Actinometry Method Research Articles

A novel state-resolved actinometry method to determine the nitrogen atom number density in the ground state and intra-shell excited states in low-pressure electron cyclotron resonance plasmas

The active-particle number density is a key parameter for plasma material processing, space propulsion, and plasma-assisted combustion. The traditional actinometry method focuses on measuring the density of the atoms in the ground state, but there is a lack of an effective optical emission spectroscopy method to measure intra-shell excited-state densities. The latter atoms have chemical selectivity and higher energy, and they can easily change the material morphology as well as the ionization and combustion paths. In this work, we present a novel state-resolved actinometry (SRA) method, supported by a krypton line-ratio method for the electron temperature and density, to measure the number densities of nitrogen atoms in the ground and intra-shell excited states. The SRA method is based on a collisional-radiative model, considering the kinetics of atomic nitrogen and krypton including their excited states. The densities measured by our method are compared with those obtained from a dissociative model in a miniature electron cyclotron resonance (ECR) plasma source. Furthermore, the saturation effect, in which the electron density remains constant due to the microwave propagation in an ECR plasma once the power reaches a certain value, is used to verify the electron density measured by the line-ratio method. An ionization balance model is also presented to examine the measured electron temperature. All the values obtained with the different methods are in good agreement with each other, and hence a set of verified rate coefficient data used in our method can be provided. A novel concept, the ‘excited-state system’, is presented to quickly build an optical diagnostic method based on the analysis of quantum number propensity and selection rules.

Atomic hydrogen production in a cold plasma for application in a metal foil pump

Any good design of fuel cycles for thermonuclear fusion reactors, which operate on deuterium-tritium fusion, comes with minimized tritium inventory. The direct internal recycling concept can significantly reduce the tritium inventory of a fusion power plant by introducing a bypass for most of the unburned fuel from the torus exhaust. It requires a technology that can sharply separate hydrogen isotopes from other gases in the given environment in the reactor's pump duct. The prime candidate for this task is a metal foil pump (MFP) using plasma-driven permeation. A workflow toward a performance predicting modeling tool of a MFP is introduced. It is based on the characterization of the employed cold plasma by using a plasma simulation, which is experimentally validated using optical emission spectroscopy and the actinometry method. The used approach accounts for the radial inhomogeneity of the linearly extended plasma. We determine the atomic hydrogen content down to pressures of 1 Pa and condense the complex processes that contribute to the hydrogen atom production into a single excitation probability. This value can be used in Monte Carlo based modeling approaches to determine the particle exhaust performance of the vacuum pump.

Optimizing UVC-disinfection using LEDs as an energy efficient pre-treatment for biofouling control in spiral-wound membrane systems

Biofouling remains a major challenge for reverse osmosis (RO) systems. Pulsed ultraviolet (UV) pre-treatment has been proposed as a mitigation strategy for biofouling control of RO membranes. This study investigated whether increasing fluence rate during pulsed UV disinfection leads to enhanced inactivation. Further, UV irradiation from 1.5 to 61.3 mJ cm−2 was tested for optimal biofouling control. Therefore, an UVC-LED reactor was characterized by successfully adapting an actinometry method for flow-through mode. The inactivation of microorganisms was compared in flow-through biodosimetry experiments in pulsed and continuous irradiation. Finally, several settings were applied as pre-treatment in lab-scale biofouling experiments and membrane performance and biofilm removability elucidated. Whereas no enhanced inactivation was observed during biodosimetry experiments, pulsed UV disinfection resulted in an average of 20.6 % increased delay of biofilm formation. On the contrary, for pulsed UV disinfection, the biofilm hydraulic resistance seemed higher than continuous equivalents, but not significantly. Overall, savings of operational expenditures per fluence applied was highest around 4 mJ cm−2. UV pre-treated biofilms showed no enhanced removability, but delay in biofilm formation was noticeable in two of three experiments. In case the effects translate to up-scaled applications over several cleanings, UV pre-treatment for biofouling control is an interesting option.

