Synthesis Of Modified Activated Carbon-Alginate Beads And Their Adsorption Characteristic For Bisphenol-AF

The problem of endocrine disrupting chemicals(EDCs)in the aquatic environment has attracted considerable interests in recent years.As one of the EDCs,bisphenol-AF(BPAF)has been extensively used in many fields,and it is more dangerous than bisphenol-A(BPA).While little report has been published regarding the efficient removal of BPAF from wastewater,thus,a simple,rapid,and reliable method is of great importance.Adsorption has been proved to be a potential treatment options for the effective removal of organic contaminants by many researchers.And activated carbon(AC)shows great performance in adsorbing EDCs due to its high porosity and large surface area.While difficulties in the recycling of AC powder and its low affinity to hydrophobic organic compounds both limited its application,thus two methods were proposed to modify AC in this study,and the better one was choose to be futher studied.Basing on the fits of kinetic and isotherm models,several mechanisms have been discussed to explain the enhanced adsorption behavior of BPAF on AC-AB.Also,two eluents were investigated to regenerate AC-AB.Further,the efficiency of AC-AB in the coadsorption of BPAF and BPA were explored,suggesting its extensive application in industrial processes.The conclusions of this work are summarized as follows:(1)Characterization indicated that the introduction of alginate and CTAB solved the difficulties in recycling of AC powder,and enhanced its adsorption affinity to BPAF.As a typical immobilized agent,alginate achieved the effective collection of AC in industrial processes by enlarging its particle size.CTAB changed the surface natures of AC-AB from hydrophilicity to hydrophobicity,leading to the significant increases in the cation exchange capacity,oxygen functional groups,and positive charge.(2)Compared with the traditional two-step method,one-step method showed better performances in equilibrium time and adsorption capacity.Two methods were used to synthesize the adsorbent:the one-step method dispersed AC-AB and CTAB in wastewater,followed by the removal of BPAF accompanied with the synthesis of CTAB-modified AC-AB(AC-AB-CTAB).The maximum amount of BPAF was achieved with 96.69 mg/g when the concentration of CTAB reached 1.1 mmol/L,while a significant decrease could be observed when the concentration exceeded 1.1 mmol/L,and this was due to the competition between micelles and monomer of CTAB.Two-step method first synthesized AC-AB-CTAB,then used it to remove BPAF by adsorption,which reached equibrium within 16 h.The adsorption of BPAF increased with increasing concentration of CTAB until 1.1 mmol/L,and the maximum amount of BPAF was 94.78 mg/g,then it remained almost constant.(3)Results indicated that the removal of BPAF on AC-AB was distinctly enhanced in one-step method,and the maximum removal amount of BPAF approximately 284.6 mg/g was achieved in a system containing 0.5 g/L AC-AB and 1.1 mmol/L CTAB.Kinetic studies and adsorption isotherms demonstated that the adsorption of BPAF on AC-AB could be expressed by Pseudo-second-order model and Dubinin-Ashtakhov(D-A)isotherm,respectively.And the calculation of thermodynamic parameters suggested the spontaneous,random,and exothermic nature of the adsorption.The most suitable range of pH was 5.0?8.0,and both the ionic strength and inorganic ions showed negative effects on the adsorption of BPAF.Thus,several conclusions could be made:the rate-limiting step of BPAF on AC-AB was external mass transfer,also intra-particle diffusion attributed to this system;hydrophobic interactions,hydrogen bonds,and ?-?electron donor-acceptor(EDA)interactions could be used to explain the enhanced adsorption behavior of BPAF on AC-AB with CTAB;the high stability of AC-AB within five regeneration cycles was verified in this part.(4)The maximum amount of BPAF and BPA in double system reached 383.3 mg/g under the optimum dosages of AC-AB and CTAB.BPAF and BPA were choose to be studied the application of AC-AB in double system.Results indicated that the weak competition between BPAF and BPA in double system could be observed,and Pseudo-second-order model and Redlich-Peterson(R-P)isotherm described the total adsorption behavior of BPAF and BPA on AC-AB well.The-F groups of BPAF impeded its movement from liquid to the particle surface,which reduced its adsorption capacity and showed a relative disadvantage in the competition with BPA.