Bimetallic Fe/Al-MOF for the adsorptive removal of multiple dyes: optimization and modeling of batch and hybrid adsorbent-river sand column study and its application in textile industry wastewater.

Bimetallic metal organic framework (MOF) has garnered interest over the years with its applications in industrial wastewater treatment. In this work, Fe-Al-1,4-benzene-dicarboxylic acid (FeAl(BDC)) MOF was synthesized, and adsorptive removal of Rhodamine B dye in batch and unique hybrid FeAl (BDC)-river sand fixed-bed column was studied. The experimental data from the batch studies corroborated well with the pseudo-second-order (PSO) (R2: 0.97) and Freundlich adsorption isotherm models (R2: 0.98) and achieved a maximum adsorption capacity of 48.59 mg/g in 90 min. Furthermore, a fixed-bed column study was conducted to assess the effect of varying flow rate (2, 5, 8 mL/min), bed height (5, 9, 13 cm), and feed concentration (10, 20, 30 mg/L) on the adsorption performance of FeAl(BDC) in continuous mode of operation. A uniform mixture of river sand and FeAl(BDC) by weight ratio (9:1) was packed into the column. The sand-FeAl(BDC) fixed-bed column could achieve the maximum adsorption capacity (qexp) of 113.05 mg/g at a 5 mL/min flow rate, feed concentration of 20 mg/L, and a bed height of 13 cm. The experimental data of the column study were successfully fitted well with BDST, Thomas (qcal: 114.94 mg/g), Yoon-Nelson, and dose-response models (qcal: 113.41 mg/g) and R2: 0.97-0.99. The fitting parameter values from the BDST model raise the scope of viable upscaling of the fixed-bed column. In all, it is proposed that these river sand-FeAl(BDC)-based filters can be widely used in areas facing critical contamination and in poor communities with a high demand for water.