Plasma activated water works by introducing reactive species created by electrical plasma into the water, which then interact to form various beneficial compounds.
Understanding Plasma Activated Water (PAW)
Plasma activated water (PAW), sometimes referred to as plasma water or cold plasma treated water, is water that has been treated using electrical plasma. Plasma is often called the "fourth state of matter," consisting of a gas that is ionized, meaning it contains a significant number of free ions and electrons. When this energetic plasma interacts with water, it creates a unique solution with altered physicochemical properties.
The Activation Process
The core mechanism behind PAW's function lies in the interaction between the plasma and the water molecules.
- Plasma Generation: An electrical discharge (like a spark or glow) is used to generate plasma in contact with or in the vicinity of water.
- Air-Liquid Interface Reaction: As the plasma comes into contact with water, various Reactive Oxygen and Nitrogen Species (RONS) are produced at the air–liquid interface. This is a crucial step, as highlighted in the reference: "As the plasma comes into contact with water, various RONS are produced at the air–liquid interface."
- Secondary Species Formation: The generated primary reactive species then react with the water molecules and each other within the bulk water. These reactions lead to the formation of various secondary species that are crucial to the applications.
This complex interplay of species gives PAW its unique properties.
Key Reactive Species in PAW
The effectiveness of PAW is largely attributed to the cocktail of RONS it contains. These species can include:
- Hydrogen peroxide (H₂O₂)
- Nitrite ions (NO₂⁻)
- Nitrate ions (NO₃⁻)
- Ozone (O₃)
- Hydroxyl radicals (•OH)
- Superoxide radicals (O₂•⁻)
Table: Examples of RONS in PAW and Their Potential Roles
| Reactive Species | Chemical Formula | Potential Role/Property |
|---|---|---|
| Hydrogen Peroxide | H₂O₂ | Oxidizing agent, antimicrobial |
| Nitrite Ions | NO₂⁻ | Precursor to other reactive species, antimicrobial |
| Nitrate Ions | NO₃⁻ | Potential role in plant growth stimulation |
| Hydroxyl Radicals | •OH | Highly reactive oxidizing agent, germicidal |
| Superoxide Radicals | O₂•⁻ | Involved in oxidative processes, antimicrobial activity |
Note: The exact composition and concentration of RONS in PAW depend heavily on the type of plasma source, treatment time, gas mixture used, and water properties.
How These Species Contribute to PAW's Effects
The RONS in PAW alter the water's chemical properties, leading to various applications:
- Antimicrobial Action: RONS can damage cell membranes, proteins, and DNA of bacteria, fungi, and viruses, making PAW effective for disinfection. This mechanism is often non-specific, reducing the likelihood of microbial resistance.
- Plant Growth Stimulation: The presence of nitrogen species like nitrates can act as a nutrient source for plants. Additionally, RONS might trigger beneficial stress responses in seeds and plants, improving germination and growth.
- Other Applications: PAW is being researched for use in food processing (disinfection), wound healing, and even potential therapeutic applications due to its oxidizing and reactive nature.
In summary, plasma activated water works by converting dissolved gases and water molecules into a complex mixture of reactive species through contact with plasma, giving the water novel chemical and biological properties.
