Controlled release of H 2 S and NO gases through CO 2 -stimulated anion exchange

Difficulties related to handling gases are a common bottleneck for applications. Although solid materials that release gas molecules under external stimuli exist, they require an external energy or a device for reliable operation. Herein, we report a CO 2 stimulus for controlled release of p.p.m.-level functional gases from solid materials. A CO 2 -preferential anion-exchange property of layered double hydroxides and redox reactions in gas molecules are combined to release various gases (including H 2 S and NO) under ambient air from HS − and NO 2 − -incorporated layered double hydroxides, respectively. The profiles of gas release are mainly governed by the difference of p K a between H 2 CO 3 and resulting acids (formed through protonation of interlayer anions), and are not so susceptible to the variation of relative humidity in air. Moreover, structural modulation of solid materials enables fine control of the gas release profiles. The use of safe, ubiquitous, and nearly constant (~400 p.p.m. in atmosphere) CO 2 stimulus offers broad applications for functional gases.