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Green Synthesis of Nano Silver on TiO2 Catalyst for Application in Oxidation of Thiophene
摘要： The present research work describes the preparation of silver nanoparticles from silver nitrate, and Tulsi (Ocimum tenuiflorum) leaf extract, impregnation on titanium dioxide (TiO2) and evaluation of the catalytic activity of this nano silver impregnated TiO2 in the oxidation reaction of thiophene. Tertiary-butyl hydroperoxide was used as an oxidant in the reaction. The catalyst was characterized by BET, SEM, XRF, TEM, UV-Vis spectroscopy, XPS and TPR. The effect of process parameters such as speed of agitation, catalyst weight, oxidant to sulfur mole ratio, silver loading in the catalyst and temperature on the oxidation reaction was studied. Both pseudo-homogeneous and heterogeneous kinetic models were considered and applied for the result. The pseudo-homogeneous form of rate equation shows the reaction follows second order kinetics and is endothermic. Langmuir-Hinshelwood kinetic model is proposed, considering the reaction as a heterogeneous one with solid catalyst and found that surface reaction is the rate controlling step. This model is well fitted with experimental data.
关键词： Kinetic model,Tulsi leaf extract,Thiophene,Catalytic oxidation,Titanium dioxide,Silver nanoparticles
更新于2025-09-19 17:15:36
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Synergistic removal of ammonium by monochloramine photolysis
摘要： The presence of ammonium (NH4+) in drinking water treatment results in inhibition of disinfection efficiency and formation of nitrogenous disinfection by-products. Our previous study found monochloramine (NH2Cl) photolysis under 254 nm UV irradiation can be effective for removal of NH4+; however, the mechanisms of NH4+ degradation in this process were unknown. The kinetics and fundamental radical chemistry responsible for NH4+ removal in the UV/NH2Cl process were investigated in this study. The results showed that the pseudo first-order rate constant for NH4+ degradation in the UV/NH2Cl process ranged between 3.6 × 10?4 to 1.8 × 10?3 s?1. Solution pH affected radical conversion and a higher NH4+ degradation efficiency was achieved under acidic conditions. The effects of chloride were limited; however, the presence of either bicarbonate or natural organic matter scavenged radicals and inhibited NH4+ removal. NH2Cl photolysis generated an aminyl radical (NH2?) that further transformed to a chlorine dimer (Cl2??) and a hydroxyl radical (HO?). The second-order rate constants for Cl?, Cl2??, and HO? reacting with NH4+ were estimated as 2.59 × 108 M?1s?1, 3.45 × 105 M?1s?1, and 1.4 × 107 M?1s?1 at pH 3.9, respectively. Cl?, Cl2??, and HO? contributed 95.2%, 3.5%, and 1.3% to NH4+ removal, respectively, at the condition of 3 mM NH2Cl and pH 7.5. Major products included nitrite and nitrate, possibly accompanied by nitrogen-containing gases. This investigation provides insight into the photochemistry of NH4+ degradation in the UV/NH2Cl process and offers an alternative method for drinking water production.
关键词： Ammonium,Reactive chlorine radicals,UV/NH2Cl process,Kinetic model
更新于2025-09-19 17:15:36
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ZnSe/ZnS Core/shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth
摘要： Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and bio-tagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission linewidth. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on-off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.
关键词： thermodynamic,core/shell QDs,heavy-metal-free,ZnSe/ZnS,kinetic
更新于2025-09-19 17:13:59
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Controlled Growth of CH <sub/>3</sub> NH <sub/>3</sub> PbBr <sub/>3</sub> Perovskite Nanocrystals via a Water–Oil Interfacial Synthesis Method
摘要： Fundamental insights into the reaction kinetics of organic–inorganic lead halide perovskite nanocrystals (LHP NCs) are still limited due to their ultrafast formation rate. Herein, we develop a water–oil interfacial synthesis of MAPbBr3 NCs (MA = CH3NH3+), which prolongs the reaction time to tens of minutes. This method makes it possible to monitor in situ the formation process of MAPbBr3 NCs and observe successive spectral evolutions from 438 to 534 nm in a single reaction by extending reaction time. The implementation of this method depends on reducing the formation rate of PbBr64? octahedra and the diffusion rate of MA. The formation of PbBr64? is a rate-determining step, and the biphasic system offers a favorable reaction condition to control the mass transfer of MA. The effects of temperature and concentration of precursor and ligand are investigated in detail.
