Chemical modification of lignin derived from spent coffee grounds for methylene blue adsorption

Abstract

In this work, spent coffee grounds (SCG) were treated using sulfuric acid hydrolysis in order to isolate the sulfuric acid lignin (SAL). The reactivity of SAL was improved through phenolation and acetylation. Spectroscopic analysis showed that the isolated lignin is composed of GHS type and it was characterized by a high amount of (C–C) and β-O-4 bonds. The thermal analysis showed that the phenolated sulfuric acid lignin (Ph-SAL) present higher thermal stability compared to SAL and acetylated sulfuric acid lignin. In addition, the phenolic hydroxyl group content increases from 2.99 to 9.49 mmol/g after phenolation. Moreover, a methylene blue (MB) adsorption test was established in order to find out the sorption capacity of different samples. The study showed that the adsorbed amount of dye increase after the chemical modification of SAL, especially after phenolation. The removal efficiency was enhanced after modification to reach 99.62% for Ph-SAL. The evaluation of the adsorption experimental data with the theoretical models of Langmuir and Freundlich showed that the best fitting was expressed by the Langmuir model for all samples. Finally, this study showed that lignin isolated from SCG can be simply and easily chemical modified and exhibits excellent adsorption ability towards cationic dyes (MB) in aqueous solutions. As a renewable, low-cost, and natural biomass material, lignin from SCG shows a promising practical and economical application of biomass in the field of wastewater purification.

Carbon Adsorbents from Spent Coffee for Removal of Methylene Blue and Methyl Orange from Water

“…The comparison of 13 C CP NMR spectra of the same material before (SCD, Figure A2 a) and after pyrolysis (PSC50, Figure A2 b) shows the influence of the temperature treatment. In the spectrum of raw SCD, well-resolved signals corresponding to all organic matter present in SCD such as cellulose, hemicellulose, and lignin, as well as proteins and lipids, can be observed [ 36 , 37 , 38 , 39 , 40 ]. Carbons of different polysaccharides such as cellulose and hemicellulose cause the intense and narrow signals between 60 and 110 ppm ( Figure A2 a).…”

“…A second and rather broad step (70.9% weight loss) is observed between 200 and 450 °C. This step can be assigned to the slow decomposition of hemicellulose, cellulose, and lignin (in that order), the main components of spent coffee [ 35 , 40 , 42 , 43 , 44 ]. Subsequently, the TGA data indicate a continuous weight loss until 1000 °C showing the decomposition of the sample [ 40 ].…”

“…3400 cm −1 appear (Figure 2a). All bands can be assigned to the cellulose and lignin present in the materials [35,40,44,[46][47][48][49] (Table 3). shows scanning electron microscopy (SEM) images of SCD after different treatments.…”

“…Classification of infrared bands[35,40,44,[46][47][48][49]. Bands in the area of 2000 cm −1 represent the natural resonance of the diamond crystal used for measuring.…”

Hybrid Biocomposites Based on Used Coffee Grounds and Epoxy Resin: Mechanical Properties and Fire Resistance

“…Coffee is one of the most important agricultural products sold worldwide [1]. World coffee exports reached 11.94 million bags in March 2021, compared with 11.66 million bags in March 2020 [2].…”