Thermal Condensation Research Articles

Graphitic-polytriaminopyrimidine (g-PTAP): A novel bifunctional catalyst for photoelectrochemical water splitting

In this study, an electrode of g-PTAP, a novel bifunctional catalyst for photoelectrochemical was fabricated and utilized for water splitting. The graphitic-poly (2,4,6-triaminopyrimidine (g-PTAP) was synthesized by the thermal vapor condensation polymerization (TVCP) method on FTO glass. The structure, morphology, and optical characteristics of the resultant g-PTAP were analyzed using analytical techniques such as FT-IR, Raman, XRD, XPS, CHNS, FE-SEM, EDS, and DRS. The synthesized g-PTAP was graphitic with sheet-like morphology and revealed maximum light absorbance capacity in the visible range. The DFT calculation showed an appropriate HOMO-LUMO band position for overall water splitting which was verified experimentally for H2 and O2 generation at photocathode and photoanode, respectively. Moreover, the g-PTAP sample exhibited good photo-stability as a photocathode as compared to a photoanode. This work can provide a pathway for fabricating highly efficient semiconductor photocatalyst for overall water splitting and solar energy such as conversion.

A Highly Stable and Sustainable Low-Temperature Selective Absorber: Structural and Ageing Characterisation

Solar absorbers in a three-layer configuration have been prepared by dip-coating onto aluminium substrates. They are constituted by two spinel layers with one silica layer on the top and values of solar absorptance above 0.950 and thermal emittance below 0.04 were obtained. The effects of using different sintering conditions of the upper silica layer on the optical behaviour and durability tests have been studied. Results obtained in accelerated ageing methods, such as thermal stability tests and condensation tests, clearly show that the proposed selective absorber exhibits excellent thermal stability and very good humidity resistance. The results show that the protective action is due not only to the silica layer but also to the alumina layer produced during the absorber preparation. The phase composition of the individual layers was independently confirmed using X-ray diffraction and corroborated by X-ray Photoelectron Spectroscopy. Spinel-like phases were obtained in both the first and second layers. The ageing study shows that the three-layer configuration proposed has a very high potential, in terms of both durability and optical behaviour, for solar thermal low-temperature applications.

Photocatalytic Dinitrogen Fixation with Water on High-Phosphorus-Doped Carbon Nitride with Surface Nitrogen Vacancies.

Sunlight-driven photocatalytic dinitrogen (N2) fixation with water at ambient conditions is of vital importance for a sustainable energy society. The efficiency of this reaction, however, is still low because of the difficulty in promoting both water oxidation and N2 reduction reactions. Herein, we report that a high-phosphorus-doped carbon nitride with surface nitrogen vacancies (PCN(V)) synthesized by thermal condensation under a hydrogen (H2) atmosphere using phosphorus oxide (P2O5) as a phosphorus source efficiently promotes N2 fixation. The large numbers of the doped P atoms on the PCN(V)-P2O5 catalysts enhance the oxidation of water, while the N vacancies reduce N2, facilitating efficient ammonia (NH3) generation with an apparent quantum yield at 420 nm of 3.4%. Simulated sunlight illumination of the catalyst in water under N2 bubbling produces NH3 with a solar-to-chemical conversion efficiency of 0.16%, which is the highest efficiency among the previously reported powder photocatalysts.

Carbon Nitride Thin Film‐Sensitized Graphene Field‐Effect Transistor: A Visible‐Blind Ultraviolet Photodetector

