In-Situ monitoring via alternation of electroconductivity for solar-driven water purification based on thermo-reversible pore size of hydrogel

A thermo-reversible electroconductive hydrogel composed of carbon dots (CDs)/TiO₂ fluorinated silica facilitates solar-driven water purification through pore size modulation, governed by a transition between hydrophobic and hydrophilic states. This transition is monitored by changes in electrical resistance. The inclusion of the photocatalyst TiO₂ in the CDs enhances hydrophilicity under visible light irradiation, enabling a reversible shift in surface affinity. This shift influences the volume transition of the CD-hydrogel within temperature ranges of 35 °C–55 °C and 0 °C–25 °C, corresponding to upper and lower critical solution temperatures, respectively. The hydrogel exhibits a temperature increase of 52.4 °C and a swelling ratio of 223 % upon solar light exposure. Water purification is achieved through water absorption and release cycles involving immersion and irradiation for 100 min, leading to a mass reduction of 2.435 kg/m². Moreover, bacterial contamination in water is purified and monitored through a measurable change in electrical resistance from 12.5 to 27.6 kΩ. These resistance variations enable real-time observation of water purification using electrochemical analysis and smartphone connectivity.