A novel exploration of metal–organic frameworks in flame-retardant epoxy composites

In this work, a series of transition metal–organic frameworks (MOFs) were prepared through self-assembly of organic bridging ligands and transition metal ions. The structure of MOFs samples was analyzed by XRD, FTIR, TG, and TEM. The influences of MOFs on flame resistance, toxicity reduction, and smoke suppression of epoxy were explored in detail. The findings presented that low addition amount of MOFs had a positive effect on decreasing the fire hazards of epoxy. Loading of 2 mass% MOFs into epoxy led to the decrease in thermal degradation rate and increase in char yields. Meanwhile, the values of peak heat release rate, total heat release, and average mass loss rate of epoxy composites were cut down effectively, in comparison with neat epoxy. Moreover, the remarkable decrease in smoke production rate, total smoke production, and CO, CO₂ yield could be provided by cone calorimeter test. The char residues after cone calorimeter test were investigated by SEM and Raman spectra, and the flame-retardant mechanism was discussed.

     

Synthesis of MoO3 with different morphologies and their effects on flame retardancy and smoke suppression of polyurethane elastomer

Molybdenum trioxide (MoO₃) microrods, nanofibers, and nanoplates were synthesized via the hydrothermal method and high‐temperature calcination method, respectively. Then the MoO₃ was added into polyurethane elastomer, respectively. The flame retardancy and smoke suppression of the composites added with different MoO₃ were studied by thermal gravimetric analysis, cone calorimeter, and smoke density. The results show that the three kinds of MoO₃ with different morphologies could promote the formation of char and possess flame retardancy and smoke suppression, and MoO₃ nanofibers exhibit a higher degree of flame retardancy, and 1 wt% addition could make the peak heat release rate of polyurethane elastomer composites reduce from 881.6 kW m^?2 for a pure sample to 343.4 kW m^?2, a decrease by 61.0%. As for smoke suppression, MoO₃ nanoplates possess the best smoke suppression; 5 wt% could decrease a pure sample's smoke density by 41.3% from 361 to 212. Moreover, the char residue of composites after combustion was analyzed by Raman spectra and X‐ray photoelectron spectroscopy, and the flame retardancy and smoke suppression mechanisms of MoO₃ were discussed.     

Using cone calorimeter to study thermal degradation of flexible PVC filled with zinc ferrite and Mg(OH)2

Flame-retarded poly(vinyl chloride) (PVC) materials have been prepared by using zinc ferrite (ZnFe₂O₄ (ZFO)) combined with magnesium hydroxide (Mg(OH)₂ (MH)). The effects of these additives on the combustion and thermal degradation of PVC samples were studied using the limiting oxygen index test, the smoke density rating test, thermogravimetric–differential thermogravimetry, and the cone calorimeter test. The results showed that ZFO and MH were good synergists for improving the flame retardancy and smoke-suppressing of PVC/MH/ZFO blends. ZFO can significantly improve the maximum mass loss velocity in the first stage, and reduce the initial decomposition temperature and the decomposition range in the PVC/MH/ZFO blends. The char yield at 700 °C of flame-retarded PVC clearly decreased below theoretical values due to the cationic cracking reactions in the presence of ZFO. Furthermore, the PVC/10MH/10ZFO showed strong flame-retarding synergism since the decreased average heat release rate value. And the PVC/19MH/1ZFO presented a significant smoke-suppressing effect by the least average specific extinction area, peak smoke production rate, and total smoke produce. Moreover, the CO and CO₂ production was increased because of a large amount of fragment of char residue in contact air in the presence of ZFO.     

Hydrogen Production From Crude Bio-oil and Biomass Char by Electrochemical Catalytic Reforming

We reports an efficient approach for production of hydrogen from crude bio-oil and biomass char in the dual fixed-bed system by using the electrochemical catalytic reforming method. The maximal absolute hydrogen yield reached 110.9 g H₂/kg dry biomass. The product gas was a mixed gas containing 72%H₂, 26%CO₂, 1.9%CO, and a trace amount of CH₄. It was observed that adding biomass char (a by-product of pyrolysis of biomass) could remarkably increase the absolute H₂ yield (about 20%-50%). The higher reforming temperature could enhance the steam reforming reaction of organic compounds in crude bio-oil and the reaction of CO and H₂O. In addition, the CuZn-Al₂O₃ catalyst in the water-gas shift bed could also increase the absolute H₂ yield via shifting CO to CO₂.     

