- Use of melem as a nucleophilic reagent to form the triphthalimide C 6N7(phthal)3-New targets and prospects
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Melem (1), as one of the most important representatives of the tri-s-triazine compounds, can be used as a nucleophilic reagent in reactions with phthalic acid derivatives. The synthesis of 2,5,8-triphthalimido-tri-s- triazine (C6N7(phthal)3, 2) was investigated starting from phthalic anhydride or phthalic dichloride in various solvents, at different temperatures as well as in the solid state. NMR measurements (solution and solid state), IR spectroscopy and elemental analysis indicated the formation of a cyclic imide. Single-crystal structure analysis of a 1:1 adduct of 2 with nitromethane proved the molecular structure expected for a phthalimido-s-heptazine. DFT calculations were performed to obtain a better insight into the structural features of compound 2, especially the interaction of the carbonyl groups with the tri-s-triazine nitrogen atoms. The title compound 2 shows promising properties: it is thermally stable up to 500 °C in air and shows strong photoluminescence with a maximum emission at around 500a nm. The potential of the nucleophilic reaction of melem with other strong electrophiles provides new targets and prospects. Copyright
- Schwarzer, Anke,Boehme, Uwe,Kroke, Edwin
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p. 12052 - 12058,7
(2012)
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- Carbon nitride as a ligand: Edge-site coordination of ReCl(CO)3-fragments to g-C3N4
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IR spectroscopy and model structural studies show binding of ReCl(CO)3-fragments to carbon nitride (g-C3N4) occurs via κ2 N,N′ bidentate coordination.
- Coulson, Ben,Isaacs, Mark,Lari, Leonardo,Douthwaite, Richard E.,Duhme-Klair, Anne-K.
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- Functionalizing carbon nitride with heavy atom-free spin converters for enhanced 1O2 generation
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Carbon nitride as a metal-free conjugated polymer exhibits an intriguing prospect for the design of advanced photosensitizers for singlet oxygen (1O2) generation. However, the intersystem crossing (ISC) process is quite insufficient in carbon nitride, limiting the 1O2 generation. Here, we report a facile and general strategy to confined benzophenone as a heavy atom-free spin converter dopant in carbon nitride via the facile copolymerization. With proper energy level matching between the heavy atom-free spin converter and various ligands based on carbon nitride precursors, the proper combination can decrease the singlet-triplet energy gap (ΔEST) and hence generate 1O2 effectively. Due to its significant and selectivity for 1O2 generation, the as-prepared carbon nitride-based photosensitizer shows a high selective photooxidation activity for 1,5-dihydroxy-naphthalene (1,5-DHN). The product yield reached 71.8% after irradiation for 60 min, which was higher than that of cyclometalated PtII complexes (53.6%) in homogeneous photooxidation. This study can broaden the application of carbon nitride in the field of selective heterogeneous photooxidation due to simple operation, low cost, and high efficiency, making it a strong candidate for future industrialization.
- Wu, Wenting,Han, Congcong,Zhang, Qinhua,Zhang, Qinggang,Li, Zhongtao,Gosztola, David J.,Wiederrecht, Gary P.,Wu, Mingbo
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- Understanding the Surface of g-C3N4, an Experimental Investigation of the Catalytic Active Site on the Interface
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Abstract: g-C3N4 has shown poor photocatalytic activity without co-catalyst. Studies on the chemical and physical properties of the g-C3N4 surface can help to understand the way how co-catalyst species interact with g-C3N4. To identify the role of the surface NH2 group in the formation of heterojunction photo-catalysts, g-C3N4/Melem was functionalized by different alkyl groups and characterized systematically by NMR, IR, UV–Vis, XPS and TEM. The surface alkyl groups affected the coordination of the Pt ion with the surface, and a significant photo-catalysis activity decrease was observed in turn. The results disclosed that the terminal NH2 played an important role in the formation of the co-catalyst heterojunctions and the surface catalysis active sites, and provided experimental evidence to understand the reaction mechanism. Graphic Abstract: [Figure not available: see fulltext.]
