Biochars obtained from freshwater biomass—green macroalga and hornwort as Cr(III) ions sorbents

Two different aquatic biomass sources—freshwater hornwort ( Ceratophyllum demersum L.) and macroalga ( Cladophora glomerata L.)—were used to produce biochars, which were investigated as Cr(III) ion sorbents. Wide range of pyrolysis temperatures from 250 to 800 °C was examined. Resultant biochars were characterized in detail by means of proximate analysis, ultimate analysis, FT-IR, SEM imaging, Boehm titration, and mercury porosimetry. The sorption capacities of the macroalga biochars varied from 104.2 to 163.9 mg g −1 , whereas for hornwort biochars from 37.6 to 60.2 mg g −1 . Obtained results were compared with literature data, suggesting that pyrolysis temperature and mineral matter content have crucial impact on the sorption capacities of Cr(III) ions. Simple thermal valorization of invasive aquatic macrophytes, i.e., hornwort or macroalga, allows to produce efficient adsorbents for chromium(III) ion removal from water.