Hierarchical embedding of micro-mesoporous MIL-101(Cr) in macroporous poly(2-hydroxyethyl methacrylate) high internal phase emulsions with monolithic shape for vapor adsorption applications Martin Wickenheisser, Christoph Janiak ⇑ Institut für Anorganische Chemie und Strukturchemie I, Universitätsstraße 1, 40225 Düsseldorf, Germany article info Article history: Received 3 September 2014 Received in revised form 14 October 2014 Accepted 22 November 2014 Available online 4 December 2014 Keywords: Metal-organic framework Hierarchical porosity High internal phase emulsion (HIPE) Monoliths Heat transformation abstract Shaping metal-organic frameworks (MOFs), normally obtained as powders or microcrystals, e.g., into monoliths is one indispensable factor for potential applications of MOFs. MIL-101(Cr) as a water stable micro- and mesoporous network was successfully embedded into a macroporous and monolithic oil– water (o/w) high internal phase emulsion (HIPE) foam, based on crosslinked poly(2-hydroxyethyl meth- acrylate). These hierarchical and mechanically stable monolithic composite materials with up to 59 wt% of MIL-101(Cr) show higher methanol and water vapor uptake capacities compared to the pure HIPE. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction MOFs (metal-organic framework) are three-dimensional per- manently porous networks based on metal ions or metal clusters, connected by organic ligands [1,2]. Metal organic frameworks have uniform micropore structures with high surface areas and large pore volumes. An immense research advancement has been made in the utilization of MOFs since the past 10–15 years [3–5], such as catalysis [6–9], gas storage [10–13] and gas separation [14–18]. Numerous overview or review articles has been published in the last years indicating the increasing interest in MOF chemistry [19–24]. Microporous materials with a high vapor uptake capacity are of increasing interest for low temperature heat transformation appli- cations in thermally driven adsorption chillers (TDCs) or adsorp- tion heat pumps (AHPs). TDCs or AHPs could be an alternative to traditional compressor air conditioners or heat pumps run by elec- tricity or fossil fuels. The use of solar or waste heat as the driving energy in TDCs or AHPs can minimize primary energy consump- tion. In Fig. A.8 the thermodynamic principle for adsorption chillers or heat pumps is displayed [25–31]. In the case of a cooling appli- cation Q evap is used as useful cold and Q ads and Q cond are released to the environment. During a heat pump application Q evap can be delivered from the environment at low temperature and Q ads and Q cond will be useful higher temperature heat. The working fluid is exchanged reversibly between the evaporation/condensation ves- sel and the porous material where ad- and desorption takes place. Alcohols like methanol or water are suitable, vaporizable working fluids due to their high evaporation enthalpies. Water is often the working fluid of choice because of its high evaporation enthalpy (2440 kJ kg 1 at 25 °C) and non-toxicity despite the need to work under vacuum because of the low vapor pressure of only 3.17 kPa at 25 °C. Alcohols like methanol and ethanol are interest- ing alternatives because of the lower boiling points so that evapo- rator temperatures below 0 °C are possible [32]. New research developments aim for new porous materials as adsorbents due to disadvantages of classical adsorbents (silica gels, zeolites, aluminophosphates) [33–38]. Zeolites have a high affinity to water and therefore require high desorption temperatures with a not too high water uptake capacity. Silica gels have a lower hydrophilic character than zeolites which leads to lower desorp- tion temperatures but a low water loading lift in the ideal interval 0.05 < P  P 0 1 < 0.35. Hence, MOFs have been studied as adsorbents for cycling vapor sorption (mostly water and methanol) over the last years [33–35,39–50]. MIL-101(Cr) (Fig. A.9) [51–53] is a prom- ising material for potential heat transformation processes with its high BET surface (>3000 m 2 g 1 ), the large water and methanol http://dx.doi.org/10.1016/j.micromeso.2014.11.025 1387-1811/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Tel.: +49 2118112286. E-mail address: janiak@uni-duesseldorf.de (C. Janiak). Microporous and Mesoporous Materials 204 (2015) 242–250 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso