Pseudo-Janus Zn/Al-based nanocomposites for Cr(VI) sorption/remediation and evolved photocatalytic functionality

•Janus-like behaved Zn/Al composite oxide were fabricated.•Cr(VI) remediation/sorption phenomena was authenticated.•Subsequent evolved photocatalysis was demonstrated.•Simultaneously rendering of less toxic Cr(III) was proved.

An ingenious strategy for the recycling of Cr(VI)-enriched sorbents is presented herein. These adsorbents, which are Zn/Al-based nanocomposites with a Zn to Al ratio of 4:1, have shown great promise as a type of “Janus material” in which they not only behave as a sorbent, but a photocatalytic function can be evolved by calcination. The Zn/Al composite sorbents were prepared via a co-precipitation method followed by calcination at 500 °C to show good removal capacity for Cr(VI) even after repeated absorption cycles. The Cr(VI)-saturated adsorbent could then be transduced to a highly crystallized Cr(VI)-containing ZnO/ZnAl2O4 nanocomposite by calcination at 900 °C. It was found that the resultant Cr(VI)-containing ZnO/ZnAl2O4 nanocomposites possess a photocatalytic performance that is very similar to titania P25 and not compromised by the co-localization of Cr(VI). In fact, the adsorbed Cr(VI) is sufficiently well bound to not easily release into aqueous medium, while also, it can be serendipitously photo-reduced to a less toxic valency, i.e., Cr(III), after the application of the nanocomposites as a photocatalyst. Therefore, the nanocomposites exhibit a very promising Janus-like chemical behavior as exhibited by absorption of highly toxic Cr(VI) and subsequent evolved photocatalysis and remediation of Cr(VI) to Cr(II).

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