With the development of modern industry and modern economies, environmental problems, especially water pollution and water scarcity, have become the most serious global challenges.^1–4  In dealing with these challenges, various kinds of functionalized materials and devices are purposefully developed, fabricated, and utilized.^5–10  For instance, to clean up spilled oil from an oil leakage accident, absorbent materials have been widely used to selectively remove the oil from the aqueous system.^9,10  Shown in Figure 1.1 are examples of absorptive pads used in the Kalamazoo River oil spill (Michigan, US, 2010) and the Huangdao oil pipeline explosion incident (Qingdao, China, 2013). These absorptive pads are generally made of recycled cellulose or polypropylene, and have highly porous structures.¹⁰  Upon the oil removal, the pads, which have the absorbed oil, are collected and disposed of by direct burning. In other areas, such as wastewater treatment and seawater desalination, membrane-based separation processes are essential, which necessitate specifically functionalized membranes, such as nanofiltration (NF), ultrafiltration (UF), and reverse osmosis (RO) membranes.^11–16  Therefore, it is now a popular perception that the solutions to existing and future environmental problems highly rely on developments in material sciences.