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Kinetics of singlet oxygen sensing using 9-substituted anthracene derivatives$$^{\#}$$#
摘要： Singlet oxygen (1O2), the lowest excited-state of molecular oxygen receives great attention in basic research and clinical and industrial settings. Despite several spectroscopic methods available for 1O2 sensing, fluorescence sensing receives great attention, for which many fluorogenic sensors based on substituted anthracene are reported. Nonetheless, the roles of substituents on the sensing efficiency, in terms of detection time, remain largely unknown. In this work, we examine the 1O2 sensing efficiency of a fluorescence sensor based on a coumarin–anthracene conjugate, which is an electron donor-acceptor dyad, and compare the efficiency with that of 9-methylanthracene. Here, 1O2 is generated using the standard photosensitizer Rose Bengal, which is followed by estimation of the rate of reaction of 1O2 to the sensor and 9-methylanthracene. The second order reaction rate of the sensor is an order of magnitude less than that of 9-methylanthracene. The lower reactivity of the sensor to 1O2 suggests that the roles of substituents, such as electronic interactions, steric interactions and the reactivity of precursor complexes, on sensing efficiency should be carefully considered during construction of fluorogenic molecular sensors.
关键词： photochemistry,reaction kinetics,anthracene,fluorescence sensing,Singlet oxygen
更新于2025-09-23 15:23:52
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Kinetic effects and oxidation pathways of sacrificial electron donors on the example of the photocatalytic reduction of molecular oxygen to hydrogen peroxide over illuminated titanium dioxide
摘要： Sacrificial electron donors are frequently used in photocatalytic reactions to enhance the performance of the reaction, typically short-chain alcohols as well as their respective aldehydes and acids are used. This study focuses on the differences between the individual electron donors regarding their oxidation rates, mechanistic pathways, the influence of the intermediates and their direct impact on the H2O2 generation. The individual H2O2 formation rates of 16 different electron donors, photonic and faradaic efficiencies for H2O2 production are carefully discussed. Furthermore, a new multi-reaction pathway for t-butanol oxidation is postulated and critically examined.
关键词： Alcohol oxidation,Reaction kinetics,Reaction pathway,Hydrogen peroxide,Photocatalysis,Sacrificial electron donors
更新于2025-09-23 15:22:29
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The photocatalytic degradation kinetics of gaseous formaldehyde flow using TiO2 nanowires
摘要： A high performance TiO2 nanowires photocatalyst was successfully prepared by a hydrothermal method to decompose gaseous formaldehyde into CO2 and H2O in a homemade tube reactor without secondary pollution under UV irradiation. The photocatalytic oxidization (PCO) kinetics fit well with the traditional Langmuir-Hinshelwood-Hougen-Watson (LHHW) model. Multiple parameters including formaldehyde concentration, flow rate, and light intensity were monitored online and proved to be key factors affecting the rate in the photocatalytic reactions. The crystallinity of photocatalyst and its surface reactive site density determined the adsorption equilibrium constant (KHCHO) of formaldehyde on TiO2. The experimental results show that the degradation kinetics of mobile gas-phase formaldehyde by TiO2 nanowires did not strictly conform to the first-order reaction kinetics, and its photocatalytic degradation rate increases with the increase of ultraviolet LED irradiation intensity. It takes only 8.6 minutes to completely degradate formaldehyde at a flow rate of 50 ml/min by 50 mg 700TiO2, and the reaction performance remains unchanged during the decomposing process of 1200 minutes.
关键词： reaction kinetics,formaldehyde,Titanium oxide nanowires,photocatalyst,photocatalytic oxidization
更新于2025-09-23 15:22:29
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Self-Adaptable Quinone-Quinol Exchange Mechanism of Photosystem II
摘要： The step of plastoquinone (PQ) reduction to plastoquinol (PQH2) can regulate the photo-reaction rate of photosystem II (PSII). To experimentally unravel the PQ-PQH2 exchange mechanism of PSII, we investigate the reaction kinetics of plant PSII membranes and the subunits-trimmed PSII core complexes with various PQ analogues, and directly probe the reductions of PQ and other quinones by 257-nm resonance Raman scattering. Two phases of quinone concentration effect on the reaction rate originate from the quinone-quinol exchange mechanism. The results indicate that high concentrations of quinone, more than one movable quinone molecule per PSII reaction center, could trigger quinone-quinol exchange adapting to the unidirectional route: quinones enter through channel I and/or III, and quinols leave through channel II. A weak quinone binding site near QB probably plays a crucial role in pushing quinone-quinol exchange forward in the unidirectional route. Our work provides experimental proofs demonstrating a self-adaptable quinone-quinol exchange mechanism of PSII.
