Birnessite-Type MnO2 Modified Sustainable Biomass Fiber toward Adsorption Removal Heavy Metal Ion from Actual River Aquatic Environment

In this work, a novel birnessite-type MnO₂ modified corn husk sustainable biomass fiber (MnO₂@CHF) adsorbent was fabricated for efficient cadmium (Cd) removal from aquatic environments. MnO₂@CHF was designed from KMnO₄ hydrothermally treated with corn husk fibers. Various characterization revealed that MnO₂@CHF possessed the hierarchical structure nanosheets, large specific surface area, and multiple oxygen-containing functional groups. Batch adsorption experimental results indicated that the highest Cd (II) removal rate could be obtained at the optimal conditions of adsorbent amount of 0.200 g/L, adsorption time of 600 min, pH 6.00, and temperature of 40.0 °C. Adsorption isotherm and kinetics results showed that Cd (II) adsorption behavior on MnO₂@CHF was a monolayer adsorption process and dominated by chemisorption and intraparticle diffusion. The optimum adsorption capacity (Langmuir model) of Cd (II) on MnO₂@CHF was 23.0 mg/g, which was higher than those of other reported common biomass adsorbent materials. Further investigation indicated that the adsorption of Cd (II) on MnO₂@CHF involved mainly ion exchange, surface complexation, redox reaction, and electrostatic attraction. Moreover, the maximum Cd (II) removal rate on MnO₂@CHF from natural river samples (Xicheng Canal) could reach 59.2% during the first cycle test. This study showed that MnO₂@CHF was an ideal candidate in Cd (II) practical application treatment, providing references for resource utilization of agricultural wastes for heavy metal removal.