Module 3 · published data only
ZnAl₂O₄ or MgAl₂O₄?
The two spinels, prepared by the same method, compared on their properties and their performance in degrading tetracycline under sunlight.
k₂ constant versus concentration
Second order, tables 2 of the papers (log scale).
Recomputed half-life
t½ = 1/(k₂·C₀) with the measured concentration, for a like-for-like comparison.
Active species (scavengers)
Degradation after 4 h with each scavenger. For ZnAl₂O₄, the “no scavenger” value is the maximum yield given in the abstract, and isopropanol is not quantified in the text.
Reuse
Yield over 5 cycles. For ZnAl₂O₄, only the first and fifth cycles are given in the text.
Key takeaways
- ZnAl₂O₄ is faster: at a comparable concentration (≈ 12 mg/L), k₂ is 3.70×10⁻³ versus 1.47×10⁻³ L/mg/min, i.e. a half-life about 2.5 times shorter.
- MgAl₂O₄ absorbs slightly further into the visible (gap 2.88 eV versus 3.02 eV) and adsorbs more tetracycline in 30 min (58 % versus 42 %).
- MgAl₂O₄ needs less catalyst (0.75 g/L versus 1 g/L at the optimum).
- For both, O₂•⁻ radicals and h⁺ holes dominate; •OH radicals play a minor role.
- The loss of activity after 5 cycles is comparable (−17 and −18 points).