Modeling competitive biosorption for methylene blue removal on rape straw powders using response surface methodology in a ternary dye aqueous solution

Abstract

The improvement of biosorption efficiency for selective dye removal in a multi-dye aqueous system has become an increasingly significant research topic. However, the competitive effects of coexisting dyes and the target dye in such systems remain uncertain due to complex interactions between adsorbent and coexisting dyes. Therefore, in this research, response surface methodology (RSM) model was effectively employed to investigate the competitive effects of allura red (AR) and malachite green (MG) on methylene blue (MB) removal in a ternary dye aqueous system using three different parts of rape straw powders. In the current design of RSM, the initial concentrations of AR and MG dyes ranging from 0 mg·L⁻¹ to 500 mg·L⁻¹ were considered as influencing factors, while the removal rates of MB on adsorbents at an initial concentration of 500 mg·L⁻¹ were established as response values. The RSM models exhibited high correlation coefficients with adjusted R² values of 0.9908 (pith core), 0.9870 (seedpods), and 0.9902 (shells), respectively, indicating a close fitted between predicted and actual values. The proposed models indicated that the perturbation effects of initial AR and MG concentrations were observed on the removal rates of MB by three types of rape straw powders in a ternary dye aqueous system, resulting in a decrease in MB removal rates, particularly at higher initial AR concentration due to stronger competitive effects compared to initial MG concentration. The structures of rape straw powders, including pith core, seedpods and shell, were analyzed using scanning eletron microscoe (SEM), energy dispersive spectroscopy (EDS), N₂ physisorption isotherm, frourier transform infared spectroscopy (FTIR), Zeta potential classes and fluorescence spectrum before and after adsorption of MB in various dye aqueous systems. The characteristics of rape straw powders suggested that similar adsorption mechanisms, such as electrostatic attraction, pore diffusion, and group complex formation for MB, AR, and MG, respectively, occurred on the surfaces of adsorbents during their respective adsorption processes. This leads to significant competitive effects on the removal rates of MB in a ternary dye aqueous system, which are particularly influenced by initial AR concentrations as confirmed through fluorescence spectrum analysis.

HIGHLIGHTS

• Impact of AR and MG on MB removal was analyzed using simple methodologies.

• Competitive behaviors between AR, MG and MB were understood through RSM.

• Intense restrain effects on MB removal were revealed by AR concentration.

Keywords:

• Allura red
• competitive biosorption
• malachite green
• methylene blue
• response surface methodology
• ternary dye aqueous systems

Additional information

Funding

This research was supported by the funding of the Sichuan Science and Technology Program of China (Grant Nos. 2018SZ0306 and 2022YFS0498); Undergraduate Innovation and Entrepreneurship Training Program, China (Grant Nos. 202213705020).