Sonochemistry in waste minimisation

Sonochemical Removal of Nitric Oxide from Flue Gases

“…The sonolysis of water results in the formation of •H and •OH as primary free radical intermediates, attributable to the thermal dissociation of water vapor present in the cavities during the compression phase of the wave. The formation of these active species and their subsequent recombination at low scavenger concentrations to produce typical molecular products of aqueous sonolysis, hydrogen peroxide (H 2 O 2 ) and hydrogen, are represented by the following reactions: [20][21][22][23][24][25][26] Nitric oxide undergoes gas-phase reactions either in the acoustic cavities or with hydroxyl radicals in the interfacial zone and in bulk solution, ultimately resulting in the formation of nitrous and nitric acids: 20…”

“…The collapse of these bubbles leads to local transient high temperatures (g5000 K) and pressures (g1000 atm), resulting in the generation of highly reactive species including hydroxyl (•OH), hydrogen (H•), and hydroperoxyl (HO 2• ) radicals and hydrogen peroxide. [20][21][22][23][24] A number of studies have demonstrated the effectiveness of ultrasound for the oxidation of organics, destruction of pathogenic organisms, and treatment of water and wastewater either as a sole means of treatment or in combination with other oxidation processes such as ozonation, UV irradiation, and photocatalysis. [25][26][27][28][29][30][31] Despite recent advances in homogeneous sonochemistry, the mechanisms of heterogeneous sonochemistry remain poorly understood.…”

“…Sonochemical techniques utilize ultrasound to produce an oxidative environment via acoustic cavitation due to the formation and subsequent collapse of microbubbles from acoustical wave-induced compression/rarefaction. The collapse of these bubbles leads to local transient high temperatures (≥5000 K) and pressures (≥1000 atm), resulting in the generation of highly reactive species including hydroxyl (•OH), hydrogen (H•), and hydroperoxyl (HO 2 • ) radicals and hydrogen peroxide. − A number of studies have demonstrated the effectiveness of ultrasound for the oxidation of organics, destruction of pathogenic organisms, and treatment of water and wastewater either as a sole means of treatment or in combination with other oxidation processes such as ozonation, UV irradiation, and photocatalysis. − Despite recent advances in homogeneous sonochemistry, the mechanisms of heterogeneous sonochemistry remain poorly understood. There is a need to improve our understanding of the extent of mass transfer and reaction intensification resulting from ultrasonic irradiation as a function of process and operating parameters in heterogeneous gas−liquid, liquid−liquid, and gas−liquid−solid systems. − Shojaie et al presented experimental results on the sonication of SO 2 and NO species in water and NaOH solutions at 20 kHz in the presence of argon and suggested that the yields of H 2 SO 4 , nitrous acid (HNO 2 ), and HNO 3 resulted from interactions with H 2 O 2 generated from water during the adiabatic collapse of the microbubbles in solution since the formation rate of H 2 O 2 limited the yields of oxidation products.…”

Environmentally Friendly Chemistry Using Supported Reagent Catalysts: Chemically-Modified Mesoporous Solid Catalysts

“…Rates of reaction could be signiÐcantly increased by using ultrasound as a catalyst pretreatment method and we believe this is due to the removal of pockets of gas trapped on the catalyst surface which might otherwise prevent some of the catalytic centres from becoming involved in the reaction. 22 Ultrasound did not a †ect the activity of the supported reagent catalysts in the nucleophilic substitution PTC reaction presumably because of the higher temperature used in this reaction.…”

Ultrasound for Hydrothermal Treatments of Aqueous Wastes: Solution for Overcoming Salt Precipitation and Corrosion

“…In environmental protection, ultrasound effects are used in biological and chemical decontamination in more conventional processes. − …”