Enhanced adsorption properties of organic ZnCr-LDH synthesized by soft template method for anionic dyes

Organic ZnCr-LDH (ST-LDH) was synthesized by a facile one-step hydrothermal technique using methyl orange (MO) as a soft template agent, which can efficiently remove methyl orange (MO), Congo red (CR), and orange II (OII) from aqueous solution. The microstructure of ST-LDH by modifying changed obviously, from the cellular structure to the stacking structure formed by the face-face contact of hydrotalcite nanosheets, which resulted in much more exchangeable nitrate ions to remain in the interlayer space. The pre-insertion of benzene sulfonate as a pillar expanded the interlayer gallery, which facilitated the pollutant anions (MO, CR, and OII) into the interlayer of LDH in the subsequent adsorption process. The maximum adsorption capacity of ST-LDH for MO, CR, and OII was 4200.8 mg/g, 1252.0 mg/g, and 1670.6 mg/g, respectively, which is approximately 1.86 times, 1.8 times, and 2.32 times that of the pristine NO3-LDH, respectively. The removal mechanism of anionic dyes was determined as anion exchange between NO3- anions and dye molecules. The adsorption behavior for MO and OII is multilayer adsorption, while the adsorption behavior for CR is monolayer adsorption. The adsorption process mainly was controlled by the chemical bonding between the dye molecules and adsorbent active sites. The LDH can be effectively regenerated by photocatalysis after MO adsorption. The ST-LDH has a great potential to be used as a high-efficient adsorbent to remove anionic dyes from aqueous solution.

Automated summary

The organic ZnCr-LDH (ST-LDH) was successfully synthesized using a one-step hydrothermal technique, with methyl orange acting as a soft template agent for efficient removal of methyl orange, Congo red, and orange II from aqueous solution. The modified microstructure of ST-LDH led to increased exchangeable nitrate ions in the interlayer space, providing higher adsorption capacities for the dyes. ST-LDH has the potential to be a high-efficient adsorbent for anionic dye removal.