AbstractUltraviolet (UV) photodetectors often suffer from the lack of spectral selectivity due to strong interference from visible light. In this study, the exceptional electrical properties of graphene and the unique optical properties of carbon nitride thin films (CNTFs) are used to design visible‐blind UV photodetectors. First, polycrystalline CNTFs with different thicknesses (12–94 nm) are produced by thermal vapor condensation. Compared to the bulk carbon nitride powder, these films have a considerable sp2 nitrogen deficiency, which is thickness dependent. In addition to showing a wider bandgap than the bulk counterpart, their optical absorption profile (in the ultraviolet–visible range) is unique. Critically, the absorbance falls sharply above 400 nm, making the CNTFs suitable for ultraviolet photodetection. As a result, graphene field‐effect transistors (GFETs) sensitized with CNTFs show 103 A W−1 responsivity to UV radiation, a stark contrast to the negligible value obtained in the visible spectrum. The effect of film thickness on the photoresponse is determined, with the thinner CNTF leading to much better device performance. The CNTF/GFET photodetectors are also characterized by their fast response and recovery times, 0.5 and 2.0 s, respectively. These findings pave a simple route for the development of sensitive, visible‐blind UV photodetectors.

A photocatalytic dye-degradation study on methylene blue by graphitic nitride based polyimides synthesized via a facile thermal-condensation approach

The frequent use of methylene blue (MB) and other organic dyes pose serious environmental concerns subjected to their resistance towards traditional degradation procedures. Therefore, it is important to develop efficient degradation treatments to degrade such dyes. We report a facile thermal condensation methodology to synthesize graphitic nitride (GN) and its derived polyimides by using three different dianhydrides. The obtained results from physicochemical characterization; FTIR, XRD, XPS, and BET/BJH confirmed the formation of GN and its derived polyimides. The synthesized photocatalyst materials were tested for MB degradation under light irradiation for 60 min. Interestingly, the superior photocatalytic performance (96% MB degradation efficiency) despite of decreased surface area of polyimide, GN-FDA (6.78 m2 g−1) has been attributed to its relatively improved degree of crystallinity, greater HOMO-LUMO charge separation, high quaternary nitrogen content, and appropriate porosity. This study can be concluded as follows; firstly the π conjugated polyimides surprisingly undergo significant shrinkage in surface area probably due to π-π interactions. Secondly, derived polyimides exhibited essential features of photocatalytic materials viz greater HOMO-LUMO charge separation evidenced by DFT studies, improved hydrophilicity, appropriate surface area/ porosity, and surface nitrogen functionalities that improve their degradation efficiency. Quantum mechanical calculations reveal that modification of GN results in improved electronic properties and enhanced dye degradation attributed to modified charge transfer. This work may open new opportunities to develop efficient metal-free photocatalysts based on GN that are a significant contribution in designing suitable photocatalyst materials for degradation of other organic dyes/ contaminants.

Synthesis, Characterization and Biological Activities of New Schiff Base Compound and Its Lanthanide Complexes.

The thermal condensation of 3-(2-Furyl)acrolein with 2-Amino-6-ethoxybenzothiazole generated a new Schiff base, (1E,2E)-N-(6-ethoxybenzo[d]thiazol-2-yl)-3-(furan-2-yl)prop-2-en-1-imine (L), with general formula of C16H14N2O2S. Also, a series of lanthanide complexes of gadolinium, samarium, and neodymium (La–Lc) were synthesized utilizing acetonitrile as the solvent and triethylamine as a buffer and catalyst. Based on elemental analysis, mass spectroscopy, and FTIR analysis, all of the Bis-(1E,2E)-N-(6-ethoxybenzo[d]thiazol-2-yl)-3-(furan-2-yl)prop-2-en-1-iminetri-nitratolanthanide(III) complexes with the general formula [LnL2(NO3)3]·H2O are solids with a 2:1 molar ratio (ligand: metal). Based on conductivity estimates, they are nonelectrolytes and monoatomic paramagnetic according to the magnetic moment measurements, and one mole of lattice water was found after thermal gravimetric measurements and FTIR analysis. Therefore, the lanthanide complexes show a ten-coordination structure with a deformed bicapped square antiprismatic. The Schiff base and its complexes were screened for their antimicrobial, antifungal, antioxidant, and antitumor properties. Their antimicrobial and antifungal activities were strong, and they also produced good antioxidant and antitumor effects.

