Nanomaterial interfaces play a critical role in governing charge transport, surface reactivity, and mass transfer in energy and environmental systems. However, many existing designs fail to fully exploit interfacial effects, resulting in inefficient charge utilization in photocatalysis and limited surface reactivity in chemical processes, particularly under ambient conditions. In this talk, I present interface-centric nanomaterials strategies that demonstrate how deliberately designed interfacial architectures overcome these fundamental performance limitations across distinct application regimes. The first study introduces a light-driven photocatalytic ensemble in which a surface-degenerate semiconductor is hybridized with metal-organic framework (MOF) interfaces.1 This interfacial design promotes efficient photocarrier separation and directional transport, enabling enhanced sacrificial-agent-free hydrogen evolution during water splitting. The second study investigates a non-catalytic, metal-oxide-based interfacial nanoreactor rendered highly reactive through a reticular chemistry-driven approach.2 This design implements an activate-react-lock mechanism that enables rapid and efficient toxic gas sequestration. As a result, the system achieves high-capacity H2S capture under ambient conditions through interface-induced chemical activation that is unattainable in conventional metal oxide absorbents. Together, these studies demonstrate that nanomaterial interface design provides a versatile and powerful framework for advancing energy conversion and environmental remediation technologies, even without relying on sacrificial reagents or bulk material modification.