Cobalt-Doped Hydrochar Derived from Microalgae as an Efficient Peroxymonosulfate Activator for Paraben Degradation

Hydrochar, an attractive member of the carbonaceous materials, is derived from biomass and projects great potential in peroxymonosulfate (PMS) activation, but has not been studied much. Herein, by using the large-scale cultured Chlorella vulgaris and field-collected bloom algae, a series of porous hydrochar was synthesized via a facile hydrothermal carbonization reaction, while Co doping significantly increased their specific surface areas, carbonization degree, and surface functional groups. These Co-doped hydrochar (xCo-HC, x: amount of the Co precursor) could efficiently activate the PMS, resulting in nearly 100% removal of five common paraben pollutants within 40 min. A dosage of 0.2Co-HC of 0.15 g/L, a PMS concentration of 0.6 g/L, and an unadjusted pH of 6.4 were verified more appropriately for paraben degradation. The coexistence of Cl⁻, SO₄²⁻, and humic acid inhibited the degradation, while HCO₃⁻ showed an enhancing effect. No observable change was found at the presence of NO₃⁻. Quenching results illustrated that the produced •SO₄⁻ during the conversion of doped Co³⁺/Co²⁺ acted as the dominant active species for paraben degradation, while •O₂⁻, ¹O₂, and •OH contributed relatively less. The algae-based hydrochar potentially facilitated the electron transfer in the xCo-HC/PMS system. Overall, this study develops a new strategy for resource utilization of the abundant algae.