Removal of methyl orange from aqueous solutions using a bentonite modified with a new gemini surfactant

Glycol bis-N-cetylnicotinate dibromide (designated as GN16-1-16), a new cationic gemini surfactant, was prepared and used to modify bentonite. Bentonite modified with commercial cetyltrimethylammonium bromide (CTMAB) was also prepared for comparison purposes. FTIR and XRD revealed that both surfactants successfully intercalated into the bentonite layers. The basal spacing was 2.65 nm for GN-Bt (the bentonite modified by GN16-1-16) and 2.14 nm for C-Bt (the bentonite modified by CTMAB), indicating that GN16-1-16 was more efficient than CTMAB in expanding the interlayer space of montmorillonite. The optimum reaction time and temperature in the modification were 1 h and 30 °C for GN16-1-16 and 3 h and 70 °C for CTMAB. The GN16-1-16 reacted with bentonite faster than CTMAB. The decoloration rate and the COD removal of methyl orange (MO) solution were 99.02% and 90.62% for GN-Bt and 80.12% and 75.49% for C-BT. Therefore, GN-Bt was more effective than C-Bt to remove MO from aqueous solution. However, the efficiency of GN-Bt decreased rapidly at pH > 6, which might be due to the hydrolysis of the ester groups in GN16-1-16 molecule under alkaline environment.

► GN16-1-16 is prone to react with bentonite with respect to CTMAB.
► GN16-1-16 is more capable of expanding clay basal spacing than CTMAB.
► Compared with CTMAB, GN16-1-16 is both effective and efficient in MO removal.
► The efficiency of GN-Bt decreases rapidly due to alkaline hydrolysis of ester groups.