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Latest Applications of TEMPO-Oxidized Cellulose Nanofibres Obtained from an Ultrasound-assisted Process
Published in Tatjana Stevanovic, Chemistry of Lignocellulosics: Current Trends, 2018
Éric Loranger, Claude Daneault
This effect facilitates, afterwards, the nanocellulose preparation using a light mechanical treatment (refining, ultrasounds) after the oxidation step. In the fine chemistry field, from organic to environmental chemistry, the use of sonochemistry is well known. On the other hand, the transposition up to the industrial scale of promising laboratory results is not an obvious thing. The laboratory experiments of Qin et al. (Qin et al. 2011) showed that treating cotton with the TEMPO/NaOCl/ NaBr system in the presence of ultrasound has allowed achieving higher levels of carboxylic groups. Therefore leading to the production of more nanocellulose and more stability in an aqueous environment. In all these studies, the sonochemical reactors were used either in ultrasonic bath (40 kHz) or ultrasound probes (20 kHz) at low power (300–600 W), mostly operated in batches. This is really a laboratory approach since these reactors must work at low concentrations to keep a homogeneous environment. The inhomogeneity of the ultrasonic field is problematic in scaling up since the geometric parameters of the reactor influence the efficiency of the ultrasounds. The results of the research work of Mishra (Mishra et al. 2011) on the use of ultrasound to catalyze ‘in situ’ oxidation reaction of bleached Kraft fibres with the TEMPO reagent has served a reference to develop a 40-liters pilot sonoreactor with variable frequency (40–170 kHz) and a nominal input power capacity of 2000 W shown in Fig. 2 (Loranger et al. 2011, Paquin et al. 2013).
Basic Concepts
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
The study of sonochemistry is concerned with understanding the effect of ultrasound in forming acoustic cavitation in liquids, which is responsible for the initiation or enhancement of the chemical activity in the solution. The chemical effects of ultrasound are not due to a direct interaction of the ultrasonic sound wave with the molecules present in the solution. Sound waves propagating through a liquid at ultrasonic frequencies do these changes with a wavelength that is significantly longer than the bond length between atoms of the molecule. Therefore, the sound waves cannot affect vibrational energy of the bond, and therefore, it cannot increase the internal energy of a molecule directly (Suslick, 1990; Suslick and Flan- nigan, 2008). Sonochemistry arises from acoustic cavitation, that is, the formation, growth, and implosive collapse of bubbles in a liquid (Suslick and Kenneth, 1989).
Chemical Synthesis of Hybrid Nanoparticles Based on Metal–Metal Oxide Systems
Published in Inamuddin, Rajender Boddula, Mohammad Faraz Ahmer, Abdullah M. Asiri, Morphology Design Paradigms for Supercapacitors, 2019
Vivek Ramakrishnan, Neena S. John
Sonochemistry is the application of ultrasound to chemical reactions. In this method, agitation of materials in a medium is achieved by sound energy in terms of ultrasonic frequencies, and it can be used in various fields depending on its requirement. Acoustic cavitation is the phenomenon that causes the sonochemical effects in liquids. A number of studies have used the ultrasound-assisted physical and chemical effects generated by acoustic cavitation for synthesizing nanomaterials and for degradation of organic pollutants in last decade. Figure 8.11 demonstrates the nanoparticle formation by sonochemical method typically for an Sn-C system (Kumar et al. 2016).
Metal extraction from ores and waste materials by ultrasound-assisted leaching -an overview
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Xiangning Bu, January Kadenge Danstan, Ahmad Hassanzadeh, Ali Behrad Vakylabad, Saeed Chehreh Chelgani
Several thousands of fine bubbles would be generated from liquid vibration when a liquid vessel is exposed to the ultrasonic waves, that is, cavitation bubbles (Avvaru et al. 2008). The generated bubbles spread throughout the negative pressure zone developed by the ultrasonic wave longitudinal propagation and quickly near the positive pressure zone (Singh et al. 2019; Swamy et al. 1995). Bubble implosions associated with acoustic cavitation release high energy and develop a microjet with the speed of around 110 m/s beside a strong impact force, leading to a collision density as strong as 1.5 kg/cm2 (Qiang et al. 2021). The instant of rapid bubble collapse creates local high temperature (1000s of Kelvin) and high pressure (100s of atmospheres), and the cooling rate may reach 109 K/s (Nagarajan et al. 2006). This ultrasound phenomenon significantly enhances the heterogeneous reaction rate, uniforms the mixture of heterogeneous reactants, accelerates the diffusion of reactants and products, increases forming of new solid phases, and controls the particle size distribution (PSD) (Tyagi et al. 2014; Vyas and Ting 2018). During the UAL process, when the ultrasonic wave propagates through the liquid phase, the environment undergoes physical and chemical changes due to bubble cavitation. The ultrasonic wave continuously produce bubbles, and their collapsing cause mechanical, thermal, and sonochemistry impacts (Figure 3) (Suslick 1990; Thompson and Doraiswamy 1999). These effects have different pluses and minuses (Table 1).
Liquid compressibility effect on the acoustic generation of free radicals
Published in Journal of Applied Water Engineering and Research, 2020
Slimane Merouani, Oualid Hamdaoui, Nassim Kerabchi
The basic underlying phenomenon behind the effects of ultrasound in aqueous systems, whether physical, chemical, or biological, is acoustic cavitation (Bhangu and Ashokkumar 2016). The word cavitation refers to the formation, growth and collapse of vapor/gas bubbles in liquids subjected to power ultrasound (frequency: 20–1000 kHz) (Leighton 1994). Depending on the frequency and intensity of the ultrasound wave, the bubbles can undergo either a stable, oscillatory motion for several acoustic cycles or a transient motion comprising a single growth and collapse phase in one or less than one acoustic cycle (Thompson and Doraiswamy 1999). On collapse, the transient cavitation bubbles produce very high temperatures and pressures therein (∼ 5000 K and up to 700 atm) (Didenko et al. 1999; Suslick et al. 1999; McNamara et al. 2003; Rae et al. 2005; Ashokkumar 2011; Suslick et al. 2011; Merouani et al. 2014a), which are responsible for all observed effects of ultrasound, such as erosion, sonoluminescence, sonochemistry, etc. In aqueous solution, water vapor trapped inside the bubble dissociates into H• and •OH radicals which then conduct a reaction chain inside the bubble to yield other reactive species, i.e. HO2•, O and O3 (Yasui et al. 2005). These radical species are the origin of the chemical effect of ultrasound (Adewuyi 2001). Radical’s recombination yields hydrogen peroxide and hydrogen, which are the major products of water sonolysis (Merouani et al. 2010; Merouani et al. 2015).