Highly fluorescent carbon nitride oligomer with aggregation-induced emission characteristic for plastic staining

Polymeric carbon nitride often displays weak photoluminescence in solid state due to the aggregation-caused quenching effect. Herein, highly fluorescent carbon nitride oligomer (CNO) with aggregation-induced emission (AIE) characteristic was prepared via one-step solid-phase thermal condensation of 2,4-diamino-6-phenyl-1,3,5-triazine (DPT) at 350 °C. CNO is mainly composed of DPT dimer connected by rotatable imine groups, and exhibits weak fluorescence in the dispersed state and strong blue-green emission in the aggregated state and solid state. Density functional theory calculations indicate that the restriction of phenyl and triazine ring twisting motions is the main origin of the AIE phenomenon of CNO. Finally, CNO was preliminarily applied for fluorescent staining of plastic pellets. This work not only provides a solid-state strategy to synthesize fluorescent material with AIE characteristic but also extends the application of polymeric carbon nitride.

Calculation of the Rate Constants of Thermal Cracking and Condensation Reactions of High-Sulfur Tar Asphaltenes

Calculation of the Rate Constants of Thermal Cracking and Condensation Reactions of High-Sulfur Tar Asphaltenes

Influence Mechanism of Water-Soluble Sodium on Zhundong Coal Pyrolysis.

An inherent water-soluble sodium-loaded coal sample was prepared using crown ether for this study. The pyrolysis process of an inherent water-soluble sodium-loaded coal sample and a water-soluble sodium compound-loaded coal sample was researched by thermogravimetric analysis (TGA). Also, the pyrolysis kinetics of the coal samples were analyzed and researched by the distributed activation energy model (DAEM). The results show that the inherent water-soluble sodium is mainly concentrated on coal particles, which further aggravates the degree of the pyrolysis reaction. The presence of sodium can promote the weight loss of coal samples in the preliminary stage of pyrolysis and the thermal condensation stage, block the escape of volatile matter during the main pyrolysis period, and inhibit the process of graphitization of char. The activation energy of pyrolysis increases with the carbon conversion rate, and the presence of sodium can reduce the activation energy under the same carbon conversion rate.

From urea to melamine cyanurate: Study of a class of thermal condensation routes for the preparation of graphitic carbon nitride

This work presents a survey of the intermediates in the well-known thermal synthesis of graphitic carbon nitride from urea. The analysis of the crystalline phases depicts a successive transformation of the precursor into different substances previously used as starting reactants, whereby melamine cyanurate arises as the ultimate precursor of a class of thermal condensation routes to obtain graphitic carbon nitride. The study of the optical properties of the synthesized materials evidences the simultaneous production of an amorphous phase with a significant presence of melon oligomers. These results are also supported by the further characterization of the materials performed using THz-TDS, FTIR, HRTEM, and XPS techniques, and by theoretical studies conducted using semi-empirical quantum chemistry methods.

The effect of biodegradation on bound aromatic hydrocarbons released from intermediate-temperature gold-tube pyrolysis of severely biodegraded Athabasca bitumen

Polycyclic aromatic hydrocarbons (PAHs) from two severely biodegraded Athabasca oil sand bitumens released by gold-tube pyrolysis at 300–525 °C with 2 °C/h heating rate were characterized by gas chromatography-mass spectrometry. Alkylnaphthalenes, alkylphenanthrenes and alkyldibenzothiophenes were fully removed by biodegradation from the free phase aromatic hydrocarbon fraction in raw bitumens, while tetracyclic aromatics were partially attacked. Sample A has suffered less extensive biodegradation influence than sample B due to different oil-water-contact situations. Pronounced changes were observed in the distribution of various compound classes after pyrolysis due to thermal cracking, aromatization and condensation. PAHs released from occluded phase at intermediate–temperature (< 425 °C) exhibit clear biodegradation impact. The proportion of alkylnaphthalenes released in initial pyrolysates is much lower than those highly fused aromatics, reflecting more biodegradation influence on lower ring number aromatic hydrocarbons. Within alkylnaphthalenes, naphthalene and methylnaphthalenes with less substituents are largely depleted in the pyrolysates, indicating preferential removal of less alkylated homologues from the occluded phase by biodegradation. Isomer selectivity from the occluded aromatic hydrocarbons follows the same sequences as those observed from the free phase, resulting in poor correlation between isomerization based maturity parameters and heating temperatures. PAHs released from extremely biodegraded bitumens in intermediate–temperature pyrolysates might differ totally from those in the non-degraded oils. Caution should be taken when molecular parameters derived from occluded phase are applied for organic source input and maturity assessment.

