Synthesis of Fluorescent Tremella-like Carbon Nanosheets and Their Application for Sensing of 2,4,6-trinitrophenol

Abstract

Fluorescent tremella-like carbon nanosheets (TCNs) were hydrothermally synthesized using citric acid and adenosine as the starting materials. The resulting product had high quantum yield, water-solubility, and photostability. The addition of 2,4,6-trinitrophenol (TNP) induces remarkable fluorescence quenching, and this phenomenon was used to construct a TNP fluorescence sensor. The fluorescence quenching of TCNs by TNP was shown to be likely due to the inner filter effect. The developed sensor has a wide linear range from 0.05 to 50.0?μM with a detection limit of 5?nM. The TCN-based sensor was used for the determination of TNP in lake water with satisfactory recoveries from 98% to 103%.     

Effect of chloride ions on the kinetics of nitrobenzene reduction by powdered iron

The effect of different chloride ions concentrations on the reactivity of iron particles was studied using chronopotentiometry. It was found that the increase of Cl⁻ ions concentration accelerated anodic dissolution of iron, thus enhancing its surface reactivity. This fact was confirmed also by the rate of nitrobenzene reduction by iron particles. The reactivity of powder particles of various sizes, hence of different specific surface, was investigated in chloride-free and chloride-containing acetate buffer electrolytes. Experimental results indicated that the rate of nitrobenzene reduction in the presence of chloride ions in the reaction system is faster in comparison with the rate in chloride-free medium for each studied grain fraction of particulate material.     

Influence of DSC Measurement Conditions on Kinetic Parameters of Thermal Decomposition of 2,4,6-trinitrotoluene

An autocatalytic model involving the limited solubility of volatile catalytic products was applied to the thermal decomposition of 2,4,6-trinitrotoluene. The critical supersaturation of the thermal decomposition products with the catalytic properties was higher at a low heating rate. Decrease of the sample mass led to an increased critical supersaturation of the decomposition products. This is probably a result of the greater contribution of products adsorption on the aluminium pan surface. It is presumed that the differences observed in the rate constant are connected with the uncontrolled critical supersaturation of the volatile thermal decomposition products. This revised version was published online in August 2006 with corrections to the Cover Date.     

甲烷在金属铁及氧化铁表面还原NO的研究

在程序控温电加热水平陶瓷管反应器、N₂气氛和模拟烟气气氛及300~1 100℃时,对甲烷在金属铁及其氧化铁表面还原NO的特性进行了实验研究。为使甲烷在脱硝反应后完全燃尽以及脱硝反应过程生成的CO等中间产物完全燃尽,在第一段加热炉后串联了第二段加热炉,补充氧气,实现燃尽。结果表明,甲烷在金属铁及氧化铁表面能够高效地还原NO。在N₂气氛中,在900℃以上温度范围内甲烷在金属铁表面的脱硝效率超过95%,与甲烷在氧化铁表面的脱硝效率差别很小。在模拟烟气条件下,当过量空气系数小于1.0时,在900℃以上时,甲烷在金属铁和氧化铁表面的脱硝效率都能超过90%,且未燃尽和燃尽两种条件下NO的还原率相差不大。NO同时通过金属铁的直接还原和甲烷的再燃还原两种反应机理脱除。而甲烷则通过还原氧化铁为金属铁,从而使金属铁直接还原NO可持续进行。同时,甲烷再燃反应的中间产物HCN/NH₃等被氧化铁还原,从而使燃尽后的脱硝效率不下降。研究结果表明,甲烷和金属铁或氧化铁在富燃料条件下可有效地还原NO。     

丙烷在金属铁表面还原NO的实验研究

在程序控温电加热水平陶瓷管反应器、N2气氛和模拟烟气气氛以及300~1 100℃时,对丙烷在金属铁表面还原NO的特性进行了实验研究,并且与相同条件下甲烷在金属铁表面脱硝的效率进行了对比。结果表明,丙烷在金属铁表面能够高效地还原NO。N2气氛中在500~900℃,丙烷在金属铁表面的脱硝效率高于相同含量的甲烷脱硝效率,900℃以上丙烷在金属铁表面的脱硝效率超过95%,并且与甲烷的脱硝效率差别很小。模拟烟气条件下,当过量空气系数SR1小于1.0时,温度超过900℃后丙烷在金属铁表面还原NO的效率能够达到90%以上,且有、无燃尽的情况下,NO的还原率相差不大。在相同的条件下,丙烷在金属铁表面的脱硝效率高于相同条件下甲烷的脱硝效率。SO2对丙烷在金属铁表面还原NO的效率影响很小,可以忽略。     

