB. Followed by calcination of the resultant precursors at 800 °C, porous N-MCs were produced, which were characterized by means of different techniques including FT-IR analysis, N2 sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental analysis. It was demonstrated that the pore diameters of N-MCs could be tuned by changing the MA: TNPB ratio for preparing azo-polymer precursors, and N-MCs with pore size centered at 0.72 and 1.06 nm were obtained. The resultant N-MCs showed excellent CO2 uptake capacity up to 191 mg g−1 at 1 bar and 273 K, with a CO2/N2 selectivity of 58 at 298 K and good H2 adsorption capacity of 14.7 mg g−1 at 77 K.

Boosting Hydrogen Production from Formic Acid over Pd Catalysts by Deposition of N-Containing Precursors on the Carbon Support

Formic acid is a promising liquid organic hydrogen carrier (LOHC) since it has relatively high hydrogen content (4.4 wt%), low inflammability, low toxicity and can be obtained from biomass or from CO2. The aim of the present research was the creation of efficient 1 wt% Pd catalysts supported on mesoporous graphitic carbon (Sibunit) for the hydrogen production from gas-phase formic acid. For this purpose, the carbon support was modified by pyrolysis of deposited precursors containing pyridinic nitrogen such as melamine (Mel), 2,2′-bipyridine (Bpy) or 1,10-phenanthroline (Phen) at 673 K. The following activity trend of the catalysts Pd/Mel/C &gt; Pd/C ~ Pd/Bpy/C &gt; Pd/Phen/C was obtained. The activity of the Pd/Mel/C catalyst was by a factor of 4 higher than the activity of the Pd/C catalyst at about 373 K and the apparent activation energy was significantly lower than those for the other catalysts (32 vs. 42–46 kJ/mol). The high activity of the melamine-based samples was explained by a high dispersion of Pd nanoparticles (~2 nm, HRTEM) and their strong electron-deficient character (XPS) provided by interaction of Pd with pyridinic nitrogen species of the support. The presented results can be used for the development of supported Pd catalysts for hydrogen production from different liquid organic hydrogen carriers.

Crystalline Carbon Nitride Semiconductors for Photocatalytic Water Splitting.

Conjugated carbon nitride (CN) is an emerging and promising semiconductor photocatalyst for water photolysis owing to its unique properties. However, the traditional thermally induced polymerization of N-containing precursors typically produces melon-based CN solids with amorphous or semi-crystalline structures with only moderate photocatalytic performance. Many strategies have been developed to prepare crystalline CNs (CCNs), such as high-temperature and high-pressure routes, ionothermal synthesis, and microwave-assisted synthesis. In this Minireview, we summarize the progress that has been made in the synthesis of CCNs and their application in photocatalytic water splitting reactions. Three kinds of CCNs are mainly discussed according to their polymeric subunits. Challenges associated with CCNs and their future development are also included.

Template-Free Synthesis of Highly Porous Boron Nitride: Insights into Pore Network Design and Impact on Gas Sorption.

Production of biocompatible and stable porous materials, e.g., boron nitride, exhibiting tunable and enhanced porosity is a prerequisite if they are to be employed to address challenges such as drug delivery, molecular separations, or catalysis. However, there is currently very limited understanding of the formation mechanisms of porous boron nitride and the parameters controlling its porosity, which ultimately prevents exploiting the material's full potential. Herein, we produce boron nitride with high and tunable surface area and micro/mesoporosity via a facile template-free method using multiple readily available N-containing precursors with different thermal decomposition patterns. The gases are gradually released, creating hierarchical pores, high surface areas (>1900 m2/g), and micropore volumes. We use 3D tomography techniques to reconstruct the pore structure, allowing direct visualization of the mesopore network. Additional imaging and analytical tools are employed to characterize the materials from the micro- down to the nanoscale. The CO2 uptake of the materials rivals or surpasses those of commercial benchmarks or other boron nitride materials reported to date (up to 4 times higher), even after pelletizing. Overall, the approach provides a scalable route to porous boron nitride production as well as fundamental insights into the material's formation, which can be used to design a variety of boron nitride structures.

Challenges in atomic layer deposition of carbon-containing silicon-based dielectrics

The authors have designed experiments to test three different approaches for the incorporation of carbon atoms into amorphous SiNx or SiO2 films grown using atomic layer deposition (ALD). In each approach, the surface reactions of the precursors were monitored in situ using attenuated total reflection Fourier transform infrared spectroscopy. In the first approach, for depositing carbon-containing SiNx films using ALD, carbon was introduced into the process through a silicon precursor, SiCl2(CH3)2, followed by NH3 plasma exposure. While our infrared data show that SiCl2(CH3)2 reacts with an –NHx (x = 1, 2) terminated surface created after NH3 plasma exposure, –CH3 groups are eliminated in the precursor adsorption step leading to no significant carbon in the films. In the second approach, the authors hypothesized a three-step ALD process, which would involve Si-, C-, and N-containing precursors, and tested the reactivity of two carbon-containing precursors, CH3I and Al(CH3)3, with H- and Cl-terminated silicon surfaces, respectively. The authors show that both precursors readily react with the silicon surfaces, but neither one provides the appropriate surface termination. CH3I reacts with surface –SiHx (x = 1, 2, 3) to create surface –SiIx (x = 1, 2, 3) species with CH3 as the leaving groups. While Al(CH3)3 reacts with the Cl-terminated Si surface to form a surface –SiCH3 group, residual aluminum remains on the surface as –Al(CH3)x (x = 1, 2) groups that are not completely removed as volatile Al(CH3)xCl3−x (x = 1, 2). Finally, in the third approach for ALD of carbon-containing SiO2 films, the authors used Si2Cl6 with CO and CO/O2 plasmas. A pure CO plasma led to amorphous carbon growth, and a CO plasma diluted with of O2 led to no detectable carbon incorporation in the SiO2 film.

