Synthesis of defective MOF-801 via an environmentally benign approach for diclofenac removal from water streams

Diclofenac is one of the most popular non-steroidal anti-inflammatory drugs (NSAIDs) which has been widely used worldwide. Despite its popularity, its accumulation in the environment poses danger to the aquatic lives and its removal from the environment is paramount important. Although some conventional adsorbents such as activated carbon can be readily used to address this issue, they usually suffer from low diclofenac adsorption capacity (around 200 mg g$^{−1}$), resulting in bulky adsorption systems. To overcome this problem, high performance materials such as metal organic frameworks (MOFs) can be employed. Here, we report that we synthesised defective MOF-801 for enhanced diclofenac adsorption via a simple and environmentally benign approach. Differing from a conventional MOF synthesis that usually requires the use of organic solvents at high temperature, the defective MOF-801 could be synthesised at room temperature and by changing the reaction medium from dimethylformamide to water. In addition, we have also successfully shown in this study that the defect concentration in MOF-801 can be rationally tuned by adjusting the modulator concentration (formic acid) in the synthesis solution. The resulting defective MOF-801 can then be used for environmental remediation, which we have shown here by employing them as an adsorbent for diclofenac removal from water streams. The enhanced adsorption of defective MOF-801 in comparison to its non-defective counterpart is due to the pore enlargement of the defective MOF-801 which provides a better pathway to access the adsorption sites. The maximum diclofenac adsorption capacity in a highly defective MOF-801 can reach as high as 680 mg g$^{−1}$, which is almost 4 times higher than its non-defective counterpart. This study then opens possibilities to engineer the MOF particles for environmental remediation