Melamine-cyanuric Acid Complex Research Articles

A NEW STRATEGY FOR THE SYNTHESIS OF HIGHLY ACTIVE CATALYSTS BASED ON <i>g-</i>C<sub>3</sub>N<sub>4</sub> FOR THE PHOTOCATALYTIC PRODUCTION OF HYDROGEN UNDER VISIBLE LIGHT

In this work, materials based on graphite-like carbon nitride were synthesized by thermal treatment of a mixture of melamine and urea and the effect of synthesis conditions on the photocatalytic activity of the samples was studied. As a cocatalyst, platinum (1 wt. %) was deposited on the surface of the synthesized g‑C3N4 samples. The photocatalysts were characterized by X-ray phase analysis, diffuse reflectance UV-vis spectro-scopy in the UV and visible range, and low-temperature nitrogen adsorption. Photocatalytic activity was determined in the reaction of hydrogen evolution from an aqueous solution of triethanolamine (10 vol. %) under visible light irradiation (λ = 425 nm). The optimal conditions for the synthesis of the photocatalyst 1% Pt/g-C3N4, obtained by calcination of a mixture of melamine and urea (1 : 3), were found, using which the rate of H2 evolution was 5.0 mmol g–1 h–1 with an apparent quantum efficiency of 2.5%. The developed synthetic approach makes it possible to obtain highly active catalysts due to the formation of an intermediate supramolecular melamine-cyanuric acid complex during the synthesis, which, upon further heating, turns into g-C3N4, which is characterized by a high specific surface area exceeding 100 m2 g–1.

Visible-light-driven photocatalysis for the sustainable synthesis of (±)-pregabalin using carbon nitride from melamine-cyanuric acid complex

The pharmaceutical industry has long sought efficient and environmentally sustainable methods for the synthesis of pharmaceutically significant molecules, particularly potent γ-amino butyric acid (GABA) derivatives. Photocatalysis has emerged as a promising approach, offering mild reaction conditions and utilizing renewable energy sources. In this study, we present a novel and sustainable photocatalytic strategy for the synthesis of (±)-pregabalin, a valuable GABA derivative, using carbon nitride derived from the complex of melamine and cyanuric acid (CN-MC) as the catalyst. Under visible light irradiation, CN-MC demonstrated outstanding photocatalytic performance, achieving an excellent 99% yield in the visible-light-driven decarboxylative radical conjugate addition. The formed β-substituted γ-lactam intermediate serves as a crucial building block for the synthesis of (±)-pregabalin. Moreover, the recyclability and scalability of CN-MC as a photocatalyst enhance the process's eco-friendliness, making it an appealing option for large-scale pharmaceutical synthesis.

Multiple active cobalt species embedded in microporous nitrogen-doped carbon network for the selective production of hydrogen peroxide

To obtain excellent electrocatalysts for improving H2O2 yield and selectivity, we formulated a novel method for embedding cobalt catalytic active sites in porous two-dimensional nitrogen-doped carbon network (CNy) network and employed them as excellent two-electron oxygen reduction reaction (2e−-ORR) electrocatalysts. The polymeric cobalt-based metal–organic framework (polyCo-MOF) and melamine–cyanuric acid–complex (MCA) hybrid (denoted as polyCo-MOF@MCA) was used as a precursor for preparing a series of electrocatalysts comprising multiple active sites such as metallic Co, CoOx, or Co-N, which are homogeneously embedded in the porous two-dimensional CNy network through pyrolysis at high temperatures (600 °C, 700 °C, and 800 °C) under N2 atmosphere. The obtained CoOx/Co@CNy,700 hybrid by pyrolyzing polyCo-MOF@MCA at 700 °C displayed remarkably high H2O2 production and large selectivity in an alkaline solution. The possible catalytic mechanism of CoOx/Co@CNy,700 toward 2e−-ORR was identified by determining the catalytic kinetics and control experiments. The cathode assembled with the CoOx/Co@CNy,700 hybrid showed the maximum H2O2 production of 405 mmol L−1gcat.−1h−1 with a high Faradaic efficiency of 88.9 % at 0.65 V. The present work demonstrated a novel strategy for identifying excellent electrocatalysts with homogeneously dispersed multiple active sites and high production and selectivity for H2O2 synthesis, extending the applications of porous organic frameworks to the field of clean energy.

