Adsorption Studies of Some Dyes on Different Adsorbent Surfaces

          Orange peels are a promising agro industry-waste that can be implemented in the extraction and production of pectin, as dietary fiber in food formulations, and as a biopolymer for metal adsorption in water treatment. In the present work, the adsorption behavior of methylene blue (MB) and erichrome black T (EBT) dyes by using cheap and eco-friendly orange peels which was chemically modified by sodium hydroxide (NaOH) and a cetyltrimethyl ammonium bromide (CTAB) have been studied. Physical and chemical properties of sorbents were determined by using Fourior transform Infrared (FTIR), Scanning Electron Microscopy (SEM),Atomic Force Microscopy (AFM), Gas Chromatography Mass (GCMS) and Zeta Potential Analyzer techniques. The particle size of orange peels (OP)and its modified forms surfaces were measured by particle size analyzer and the results of surface area of OP (0.7069), SOP (1.1705) and CTAB-OP (1.2606) m2 / g The adsorption properties of unmodified orange peels  and modified orange peels surfaces includes a study of the adsorption of methylene blue and erichrome black T dyes from their aqueous solutions adsorption measurements was done using UV-Visible Spectrophotometry to follow adsorption capacity of surfaces under investigation. The influential factors upon the adsorption process were studied which include the effect of initial concentration of dyes, the solutions-pH, contact time, sorbent dosage and temperature, all studies  achieved  was studied in batch experiments. Contact time and kinetic behavior  were studied for methylene blue and  erichrome black T  dyes with all sorbents  at fixed concentrations ( 25,9) mg/L,  pH =(3,4,9,12)   at different temperatures.The experimental results show that the obtained equilibrium contact time for MB adsorption was (30, 30, 25) min on OP, SOP and CTAB-OP surfaces, respectively. The  MB and EBT dyes percentage   removal were increased with the increase in contact time, the % R for  MBOP reach ( 47%), MB SOP   (97%), EBTOP ( 75  %), EBT SOP  (54  %) and EBT CATB(95 %)  .The experimental data were fitted into the following kinetics model: pseudo-first order model, pseudo-second order model and intra particle diffusion models. It was observed that pseudo-second order described the adsorption with high correlation factor (R 2) better than any other kinetic models. The equilibrium isotherms, for the adsorption of (MB) and   (EBT) dyes on the sorbents surfaces were analyzed considering the Langmuir,Freundlich and Temkin isotherms models. The Freundlich isotherm provided the best fit for MB and EBT dyes on the sorbents surfaces. The thermodynamic of adsorption of the MB and EBT dyes on the sorbents surfaces were also investigated over the range of temperatures (298- 318) K.The thermodynamic values of ΔG are negative in all system indicating a
spontaneous process. Negative values of ΔH indicate an exothermic process in nature and indicating that the process occurs is physical adsorption because its values less than 40 kJ / mol   .