# Evaluation of Metal-Organic Frameworks as Potential Adsorbents for Solar Cooling Applications
## 4 MOF-Based Adsorption Cooling  
MOFs are novel crystalline porous materials with high porosity, flexible structure, and high adsorption capacity. The basic structure of an MOF is shown in Figure 7[52]. A typical MOF material consists of an organic linker and a metal ion. The choice of metal ion and organic linker offers a great variety of flexibility for different applications. The combination of metal ion and organic linker can be chosen depending upon the gases and how much is to be adsorbed/absorbed. These materials can have great heat and mass transfer potential depending upon the choice of structure. The associated properties of MOFs offer a broader look and possibility of developing the MOF-based cooling system. MOFs have recently attracted great interest in the gas storage sector, but there have been some reports of aspiring cooling applications. The potential use of MOFs for cooling applications needs to be explored because of their high mass loading capacity and relatively low heats of adsorption. They could prove to be an excellent adsorbent for adsorption chillers and desiccant dehumidifiers. The wide variety of topologies, the high scope of porosity and surface area [53; 54], and post/pre-synthesis functionalization possibilities [55; 56; 57; 58; 59] make MOFs suitable for a wide variety of applications such as storage [60; 61], adsorption and separation [62; 63; 64; 65], and catalysis [66; 67; 68; 69]. Computational studies have shown that the use of an MOF in adsorption chillers can help to achieve a coefficient of performance greater than one [70]. This is a great achievement because these systems always had a COP value of less than one. Only limited work is available for MOF-based cooling such as that of [PERSON] et al. [71], who depicted the potential use of MOFs in adsorption technology. The instability of MOFs is a hurdle for their use as an adsorbent for cooling applications but, to date, many stable MOFs have been developed. Many MOFs are less stable toward water [72; 73; 74; 75] but more stable towards methanol, ethanol, and ammonia [76]. That is why the choice of a suitable MOF material should also consider the nature of the working fluid. \begin{table}
\begin{tabular}{c c c} \hline \hline
**adsorbent** & **Properties** & **Potential Applications** \\ \hline \multirow{3}{*}{Activated Carbon} & Surface area: 500–1500 m\({}^{2}\)/g & Organic removal \\  & Porosity: 0.3–1.5 cm\({}^{3}\)/g & Separation of air \\  & & Purification of gases \\ \hline \multirow{3}{*}{Activated Alumina} & Surface area: 300–400 m\({}^{2}\)/g & Air separation \\  & Porosity: 0.25 cm\({}^{3}\)/g & Gas purification \\ \hline \multirow{2}{*}{Silica Gel} & Surface area: 100–1000 m\({}^{2}\)/g & Desiccant HVAC systems \\  & Porosity: 0.4–1.2 cm\({}^{3}\)/g & Humidity control of air \\ \hline \multirow{3}{*}{Molecular Sieves (Zeolites)} & \multirow{3}{*}{Surface area: 2800–3500 m\({}^{2}\)/g} & Deodorization of air \\  & Porosity: 1.4–2 cm\({}^{3}\)/g & Gas masks \\ \cline{1-1}  & & Wastewater purification \\ \cline{1-1}  & & Storage material \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of commonly used adsorbents and their potential uses. Figure 7: Basic structure of a metal–organic framework (MOF) [52]. [PERSON] et al. [77] tested 18 different MOFs in combination with either methanol or ethanol as a working pair for their potential applications in heat pumps. The results showed that thermodynamically CAU-3, UiO-67, and ZIF-8 can be employed with both methanol and ethanol but UiO-67 will show some instability during the operation. CAU-3 and ZIF-8 will be more effective and stable for utilization in adsorption chillers with both methanol and ethanol. [PERSON] et al. [78] observed and reported the behavior of microporous and mesoporous MOFs for their adsorption capacity. The saturation uptake capacity for microporous MOFs at low saturation pressure (P/P\({}_{\mathrm{o}}\) = 0.02) is observed to be greater than 4 mmol g\({}^{-1}\).