N-doped polymer-derived Si(N)OC: The role of the N-containing precursor

Abstract

Pyrolytic synthesis and characterization of N-doped carbon nanoflakes for electrochemical applications

Nitrogen doped carbon nanoflakes, which are very important for many electrochemical applications, were synthesized by pyrolysis of nitrogen containing organic compounds over metal oxide template. Acetonitrile, pyridine and butylamine, which are of different volatility were tested as N-containing precursors. Morphology, structure and chemical composition of the as-synthesized materials were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that materials are highly defective and consist of a few malformed graphene layers. X-ray photoelectron spectra reflect the dominant graphitic and pyridinic N-bonding configuration. It was also noted that specific surface area depends on the duration and temperature of the reaction. Increase in duration and temperature led to decrease of the specific surface area from 1000 to 160m2/g, 1170 to 210m2/g and 1180 to 480m2/g for acetonitrile, butylamine and pyridine precursors, respectively.

Effect of N and S co-doping of multiwalled carbon nanotubes for the oxygen reduction

The co-incorporation of S and N into multiwalled carbon nanotubes (CNTs) and the effects for the catalytic performance for the oxygen reduction reaction (ORR) in acidic and alkaline electrolytes has been studied. Subjecting CNTs to different ballmilling periods results in the formation of defects in their graphitic structure. Heteroatoms such as N and S can be actually incorporated into such defects leading to active catalysts for the ORR. In fact, the ORR activity in acid and alkaline media increases with the increasing amount of heteroatoms, especially N, actually incorporated in the catalysts. The use of precursors containing both N and S into their structure such as thiourea, results in a higher incorporation of surface N atoms than with similar N-containing precursors. As a consequence the ORR activity of the S/N/CNTs based catalysts is higher than that of N/CNT ones. This promotional effect of the presence of S is more significant when the ORR is measured in alkaline media suggesting that S-incorporation into the carbon matrix could actually play a direct role for the ORR.

Carbon Nitrides: New Electroactive Materials for Energy Conversion and Storage Applications

Polymeric / graphitic carbon nitride materials (gCNMs) were first reported by Berzelius and termed ‘melon’ by Liebig in 1834.[i] Their amorphous / nanocrystalline nature has complicated the structural characterisation but, thanks to the application of new advanced techniques, the structures are now becoming understood. gCNMs consist of s-triazine or heptazine (tri-s-triazine) units linked by bridging –NH- or –N= groups to form polymeric 2D structures with different degree of condensation (Fig. 1). These structures differ from graphitic carbon or graphene in that the presence of N atoms and C-N bonds creates voids within the extended layered structure. These voids are lined with N lone pairs and / or N-H functional groups, being ideally suited for acid / base and host / guest chemistry. This includes intercalation reactions, charge storage, ionic diffusion, gas sorption and support of catalytically or electrochemically active species. Due to their extraordinary compositional and structural flexibility, a high degree of control and tuneability can be achieved. We have demonstrated that the band gap of gCNMs can be controlled by modifying the preparation experimental conditions via the extent of condensation, layer buckling and potentially charge transfer processes with guest ions.[ii]Graphitic carbon nitrides are easily prepared by condensation of C, N-containing precursors at temperatures between 550 and 650 oC in N2 (g) flow. Alternative approaches to improve crystallinity, conductivity or porosity include the use of molten eutectic mixtures, anion doping or soft / hard templates, respectively. We have recently revealed the ability of gCNMs to act as electrodes for Li intercalation.[iii] Cyclic voltammetry results showed that the gCNMs can incorporate Li+ with a peak near 1.0 V for the delithiation process (Fig. 2a). We have also demonstrated that gCNMs exhibit excellent performance as catalyst support in direct methanol fuel cells.[iv],[v] We studied gCNMs synthesised following different routes: (a) gCNM: prepared by condensation at 550 oC in N2 (g), (b) PTI-Li+Cl-: Poly(triazine imide) prepared by molten eutectic LiCl/KCl route,[vi],[vii] and (c) B-gCNM: prepared by using ionic liquid BmimBF4.[viii] They also showed improved performance when compared to commercial Vulcan (Figs. 2b and 2c). Here, we describe the differences between carbon nitrides and N-doped carbons / graphene and the promising potential of these materials for energy storage and conversion applications.[i] J. Liebig, Ann. Pharm. 1834, 10, 1.[ii] A.B. Jorge, D. J. Martin, M. T. S. Dhanoa, A. S. Rahman, N. Makwana, J. Tang, A. Sella, F. Corà, S. Firth, J. A. Darr, P. F. McMillan, J. Phys. Chem. C 2013, 117, 7178.[iii] A.B. Jorge, F. Corà, D. J. L. Brett, A. Sella, P. F. McMillan, Int. J. Nanotechnol., awaiting publication.[iv] N. Mansor, A. B. Jorge, F. Corà, C. Gibbs, R. Jervis, P. F. McMillan, X. Wang, D. J. L. Brett, ECS Trans 2013, 58, 1767.[v] N. Mansor, A. B. Jorge, F. Corà, C. Gibbs, R. Jervis, P. F. McMillan, X. Wang, D. J. L. Brett, J. Phys. Chem. C, just accepted, doi: 10.1021/jp412501j. [vi] M. J. Bojdys, J.-O. Müller, M. Antonietti, A. Thomas, Chem. Eur. .J. 2008, 14, 8177-8182.[vii] E. Wirnhier, M. Döblinger, D. Gunzelmann, J. Senker, B. V. Lotsch, W. Schnick, Chem. Eur. .J. 2011, 17, 3213.[viii] Y. Wang, J. Zhang, X. Wang, M. Antonietti, H. Li, Angew. Chem. Int. Ed. 2010, 49, 3356.

