Adsorptive removal of crystal violet dye by Azadirachta indica (neem) sawdust: A low-cost bio-sorbent

Abstract

The potentiality of Azadirachta indica sawdust as a cost-effective natural adsorbent for adsorptive elimination of a cationic dye crystal violet from aqueous emulsion was investigated. Because sawdust is plentiful and low-cost by-product. Additionally, sawdust can be composted to replace the regeneration stage that other adsorbents like activated carbon requires. Kinetic and isotherm analyses were conducted under variable experimental conditions including adsorbent dose, dye concentration, contact time, pH, and temperature. A maximum adsorption capacity of 8.264 mgg−1 was obtained at optimized conditions of 2.5 gl−1, 100 mgl−1 30 min, 6, and 25 °C for adsorbent dose, adsorbate, contact time, pH and temperature. The nature of any probable interaction between adsorbent and crystal violet was analyzed by FTIR technique, to investigate the type of functional groups in saw dust responsible for dye binding process. The FTIR studies showed the existence of C-H, C=O, C-O, C=C, O-H, C-N, -COO- and Si-O functional groups. It was noted that the sorption kinetics followed a pseudo-second order kinetic model after the sorption was examined using pseudo-first and pseudo-second order kinetic models. The magnitude of dye removal increased with increase of adsorbent dose and slightly decreased with increase in adsorbate concentration. Up to 45 °C temperature, there was no significant impact on sorption only 2–5% higher than the 25 °C and 35 °C treatments. The Langmuir isotherm model provided a good representation of the equilibrium data in aqueous solutions. The adsorption capability of crystal violet onto the sawdust of Azadirachta indica was found to be as high as 8.278 mgg−1, at pH 6.0, temperature 25 °C, and at equilibrium time of 60 min after applying Langmuir isotherm equation. Azadirachta indica sawdust seems to be a very promising adsorbent for the removal of crystal violet from aqueous solution.