Biochar derived from coffee grounds with molybdenum disulfide composites for Cr (VI) removal from wastewater

Discharging pollutants containing toxic metal ions has become a global problem, and improper disposal of coffee grounds can also cause environmental pollution. In this work, 1T-MoS2@STC (Solvothermal Carbonization, STC) was prepared from coffee grounds and molybdenum disulfide by a one-step solvothermal method that is simple in operation, low in energy consumption and low in cost, which possesses efficient adsorption of Cr (VI) in wastewater. The 1T-MoS2@STC was characterized by SEM, TEM, XRD, XPS, Zeta potential, FTIR, and BET analyses. The results showed that MoS2 was successfully loaded on coffee grounds. According to the pseudo-second order (R2 = 0.99) kinetics model, chemisorption was the main cause of adsorption. The adsorption process followed the Langmuir (R2 = 0.99) isothermal model, and the maximum adsorption capacity was 795.17 mg/g. The adsorption mechanism can be attributed to electrostatic interaction, redox reaction between Cr (VI) and active sites, and chelation between Cr (III) and hydroxyl. When 1T-MoS2@STC was applied to the treatment of actual water samples, the removal rate was also maintained at a high level (90%). In addition, 1T-MoS2@STC can maintain long-term stability (90 days) and low leaching of molybdenum (<3 mg/L) in wastewater. Therefore, in the treatment of chromium-containing wastewater, the 1T-MoS2@STC composite material simultaneously exhibited significant adsorption capacity, high interference resistance, stability and low leaching rate. This study provides a new efficient and stable Cr (VI) adsorbent and promotes the practical application of MoS2 biomass derivatives composites in water purification.