The intergrated nanostructure of bimetallic CoNi-based zeolitic imidazolate framework and carbon nanotubes as high-performance electrochemical supercapacitors

In this study, a series of one-dimensional (1D)/two-dimensional (2D) heterostructure hybrids were fabricated through the in situ growth of a Co and Ni bimetallic zeolitic imidazolate framework (CoNi-ZIF) around N-doped carbon nanotubes (N-CNTs). The hybrids were further exploited as effective supercapacitor materials. The N-CNTs were prepared by carbonizing a mixture of glucose and the melamine–cyanuric acid complex at a high temperature (900 °C) under N2 atmosphere and applied as the template for the in situ synthesis of CoNi-ZIF nanosheets (NSs). The 1D N-CNTs in the hybrids can act as the high-way for charge transfer to boost the faradaic reactions. Changing the usage of metal precursors not only provided abundant redox reaction sites in 2D CoNi-ZIF NSs but also modulated the microstructures and chemical components of the hybrids. The integration of the features of N-CNTs and CoNi-ZIF NSs can result in a synergistic effect between N-CNTs and CoNi-ZIF NSs. Therefore, the obtained CoNi-ZIFs and N-CNTs hybrid (CoNi-ZIF@N-CNT) exhibited superior electrochemical capacitive performance. Comparison revealed that the CoNi-ZIF@N-CNT-2 hybrid, which was prepared with a 1:1 mass ratio of Co(NO3)2·6H2O and Ni(NO3)2·6H2O, displayed the largest specific capacitance of 1118F g−1 at 1 A g−1, which was higher than the capacitance of most reported metal–organic framework (MOF)-based supercapacitor electrodes. Moreover, the asymmetric supercapacitor based on the CoNi-ZIF@N-CNT-2 electrode exhibited a high energy density of 51.1 Wh kg−1 at the power density of 860.1 W kg−1 and good cycle stability. This work can provide a facile and effective way for the fabrication of heterostructured 1D/2D nanostructures based on 2D MOFs for advanced energy storage.

Multiple catalytic sites of Fe-Nx and Fe-N-C single atoms embedded N-doped carbon heterostructures for high-efficiency removal of malachite green

A series of Fe-N-C single atom catalysts embedded within the carbon nitride network (Fe-N-C/CNx) were developed to effectively degrade a commonly used organic dye, Malachite green (MG). Fe-N-C/CNx catalysts were achieved by pyrolyzing the hybrid of polypyrrole (PPy) and Melamine–cyanuric acid complex (MCA) containing trace Fe3+ (Fe/PPy@MCA) at different temperatures. Given the structural change of polymeric networks and nitridation of Fe3+, the mesoporous Fe-N-C/CNx hybrids comprise multiple components, including Fe-N-C, Fe4N, and CNx species, which show enhanced photocatalytic performance toward MG by integrating the high catalytic ability of Fe components and efficient visible-light harvest of CNx network. Notably, the Fe-N-C/CNx-700 hybrid obtained at 700 °C exhibits the high removal efficiency of 92.1% toward MG under visible light, with good reproducibility and stability. The biotoxicity of degraded products was further investigated by antibacterial experiment and plant growth effect. This work provides new insights into the development of efficient photocatalysts of nanohybrids for treating organic dyes.

Boron and phosphorus co-doped one-dimensional graphitic carbon nitride for enhanced visible-light-driven photodegradation of diclofenac

In this study, the boron (B) and phosphorous (P) co-doped one-dimensional graphitic carbon nitride (CN) (1D BPCN) photocatalysts with various P loadings have been synthesized by hydrothermal-assisted thermal polymerization method for rapid and efficient photodegradation of diclofenac (DCF) under visible light irradiation. The hydrolysis of melamine produces cyanuric acid during the hydrothermal treatment, and then the layered melamine-cyanuric acid complex serves as the supramolecular unit to form the 1D hexagonal-shaped BPCN after thermal polymerization at 500 °C for 4 h. The B and P heteroatoms can be doped inside the CN framework to form P-N and B-C bonds, resulting in the decrease in electric resistance to accelerate the electron transfer as well as the reduction of hole-electron recombination rate to enhance the photocatalytic activity of BPCN. Addition of 3 mL of phosphoric acid significantly enhances the visible-light-responsive photocatalytic activity of 1D BPCN toward DCF degradation. The photodegradation efficiency and rate of DCF over BPCN is a function of initial DCF concentration, pH and anions. Moreover, the BPCN exhibits an excellent reusability which can be effectively photodegrade DCF for at least 5 consecutive cycles. The reactive species of h+ and O2−• play an crucial role in the enhanced photodegradation of DCF, and, therefore, the plausible reaction mechanism and pathway for DCF photodegradation over 1D BPCN are proposed. These results clearly demonstrate that the BPCN is a superior visible-light-driven photocatalyst, and can pave a gateway to develop metal-free 1D nanocatalysts for the photodecomposition of emerging pollutants in water and wastewater.

