Beamed UV sonoluminescence by aspherical air bubble collapse near liquid-metal microparticles

Abstract

Irradiation with UV-C band ultraviolet light is one of the most commonly used ways of disinfecting water contaminated by pathogens such as bacteria and viruses. Sonoluminescence, the emission of light from acoustically-induced collapse of air bubbles in water, is an efficient means of generating UV-C light. However, because a spherical bubble collapsing in the bulk of water creates isotropic radiation, the generated UV-C light fluence is insufficient for disinfection. Here, we show that we can create a UV light beam from aspherical air bubble collapse near a gallium-based liquid-metal microparticle. The beam is perpendicular to the metal surface and is caused by the interaction of sonoluminescence light with UV plasmon modes of the metal. We calculate that such beams can generate fluences exceeding 10 mJ/cm 2 , which is sufficient to irreversibly inactivate most common pathogens in water with the turbidity of more than 5 Nephelometric Turbidity Units.Introduction.-The ability of UV-C light (200 − 280 nm) to inactivate bacteria, viruses and protozoa is widely used as an environmentally-friendly, chemical-free and highly effective means of disinfecting and safeguarding water against pathogens responsible for cholera, polio, typhoid, hepatitis and other bacterial, viral and parasitic diseases 1 . UV-C light inactivates pathogens through absorption of radiation energy by their cellular RNA and DNA prompting the formation of new bonds between adjacent nucleotides. This results in a photochemical damage that renders pathogens incapable of reproducing and infecting 1 .However, some pathogens can recover from photochemical damage when the initial UV dosage (fluence) is not sufficiently high 1 . Thus, the fluence must exceed 5 and 10 mJ/cm 2 , respectively, to inactivate 99% and 99.9% of Giardia and Cryptosporidium pathogens 2 . These specifications are for water purified from solid particles larger than 5 − 10 µm [turbidity less than 5 Nephelometric Turbidity Units (NTU)] 2 . Otherwise, particles can shield pathogens from the UV light, thereby allowing many pathogens to recover and infect.The filtration of natural water presents significant challenges for remote communities and developing nations 2 . Moreover, filtered water, dissolved iron, organic salts and the pathogen population itself absorb UV-C light. Therefore, a 50% UV radiation loss has been accepted as suitable for practical use 1 .To enable UV disinfection of turbid water, we use the effect of sonoluminescence-the emission of broadband UV light in acoustically-induced collapse of air bubbles in water 3,4 . Air bubbles suitable for sonoluminescence can be created in natural water 5 and we show that they can act as compact sources of germicidal radiation lo-

Nanostructured TiO2 cavitation agents for dual-modal sonophotocatalysis with pulsed ultrasound

“…Second, sonoluminescence from a collapsing bubble is a source of light [48] for photocatalysis of water into the aforementioned chemical species and other free radicals. The proximity of cavitation events relative to the TFNs is important as it has been reported that sonoluminescent emissions follow isotropic radiation behaviour [32] , [33] . Therefore, cavitation away from the TFNs surface will limit light interaction with the particles and reduce the efficacy of ROS generation.…”

“…These cavitation agents have been used in conjunction with photosensitizers recently to allow ROS generation with pulsed ultrasound [25] . Unfortunately, due to the limited fluence of sonoluminescence [32] , [33] , this sonochemical method requires cavitation to occur nearby the photosensitizer to maximize light interaction. This spatial decoupling of inertial cavitation events from photocatalytic sites remains a key limitation for heterogenous sonochemistry.…”

Acoustic frequency combs using gas bubble cluster oscillations in liquids: a proof of concept

“…Thus, it should be possible to use bubbles oscillating in water contaminated with pathogens (e.g. bacteria) to obtain information about their presence and concentration that are required for choosing an adequate strategy for their removal 73 or disinfection 74 , 75 .…”

Multibubble Sonoluminescence from a Theoretical Perspective

“…Boyd et al [ 114 ] numerically suggested that relatively strong UV light is radiated by the interaction of SL light with UV plasmon modes of the metal under the condition of aspherical air bubble collapse near a gallium-based liquid-metal microparticle. This may be applied to disinfecting water contaminated by pathogens such as bacteria and viruses.…”