Visible Chemiluminescence Research Articles

Visible chemiluminescence of ammonia premixed flames and its application for flame diagnostics

We report a spatially resolved spectroscopic study of the visible chemiluminescence emission from different premixed ammonia-air-oxygen flames stabilized on a laminar flat flame burner, with equivalence ratio ranging from 0.7 to 1.35 and an O2/N2 ratio of 0.4. In the reaction zone of the observed flames, the visible emission was recognized to be the chemiluminescence of excited NH2* radicals, while in the post-flame zone, two types of chemiluminescence were observed: NO2* chemiluminescence dominated in the fuel-lean flames and NH2* chemiluminescence dominated in the fuel-rich flames. The high-resolution spectra of the NO2* and NH2* chemiluminescence in the visible region (400-700 nm) were recorded. The intensity of both spectra increased gradually with wavelength. However, the NO2*-chemiluminescence spectrum appeared to be continuous and unstructured, while the NH2*-chemiluminescence spectrum consisted of groups of distinct emission lines. Based on the spectral feature, the ratios of the integrated chemiluminescence intensities over the 598-603 nm wavelength range to the intensities over the 586-592 nm range and 447-453 nm range were used to sense equivalence ratio. In addition, slightly different colors of the fuel-lean and fuel-rich flames were observed, due to the fact that NO2* chemiluminescence had a relatively stronger signal in the blue region than NH2* chemiluminescence. The difference was used to infer flame equivalence ratio using the flame images recorded by a RGB digital camera, where the ratio of the signal from the red channel to the signal from the blue channel was calculated.

UV-visible chemiluminescence signature of laminar ammonia-hydrogen-air flames

This work investigates the UV and visible chemiluminescence signatures of laminar ammonia-hydrogen-air flames. A counterflow burner was used to stabilize flat and steady premixed ammonia-hydrogen-air twin-flames for wide ranges of ammonia fuel fractions (0.55≤XNH3≤0.90), equivalence ratios (0.35≤ϕ≤1.70), and strain rates (50≤a≤300/s). The chemiluminescence spectra in the UV and visible regions were measured. The important contributors to the chemiluminescence of ammonia-hydrogen-air flames were first identified and their sensitivities to equivalence ratio and ammonia fuel fraction were then quantified. Promising ratios of chemiluminescence intensities for the non-intrusive optical sensing of equivalence ratio and ammonia fuel fraction in premixed ammonia-hydrogen-air flames were also identified. Among the 36 ratios that could be formed with the 9 contributors to chemiluminescence that were defined, 3 are particularly promising, namely, OH*/NO*, OH*/violet (violet refers to the 350 to 400 nm range), and red/blue (blue and red refer to the 450 to 500 nm and 650 to 750 nm ranges, respectively). Ratios OH*/NO* and OH*/violet were found to provide suitable measures of equivalence ratio for lean and rich ammonia-hydrogen-air flames, respectively, because these ratios are very sensitive to equivalence ratio, are insensitive to ammonia fuel fraction, and are marginally sensitive to strain rate. Once equivalence ratio is known, the ammonia fuel fraction can then be measured with ratio red/blue because it is sensitive to the ammonia fuel fraction and it is globally insensitive to strain rate.

Cobalt-imidazole metal-organic framework loaded with luminol for paper-based chemiluminescence detection of catechol with use of a smartphone.

Chemiluminescence (CL) reagent luminol was loaded into the porous structure of cobalt-imidazole metal-organic framework (MOF) ZIF-67 to obtain luminol-functionalized ZIF-67 (luminol@ZIF-67) with CL property. The morphology, composition, CL property, and CL mechanism of luminol@ZIF-67 were carefully investigated. The obtained luminol@ZIF-67 exhibited strong, stable, and visible CL emission that reacted with H2O2, attributed to the strong catalytic effect of ZIF-67 combined with the shortened diffusion distance between luminol and the catalytic center. The CL intensity of luminol@ZIF-67 was more than 550 times higher than that of luminol. Catechol can effectively quench the CL emission of luminol@ZIF-67 that reacted with H2O2. Then, a simple paper-based CL imaging detection method was developed for the detection of catechol by using a smartphone as a portable detector. The linear calibration curve of the developed CL assay for catechol ranged from 5 to 100mg/L with detection limit of 1.1mg/L (S/N = 3δ). The strong CL emission of luminol@ZIF-67 combined with the effective quench ability of catechol guaranteed high sensitivity of the detection method. The practical application ability of the developed CL assay was tested by the determination of catechol in tea and tap water samples, resulting in acceptable results. This work provides an effective paper-based CL detection method for catechol and enriches the species of the chemiluminescent MOF material.