关键词： CH3NH3PbBr3,perovskite nanocrystals,interfacial synthesis,kinetic study,formation mechanisms
更新于2025-09-19 17:13:59
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Clinically Colorimetric Diagnostics of Blood Glucose Levels based on Vanadium Oxide Quantum Dots Enzyme Mimics
摘要： The environmental vulnerability of the natural enzyme have always been the most concerned issue in the diagnosis of blood glucose levels, which could be settled by the discovery and application of nanozyme mimics. However, the nanozyme still encountered with the problem of complex preparation process or low enzymatic activities. Herein, peroxidase-like vanadium oxide quantum dots (VOxQDs) were synthesized via a one-step bottom-up solvothermal method using vanadium (Ⅲ) trichloride (VCl3) powder as the precursor. Besides, the most favorable temperature and solvent for VOxQDs synthesis were confirmed. Due to the inherent properties of quantum dots, including larger specific surface areas and more active sites, the as-prepared VOxQDs exhibited 43 times lower value of Km and 32 times higher one of Vmax than those of natural peroxidase using H2O2 as the substrate, indicating the higher affinity and stronger peroxidase-like activity of the VOxQDs nanozymes. Accordingly, a facile and sensitive colorimetric sensor to detect glucose was designed via the integrated enzyme system of VOxQDs and glucose oxidase, which showed wider linear range of 0.005 - 2 mM glucose and lower limit of detection of 1.7 μM compared with those of many other peroxidase-like nanozymes. Especially, the colorimetric sensor was demonstrated with reliable and satisfactory performance in detection of glucose in human serum, which was in good accordance with the clinical results provided from the domestic hospital.
关键词： Peroxidase-like activity,Vanadium oxide quantum dots,Kinetic study,Detection of H2O2 and glucose
更新于2025-09-19 17:13:59
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Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis
摘要： Simulated photo-degradation of fluorescent dissolved organic matter (FDOM) in Lake Baihua (BH) and Lake Hongfeng (HF) was investigated with three-dimensional excitation-emission matrix (3DEEM) fluorescence combined with the fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and multi-order kinetic models. In the FRI analysis, fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM. Four individual components were identified by use of PARAFAC analysis as humic-like components (C1), fulvic-like components (C2), protein-like components (C3) and unidentied components (C4). The maximum 3DEEM fluorescence intensity of PARAFAC components C1eC3 decreased by about 60%, 70% and 90%, respectively after photo-degradation. The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient (Radj2) (0.963e0.998). The photo-degradation rate constants (kn) showed differences of three orders of magnitude, from 1.09(cid:1) 10(cid:3)6 to 4.02 (cid:1) 10(cid:3)4 min(cid:3)1, and half-life of multi-order model (Tn1=2) ranged from 5.26 to 64.01 min. The decreased values of fluorescence index (FI) and biogenic index (BI), the fact that of percent fluorescence response parameter of Region I (PI,n) showed the greatest change ratio, followed by percent fluorescence response parameter of Region II (PII,n), while the largest decrease ratio was found for C3 components, and the lowest Tn1=2 was observed for C3, indicated preferential degradation of protein-like materials/components derived from biological sources during photo-degradation. This research on the degradation of FDOM by 3DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FDOM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.
关键词： Fluorescence regional integration,Parallel factor analysis,Photo-degradation,Fluorescent dissolved organic matter,Multi-order kinetic models,Three-dimensional excitation-emission matrix
更新于2025-09-16 10:30:52
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Nonlinear dynamics of laser-generated ion-plasma gratings: A unified description
摘要： Laser-generated plasma gratings are dynamic optical elements for the manipulation of coherent light at high intensities, beyond the damage threshold of solid-state-based materials. Their formation, evolution, and final collapse require a detailed understanding. In this paper, we present a model to explain the nonlinear dynamics of high-amplitude plasma gratings in the spatially periodic ponderomotive potential generated by two identical counterpropagating lasers. Both fluid and kinetic aspects of the grating dynamics are analyzed. It is shown that the adiabatic electron compression plays a crucial role as the electron pressure may reflect the ions from the grating and induce the grating to break in an X-type manner. A single parameter is found to determine the behavior of the grating and distinguish three fundamentally different regimes for the ion dynamics: completely reflecting, partially reflecting or passing, and crossing. Criteria for saturation and lifetime of the grating as well as the effect of finite ion temperature are presented.