One-step fabrication of mesoporous sulfur-doped carbon nitride for highly selective photocatalytic transformation of native lignin to monophenolic compounds

Photocatalytic selective transform native lignin into valuable chemicals is an attractive but challenging task. Herein, we report a mesoporous sulfur-doped carbon nitride (MSCN-0.5) which is prepared by a facile one-step thermal condensation strategy. It is highly active and selective for the cleavage Cα−Cβ bond in β−O−4 lignin model compound under visible light radiation at room temperature, achieving 99% substrate conversion and 98% Cα−Cβ bond cleavage selectivity. Mechanistic studies revealed that the Cβ−H bond of lignin model compounds activated by holes and generate key Cβ radical intermediates, further induced the Cα−Cβ bond cleavage by superoxide anion radicals (•O2−) to produce aromatic oxygenates. Waste Camellia oleifera shell (WCOS) was taken as a representative to further understand the reaction mechanisms on native lignin. 33.2 mg of monophenolic compounds (Vanillin accounted for 22% and Syringaldehyde for 34%) can be obtained by each gram of WCOS lignin, which is 2.5 times as that of the pristine carbon nitride. The present work offers useful guidance for designing metal-free heterogeneous photocatalysts for Cα−Cβ bond cleavage to harvest monophenolic compounds.

On the chemical condensation of the layers of zeolite precursor MCM-22(P)

Chemical condensation of layers of silicates has been often proposed as an alternative to thermal condensation, finding limited success. The formation of the industrially relevant MCM-22 zeolite (MWW IZA code) from a mild hydrothermal precursor is the most important example of 2D-3D aluminosilicate condensation. Silanols of opposed layers have been condensed by acid-driven dehydration in concentrated nitric acid, as confirmed by powder XRD and 29Si NMR spectroscopy, implying interlayer template extraction and corresponding dealumination. Milder acid treatments favour template extraction and shrinkage of interlayer distance, but do not provide significant silanol condensation. Template extraction is further favoured by degradation of the organics in the presence of a Cu2+ homogeneous catalyst.

Optimization of supercritical carbon dioxide recompression Brayton cycle considering anti-condensation design of centrifugal compressor

Supercritical carbon dioxide Brayton cycle has the advantages of high-efficiency and compactness, and is one of the most promising propulsion and power system options in shipboard application. The high-efficiency design of supercritical carbon dioxide Brayton cycle requires the compressor to operate near the critical point of carbon dioxide where the carbon dioxide changes dramatically in thermophysical properties resulting in inaccurate performance prediction for compressor and condensation tends to occur especially at the inlet of compressor impeller. So far, most of the studies on supercritical carbon dioxide cycle optimization have taken thermal efficiency and exergy performance into account while the anti-condensation performance is rarely considered. In this context, a design optimization strategy is proposed for supercritical carbon dioxide Brayton cycle, in which both the thermal efficiency and condensation margin are considered as objective functions in an attempt to improve the performance and anti-condensation. In addition, an aerodynamic design method is developed for supercritical carbon dioxide centrifugal compressor by using real gas two-zone model to alleviate the reliance on model empiricisms. The proposed strategy and the developed method are validated and then applied to a 50 MW shipboard supercritical carbon dioxide Brayton recompression cycle optimization and the main compressor design. The analysis results show that condensation margin and cycle thermal efficiency are conflictive with each other. The higher temperature and lower pressure at the compressor inlet can improve cycle anti-condensation while the opposite is true for the cycle thermal efficiency. As the condensation margin is 0.1, the thermal efficiency of optimized cycle is 48.16%. The computational fluid dynamics simulations confirm that the designed main compressor meets the anti-condensation requirements as condensation margin is above 0.1. This work is of certain significance to promote the application of supercritical carbon dioxide cycle in shipboard usage.