SpraySyn-A standardized burner configuration for nanoparticle synthesis in spray flames.

In many scientific communities, the definition of standardized experiments has enabled major progress in process understanding. The investigation of the spray-flame synthesis of nanoparticles at a well-defined standard burner by experiment and simulation makes it possible to produce a comprehensive data set with various established and novel measuring methods. In this work, we introduce the design of the SpraySyn burner as a new standard for a free-jet type burner that offers well-defined and simulation-friendly boundary conditions and geometries as well as accessibility for optical diagnostics. A combustible precursor solution is fed through a centrally located capillary and aerosolized with an oxygen dispersion gas flow. The spray flame is stabilized by a premixed flat methane/oxygen pilot flame fed via a porous bronze matrix surrounded by a stabilizing nitrogen coflow emanating through the same porous matrix, providing easy-to-calculate boundary conditions for simulations. This burner design enables the use of a wide choice of solvents, precursors, and precursor combinations. Best-practice operating instructions and parameters are given, and large-eddy simulations are performed demonstrating the suitability of the SpraySyn burner for computational fluid dynamics simulations. For ensuring reproducible operation across labs, we define a consumer-camera-based flame characterization scheme for the quantitative assessment of the flame geometry such as flame length, diameter, tilt angle, and photometric distribution of visible chemiluminescence along the center axis. These parameters can be used for benchmarking the pilot and spray flame by each user of the SpraySyn burner with the reference flames.

Development of a semi-empirical convective heat transfer correlation based on thermodynamic and optical measurements in a spark ignition engine

Internal combustion engines are still the main technology for energy conversion in automotive transport and are set to remain the main choice of propulsion solutions for some time to come. Development and design of these power units in the quest for improved efficiency and reduced environmental impact is increasingly reliant on simulations in order to reduce costs. Therefore, continuous improvement of sub-models used for numerical investigation is required so that correct and pertinent results are obtained. Convective heat transfer is receiving much attention in this respect, especially as direct injection spark ignition (DISI) engines can feature abnormal combustion phenomena such as mega-knock, mainly driven by local hot spots in the combustion chamber, that can be extremely damaging as they cannot be mitigated with existing control procedures. As a result, thermal stratification is more and more investigated through both quasi-dimensional and more complex computational fluid dynamics (CFD) codes. Alternative fuels are also extensively studied, especially as their specific properties that are different from those of gasoline can make their application challenging, thus requiring further insight in order to identify suitable injection and ignition control strategies. A new convective heat transfer correlation was developed for application in quasi-dimensional models, with a more fundamental basis combined with the application of a flow field model; results were compared to existing and extensively used empirical equations. Assessments were based on in-cylinder pressure measurements performed on a DISI engine fueled with gasoline, combined with the evaluation of flame area through optical techniques. Crank angle resolved UV–visible chemiluminescence was used for the analysis of early stage flame development and cycle resolved acquisitions were employed in order to visualize the main combustion phase. The effect of engine speed, load, spark advance and air–fuel ratio was investigated. Thermodynamic and optical data were found to be well correlated when applying the proposed model that also features simpler calibration. Further validation was performed by using heat flux measurements on another experimental power unit fueled with methane and hydrogen.

π‐Conjugated Carbon Radicals at Graphene Oxide to Initiate Ultrastrong Chemiluminescence

AbstractGraphene oxide has widely been employed in various fields, but its structure and composition has still not been fully understood. Here we report that freshly prepared graphene oxide exhibits a large number of π‐conjugated carbon radicals at its π‐network plane, which result from the addition reaction of hydroxyl radicals from H2O2 onto the conjugated double bonds of graphene oxide. The π‐conjugated carbon radicals can directly initiate the long‐lasting visible chemiluminescence of luminol, which is even stronger than that obtained when horseradish peroxidase and H2O2 are used. Previously, graphene oxide was mainly reported to be a quencher of chemiluminescence instead. Remarkably, the reacted radicals can be regenerated, thereby enabling the repetitive initiation of chemiluminescence by re‐treatment of graphene oxide. The results reported here provide a new understanding of the structure, properties, and applications of graphene oxide.

π-conjugated carbon radicals at graphene oxide to initiate ultrastrong chemiluminescence.