关键词： ponderomotive potential,fluid and kinetic aspects,ion dynamics,adiabatic electron compression,laser-generated ion-plasma gratings,nonlinear dynamics
更新于2025-09-16 10:30:52
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Plasma and Plasmonics || 3 Plasma Kinetic Theory
摘要： In the previous chapter, we have studied the dynamics of single particles in the presence of various kinds of electromagnetic (EM) fields. In this chapter, we will take this to the next level and study the dynamics of a collection of charged particles (also called a plasma) in these field configurations. For single particle motion, all that needs to be studied is the time-evolution of its position and velocity. However, when we have several particles, keeping track of the individual trajectories is very data intensive. So, we do a kind of averaging and for a given position and velocity, we study how many particles have positions and velocities close to these values. And this number keeps changing with time and essentially represents the density in phase space (configuration space is made of only position whereas phase space is made of position and velocity/momentum). This number is popularly called the plasma distribution function and usually denoted by f (x, v, t) or P (x, v, t). In this book, we will stick to f. In the language of probability theory, this quantity is known as the probability density function (PDF). Strictly speaking, f is a function of 7 variables, viz. three position variables, three velocity variables and one time variable. But in this chapter and next, we will only consider the 1D case for simplicity and hence we consider f to be a function of only 3 variables. For a given problem, we sometimes have several different possibilities for the function f and this choice is not always easy to make. However, in any case, the integral of f over x and v must be finite and constant for all time (unless we are studying an open system where number of particles can change with time).
关键词： plasma,kinetic theory,Liouville theorem,electromagnetic fields,Vlasov equation
更新于2025-09-16 10:30:52
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Plasma and Plasmonics || 4 Plasma Fluid Theory
摘要： In the previous chapter, we have studied the plasma kinetic theory and seen how to solve for the plasma distribution function in various configurations of electric field. The 1D plasma distribution function is a function of three independent variables (position, velocity, time) and contains lot of information about the state of the plasma at any given time. However, in many practical situations it is very difficult to solve the Vlasov equation in order to get the distribution function. In order to make life easier, what can be done is to write an equation for the moments of the distribution function (moments as in integrals over velocity) which turn out to be lot simpler to solve. These set of equations are known as the fluid equations since now instead of considering the plasma as being composed of a collection of particles, it is considered to be made of various fluid components (usually one component for each charged particle species). The difference between particles and fluids is very important. Particles are discrete entities which exist at a point in phase space. Fluids on the other hand are spread out over a continuous range of configuration space (or position space) and can have different velocities at different spatial points. So in some sense, a fluid description captures the average of the particle behavior due to which it obviously misses out some of the effects that are seen only in the particle (or discrete or kinetic) picture. One example of such an effect is Landau damping (described in the previous chapter) which cannot be recovered from the collisionless fluid equations. So, for a given problem, it is important to know apriori whether kinetic effects are going to be important in the phenomenon of interest. If kinetic effects are going to be important, it is imperative to solve for the plasma distribution function. However, if kinetic effects can be ignored and only the averaged fluid-like behavior is of interest, then it is sufficient to solve the fluid equations. Here it is important to note that solving the fluid equations is also not a trivial job. Just that it is easier than solving the Vlasov equations in many problems. There are also several problems where solving the fluid equations analytically is also very tedious and recourse must be made to computer simulations. One example of such a problem is turbulence which is considered to be one the toughest challenges in physics.
关键词： plasma,kinetic theory,electromagnetic waves,permittivity,electrostatic waves,conductivity,Vlasov equation,fluid theory
更新于2025-09-16 10:30:52
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Enhancement of oxidation resistance of modified P91 grade ferritic-martensitic steel by surface modification using laser shock peening
摘要： In this paper, effect of laser shock peening (LSP) on high temperature oxidation behavior of P91 steel has been studied. P91 samples were subjected to single and triple LSP treatments at a constant laser power density of 3.9 GW.cm?2. Single and triple LSP treatment led to the formation of ultrafine subgrains of sizes ~300 ± 30 and ~105 ± 10 nm respectively at near surface comparing to unpeened P91 sample (~1200 ± 120 nm). Further, unpeened and LSP treated samples were oxidized at temperatures of 600, 650 and 700 °C for time 5 to 200 h in air. Compare to unpeened sample, single and triple peened samples exhibited two and five fold reduction in weight gain after 200 h of oxidation at highest test temperature (700 °C). Improvement of oxidation resistance in LSP treated samples is attributed to the formation of continuous layer of protective oxides such as (Fe,Cr)2O3, Cr2O3 and MnCr2O4 due to enhanced diffusivity of Cr and Mn from bulk during early stage of oxidation. The enhanced diffusivity Cr and Mn in LSP treated samples have been further supported by reduction in apparent activation energy of oxidation, which is evaluated by modelling the time-temperature dependence of weight gain data in purview of kinetics theory.
关键词： Kinetic energy,Laser shock peening,Oxidation resistance,Diffusivity,P91 steel
更新于2025-09-16 10:30:52