Two kinds of activated carbon spheres-supported metal oxides for reducing smoke release volume and fire hazard in flexible poly(vinyl chloride)

Two kinds of activated carbon spheres (ACS)-supported metal oxides, ACS-supported Fe₃O₄ (ACS@Fe₃O₄) and ACS-supported NiO (ACS@NiO), were synthesized and used as flame retardants for reducing smoke release volume and fire hazard in flexible poly(vinyl chloride) (PVC). Scanning electron microscope measurement, Fourier transform infrared spectrum, X-ray diffraction and thermogravimetric analysis (TGA) were utilized to investigate the morphology, chemical structure and stability of the flame retardants. The TGA coupled with mass spectrometry (TG-MS) results of PVC composites showed that ACS could retard the heat and oxygen transfer between gas and polymers. Under the same condition, ACS@Fe₃O₄ could promote the dehydrochlorination reaction of PVC in lower temperature, while the ACS@NiO could make the dehydrochlorination reaction faster. Therefore, both ACS@Fe₃O₄ and ACS@NiO effectively promoted the cross-linked carbonization reaction of PVC and then generated a large amount of stable char residues. Limiting oxygen index (LOI) and cone calorimeter test results of the PVC composites showed that ACS@Fe₃O₄ and ACS@NiO were much more efficient than ACS alone to improve the flame retardancy and smoke suppression of PVC. The incorporation of ACS@Fe₃O₄ and ACS@NiO increased the LOI from 24.9 to 27.4% and 26.9% and reduced the peak of heat release rate by 47.2 and 30.8%, respectively, compared with pure PVC.

     

Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system

The effects of lanthanum oxide (La₂O₃) as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (IFR-PP) were studied, and the new IFR system mainly consisted of the charring-foaming agent (CFA) and ammonium polyphosphate (APP). The limiting oxygen index (LOI), UL-94 test, thermogravimetric analysis (TGA), cone calorimeter (CONE) and scanning electron microscopy (SEM) were used to evaluate the synergistic effects of La₂O₃. It was found that when IFR was fixed at 20 wt% in IFR-PP composites, only a little amount of La₂O₃ could enhance LOI value and pass the UL-94 V0 rating test (1.6 mm). The TGA data showed that La₂O₃ could enhance the thermal stability of the IFR-PP systems at high temperature and effectively increase the char residue formation. The CONE results revealed that La₂O₃ and IFR could clearly change the decomposition behavior of PP and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSP), ignition time (IT) and so on. The morphological structures observed by SEM demonstrated that La₂O₃ could promote to form the homogenous and compact intumescent char layer. Thus, a suitable amount of La₂O₃ plays a synergistic effect in the flame retardancy and smoke suppression of IFR composites.     

Catalytic reforming of tar using corncob char and char-supported potassium catalysts

This work aims to investigate the importance of biomass char and the metal oxides in the ash in tar cracking during the volatile–char interactions. Experiments were carried out in a two-stage fixed reactor, and corncob, one typical agricultural biomass rich in potassium, was chosen as raw material. Results showed that char and char-supported potassium catalysts have good activity for tar elimination due to the good absorbability of char and catalytic property of potassium. In particular, tar conversion efficiency can reach 95.8% by using 1.5 K-char catalyst at 700 °C. The reforming reactions can be significantly enhanced during the volatile–char interactions in the presence of char and char-supported potassium catalysts. As a result, the syngas yield increased significantly with increasing temperature and supported K⁺, particularly the combustible gases including H₂, CO and CH₄. Physical and chemical structure of char changed due to reforming reactions related to the carbon, while the content of potassium was almost unchanged.     

Fire reaction properties of polystyrene-based nanocomposites using nanosilica and nanoclay as additives in cone calorimeter test

Using nanofiller additives in the polymer matrix to form nanocomposites is a potential way of reducing the flame spread and enhancing flame retardancy of polymeric materials during fire. To understand the fire reaction properties and the relative performance of flame-retardant additives in polymer during well-developed fire, neat polystyrene, polystyrene–silica and polystyrene–nanoclay (MMT) have been tested in a cone calorimeter. The neat polystyrene and the polystyrene nanocomposites have been prepared via an in situ polymerization method. An external heat flux of 50 kW m^?2 was applied in the test, and parameters such as heat release rate, peak heat release rate, time to ignition, smoke toxicity, CO and CO₂ yield have been investigated. Both neat polystyrene and polystyrene nanocomposites have shown the trend of a thermally thick charring polymer in the heat release rate over time data. The nanocomposites had an overall better flame retardancy than the neat polystyrene in terms of lower peak heat release rate, lower average mass loss rate and enhanced char formation. The nanocomposites had also reduced smoke emission with lower CO and CO₂ yield compared to the neat polystyrene. The overall flame retardancy was enhanced as the nanofiller loading was increased for both the nanosilica and MMT nanocomposites.