Graphene oxide has widely been employed in various fields, but its structure and composition has still not been fully understood. Here we report that freshly prepared graphene oxide exhibits a large number of π-conjugated carbon radicals at its π-network plane, which result from the addition reaction of hydroxyl radicals from H2O2 onto the conjugated double bonds of graphene oxide. The π-conjugated carbon radicals can directly initiate the long-lasting visible chemiluminescence of luminol, which is even stronger than that obtained when horseradish peroxidase and H2O2 are used. Previously, graphene oxide was mainly reported to be a quencher of chemiluminescence instead. Remarkably, the reacted radicals can be regenerated, thereby enabling the repetitive initiation of chemiluminescence by re-treatment of graphene oxide. The results reported here provide a new understanding of the structure, properties, and applications of graphene oxide.

Chemiluminescence arising from the decomposition of 1,4-dimethylnaphthalene endoperoxide applied to silica gel in the presence of NdIII, YbIII, and EuIII β-diketonates

Visible and near-IR chemiluminescence was observed upon the decomposition of 1,4-dimethylnaphthalene endoperoxide applied to silica gel in the presence of the β-diketonate complexes Nd(L)3·nH2O, Yb(L)3·nH2O, and Eu(L)3·nH2O (L is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dionate, 1,1,1-trifluoro-3-thenoylacetonate, and acetylacetonate). Excited lanthanide ions serve as luminescent emitters with emission maxima at λ = 870 and 1060 nm for NdIII, 990 nm for YbIII, and 615 nm for EuIII. Singlet oxygen generated by decomposing endoperoxide was found to play a key role in the chemiluminescence mechanism.

Impinging flame ignition and propagation visualisation using Schlieren and colour-enhanced stereo imaging techniques

An innovative 3D flame visualisation and digital reconstruction technique was developed on the basis of digital flame colour enhancement and conventional stereo reconstruction methods. This combined methodology, together with Schlieren visualisation technique, was utilized to investigate the ignition process of propane impinging diffusion flame. Through the application of flame colour analysis, it was shown that majority of the flame feature observed during the initial stage of the ignition process resembles a bluish colouration similar to the colouration induced by visible chemiluminescence observed from lean premixed hydrocarbon flames. Digital flame colour analysis principle was applied to identify and enhance the weak chemiluminescence signals from the raw image data. The colour-enhanced images were able to clearly depict the details of local flame structures and allow the application of 3D stereo reconstruction on these flame features. The results from 3D reconstruction and direct high speed imaging showed that the initial flame kernel, which led to the eventual flame establishment, was very sensitive to the ignition location. Furthermore, this flame feature expands outward with time. The combined colour-enhanced stereo technique has the advantage over traditional stereo method in enabling the visualisation and reconstruction of a wider range of flame structures and shows great potential for application in future combustion research.

Shock-Tube Measurements of Toluene Ignition Times and Radical Chemiluminescent Spectra at Low Pressures

Autoignition delay time measurements were performed for toluene/oxygen/argon mixtures at pressures of approximately 1.0 and 3.0 atm, temperatures of 1312–1713 K, oxygen mole fractions of 1.8–18.0%, and equivalence ratios of 0.5, 1.0, and 2.0 in a shock-tube facility. Ignition times were determined using electronically excited CH* and OH* emissions and reflected shock pressure monitored through the shock-tube sidewall. The dependence of the ignition delay times upon pressure, oxygen mole fraction, and equivalence ratio has been characterized. An empirical correlation for the ignition delay has been deduced by linear regression of the ignition data. Experimental results are compared to simulations of three recent chemical kinetic mechanisms for the oxidation of toluene. The overall trends are captured fairly well by the mechanisms. In addition, the important reaction pathways have been elucidated by both flux and sensitivity analyses. Ultraviolet and visible chemiluminescence of toluene combustion were meas...

