The influence of the ammonia concentration and the water content on the water sorption behavior of ambient pressure drie
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ORIGINAL PAPER: NANO- AND MACROPOROUS MATERIALS (AEROGELS, X E R O G E L S , CR Y O G E L S , E T C. )
The influence of the ammonia concentration and the water content on the water sorption behavior of ambient pressure dried silica xerogels Lukas Huber
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Silvia Paz Comesaña1 Matthias M. Koebel1 ●
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© The Author(s) 2020
Abstract Porous silica xerogels were synthesized within 10 h by a two-step sol–gel process under atmospheric conditions. In the first step, tetraethylorthosiloxane (TEOS) was hydrolyzed with water using sulfuric acid as a catalyst. In the second step, water and ammonia were added to the prehydrolyzed silica sol prior to the drying of the samples at 150 °C. The influence of the ammonia concentration and the water content on the physicochemical properties and the water sorption behavior of silica xerogels produced in the aforementioned way was investigated. The resulting silica xerogels were characterized by helium pycnometry, scanning electron microscopy, fourier-transform infrared spectroscopy, nitrogen sorption, and water sorption. It was shown that a higher ammonia concentration leads to an increased pore size of the silica xerogel which starts to adsorb water at a higher relative pressure. With an increased water content during gelation, the silica xerogel has a higher specific surface area and a higher water sorption capacity. Furthermore, silica xerogels can be tailored by a controlled addition of ammonia and water to have a higher water sorption capacity than the reference silica gel over the whole range of relative pressure. Graphical Abstract
Keywords
Adsorption Silica gel Xerogel Water sorption Sorben ●
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Supplementary Information Supplementary information The online version of this article (https://doi.org/10.1007/s10971-02005349-1) contains supplementary material, which is available to authorized users. * Matthias M. Koebel [email protected] 1
Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Building Energy Materials and Components, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
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Journal of Sol-Gel Science and Technology
Highlights ● Silica xerogels were synthesized within 10 h by a hydrolysis-condensation sol–gel process. ● An increased ammonia concentration during the condensation reaction leads to a higher porosity and larger average pore size of the silica xerogel. ● A higher water content during the condensation reaction increases the specific surface area and the water sorption capacity of the silica xerogel.
1 Introduction Adsorption heat pumps (AHPs) have gained a lot of interest in the past couple of decades since they are considered an environmentally friendly and cost-effective alternative to compressor-based heat pumps. AHPs utilize waste heat rather than electrical energy to provide space heating and cooling. Conventional AHPs are equipped with silica gel as an adsorbent, however, the widespread application of AHPs has not been achieved due to the low water adsorptivity and the poo
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