Structural characteristics of biochar-graphene nanosheet composites and their adsorption performance for phthalic acid esters

To create more active sites on biochar surface, biochar-graphene (BG) nanosheet composites were prepared by one step facile dip coating following thermal route at three different temperatures, in addition to biochars (300, 500, 700   °C). The morphology and structural composition of biochars and BG composites were examined by SEM, TEM, BET–N 2 and CO 2 , Raman, FTIR, XPS, TGA and CHN elemental analysis. It was found that graphene nanosheets (GNS, ∼1   µm, 0.1% mass) could ensure relatively higher surface area (N 2 and CO 2 ), porous structure and thermal stability within BG composites. BG composites portrayed the existence of GNS bearing cavities and evidently increased the graphitic structure. The adsorption capabilities of biochars and BG composites towards dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP) as model phthalic acid esters (PAEs) were examined by batch sorption technique. The BG composites exhibited the increased adsorption capacity comparatively to biochars. The pseudo-second-order kinetic rate ( k 2 ) illustrated that adsorption of PAEs was efficient and smaller molecule (DMP) was quicker to pore-diffusion mechanism. The aromatic sheets of biochars and GNS on biochars dominated the π–π EDA (electron donor–acceptor) interaction for ring structure of DMP molecule, whereas adsorption of DBP was attributed to hydrophobicity. The surface morphology and composition of biochars can be regulated with GNS to promote the adsorption capacity and kinetics for effective pollutant remediation and could be considered as promising adsorbent for various organic contaminants.