Spectroscopic and electrical characterization of oxygen microwave discharge used for downstream plasma oxidation of Si

Actinometry optical emission spectroscopy (AOES), single cylindrical Langmuir, probe and electrostatic planar probe were used to characterize oxygen microwave plasma, at two distances from the plasma source (Z1 = 15 cm and Z2 = 25 cm), using three values of applied microwave power (800, 1000, and 1400 W) at a constant pressure of 70 Pa, involving different parameters, which are electron density (ne), effective electron temperature (Teff), plasma potential (Vp), floating potential (Vf), positive ion flux (Гi), negative ion ratio (α = n−/ne, n− is the negative ion density), and atomic oxygen density (AO: [O]). The electron density and the effective electron temperature were deduced from (I‐V) Langmuir probe characteristics. The atomic oxygen density was measured using actinometry method. Positive ion flux was evaluated from the positive ion saturation current (Isat) of the planar probe. The combination of both single Langmuir probe and the planar one enabled the calculation of electronegativity of the oxygen plasma. An application of this oxygen plasma is presented, which is the silicon surface oxidation. The formed SiO2 layer has been characterized by both scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis.

A scalable light-diffusing photochemical reactor for continuous processing of photoredox reactions

In the last decade, photoredox catalysis has received a remarkable attention for its unique reactivity for synthesizing fine chemicals and active pharmaceutical ingredients. However, the coupled photon and heat generation of light sources create challenges for achieving a proper heat management of photochemical reactors, thus inhibiting large-scale applications. In this work, we proposed a strategy to decouple photon and heat using light guide plate (LGP) technology, and accordingly designed a continuous light-diffusing photochemical reactor (LDPR). In LDPR, the photons emitted from the edge light source are distributed uniformly on the top surface of LGP where the fluidic channels are located. This configuration isolates heat generation location from where photons are utilized, benefiting the heat management of the reaction zone. The photon flux of LDPR was characterized with a chemical actinometry method. Two important photocatalytic bond-forming reactions, α-amino arylation and C(sp2)–N cross-coupling, were demonstrated in LDPR with high efficiency. To show the scalability of LDPR, we increased the throughput via a hybrid strategy of scaling-up and scaling-out, achieving a continuous 10-gram synthesis of an α-amino arylation product.

Photochemical reactions and surface ozone measurements in Tehran city center

Efforts have been made for surface ozone concentration measurements considering secondary reactions via actinometry. Pyro heliometry, pyranometry and spectrophotometry, idometry in Amir Abad station of Tehran city center in parallel. In actinometry method consideration were made to show solar radiation in all different filters of green, yellow, red and dark red by means of 525 nm, 630 nm, 695 nm and 721 nm in parallel by the same time during 1991–1992. Resulted as solar radiation reduction in all filters and concluded for secondary reactions at Amirabad station for the first time in Iran. Measurements were made daily and seasonally at midday in Amirabad station. Where in idometry and spectrophotometry method consideration were made in certain wavelengths of 276.5 nm and 301 nm, for surface ozone measurements during autumn winter considering, October, November, December 1991–1992 and 1999–2001, using rain samples. Which has shown a concentration range of 30–60 (ppb) and 80–115 (ppb), respectively. The concentration measurements of surface ozone were made as a function of photochemical reactions of NO2. NO and photon rays in agreement with the results of spectrometry method by the same time due to F.M. Shahrtash for the first time in Iran. This study was in agreements with the works in Montreal, Ca (1992). Other consideration was made for surface ozone data collection analysis of (MOI) from Mehrabad station of Tehran city center via Dobson method during summer–autumn 2015. Which has shown a range of concentration of 80–92 (ppb), in comparison with the measurements of Amirabad station. Besides consideration was made for recent research work in China, which has detected the surface ozone concentration of 70–100 ppb during 2013–2018, mainly in North China and Yangtze river plain” by means of “photochemical reactions and surface ozone” in agreement with this study as a whole.

Effect of plasma-species to functionalize isocyanate-groups on multiwalled carbon nanotubes

This article reports our recent investigation of the relationship between the density of the active species in nitrogen-oxygen plasma and the degree of isocyanate (R-NCO) functionalization onto multiwalled carbon nanotubes. We first monitored the plasma active species with optical emission spectroscopy focusing on atomic nitrogen and oxygen species, which are the major components to form NCO groups. The optical emission intensity allowed us to find the density of atomic nitrogen and oxygen in plasma through the plasma optical actinometry method. The actinometry result showed that the density of atomic nitrogen and oxygen becomes as close as the nitrogen content in plasma increased to 90%. We then investigated the functionalization ratio with the fluorescent method and Raman spectroscopy to monitor the degree of NCO functionalization. The results suggested that NCO groups on carbon nanotubes should increase as the content ratio of atomic nitrogen and oxygen becomes equal in the plasma.

