Adsorption of methylene blue and rhodamine B dyes from aqueous solutions with nano-composites obtained from pumpkin and melon peel

It is very important that water, which is an indispensable source of life, is clean for the sustainability of living life. With the development of the industry and the establishment of many production plants, wastewater discharged into aquatic environments poses an environmental threat as it pollutes drinking water sources. Therefore, clean water resources are decreasing day by day and it has become important to treat wastewater mixed with existing water resources. Adsorption, which is one of the treatment methods widely used in treatment plants, is a very effective method in the removal of dyestuffs and similar organic pollutants. In this process, many materials with different properties are used as adsorbents, and research on the development of more efficient and environmentally friendly adsorbents is increasing. Polluted water caused by discharges of the textile industry contains organic, inorganic chemicals, and dyestuffs of different structures. In recent years, it has become important to remove dyestuffs from the aqueous environment, which cause serious health problems on living things in the environment and threaten living life. In this study, various adsorbents were synthesized from naturally derived adsorbents, namely pumpkin peel (BKK), melon peel (KK), pumpkin peel biochar (BKK-BC), melon peel biochar (KK-BC), pectin pumpkin peel biochar composite (P@BKK-BC), pectin melon peel biochar composite (P@KK-BC) and nano-iron-modified biochar composites (nMe0-P@BKK-BC and nMe0-P@KK-BC). Batch vessel adsorption experiments were performed to remove methylene blue (MB) and rhodamine B (RhB) dyestuffs prepared in certain concentrations with the obtained adsorbents (BKK, KK, BKK-BC, P@BKK-BC, P@KK-BC, nMe0-P@BKK-BC and nMe0-P@KK-BC). The adsorbents used in experimental studies were characterized by FT-IR, SEM, XRD and EDX analyses. The effects of parameters such as dye concentration, contact time, solution pH, adsorbent amount and temperature on dye removal were investigated in adsorption processes carried out in batch vessels. According to the experimental results obtained, the parameters that provide optimum removal were calculated. Among these parameters, solution pH (pH 9 and pH 11) and adsorbent dose were found to be (0,3-0,4 g) for biomasses, 0,2 g for biochars, 0,05 g for biochar composites and nanocomposites. Equilibrium contact time was studied as 120 min for biomass (BKK) and 180 min for biochar and nano-composites adsorbents. For MB and RhD removal, equilibrium was reached within 90 min for biomass (BKK) and 120 min for biochars, biochar composites, and nano-composites. For equilibrium isotherm studies, appropriate isotherms were drawn and adsorbent capacities were calculated for each adsorbent type. The results obtained from the isotherm formulas applied to the equilibrium studies conducted with the produced adsorbents showed that the Langmuir isotherm model was more suitable for the equilibrium study. The maximum adsorption capacities calculated from these isotherms for RhB removal were 181,82 mg/g for BKK, 185,19 mg/g for BKK-BC, 370,37 mg/g for P@BKK-BC, 370,38 mg/g for nMe0-P@BKK-BC, 370,37 mg/g for KK, 370,06 mg/g for KK-BC, 357,14 mg/g for P@KK-BC and 357,14 mg/g for nMe0-P@BKK-BC, respectively. In MB removal; maximum adsorption capacities based on the Langmuir isotherm were calculated as 384,62 mg/g for BC, 370,37 mg/g for BC, 370,37 mg/g for P@BKK-BC, 370,38 mg/g for nMe0-P@BKK-BC, 370,41 mg/g for KK, 370,10 mg/g for KK-BC, 357,12 mg/g for P@KK-BC, and 357,14 mg/g for nMe0-P@KK-BC. As a result of kinetic studies for both types of dyestuffs, it was observed that the adsorption was compatible with the pseudo-second-order kinetic model. Gibbs free energy change values were found to be negative. This shows that the adsorption process takes place spontaneously. As a result, it was concluded that the new adsorbents can be used in the removal of dyestuffs from aqueous solutions.