Towards sustainable re-construction systems: from waste ruins to eco-efficient buildings

Building reconstruction projects are mainly motivated by social factors, without a deep evaluation of the Best Available Techniques. The main aim of this work is to analyze the advantages of defining sustainable retrofitted buildings, previously building the edifice, by using methodologies towards sustainable systems. A real re-constructed building is considered as a case study. Three scenarios are investigated to analyze its sustainability, including the waste ruins of the old building (Scenario 1), the current re-constructed building (Scenario 2), and a hypothetical sustainable retrofitted building (Scenario 3). Firstly, the current energy consumption is studied including heating flow through walls (thermal bridges and condensation risk) as well as operational costs. Secondly, a new scenario is proposed adding passive solutions to this existing building, to improve its energy efficiency; also, energy consumption and costs of the refurbishment are analyzed. Results show that Scenario 1 leads to a bad image of a city involving the environment and social fields. Scenario 2 entails expensive operational costs. On the other hand, Scenario 3 results in approximately 90% of cost savings in heating energy demand, which would be traduced on high economic savings. Taken into account not only economic factors but environmental and social ones, it can be concluded that it is more sustainable and profitable constructing an efficient building from the beginning by using waste ruins and simulation software despite refurbishing a re-built edifice.

Confined synthesis of condensed π-conjugation C-PAN/MS-CN nanotubes for efficient photocatalytic H2 evolution

Condensed π-conjugation C-PAN/MS-CN nanotubes were obtained via a facile polyacrylonitrile (PAN)-confined molten salt (MS) thermal condensation of melamine. Carbonized PAN (C-PAN) nanosheets with a conjugate network structure in the molten salt system acted as partition plates confining the thermal condensation of melamine, which promoted the formation of condensed π-conjugation carbon nitride (CN) for the effective charge carrier separation and photocatalytic H2 evolution.

Ultra-thin graphene/g-C3N4 nanosheets with in-plane heterojunction for enhanced visible-light photocatalytic hydrogen evolution performance

ABSTRACT Ultra-thin graphene/g-C3N4 nanosheets (CN/G) with in-plane heterojunction were prepared by facial two-step thermal condensation of urea and glucose under mild conditions to improve photocatalytic hydrogen evolution under visible-light irradiation. The characterisation indicated that graphene was connected to the end of g-C3N4. The thermal exfoliation process can transform the bulk structure of g-C3N4 into ultra-thin nanosheets. Consequently, photocatalytic activity for hydrogen evolution rate of CN/G-0.1 was 704 µmol g–1 h–1, about 14 times higher than that of pure g-C3N4 under visible light irradiation (λ > 420 nm). CN/G-0.1 also exhibited high stability from the cycling tests for 18 h and superior photocatalytic properties at 500 nm. In-plane graphene modification can significantly enhance visible-light absorption and promote photogenerated electron-hole pair separation. On the other hand, ultra-thin nanosheets can increase specific surface area (153.8 m2 g–1) and provide abundant active sites. This study provides a suitable method to prepare g-C3N4 based on highly efficient photocatalysts for metal-free photocatalytic hydrogen evolution.

