Surface Structure Analysis and Formaldehyde Removal Mechanism of Lotus Shell Biochar: An Experimental and Theoretical Perspective

The adsorption of gaseous HCHO by raw lotus shell biocharcarbonizedat 500, 700, and 900 & DEG;C from the perspective of its internalcrystal structure and surface functional groups was investigated byan integrated approach of experiments and density functional theorycalculations. The results showed that lotus shell biochar carbonizedat 700 & DEG;C had the best adsorption effect at a HCHO concentrationof 10.50 & PLUSMN; 0.30 mg/m(3), with an adsorption removalrate of 87.64%. The HCHO removal efficiency by lotus shell biocharcarbonized at 500 and 900 & DEG;C was determined to be 80.96 and 83.07%,respectively. The HCHO adsorption on lotus shell biochar carbonizedat 700 & DEG;C conformed to pseudo-second-order kinetics and was predominantlycontrolled by chemical adsorption. The Langmuir isotherm was the underlyingmechanism for the monomolecular layer adsorption with a maximum adsorptioncapacity of 0.329 mg/g. The density functional theory calculationsrevealed that the adsorption of HCHO on the surface of CaCO3 and KCl in lotus shell biochar carbonized at 700 & DEG;C was a chemicaladsorption process, with adsorption energies ranging from -64.375to -87.554 kJ/mol. The strong interaction between HCHO andthe surface was attributed to the electron transfer from HCHO to thesurface, facilitated by metal atoms (Ca or K) and the oxygen atomsof HCHO. The carboxyl group on the surface of lotus shell biocharcarbonized at 700 & DEG;C was identified as the key functional groupresponsible for HCHO adsorption. This study advanced our understandingof the environmental functions of inorganic crystals and surface functionalgroups in raw biochar and will enable the further development of biocharmaterials in environmental applications.