Sonochemistry Ultrasonics Research Group
We work with the propagation of ultrasound waves through a liquid medium that can lead to the creation of acoustic cavitation bubbles. These cavitation bubbles can emit light (sonoluminescence) and undergo violent collapse to generate extreme temperatures (> 5000 k), pressures (> 1000 atm) and jet velocities (up to 120 m/s has been reported).
It is these remarkable conditions that allow ultrasound to create unusual physical and chemical properties ideal for degradation of pollutants, synthesis of polymers and nanomaterials. However, to capitalise on these effects, one needs to understand how the physical and chemical properties vary under different solution and sonication conditions such as frequency and power.
Ultrasonic processing has applications in heterogeneous and homogeneous environments, and is able to augment chemical processes via the well-known mechano acoustic and sonochemical effects from the cavitation bubbles. This can enhance radically driven processes, as well as mixing, emulsification and molecular accessibility.
The mechanism and level of enhancement is influenced by the reactor configuration (geometry, transducer type, frequency, flow, power) and the characteristics of the medium (gases present, solid loading, form of the solute, pH etc). Therefore it is of interest to investigate the effect of these parametric variations to further capitalise on the bubble dynamics to enhance the desired ultrasonic effects.
The equipment we have available is able to investigate the various parametric effects of ultrasound on a multitude of processes, aimed at understanding the fundamental interactions toward process improvement and optimisation.
We use ultrasound to enhance the extraction of natural products from plants and food waste/by-products. Ultrasound is well known to enhance extractions in pharmacuetical and cosmetic industries and can reduce the time taken and chemical loading required, hence can be used to promote green chemistry.
We also research into dye uptake using ultrasound and have shown that ultrasound can enhance dyeing of goat hair, with shorter dyeing times and better hair colouration.
A sonochemically active bubble within a solution has three areas of interest, inside the bubble, the bubble-liquid interface and the bulk solution. The inner bubble may be considered as a little reactor with plasma-like reactions facilitated within the extreme conditions present.
The characteristics of the bubble are effected by the wave frequency and power, solution characteristics and gases present. What happens in the inner bubble, will then effect which species are produced and diffuse into the interfacial region, which is characteristically at less extreme conditions than the inner bubble. Then, the bulk reactions are in turn a result of a combination of the inner bubble and interfacial reaction chemistry.
A focus of our research is to elucidate these effects under various gas atmosphere using a systematic method aimed at the identification of the most influential parameters. This can lead to an ability to control the reaction mechanism to obtain tuneable mini bubble reactors for targeted applications.
Crystallisation is a common technique adopted by many industries for separation and purification operations. However, this method can suffer from unpredictable nucleation rates and inconsistencies in product qualities. To remediate this, seeds are often added, but this can pose additional issues such as product contamination.
Ultrasound induced cavitation have shown to facilitate and control nucleation of crystals (sonocrystallisation), resulting in a more consistent and narrower size distribution of products. However, crystallisation and acoustic cavitation are two complex dynamic systems and when coupled together in this manner, the complexity is compounded. For this reason, mechanism behind crystallisation is still contentious.
At SURG, we are interested in understanding the mechanism of sonocrystallisation and determining the effective application of ultrasound in crystallisation processes. Some of the systems we are currently looking into are sodium chloride, paracetamol, lactose and dairy whey by-products.
The unique chemical and physical effects created by ultrasound cavitation bubbles provides an ideal environment for effective chemical synthesis of materials. Here in SURG we are interested in the use of ultrasound to synthesis, but not limited to, protein shelled microbubbles, nanoparticles and metal organic frameworks (MOFs).
Ultrasonic effects have potential applications in the processing of lignocellulose at various stages along the conversion process. Within SURG, we have interest in ultrasonic pretreatment of lignocellulose, as well as the ultrasonic enhancement of the conversion of fractionation products.
Pretreatment of lignocellulose occurs in a heterogeneous solution where the collapse of cavitation bubbles can enhance the accessibility of biomass components from pits and cracking observed on the surface of the biomass. In addition, the chemical effects of ultrasound have applications for enhanced purification of the polymeric component of the lignocellulosic biomass.
Ultrasound is able to effect cells in physically from micro jetting and shear forces and chemically via ultrasonically-produced radicals. The microjets and shear forces produced in the sonicated solution are able to break the cell wall, killing or deactivating the cell.
This can enhance cell breakage or deactivation of cell growth In addition the shear forces from the cavitating bubble can lead to a pulsation of the cell which can weaken the cell wall and enhance the permeability of the cell membrane. This has application in the ability of the delivery of drugs in the case of cancerous cells, or for delivery of anti-microbial in the case of bacteria.
The cells are also subject to the radical oxidative species (ROS) produced by ultrasound. The production of ROS can enhance anti-microbial effects of ultrasound on bacteria and can interact positively with therapeutic agents or antibiotics that work via a ROS – initiated mechanism.
The efficacy of ultrasound is dependent on the targeted application, and can be influenced by the means and mode of the ultrasound applied to the cells of interest. Within SURG we have teamed up with the BB group (link) to investigate ultrasound in different biological applications. This includes the deactivation of bacteria in food systems and the treatment of pancreatic cancer using novel therapeutic agents.
With fresh water making up less than 1% of the world’s water, coupled with the ever growing demand and increase in water pollution, industries are forced to meet strict waste water discharge guidelines.
The conditions produced by cavitation bubbles have shown to accelerate the degradation of certain pollutants and within SURG we are investigating the use of ultrasound for the treatment of per- and polyfluoroalkyl substance (PFAS) contaminations, abattoir waste, pharmaceutical drugs in hospital wastewater, sulphates and phenols.
Select the profiles below to view their publications.
Dr Devendra Saroj
Reader and Head of Centre for Environmental Health and Engineering (CEHE), Director of Research - Department of Civil and Environmental Engineering