Polyphenol rich green tea waste hydrogel for removal of copper and chromium ions from aqueous solution

Lei Nie,Dangling Hua,Shuang Liang,Tongchao Wang,Amin Shavandi,Kehui Hu,Meng Sun,Shiliang Liu,Oseweuba Valentine Okoro,Pengbo Chang,Jinfang Sun

doi:10.1016/j.clet.2021.100167

Abstract

In this study, green tea waste (GTW) was used to synthesize the iron oxide (IO) nanoparticles ([email protected]) to facilitate the adsorption of heavy metals from wastewaters. To satisfy structural integrity needs, the synthesized [email protected] was incorporated into a polyvinyl alcohol (PVA)/alginate polymer network to obtain PVA/alginate/IO (PAI) hydrogels. Experimental techniques of transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were subsequently used to confirm the successful synthesis of IO nanoparticles. Scanning electron microscopy (SEM) established the porous microstructure of PAI hydrogels, while FT-IR analysis revealed the physical incorporation of [email protected] in PAI hydrogels. The adsorption of Cu2+ and Cr6+ on PAI hydrogels was subsequently investigated. The present study was able to show that the removal ratio and adsorption capacity of the synthesized PAI hydrogels depended on the pH, initial concentration of metal ions in the solution, and contact time. The equilibrium isotherms of Cu2+ and Cr6+ adsorption were well-described using Langmuir and Freundlich isotherm models. The adsorption kinetics of Cu2+ can be modelled using the pseudo-second-order model, and the adsorption kinetics of Cr6+ can be modelled using both pseudo-first-order and intraparticle diffusion models. This study, therefore, demonstrates the functionality of integrating green tea waste in a polymeric composite to perform as an effective and green adsorbent for heavy metal removal, thus indicating the viability of its future application in wastewater treatment operations.

Highlights

The discharges of toxic metal ions in aquatic ecosystems may cause severe environmental contamination due to the bioaccumulation in the food chain (Gong et al, 2012)
The dried iron oxide (IO)@green tea waste (GTW) nanocomposite powder could be stored in a glass bottle at room temperature (RT), as shown in the photo inserted at the right-bottom of Fig. 2b
The iron oxide using green-tea-waste (IO@GTW) nanocomposite was dispersed in ultrapure water, and the hydrodynamic diameter was quantitatively evaluated by dynamic light scattering (DLS) (Fig. 2c)

Summary

Introduction

The discharges of toxic metal ions in aquatic ecosystems may cause severe environmental contamination due to the bioaccumulation in the food chain (Gong et al, 2012). According to the work of Nriagu and Pacyna (1988) heavy metals such as copper, nickel, zinc, cadmium, and lead are toxic. Liu et al (2008) identified chromium and mercury as highly toxic. Copper (Cu) exists extensively in the environment since it is widely used in paints and pigments, paper, and pulp and copper polishing (Qiu et al, 2012). Cr exists in two oxidation states, namely, Cr3+ and Cr6+ (Cr(III) and Cr(VI)), where Cr6+ is shown to be 500 times more toxic to humans than Cr3+ (Kowalski 1994)

Methods

Results

Conclusion