Terminal-Hydroxyl-Engineered Amorphous ZrO2 for Sulfate Polishing of Peroxymonosulfate-Treated Effluent

Peroxymonosulfate-based oxidation inevitably generates sulfate in the effluent, which may stimulate sulfate-reducing bacteria and pipeline corrosion. Sulfate-polishing adsorbents suitable for acidic effluent remain limited. Herein, we report an ethanol-assisted solvothermal strategy to tailor surface hydroxyl speciation on amorphous ZrO2. The optimized material reached adsorption equilibrium within 10 min and showed an adsorption capacity of 110.6 mg/g. In fixed-bed operation using acidic sulfate-containing feed, the dynamic capacity was 82.9 mg/g, and the 50% breakthrough occurred at 3400 bed volumes. The terminal hydroxyl fraction increased from 15.2% to 59.8% as the ethanol/water volume ratio increased from 3:1 to 10:1. Ethanol addition is proposed to reduce hydrogen-bond-network connectivity, thereby suppressing condensation into bridging-hydroxyl. Terminal-hydroxyl abundance, estimated by thermogravimetric mass spectrometry (TG-MS) combined with solid-state1H magic-angle-spinning nuclear magnetic resonance (1H MAS NMR) showed a positive trend with adsorption capacity. Site-blocking tests established an 87% terminal-hydroxyl-associated contribution to sulfate uptake. Zeta-potential and electrostatic-potential analyses supported preferential sulfate approach to terminal-hydroxyl-rich positive domains, whereas density functional theory (DFT) identified dual-site binding to terminal hydroxyls on separate Zr centers as the most stable configuration. These results identify regulation of hydroxyl speciation as a dopant-free strategy for sulfate polishing after peroxymonosulfate oxidation.