Enhancing methylene blue sorption on spotted golden thistle stalks by soft chemical pretreatments

Abstract

Soft chemical treatments of dried stalks of the spotted golden thistle yielded novel sorbents; both the stiff nature and mass of the raw material were preserved. For minimal environment impact, the solution concentrations of the tested reagents were optimized at ambient temperature. The sorbents obtained were tested for the removal of methylene blue. The approach used kinetics and equilibrium studies. NaOH (0.1 mol L⁻¹) treatment was efficient and afforded two new materials with seriously improved sorption features: the equilibrium time was reduced from 17–19 h to 10–12 h whilst, maximal sorption capacity increases from 65 to 100 and 112 mg g⁻¹ i.e., enhancements of 54 and 72%. The Avrami model followed by the pseudo second-order model, best fitted the kinetic data. The isotherms were of Hmx type and were satisfactorily fitted to the Redlich-Peterson model. The Langmuir, Tóth, and Sips models were suitable to describe the H type isotherms relating to limited data ranges. Microanalysis, scanning electron microscopy (SEM), SEM coupled to energy dispersive X-ray, and attenuated total reflectance infrared spectroscopy showed an increase of the lignocellulosic content and the strengthening of the interactions between the dye and the sorbent. However, zeta potential measurements showed that the charge of the surface became almost inexistent after the pretreatment.

Keywords:

• Hmx type isotherm
• kinetics
• methylene blue
• modeling
• soft chemical treatments
• sorption
• spotted golden thistle

Acknowledgments

The authors are grateful to the following professors of UMR CNRS 6226 of Rennes 1 University, France: A. Amrane, A. Szymczyk, M. Rabillet-Baudry, and O. Merdrignac-Connanec for SEM and SEM-EDX, Zeta potential, ATR-FTIR and BET experiments, respectively. However, we mourn the passing of the Professor Benaïssa Houcine in his 61^st year. He was a teacher and a researcher devoted to all his students and colleagues. After a doctorate thesis about adsorption of gazes on solids that he prepared in France, he returned to his native Algeria. He was full of ambition to develop research axis which must be useful and above all adapted to the means available in developing countries: the valorization of agricultural wastes for water treatment was his main concern. He focused on sorption of notorious metals and dyes on a variety of low cost sorbents issued from agricultural residues. What a pity for his unfinished projects of writing unconventional sorbents articles review as well as pedagogical books in surface chemistry. My special thanks go to the Editor-in-Chief for publishing this posthumous tribute.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of High Education and Scientific Research, Algeria (CNEPRU Project J01020200110020).