Photocatalytic Evolution of Hydrogen on the Spinel ZnMn2O4 Under Visible Light Irradiation

The nanocrystalline ZnMn
2
O
4
with specific properties was successfully developed by sol gel method. It is very encouraging to note that the synthesized ZnMn
2
O
4
showed satisfactory results as photocatalyst for H2 production. Structural analyses, including X-ray diffraction (XRD) and spectroscopy FT-IR spectroscopy, confirmed that ZnMn
2
O
4
is a pure phase. The optical gap (E
g
= 1.3 eV), determined from the diffuse reflectance, proves its activity in the visible region of the electromagnetic spectrum. The flat band potential
$(\mathbf{E}_{\text{fb}}=0.18 \mathbf{V}_{SCE})$
was determined from the Mott Schottky method. Chronoamperometric analysis suggests that ZnMn
2
O
4
exhibits p- type and was found to be photo-electrochemically active under visible light. It showed
$\mathbf{H}_{2}$
generation capacity with H2 release of 0.19 μmol mg
⁻¹
min
⁻¹
and a quantum efficiency of 0.79% under a light flux of 28 mW cm
⁻²
, pH 12 and an optimal temperature of 50°C in the presence of
$\mathbf{S}_{2}\mathbf{O}_{2^{-3}}$
(0.05 mol dm
⁻³
) as hole scavenger and ZnMn
2
O
4
dose of 1 mg/mL.