乙烷在金属铁表面还原NO的实验研究

温度300~1 100 ℃时,由程序控温电加热水平陶瓷管反应器在N₂气氛和模拟气氛下,对乙烷在金属铁表面还原NO的特性进行了实验研究。结果表明,乙烷在金属铁表面能够高效地还原NO。在N₂气氛中,温度高于900 ℃时,乙烷在金属铁表面的脱硝效率超过95%。在模拟烟气条件下,当温度超过900 ℃,且过量空气系数小于1.0时,乙烷在金属铁表面还原NO的效率能够达到90%以上。相同条件下,乙烷在金属铁表面脱硝效率高于甲烷的脱硝效率。SO₂对乙烷在金属铁表面还原NO的效率影响可以忽略。对反应后的铁样品的组分进行了XRD表征,在此基础上对反应机理进行了分析。结果表明,在模拟烟气条件下NO的还原通过乙烷的再燃脱硝和金属铁直接还原两个机理完成。金属铁直接还原NO时生成的氧化铁则被乙烷还原为金属铁,从而使得金属铁能够持续对NO进行直接还原。乙烷再燃还原NO的中间产物HCN被氧化铁氧化为N₂,同时氧化铁也被HCN还原为金属铁。这一过程增强了NO的持续还原反应,同时避免了在燃尽时HCN二次氧化重新生成NO,从而保证了较高的NO还原效率。     

Evolution of surface chemistry during sintering of water-atomized iron and low-alloyed steel powder

Water-atomized iron and steel powder is commonly used as the base material for powder metallurgy (PM) of ferrous components. The powder surface chemistry is characterized by a thin surface oxide layer and more thermodynamically stable oxide particulates whose extent, distribution, and composition change during the sintering cycle due to a complex set of oxidation–reduction reactions. In this study, the surface chemistry of iron and steel powder was investigated by combined surface and thermal analysis. The progressive reduction of oxides was studied using model sintering cycles in hydrogen atmospheres in a thermogravimetric (TG) setup, with experiments ended at intermediate steps (500–1300°C) of the heating stage. The surface chemistry of the samples was then investigated by means of X-ray photoelectron spectroscopy (XPS) to reveal changes that occurred during heating. The results show that reduction of the surface oxide layer occurs at relatively lower temperature for the steel powder, attributed to an influence of chromium, which is supported by a strong increase in Cr content immediately after oxide layer reduction. The reduction of the stable oxide particulates was shifted to higher temperatures, reflecting their higher thermodynamic stability. A complementary vacuum annealing treatment at 800°C was performed in a furnace directly connected to the XPS instrument allowing for sample transfer in vacuum. The results showed that Fe oxides were completely reduced, with segregation and growth of Cr and Mn oxides on the particle surfaces. This underlines the sequential reduction of oxides during sintering that reflects the thermodynamic stability and availability of oxide-forming elements.     

The effect of calcination on morphology of phosphate coating and microstructure of sintered iron phosphated powder

