Synthesis and spectroscopic characteristics of chitosan composite of zinc-based metal-organic framework for rapid adsorption of organic pollutants from aqueous media

ABSTRACT

The efficiency of the metal-organic framework of zinc (MOF-74) and its chitosan composite (CS/MOF-74) as a potential sorbent for the elimination of azo in addition to thiazine-type dyes from water by subsequent adsorption was studied. The synthesized adsorbents were characterized by various characterization techniques. The chitosan composite exhibited tremendous adsorption properties toward methyl orange (MO) and methylene blue (MB) at pH < 5.5 and pH > 5.5, respectively. The equilibrium data were evaluated by Dubinin-Radushkevich, Langmuir, Freundlich, and Tempkin isotherm models where the Langmuir model was best fitted to the adsorption data. The mono-layer sorption capacity values were found to be in the order 2047 mg/g and 1363 mg/g for MO and MB respectively onto CS/MOF-74 which are almost 6–8 epochs superior to MOF-74 and CS. In addition, pseudo-first, pseudo-second, intraparticle diffusion and Richenberg kinetic models were assessed to the kinetic data where the pseudo-second-order fitted very well to the adsorption data. The higher values of diffusion coefficient confirmed the greater involvement of the film diffusion than the pore and surface diffusion for the elimination of basic as well as acidic dyes onto CS/mOF-74. Thermodynamically, the negative value of isosteric heat of adsorption (Δ$\bar{\mathrm{H}}$) concluded that the current study was found exothermic in nature. Moreover, electrostatic interactions, hydrogen bonding, and electron donor–acceptor interactions were suggested as probable mechanisms in the current adsorption process. The current study estimates the industrial importance of a chitosan composite of MOF-74 as it requires a short adsorption equilibrium time for the removal of the dyes and is satisfactorily reusable.

KEYWORDS:

• Chitosan
• kinetics
• mofs
• methyl orange
• polymer
• thermodynamics

Highlights

• The adsorption capacity of CS/MOF-74 6–8 times greater than its counterparts.

• The dominant interactions for dyes removal were electrostatic and hydrogen bonding.

• After five cycles of regeneration, the adsorption capacity was found to be 70%.

Acknowledgments

The authors would like to convey their gratitude to the Prince Sattam Bin Abdulaziz University (project number PSAU/2023/R/1444), Al-Kharj 16278, Saudi Arabia, National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar Pakistan, and Bacha Khan University, Charsadda, Pakistan for providing us with the necessary support and facilities to carry out this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Novelty statement

The literature revealed that the porous structure and ultra-high surface area make Zinc MOF (MOF-74) an excellent adsorbent for the removal of dyes from aqueous media. However, to date, less consideration has been paid to the chitosan composite of MOF-74 for the efficient removal of dyes. The current study focuses on the novel adsorbent, i.e. chitosan (CS) composite of MOF-74 for the removal of MB and MO for the first time. Due to the presence of functional groups (NH₂ and OH), the CS has been found as an excellent candidate to productively increase the surface area and adsorption active sites as a result, the adsorption capacity of CS/MOF-74 must be increased.