- Li, Qianqian,Jiang, Jing,Lin, Bin,Ding, De,Xu, Hai,Wang, Pingshan,Chen, Yin
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- Photophysics and Photocatalysis of Melem: A Spectroscopic Reinvestigation
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Graphitic carbon nitride (g-CN) is one potential metal-free photocatalyst. The photocatalytic mechanism of g-CN is related to the heptazine ring building unit. Melem is the simplest heptazine-based compound and g-CN is its polymeric product. Thus, studies on the photophysical properties of melem will help to understand the photocatalytic mechanism of heptazine-based materials. Herein, the spectroscopic features of melem were systematically explored through measuring its absorption spectrum, fluorescence spectrum, and fluorescence decay. Both fluorescence spectroscopy and fluorescence decay measurements show that the condensation of melamine to melem causes stronger photoluminescence, whereas the condensation of melem to g-CN causes weaker photoluminescence. In addition, all observations reveal that a mixture of monomer melem and its higher condensates is more easily obtained during the preparation of melem, and that the higher condensates of melem affect the photophysical properties of melem dominantly. The photocatalytic hydrogen evolution of melem has also been measured and the monomer melem has negligible photoinduced water-splitting activity.
- Wen, Jing,Li, Ruiyu,Lu, Rong,Yu, Anchi
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- Low-molecular-weight carbon nitrides for solar hydrogen evolution
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This work focuses on the control of the polymerization process for melon ( graphitic carbon nitride ), with the aim of improving its photocatalytic activity intrinsically. We demonstrate here that reduction of the synthesis temperature leads to a mixture of the monomer melem and its higher condensates. We show that this mixture can be separated and provide evidence that the higher condensates are isolated oligomers of melem. On evaluating their photocatalytic activity for hydrogen evolution, the oligomers were found to be the most active species, having up to twice the activity of the monomer/oligomer mixture of the as-synthesized material, which in turn has 3 times the activity of the polymer melon, the literature benchmark. These results highlight the role of defects , i.e., chain terminations, in increasing the catalytic activity of carbon nitrides and at the same time point to the ample potential of intrinsically improving the photocatalytic activity of carbon nitride , especially through the selective synthesis of the active phase. (Chemical Equation Presented).
- Lau, Vincent Wing-Hei,Mesch, Maria B.,Duppel, Viola,Blum, Volker,Senker, Jürgen,Lotsch, Bettina V.
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- Single-crystalline melem (C6N10H6) nanorods: A novel stable molecular crystal photocatalyst with modulated charge potentials and dynamics
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It is still challenging to control the crystallization and morphologies of molecular crystal nanostructures with excellent photocatalytic activities. In this study, single-crystalline melem (C6N10H6) nanorods (MNRs) were prepared by a facile thermal polymerization route under a flowing argon atmosphere. Compared with the bulk melem counterpart and g-C3N4, the MNRs exhibited substantially improved efficiency and stability towards the photodegradation of diverse organic pollutants including methyl orange, rhodamine B, and methylene blue. Moreover, the average photocatalytic hydrogen evolution rate of MNRs was about 2.6 folds higher than that of bulk melem under the same conditions. The enhanced photocatalytic redox performance of MNRs arises from the single-crystal nature and novel one-dimensional (1D) nanorod morphology, contributing to elevated conduction band potentials and promoting charge transport dynamics. This study not only reports single-crystalline melem 1D nanostructures as novel highly efficient and stable molecular-crystal photocatalysts, but also reveals the important roles of synergetic tuning of charge potentials and dynamics in enhancing the photocatalytic activity of molecular-crystal photocatalysts.
- Lei, Renbo,Du, Bingsheng,Lai, Xiaofang,Wu, Jing,Zhang, Zhihua,Liu, Shengwei,Wu, Rong,Li, Xin,Song, Bo,Jian, Jikang
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- Melemium Methylsulfonates HC6N7(NH 2)SH2C6N7(NH2)S(SO 3Me)3·H2O and H2C 6N7(NH2)3(SO3Me) 2·H2O
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Melem C6N7(NH2)3 was shown to form a variety of adduct phases and salts. Salts of melem can be yielded by reaction of melem with strong acids. We investigated the reaction of melem with methylsulfonic acid, thus identifying two new melemium salts with formulas HC6N7(NH2)3H2C 6N7(NH2)3(SO3Me) 3·H2O (1) and H2C6N 7(NH2)3-(SO3Me)2· H2O (2), respectively. The structures of both compounds were elucidated using single-crystal XRD compound 1: (P1 no. 2, Z = 2, a = 10.096(2), b = 12.865(3), c = 13.369(3) A, α = 63.28(3), β = 81.19(3), γ = 72.92(3)°, V = 1461.4(7) A3) compound 2: (P21/n, no. 14, Z = 4, a = 8.0757(16), b = 7.6937(15), c = 27.540(6) A, β = 92.03(3)°, V = 1710.6(6) A3). Both compounds are discussed in comparison to structural data from the literature of other melemium salts. We also present new synthetic approaches for the preparation of melem in larger quantities.
