In this study, zinc-doped ($\alpha$-Fe${}_2$O${}_3$:Zn), silver-doped ($\alpha$-Fe${}_2$O${}_3$:Ag) and zinc/silver co-doped hematite ($\alpha$-Fe${}_2$O${}_3$:Zn/Ag) nanostructures were synthesized by spray pyrolysis. The synthesized nanostructures were used as photoanodes in the photoelectrochemical (PEC) cell for water-splitting. A significant improvement in photocurrent density of 0.470 mAcm${}^{-2}$ at 1.23 V vs. reversible hydrogen electrode (RHE) was recorded for $\alpha$-Fe${}_2$O${}_3$:Zn/Ag. The $\alpha$-Fe${}_2$O${}_3$:Ag, $\alpha$-Fe${}_2$O${}_3$:Zn and pristine hematite samples produced photocurrent densities of 0.270, 0.160, and 0.033 mAcm${}^{-2}$, respectively. Mott–Schottky analysis showed that $\alpha$-Fe${}_2$O${}_3$:Zn/Ag had the highest free carrier density of 8.75 × 10${}^{20}$ cm${}^{-3}$, while pristine $\alpha$-Fe${}_2$O${}_3$, $\alpha$-Fe${}_2$O${}_3$:Zn, $\alpha$-Fe${}_2$O${}_3$:Ag had carrier densities of 1.57 × 10${}^{19}$, 5.63 × 10${}^{20}$, and 6.91 × 10${}^{20}$ cm${}^{-3}$, respectively. Electrochemical impedance spectra revealed a low impedance for $\alpha$-Fe${}_2$O${}_3$:Zn/Ag. X-ray diffraction confirmed the rhombohedral corundum structure of hematite. Scanning electron microscopy micrographs, on the other hand, showed uniformly distributed grains with an average size of <30 nm. The films were absorbing in the visible region with an absorption onset ranging from 652 to 590 nm, corresponding to a bandgap range of 1.9 to 2.1 eV. Global analysis of ultrafast transient absorption spectroscopy data revealed four decay lifetimes, with a reduction in the electron-hole recombination rate of the doped samples on a timescale of tens of picoseconds.

Herein we report on the effect of varied spin-coated seed layer concentrations of Iron (III) chloride hexahydrate (FeCl₃.6H₂O) on the photoelectrochemical performance of hydrothermally synthesized hematite nanorods. The seed layers were prepared from 0.05, 0.07, 0.09, 0.11, and 0.13 M concentrations of FeCl₃.6H₂O. The nanorods were vertically aligned with slight inclinations over the seed layers with the two lowest molar concentrations (0.05 and 0.07 M) of FeCl₃.6H₂O. A further increase in seed layer concentrations transformed the nanorods as they grew over others and agglomerated into clusters. Structural analysis using x-ray diffraction (XRD) and Raman spectroscopy demonstrated uniform hematite crystalline peaks for all the samples. All samples absorbed highly in the visible region within an onset absorption edge wavelength ranging from 624 to 675 nm. Overall, the nanorods synthesized over the lowest seed layer concentration of 0.05 M of FeCl₃.6H₂O exhibited the highest photocurrent density of 0.077 mA cm⁻² at 1.5 V versus reversible hydrogen electrode. The results obtained provide important information about the structural, optical, and photoelectrochemical properties of hematite nanorods synthesized over varied seed layer concentrations. This is a key contribution in understanding and enhancing the hematite nanorods performance for photocatalytic applications.

Development of efficient inorganic luminescent tracers is essential for various applications, including plastic sorting.