What is the process of attracting and holding particles to a surface called?

The process of attracting and holding particles to a surface is called adsorption. This phenomenon occurs when molecules from a gas or liquid adhere to the surface of a solid or liquid, forming a film of the adsorbed substance. It differs from absorption, where one substance permeates or becomes integrated into another. In adsorption, the concentration of adsorbate is higher at the surface than in the bulk phase, leading to distinct boundary layers.

This concept is critical in various applications, particularly in water treatment processes, where adsorption can help remove contaminants by collecting them on filter materials or activated carbons. The effectiveness of adsorption can depend on several factors, such as the surface area of the adsorbent, the nature of the adsorbate, and environmental conditions like temperature and pH.

The other processes listed—absorption, filtration, and precipitation—refer to different mechanisms of interaction between substances and do not involve the selective surface attraction characteristic of adsorption.