     

烟煤焦在H2O和CO2气氛下的结构演变与气化反应性关联

本研究以烟煤在1000 ℃热解所制得的焦样为研究对象,考察了其在H₂O、CO₂及两者混合气氛下的结构演变,以及气化反应性的影响。为了探究焦样在气化过程中的结构演变,利用氮吸附、SEM和拉曼光谱等表征手段分析不同碳转化率下的焦样结构。结果表明,H₂O气氛对焦样结构的演变明显不同于CO₂气氛,揭示了焦样在两种气氛下的反应路径不同。因结构演变的不同,随碳转化率的增加,焦样在两种气氛下表现出不同的气化反应性能。在CO₂气氛下,焦样的气化反应速率随碳转化率的增加而逐渐降低,与H₂O气氛存在下变化趋势相反。在H₂O和CO₂共气化条件下,煤焦在H₂O和CO₂混合气氛下的反应速率高于单气氛下的反应速率的计算值,表现出一定的协同作用。这是因为焦样与H₂O反应能够产生较大的比表面积,为焦样与CO₂反应提供更多的反应场所,促进了焦样与CO₂的反应。     

Study on carbon dioxide reduction with water over metal oxide photocatalysts

Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO₂ reduction with water. Among all the prepared Ag-loaded metal oxides, Ga₂O₃, ZrO₂, Y₂O₃, MgO, and La₂O₃ showed activities for CO and H₂ productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d⁰, d¹⁰, and s⁰ had the potential for CO₂ reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO₂ adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO₂ enhanced H₂ production rather than CO production due to very little CO₂ adsorption. Ag/Ga₂O₃ exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La₂O₃, Ag/Y₂O₃, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H₂ production. However, the adsorbed carbonate species were hardly converted to the bidentate formate.     

Promotion effect of metal oxides on C-O bond dissociation in CO hydrogenation over Rh/SiO2 Catalyst — possible role of partially reduced state cations

In CO hydrogenation over Rh/SiO₂ catalysts, the effect of additive metal oxides on C-O bond dissociation was studied by using pulse surface reaction rate analysis (PSRA). The addition of oxides of Al, Ti, Cr, V, and Mn resulted in an increase in the rate constant for the dissociation according to this sequence, while the oxides of Cu, Zn, and Ag added decreased the rate constant to almost the same extent. In contrast to these metal oxides, MoO₃ and WO₃ did not change the dissociation activity. CO adsorption measurement indicated that all of the added metal oxides covered a considerable portion of the Rh metal surface, although the efficiency of covering was different from one metal oxide to another. Covering the Rh metal surface with an added metal oxide should decrease the rate constant of C-O bond dissociation, because ensemble sites, consisting of a group of surface Rh atoms and considered necessary for the dissociation, were destroyed. The suppression effect resulted from the destruction of the ensemble sites by adding the oxides of Cu, Zn, and Ag. For other metal oxides, temperature-programmed reduction (TPR) or O₂ uptake measurement revealed that the added oxides, especially those existing on the Rh metal surface, were in a partially reduced state under reaction conditions. Owing to its high affinity for an oxygen atom, the cation in a partially reduced state participated in the reaction in such a way that the oxygen end of adsorbed CO species was bound to the cation so as to dissociate the C-O bond, which resulted in promotion of the dissociation. The observed promotion was explained in terms of the enhancement owing to the high affinity sufficient to overcome the suppression caused by destroying ensemble sites. Lack of the promotion effect of MoO₃ and WO₃ might result from a balance between promotion due to the high affinity of the partially reduced Mo or W and suppression caused by destroying ensemble sites. Excellent correlation was observed between the intrinsic activity increase, from which the suppression effect was excluded, and the heat of formation of metal oxide including MoO₃ and WO₃. Since the heat of formation of metal oxide is considered to be a measure of the affinity, this correlation supports the idea that the high affinity of additive cations for an oxygen atom is of primary importance in the promotion of C-O bond dissociation in CO hydrogenation.     

