CELLULOSE CHEMISTRY AND TECHNOLOGY Cellulose Chem. Technol., 56 (7-8), 881-890(2022) CELLULOSE HYDROGEL FIBRE FROM NIPA PALM (NYPA FRUTICANS) SHELL USED FOR ADSORPTION OF METHYLENE BLUE FROM WASTEWATER KHOA DANG NGUYEN Faculty of Environment, School of Engineering and Technology, Van Lang University, 69/68 Dang Thuy Tram Str., Ward 13, Binh Thanh District, Ho Chi Minh City, Vietnam Corresponding author: khoa.nd@vlu.edu.vn Received March 21, 2022 Cellulose was chemically extracted from nipa palm (Nypa fruticans) shell, which was used to prepare hydrogel fibre and applied as an environment-friendly adsorbent for methylene blue. The purified cellulose was dissolved in N,N- dimethylacetamide (DMAc), with the addition of 6% lithium chloride (LiCl), at room temperature for 5 days. Then, the cellulose solution was coagulated by the phase inversion process under ethanol vapor to obtain cellulose hydrogel fibre. The adsorption results showed that when the initial concentration of the methylene blue solution was increased from 20 to 100 mg/L at pH 10, the adsorption capacity also rose from 3 to 11.53 mg/g after 15-minute immersion. In addition, the equilibrium adsorption isotherm was well-fitted to the Langmuir isotherm model and the maximum adsorbed amount was 13.23 mg/g. Furthermore, the cellulose hydrogel fibre showed high reusability, as the removal efficiency of methylene blue remained at a level of approximately 80% after five recycles. Keywords: adsorption, cellulose, hydrogel, methylene blue, nipa palm INTRODUCTION In recent years, the intense development of the textile dyeing industry in Vietnam has contributed greatly to the country’s overall economic development. The textile dyeing industry does not only meet the needs of domestic consumption, but also brings great economic value from exports. Besides, the textile dyeing industry also creates jobs for a large labour force. However, most textile processing wastewater has high alkalinity and colorants, thus large amounts of chemicals are discharged directly into rivers, streams, ponds, lakes etc. Such wastewater is toxic to aquatic species. Therefore, it is necessary to treat dye- contaminated wastewater prior to discharging it into the environment by conventional processes, such as chemical precipitation, 1 ion exchange, 2 advanced oxidation, 3 and electrochemical processes. 4 However, these processes have significant disadvantages, for instance, incomplete removal, high energy requirements, chemical agents and massive production of toxic sludge. 5 Dye adsorption has been in the research focus in recent years due to its significant advantages in wastewater treatment. Various agricultural by- products have been investigated as adsorbents for the removal of dyes from wastewater. 6 Using low- cost alternative adsorbents to the expensive carbon materials is important due to its double benefits, in water treatment and in waste management. 7 Among the adsorption techniques, biosorption uses an inactive (non-living) sorbent of biological origin to bind different organic substances, including dye ions. Several functional groups, such as hydroxyls and amines in biopolymer-based adsorbents are able to increase the removal of the dye. As a biopolymer, cellulose is the most abundant polysaccharide in nature, the major source of cellulose being plant fibre (Fig. 1a). Approximately 40% of the plant composition represents cellulose, which serves as a solid structural fraction within the complex architecture of cell walls. Independently of its source, cellulose consists of D-glucopyranose ring units.