The challenges of the global water shortage and increasing energy consumption are related problems that need to be addressed by creative solutions. This urges the development of multifunctional materials capable of combining water purification and sustainable energy recovery. MXene-quantum dot heterostructures have recently emerged as an outstanding dual-functional platform, which integrates the high electrical conductivity, hydrophilicity, and flexible surface chemistry of MXenes with the tunable optoelectronic features of quantum dots. Since their discovery in 2011, MXenes have garnered significant interest for energy storage due to their metallic conductivity (reaching 15,000 S/cm) and layered structures, driving modification strategies such as double-transition metal integration and heteroatom doping to overcome challenges like layer restacking and enhance capacitance up to 520 F/g. Concurrently, next-generation biosensors leverage advanced platforms including hexagonal boron nitride, covalent triazine frameworks, and surface-engineered M5X4 MXenes to achieve detection limits as low as 10 pM and sensitivities reaching 0.1 ppb through enhanced conductivity and multimodal detection capabilities. In this review, we discuss the synergistic construction of the MXene-quantum dots interface for dual functional purposes of both photocatalytic degradation of pollutants and electrochemical energy storage. While the distinctive 0D/2D and 2D/2D architectures enable high-speed charge transfer for depletion of surface charges as well as recombination suppression, the tailored surface terminations promote ion diffusion and pollutant capture. These heterostructures exhibit high efficiency in reactive oxygen species generation and can lead to the degradation of organic dye, heavy metals, and recalcitrant micropollutants, such as per- and polyfluoroalkyl substances (PFASs) and pharmaceuticals. Simultaneously, the addition of quantum dots brings pseudo capacitive characteristics and band gap engineering to supercapacitors, exhibiting high areal capacitances (>5 F cm-2) and Coulombic efficiencies >98%. Rigorous electronic coupling and long-lived charge separation are validated by operando Raman and femtosecond transient-absorption spectroscopy, which support the Z-scheme charge transfer processes driving dual-functionality. Such demonstrations of concepts, as flow-through photosupercapacitors, show that recovery of energy during solar-driven wastewater treatment is feasible. Although hurdles in material manufacturability and stability remain, progress in roll-to-roll production and AI-supported discovery should fast-track industrial uptake. Ultimately, the goal is to transition from proof-of-concept devices, like photorechargeable supercapacitors, to integrated, solar-powered systems that treat wastewater while offsetting their own energy consumption. Further, we discuss the future progress hinges on defect engineering at the interface, scalable fabrication of 3D macrostructures, and address the inherent stability challenges of both MXenes and quantum dots in aqueous environments.
Sarkar et al. (Sun,) studied this question.