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The Atmosphere and Atmospheric Chemistry
Published in Stanley E. Manahan, Environmental Chemistry, 2022
In order for a photochemical reaction to occur, light must be absorbed by the reacting species. If the absorbed light is in the visible region of the sun's spectrum, the absorbing species is colored. Colored NO2 is a common example of such a species in the atmosphere. Normally, the first step in a photochemical process is the activation of the molecule by the absorption of a single unit of photochemical energy characteristic of the frequency of the light called a quantum of light. The energy of one quantum is equal to the product hν, where h is Planck's constant, 6.63 × 10−34 J.s (6.63 × 10−27 erg.s), and ν is the frequency of the absorbed light in s−1 (inversely proportional to its wavelength, λ).
Bimodal Reaction Sequences in Oxidation with Dioxygen in Photocatalysis
Published in Robert Bakhtchadjian, Bimodal Oxidation: Coupling of Heterogeneous and Homogeneous Reactions, 2019
Photochemical reaction takes place when the reactants or other components of the reaction media (atoms, molecules, ions, radicals, excited species, solid-phase substances, etc.) absorb the energy of light (photons) and use it for the chemical transformations. Light, being one of the forms of electromagnetic irradiation, is characterized by the wavelength (λ) and frequency (ν). On the scale of electromagnetic waves, it occupies the diapason of the wavelength about 100–2500 nm. In turn, it is divided into diapasons of UV irradiation (100–400 nm), visible light (400–750 nm), and infrared irradiation (750–2500 nm). It is obvious that the energy of light decreases with increases in wavelength, as E = hν and ν = 1/λ. Correspondingly, in the 150–800 nm range, light possesses 800–150 kJ/mol energy that is comparable to energies sufficient to break the chemical bonds.8 For example, molecular oxygen absorbing the energy of photons below λ = 200 nm that corresponds to the energy 143 kcal/mol (598 kJ/mole), can be dissociated into oxygen atoms, as the energy of O=O bond is only 119 kcal/mol (498 kJ/mol).
Introduction
Published in Sampa Chakrabarti, Solar Photocatalysis for Environmental Remediation, 2019
A photocatalyst is defined as a species that can produce chemical changes in a reaction partner upon absorption of light. The term photocatalysis is used broadly to describe the activity of photoactive semiconductor materials in a variety of applications. Photosensitizers are molecules that mediate photochemical reactions by first absorbing light and then using that energy to activate a less photo-active reactant towards some chemical transformation. Effective photosensitizers must have absorption features suitable for strong interaction with light, and they should also have relatively long excited state to facilitate bimolecular reaction with substrate molecules. Photosensitizers are typically catalytic species that remain unchanged in the overall balanced reaction. In this case, the terms photosensitizers and photocatalysts can be used interchangeably.
Photodegradation of the pure and formulated scoparone in liquid solutions: kinetics and mechanism
Published in Environmental Technology, 2022
Jinxiang Luo, Huijun Xie, Wei Ding, Yongqiang Zhang
These results indicated that the photolysis rates of SPR increased rapidly with the temperature increase at the low temperature range (15℃ to 35℃). However, photochemical reaction is different from ordinary thermal reaction, the required activation energy is mainly from light energy, not heat energy. Therefore, the increase of photolysis rate is limited effecting by temperature, when the temperature rises to a certain extent (35℃), the photolysis rate of SPR increased slowly and maintained at a stable level. These results were consistent with the effects of temperature on chloroyrifls photolysis [34].
Functionalized photosensitive gelatin nanoparticles for drug delivery application
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Janicy Arantes Carvalho, Alexandro da Silva Abreu, Antonio Claudio Tedesco, Milton Beltrame Junior, Andreza Ribeiro Simioni
From the major proteins of blood that absorb light, the most important quantitatively is hemoglobin. Hemoglobin has significant absorption near 425, 544, and 577 nm, necessitating illumination of tissue at wavelengths >600 nm to ensure significant penetration. At wavelengths >1200 nm, light absorption by water molecules becomes substantial. For wavelengths >850-900 nm, the photons may not have sufficient energy to participate in a photochemical reaction. Therefore, the wavelength range between 600 and 800 nm has been determined as the practical therapeutic window for clinical PDT [53].