Nanomaterials for Environmental Solar Energy Technologies: Applications & Limitations

Environmental remediation and energy production are currently listed among the priority tasks by administration bodies, stakeholders and market competition. In this context, nanomaterials present competitive advantages in terms of performance and production costs. In the present critical review, the current state of the art of nanomaterials used in environmentally benign technologies exploiting solar irradiation such as H-2 production, water-splitting and photocatalysis are discussed. Factors determining the overall efficiency are articulated in a single "photophysical efficiency" equation. The physical meaning, limits and constraints of each factor are analyzed, updated and examples are discussed. The article highlights the main structure-function relationships in tandem with the limitations posed by the particle's physicochemical properties, production method, and the prerequisites posed by regulatory bodies and market needs. Several misconceptions are highlighted with regard to performance and yields that ultimately impact the end use of the nanomaterials. Current targets/limitations posed by the US Department of Energy are discussed as case studies. For context-coherence reasons, the present review focuses on metal and metal-oxide nanoparticles, i.e. carbon nanomaterials are not covered herein.