A novel and facile preparation of Superhydrophilic/Superoleophobic nanofilter using carbon nitride nanosheet for W/O emulsion separation

In this research, a novel superhydrophilic/ superoleophobic thermoplastic polyurethane@graphitic-carbon nitride@perflourooctanoic acid (TPU@g-C3N4 @PFOA) coated stainless steel mesh was prepared to separate water/oil emulsion. g-C3N4 nanosheets were synthesized with a facile thermal condensation process followed by exfoliation using acid. TPU as a binder is commercially available and provides strong bonding of the nanocomposite coating to the substrate. Wettability characteristics of nanocomposite coated mesh showed the water contact angle of 18.9° and oil contact angle of 151°, which confirmed the special wettability of superhydrophilicity and superoleophobicity. The prepared nanocomposite-coated filter with the surface energy of 92.87 mN/m (dispersive and polar surface energy of 0.199 and 92.68 mN/m) was able to separate water from a 10 wt % water/oil emulsion. Ultimately excellent water–oil separation efficiency of 99% and the filtration flux of 50.5 L.m−2.h−1 were attained under gravity. The particular behavior of the surface is justified with small pore size of mesh, higher roughness and superoleophobic wettability due to the presence of g-C3N4 nanosheets, as well as with the reduction of the surface energy of the synthesized TPU@g-C3N4 by PFOA, as a surfactant with the fluorine tail groups. As-prepared mesh can also separate free crude oil–water mixtures with the separation efficiency and flux of 99.9% and 2157.4 L.M−2.h−1, respectively.The anti-fouling and mechanical stabilities of the as-prepared coated mesh were investigated. This result implied that the as-prepared water-removing filter has great potential for separation of the water-in-oil emulsion, which has long been a problem in industry and is often separated using oil-removing filters in the literature.

A broom-like tube-in-tube bundle O-doped graphitic carbon nitride nanoreactor that promotes photocatalytic hydrogen evolution

Metal-free graphite carbon nitride (g-C3N4) is an ideal catalyst in the field of photocatalytic hydrogen evolution due to its visible light response, thermochemical stability and low cost. However, limited by the high photogenerated electron-hole recombination rate and poor light trapping ability of bulk g-C3N4 prepared by thermal condensation, it remains a great challenge in boosting the photocatalytic hydrogen (H2) evolution performance. Herein, a broom-like O-doped g-C3N4 nanoreactor (O-CN-NTs) oriented by tube-in-tube was developed for the first time through the “calcination-hydrothermal-calcination” method. The tube-in-tube nanoreactor not only can facilitate the scattering of incident light inside the cavity to enhance the utilization of light, but also can reduce the transport distance of carriers from the bulk to the surface to facilitate electron-hole separation. The morphology design of the tube-in-tube nanoreactor plays a very important role in improving the performance of photocatalytic H2 production. Furthermore, the density functional theory (DFT) calculation results manifest that the charge redistribution around the doped oxygen atoms accelerates the separation of electron-hole. The doping of oxygen atoms in g-C3N4 nanoreactor further enhanced the photocatalytic H2 production performance. Attributed to above advantages, the visible-light-driven (≥420 nm) photocatalytic H2 production rate of O-CN-NTs can achieve 13.61 mmol g-1h−1, which is approximately 71.63 times that of bulk g-C3N4 (CN550).

Versatile Covalent Postsynthetic Modification of Metal Organic Frameworks via Thermal Condensation for Fluoride Sensing in Waters.

Having access to safe drinking water is one of the 17 sustainable development goals defined by the United Nations (UN). However, many settlements around the globe have limited access to drinkable water due to non-anthropogenic pollution of the water sources. One of those pollutants is fluoride, which can induce major health problems. In this manuscript, we report on a post synthetic functionalization of metal organic frameworks for the sensing of fluoride in water. The proposed thermal condensation methodology allows for a high yield of functionalization using few steps, reducing reagent costs and generating minimal by-products. We identified a Rhodamine B functionalized Al-BDC-NH metal organic framework as one particularly suitable for fluoride detection in water.