The role of cellulose nanocrystals in stabilizing iron nanoparticles

Abstract

Iron nanoparticles are strong reducing agents with a variety of applications. Their reactivity is governed by their valence state as well as their available surface. As such their widespread use is limited by their colloidal instability. This work investigated the role of cellulose nanocrystal stabilizers on the shape, size, density, and colloidal stability of iron nanoparticles. Colloidally-stable zero-valent iron nanoparticles (nZVI) were synthesized through a classical redox reaction of iron sulfate using cellulose nanocrystals (CNCs) as stabilizers. Spherical nZVI nanoparticles were formed with high surface roughness and mean size of ~ 130 nm. CNC:nZVI nanoparticles made with greater amounts of CNCs were measured to have lower solidity, indicating that these nanocomposite nanoparticles are less compact. Low solidity nanoparticles were observed to be irregular aggregates composed of ~ 10 nm nZVI particles stabilized on CNCs. CNC:nZVI nanoparticles remained colloidally stable after more than 40 days. Mobility studies confirmed both their colloidal stability under flow conditions as well as the strong interaction between CNCs and nZVI as demonstrated by achieving over 97% breakthrough within 2 pore volumes and no measurable particle retention, respectively. It was hypothesized that cellulose nanocrystals play a triple role in nZVI stability: as a foreign surface to encourage stable nucleation over fast aggregation, as a capping agent to control particle growth, and as a stabilizer to prevent iron nanoparticles from aggregating into colloids. Our results highlight the impact of the presence of CNCs on the rates of nucleation, growth, aggregation, and aging of nZVI particles, demonstrating that CNCs have the potential to act as nZVI stabilizers.