A novel CoFe layered double hydroxides adsorbent: High adsorption amount for methyl orange dye and fast removal of Cr(VI)

• Novel sorbents, CoFe-LDH for the removal of MO and Cr(VI) were prepared.
• Adsorption kinetics and isothermals of MO and Cr(VI) were studied.
• The adsorption mechanisms were discussed in detail.
• High adsorption amount of MO and fast removal of Cr(VI) were obtained in CoFe-LDHs.

CoFe-nitrate-layered double hydroxides (LDHs) with Co2+/Fe3+ molar ratios of 2, 3 and 4 were synthesized by a simple co-precipitation method. The as-prepared CoFe-LDHs exhibited a high adsorption activity to the methyl orange (MO) dye and Cr(VI). The adsorption characteristics including adsorption kinetics and isothermals were investigated. Structure analysis of the as-synthesized LDHs before and after adsorption revealed that adsorption proceeds in two processes: external surface adsorption and interlayer anion exchange. The results of MO adsorption experiments showed that LDHs with Co2+/Fe3+ molar ratios of 4 worked best with the largest MO adsorption amount up to 1290 mg/g at an initial concentration of 300 mg/L due to the porous structures. We have also noted that Cr(VI) in a range of 2–25 mg/L can be quickly removed with the maximum adsorption capacity of 27.62 mg/g in the initial 5 min, much faster than other LDH materials. Therefore, CoFe-LDHs are potential cost-effective adsorbents for both MO dye and Cr(VI).

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