Phototransformation of 2,4,6-trinitrotoluene: sensitized by riboflavin under different irradiation spectral range

Riboflavin-sensitized phototransformation of 2,4,6-trinitrotoluene (TNT) under natural sunlight was investigated with reverse-phase high performance liquid chromatography/mass spectrometry (HPLC/MS) and gas chromatography/mass spectrometry (GC/MS). The effect of different spectral region of sunlight on TNT phototransformation in the absence or presence of riboflavin was also investigated by using optical filters with cut-off at 400 or 455 nm. The concentration of riboflavin in the phototransformation of TNT was optimized. Concentration of riboflavin and TNT was 1.0 and 50 microM, respectively. The rates of phototransformation of TNT under natural sunlight in the presence or absence of riboflavin were conformed to initial pseudo-first-order rate equation. The photolysis half life of TNT in the presence of riboflavin was 21.87 min, compared to 39 min in the absence of riboflavin under natural sunlight. Two major phototransformation products of TNT, 3,5-dinitroaniline (3,5-DNA) and 1,3,5-trinitrobenzene (1,3,5-TNB), were detected in the samples in the presence of riboflavin receiving irradiation at full wavelength or wavelength >400 nm. The results indicate that riboflavin mediates TNT sensitized-phototransfomation under natural sunlight or near-UV-vis light.     

Statistical factor-screening and optimization in slurry phase bioremediation of 2,4,6-trinitrotoluene contaminated soil

Since slurry phase bioremediation is a promising treatment for recalcitrant compounds such as 2,4,6-trinitrotoluene (TNT), a statistical study was conducted for the first time to optimize TNT removal (TR) in slurry phase. Fractional factorial design method, 2(IV)(7-3), was firstly adopted and four out of the seven examined factors were screened as effective. Subsequently, central composite design and response surface methodology were employed to model and optimize TR within 15 days. A quadratic model (R(2) = 0.9415) was obtained, by which the optimal values of 6.25 g/L glucose, 4.92 g/L Tween 80, 20.23% (w/v) slurry concentration and 5.75% (v/v) inoculum size were estimated. Validation experiments at optimal factor levels resulted in 95.2% TR, showing a good agreement with model prediction of 96.1%. Additionally, the effect of aeration rate (0-4 vvm) on TR was investigated in a 1-liter bioreactor. Maximum TR of 95% was achieved at 3 vvm within 9 days, while reaching the same removal level in flasks needed 15 days. This reveals that improved oxygen supply in bioreactor significantly reduces bioremediation time in comparison with shake flasks.     

Electrochemical destruction of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process

Mineralization of dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid was conducted by in situ electrogenerated hydrogen peroxide. The electrolytic experiments were carried out to elucidate the influence of various operating parameters on the performance of mineralization of total organic compounds (TOC) in spent acid, including electrode potential, reaction temperature, oxygen dosage and concentration of sulfuric acid. It is worth noting that organic compounds could be completely mineralized by hydrogen peroxide obtained from cathodic reduction of oxygen, which was mainly supplied by anodic oxidation of water. Based on the spectra identified by gas chromatograph/mass spectrometer (GC/MS), it is proposed that oxidative degradation of 2,4-DNT and/or 2,6-DNT, 2,4,6-TNT results in o-mononitrotoluene (MNT) and 1,3,5-trinitrobenzene, respectively. Due to the removal of TOC and some amount of water, the electrolytic method established is promising for industrial application to regeneration of spent acid from toluene nitration process.     

Reductive transformation of 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, and nitroglycerin by pyrite and magnetite

Reductive transformation of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and nitroglycerin (NG) by pyrite (FeS(2)) and magnetite (Fe(3)O(4)) was investigated to determine the role of Fe(II)-bearing minerals on the fate of toxic explosives in Fe/S-rich natural environment. Results from batch experiments showed that 65% of TNT and 45% of RDX were transformed from solution in the presence of pyrite under pH 7.4 buffered conditions within 32 days. Without a buffered solution, transformation of TNT and RDX decreased. NG was continuously and rapidly transformed by pyrite under both conditions. Complete removal of NG was achieved in 32 days under buffered conditions. NH(4)(+) was identified as a reduction product for RDX and NG in the pyrite-water system. Reductive transformation of RDX and NG by magnetite was slower than that by pyrite. The results suggest that abiotic transformation of the explosives by pyrite and magnetite may be considered when determining the fate of explosives in Fe/S-rich subsurface environments.     

