Near-complete (>99.9%) removal of dissolved oxygen from water via nanobubbles: A sustainable and high-efficiency process under standard atmospheric conditions

• N 2 nanobubbles (NBs) can readily decrease a dissolved oxygen (DO) level to < 5 ppb. • DO removal with N 2 NBs is effective for a broad range of initial DO level < 50 mg/L. • CO 2 NBs are more difficult in reaching DO level < 0.03 mg/L than N 2 NBs. • NBs experience significant Ostwald ripening at DO of < 5 ppb to 0.03 mg/L. Controlling and reducing dissolved gas levels is vital for process quality, equipment integrity, and product stability. However, current techniques for dissolved gas removal are generally limited by high costs, process inefficiencies, the potential to introduce undesirable solids, and the requirement for extreme pressures and temperatures. Here, we experimentally demonstrate that environmental-friendly nanobubbles (NBs), with a mean bubble size ≤ 50 nm and number density ≤ 2 × 10 10 bubbles/mL, can efficiently remove dissolved oxygen (DO) from water under standard atmospheric pressure and temperature conditions. Notably, N 2 NBs readily reduce DO concentrations to near-zero levels (<5 ppb, or effectively “below detection limit”), achieving a > 99.9% DO removal, a level unattainable by conventional N 2 gas bubbling. The NBs-driven DO removal is highly effective across a broad range of initial DO levels, up to ∼ 49 mg/L. While CO 2 NBs can reduce DO levels to ≤ 0.03 mg/L, the results indicate N 2 NBs are superior due to the inherent physicochemical properties of the gas. Mechanistically, NBs significantly alter gas exchange dynamics by enhancing gas transfer and Ostwald ripening, leading to O 2 outgassing as NB gas dissolves into the water. The experimentally observed DO removal efficiency aligns closely with our first-order numerical simulations, which account for the diameter and number density of the generated NBs. Furthermore, our method is reversible, allowing DO levels to naturally re-equilibrate under atmospheric conditions. These findings highlight that NBs offer a promising, environmentally friendly, and cost-effective approach for dissolved gas replacement, opening new avenues for sustainable water treatment.