CoOx/CoNy nanoparticles encapsulated carbon-nitride nanosheets as an efficiently trifunctional electrocatalyst for overall water splitting and Zn-air battery

A novel and efficient trifunctional electrocatalyst composed of cobalt oxide (CoOx) and cobalt nitride (CoNy) embedded in carbon–nitride nanosheets (CNz, represented by CoOx/CoNy@CNz) has been developed by calcining the composite of cobalt phthalocyanine (CoPc) and melamine–cyanuric acid complex at high temperatures. Multiple active sites of Co, CoOx, CoNy, and CNz containing in hybrids resulted in superior catalytic activities toward hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction in an alkaline medium. Among different catalysts, the CoOx/CoNy@CNz,700 catalyst not only displayed outstanding electrocatalytic ability for overall water splitting but also showed a high power density as high as 204.8 mW cm−2, high gravimetric energy density of 1008.6 W h kg−1, low charge–discharge polarization, and excellent reversibility after 86 h at 10 mA cm−2 in a Zn-battery system. This work presents a feasible strategy for developing multifunctional metal–carbon–nitride electrocatalysts for clean energy and energy transfer.

Carbon doped honeycomb-like graphitic carbon nitride for photocatalytic hydrogen production

Carbon doped honeycomb-like graphitic carbon nitride (g-C3N4) was prepared by one-step thermal polymerization, which derived from chitosan as a carbon source together with the melamine-cyanuric acid complex as a supramolecular precursor. Interestingly, the carbon doped g-C3N4 displayed an increased specific surface area and a more negative conduction band energy level, which not only provided a large number of reaction sites for the photocatalytic hydrogen production, but also effectively enhances the separation of photogenerated electrons-holes. And the experimental results showed that the hydrogen evolution rate of the optimal sample was as high as 320 μmol·h−1, which is 29.10 times than that of bulk g-C3N4 (11 μmol·h−1). More importantly, this work may provide a promising idea for the design of efficient g-C3N4 by controlling the material morphology and combining the electronic modulation strategy.

Free Standing Nitrogen Deficient Carbon Nitride Oxygen Electrodes for Metal-Air Batteries

Designing highly active, long-life durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgently required for bringing future renewable energy conversion and storage devices. However, poor conductivity and resulting serious irreversible capacity loss were pronounced for carbon nitride due to its high nitrogen content. Herein, one-dimensional (1D) nitrogen deficient g-C3N4 microtubes based electrocatalysts were fabricated using thermal polymerization of melamine-cyanuric acid complex precursors, followed by denitriding technology to reduce the nitrogen. The resultant ND-g-C3N4 exhibited outstanding bifunctional ORR/OER performances with overpotential of ~ 0.9 V comparable to the commercial noble metal catalysts (such as Pt/C & RuO2). This excellent catalytic performance was attributed to unique one-dimensional tubular structure having abundant active sites, high electrical conductivity, and efficient mass transport in the frameworks. The obtained bifunctional catalysts displayed the outstanding Zn-air battery performance for 400 h stability at 10 mA cm-2 with fast rate capability, open circuit potential of 1.48 V, and high power density of 230 mW cm-2. The outstanding electrochemical performances evidently stimulate the application of g-C3N4 materials in the energy storage devices.

Template-free large-scale synthesis of g-C3N4 microtubes for enhanced visible light-driven photocatalytic H2 production

A template-free hydrothermal-assisted thermal polymerization method has been developed for the large-scale synthesis of one-dimensional (1D) graphitic carbonnitride (g-C3N4) microtubes. The g-C3N4 microtubes were obtained by simple thermal polymerization of melamine-cyanuric acid complex microrods under N2 atmosphere, which were synthesized by hydrothermal treatment of melamine solution at 180 °C for 24 h. The as-obtained g-C3N4microtubes exhibited a large surface area and a unique one-dimensional tubular structure, which provided abundant active sites for proton reduction and also facilitated the electron transfer processes. As such, the g-C3N4 microtubes showed enhanced photocatalytic H2 productionactivity in lactic acid aqueous solutions under visible light irradiation (λ ≥ 420 nm), which was ∼ 3.1 times higher than that of bulk g-C3N4 prepared by direct thermal polymerization of the melamine precursor under the same calcination conditions.

Melamine Adulteration of Food:Detection by Point-of-Care Testing Tool

Melamine has emerged as one of the major food adulterants world over. Its high nitrogen content makes it a cheaper protein alternative, resulting in illegal adulteration of food and feed. Despite past incidences showing a higher risk to humans, there is no single method available to detect melamine in human samples at a lower cost-setting. Since melamine is excreted in the urine in an unchanged form, it can be detected directly by the development of a test at a patient's bedside via exploiting the intrinsic fluorescence ability of melamine cyanuric acid complex. Such a simple test will encourage huge public awareness and participation.