- Sattler, Andreas,Schoenberger, Stefanie,Schnick, Wolfgang
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- C3N5: A Low Bandgap Semiconductor Containing an Azo-Linked Carbon Nitride Framework for Photocatalytic, Photovoltaic and Adsorbent Applications
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Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1-xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive supramolecular adsorbent for environmental applications.
- Kumar, Pawan,Vahidzadeh, Ehsan,Thakur, Ujwal K.,Kar, Piyush,Alam, Kazi M.,Goswami, Ankur,Mahdi, Najia,Cui, Kai,Bernard, Guy M.,Michaelis, Vladimir K.,Shankar, Karthik
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- Melem (2,5,8-triamino-tri-s-triazine), an important intermediate during condensation of melamine rings to graphitic carbon nitride: Synthesis, structure determination by x-ray powder diffractometry, solid-state NMR, and theoretical studies
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Single-phase melem (2,5,8-triamino-tri-s-triazine) C6N 7(NH2)3 was obtained as a crystalline powder by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C3N3(NH2)3, dicyandiamide H4C2N4, ammonium dicyanamide NH 4[N(CN)2], or cyanamide H2CN2, respectively) at temperatures up to 450°C in sealed glass ampules. The crystal structure was determined ab initio by x-ray powder diffractometry (Cu Kα1: P21/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, β = 99.912(2)°, and Z = 4). In the solid, melem consists of nearly planar C6N7(NH2) 3 molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed 13C and 15N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent x-ray powder diffractometry investigations above 560°C, melem transforms into a graphite-like C-N material.
- Juergens, Barbara,Irran, Elisabeth,Senker, Juergen,Kroll, Peter,Mueller, Helen,Schnick, Wolfgang
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- From Heptazines to Triazines – On the Formation of Poly(triazine imide)
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Poly(triazine imide), a 2D extended carbon nitride network compound that is obtained from ionothermal synthesis in LiCl/KCl or LiBr/KBr salt melt has been known for over a decade. We now have investigated the formation process of this material starting from various triazine- and heptazine-based precursors as well as the differences between ionothermal and conventional synthesis via thermal condensation. Independent of chosen starting material, melem (triamino-s-heptazine) is initially formed from the starting material as the imminent precursor to poly(triazine imide). We elucidate the impact of various different carbon nitride precursor compounds on the formation process, propose a mechanism for the back reaction of heptazines to triazines, and rationalize the occurring processes.
- Kessler, Fabian K.,Schnick, Wolfgang
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- Cathodic and anodic photocurrents generation from melem and its derivatives
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Melem and its derivatives were synthesized from melamine by a two-step heat treatment method between 400 and 650°C in air. It was demonstrated that such polymeric C-N semiconductors possess a photoelectrochemical (PEC) conversion effect with both photocathodic and photoanodic characteristics, which was proposed to be caused by the formation of tri-s-triazine ring. The dimelem synthesized at 450°C exhibited the highest PEC conversion activity. The possible reasons were discussed. The unique bidirectional photocurrent generation makes melem and its derivatives attractive photoelectrochemical materials.