Al(OH)3和Mg(OH)2对PVC热解特性的影响研究

利用热重分析仪并借助电导率测定法探讨了Al(OH)3和Mg(OH)2对PVC热解特性的影响,简要分析了其机理。结果表明:加入Al(OH)3和Mg(OH)2后均能增加PVC体系在第一阶段的最大热解速率和残炭量,最大热解速率增加约1倍,残炭量增加约4倍。并且分解产生的结晶水吸收大量的热量,惰性金属氧化物也有利于成核、炭层生长和凝聚,有着明显的阻燃和抑烟作用。HCl毒性气体的释放主要集中在体系的第一阶段,Al(OH)3能促使HCl提前释放,HCl的释放总量增加,Mg(OH)2也能促使HCl提前释放,但HCl的释放总量却是减少的。     

Polyaniline‐coupled graphene/nickel hydroxide nanohybrids as flame retardant and smoke suppressant for epoxy composites

Graphene‐polyaniline/nickel hydroxide ternary hybrid (RGO‐PANI/Ni(OH)₂) was synthesized and incorporated into epoxy resin (EP) to improve the fire retardant property. Thermogravimetric analysis results showed that the RGO‐PANI/Ni(OH)₂ nanohybrid could catalyze the thermal degradation of epoxy matrix that was essential to trigger the char formation. The char yield of the RGO‐PANI/Ni(OH)₂/EP composite was improved compared with that of the samples with graphene and polyaniline only. With 3.0‐wt% RGO‐PANI/Ni(OH)₂, significant reduction in peak heat release rate (40%) and peak smoke production rate (36%) was observed in the cone calorimeter tests. Thermogravimetric analysis/infrared spectrometry (TG‐IR) results indicated that the flammable volatiles of the RGO‐PANI/Ni(OH)₂/EP composite was reduced compared with those of the EP and RGO‐PANI/EP. The superior flame retardant and smoke suppressant behaviors of the RGO‐PANI/Ni(OH)₂ nanohybrid over RGO‐PANI were attributed to the combination of good barrier effect of graphene with catalytic ability of char formation of PANI and metal hydroxide.     

Synergistic effect of bismuth oxide and mono‐component intumescent flame retardant on the flammability and smoke suppression properties of epoxy resins

A novel mono‐component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS)‐hybrid bismuth oxide (PPMS‐Bi₂O₃) was synthesized and carefully characterized by FTIR, ¹H NMR, ³¹P NMR, SEM‐EDS, and TG analyses. Then, PPMS‐Bi₂O₃ was utilized as flame retardant for epoxy resins (EPs), and the thermal stability, flame retardancy, and smoke suppression properties of EP composites were investigated. TG results show that PPMS‐Bi₂O₃ is more conducive to enhance the thermal stability and char forming ability of EP composites compared with the same addition of PPMS or the mixture of PPMS and Bi₂O₃, and this positive effect is enhanced with the increasing Bi₂O₃ content. Cone calorimeter test reveals that the PPMS‐Bi₂O₃ can effectively reduce the heat release and smoke production in comparison with PPMS or the mixture of PPMS and Bi₂O₃ due to the formation of a more compact and intumescent char against fire, as judged by digital photographs and SEM images. EDS analysis indicates that the combination PPMS and Bi₂O₃ by hydrogen bonds promotes to generate more phosphorus‐rich and aromatization structures in the condensed phase that enhance the barrier effect and anti‐oxidation ability of the char, thus imparting higher flame retardant and smoke suppression efficiencies to EP composites.     

Effect of metal oxides on the reforming of methane with carbon dioxide

The effect of basic and rare earth metal oxides on the stability of nickel-based catalysts for the CO₂ reforming of CH₄ has been studied. The addition of metal oxides increased the stability of Ni-based catalysts and reversed the values of the reaction orders with respect to both CH₄ and CO₂. In the presence of metal oxides, the values of the reaction orders with respect to CO₂ partial pressure followed the same trend of catalyst stability.     