Experimental Approach for Efficiency Determination of Photocatalytic Hydrogen Evolution

This paper presents two related experiments aimed at determining the efficiency of photocatalytic hydrogen production on ZnS/CdS nanoparticles. In the first experiment, the method of chemical actinometry is applied to measure the number of light quanta emitted by the UV LEDs used. This utilizes the formation of an iron(II)-1,10-phenanthroline complex (ferroin), the concentration of which can be determined photometrically. In the second experiment, hydrogen is produced on prepared ZnS/CdS with the aid of these LEDs, the yield is determined by collecting the generated volume of hydrogen gas and the efficiency is calculated.

A revised 1D equivalent model for the determination of incident photon flux density in a continuous-flow LED-driven spiral-shaped microreactor using the actinometry method with Reinecke’s salt

Continuous-flow microstructured technologies are now recognized as promising alternatives to batch processing for organic photochemistry, especially when light emitting diodes (LEDs) are employed as light sources. To evaluate and optimize productivity and energetic efficiency, the knowledge of the incident photon flux density is crucial. In this context, the objectives of the present work are dual: first, to transfer the classical actinometry method with Reinecke’s salt to a continuous-flow LED-driven spiral-shaped reactor and second, to propose a revised one-dimensional equivalent model for the accurate determination of the incident photon flux density in this microreactor. Experimental measurements were carried out under controlled conditions. The effects of the spectral domain and radiant power emitted, the tubing length, the presence of gas-liquid Taylor flow, and the material of the support plate were especially investigated. An expression was established for the revised one-dimensional Cartesian model, taking into account the diffuse emission of the LED array and the reflection induced by the material of the plate in which the tubing was inserted (i.e. the reflection by the backside of the microreactor wall). In this way, the incident photon flux density could be estimated with an acceptable level of accuracy, which was not the case if the usual 1D model was applied (collimated emission and no reflection).Graphical abstract

Effect of Gliding Arc Plasma-Induced UV Light During the Photo-Fenton Oxidation of 4-Chlorophenol in Aqueous Solution

4-chlorophenol (4-CP) is recognized as a highly toxic organic which can cause damage effects on human life and the aquatic environment. Since conventional wastewater techniques were unable to remove non-biodegradable chlorophenols, advanced oxidation process was investigated to achieve this goal. Amongst them, non-thermal plasma was recently proposed as an alternative and promising technique. However, the energy efficiency of most non-thermal plasma technique is very low as well as the input energy is dissipated in many forms such as heat, UV radiation, electromagnetic waves, etc., that are not totally involved in the pollutant degradation. In this work, quantitative analyses of UV radiation and H2O2 in a moist air gliding arc plasma (glidarc) were performed using potassium ferrioxalate actinometry and peroxytitanyl complex method, respectively. The role of UV light emitted in gliding arc plasma was elucidated by performing parallel experiments: H2O2, glidarc alone, glidarc + H2O2, glidarc + H2O2 + Fe3+ (plasma-Photo-Fenton). The results show that the incorporation of Fenton reagents in 4-CP solution exposed to the plasma enhanced the yields of chemical active species, which were available for efficient removal and mineralization of 4-CP.

