Ž . Applied Clay Science 15 1999 367–380 Adsorption–desorption of water vapor by natural and heat-treated sepiolite in ambient air F. Caturla, M. Molina-Sabio, F. Rodriguez-Reinoso ) Departamento de Quımica Inorganica. UniÕersidad de Alicante Apartado 99. 03080 Alicante, ´ ´ Spain Received 17 December 1998; accepted 6 May 1999 Abstract Ž . A sepiolite from Yunclillos Spain has been heat-treated in air in the temperature range of 110–5008C. The heat treatment up to 2008C does not modify the volume of micropores or the non-microporous surface area of the original sepiolite. As the temperature of the heat treatment increases to 5008C there is a decrease in the non-microporous surface area and a loss of microporosity, the original structure not being restored after rehydration for sepiolite heat-treated at 400 and 5008C. In order to analyze the behavior of sepiolite as controller of humidity, working Ž . cycles of 24 h with variable temperature and relative humidity RH have been simulated and the experimental results have been compared with the adsorption isotherms of water vapor in air. These isotherms are a very good guide to predict the amount of water that the sepiolite can retain–liberate when the RH of the air is modified. Considering the shape of the isotherms, showing a faster increase in the amount of water retained at RH )50%, it is possible to deduce that sepiolite will be especially useful as controller of humidity in environments where the RH is Ž . Ž . usually very high 80–90% and sporadically is considerably decreased below 60% . On the other hand, the thermal treatment of sepiolite at 5008C does not improve the capacity to control the humidity of the environment. q 1999 Elsevier Science B.V. All rights reserved. Keywords: sepiolite; water adsorption; heat-treatment; humidity control ) Corresponding author. Fax: q34-96-590-3454; E-mail: reinoso@ua.es 0169-1317r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-1317 99 00030-7