Florida International University

Water pollution has become a serious environmental challenge, threatening aquatic environment and human health as a result of continuous pollutants discharged from untreated wastewater, particularly from textile industries which often contains cationic and anionic dyes. To solve the problem, there is a need to develop a sustainable and effective adsorbent material which has the capability to remove these dyes from wastewater before being discharge into water bodies. In this study, we employed a waste biomass material, Albizia lebbeck pod (ALP) to construct X-ZnO@ALP composites (where x = 0.05 and 0.1 M, loading concentration of ZnO) via in-situ co-precipitation method for effective methylene blue (MB) and congo red (CR) adsorption from aqueous environments in a single batch adsorption system. The composite’s structure was examined using FTIR, SEM/EDS, BET, and XRD techniques. The successful incorporation of ZnO enhanced the surface potential of ALP, providing additional adsorption sites for MB and CR and increasing the BET surface areas to 40.56 and 32.71 m²/g. The maximum adsorption capacities were 82.2 mg/g (MB) and 75.6 mg/g (CR) for 0.05 M-ZnO@ALP, and 61.8 mg/g (MB) and 56.2 mg/g (CR) for 0.1 M-ZnO@ALP, respectively. The performance of 0.05 M-ZnO@ALP surpass that of 0.1 M-ZnO@ALP because increasing the ZnO content led to larger particle sizes, which could limit the available adsorption active sites responsible for MB and CR adsorption due surface blockage or aggregation. The MB and CR adsorption process of UMALP, 0.05 M-ZnO@ALP, and for 0.1 M-ZnO@ALP conform to the Langmuir isotherm and pseudo-second order kinetic models. Thermodynamic measurement confirmed that the MB and CR adsorption reaction is spontaneous, feasible and exothermic in character. The recycling experiments revealed that the MB and CR adsorption by 0.05 M-ZnO@ALP, and for 0.1 M-ZnO@ALP still maintained > 90% efficiency after three cycles, making them a suitable adsorbent materials for practical applications. Overall, ZnO-loaded Albizia lebbeck pod biomass showed a good potential for dye treatment from wastewater, • A novel nanocomposite material of x-ZnO@ALP was synthesized via an in-situ co-precipitation method. • XRD, SEM/EDX, and FTIR confirmed the successful synthesis of x-ZnO@ALP. • The constructed composite materials exhibit good adsorption performance toward MB and CR. • The MB and CR adsorption follows the pseudo-second-order kinetic and Langmuir isotherm models. • x-ZnO@ALP, effective, sustainable, and still maintain more than > 90 efficiency for MB and CR removal after 3 cycles.