Room-temperature phosphorescence chemosensor and Rayleigh scattering chemodosimeter dual-recognition probe for 2,4,6-trinitrotoluene based on manganese-doped ZnS quantum dots

Rayleigh scattering (RS) as an interference factor to detection sensitivity in ordinary fluorescence spectrometry is always avoided in spite of considerable efforts toward the development of RS-based resonance Rayleigh scattering (RRS) and hyper-Rayleigh scattering (HRS) techniques. Here, combining advantages of quantum dots (QDs) including chemical modification of functional groups and the installation of recognition receptors at their surfaces with those of phosphorescence such as the avoidance of autofluorescence and scattering light, l-cys-capped Mn-doped ZnS QDs have been synthesized and used for room-temperature phosphorescence (RTP) to sense and for RS chemodosimetry to image ultratrace 2,4,6-trinitrotoluene (TNT) in water. The l-cys-capped Mn-doped ZnS QDs interdots aggregate with TNT species induced by the formation of Meisenheimer complexes (MHCs) through acid-base pairing interaction between l-cys and TNT, hydrogen bonding, and electrostatic interaction between l-cys intermolecules. Although the resultant MHCs may quench the fluorescence at 430 nm, interdots aggregation can greatly influence the light scattering property of the aqueous QDs system, and therefore, dominant RS enhancement at defect-related emission wavelength was observed under the excitation of violet light of Mn-doped ZnS QDs, which was applied in chemodosimetry to image TNT in water. Meanwhile, Mn-doped ZnS QDs also exhibited a highly selective response to the quenching of the (4)T(1)-(6)A(1) transition emission (RTP) and showed a very good linearity in the range of 0.0025-0.45 μM TNT with detection limit down to 0.8 nM and RSD of 2.3% (n = 5). The proposed methods are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.     

A kinetic model of fracture of simple liquids

The molecular-dynamic (MD) simulation is performed of the processes of generation and growth of cavities in stretched Lennard-Jones liquid. The process of homogeneous generation of cavities in a constant-volume cell is considered. The averaging of the lifetime of the homogeneous phase over the ensemble of MD trajectories is used to determine the nucleation rate as a function of pressure and temperature. The resultant correlation is compared with the classical theory of homogeneous nucleation. The initial stage of growth of spherical cavity is simulated, and the dependence of the rate of growth on pressure is determined along two isotherms. A kinetic model is suggested of fracture of liquid upon stretching at a constant rate. This model relates the volume of pores at an arbitrary instant of time to the kinetic characteristics of their generation and growth determined in MD models for single isolated cavities. The spallation strength of liquid, calculated using this kinetic model and MD data, only slightly depends on the rate of stretching. The calculation results agree well with the experimentally obtained dependence of spallation strength of hexane on the rate of stretching.     

A facile aqueous-phase route for the synthesis of silver nanoplates

A new seed-mediated method for the synthesis of silver nanoplates is reported, in which tannin (C₇₆H₅₂O₄₆) is used to reduce silver salt in aqueous solution. This synthesis is performed at room temperature, and doesn't need any surfactant or polymer to direct the anisotropic growth. The obtained nanoplates exhibit polygonal morphologies and their size can be tuned through adjusting the amounts of seeds. Due to the anisotropic shape feature, the absorption spectra of the nanoplates prove to be quite different from that of spherical nanoparticles.     

A kinetic energy model of two-vehicle crash injury severity

An important part of any model of vehicle crashes is the development of a procedure to estimate crash injury severity. After reviewing existing models of crash severity, this paper outlines the development of a modelling approach aimed at measuring the injury severity of people in two-vehicle road crashes. This model can be incorporated into a discrete event traffic simulation model, using simulation model outputs as its input. The model can then serve as an integral part of a simulation model estimating the crash potential of components of the traffic system. The model is developed using Newtonian Mechanics and Generalised Linear Regression. The factors contributing to the speed change (ΔV_s) of a subject vehicle are identified using the law of conservation of momentum. A Log-Gamma regression model is fitted to measure speed change (ΔV_s) of the subject vehicle based on the identified crash characteristics. The kinetic energy applied to the subject vehicle is calculated by the model, which in turn uses a Log-Gamma Regression Model to estimate the Injury Severity Score of the crash from the calculated kinetic energy, crash impact type, presence of airbag and/or seat belt and occupant age.     

A novel surface plasmon resonance immunosensor for 2,4,6-trinitrotoluene (TNT) based on indirect competitive immunoreaction: a promising approach for on-site landmine detection

A surface plasmon resonance (SPR) immunosensor for the determination of 2,4,6-trinitrotoluene (TNT) has been developed based on the principle of indirect competitive immunoreaction. 2,4,6-trinitrophenol-bovine serum albumin (TNP-BSA) conjugate was immobilized onto a SPR gold chip by means of simple physical adsorption. Binding of anti-TNP antibody with TNP-BSA conjugate was detected based on an increase in resonance angle due to antigen-antibody interaction. Preincubation of anti-TNP antibody with TNT suppresses its interaction with immobilized TNP-BSA conjugate, which leads to a decrease in resonance angle shift. Following the dependence of the resonance angle shift, concentration of TNT was detected. Pepsin solution was used for the regeneration of the sensing surface. The response time for TNT measurement is about 22 min. The immunosensor showed excellent sensitivity to TNT in a wide concentration range from 60 ppt to 1000 ppb with good selectivity, stability, and reproducibility. The proposed system is promising for future application for the on-site detection of landmines.     