Biodiesel Preparation from Jatropha curcas Oil Catalyzed by Hydrotalcite Loaded With K2CO3

This paper discusses the synthesis of biodiesel catalyzed by solid base of K₂CO₃/HT using Jatropha curcas oil as feedstock. Mg–Al hydrotalcite was prepared using co-precipitation methods, in which the molar ratio of Mg to Al was 3:1. After calcined at 600 °C for 3 h, the Mg–Al hydrotalcite and K₂CO₃ were grinded and mixed according to certain mass ratios, in which some water was added. The mixture was dried at 65 °C, and after that it was calcined at 600 °C for 3 h. Then, this Mg–Al hydrotalcite loaded with potassium carbonate was obtained and used as catalyst in the experiments. Analyses of XRD and SEM characterizations for catalyst showed the metal oxides formed in the process of calcination brought about excellent catalysis effect. In order to achieve the optimal technical reaction condition, five impact factors were also investigated in the experiments, which were mass ratio, molar ratio, reaction temperature, catalyst amount and reaction time. Under the best condition, the biodiesel yield could reach up to 96%.     

Thermal degradation and flame retardancy of flexible polyvinyl chloride containing solid superacid

The objective of the present article was to study the thermal degradation behavior and flame retardancy of flexible polyvinyl chloride (PVC) composites containing TiO₂/SO ^2?₄ solid superacid because of its strong catalytic ability for esterification and dehydration. The TiO₂/SO ^2?₄ solid superacid was synthesized by using precipitation immersion method, and its structure was investigated by X-ray diffraction. As expected, the value of limiting oxygen index for PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was 32.5% and the char yield of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was significantly improved compared to neat PVC in thermogravimetry tests. In addition, the peak heat release rate and smoke production rate of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) decreased by 14% and 42%, respectively, compared with neat PVC. Moreover, the results of cone calorimetry tests and electron micrograph of char residue showed that the char yield of TiO₂/SO ^2?₄ was enhanced, resulting in a strong char layer structure with outstanding fire retardance cone. In conclusion, the results of this work showed that the addition of solid superacid promoted the decomposition and dehydration of PVC, which formed a compact and continuous char layer on the surface of the material. Hence, the study provides a new perspective for producing composites with excellent flame retardancy and smoke suppression properties of PVC.

     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.     

Characterization of the active phase of NiMo/Al2O3 hydrodesulfurization catalysts

The active phase of the NiMo/Al₂O₃ catalyst for hydrodesulfurization reactions has been investigated in this work. Special attention has been focused on the effect of the order of metal impregnation on the formation of the active phase in the reaction. The Mo and Ni oxides and their sulfides on the alumina were investigated by XPS and DRS analyses. The Ni-Mo oxides or precursor of the active phase which are chemically bonded between Mo and Ni were also confirmed from the binding energy shifts of the XPS peaks. The amount of Ni-Mo oxides was determined after the formation of metal oxides during calcination. The Ni-Mo sulfide (active phase) was then induced through sulfidation. It was important that Mo should be located at the tetrahedral sites on the alumina with a high Mo dispersion. These results indicated that there are two important factors in preparing highly efficient Ni-Mo catalysts; one is that Mo should be located at the tetrahedral coordination on Al₂O₃ in high dispersion (Mo/Al₂O₃) and the other is that the Ni species should be supported on MoAl₂O₄ to form Ni-Mo oxides which change into the Ni-Mo sulfide active sites by sulfidation.     

Emission profile of rapeseed methyl ester and its blend in a diesel engine

Fatty acid methyl esters, also known as biodiesel, have been shown to have a great deal of potential as petro-diesel substitutes. Biodiesel comprise a renewable alternative energy source, the development of which would clearly reduce global dependence on petroleum and would also help to reduce air pollution. This paper analyzes the fuel properties of rapeseed biodiesel and its blend with petro-diesel, as well as the emission profiles of a diesel engine on these fuels. Fuels performance studies were conducted in order to acquire comparative data regarding specific fuel consumption and exhaust emissions, including levels of carbon monoxide (CO), carbon dioxide (CO₂), smoke density, and NO_x, in an effort to assess the performance of these biodiesel and blend. The fuel consumption amount of oil operations at high loads was similar or greater than that observed during petro-diesel operation. The use of biodiesel is associated with lower smoke density than would be seen with petro-diesel. However, biodiesel and its blend increased the emission of CO, CO₂, and nitrogen oxides, to a greater degree than was seen with petro-diesel. The above results indicate that rapeseed biodiesel can be partially substituted for petro-diesel under most operating conditions, regarding both performance parameters and exhaust, without any modifications having to be made to the engine.