Carbonyl iron powder was coated with phosphate layer using phosphating precipitation method. The phosphated powder was dried at 60 °C for 2 h in air and heat treated by calcination at 400 and 800 °C for 3 h in air. Cylindrical specimens density of ~6.5 g.cm^?3 based on iron phosphated powder calcined at 400 °C were sintered at 820, 900, 1110 °C in N₂ + 10%H₂ atmosphere and 1240 °C in vacuum for 30 min. The morphology and phase composition of the phosphate coating and sintered compacts were studied by scanning electron microscopy, atomic force microscopy (AFM) and X‐ray diffraction (XRD) analysis. Gelatinous morphology of dried phosphate coating (thickness of ~100 nm) containing nanoparticles of iron oxyhydroxides and hydrated iron phosphate was observed. From XRD, diffractogram indicated the presence of goethite α‐FeOOH, lepidocrocite γ‐FeOOH and ludlamite Fe₃(PO₄)₂.4H₂O. The calcined phosphate coating (thickness of ~ 400 nm) contained non‐homogeneous consistency of α‐Fe₂O₃ layer on iron particles, an inter‐layer of amorphous FePO₄ and Fe₃O₄ top layer. The transformation to crystalline FePO₄ structure occurred during calcination at 800 °C with the presence of α‐Fe₂O₃ forming a light top zone (rough morphology). The microstructure of compacts sintered in solid state at temperatures up to 900 °C has retained composite network character. A fundamental change in microstructure due to the liquid phase sintering occurred after sintering at temperatures of 1100 and 1240 °C. It was confirmed that the microstructure complex consists of spheroidized α‐Fe and α‐Fe₂O₃ phases surrounded by solidified liquid phase consisting various phosphate compounds. Copyright © 2013 John Wiley & Sons, Ltd.     

水蒸气对甲烷在金属铁表面还原NO行为的影响

采用程序控温电加热水平陶瓷管反应器,在N2气氛和模拟烟气气氛中、300~1100℃下,研究了水蒸气对甲烷在金属铁表面还原NO行为的影响,并对反应前、后铁样品进行了X光衍射(XRD)、扫描电子显微镜(SEM)及X光电子能谱(XPS)等表征。结果表明,水蒸气对甲烷在金属铁表面还原NO行为的影响较小。在N2气氛中,水蒸气参与了金属铁的氧化;与无水蒸气时相比,水蒸气存在时NO还原效率有所下降。当水蒸气含量从2.5%增加到7%时,由于水蒸气对金属铁的氧化导致其表面形成疏松的微观孔隙,使得NO的还原效率随水蒸气含量的增加而提高。甲烷则参与了铁氧化物的还原,使铁样品表面形成相对致密的Fe3O4和FeO氧化层,不利于NO与金属铁的接触,使得NO的还原效率低于无甲烷时的结果。在模拟烟气条件下,水蒸气使得甲烷在金属铁表面还原NO的效率增加;在1050℃下,反应段过量空气系数SR1=0.7和燃尽段过量空气系数SR2=1.2时,含7%的H2O和无H2O条件下脱硝效率分别为96.7%和90.6%。而在湿烟气中SO2使NO还原效率略有下降。持久性脱硝实验结果表明,当反应温度为1050℃时,在含7%的H2O、0.02%的SO2的模拟烟气中,1.14%的甲烷在金属铁表面持续50h都能保持90%以上的脱硝效率。     

甲烷在氧化铁表面还原NO的特性与反应机理研究

在程序控温电加热水平陶瓷管反应器中,在300~1 050 ℃,对N₂气氛中甲烷在氧化铁(充分氧化后的铁丝网卷)表面还原NO的特性进行了实验研究,测试了NO脱除效率、CO生成量以及反应后铁样品表面组分和微观状态的变化特点,分析了甲烷在氧化铁表面还原NO的反应机理。在此基础上,在1 000 ℃时,对模拟烟气条件下甲烷在氧化铁表面还原NO的持久性进行了实验研究。结果表明,甲烷在氧化铁表面能够高效地还原NO。在N₂气氛下,在850 ℃以上达到100%的NO脱除效率。在模拟烟气中,甲烷在氧化铁表面脱除NO的能力具有很好的持久性。实验结果表明,在1 000 ℃时,采用由体积分数为2.0%的O₂、16.8%的 CO₂和524×10^-6的 NO,N₂配平的模拟烟气,1.17% CH₄能够在连续100 h内保持100%的NO脱除效率,而未出现下降的趋势。对反应机理的研究结果表明,甲烷在氧化铁表面还原NO的机理包括甲烷通过再燃机理还原NO以及甲烷通过在氧化铁表面还原氧化铁为金属铁、金属铁进而直接还原NO两种主要反应机理。其中,后者为主要反应机理。     

Spectroscopic and thermal studies on the decomposition of l,3,5-triamino-2,4,6-trinitrobenzene (TATB)

