Abstract: Biocarbon (BC) has been widely employed as a support to disperse nanoscale zerovalent iron (nZVI) particles to prevent their aggregation and rapid oxygen passivation. Here, we compare the chemical stability of nanozerovalent iron composites (nZVI@BC) made by liquid-phase reduction (LPR) versus carbothermal reduction (CTR). In the LPR route, Fe 3+ was impregnated onto demineralized bamboo-BC formed at 600 °C, followed by NaBH 4 reduction under N 2. The CTR method employed aqueous FeCl 2 -impregnated bamboo-BC, which was dried and carbonized from 50 to 1000 °C under N 2 . nZVI@BC’s chemical stabilities were compared in air, water, and soil. Both routes produced Fe 0 , confirmed by the XRD peak at 2θ = 44.6°. Fresh LPR-nZVI@BC vs. CTR-nZVI@BC exhibited efficient Cu 2+ uptakes of 32 mg/g (212 mg/g Fe 0 ) and 40 mg/g (266 mg/g Fe 0 ) in 30 min, respectively, via Fe 0 reduction of Cu 2+ to Cu 0 . Exposing LPR-nZVI@BC samples to water for 4 h led to the complete disappearance of the Fe 0 XRD peak and the appearance of the Fe 3 O 4 peak at 2θ = 35.0°, reducing Cu 2+ uptake by 98%. In contrast, CTR-nZVI@BC only experienced a 51% drop in capacity due to the presence of a layered graphene sheet shell, preventing Fe 0 from rapid oxidation. No Fe 3 O 4 XRD peaks were observed in CTR-nZVI@BC after 7 days of air and soil exposure, unlike in LPR samples. Resistance to passivation in air, water, and soil makes the CTR a promising synthetic route to nZVI@BC.
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