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.This research was funded by the National Funds by Foundation for Science and Technology (FCT) and by the FEDER funds through POCI-COMPETE 2020-Operational Programme Competitiveness and Internationalization in Axis I: Strengthening research, technological development and innovation (UID/QUI/00616/2013, UID/QUI/50006/2019, UID/Multi/00709/2013, UID/QUI/00313/2019, UID/CTM/50025, POCI-01-0145-FEDER-007491, POCI-01-0145-FEDER-007688, UID/CTM/50025, POCI-01-0145-FEDER-016884, PTDC/CTM-NAN/0956/2014, SAICT/PAC/0032/2015, POCI-01-0145-FEDER-016422, and NORTE-01-0145-FEDER-030858). R.F.P.P. acknowledges FCT-MCTES for SFRH/BPD/87759/2012 grant. R. Rego and M. Fernandes (UTAD, Vila Real) and E. Pereira (FCUP, Porto) are acknowledged for their assistance.