Electrochemical properties of graphitic carbon nitrides

Lithium-ion batteries (LIBs) are the current devices of choice for portable energy storage applications; however, improvements in energy and power densities are required to sustain future more demanding tasks, such as those associated with automotive transport. Commercially, LIB anodes are typically made from graphitic carbon-based systems that present bottlenecks associated with surface passivation and slow intercalation kinetics. We have investigated layered/graphitic carbon nitrides (gCNMs) as alternative anode materials; their unique structure and chemistry enable new intercalation processes not available for pure-C graphite. Our gCNMs are prepared from C, N-containing precursors treated at different temperatures. Cyclic voltammetry showed clear oxidation/reduction cycles in the 0.5–1.5 V range indicating that Li + intercalation took place resulting in electric conduction properties of the previously semiconducting material. Higher reaction temperatures lead to buckling of the graphitic layers and consequent loss of planarity, with a negative effect on their electrochemical performance.

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH3, CO2 and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH3, CO2, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H2 and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.

Novel N-Containing Precursors of Nickel(II) for Film Deposition by MOCVD

The synthesis of volatile nickel(II) complexes with N-containing ligands like CH3C(O,NCH3)CH2C(NR)CH3 (R - H, CH3) was performed. The substances were identified by various physico-chemical methods. The thermal behavior of the compounds in the solid state was investigated by the method of thermogravimetry and difference-scanning calorimetry in vacuum and helium. Using the Knudsen method and static method the temperature dependences of saturated vapor pressure were studied, the standard thermodynamic parameters of sublimation and evaporation process were calculated. By means of high temperature mass spectrometry the thermolysis of complex vapor was studied in vacuum and gas by-products were determined. One of the complexes has been used as precursor for the film deposition. The films obtained were investigated by using XRD analysis.

Novel N-Containing Precursors of Nickel(II) for Film Deposition by MOCVD

not Available.

X-ray photoelectron spectroscopy study of TiN films produced with tetrakis(dimethylamido)titanium and selected N-containing precursors on SiO2

Low pressure chemical vapor deposition TiN films were produced on SiO2 by codosing tetrakis(dimethylamido)titanium (TDMAT) with selected N-containing precursors. The films were grown at total pressures ranging from 10−4 to 10−3 Torr and temperatures between 523 and 773 K. Film composition and chemical states were determined, without exposure to ambient pressure, using x-ray photoelectron spectroscopy (XPS). Our primary goal was to evaluate how precursor ligands affect C and N incorporation into TiN films. To this end, methylhydrazine (MH), dimethylhydrazine (DMH), and 1-aminopiperidine (AP) were chosen for their steric differences, and t-butylamine (TBA) and aniline allowed us to assess how C and N incorporation are affected by the C–N bond in the aminolike compounds versus the N–N bond in the hydrazinelike compounds. At all growth temperatures, a decrease in the carbon concentration and an increase in the N concentration were observed for the MH and DMH cases when compared to TDMAT alone, while C content increased for aniline. AP caused only a slight reduction of C at temperatures of 673 K and above. Growth temperature affected film composition and the chemical states of C, N, and Ti. At 623 K, DMH and MH reduced the C/Ti ratio from 1.0 with TDMAT alone to 0.2, while aniline increased C/Ti to 2.0 and AP and TBA had little effect. The addition of the N-containing precursors causes the XPS C 1s peak to broaden and shift to higher binding energy; the N 1s peak also broadened, suggesting that, compared to TDMAT alone, more C–N bonds are formed. Furthermore, the Ti 2p peak shifted to higher binding energy and became broader upon codosing, suggesting the incomplete conversion of Ti (IV) to Ti (III) in the TiN film. Postdosing with MH and DMH supports the conclusion that surface reactions occur between TDMAT and the hydrazinelike precursors.