Chemiluminescence Reactions of a Luminol System Catalyzed by ZnO Nanoparticles

Colloidal ZnO nanoparticles were synthesized by the sol−gel method and were characterized by UV−visible spectroscopy and photoluminescence spectroscopy. The effect of ZnO nanoparticles on the luminol−H2O2 chemiluminescence (CL) system, a popular model CL system, was investigated. It was found that ZnO nanoparticles with a size regime from 6 to 21 nm could enhance the CL of the luminol−H2O2 system, and the strongest CL signal was obtained when the mean diameter of ZnO nanoparticles was 6 nm. To investigate the enhancement mechanism of the CL, we used UV−visible spectroscopy, FT-IR spectroscopy, and CL spectroscopy to study optical properties before and after the CL reaction in the presence/absence of ZnO nanoparticles. The CL enhancement of the luminol−H2O2 system by ZnO nanoparticles should originate from the catalysis of ZnO nanoparticles, which could catalyze the decomposition of H2O2 to produce some reactive intermediates such as hydroxyl radical and superoxide anion. Then, the resulting hydroxyl radical reacted with luminol to form luminol radical, which rapidly reacted with superoxide anion or monodissociated hydrogen peroxide. As a result, the emission was enhanced. Experimental results showed that some organic compounds containing -OH, -NH2, and -SH groups, such as amino acid, ascorbic acid, and dopamine, could inhibit the CL signal of the luminol−H2O2−ZnO system. The above facts indicated that the present system had a wide application for the determination of such compounds.

Multichannel Microchemical Reactor Comprising Replica-Molded Microplasma Devices: Chemiluminescence and Sulfur Deposition in $\hbox{Ar/CS}_{2}$ Flows

Microchemical reactors consisting of parallel linear arrays of interconnected cylindrical microcavity plasma devices have been fabricated by replica molding in ultraviolet-curable polymer. Tests of 10 times 10 arrays of 400-mum-diameter devices with 125-mum-wide gas flow channels have been conducted in rare gas and Ar/CS2 flows and excitation of the array with a sinusoidal voltage. Visible chemiluminescence (lambda ~ 505 nm) resulting from the A tilde rarr X tilde transition of CS2 + and the deposition of a (C-S)n microstructured polymer have been observed in the Ar/CS2 flow experiments.

CdS nanocrystal induced chemiluminescence: reaction mechanism and applications

Water-soluble CdS nanocrystals (NCs) capped with mercaptoacetic acid (MA) weresynthesized in aqueous solution. Hydrogen peroxide directly oxidized the MA-capped CdSNCs and produced strong chemiluminescence (CL) emission in basic conditions. It wasfound that the CL of CdS NCs was size-dependent, and the CL intensity increased withincreasing CdS NCs size. UV–visible spectra, CL spectra, photoluminescence (PL) spectra,and transmission electron microscopy (TEM) were used to investigate the CLreaction mechanism. Moreover, the effects of reactant concentrations, surfactants,and some biological molecules and metal ions were carefully investigated. Somebiological molecules and metal ions were observed to inhibit the CL signal of theH2O2–CdS NCs system, which makes it applicable for the detection of such species.

OH and CH luminescence in opposed flow methane oxy-flames

Emission spectroscopy is a 2-D nonintrusive diagnostic technique that offers spatially resolved data for combustion optimization and control. The UV and visible chemiluminescence of the excited radicals CH( A 2 Δ , B 2 Σ − ) and OH( A 2 Σ + ) is studied experimentally and numerically in opposed-flow diffusion flames of methane and oxygen-enriched air. The oxidized oxygen content is varied from 21 to 100% while the range of the studied strain rates spans from 20 to 40 s −1. The spectrally resolved imaging is obtained by two different methods: scattering through a grating monochromator and interposition of interference filters along the optical path. Absolute measured chemiluminescence intensities, coupled with a numerical model based on the opposed flow flame code, are used to evaluate the chemical kinetics of the excited species. The predictions of the selected model are in good agreement with the experimental data over the range of the studied flame conditions.

Bioluminescence Imaging of the Response of Rat Gliosarcoma to ALA‐PpIX‐mediated Photodynamic Therapy¶

ABSTRACTPhotodynamic therapy (PDT) is a promising modality for the treatment of solid tumors that combines a photosensitizing agent and light to produce cytotoxic reactive oxygen species that lead to tumor cell death. The recent introduction of bioluminescence imaging (BLI), involving the use of the luciferase gene (luc) transferred into target tumor cells, followed by systemic administration of luciferin and detection of the emitted visible chemiluminescence photons, offers the potential for longitudinal imaging of tumor growth and therapeutic response in single animals. We demonstrate in this study the first results of the use of BLI to assess the response of an intracranial brain tumor model (9L rat gliosarcoma) to aminolevulinic acid (ALA)‐mediated PDT. Complementary in vitro experiments with the luciferase‐transfected 9L cells show that the decrease in the luminescent signal after PDT correlates with cell kill. In vivo imaging shows a decrease in the BLI signal from the tumor after ALA‐PDT treatment, followed by tumor regrowth. Furthermore, preliminary studies using cells transfected with a hypoxiaresponsive vector show an increase in bioluminescence within 4 h after Photofrin‐mediated PDT, demonstrating the ability to observe stress‐gene responses. These results suggest that BLI can be used to provide spatiotemporal information of intracranial brain tumor responses after PDT and may serve as a valuable response‐endpoint measure.