- Wei, Xiaoqing,Qiu, Yu,Duan, Weiyuan,Liu, Zhengxin
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- Nitrogen-rich compounds: s-triazine and tri-s-triazine derivatives as high energy materials
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Abstract: This article describes the syntheses, characterization, and energetic properties of 4, 6-diazido-N, N-dimethyl-1, 3, 5-triazin-2-amine and 2, 4, 6-tris (5-(3, 5-dinitrophenyl)-1H-tetrazol-1-yl)-1, 3, 5-triazine. Also, this paper emphasizes the i
- Hanumantha Rao, Muddamarri,Ghule, Vikas D,Muralidharan, Krishnamurthi
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- Unmasking melon by a complementary approach employing electron diffraction, solid-state NMR spectroscopy, and theoretical calculations - Structural characterization of a carbon nitride polymer
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Poly(aminoimino)heptazine, otherwise known as Liebig's melon, whose composition and structure has been subject to multitudinous speculations, was synthesized from melamine at 630°C under the pressure of ammonia. Electron diffraction, solid-state NMR spectroscopy, and theoretical calculations revealed that the nanocrystalline material exhibits domains well-ordered in two dimensions, thereby allowing the structure solution in projection by electron diffraction. Melon ([C6N7(NH2)(NH)] n, plane group p2gg, a = 16.7, b = 12.4 A, γ = 90°, Z=4), is composed of layers made up from infinite 1D chains of NH-bridged melem (C6N7(NH2)3) monomers. The strands adopt a zigzag-type geometry and are tightly linked by hydrogen bonds to give a 2D planar array. The inter-layer distance was determined to be 3.2 A from X-ray powder diffraction. The presence of heptazine building blocks, as well as NH and NH2 groups was confirmed by 13C and 15N solid-state NMR spectroscopy using 15N-labeled melon. The degree of condensation of the heptazine core was further substantiated by a 15N direct excitation measurement. Magnetization exchange observed between all 15N nuclei using a fp-RFDR experiment, together with the CP-MAS data and elemental analysis, suggests that the sample is mainly homogeneous in terms of its basic composition and molecular building blocks. Semiempirical, force field, and DFT/ plane wave calculations under periodic boundary conditions corroborate the structure model obtained by electron diffraction. The overall planarity of the layers is confirmed and a good agreement is obtained between the experimental and calculated NMR chemical shift parameters. The polymeric character and thermal stability of melon might render this polymer a pre-stage of g-C3N4 and portend its use as a promising inert material for a variety of applications in materials and surface science.
- Lotsch, Bettina V.,Doeblinger, Markus,Sehnert, Jan,Seyfarth, Lena,Senker, Juergen,Oeckler, Oliver,Schnick, Wolfgang
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- Formation of a hydrogen-bonded heptazine framework by self-assembly of melem into a hexagonal channel structure
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Self-assembly of melem C6N7(NH2) 3 in hot aqueous solution leads to the formation of hydrogen-bonded, hexagonal rosettes of melem units surrounding infinite channels with a diameter of 8.9 A. The channels are filled with strongly disordered water molecules, which are bound to the melem network through hydrogen bonds. Single-crystals of melem hydrate C6N7(NH2) 3·xH2O (x≈2.3) were obtained by hydrothermal treatment of melem at 200 °C and the crystal structure (R βar 3χ, a=2879.0(4), c=664.01(13) pm, V=4766.4(13)× 106 pm3, Z=18) was elucidated by single-crystal X-ray diffraction. With respect to the structural similarity to the well-known adduct between melamine and cyanuric acid, the composition of the obtained product was further analyzed by solid-state NMR spectroscopy. Hydrolysis of melem to cyameluric acid during syntheses at elevated temperatures could thus be ruled out. DTA/TG studies revealed that, during heating of melem hydrate, water molecules can be removed from the channels of the structure to a large extent. The solvent-free framework is stable up to 430 °C without transforming into the denser structure of anhydrous melem. Dehydrated melem hydrate was further characterized by solid-state NMR spectroscopy, powder X-ray diffraction, and sorption measurements to investigate structural changes induced by the removal of water from the channels. During dehydration, the hexagonal, layered arrangement of melem units is maintained whereas the formation of additional hydrogen bonds between melem entities requires the stacking mode of hexagonal layers to be altered. It is assumed that layers are shifted perpendicular to the direction of the channels, thereby making them inaccessible for guest molecules. Copyright
- Makowski, Sophia J.,Koestler, Pia,Schnick, Wolfgang
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- Promoting condensation kinetics of polymeric carbon nitride for enhanced photocatalytic activities
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Polymeric carbon nitride (CN) semiconductor by thermal condensation of N-rich precursors has attracted much attention for its capability ranging from photocatalytic and photoelectrochemical energy conversion to biosensing. However, the influence of condensation process on the final structure of CN was rarely studied, making the condensation kinetic far from be fully optimized. Herein, we report the preparation of CN by a simple condensation kinetics modulation using a faster ramping rate during the polymerization process. The modified condensation recipe was even simpler than the conventional one, but led to an improved photocatalytic H2 evolution up to 3 times without any additional chemicals or other complements. Detailed mechanism studies revealed the increase of crystallinity and surface area due to the rapid condensation played the key roles. This work would offer a more facile and effective way to prepare bulk CN for large-scale industrial applications of bulk CN with higher photocatalytic actives for sustainable energy, environmental and biosensing.
