Caffeine removal using Elaeis guineensis activated carbon: adsorption and RSM studies

Abstract

The palm (Elaeis guineensis), known as dendê, is an important oleaginous Brazilian plant with a high performance of oil production. In this work, a 2 3 full experimental design was performed and the response surface method (RSM) was used to indicate the optimum parameter of caffeine adsorption on Elaeis guineensis endocarp activated carbon, since the endocarp is the main by-product from dendê oil production. It was set the adsorbent point of zero charge (pH pzc), and the material was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The RSM results indicate removal efficiency (%) at the optimal conditions, 0.20 g of adsorbent, and caffeine initial concentration of 20 mg/L, and acidic medium was about 95%. Based on ANOVA and F test (F calculated > F standard), the mathematical/statistical model obtained fits well to the experimental data. The overall kinetic studies showed time was achieved after 5 h and caffeine adsorption followed the pseudo-second-order model suggesting chemisorption is a predominant mechanism. Redlich-Peterson and Sips models best represented the experimental data (0.967 < R 2 < 0.993). Thermodynamic revealed that caffeine adsorption was spontaneous at all temperatures studied, exothermic, and probably with changes in the adsorbate-adsorbent complex during the process. The tests conducted in different water matrixes corroborate the suitability of this adsorbent to be used in caffeine removal even in a complex solution.

Mechanism and behavior of caffeine sorption: affecting factors

“…It exhibits the Freundlich isotherm characteristics at low adsorbate concentrations and the Langmuir isotherm characteristics with monolayer capacity at high concentrations. 70 When Table 2 is examined, it is concluded that most of the adsorption studies are in agreement with the Langmuir and Freundlich isotherm models.…”

“…It exhibits the Freundlich isotherm characteristics at low adsorbate concentrations and the Langmuir isotherm characteristics with monolayer capacity at high concentrations. 70 …”

Highly effective adsorption of caffeine by a novel activated carbon prepared from coconut leaf

“…With the intention of assess the effect of different aqueous mediums on the caffeine removal, adsorption experiments were achieved using lagoon (Mundaú Lagoon, Maceió/AL, Brazil), tap and mineral water. The initial caffeine concentration was 75 mg.L -1 , 50 mg of CLAC, 30° C and 40 min contact time were used for the tests [36].…”

A Review of Caffeine Adsorption Studies onto Various Types of Adsorbents

“…Regarding pH, acidic pHs in the range 2-5 tend to yield the best results, such as produced as follows: at pH 2, a maximum adsorption capacity of 13 mg/g for the activated carbon obtained from Elaeis guineensis (palm oil) [93]; at pH 3, a Q max of 212.3 mg/g for biomass-derived activated carbons (dende coco and babassu coco) [94]; at pH 4, a Q max of 916.7 mg/g for grape stalk activated carbon [92]; and at pH 5, a Q max of 500 mg/g for pine activated carbon with K 2 CO 3 [91]. For pH values between 6.3 and 7.7, a Q max of 30.3 to 270 mg/g has been reported, being the case of activated carbons obtained from residues of Acacia mangium wood, pineapple plant leaves, Eragrostis plana, and peach stones [51,54,95,96].…”