Coconut Husk Ash Fabricated CoAl-Layered Double Hydroxide Composite for the Enhanced Sorption of Malachite Green Dye: Isotherm, kinetics and thermodynamic studies

In this work, the new composite material has been designed by using coconut husk ash (CHA) as the supporting material for CoAl layered double hydroxide (LDH), and investigated the adsorptive removal of organic dye malachite green (MG) from the aqueous media. The as-synthesized sorbent was prepared via simple co -precipitation method by loading 3 g of coconut husk derived carbon on to the structure of CoAl-LDH. The physicochemical properties and the formation of the composite material was confirmed by various character-ization techniques such as powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), Scanning emission microscopy (SEM), Energy dispersive X-ray (EDX), Transmission emission microscopy (TEM) and Brunauer-Emmett-Teller (BET). The experimental results envisages that the proposed adsorbent CHA/CoAl-LDH composite showed the significant removal efficiency up to 98.16 % at 0.015 g dosages under initial dye concentration of 100 mg/L and pH 10. In addition, the maximum monolayer adsorption capacity exhibited by CHA/CoAl-LDH from the isotherm studies was 666.4 mg/g. The isotherm and kinetics data was fitted well ac-cording to Langmuir and pseudo second order model. The thermodynamic studies obtained positive value of delta H (CHA = 72.49 KJ/mol, CHA/CoAl-LDH = 110 KJ/mol) and negative delta G values (CHA =-9.36 KJ/mol, CHA/ CoAl-LDH = -6.62KJ/mol) at 303 K, which further confirmed the spontaneous and endothermic nature of adsorption process. Furthermore, the estimated value of activation energy (E-a) determined from the modified Arrhenius equation was 101.35 KJ/mol and 69.50 KJ/mol for CHA and CHA/CoAl-LDH, respectively. Besides, the proposed adsorbent also reveals excellent reusability up to third cycle, as well as effective for the removal of other cationic and anionic dyes. Therefore, the overall result advocated that the adsorbent CHA/CoAl-LDH can be chosen as an alternative for dye treatment in aqueous media.

Automated summary

In this study, a new composite material was designed using coconut husk ash as the supporting material for CoAl layered double hydroxide, and its adsorptive removal of an organic dye from aqueous media was investigated. The experimental results showed that the composite material exhibited high removal efficiency and adsorption capacity under specific conditions, and it possessed favorable thermodynamic and kinetic properties, making it suitable for dye treatment.