Recycling Rusty Iron with Natural Zeolite Heulandite to Create a Unique Nanocatalyst for Green Hydrogen Production.

Corrosion-induced iron rust causes severe danger, pollution, and economic problems. In this work, nanopowders of FeO and FeO/zeolite are synthesized for the first time using rusted iron waste and natural zeolite heulandite by chemical precipitation. The chemical composition, nanomorphologies, structural parameters, and optical behaviors are investigated using different techniques. The FeO/zeolite nanocomposite showed smaller sizes and greater light absorption capability in visible light than FeO nanopowder. The XRD pattern shows crystalline hematite (α-FeO) with a rhombohedral structure. The crystallite sizes for the plane (104) of the FeO and FeO/zeolite are 64.84 and 56.53 nm, respectively. The FeO and FeO/zeolite have indirect bandgap values of 1.87 and 1.91 eV and direct bandgap values of 2.04 and 2.07 eV, respectively. FeO and FeO/zeolite nanophotocatalysts are used for solar photoelectrochemical (PEC) hydrogen production. The FeO/zeolite exhibits a PEC catalytic hydrogen production rate of 154.45 mmol/g.h @ 1 V in 0.9 M KOH solution, which is the highest value yet for FeO-based photocatalysts. The photocurrent density of FeO/zeolite is almost two times that of FeO catalyst, and the IPCE (incident photon-to-current conversion efficiency) reached ~27.34%@307 nm and 1 V. The electrochemical surface area (ECSA) values for FeO and FeO/zeolite photocatalysts were 7.414 and 21.236 m/g, respectively. The rate of hydrogen production for FeO/zeolite was 154.44 mmol h/g. This nanophotocatalyst has a very low PEC corrosion rate of 7.6 pm/year; it can retain ~97% of its initial performance. Therefore, the present research can be applied industrially as a cost-effective technique to address two issues at once by producing solar hydrogen fuel and recycling the rusted iron wires.