The kinetics of the thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in condensed state has been investigated by high temperature infrared spectroscopy (IR) and thermogravimetry (TG) in conjunction with pyrolysis gas analysis, differential thermal analysis (DTA) and hot stage microscopy. The decomposition proceeds in two main stages under isothermal conditions and the initial stage involving about 24% loss in weight obeys Avrami-Erofe'ev equation (n= 1), and is governed by an activation energy (E) of 150.58 kJ·mol^–1 and log(A in s^–1) 12.06. The second stage corresponding to 24 to 90% loss in weight gave best fit for Avrami-Erofe'ev equation,n=2, withE=239.56 kJ·mol^–1 and log(A in s^–1) 19.88 by isothermal TG. The effect of additives, on the initial thermolysis of TATB has also been studied. Evolved gas analysis by IR showed that NH₃, CO₂, NO₂, HCN and H₂O are produced in the initial stage of decomposition. The decomposition in KBr matrix in the temperature range 272 to 311.5°C shows relative preferential loss in the -NH₂ to -NO₂ band intensity which indicates that the rupture of C-NH₂ bond, weakened also by the interaction of the NH₂ with the neighbouring NO₂ group, appears to be the primary step in the thermolysis of TATB.     

Thermal investigations of direct iron ore reduction with coal

In this paper, fundamental mechanisms for iron ore reduction in coal–ore mixtures have been investigated using several advanced experimental techniques. Firstly, the thermal properties of coal–ore mixtures were studied and apparent specific heat of coal–ore mixtures against temperature was obtained at a heating rate of 10 °C/min. Several exothermic and endothermic peaks were observed which were related to the decomposition reactions and reduction. The flue gases from the mixture were analysed using a mass spectrometer. Secondly, the X-ray diffraction (XRD) and the iron phase analytical techniques were applied to identify the iron phase changes with the temperature. It has been found that coal devolatilisation and iron oxides reduction occur simultaneously during the heating of the mixture. H₂ and CO gases produced from coal devolatilisation and char gasification were responsible for the reduction of iron oxides at these temperatures. Iron oxides undergo step-wise reduction over the whole process. The results in this work provide a fundamental understanding for the direct reduced ironmaking processes.     

SO_2对甲烷在金属铁表面还原NO的反应影响

采用卧式程序控温电加热陶瓷管反应器,在N2和模拟烟气气氛中、300~1 100℃下,研究了SO2对甲烷在金属铁及其氧化物表面还原NO反应的影响。采用XRD等手段对反应前后铁催化剂样品的组成变化进行了表征,分析了SO2在甲烷-铁脱硝反应中的作用机理。结果表明,甲烷在金属铁及氧化铁表面能够高效率地还原NO,NO还原效率不受烟气中SO2的影响。在SO2体积分数为0.01%~0.04%的N2气氛中,温度高于700℃时,金属铁上NO还原率和SO2脱除率可同时达到100%。在SO2体积分数为0.01%~0.04%的模拟烟气中,当温度高于850℃时,NO还原效率达到90%以上;温度为950℃时,NO还原效率达到98%,SO2对NO还原效率的影响可忽略。当反应温度为1 000℃时,在含0.02%SO2的模拟烟气中,甲烷的体积分数为1.13%时,持续100 h金属铁表面上的NO还原效率都能保持95%以上。     

纳米铜粉氧化反应动力学研究

以五水硫酸铜为原料,以Vc为还原剂,以EDTA为络合剂,聚乙烯吡咯烷酮(PVP)为保护剂和分散剂,采用液相还原法制备了纳米铜粉.不同粒度的纳米铜粉在空气中放置1 h,再用XRD进行分析;对纳米铜粉氧化成氧化亚铜的反应进行了动力学分析;对纳米铜粉进行了TEM分析.结果表明:纳米铜粉的平均粒度大于75 nm时,常温条件下在空气中不易被氧化;平均粒度为75 nm铜粉120℃开始起氧化反应,粒度越大氧化反应起始温度和差热曲线的峰值温度越高;纳米铜粉氧化反应的活化能很低,平均粒度为75nm铜粉氧化成氧化亚铜的反应活化能在1~2 kJ.mol-1之间;纳米铜粉的熔点低,在TEM检测电子束照射下很快熔融长大.     

