Nanofluid Based on Glucose-Derived Carbon Dots Functionalized with [Bmim]Cl for the Next Generation of Smart Windows

The design of new advanced materials and technologies is essential for the development of smart windows for the next generation of energy-efficient buildings. Here, it is demonstrated that the functionalization of glucose-derived carbon dots with 1-butyl-3-methylimidazolium chloride results in a self-standing, water-soluble, viscous, reusable nanofluid with self-improving conductivity, thermotropy around 30–40 °C, and ultraviolet blocking ability. Its synthesis is straightforward, clean, fast, and cheap. At 36 °C (hot summer day), a sun-actuated thermotropic (TT) device incorporating a 95% w/w nanofluid aqueous solution exhibits a transmittance variation (ΔT) of 9% at 550/1000 nm, which is amplified to 47/31% via the surface plasmon resonance effect. An integrated self-healing system enabling independent sun-actuated TT and voltage-actuated electrochromic (EC) operation is also produced. The low-energy EC device offers bright hot and dark cold modes (ΔT = 68/64%), excellent cycling stability, unprecedented coloration efficiency values (−1.73 × 10⁶/−1.67 × 10⁶ cm² C⁻¹ (coloring) and +1.12 × 10⁷/+1.08 × 10⁷ cm² C⁻¹ (bleaching) at ±2.5 V), and impressive memory effect. The disruptive design and sustainable synthesis of the new nanofluid proposed here will foster the agile development of novel products with improved ecological footprint.