Oxidative Capacity of Oxygen Nanobubbles and Their Mechanism for the Catalytic Oxidation of Ferrous Ions with Copper as a Catalyst in Sulfuric Acid Medium

Abstract

Nanobubble (NB) technology has demonstrated the potential to enhance or substitute for current treatment processes in various areas. However, research employing it as a novel advanced oxidation process has thus far been relatively limited. Herein, we focused on the oxidative capacity of oxygen NBs and investigated the feasibility of utilizing their enhanced oxidation of ferrous ions (Fe 2+ ) in a sulfuric acid medium when using copper as a catalyst and their effect mechanism. It was demonstrated that oxygen NBs could collapse to produce hydroxyl radicals (•OH) in the absence of dynamic stimuli using electron spin resonance spectroscopy, and methylene blue was used as a molecular probe for •OH to illustrate that NB stability, determined by their properties, is the critical factor affecting •OH release. In subsequent Fe 2+ oxidation experiments, it was discovered that both strong acidity and copper ions (Cu 2+ ) contribute to accelerating the collapse of NBs to produce •OH. While •OH derived from the collapse of NBs acts on Fe 2+ , the molecular oxygen generated homologously with •OH will further activate the catalytic oxidation of Fe 2+ by interacting with Cu 2+ . With the synergistic effect of the above two oxidationdriven mechanisms, the oxidation rate of Fe 2+ can be significantly increased up to 88% due to the exceptional properties of oxygen NBs, which facilitate the formation of an atmosphere with persistent oxygen supersaturation and the generation of oxidation radicals. This study provides significant insight into applying NBs as a prospective technology for enhanced oxidation processes.

Rational Design and Evaluation of Photoactive Molecularly Imprinted Nanoparticles for Tetracycline Degradation Under Visible Light

“…To further test the degradation efficacy mediated by photoactive polymeric nanoparticles, we conducted additional photodegradation experiments using TC solutions supplemented with oxygen nanobubbles (ONBs). ONBs are stable nanoscale aggregates of molecular oxygen with intrinsic photodynamic activity and promissory applications as enhancers of advanced oxidation processes without secondary pollution effects at minimal costs. − ONBs have been reported to improve the photodegradation of antibiotic pollutants such as oxytetracycline under visible light through “high mass transfer and generation of reactive radicals during the nanobubble collapse” including hydroxyl radical, superoxide radical, and singlet oxygen . ONBs have also been reported to interact strongly with positive nanoparticles by nucleation at the solid–liquid interface. , This evidence offers the opportunity to test whether ONBs can synergize with MINs to achieve higher TC degradation ratios.…”

“…ONBs are stable nanoscale aggregates of molecular oxygen with intrinsic photodynamic activity and promissory applications as enhancers of advanced oxidation processes without secondary pollution effects at minimal costs. 70 − 74 ONBs have been reported to improve the photodegradation of antibiotic pollutants such as oxytetracycline under visible light through “high mass transfer and generation of reactive radicals during the nanobubble collapse” including hydroxyl radical, superoxide radical, and singlet oxygen. 75 ONBs have also been reported to interact strongly with positive nanoparticles by nucleation at the solid–liquid interface.…”

Polarizing Perspectives: Ion- and Dipole-Induced Dipole Interactions Dictate Bulk Nanobubble Stability

“…Bulk nanobubbles (NBs) are a class of materials that consist of bubbles with dimensions on the nanometer scale that have captured the interest of scientists and engineers from a variety of disciplines. − These materials have found application in an assortment of areas, such as water treatment and disinfection, − agriculture and hydroponics, − and most recently, advanced chemical oxidation processes. − Unlike bubbles of larger diameter (>1 μm), NBs are known to be stable in water for long periods of time. − The standard model currently adopted in the literature to explain this stability involves a balance between the Laplace pressure and the pressure from electrostatic interactions at the NB-solvent interface. In general, we can express this balance using the Young–Laplace equation as follows: P 0 + P YL = P NB + P e where P 0 is the pressure of the atmosphere outside the solution, P YL is the Laplace pressure, P NB is the pressure inside the NB, and P e is the electrostatic pressure.…”