Early events in 2,4,6-trinitrotoluene (TNT) degradation by porphyrins: binding of TNT to porphyrin by hydrophobic and hydrogen bonds

The interaction of meso-tri(4-sulfonatophenyl)mono(4-carboxyphenyl) porphyrin (C1TPP) with 2,4,6-trinitrotoluene (TNT) has been explored by UV-vis and fluorescence spectroscopy. The influence of temperature on the interaction has also been studied. C1TPP binds to TNT at pH 7.0 at room temperature via 1.94 kcal/mole hydrogen bonds with absorbance loss at 412-413 nm and the appearance of a new peak at 422-424 nm. The hydrogen binding of TNT to C1TPP was confirmed by the dissolution of the complex upon the addition of urea. Increasing the temperature results in the appearance of a new absorbance peak at 540 nm and absorbance loss at 515 nm with activation energy of 29.7 kcal/mole in the range of the hydrophobic bond energy. This suggests the hydrophobic bonding of TNT with the pyrrole nitrogens in the porphyrin. Increasing the concentration of the TNT in the solution quenches the fluorescence of the porphyrin following the Stern-Volmer equation. The association constants calculated from absorbance and fluorescence are expectedly similar.     

Turn-on and near-infrared fluorescent sensing for 2,4,6-trinitrotoluene based on hybrid (gold nanorod)-(quantum dots) assembly

In this study, we design a FRET system consisting of gold nanorod (AuNR) and quantum dots (QDs) for turn-on fluorescent sensing of 2,4,6-trinitrotoluene (TNT) in near-infrared region. The amine-terminated AuNR and carboxyl-terminated QDs first form a compact hybrid assembly through amine-carboxyl attractive interaction, which leads to a high-efficiency (>92%) FRET from QDs to AuNRs and an almost complete emission quenching. Next, added TNT molecules break the preformed assembly because they can replace the QDs around AuNRs, based on the specific reaction of forming Meisenheimer complexes between TNT and primary amines. Thus, the FRET is switched off, and a more than 10 times fluorescent enhancement is obtained. The fluorescence turn-on is immediate, and the limit of detection for TNT is as low as 0.1 nM. Importantly, TNT can be well distinguished from its analogues due to their electron deficiency difference. The developed method is successfully applied to TNT sensing in real environmental samples.     

A kinetic model for radio frequency plasma-activated chemical vapour deposition

A kinetic model for r.f. plasma-activated chemical vapour deposition is proposed. With this model we are able to explain the deposition profiles of silicon nitride films obtained from a gaseous mixture of SiH₄ and N₂. The plasma reactor is modelled in three zones: a central zone with electron impact dissociation, diffusion and convection and two lateral zones with only diffusion and convection. The mass transfer equation is solved for the case of convective diffusion (Péclet numbers from 0 to 2). The axial concentration of the activated species in the gas phase is correlated with the deposition profile. The model explains why the deposition profile is influenced by the r.f. power and the gas flow rate. The agreement between calculation and the Si₃N₄ mass profile is good for the deposition range investigated.     

A hydriding kinetic model of the Mg2Ni-H2 system

The hydriding kinetics of an Mg₂Ni alloy are investigated under hydrogen pressures from 2.5 to 8 bar (0.25 to 0.8 MPa) at various temperatures (543 ?T ? 583 K). The hydriding reaction of Mg₂Ni progresses by a nucleation and growth mechanism. The rate-controlling step is analysed to be the forced flow of hydrogen molecules through pores, interparticle channels or cracks of the sample, involving heat-transfer control.     

A novel aqueous-phase route to synthesize hydrophobic CaCO3 particles in situ

Hydrophobic CaCO₃ particles were prepared in situ by carbonation of Ca(OH)₂ slurry in the presence of the ethanol solution of oleic acid by mimicking the process of biomineralization. The weight ratio of oleic acid to CaCO₃ changed from 0.3 to 3 wt.%. By changing the weight ratio of oleic acid to CaCO₃, the surface property of CaCO₃ particles was changed from hydrophilic to hydrophobic. Floating test and contact angle analysis of the obtained product indicated that the final CaCO₃ obtained was hydrophobic. From the floating test, the active ratio of the modified CaCO₃ might reach 100%. The contact angle of the modified CaCO₃ was 108.77. IR spectrums of the CaCO₃ particles showed the appearance of the alkyl groups from the oleic acid. We have succeeded in surface modification of CaCO₃ with the hydrophobic oleic acid.     

阳极连接中碱金属双离子迁移模型

在假设玻璃中仅有两种可动碱金属离子的情况下，提出了一个金属—玻璃电场辅助阳极连接模型。根据该模型，玻璃中Na和K耗尽层厚度在演化过程中成比例，它们的演化规律决定于耗尽层迫上的负电荷层。数据拟合结果表明，文献^[4]报道中的Na和K耗尽层厚度与连接时间的关系可用时间的对数函数很好地描述。K富集层起因于K^ 离子的中和，Na耗尽层边上的负电荷产生的电场引起了实验中测得K^ 离子跃迁激活能与Na^ 离子的激活能几乎相等。阳极连接过程中不存在稳态，总可观测到微小电流，该电流仍源于离子电导。