Antimonite Nanoparticle Photocatalysis: Sb(III) to Sb(V) Oxidation

Reaction Conditions

UV intensity 70%

Catalyst loading 90 NPs

Solution pH 6.5

Initial Sb(III) load 220 ions

Live Water Chemistry

Sb(III) antimonite (toxic, mobile)

Sb(V) antimonate (adsorbs, removed)

Sb(III) 100%Sb(V) 0%

Sb(III) remaining

220

Sb(V) formed

Observed rate k_obs

0.000 s⁻¹

Elapsed time

0.0 s

How it works

Antimonite ≠ antimonide. Antimonide nanocrystals (InSb, GaSb) are III–V semiconductors where Sb³⁻ bonds to a metal cation. Antimonite is the opposite chemistry: the oxoanion of trivalent antimony, Sb(OH)₃ / SbO₂⁻, the dominant dissolved form of the toxic pollutant Sb(III) in near-neutral water — chemically the direct analogue of arsenite (As(III)).

Metal-oxide nanoparticles (TiO₂, ferrihydrite, MnO₂) act as photocatalysts: absorbed UV photons create electron–hole pairs at the surface, and the holes drive water/hydroxide into hydroxyl radicals:

NP + hν → e⁻ + h⁺
h⁺ + OH⁻ → •OH
Sb(OH)₃ + 2•OH → Sb(OH)₆⁻ + (2 e⁻, 2 H⁺)   [Sb(III) → Sb(V)]

Sb(V) antimonate binds far more strongly to the oxide surface than Sb(III) does, so this oxidation step is the rate-limiting move in real antimony water-treatment trains — oxidize first, then adsorb/filter. The bulk kinetics follow a pseudo-first-order law once catalyst and •OH supply are in excess:

-d[Sb(III)]/dt = k_obs·[Sb(III)]
k_obs ∝ (UV intensity) × (catalyst surface area) × f(pH)

UV intensity — sets the •OH generation rate at every catalyst nanoparticle.
Catalyst loading — more nanoparticles means more total surface area, raising k_obs roughly linearly.
Solution pH — antimonite adsorption onto oxide surfaces peaks near mildly acidic-to-neutral pH (~6–7) and falls off on either side, exactly as plotted by the bell-shaped multiplier here.
Reseed — restores a fresh Sb(III) population without resetting the catalyst bed, so you can compare conditions back to back.

Orange spheres are dissolved Sb(III) ions doing Brownian diffusion above the catalyst bed (teal, fixed); on a close, UV-driven encounter they flip to blue Sb(V) and drift toward the surface, exactly as antimonate does once oxidized.

Photocatalyst nanoparticle Sb(III) antimonite Sb(V) antimonate

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Antimonite Nanoparticle Photocatalysis: Sb(III) → Sb(V) Oxidation