Biosorption of Cr(VI) Using Cellulose Nanocrystals Isolated from the Waterless Pulping of Waste Cotton Cloths with Supercritical CO2: Isothermal, Kinetics, and Thermodynamics Studies.

Siti Hajar Mohamed,Md Sohrab Hossain,Venugopal Balakrishnan,Mohamad Haafiz Mohamad Kassim,Ahmad Naim Ahmad Yahaya,Mohamed A Habila,Azham Zulkharnain,Muzafar Zulkifli

doi:10.3390/polym14050887

Abstract

In the present study, supercritical carbon dioxide (scCO2) was utilized as a waterless pulping for the isolation of cellulose nanocrystals (CNCs) from waste cotton cloths (WCCs). The isolation of CNCs from the scCO2-treated WCCs’ fiber was carried out using sulphuric acid hydrolysis. The morphological and physicochemical properties analyses showed that the CNCs isolated from the WCCs had a rod-like structure, porous surface, were crystalline, and had a length of 100.03 ± 1.15 nm and a width of 7.92 ± 0.53 nm. Moreover, CNCs isolated from WCCs had a large specific surface area and a negative surface area with uniform nano-size particles. The CNCs isolated from WCCs were utilized as an adsorbent for the hexavalent chromium [Cr(VI)] removal from aqueous solution with varying parameters, such as treatment time, adsorbent doses, pH, and temperature. It was found that the CNCs isolated from the WCCs were a bio-sorbent for the Cr(VI) removal. The maximum Cr(VI) removal was determined to be 96.97% at pH 2, 1.5 g/L of adsorbent doses, the temperature of 60 °C, and the treatment time of 30 min. The adsorption behavior of CNCs for Cr(VI) removal was determined using isothermal, kinetics, and thermodynamics properties analyses. The findings of the present study revealed that CNCs isolated from the WCCs could be utilized as a bio-sorbent for Cr(VI) removal.

Highlights

The cellulose nanocrystals (CNCs) were isolated from Supercritical CO2 (scCO2) pulped fibre using 64 wt.% H2 SO4 solution at a temperature of 45 ◦ C and 1:10 (g/mL) of solid to liquid ratio for a 1 h treatment time to enhance the crystallinity of cellulose by hydrolyzing the amorphous cellulose
CNCs isolated from scCO2 -treated waste cotton cloths (WCCs) were utilized as an adsorbent for Cr(VI) removal from aqueous solution
The morphological analyses showed that scCO2 CNCs had a porous surface, and a crystalline and rod-like structure, with a length of

Summary

Introduction

There is a growing attentiveness to the sustainable utilization of WCCs to reduce carbon footprints and environmental pollutions [1]. The most preferred disposal method of WCCs is open dumping in landfill sites, along with other domestic and municipal wastes [1,2,3]. This inappropriate disposal practice leads to the demolition of valuable cellulosic materials and poses severe environmental pollutions. The anaerobic decomposition of organic materials in WCCs in landfill sites causes greenhouse gas (GHGs) emissions such as methane (CH4 ) and carbon dioxide (CO2 ) [4,5]. The WCCs are rich in cellulose, which can be recycled and reused to produce value-added products [5]

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