Nondestructive in‐depth composition profile of oxy‐hydroxide nanolayers on iron surfaces from ARXPS measurement

In this work the maximum entropy method (MEM) is applied, for the first time, to angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data from oxy‐hydroxide films on iron surfaces. This nondestructively derives information on the in‐depth distribution of the composition and chemical state. An MEM algorithm was created and first tested on the simulated data. The reconstructed composition depth profiles agreed very well with the theoretical ones up to 5% Gaussian noise added to the data. The same algorithm was then applied to ARXPS data from iron samples to investigate the in‐depth variations in the composition and chemical state of the nanosized oxy‐hydroxide film naturally grown on the iron surface. The resulting surface film presents a complex multilayer structure with concentration gradients. The effect of air exposure on the structure was also investigated. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of calcination temperature on structure and characteristics of calcium oxide powder derived from marine shell waste

Marine fishery wastes such as bivalve shells, crab shells and cuttlebone are rich in calcium. Calcium carbonate derived from these materials can be transformed into calcium oxide by calcination, which is used in a wide variety of applications (e.g., biomaterials for bone and teeth implants and drugs). In this study we analyze the effects of calcination temperatures (550 °C, 700 °C and 900 °C) on characteristics and elemental composition of calcium oxide derived from shells of four marine species collected in Thailand: oyster (Saccostrea cucullata), green mussel (Perna viridis), blue swimming crab (Portunus pelagicus), and cuttlefish (Sepia brevimana). The XRD patterns indicated the complete transformation of calcium carbonate into calcium oxide, observed by the changes of diffraction angles at 900 °C for all calcined samples, except cuttlebone, which was calcined successfully at 700 °C. Likewise, the FT-IR results revealed changes of functional groups at the same calcination temperatures. In addition, ICP-OES showed the effects of calcination temperature on elemental contents: major elements (Ca, P and K) increased in all samples, and some minor elements increased in blue swimming crab shell (Zn and Cu) and oyster shell (Fe) as a result of increasing the calcination temperature. This study demonstrates the optimum calcination temperature of calcium oxide production from four types of marine wastes that might be benefit for the chemical compound production industry.     

Hexafluoro-2-propanol-assisted quick and chemoselective nitro reduction using iron powder as catalyst under mild conditions

Hexafluoro-2-propanol as the promoter for the quick nitro reduction using a combination of iron powder and 2 N HCl aqueous solution is reported. This methodology has several positive features, as it is of room temperature, remarkably short reaction time. A wide range of substrates including those bearing reducible functional groups such as aldehyde, ketone, acid, ester, amide, nitrile, halogens, even allyl, propargyl and heterocycles are chemoselectively reduced in good to excellent yields, even on gram scale. Notably, the highly selective reduction of 3-nitrophenylboronic acid is achieved quantitatively. The reduction is also tolerant of common protecting groups, and aliphatic nitro compound, 1-nitrooctane can be reduced successfully.     

Kinetics and mechanism of oxidation of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) by vanadium(V), periodate and iodate ions in acetate buffers

The kinetics of oxidation of bis(2,4,6-tripyridyl 1,3,5-s-triazine)iron(II) by vanadium(V), periodate and iodate has been studied in acetate buffers by stopped-flow and spectrophotometric methods. The oxidation reaction of bis(2,4,6-tripyridyl 1,3,5-s-triazine)iron(II) by vanadium(V), periodate and iodate follows first order kinetics for the substrate and oxidant. Hydrogen ion has no significant effect on the rate. A generalized mechanism was proposed for these reactions and these reactions follow the rate law: Rate = k [oxidant] [Fe(tptz)₂ ²⁺].     

Non-isothermal degradation of a thermoset powder coating in inert and oxidant atmospheres

This paper studies the thermal stability of an epoxy powder coating. The study was carried out in a thermobalance at various heating rates and in different atmospheres: nitrogen, air and oxygen. Degradation in air and oxygen leads to a kinetic process which is clearly different from degradation in an inert atmosphere. To characterise each process, the DTG signal peaks were separated and kinetic parameters were associated to each by means of the isoconversional method and other standard methods. The results obtained were compared with the experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.