Mesoporous Biobased Carbonaceous Adsorbent for Dye Removal from Water: Eutectic Molten Salts Effect and Adsorption Mechanisms

Dye-polluted wastewater is released from various industries, such as textile and paint industries. Among different reclamation techniques, adsorption has been widely used for dye removal. Carbonaceous adsorbents, such as graphene, are among the most sought-after compounds for adsorption applications because of their high specific surface area and adjustable surface features. In this study, graphene-like carbon (GLC) was prepared from biomass as it is a facile and eco-friendly approach. Biomass-derived GLC was prepared by pyrolyzing waste wood in the presence of FeCl3/ZnCl2 as a eutectic binary mixture. Brunauer–Emmett–Teller (BET) and Raman analyses revealed that FeCl3 had a template effect during pyrolysis, whereas ZnCl2 acted as a pore former. Moreover, FeCl3 and ZnCl2 concentrations positively affected the BET value, regardless of the salt type. Further, waste wood-derived graphene-like carbon (WGLC) pyrolyzed at 900 °C with biomass: FeCl3: ZnCl2 at a ratio of 1:2:1 (WGLC-121) showed the highest specific surface area (2073.78 m2 g−1) and could remove >90 % of rhodamine B (RhB) and Congo red (CR) dyes. The pseudo-second order kinetic model showed a stronger correlation with the experimental data than the pseudo-first order model. While intra-particle diffusion was the rate-determining step in RhB adsorption, it did not influence CR adsorption. Further, the Freundlich model better explained the RhB (qmax = 633.86 mg g−1) and CR (qmax = 141.28 mg g−1) adsorption and revealed the superiority of WGLC-121 in dye removal compared to the previously reported adsorbents. The adsorption isotherm, energy, and thermodynamic parameters confirmed that the dyes were adsorbed through physisorption. Furthermore, the inter-molecular interaction between the RhB and CR molecules influenced the dye adsorption rate and isotherm. The findings of this study demonstrate the high potential of a binary mixture of FeCl3 and ZnCl2 for preparing carbonaceous adsorbents from waste wood to remove dyes from industrial wastewater.