Synthesis of nano-composites using laurel (laurus nobilis) and black halile (terminalia chebula) seeds as raw materials and removal of some dyes from aqueous media

Water is an indispensable resource for the sustainability of life. The damage caused to nature and the environment by polluted water sources created by developing technology is rapidly increasing daily. As clean water resources are dwindling and even near-depletion is imminent, wastewater recycling processes are being developed. Adsorption is a widely used method in wastewater treatment. Textile industry wastewater contains high concentrations of organic and inorganic chemicals, dissolved dyes and dyes of various structures. Removal of dyes, which cause serious adverse effects on the environment and especially on living things, from the aquatic environment is of great importance in terms of minimizing environmental damage and ensuring pollution control. In this study, a total of eight different adsorbents were synthesized from natural source adsorbents, namely laurel seed (DT), black halile seed (KH), laurel seed biochar (DT-BC), black halile seed biochar (KH-BC), Ca-alginate laurel seed biochar composite (Alj@DT-BC), Ca-alginate black halile seed biochar composite (Alj@KH-BC) and nano-iron (magnetic) modified biochar composites (nMe0-Alj@DT-BC and nMe0-Alj@KH-BC). Batch-vessel adsorption experiments were carried out for the removal of methyl violet (MV) and malachite green (MG) dyes from synthetically prepared aqueous solutions with the obtained adsorbents (DT, KH, DT-BC, KH-BC, Alj@DT-BC, Alj@KH-BC, nMe0-Alj@DT-BC and nMe0-Alj@KH-BC). The synthesized adsorbents were characterized by FT-IR, SEM, XRD and EDX analyses. In adsorption studies, the effects of parameters such as dye concentration, contact time, solution pH, adsorbent amount, and temperature on dye removal were investigated. The results showed that the values providing maximum removal were found to be between basic solution pH values (pH 9.0-10.5), adsorbent dosages of 0.30-0.40 grams for biomass, 0.20-0.40 grams for biochars, and 0.05 grams for biochar composites. The equilibrium contact time for adsorption was 90-120 minutes for biomass adsorbents, while it took 120 minutes for biochar and biochar composite adsorbents. Isotherms from the equilibrium isotherm studies were drawn, and the adsorbent capacities were calculated from the appropriate isotherms. The equilibrium isotherms for all adsorbents were found to be compatible with the Langmuir isotherm model. The maximum adsorption capacities obtained for MV dye removal were found to be 370.28 mg/g for DT, 183.92 mg/g for KH, 370.11 mg/g for DT-BC and 185.20 mg/g for KH-BC. The maximum adsorption capacities of biochar composite adsorbents were calculated as 357.21 mg/g for Alj@DT-BC, 180.47 mg/g for Alj@KH-BC, 357.24 mg/g for nMe0-Alj@DT-BC and 370.48 mg/g for nMe0-Alj@KH-BC. The maximum adsorption capacities obtained for MG dye removal were found as 370.41 mg/g for DT, 384.62 mg/g for KH, 370.10 mg/g for DT-BC and 370.37 mg/g for KH-BC. The maximum adsorption capacities of biochar composite adsorbents were calculated as 357.12 mg/g for Alj@DT-BC, 370.37 mg/g for Alj@KH-BC, 357.14 mg/g for nMe0-Alj@DT-BC and 370.38 mg/g for nMe0-Alj@KH-BC. Kinetic studies showed that the adsorption was consistent with the pseudo-second-order kinetic model. Adsorption experiments were conducted at 25°C, 35°C, and 45°C to determine the effect of temperature on adsorption efficiency. The calculated negative ΔG° values indicated that the adsorption of MV and MG dyes by the synthesized adsorbents was thermodynamically spontaneous. The increase in ΔG° values with increasing temperature indicates that the dye adsorption process is more favorable at lower temperatures. As a result, it has been understood that the produced composite adsorbents can be used in the effective removal of harmful dyes in wastewater, providing an environmentally friendly and practical solution and bringing a new perspective to water treatment methods. Keywords: Adsorption, Black halile seed, Equilibrium, Kinetics, Laurel seed, nano-Composite, Toxic dyes