The effect of mercapto-functionalization of thermo-acid activated diatomite for dye removal from aqueous solutions

ABSTRACT

For the adsorption of malachite green (MG), ‘purified by thermo-acid (HCl) diatomite’ (D_TA) and its derivative ‘3-mercaptopropyltrimethoxysilane functionalised diatomite’ (D_TA-MTMS) were prepared as adsorbent and the effects of thermo-acid activation and surface functional groups on adsorption were investigated. Many acids dissolve certain substances in diatomite and change their chemical composition. Thermo-acid treatment and silane-modified diatomite fractions were characterised byBrunauer-Emmett-Teller (BET), scanning electron microscope (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermal analysis (TG-DTA). The effects of contact time, solution pH, temperature and initial dye concentration on adsorption were investigated. Equilibrium isotherms are defined using nonlinear Langmuir, Freundlich, Dubinin – Radushkevich (D – R) and Sips adsorption isotherm equations. Isotherm data for both adsorbents are best fitted on the Freundlich and Sips model. The q_max values determined from the Sips model are 18.8415 mgg⁻¹ and 21.4713 mgg⁻¹ for D_TA and D_TA-MTMS, respectively. It was determined that D_TA-MTMS performed better than D_TA for MG adsorption. The results showed that MG adsorption was compatible with the pseudo-second-order (PSO) kinetic model. From the adsorption energy value (E < 8 kJ mol⁻¹), it was confirmed that physical adsorption was dominant in the adsorption process. The nature of the sorption process is exothermic and spontaneous (due to negative values ΔH° and ΔG°). The results of the study showed that prepared D_TA and synthesised D_TA-MTMS can be considered as an economical and promising adsorbent in removing organic dyes from wastewater.

KEYWORDS:

• Thermo-acid activation
• mercapto-silane
• diatomite
• malachite green
• adsorption

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

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Additional information

Funding

The authors thank for the financial support of the Van Yuzuncu Yil University Scientific Research Projects Support Unit [Project number:FB A-2018-5955].