Characterization and Co-Adsorption Mechanism of Magnetic Clay-Biochar Composite for De-Risking Cd(II) and Methyl Orange Contaminated Water

Abstract

The application of the adsorption method in sewage treatment has recently become a hot spot. A novel magnetic clay-biochar composite (BNT-MBC) was fabricated by co-pyrolysis of bentonite and biomass after being impregnated with Fe (NO3)3·9H2O. Its adsorption capacity for Cd(II) and methyl orange was approximately doubled, reaching a maximum of 26.22 and 63.34 mg/g, and could be easily separated from the solution by using external magnets with its saturation magnetization of 9.71 emu/g. A series of characterizations including surface morphology and pore structure, elemental analysis, functional group analysis and graphitization were carried out, showing that the specific surface area was increased 50 times by loading 20 wt.% bentonite, while its graphitization and oxygen-containing functional groups were also enhanced. The isotherm fitting indicated that Cd(II) was adsorbed in multiple layers, while methyl orange was in both monolayer and multilayer adsorptions. The kinetic fitting indicated that chemisorption was the rate-limiting step of both, and it was also a complex process controlled by two steps with the fitting of intra-particle diffusion. In the binary system of Cd(II) and methyl orange, the co-existing pollutants facilitated the adsorption of the original one, and there was no competition between adsorption sites of Cd(II) and methyl orange. BNT-MBC also exhibited good reusability and can be magnetically recovered for recycling. Thus, the magnetic clay-biochar composite BNT-MBC is a cost-effective and promising adsorbent for simultaneous removing Cd(II) and methyl orange from wastewater.

What is the Effect of a Magnetic Field on Dye Adsorption onto Graphite Carbon?

“…Furthermore, research on rhodamine B, albeit not listed among the dyes initially mentioned but pertinent to this discourse, indicates a reduction in adsorption in the presence of a magnetic field [22]. This observation implies that magnetic fields can constrain the mobility of dye molecules, thereby impeding their optimal interaction with the graphite carbon surface [22].…”

“…This phenomenon suggests that a magnetic field can facilitate a more favorable molecular orientation, thereby fostering more robust interactions with the graphite carbon surface [21]. Conversely, methyl orange, an anionic dye encompassing an azo group, exhibit discernible thermodynamic alterations in its adsorption behavior under magnetic field exposure [22]. These alterations perturb the equilibrium between the dye molecules in the solution and those adsorbed on the graphite carbon surface, underscoring the pivotal role of magnetic fields in modulating the adsorption equilibrium conditions [22].…”