## 4 MOFs as Smart Carriers and Delivery Systems of Sensitive Volatile Compounds
### Zifs  
ZIFs, particularly ZIF-8 and ZIF-67, have demonstrated significant potential as carriers for essential oils (EOs) in agrifood applications, offering controlled release and enhanced stability [82]. ZIF-8, presenting a high specific surface area, has been found to be an efficient nanocarrier for citral (CT). Encapsulating citral in ZIF-8s' framework can significantly delay its volatilization and enhance its stability. Furthermore, ZIF-8 provides a pH-responsive controlled release, releasing CT under specific pH conditions. This is particularly useful, considering the effect of pathogenic fungi at the pH levels of specific plants and crops. More specifically, CT@ZIF-8 exhibits strong antifungal activity against _Magnaporte oryzae_, _Botryosphaeria dothidea_, and _Fusarium oxysporum_. It should be noted that the hybrid exhibits lower EC50 values compared to CT alone, indicating its enhanced antifungal action. The pH-responsive release is crucial. Acidic conditions were found to accelerate CT release, following non-Fickian diffusion involving both drug diffusion and ZIF-8 framework disruption. On the other hand, neutral and alkaline pH environments result in slower release via Fickian diffusion, while the structure of ZIF-8 remains intact. Additionally, encapsulation of citral in ZIF-8s' pore was found to be efficient towards photodegradation, ensuring prolonged effectiveness, while the high loading efficiency and controlled release contribute to sustained control efficacy against fungal infections. The bioactivity evaluation demonstrated that CT@ZIF-8 exhibited enhanced antifungal activity compared to free CT, as evidenced by lower EC50 values against _Magnaporte oryzae_, _Botryosphaeria dothidea_, and _Fusarium oxysporum_. Notably, after 3 days of treatment, CT@ZIF-8 maintained effective control of rice blast and soft rot infections, achieving inhibition rates of 75.76% and 63.69%,respectively [142]. Furthermore, ZIF-8 is also employed for the encapsulation of thymol and limonene, demonstrating its versatility as a porous medium for EO delivery. The sustained release of thymol from ZIF-8 inhibits the growth of _Colletotrichum musae_ by continuously exposing fungal cells to the antifungal compound. Thymol's antifungal properties, combined with ZIF-8's-controlled release, maintain efficacy for extended periods, showcasing ZIF-8's potential in preserving agricultural products. These examples highlight the effectiveness of ZIFs in enhancing the stability and controlled release of EOs, offering promising solutions for antifungal and antimicrobial applications in agrifood sectors [160].  
Similarly, ZIF-67 has been employed for the encapsulation and controlled release of citral [82]. Citral@ZIF-67 offers a green and sustainable alternative to traditional mildew preventives for bamboo. The encapsulation of the citral EO in ZIF-67, enables a slow-release mechanism, maintaining its antimildew properties over an extended period, even under high temperature and humidity. Encapsulation of citral in ZIF-67 enhances the EOs' stability while protecting it from oxidation and volatility. Thus, it contributes to intrinsic antibacterial properties against _E. coli_ and _S. aureus_. The Citral@ZIF-67 hybrid is produced in a one-step reaction, which involves mixing 2-methylimidazole with cobalt nitrate, citral, and solvents, resulting in citral encapsulation within the ZIF-67 cage while the framework is formed. The release of citral follows a slow-release mechanism governed by Fickian diffusion as it was also reported for ZIF-8 above. This process ensures sustained antimicrobial activity without specific external stimuli. The uniform distribution of Citral@ZIF-67 within the bamboo structure provides consistent protection, strengthening the bamboo's durability and extending its useful life [157].