Active colloids are synthetic micro- or nanoparticles that harvest ambient energy (e.g., chemical fuels, light, magnetic fields, ultrasound) to fuel their self-propelled motion through liquids. In the twenty years since they were first introduced, active colloids have attracted interest from both the basic science (as a convenient model system for active matter) and applied science communities (for applications such as removing pollutants from water, assisting microsurgery, delivering drugs to hard-to-reach places like tumors, and more). Thus far, the field has largely relied on poisonous fuels (such as hydrogen peroxide or hydrazine) and non-biodegradable materials (such as metals or silica). In this talk, I will discuss ongoing efforts in our laboratory to develop active colloids from safe materials for sustainability applications.

First, we are investigating the extent to which active colloids, especially the “micro-stirring” generated by their motion, can accelerate the mixing of thermal energy in the surrounding liquid. Such “active heat transfer fluids” could function as the working fluid in particle-based solar collectors or as high-performance coolants for hybrid electric vehicle batteries or microelectronics. Second, our group has multiple ongoing projects with the goal of synthesizing active colloids from environmentally friendly materials for wastewater remediation. For example, we recently introduced “CoffeeBots,” which are active colloids derived from spent coffee grounds rendered magnetic by coating with iron oxide nanoparticles. We developed a low-cost synthesis method for CoffeeBots and demonstrate that they can efficiently remove methylene blue (as a model dye pollutant), oil, and microplastic pollutants. Their magnetic properties allow them to be recollected after treatment and they can be reused up to four times with minimal reduction in removal efficiency. CoffeeBots could be especially useful in regions where (i) clean water is an urgent unmet need and (ii) coffee is grown and/or consumed in large quantities.

The talk will conclude with an outlook for the next twenty years of this burgeoning field.

• Assistant Professor, George Mason University (2018 – present)
• Postdoctoral Associate (2013 – 2017) and Lecturer (2016 – 2017), MIT
• PhD, University of Washington (2013)
• BS (2007) and MS (2011), Arizona State University