# Evaluation of Metal-Organic Frameworks as Potential Adsorbents for Solar Cooling Applications
## 7 The Future of MOF-Based Adsorption Cooling  
While maximum adsorption capacity of silica gel is good, the working pair of silica gel and water shows a low hydrophilic characteristic and has lower water uptake, especially at lower partial pressure. The limitations of available adsorbent materials arise in the need for the development of alternative materials with higher adsorption capacity, lower regeneration temperature, and stable nature at high temperatures. The above-mentioned literature shows that MOF materials can prove to be a good alternative to commercially available adsorbent materials for these cooling technologies.  
Currently, more than 20,000 MOF structures are known due to the flexible and rich variety of topologies associated with these crystalline materials. The porosity and surface area of these materials is increasing with the development of each new structure. Apart from that, the associated properties of these materials can be tuned by pre- or post-methods according to the desired behavior.  
The research for the use of MOFs for cooling applications is a topic of interest but is still at the initial stage. Water uptake capacity, regeneration temperature, and stability are the basic figure of merits for an MOF to be used for thermal cooling applications. New advancements are in progress to make these materials best fit for this technology but most of the developed MOFs still face issues of instability that need to be overcome. Most of the MOF compounds are synthesized at a lab-scale and only a few are available at commercial scale. These materials should be tested under real conditions to check their suitability for adsorption-based cooling. A summary of different adsorption and regeneration characteristics of MOF materials is presented in Figure 15. It can be observed that the MOF materials have a lower value of regeneration temperature and better sorption capacity, which are the positive attributes to be a good adsorbent for cooling applications. Despite promising sorption properties, the thermal stability of MOFs is still a challenge and only a few MOFs have been reported which are stable at higher temperatures. The effective use of these materials will allow the exploitation of yet mostly unused low-temperature heat sources of energy which will lower the use of carbon-emitting fuels.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Working Pair** & **Working Pressure** & **Working Temperature (\({}^{\circ}\)C)** & **Update Capacity (kgref/kgads)** & **Is Refrigerant** & **Is Refrigerant** & **Is Refrigerant** \\  & & **Temperature (\({}^{\circ}\)C)** & **(kgref/kgads)** & **Stable?** & **Toxic?** & **Flammable?** \\ \hline Activated carbon-NH\({}_{3}\) & Positive & 80 to 200 & 0.29 & Yes & Yes & Yes \\ \hline Activated carbon-Methanol & Vacuum & 80 to 100 & 0.45 & No & Yes & Yes \\ \hline Activated carbon-Ethanol & Vacuum & 80 to 120 & 0.19 & Yes & Yes & Yes \\ \hline Silica gel-H\({}_{2}\)O & Vacuum & 50 to 120 & 0.30 & Yes & No & No \\ \hline Zeolite-H\({}_{2}\)O & Vacuum & 200 to 300 & 0.17 & Yes & No & No \\ \hline SAPO 34-H\({}_{2}\)O & Vacuum & 80 to 90 & 0.29 & Yes & No & No \\ \hline MIL 101(Cr)-H\({}_{2}\)O & Vacuum & 90 to 140 & 1 & Yes & No & No \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characteristics comparison of adsorbent materials [128].