Catalytic Oxidation Extraction of Bromine from Natural Seawater Using Polyaniline

Bromine is an essential strategic chemical raw material, and seawater represents the largest reserve of bromine resources on Earth. Conventional seawater bromine extraction technologies suffer from high acid/oxidant consumption, secondary pollution, and limited cycle performance. Herein, polyaniline (PANI) with continuous π-conjugated nitrogen-containing skeleton was proposed as a metal-free catalytic medium for continuous bromine conversion from natural seawater without extra chemical additives. Multiple characterizations including scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV-Vis), inductively coupled plasma (ICP), coupled with gas-phase product capture experiments and density functional theory (DFT) calculations were applied to reveal the interface evolution and catalytic mechanism of PANI in seawater. SEM-EDS results verified obvious interface reconstruction after seawater treatment, accompanied by impurity Fe elution and trace Br signal appearance. Time-dependent UV-Vis quantitative analysis revealed an atypical dynamic curve: apparent bromine removal capacity rapidly peaked at 40 min (>2500 mg g⁻¹) and then declined to negative values, eliminating static adsorption as the dominant pathway. XPS and Raman spectra confirmed reversible electron rearrangement of PANI conjugated backbone and transient formation of tribromide ion (Br₃⁻) intermediates on the material surface. Starch-KI test paper experiments directly captured volatile Br₂ gas products, verifying the “enrichment-oxidation-desorption-evaporation” catalytic cycle. XRD proved PANI maintained stable crystalline structure without halide crystal deposition after long-term seawater contact. A complete catalytic mechanism was established: PANI provides electron transport channels to activate dissolved oxygen, oxidize enriched Br⁻ into Br₂/Br₃⁻, and regenerate active sites after gaseous bromine escapes. This work develops a green, recyclable catalytic strategy for seawater bromine recovery and provides fundamental insights into conjugated polymer-seawater interface electrocatalysis.