Absorbans

Absorbans is a generic term in materials science used to describe substances engineered to take up other materials or energy. In practice, absorbans may absorb gases or liquids into a bulk phase or adsorb onto surfaces, and it can also refer to materials that attenuate or store electromagnetic radiation.

Forms and composition: The class includes activated carbons, zeolites, metal-organic frameworks, silica gels, and polymeric networks. Key properties are high surface area, controlled porosity, chemical functionality, and stability under operating conditions. The choice of hydrophilicity or hydrophobicity influences selectivity toward particular species.

Mechanisms: Absorption relies on physical sorption (physisorption) or chemical bonding (chemisorption); capillary condensation can contribute in small pores. For optical absorption, electronic transitions within the material govern attenuation. Gas- and liquid-absorption depend on pore size, surface chemistry, and diffusion rates.

Applications: Absorbans are used for pollutant removal from air and water, gas separation (including CO2 capture), spill cleanup, and purification. They also underpin catalytic supports, energy storage materials, sensors, and protective textiles.

Synthesis and regeneration: Materials are prepared by activation of carbon, hydrothermal or solvothermal synthesis of zeolites or MOFs, polymerization, or templating. Regeneration typically involves desorption via heating, pressure swing, or solvent washing, enabling multiple cycles.

Limitations: Challenges include cost, material aging, limited selectivity, thermal and chemical stability, and environmental impact of disposal.