Bioluminescence imaging of the response of rat gliosarcoma to ALA-PpIX-mediated photodynamic therapy.

Photodynamic therapy (PDT) is a promising modality for the treatment of solid tumors that combines a photosensitizing agent and light to produce cytotoxic reactive oxygen species that lead to tumor cell death. The recent introduction of bioluminescence imaging (BLI), involving the use of the luciferase gene (luc) transferred into target tumor cells, followed by systemic administration of luciferin and detection of the emitted visible chemiluminescence photons, offers the potential for longitudinal imaging of tumor growth and therapeutic response in single animals. We demonstrate in this study the first results of the use of BLI to assess the response of an intracranial brain tumor model (9L rat gliosarcoma) to aminolevulinic acid (ALA)-mediated PDT. Complementary in vitro experiments with the luciferase-transfected 9L cells show that the decrease in the luminescent signal after PDT correlates with cell kill. In vivo imaging shows a decrease in the BLI signal from the tumor after ALA-PDT treatment, followed by tumor regrowth. Furthermore, preliminary studies using cells transfected with a hypoxia-responsive vector show an increase in bioluminescence within 4 h after Photofrin-mediated PDT, demonstrating the ability to observe stress-gene responses. These results suggest that BLI can be used to provide spatiotemporal information of intracranial brain tumor responses after PDT and may serve as a valuable response-endpoint measure.

Kinetics of the chemiluminescence associated to the reaction between peroxyl radicals and proteins.

Protein oxidation, mediated by peroxyl radicals derived from 2,2'-azobis(2-amidinopropane) dihydrochloride is sided by a significant visible chemiluminescence (CL). The light emission shows a complex dependence with the protein concentration and with the incubation time that cannot be interpreted in terms of peroxyl radicals recombination (Russell's mechanism). In all the systems studied, the chemiluminescent behavior requires to consider the participation of several oxidation products as precursors of the excited states. These compounds lead to the formation of excited states by competing radical and nonradical mediated pathways. These intermediates (most probably hydroperoxide-like compounds) would arise from the oxidation of Trp and Tyr residues. This conclusion is based on the similarity of the time profile of the chemiluminescence observed in the oxidation of the free amino acids and the proteins, both in the presence of and absence of free-radical scavengers.

Formation of hydrotrioxides during ozonation of hydrocarbons on silica gel. Decomposition of hydrotrioxides

Hydrotrioxides (HT), ROOOH, from isopentane, 1,4-dimethylcyclohexane, 1,3-dimethylcyclohexane, decalin and triphenylmethane were synthesized for the first time by low-temperature ozonation of the corresponding hydrocarbons on a silica surface. Thermal decomposition of hydrotrioxides is accompanied by the formation of radicals and by infrared and visible chemiluminescence (CL). In solution the HTs form self-associates and react reversibly with the solvent (acetone) producing Bayer–Villiger type intermediates (unsymmetrical dialkyl trioxides). These reactions cause a complex character of the decomposition kinetics of HTs, as evidenced by monitoring the dependence of CL intensity on time. Activation parameters of thermal decomposition of HTs show a compensation effect (logA vs EA) which describes well the available experimental and theoretical data for the homolysis of organic trioxides. Copyright © 2000 John Wiley & Sons, Ltd.

Linear and cyclicN-acyl-?-arylglycines. IV. Novel 3-Substituted 3-Acylaminobenzo[b]furan-2(3H)-ones: Synthesis and chemiluminescence studies

Starting from 3-acylaminobenzo[b]furan-2(3H)-ones (2) 3-arylthio substituted derivatives (3) were prepared via novel N-acylimines (5). Compounds of type 3 and 5 were found to show visible chemiluminescence upon base-induced oxidation in the presence of an oxygen source. A mechanistic interpretation for this chemiluminescence reaction is proposed.

Induced decomposition of di(tert-butyl)trioxide

Thermal decomposition of di(tert-butyl)trioxide (ButOOOBut) in a wide range of concentrations was studied by visible and IR chemiluminescence. Induced decomposition of ButOOOBut caused by its reaction with the peroxy radicals formed in the solvent (CH2Cl2) was found and investigated.