Characterization of Reversed Arc Hydrocarbon Plasma in Material Processing

A comprehensive study of the reversed arc plasma enhanced CVD (RACVD) reactor utilizing an Ar + H2 + CH4 plasma-creating mixture in the pressure range 1–100 Torr with a plasma flow direction opposite to the direction of the arc current was carried out. The reversed arc discharge has rising current–voltage characteristics showing voltage increasing with pressure and hydrogen concentration. The spectrum of the Ar-H2-CH4 plasma column includes CH, C2, and H2 molecular bands, in addition to Hα, Hβ, Hγ, and Hδ lines. The dissociation degree of H2 was estimated from the intensity ratio IHα/IArI of the Hα and ArI 750 nm lines using the optical actinometry method, yielding an average dissociation degree of hydrogen in the arc plasma of 15–20%. The average vibrational and rotational temperatures of CH radicals are Tv = Tr = 3000 K ± 300 K. The dissociation degree of hydrogen in the reversed arc discharge was calculated by the advection–diffusion-reaction model and showed reasonably good agreement both with experimental findings and with LTE calculations. The high concentration of nascent hydrogen and hydrocarbon radicals in the reversed arc plasma and its uniform distribution across the arc column makes it suitable for diamond coatings. The results obtained on the interaction of reversed arc plasma with substrates suspended within the current-carrier arc plasma column were applied to the description of a dusty reversed arc plasma in fluidized bed reactors. It was found that the energy effectiveness of the treatment of nanoparticles in the RACVD fluidized bed reactor exceeds 90%.

Spectral Methods of Control of Impurities, Their Flows and Localization in an Equilibrium Low-Temperature Plasma of Low Pressure

The state-of-art of studies of processes involving small fractions of particles formed as a result of chemical transformations of the source gas or appearing from the outside as an impurity is discussed. Various high-sensitivity methods for measuring the low concentrations of particles are considered. The main focus is on spectral methods, both classical and laser ones. The main modern fields of the application of non-equilibrium plasma, features, and achievements of the diagnostic tools used in them are highlighted. The emphasis is on spectroscopic studies of plasma purity in the low-temperature near-wall layers of thermonuclear reactors. In this case, the issue of the penetration of water molecules into the plasma chamber from the cooling circuits is of particular importance. In view of the limited accessibility to the reactors, new remote versions of spectral emission methods are being developed that are focused on the diagnostics of the ITER near-wall plasma. A new method of multispectral optical actinometry is discussed, in which intermediate chemically unstable particles can play the role of actinometers. This broadens the range of possibilities for quantitative measurements of concentrations of particles of different kinds, and increases the sensitivity. Effective actinometric pairs were found for the objects under consideration, e.g., hydrogen and deuterium atoms. The schemes are worked out on laboratory facilities, and kinetic models of plasma-chemical processes are developed. Scaling of the results of model experiments makes it possible to predict the measurement of the impurity flows at the level (10–9–10–13) Pa m3 s–1 with the localization of sources determined by the spatial resolution of the optical system.

Electrical and plasma characterization of a hybrid plasma source combined with inductively coupled and capacitively coupled plasmas for O atom generation

We developed a hybrid plasma source combined with an inductively coupled plasma (ICP) antenna and a capacitively coupled plasma (CCP) electrode. The ICP antenna and the CCP electrode are connected to a single RF power generator in parallel and a variable capacitor Cv is connected to the ICP antenna in series. The currents flowing through each source and the CCP electrode voltage are measured for analysis of the electrical characteristics, and the ion densities are measured while adjusting the capacitance of the Cv. Interestingly, when a series LC resonance occurs between the inductance of the ICP antenna and the capacitance of the Cv, different trends are observed depending on the discharge mode. In capacitive mode (E-mode), the ion density is minimized and is controlled by the CCP current. On the other hand, in inductive mode (H-mode), the ion density is maximized and is affected by the ICP current. The change of the ion density can be explained by the balance between the total power absorption and power dissipation. It is also in good qualitative agreement with the calculated plasma density from the power balance equation. By adjusting the Cv, linear control of the ion density can be achieved. To evaluate the proposed source in terms of O atom generation, the number density ratio of O atom nO to Ar nAr is obtained by using the optical emission spectroscopy actinometry method. These results show that nO/nAr is controlled. Our source can be applied to plasma processing, in which ion density and O atom generation controls are important factors.

Atomic nitrogen density measurements by actinometry method in the toroidal device NAGDIS-T

Nitrogen (N) atomic density is measured by an actinometry method in the toroidal shaped plasma device NAGDIS-T, where the plasma produced in a DC arc discharge is cooled as spiraling down inside the vacuum vessel. The plasma was characterized with an electrostatic probe, and we applied the actinometry method to obtain the N density using the deduced electron density and temperature. The actinometry method used the Ar line emissions at 750.4 or 811.5 nm and N emission at 746.8 nm. The measured N densities from the actinometry was compared with that from the vacuum ultraviolet absorption spectroscopy.

