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Oxidation/Reduction in Aquatic Chemistry
Published in Stanley E. Manahan, Environmental Chemistry, 2022
generates hydroxyl radical, HO•. Hydroxyl radical is a very reactive species that reacts with even refractory organic species, leading to their oxidation. As a consequence of reactions involving superoxide radical ion and hydroxyl radical, photochemical processes are important in promoting oxidation of oxidizable species in water.
Remediation of Wastewater
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials II, 2021
Shalini Chaturvedi, Pragnesh N. Dave
Interaction of light energy with metallic nanoparticles got attention due to their photocatalytic activities for various pollutants (Akhavan, 2009). These photocatalysts are made of semiconductor metals. It can degrade organic pollutants in wastewater like detergents, dyes, pesticides, and volatile organic compound (Lin et al., 2014). Semiconductor nanocatalysts are effective for the degradation of halogenated and non-halogenated organic compounds for heavy metals (Adeleye et al., 2016). The mechanism of photocatalysis is based on the photoexcitation of electron in the catalyst. The irradiation with light generates holes and exited electrons. In an aqueous medium, water molecules trapped the holes and hydroxyl radicals are generated (Anjum et al., 2016). The radicals act as a powerful oxidization agent. These hydroxyl radicals oxidize the organic pollutants and generate water and gaseous degradation products (Akhavan, 2009). Due to high reactivity under ultraviolet light (k< 390nm) and chemical stability, TiO2 is most applicable in photocatalysis (Akhavan, 2009). ZnO has also been extensively studied by researchers (Lin et al., 2014). Efficiency of photocatalyst depends on the factors like particle size, band gap energy, dose, pollutant concentration, and pH. CdS nanoparticles as a photocatalyst also received attention for the treatment of industrial dyes in wastewater (Tristao et al., 2006; Zhu et al., 2009).
In situ Treatment Technologies
Published in Rong Yue, Fundamentals of Environmental Site Assessment and Remediation, 2018
Numerous successful applications of ozonation ISCO processes have been reported using ozone injection alone as well as ozone in combination with hydrogen peroxide (Nelson and Brown 1994; Amarante 2000; Nimmer et al. 2000). Ozone–hydrogen peroxide reactions result in enhanced generation of hydroxyl radicals. This mechanism for the formation of hydroxyl radical during ozone–hydrogen peroxide treatment involves the production of hydroxyl radicals by direct hydrogen peroxide and ozone reactions and through intermediate ozone and hydrogen peroxide reactions.
Decolorization potential of reactive dyes by using galvanising industry’s waste (aluminum hydroxide sludge) depending on dye chromophore
Published in The Journal of The Textile Institute, 2023
Nesli Aydın, Deniz Izlen Cıfcı, Elçin Gunes, Yalçın Gunes, Rıza Atav
Many chemical and physical methods can be used for decolorizing wastewater, such as oxidation, advanced oxidation processes, adsorption, microbiological and enzymatic decomposition (El Ghazi et al., 2003). Oxidation process, for example chemical oxidation, is based on the phenomena of oxidizing reagent to the chemical matters being oxidized, so that putrescible pollutant particles are transformed into stabilized substances (Shammas et al., 2005). The aim of advanced oxidation process is to produce hydroxyl radicals for the degradation of organic substances in wastewater (Krishnan et al., 2017). AOPs are highly effective novel methods speeding up the oxidation process. AOP can combine with ozone (O3), catalyst, or ultraviolet (UV) irradiation to offer a powerful treatment of wastewater (Ghime & Ghosh, 2020). On the other hand, the adsorption process, which is the transfer of ions and molecules to the surface of a substance, provides a solution to completely separate dyes from wastewater without breaking them down, thus preventing the formation of toxic compounds. Adsorption is also advantageous compared to the other methods in terms of its simple installation, low cost, and wide application (Rashed, 2013).
Removal mechanism of persistent organic pollutants by Fe-C micro-electrolysis
Published in Environmental Technology, 2022
Dajun Ren, Yongwei Huang, Sheng Li, Zhaobo Wang, Shuqin Zhang, Xiaoqing Zhang, Xiangyi Gong
H2O2 subsequently combined with Fe2+ to form Fenton’s reagent. According to Equations (5) and (6), which are O2+4H++4e−→2O•+4[H]→2H2O and Fe2+ + H2O2 → Fe3+ + •OH + OH−. So, when filled with oxygen, •OH is produced in the system. As we all know, hydroxyl radical is an effective oxidant that can non-selectively degrade pollutants. Therefore, 2,4-DCP is easier to be degraded to a large amount of small molecular organic intermediates in the Fe-C micro-electrolysis system with gas. And some of the intermediate products therefore will be removed [55]. In addition, according to Equation (6), excess OH− could not be obtained in the Fe-C micro-electrolysis without oxygen, which was not conducive to the formation of a large amount of removal of the ferrous and ferric hydroxide flocculation sludge co-precipitation, coagulation and flocculation separation intermediate. As a result, under the same conditions of other experiments, the aeration of 1.5 L/min was regarded as optimal.
Effect of cysteine using Fenton processes on decolorizing different dyes: a kinetic study
Published in Environmental Technology, 2022
Márcio Daniel Nicodemos Ramos, Larissa Aquino Sousa, André Aguiar
In recent years, advanced oxidative processes (AOPs), which consist in generating hydroxyl radicals (HO•), have been evaluated for degrading different organic pollutants in wastewaters [3–5]. Dyes have been targets of many studies involving AOPs, mainly the ones based on Fenton reaction [6]. This reaction consists in oxidizing Fe2+ by H2O2 in order to produce HO• and Fe3+; it is commonly known as classical Fenton reaction (Equation (1)). Because of its high standard reduction potential (E° = 2.80 V), hydroxyl radicals are capable of oxidizing organic pollutants rapidly and with non-selectivity to harmless molecules, such as CO2, H2O and salts. Hydrogen peroxide can also react with Fe3+, otherwise known as a Fenton-like reaction (Equation (2)). Based on the kinetic constants of both reactions, velocity is higher in the presence of Fe2+. Moreover, Fenton-like reaction only generates a hydroperoxyl radical (HO2•), which is less reactive because its standard reduction potential is lower than HO• (E° = 1.42 V) [6,7]. In comparison with other AOPs (UV/H2O2, O3/H2O2, eletro-oxidation, heterogeneous photocatalysis), Fenton processes offer important advantages, such as mild conditions, absence of iron toxicity, possibility to separate residual iron and successful pollutant removal at relatively low operational costs [4–6].