Matrix-dispersed PEI-coated SPIONs for fast and efficient removal of anionic dyes from textile wastewater samples: Applications to triphenylmethanes

Abstract

Textile industries produce a massive amount of wastewater that should be cleaned from toxic substances such as fats, colors and any chemicals used during the production steps. Water-treatment methods should be facile, economic, fast and efficient. Here, we report the synthesis, characterization and application of matrix-dispersed superparamagnetic iron oxide nanoparticles (SPIONs) for the removal of anionic dyes from wastewater released from textile industrial plants. The matrix-dispersed SPIONs were synthesized via a solvothermal method in which a polyethyleneimine (PEI) shell was deposited onto SPIONs in order to add positive charges to their surfaces. TEM images revealed that the size of PEI-coated and uncoated SPIONs is 30–50 and 15–30 nm, respectively. Moreover, TEM images depicted that the as synthesized PEI-coated SPIONs show matrix-dispersed structures. Furthermore, the particle size obtained with DLS measurements was found to be 87.93 and 158.9 nm for uncoated and PEI-coated SPIONs, respectively. Bromophenol blue (BPB) and bromocresol green (BCG), two triphenylmethanes, were used as model anionic dyes. FTIR spectroscopy revealed the interaction between the PEI surface coating and the anionic dyes. The apparent ζ-potential measurements showed that the surface negative charges decreased from −13.5 to −4.03 mV upon coating with PEI. In order to investigate the anionic dyes removal/entrapment efficiency of SPIONs, a new derivative visible spectrophotometric method was developed for the simultaneous quantification of BPB and BCG before and after treatment where the linear ranges were 6.98–27.9 and 6.70–26.8 μg/mL and the recovery values were in the ranges of 98.10–101.7% and 99.55–104.8% for BCG and BPB, respectively. It was found that the uptake/adsorption capacity of PEI-coated SPIONs is ca.15.5 and 11.3 mg/g for BCG and BPB, respectively. The calculated thermodynamic parameters for the adsorption of BCG (ΔH = 37.08 J/mol and ΔS = 120.89 J/mol K) and BPB (ΔH = 181.26 J/mol and ΔS = 596.46 J/mol K) and the negative ΔG values indicate that the adsorption is thermodynamically favored. The adsorption processes were found to follow the pseudo-second-order kinetic model with r2 values of 0.9982 and 0.9956 for BCG and BPB, respectively.