A systematic study of hexavalent chromium adsorption and removal from aqueous environments using chemically functionalized amorphous and mesoporous silica nanoparticles

Seung Pil Pack,Eun-Hye Jang,Il Kim,Sungwook Chung

doi:10.1038/s41598-020-61505-1

Seung Pil Pack, Eun-Hye Jang + Show 2 more

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https://doi.org/10.1038/s41598-020-61505-1

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Journal: Scientific Reports	Publication Date: Mar 27, 2020
Citations: 74	License type: open-access

Affiliation: Korea University, Pusan National University

Abstract

We report on the synthesis and characterization of highly monodisperse amorphous silica nanoparticles (ASNs) and mesoporous silica nanoparticles (MSNs) with particle sizes of 15–60 nm. We demonstrate adsorption of Cr(VI) ions on amino-functionalized ASNs (NH2–ASNs) and MSNs (NH2–MSNs) and their removal from aqueous environments and show the specific surface area (SSA) of NH2–MSNs is four times as larger as that of NH2–ASNs and that more than 70% of the total SSA of NH2–MSNs is due to the presence of nanopores. Analyses of Cr(VI) adsorption kinetics on NH2–ASNs and NH2–MSNs exhibited relatively rapid adsorption behavior following pseudo-second order kinetics as determined by nonlinear fitting. NH2–ASNs and NH2–MSNs exhibited significantly higher Cr(VI) adsorption capacities of 34.0 and 42.2 mg·g−1 and removal efficiencies of 61.9 and 76.8% than those of unfunctionalized ASNs and MSNs, respectively. The Langmuir model resulted in best fits to the adsorption isotherms of NH2–ASNs and NH2–MSNs. The adsorption of Cr(VI) on NH2–ASNs and NH2–MSNs was an endothermic and spontaneous process according to the thermodynamic analyses of temperature-dependent adsorption isotherms. The removal efficiencies of NH2–ASNs and NH2–MSNs exhibited a moderate reduction of less than 25% of the maximum values after five regeneration cycles. Furthermore, NH2–MSNs were also found to reduce adsorbed Cr(VI) into less harmful Cr(III).

Highlights

We report on the synthesis and characterization of highly monodisperse amorphous silica nanoparticles (ASNs) and mesoporous silica nanoparticles (MSNs) with particle sizes of 15–60 nm
We present a comprehensive analysis of Cr(VI) adsorption and removal on both bare and NH2-functionalized ASNs and MSNs in aqueous environments
Further analyses of N2 sorption measurements using a simple geometric scaling approach revealed that more than 70% of the total specific surface area of MSNs and NH2–MSNs was attributable to nanopores within MSNs and NH2–MSNs, respectively

Summary

Introduction

We report on the synthesis and characterization of highly monodisperse amorphous silica nanoparticles (ASNs) and mesoporous silica nanoparticles (MSNs) with particle sizes of 15–60 nm. Sequestration strategies targeting the adsorption and reduction of Cr(VI) to less harmful Cr(III) attracted considerable research attention because of their obvious advantages over strategies aimed at the separation of Cr(VI)[6] Methods such as adsorption[7,8,9], ion-exchange[10,11], membrane separation[12,13], coagulation[14], chemical precipitation[15,16], extraction[17], dialysis[18], and electrochemical separation[19] have been shown to be capable of removing heavy metal ions, including hexavalent chromium from wastewater. Mesoporous silica with uniform and tailorable pore dimensions exhibits unique material properties such as high specific surface areas and excellent thermal and mechanical stabilities, and has been employed in potential applications[34] These include their use in heavy metal removal from wastewater[6], indoor air purification[35], CO2 capture[36], pervaporation membranes for the separation of water from ethanol[37]

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