Hydration effect on proton transfer in melamine-cyanuric acid complex.

Self-assembly of melamine-cyanuric acid (MC) leads to urinary tract calculi and renal failure. The hydration effects on molecular geometry, the IR spectra, the frontier molecular orbital, the energy barrier of proton transfer (PT), as well as the stability of MC were explored by density functional theory (DFT) calculations. The intramolecular PT breaks the big π-conjugated ring of melamine or converts the p-π conjugation (:N-C'=O) to π-π conjugation (O=C-N=C') of cyanuric acid. The intermolecular PT varies the coupling between melamine and cyanuric acid from pure hydrogen bonds (Na…HNd and NH…O) to the cooperation of cation…anion electrostatic interaction (NaH(+)…Nd (-)) and two NH…O hydrogen bonds. Distinct IR spectra shifts occur for Na…HNd stretching mode upon PT, i.e., blue-shift upon intramolecular PT and red-shift upon intermolecular PT. It is expected that the PT would inhibit the generation of rosette-like structure or one-dimensional tape conformer for the MC complexes. Hydration obviously effects the local geometric structure around the water binding site, as well as the IR spectra of NH…O and N…HN hydrogen bonds. Hydration decreases the intramolecular PT barrier from ~45 kcal mol(-1) in anhydrous complex to ~11.5 kcal mol(-1) in trihydrated clusters. While, the hydration effects on intermolecular PT barrier is slight. The relative stability of MC varies slightly by hydration due to the strong hydrogen bond interaction between melamine and cyanuric acid fragments. Graphical Abstract Hydration effect on proton transfer in melamine-cyanuric acid complex.

Recent developments in the detection of melamine

In recent years, there were two reported outbreaks of food borne illness associated with melamine. The presence of melamine and its related compounds in milk, feed, and other foods has resulted in the need for reliable methods for the detection and accurate quantification of this class of contaminants. The sample pretreatment for melamine in a complex matrix usually involves a liquid extraction by a polar solvent, followed by a further clean-up with solid phase extraction. Analyses of melamine and related compounds are commonly carried out by liquid or gas chromatographic methods conjugated with mass spectrometry. Other innovative screening methods, which use antibodies, molecularly imprinted polymers, capillary electrophoresis, and gold nanoparticles, are also used to develop assays and biosensors to melamine. However, many of these methods have been hindered by matrix effects, the solubility of melamine-cyanuric acid complex, and background contamination. This article reviews recent developments for detecting melamine and discusses future directions.

Elucidating the Formation Characteristics of Melamine-Cyanuric Acid Complex

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Identification and Characterization of Toxicity of Contaminants in Pet Food Leading to an Outbreak of Renal Toxicity in Cats and Dogs

This paper describes research relating to the major recall of pet food that occurred in Spring 2007 in North America. Clinical observations of acute renal failure in cats and dogs were associated with consumption of wet pet food produced by a contract manufacturer producing for a large number of companies. The affected lots of food had been formulated with wheat gluten originating from China. Pet food and gluten were analyzed for contaminants using several configurations of high-performance liquid chromatography (HPLC) and mass spectrometry (MS), which revealed a number of simple triazine compounds, principally melamine and cyanuric acid, with lower concentrations of ammeline, ammelide, ureidomelamine, and N-methylmelamine. Melamine and cyanuric acid, have been tested and do not produce acute renal toxicity. Some of the triazines have poor solubility, as does the compound melamine cyanurate. Pathological evaluation of cats and dogs that had died from the acute renal failure indicated the presence of crystals in kidney tubules. We hypothesized that these crystals were composed of the poorly soluble triazines, a melamine-cyanuric acid complex, or a combination. Sprague dawley rats were given up to 100 mg/kg ammeline or ammelide alone, a mixture of melamine and cyanuric acid (400/400 mg/kg/day), or a mixture of all four compounds (400 mg/kg/day melamine, 40 mg/kg/day of the others). Neither ammeline nor ammelide alone produced any renal effects, but the mixtures produced significant renal damage and crystals in nephrons. HPLC-MS/MS confirmed the presence of melamine and cyanuric acid in the kidney. Infrared microspectroscopy on individual crystals from rat or cat (donated material from a veterinary clinic) kidneys confirmed that they were melamine-cyanuric acid cocrystals. Crystals from contaminated gluten produced comparable spectra. These results establish the causal link between the contaminated gluten and the adverse effects and provide a mechanistic explanation for how two apparently innocuous compounds could have adverse effects in combination, that is, by forming an insoluble precipitate in renal tubules leading to progressive tubular blockage and degeneration.