Lanthanum orthoferrite-chitosan nanocomposite for reactive black 5 dye removal

Abstract

Presence of reactive dyes such as reactive black 5 (RB5) in wastewater severely interfere the photosynthetic function of plants due to low light penetration, leading to reduction in the concentration of dissolved oxygen used by aquatic organisms to breathe. This will also affect the quality of freshwater used in our everyday lives as reactive dyes are known to be toxic and carcinogenic to human if consumed in large quantity. One promising way to eliminate dyes in wastewater is by photocatalysis process by perovskite-like nanosized material such as lanthanum orthoferrite (LaFeO3). However, due to susceptibility of LaFeO3 to agglomerate because of high interparticle surface energy, scattering the nanoparticles onto a support material is believed to be an effective way. Thus, a new LaFeO3 -chitosan nanocomposite, LC15 was successfully fabricated in this work based on chemical precipitation methods. Characterization using X-Ray diffraction analysis showed that there was no change in crystallinity of LaFeO3 nanoparticles when integrated with chitosan, while the Fourier Transform Infrared Spectroscopy confirmed the formation of LaFeO3 -chitosan nanocomposites by strong hydrogen bonding. Transmission electron microscopy verified the nanocrystalline structure of synthesized LaFeO3 while field emission scanning electron microscopy and energy dispersive X-Ray spectroscopy demonstrated good distribution of LaFeO3 on chitosan matrices along with changes in elemental composition of LC15 nanocomposites. Brunauer-Emmett-Teller and Barrett-Joiner Halenda analyses exhibited reduction in specific surface area and increased average pore radius of LC15 compared to pristine LaFeO3, while UV-vis diffuse reflectance spectroscopy revealed reduction of band gap value for LC15. Apart from that, both adsorption and photocatalytic activity LC15 were also studied by varying the pH of synthetic wastewater, loading of nanocomposites, and initial concentration of RB5 dye. These studies were important to understand the behaviour of the sample and to determine the optimal condition for maximum synergistic action of LaFeO3 -chitosan nanocomposite onto RB5 dye. Following that, the reusability study was also performed in order to recognize the ability of LC15 nanocomposite to be used in real life application. Finally, the photocatalytic pathways for total removal of RB5 dye were also proposed based on species trapping experiment. Based on this study, LC15 nanocomposite showed the most prominent characteristics with high synergistic removal of RB5 dye at optimum conditions (pH 6, 2g/L loading and 30 mg/L of initial RB5 dye concentration). Moreover, the reusability experiment confirmed the stability of the nanocomposite with no dramatic changes occurred to their chemical structure, while the involvement of reactive oxygen species and positive vacant holes were established in species trapping experiment.