Experimental characterization of argon/air mixture microwave plasmas using optical emission spectroscopy

The plasma is generated by a microwave (MW) source inside a conditioned cell with an axial gas injection working at high pressure argon with a small admixture of air. Several characterization methods based on the analysis of the optical emission spectra are employed to determine rotational Trot, vibrational Tvib, excitation Tex and electron Te temperatures along the plasma flame axis. The densities of electrons and oxygen and nitrogen atoms are also determined from spectra analysis for the same plasma axis positions. The rotational and vibrational temperatures are simultaneously estimated using a new method based on the analysis of 3 consecutive band heads of the second positive system (SPS) of molecular nitrogen spectra. This new method, based on pre-calculated synthetic spectra databases, leads to Trot varying from about 2000 to 2500 K along the plasma axis while Tvib are higher (around 5000 K and more). Both temperatures are coherent when determined from N2SPS in the case of two distinct wavelength ranges (around 313 nm and 376 nm). These temperatures are in agreement with Trot determined from comparison between synthetic and experimental OH(A-X) spectra and Tvib determined from the first negative system N2+FNS spectra. The estimated electron temperatures Te are around 2.0 eV while the electron densities are in the range 1015to 1016cm−3using a literature method adapted in the present work to air diluted in argon buffer gas. The densities of atomic oxygen are estimated close to 1015cm−3and those of nitrogen close to 1016 cm−3 when using an actinometry method assuming a priori known the density of hot buffer argon gas at Trot temperature and also Tex determined using classical Boltzmann plots based on a chosen series of Ar lines. The significant deviations between the different temperatures Trot, Tvib, Tex and Te clearly underline a pronounced non thermal equilibrium of the present MW argon/air plasma. It is also shown an important chemical non-equilibrium since the measured electron, N and O densities are found much higher than the usual equilibrium densities generated by thermal dissociation and recombination processes. This therefore means that the energetic electron impacts play a significant role on the formation of the present non-equilibrium MW plasma.

Determination of water leaks flows and their surface localization in plasma reactors by the ratio of the hydrogen isotopes line intensities

A high sensitive method of multispectral actinometry developed for the measurements of the concentration of minor hydrogen-oxygen products of plasma-chemical transformation of water is presented. It is shown that in presence of deuterium the correlation between H/D density ratio and the densities of other products is practically independent of non-equilibrium plasma conditions. It was studied in the hollow cathode experimental installation and model of the processes was developed for scaling purposes. This method allows to find the sources of water leaks to plasma due to the chamber wall defects and to measure their flow rates. The penetration of water vapors into the model installation was provided with a special localized leak and H/D ratio was measured by Dα and Hα lines intensity. The scaling was performed for the specific conditions of ITER reactor near-wall plasma during testing trials. The flows of the Н2О, О2, Н2, Н, and О particles associated with the emergence of water molecules in plasma can be determined by observing disturbances suffered by the relative intensities of the emission spectral lines of particles in the vicinity of defects. The locality is limited by the spatial resolution of the optical system forming the image of the chamber wall. For testing purposes, discharge in an inert gas (He, 2 · 1016 cm−3) with small additions of D2 (1012–1010) cm−3 is ignited in the near-wall region of the ITER chamber with electron concentrations and temperatures ne = (1010–1013) cm−3, Те = (4–30) eV. For this type of discharge water leaks with flows Q = (10−13–10−9) Pa m3 s−1 can be detected. Sensitivity improves with decreasing the amount of D2 additives. With a complete examination of the internal surfaces of the chamber wall and the design requirement for the total water leakage Q < 10−7 Pa m3 s−1, more than 100 small leaks with flows Q = (10−11–10−9) Pa m3 s−1 can be detected simultaneously.

Application of atmospheric pressure discharges with a liquid cathode for determination of alkaline-earth metal ions in aqueous solutions

The concentrations alkaline-earth metal ions in water solutions were determined by the method of emission actinometry of atmospheric pressure discharge plasma with a liquid cathode. The rubidium atoms were the actinometer component in plasma, whose cations with a known concentration were added to the analyzed solution. The solutions of magnesium, calcium, barium with concentrations of 10−6-10−4 gl−1 were analyzed. It is established that the addition of electrolytes in the solution influence on the emission intensity of the metal atom lines. However, the use of the ratio of the intensities of the radiation of the analyzed components and the component-actinometer can improve the accuracy of the analysis. The water hardness factor of the tap water was determined using this method.

