Harnessing corn straw biochar: A breakthrough in eco-friendly Cu(II) wastewater treatment

To investigate an energy-efficient, environmentally friendly, and highly efficient biochar for adsorbing Cu(II)-containing wastewater, corn straw hydrothermal char prepared at 240 °C for 2 h was used as a precursor. Silicon (Si)-Manganese (Mn) impregnation modification was then performed to produce the modified biochar (b-BC). The study found that Si and Mn were loaded onto the b-BC surface in the form of oxides. The distinct hierarchical Si membrane effectively stabilized Mn oxides and increased the specific surface area. Under different pH conditions, the effect of Mn rendered b-BC consistently negatively charged in the solution, facilitating electrostatic attraction with Cu(II). Fourier-transform infrared and X-ray photoelectron spectroscopy results revealed that b-BC's surface had numerous oxygen-containing functional groups, effectively binding with Cu(II). Adsorption experiments showed that, at an addition amount of 1.47 g/L and pH of 7, b-BC displayed a significant adsorption capacity for Cu(II) at 167.884 mg/g. Pseudo-second-order adsorption kinetics and Freundlich isotherm models better described the adsorption behavior of b-BC for Cu(II). The adsorption process was primarily dominated by multilayer chemical adsorption. Webber-Morris analysis indicated that the key adsorption process occurred during the membrane diffusion stage. At this stage, Cu(II) formed bonds with the b-BC surface in the forms of Cu-O, -COOCu, Cu(OH)₂, and Si/Mn-O-Cu. Chelation emerged as the most significant mechanism for b-BC adsorbing Cu(II). Due to its environmentally friendly preparation method and high efficiency in adsorbing Cu(II) from water, b-BC can be considered as a feasible rich-carbon adsorbent in the field of waste treatment.