- Ni, Dongya,Zhang, Yuye,Shen, Yanfei,Liu, Songqin,Zhang, Yuanjian
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- Ferrocene-based porous organic polymer derived high-performance electrocatalysts for oxygen reduction
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Two nitrogen-rich porous organic polymers (POPs) were prepared via facile and low-cost Schiff base chemistry with ferrocene (Fc) and melamine/melem as building blocks. Carbonization of these POP precursors results in porous carbon nanohybrids with carbon composites containing crystalline Fe3C/Fe. Characterization based on a variety of techniques demonstrates that the porous carbon nanohybrids feature rich-nitrogen doping, good conductivity and high BET surface area with unique porous structure, endowing them with an excellent catalytic activity toward the oxygen reduction reaction (ORR) in alkaline electrolytes. The catalysts obtained by carbonization at 800 °C (N-Fc-800) exhibit favorable activity with a rather high onset potential and half wave potential of 0.96 and 0.82 V, respectively. Furthermore, a rechargeable zinc-air battery was assembled using the N-Fc-800 as the cathode catalyst. Compared with the commercial Pt/C, the N-Fc-800 based battery displays a considerably high power density of 178 mW cm-2 with a smaller charge-discharge voltage gap of 0.94 V, and holds excellent stability with a less activity decay (1.0%) over long charge-discharge cycles (200 cycles).
- Zhou, Baolong,Liu, Liangzhen,Cai, Pingwei,Zeng, Guang,Li, Xiaoqiang,Wen, Zhenhai,Chen, Long
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supporting information
p. 22163 - 22169
(2017/11/06)
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- Novel carbon nitride composites with improved visible light absorption synthesized in ZnCl2-based salt melts
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Poly(triazine imide)-based carbon nitride materials with BET surface areas up to 200 m2g-1were synthesized in ZnCl2containing salt melts without the use of hard templates. We found that the composition, structural order, optical properties and morphology of the products can be adjusted by careful selection of synthesis parameters. The nature of the salt eutectic and precursor concentration in the melt have an especially large influence, with ZnCl2being a reactive solvent. This novel synthesis route provides access to easily processable materials with improved optical absorption in the visible range that can be used as composite photocatalysts, CO2adsorbents or nanocomposite fillers. This journal is
- Fettkenhauer, Christian,Weber, Jens,Antonietti, Markus,Dontsova, Dariya
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p. 40803 - 40811
(2015/02/19)
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- Generation of melamine polymer condensates upon hypergolic ignition of dicyanamide ionic liquids
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The reaction of dicyanamide ionic liquids with nitric acid results in hypergolic ignition and the formation of a stable precipitate. The precipitate consists of cyclic triazines, including melamine and its polymers, such as melam and melem (see scheme). This study introduces a novel approach to the synthesis of cyclic azines without resorting to high temperatures and pressures. Copyright
- Chingin, Konstantin,Perry, Richard H.,Chambreau, Steven D.,Vaghjiani, Ghanshyam L.,Zare, Richard N.
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experimental part
p. 8634 - 8637
(2011/11/07)
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- IMPROVING THE MELAMINE YIELD OF CATALYTIC MELAMINE PRODUCTION PROCESSES
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The process to increase the melamine yield and improving the dust separation in the melamine production from urea in fluidized-bed catalytic processes comprises transferring the process gas of the fluid-bed reactor, which contains besides melamine non-converted isocyanic acid, melam, melem and other higher molecular nitrogen compounds, into a filter-reactor which consists of one or more ring-reactors filled with catalysts, in which the not yet converted isocyanic acid is converted to melamine, the higher molecular nitrogen compounds, especially melam and melem, are also re-converted to melamine by reaction with the ammonia in the process gas, and the catalyst fines still present in the process gas of the fluidized-bed reactor are removed.
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- Crystalline melamine
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Multicrystalline melamine powder having the following properties:d90: 50-150 μm; d50 3color APHA less than 17melamine: > 98.5 wt%melam: a high-pressure process in which solid melamine is obtained by the melamine melt coming from the reactor being transferred to a vessel where the melamine melt is cooled with an evaporating cooling medium, characterized in that the melamine melt which comes from the melamine reactor and has a temperature between the melting point of melamine and 450°C is sprayed via spraying means and cooled with an evaporating cooling medium within a vessel in an ammonia environment at an ammonia pressure of 4.5-25 MPa, the melamine melt being converted into melamine powder having a temperature between 200°C and the solidification point of melamine, the melamine powder then being cooled to a temperature below 50°C, the powder being agitated mechanically over at least part of the cooling range and being cooled directly or indirectly, and the ammonia pressure being released at a temperature below 270°C.
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