ЭКСИЛАМПЫ КАК ПЕРСПЕКТИВНЫЙ ИСТОЧНИК УФ ИЗЛУЧЕНИЯ ДЛЯ ФОТОХИМИЧЕСКОГО ОБЕЗВРЕЖИВАНИЯ МЫШЬЯКСОДЕРЖАЩИХ ВОД

Актуальность исследования обусловлена необходимостью решения проблемы поступления в водные объекты токсичных веществ, в том числе соединений мышьяка, путем поиска и разработки эффективных фотохимических методов очистки и обезвреживания мышьяксодержащих растворов с использованием экологически чистых окислителей и современных безртутных источников УФ излучения. Цель: изучить возможности использования эксиламп для обезвреживания As-содержащих вод и установить закономерности фотохимической активации окисления мышьяка пероксидом водорода с использованием безртутного источника квазимонохроматического излучения KrCl-эксилампы. Объекты: модельные водные растворы мышьяка (III) с концентрацией 2,7 мкмоль∙л–1 (~0,2 мг/л), приготовленные на дистиллированной (УЭП=2 мкСм/см, рН 5,8) и водопроводной воде. Методы: спектрофотометрическое определение ионов мышьяка (III); контроль рН потенциометрическим методом, съемка электронных спектров поглощения растворов реагирующих веществ; поглощенная мощность излучения эксилампы, определенная методом химической актинометрии с атразином; оценка доз УФ излучения. Результаты. Установлена принципиальная возможность использования безртутного источника квазимонохроматического излучения KrCl-эксилампы (222 нм) для фотохимического окисления As(III) комбинированной системой {УФ/H2O2}. Изучены основные закономерности фотохимического окисления мышьяка (III) с использованием безртутного источника УФ излучения – KrCl-эксилампы (222 нм). Проведены сравнительные исследования эффективности прямого фотолиза и комбинированного окисления мышьяка (III) в водном растворе ультрафиолетовым излучением KrCl-эксилампы в присутствии пероксида водорода. По эффективности окисления As(III) рассмотренные окислительные системы можно выстроить в ряд: {УФ/H2O2}&gt;{H2O2}&gt;{УФ}. При комбинированной обработке {УФ/H2O2} наблюдается существенная интенсификация процесса окисления, через 10 минут остаточная концентрация мышьяка в растворе – ниже ПДК (0,01 мг/л). Также рассмотрено влияние гидрокарбонат-ионов, наиболее характерных анионов природных «водных матриц», на скорость реакции окисления As(III). Предложен ион-радикальный механизм фотохимического окисления мышьяка в комбинированной окислительной системе {УФ/H2O2} с использованием УФ излучения KrCl эксилампы.

A revised experimental protocol for implementing the actinometry method with the Reinecke’s salt

The present short note aims at proposing a revised experimental protocol to implement the actinometry method with Reinecke’s salt. It consists in substituting, for the dosing of the thiocyanate anions produced, perchloric acid (HClO4) by nitric acid (HNO3), the latter being carefully chosen regarding the chemical equilibria occurring in the aqueous medium and the moderate risks of HNO3. This substitution has been rigorously validated by carrying out the experiments in a dedicated torus batch photoreactor enabling simple treatment of experimental results from a one-dimensional model.

Quantum efficiency of Pd/TiO2 catalyst for photocatalytic reforming of methanol in ultra violet region

The efficiency of Pd/TiO2 catalyst for photocatalytic reforming of methanol was investigated in ultra violet, UV region by monitoring the volume of H2 production and the number of incident photon using chemical actinometry method. 2-nitrobenzaldehyde solution was used to evaluate the number of incident photon from solar light by monitoring the rate of photochemical isomerisation to 2-nitrobenzoic acid. The activity of Pd/TiO2 catalyst varies across UV region with the ability to utilise the incident photon for H2 gas production is higher in UV-B. The quantum efficiency of the reaction was affected by the amount of catalysts concentration and the number of incident photons.