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

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.

Biomass Waste Carbonization in Piranha Solution: A Route to Hypergolic Carbons?

“…In contrast, highly crystalline graphite displays sharper reflections with smaller d 002 values [19]. It is also worth noting that the d 002 value of SCPS is higher than that of pyrolyzed spent coffee with d 002 = 3.5 Å [16]. Based on the Scherrer equation, the L c crystallite height of the particles along the c direction was estimated at about 23 Å or 2.3 nm for both samples, values which correspond to stacks of 6-7 carbon layers per particle [21].…”

“…This motivates on-going research interest for utilizing this waste as a resource for biogas/biofuel production or for the extraction of useful chemicals [7][8][9][10]. Bread and spent coffee wastes have also been employed as starting material for the development of advanced functional carbon materials with interesting properties, often produced via conventional pyrolytic or hydrothermal carbonization methods [11][12][13][14][15][16]. However, to the best of our knowledge, no report on bread and coffee biomass waste carbonization in piranha solution has been published so far.…”

Hypergolic Synthesis of Inorganic Materials by the Reaction of Metallocene Dichlorides with Fuming Nitric Acid at Ambient Conditions: The Case of Photocatalytic Titania

“…The kinetics of Cr(VI) removal with or without UV irradiation at room temperature for both the as-made and calcined samples is depicted in Figure 8, top. Solutions of 50 mL, each containing 9 mg of titania (as-made or calcined) and an initial Cr(VI) concentration of 5.5 mg/L at pH = 3 (e.g., acidic industrial wastewaters), were used to carry out the experiments [27,28]. Accordingly, total Cr(VI) removal was achieved within 9 h for the as-made titania and within 3 h for the calcined titania under UV irradiation (Figure 8, top; closed-red and blue symbols).…”

Hypergolic Synthesis of Inorganic Materials by the Reaction of Metallocene Dichlorides With Fuming Nitric Acid At Ambient Conditions: The Case of Photocatalytic Titania

“…The kinetics of Cr(VI) removal with or without UV irradiation at room temperature for both the as-made and calcined samples is depicted in Figure 8, top. Solutions of 50 mL each, containing 9 mg of titania (as made or calcined) and initial Cr(VI) concentration of 5.5 mg/L at pH = 3 (e.g., acidic industrial wastewaters), were used to carry out the experiments [27,28]. Accordingly, total Cr(VI) removal is achieved within 9 hours for the as-made titania and within 3 hours for the calcined titania under UV irradiation (Figure 8, top; closed-red & blue symbols).…”