关键词： reaction kinetics,Photosystem II,plastoquinone,resonance Raman scattering,quinone-quinol exchange
更新于2025-09-23 15:21:01
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Dynamic Interplay between Transport and Reaction Kinetics of Luminophores on the Operation of AC-driven Electrochemiluminescence Devices
摘要： Electrochemiluminescence (ECL) involves light emission accompanied by a series of electrochemical processes on luminophores, which has been recently exploited in a new light-emitting device platform, referred to as the ECL device (ECLD). Here, we investigate the influence of the transport of the ECL luminophores and their reaction kinetics on the emission properties of AC-voltage-driven ECLDs. A model based on the diffusion and reaction rate equations is developed to predict the operational frequency (f)-dependent luminance properties of the ECLD. It is found that more frequent generation of the redox precursors with a shorter time interval enhances their probability of encountering each other, and therefore, the luminance of the device increases with increasing f initially. The luminance at a higher f, however, is suppressed eventually due to the decreased rate of the electrode reactions. Using the model, the influence of diffusion and reaction rates on the performance of an ECLD is analyzed separately and systematically. The results provide insight on the operation of this emerging class of light-emitting device platform.
关键词： electrochemiluminescence,ionic transition metal complex,reaction kinetics,mass transport,ionic liquid,light-emitting device
更新于2025-09-23 15:21:01
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A UV‐LEDs based photomicroreactor for mechanistic insights and kinetic studies in the norbornadiene photoisomerization
摘要： In this work, we report a simple and inexpensive UV-LEDs based photomicroreactor assembly constructed by commercially available components. The photoisomerization of norbornadiene to quadricyclane was selected to validate this novel photomicroreactor design. Mass transport limitation was eliminated and indicated by dimensionless numbers Fo and DaII, and photons loss was evaluated considering the absorption and reflection of the microreactor walls. The solvents, photosensitizers and light sources selections were optimized for achieving better photochemical performance and mechanistic insights. The detailed comparison between the high-pressure mercury arc lamp and the UV-LEDs strip revealed great potential of UV-LEDs as appealing light source for photochemical transformations. Moreover, the reaction mechanism was thoroughly discussed and illustrated by the Jablonski diagram indicating electronic states transitions. According to possible intermediate steps, a kinetic model was proposed with the reaction rate constant being correlated with the photon flux, which is valuable for process optimization and further understanding reaction mechanisms.
关键词： photosensitization,reaction kinetics,microreactor,mass transport,UV-LED
更新于2025-09-19 17:13:59
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[Nanostructure Science and Technology] Nanowire Electronics || Metal-Semiconductor Compound Contacts to Nanowire Transistors
摘要： Semiconductor nanowires [1–4] are promising building blocks for next-generation ultrascaled devices for electronic [5–7] and optoelectronic [8–10] applications. An important aspect for the development, maturity, and ef?ciency of these ultrascaled devices is the detailed understanding of and control over the phase transformation that accompanies the formation of their compound contacts for lithography-free self-aligned gate design [11, 12]. The term “compound” here refers to the formed phases that have ?xed stoichiometry between metal and semiconductor elements, to be distinguished from the broader “alloy” term for phases that may include nonstoichiometric or amorphous structure. This distinction is important because the formation of a low resistance, crystalline, and thermally stable compound contact is most preferred for realizing reliable functionality in ultrascaled semiconductor transistors. Usually, the phase of compound contact and its interfacial property with semiconductor nanowire (NW) can largely affect the band alignment and charge injection in NW channels. This demands the detailed studies of the metal-semiconductor solid-state reactions, including the formed compound phases, reaction kinetics, and their correlation to the device performances. In this book chapter, we provide a thorough discussion of these three topics.
