Synthesis and characterization of MOF-5 incorporated waste-derived siliceous materials for the removal of malachite green dye from aqueous solution

The synthesis of MOF-5 and its modification have been investigated towards malachite green (MG) dye removal. The modified MOF-5 adsorbents have been prepared using waste-derived siliceous materials, i.e., rice husk ash (RHA) and/or coal fly ash (CFA) at different ratio. The MOF-5/RHA&CFA/2:1 has been chosen as the best adsorbent for MG dye removal from the aqueous solutions. The adsorption characteristics of the modified MOF-5 for MG dye removal was studied varying various parameters. The MG adsorption efficiency increases with increasing the shaking rate and contact time, but remained constant after 300 rpm and 4 h, respectively. The maximum adsorption capacity of 39.47 mg/g was obtained at adsorbent amount of 0.3 g, initial dye concentration of 150 mg/L, temperature of 30 °C, shaking rate of 200 rpm, contact time of 2 h, and original solution pH. The optimum temperature, pH, and amount of adsorbent for effective MG dye adsorption were 40 °C, 11.5, and 0.2 g, respectively. XRD analysis indicated the presence of crystalline materials has become reduced when RHA and CFA were being incorporated in MOF-5. FTIR analysis showed significant functional groups in the spectrum for both prepared and spent adsorbents. The SEM micrograph results revealed the rough surface morphology with many pores on the MOF-5/RHA&CFA/2:1 before MG adsorption and became smooth and less porous after MG adsorption. While BET analysis indicated that the surface area does not affect the MG dye adsorption efficiency. This study showed that modified MOF-5 adsorbents were successfully used for the removal of MG dye.