Development of nanotechnology in the past 20 years has afforded a set of novel nanomaterials, tools and processes for energy and environment technologies. This talk will select exciting examples from my group from the past ten-year research on rational nanomaterials and device design to generate novel technologies for energy and environment. Examples include: 1) High energy density batteries based on novel Si, Li metal anodes and S cathodes, which can offer 10 time specific capacity of the existing lithium ion batteries. 2) Novel nanofiber filters for efficient removal of PM2.5 pollutants from the air yet still maintaining high air flux and light transmittance. 3) Conductive nanofilters for water disinfection with little energy consumption and fast treatment speed.