Fine oil droplets and trace level of hydrocarbons in the oil and gas produced water pose technical challenges to their sustainable treatment and disposal. With the increasing demand from environmental stewardship to protect our natural environment, more efficient treatment processes to separate oil and hydrocarbon from water are critically needed. A promising solution to address this issue could be developed by tailor designing and surface engineering the so-called “Janus Particles,” a particle with two distinct physical or chemical properties. This proposal will focus on using different heterogeneous nucleation mechanisms and surface functionalization methods to design and fabricate a new generation of hybrid nanocrystals that have either multicomponent inorganic crystals or polymer-modified organic-inorganic nanoparticles with spatially controlled distribution of functionalities such as olephilic and hydrophilic. The developed Janus particles also possess magnetic and catalytic properties for easy collecting of oil/pollutant laden particles followed by catalytically activated degradation and regeneration.