Carbon-modified/embedded zero-valent aluminum microparticles will control electron release for efficient adsorption and degradation of aqueous pollutants

Zero-valent aluminum (ZVAl) possesses strong reducing power (E0(Al3+/Al0) = - 1.662 V) and can potentially reductively degrade a range of redox-active pollutants. Yet, activated ZVAl microparticles tend to release the electrons explosively under normal water conditions. As a result, the majority of the electrons are wasted due to side reactions, and moreover, ZVAl became rapidly passivated due to the formation of an inert layer of aluminum (hydr)oxides. To address this challenge, we modified commercial ZVAl microparticles with in-situ formed carbon derived from a common polysaccharide (alginate) upon pyrolysis. The optimal material, Al@Alg-C600, was obtained at a ZVAl/alginate mass ratio of 4/3 and a pyrolysis temperature of 600 degrees C. The pyrolysis not only activated the initially passivated ZVAl by defecting the passivation layer but also facilitated the preservation of the reactivity of ZVAl by coating newly exposed elemental Al with a thin layer of carbon and Al4C3. Compared to unprotected activated ZVAl, Al@Alg-C600 suppressed the initial explosive release of the electrons, and thus avoided the rapid loss of the reactivity. Al@Alg-C600 was able to remove both inorganic (Cr(VI) and organic (Reactive Black 5) over a wide pH range (3.00-11.00) and under highly oxic conditions (even with a DO of 69.84 mg/L). Al@Alg-C600 can be reused in multiple runs, especially for organic pollutants, and can be reactivated via the same pyrolysis process. The unique carbon-wrapped clustered ZVAl structure allows the material to be used in either batch or fixed-bed reactors to remove and reductively degrade a range of priority pollutants of low hydration energies.

Automated summary

In this study, the problem of the explosive release of electrons and rapid deactivation of zero-valent aluminum (ZVAl) in normal water conditions was successfully addressed by modifying commercial ZVAl microparticles with a carbon layer. The modified material, Al@Alg-C600, showed the ability to remove a variety of organic and inorganic pollutants under a wide range of conditions, and it could be reused and reactivated. The unique carbon-wrapped clustered ZVAl structure of this material has great application potential.