| Micro-nano/bubbles are tiny cavities filled with gas in a liquid.According to the difference of bubble diameter,it can be divided into macro bubble,micro bubble and nano bubble.According to the environment and physical characteristics of the nanobubbles in the liquid,they can be divided into interface nanobubbles and bulk nanobubbles.Compared with macrobubbles,micro-nano/bubbles have different characteristics,such as large specific surface area,long hydraulic retention time,high mass transfer efficiency,high interface zeta potential,and generation of ·OH.Because of its special physical and chemical properties,micro-nano/bubbles have important application value in many scientific and technical fields such as water treatment,mineral flotation,agriculture,biomedical engineering and nano materials.Therefore,the basic research of micro-nano bubbles is of great significance for its application.In this paper,two methods have been used to generate micro-/nanobubbles: ultrasonic cavitation and micro-/nanobubble generators.The size distribution,residence time,zeta potential,and ·OH of micro-/nanobubbles by dynamic light scattering and electron paramagnetic resonance technology are investigated.After in-depth research,the following conclusions were obtained:(1)The probe-type ultrasonic generator successfully produced stable bulk nanobubbles with a size between 500-1000 nm.The nanobubbles had good stability within 48 hours,and the zeta potential did not change significantly within 48 hours.By studying the effects of ultrasonic time and ultrasonic power on nanobubbles,it was found that the size of nanobubbles increased significantly with increasing ultrasonic time and power.The size and zeta potential of bulk micro-/nanobubbles are mainly affected by pH,ion concentration,and surfactant.Changing the above factors can adjust the size and zeta potential of nanobubbles.(2)The micro-/nanobubble generator has been used to generate micro-/nanobubbles with air and oxygen as the gas source,respectively,and the particle size of the micro-/nanobubbles is 100-500 nm measured by DLS.For two gases,air and oxygen,the type of gas has no significant effect on the particle size distribution of micro-/nanobubbles.The particle size of the micro-/nanobubbles decreases with the increase of the aeration time.When the aeration time exceeds 8 min,extending the aeration time again cannot reduce the particle size of the micro-/nanobubbles.(3)The concentration of ·OH produced by micro-/nano aeration was measured by EPR spectroscopy using DMPO as a capture agent.The influence parameters of ultrasound on the micro-/nano aeration and ·OH concentration are mainly ultrasound time and ultrasound power.The amount of ·OH produced is directly proportional to the ultrasonic irradiation time,that is,under the condition that other ultrasonic parameters are fixed,the production rate of ·OH is constant.Ultrasonic power is an important factor affecting the production of ·OH.Increasing the ultrasonic power can promote the production of ·OH in micro-/nanobubble aqueous solution.However,when the ultrasonic power is greater than 225 W,increasing the ultrasonic power again will not increase the concentration of ·OH.The EPR signal of DMPO-OH was not detected in the micro-/nanobubble aqueous solution generated by using air as the air source,indicating that no ·OH was produced in the solution.It was found that micro-/nano aeration with oxygen as the gas source can promote the production of ·OH,and the production of ·OH in the oxygen micro-/nanobubble aqueous solution is directly proportional to the aeration time. |
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