关键词： metal-semiconductor solid-state reactions,compound contacts,reaction kinetics,phase transformation,Semiconductor nanowires,device performances
更新于2025-09-10 09:29:36
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Shape Controllable Synthesis of Silver Particles by Selecting the Crystallization Routes
摘要： Classic crystallization describes a burst nucleation followed by a layer-by-layer atom deposition. The non-classic crystallization refers to particle mediated crystallization process. Different crystallization routes lead to the formation of diverse structured materials. Here we report a rational synthesis of silver particles by selecting the crystallization routes. Silver particles were synthesized by a solution reduction approach. The crystallization routes were regulated by adding amino acids to stabilize silver ions which leads to the decrease of the reduction rate. Without amino acids, silver dendrites were largely formed. With the addition of amino acids, flower-like (low concentration of amino acids) and spherical silver (high concentration of amino acid) particles were synthesized. Three kinds of amino acids were tested and the similar results were obtained. The time-dependent characterization on the evolution of silver particles showed that silver dendrites were formed by the classic atom deposition while the other two morphologies were formed by the combination of classic and non-classic crystallization. The silver particles synthesized were evaluated for ethylene epoxidation and the dendritic particles demonstrated a high selectivity.
关键词： catalytic selectivity,silver particles,reaction kinetics,shape control,crystallization
更新于2025-09-09 09:28:46
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Degradation of Paracetamol by an UV/Chlorine Advanced Oxidation Process: Influencing Factors, Factorial Design, and Intermediates Identification
摘要： The combination of a low-pressure mercury lamp and chlorine (UV/chlorine) was applied as an emerging advanced oxidation process (AOP), to examine paracetamol (PRC) degradation under different operational conditions. The results indicated that the UV/chlorine process exhibited a much faster PRC removal than the UV/H2O2 process or chlorination alone because of the great contribution of highly reactive species (?OH, ?Cl, and ClO?). The PRC degradation rate constant (kobs) was accurately determined by pseudo-first-order kinetics. The kobs values were strongly affected by the operational conditions, such as chlorine dosage, solution pH, UV intensity, and coexisting natural organic matter. Response surface methodology was used for the optimization of four independent variables (NaOCl, UV, pH, and DOM). A mathematical model was established to predict and optimize the operational conditions for PRC removal in the UV/chlorine process. The main transformation products (twenty compound structures) were detected by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS).
关键词： paracetamol,response surface methodology,UV/chlorine,transformation products,reaction kinetics
更新于2025-09-09 09:28:46
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Encyclopedia of Spectroscopy and Spectrometry || Ion Collision, Theory ☆
摘要： Collisions between an ion and neutral species result in a number of possible outcomes depending upon the chemical and physical properties of the two reactants, their relative velocities, and the impact parameter of their trajectories. These include elastic and inelastic scattering of the colliding particles, charge transfer (including dissociative charge transfer), atom abstraction, complex formation and dissociation of the colliding ion. Each of these reactions may be characterized in terms of their energy-dependent rate coefficients, cross sections and reaction kinetics. This article outlines a theoretical framework for discussing these processes that emphasizes simple models and classical mechanics. The discussion of collision processes has been divided into two categories: low-energy and high-energy thermal or quasi-thermal collisions. Experiments under conditions – swarms, drift tubes, chemical ionization and ion cyclotron resonance – are strongly influenced by long-range forces and often involve ‘capture collisions’ in which atom exchange and extensive energy exchange are common characteristics. High-energy collisions are typically impulsive, involve short-range intermolecular forces and are direct, fast processes.
关键词： Low-energy Collisions,Elastic and Inelastic Scattering,Reaction Kinetics,Theory,Complex Formation,Rate Coefficients,Charge Transfer,Atom Abstraction,High-energy Collisions,Ion Collision,Dissociation,Cross Sections
更新于2025-09-04 15:30:14