Preparation of low-cost and non-conventional macroalgae-based biosorbent for fast and effectively selective dye adsorption

In the present work, a low-cost, non-conventional, and novel biosorbent was developed by an easy and eco-friendly pathway using Ulva Lactuca (U. Lactuca) marine algae and calcined eggshell. The dead U. Lactuca biomass was alkali treated with a calcined eggshell which has high calcium carbonate and calcium oxide content. The new biosorbent was characterized using XRD, FTIR, SEM-EDS, XPS, TGA, and Zeta-potential and then employed for selective and individual dye adsorption. Interestingly, it was found that the biosorbent rapidly separated both cationic methylene blue (MB) and anionic Congo red (CR) from various binary dye solutions. A number of individual MB and CR adsorption studies on the biosorbent were conducted under different conditions. The results showed that the adsorption capacity of the algae was enhanced after being treated with a calcined eggshell, and it exhibited excellent adsorption performance for MB removal with a maximum adsorption capacity of 2000 mg g −1. In addition, the adsorption process was so fast that it reached equilibrium within 15 min. Over the four cycles, the biosorbent exhibited no significant loss in adsorption capacity. The MB dye adsorption data onto the biosorbent were well fitted by the second-order kinetic model and the Langmuir isotherm. Based on the possible adsorption mechanisms of the biosorbent for two dyes, the adsorption process of MB can be attributed to the unconverted calcium carbonate mineral phase in the biosorbent structure, electrostatic interactions, and hydrogen bonding, while the removal of CR can be attributed to the mineral phase and hydrogen bonding. This study shall provide a new perspective on the development of an inexpensive, easily prepared, and excellent adsorption performance biosorbent for the rapid removal of organic dyes from wastewater.