Nanoporous Activated Carbon Derived via Pyrolysis Process of Spent Coffee: Structural Characterization. Investigation of Its Use for Hexavalent Chromium Removal

Georgios Asimakopoulos,Michael A Karakassides,Vasilis Kostas,Athanasios B Bourlinos,Constantinos E Salmas,Marios Papantoniou,Radek Zbořil,Maria Baikousi

doi:10.3390/app10248812

Abstract

Hexavalent chromium (Cr(VI)) is a heavy metal that is highly soluble and exhibits toxic effects on biological systems. Nevertheless, it is used in many industrial applications. The adsorption process of Cr(VI), using activated carbon (AC), is under investigation globally. On the other hand, around six million tons of spent coffee is sent to landfill annually. In the spirit of cyclic economy, this research investigated the production of AC from spent coffee for the removal of Cr(VI) from wastewater. The AC was produced via pyrolysis process under a nitrogen atmosphere. Chemical activation using potassium hydroxide (KOH) occurred simultaneously with the pyrolysis process. The produced AC was tested as an absorber of Cr(VI). The best fitted kinetic model was the diffusion–chemisorption model. A 24-h adsorption experiment was carried out using a solution with a pH of 3 and an initial Cr(VI) concentration of 54.14 ppm. This resulted in an experimental maximum capacity of 109 mg/g, while the theoretical prediction was 137 mg/g. It also resulted in an initial adsorption rate (ri) of 110 (mg/(g h)). The Brunauer–Emmett–Teller surface area (SgBET) was 1372 m2/g, the Langmuir surface area (SgLang.) was 1875 m2/g, and the corrugated pore structure model surface area (SgCPSM) was 1869 m2/g. The micropore volume was 84.6%, exhibiting micropores at Dmicro1 = 1.28 and Dmicro2 = 1.6 nm. The tortuosity factor (τ) was 4.65.

Highlights

Nowadays, the cyclic economy spirit globally makes imperative the need for exploitation of biomass and biowaste to balance the impact of industrial activities on environmental pollution and public health
The world requirements for activated carbon (AC) are expected to increase dramatically and to reach the amount of 5424.9 kilotons by the year 2021 [6]
The main aim of this work was to combine the benefits of spent coffee biowaste valorization and wastewater purification through Cr(VI) removal by adsorption in bio-activated carbon

Summary

Introduction

The cyclic economy spirit globally makes imperative the need for exploitation of biomass and biowaste to balance the impact of industrial activities on environmental pollution and public health. One of the biomass exploitation products is the biomass derived from activated carbon (AC). Since the age of the ancient Egyptians, biomass-derived activated carbon (AC) has been used to enhance land fertility, as fuel, or in medical applications. Activated carbon (AC) is used in many advanced applications such as catalyst supports, electrode materials, air filters, and gas storage, and since 1800, as an adsorbent for wastewater treatment [1,2,3,4]. The world requirements for activated carbon (AC) are expected to increase dramatically and to reach the amount of 5424.9 kilotons by the year 2021 [6]. The USA and China will be the two largest markets of AC

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Conclusion