Iron(III) oxide-hydroxide modification on Pterocarpus macrocarpus sawdust beads for direct red 28 dye removal

Abstract

The releasing of wastewater contaminated with direct red 28 (DR28) dye into receiving water is a concern because it is a polyaromatic structure with difficult biodegradation. It results in being persistent in the environment and being toxic to the ecosystem from accumulating through a food chain. Thus, it needs to eliminate DR28 dye from contaminated wastewater. Sawdust beads (SDB) and sawdust mixed with iron(III) oxide-hydroxide beads (SDFB) are prepared and characterized for DR28 dye removals. DR28 dye removal efficiencies are examined with various affecting factors by the batch tests and adsorption–desorption tests, and their adsorption patterns, rates, and mechanisms are determined by isotherms and kinetics models. Moreover, the thermodynamic studies are examined for the temperature effect. SDFB demonstrated a higher surface area and smaller pore size than SDB. SDB and SDFB were uneven shapes and heterogeneous fibrillar structures. Carbon, oxygen, calcium, chloride, sodium, OH, CH, CC, COOH, and CO were found in SDB and SDFB. The points of zero charge of SDB and SDFB were 4.65 and 6.11. The conditions of 3.5 g, 50 ℃, pH 3, 60 mg/L and 2.5 g, 40 ℃, pH 3, 60 mg/L illustrated the highest DR28 dye removals of more than 82 % for SDB and SDFB, respectively. Thus, the material modification by iron(III) oxide-hydroxide improved the DR28 dye removal efficiency of sawdust material. Moreover, they could be reusability more than three times with DR28 dye removal of more than 63 %. SDB and SDFB corresponded to Langmuir and Freundlich models, respectively, and a pseudo-second-order was a good model to describe their adsorption mechanism. Both materials did not favor DR28 dye adsorptions with increasing temperature. Therefore, SDFB was a potential material for removing DR28 dye removal in the industrial wastewater.