To overcome the shortage of conventional synthetic methods, such as long reaction time at high temperature and pressure (HTP) or poor performance at room temperature and pressure (RTP), a facile and economical strategy was employed to prepare high-performance ZIF-90 for the first time at RTP only by adding triethylamine (TEA). Herein, we successfully prepared ZIF-90 nanocrystals by a two-step stirring method within several minutes (5–30 min) and their structure parameters (e.g., BET surface areas, 916–1235 m2·g−1) were also tuned simultaneously, which were much better than reported samples prepared at RTP. Afterwards, by changing functional ligands, hydrophobic ZIF-90-CF3 with low surface energy was also designed. With the ligand side of aldehyde (–CHO) and trifluoromethyl (-CF3) groups on ZIF-90 and ZIF-90-CF3, the water vapor uptakes and adsorption heats decreased from 7.9 to 0.79 mmol·g−1 and 20.6 to 2.6 kJ·mmol−1, respectively. Additionally, a shaped ZIF-90-CF3/melamine foam (MF) composite with both hydrophobic and oleophilic properties exhibited extraordinary organic compounds (OCs)-water separation ability, including a high adsorption capacity (40.1–108.7 g‧g−1) towards various OCs. Furthermore, owing to its excellent compressibility and mechanical stability, the ZIF-90-CF3/MF composite can be regenerated by slightly squeezing the adsorbed OCs, indicating the potential for possible commercialisation of the derived MOF/MF composites for the efficient purification of wastewater.