Dyes are chemical substances frequently used in the industry to provide stable and bright colors to a wide variety of products and materials (XUE et al., 2022). The wastewater from industries such as paper and cellulose, paint, rubber, plastic, textile, cosmetics, food, and hospitals are the primary contamination source by synthetic dyes in water bodies (SONWANI et al., 2020).
Synthetic dyes are used by industries mainly due to their low cost and the ease of producing different colors compared to available natural dyes (YAO et al., 2020). Currently, there are over 100,000 commercial dyes worldwide and approximately 280,000 tons of dyes are discharged into the water flow every year in the textile sector (KISHOR et al., 2021).
These organic molecules have potential toxicity, carcinogenicity, non-biodegradability properties, and can cause eye irritation, vomiting and reduced cardiac output (DAWOOD et al., 2017; NIDHEESH; ZHOU; OTURAN, 2018; XUE et al., 2022). When discarded in water bodies, dyes can interrupt sunlight penetration, reduce photosynthetic capacity and reoxygenation in aquatic environments (OVEISI et al., 2018). Consequently, these substances are considered as hazardous environmental pollutants.
Synthetic dyes are resistant to conventional biological treatment of wastewater due to their complex molecular structure and chemical stability (NIDHEESH; ZHOU; OTURAN, 2018). Flocculation, membrane filtration, advanced oxidation, coagulation, and adsorption have been implemented for wastewater treatment with synthetic dyes (AHMAD et al., 2020; GANG et al., 2021; XUE et al., 2022). Among these technologies, the use of adsorbent materials for water purification has gained attention due to their ease of operation, efficiency, and low cost (VRÎNCEANU et al., 2019; LI et al., 2019; AHMAD et al., 2020; GANG et al., 2021; XUE et al., 2022). This method can remove several types of synthetic dye without generating harmful substances and residues.
An ideal adsorbent must have the ability to be easily manufactured, economically viable, and have a high capacity for adsorption (GANG et al., 2021). In this context, the applicability of biochar in water treatment is gaining interest due to its sustainability and low production cost (CHOUDHARY et al., 2020).
Biochar can show a developed pore structure and high specific surface area with diverse functional groups that is advantageous for synthetic dye removal via various chemical and physical forces of attraction (XUE et al., 2022, GIRI et al., 2022). For example, biochar obtained from Chinese Fan-Palm showed adsorption capacity of 21.4 mg g− 1 for the removal of malachite green (GIRI et al., 2022). The maximum adsorption capacity of methyl orange from aqueous solution with mimosa derived biochars was 12.3 mg g− 1 (NGUYEN et al., 2021). Activation process can enhance the adsorption capacity. For instance, activated soybean-cake based biochar reached over 800.0 mg g− 1 removal of Rhodamine B and Congo Red from aqueous solution (ZHANG et al., 2022). Activated biochar produced from ashitaba biomass showed adsorption capacity higher than 400 mg g− 1 for the removal of methylene blue (XUE et al., 2022).
In the last years, the search for new biochar applied to synthetic dye removal has increased. In the researched literature, it was verified that the use of the babassu coconut mesocarp (Orbignya speciosa), has been little explored as an adsorbent of synthetic dye. Babassu coconut activated biochar is commonly commercialized in Brazil for residential water filters. In this context, the objective of this study was to evaluate the adsorption capacity of commonly used cationic dye (methylene blue) on activated babassu coconut mesocarp commercial biochar to determine the influence of operational factors on cationic dye adsorption including time, dye concentration, biochar dose and granulometric fraction.