Spontaneous Microalgae Dewatering Directed by Retrievable, Recyclable, and Reusable Nanoparticle-Pinched Polymer Brushes

Selective capture and separation of solution borne planktonic cells is a ubiquitous challenge in diverse fields ranging from biofilm mitigation, cancer diagnostics, and water treatment to microalgae biofuels. Microalgae are promising feedstocks for carbon-neutral biofuels that will alleviate our repentant dependency on fossil fuels, but current technologies for dewatering microalgae add a prohibitive cost to the final products. We report here a nanoparticle-pinched polymer brush (NPPB) design that transforms ordinary polymer flocculants into supercoagulants by mimicking bacterial outer membrane vesicles in promoting bacteria coaggregation. Importantly, the NPPBs are retrievable via cost-effective magnetophoretic separation, recyclable after algae oil extraction and residual biomass removal, and reusable for repeated cycles of operations that significantly reduces the endless material cost of flocculants and their potential contamination of downstream processes and the environment. Using DLVO and self-consistent field theory to model the colloidal stability of microalgae and the dynamic response of polymer brushes, respectively, we reveal a fundamental transition from conventional chain-like polymer flocculants to NPPBs in modulating the interalgae pair potentials. Unlike the chain-like polymer flocculants that only induce slow microalgae dewatering with dose-sensitive flocculation dissociation equilibria, NPPBs direct rapid and irreversible microalgae coagulation. Although a minimum brush size on the NPPBs is predicted to initiate the coagulation, the benefit of increasing brush size quickly wanes and there is an optimal brush size beyond which the coagulation efficiency plateaus, which is consistent with our experimental observations. We anticipate that the concept of retrievable, recyclable, and reusable NPPBs is adaptable for capturing a broad range of live cells in solution.