| Organo montmorillonites have been regarded as economic and high effective adsorbates applied in wastewater treatment.However,after reaching equilibrium,adsorbates can’t adsorb more organic contaminants.It has attracted more attention to desorption from contaminant-sorbing adsorbates and the regeneration and recycling of adsorbates.Switchable surfactants are surfactants with special structure and the surface characteristics can be reversible controlling by external stimulus.Redox of electrochemically switchable surfactants can be carried out without other regents under different potentials,which provide a new method for regeneration of organo montmorillonites and desorption of organic contaminants.In this study,a cationic electrochemical switchable surfactant(11-Ferrocenylundecyl)trimethylammonium Bromide(FTMA)and phenol were selected to prepare modified montmorillonite(FTMA-Mt)as a sorbent and targeted contaminant,respectively to do research on electrochemical characteristics,desorption behavior of phenol from phenol-sorbing montmorillonites and phenol sorbing after electrochemical regeneration.Meantime,sorption mechanism of phenol on electrochemical surfactant modified montmorillonite sorbent was first studied.The main original conclusions are drawn as following parts,(1)According to the results of characterization,with the addition amount of FTMA increased,efficiency of cation exchange decreased,and sorption state of FTMA in the interlayer of montmorillonite existed four arrangement models of lateral-monolayer,lateral-bilayer,pseudotrilayer and paraffin-monolayer.Thermodynamic stability was enhanced with the addition of surfactants.(2)Sorption isotherms of FTMA-Mt and conventional cationic surfactants modified montmorillonites(CTAB-Mt and CPC-Mt)were linear and sorption mechanism were mainly partition.Sorption capacity of FTMA-Mt was larger than that of CTAB-Mt and CPC-Mt.Sorption process can be best described by the pseudo-second-order kinetics(R2>0.99)according to the results of kinetic,and chemical sorption is the main step of controlling rate.Calculated thermodynamic parameters,sorption of phenol on FTMA-Mt is spontaneous and endothermic.The confusion of system increased due to the sorption of phenol on to the surface or interlayer of FTMA-Mt.Maximal removal efficiency of phenol on FTMA-Mt was observed at pH of 7,with the value of pH exceed 9,removal efficiency of phenol abrupt decreasing.Sorption capacity of phenol decreased as the ionic strength was added.Sorption process was inhibited by coexisting cations,and following order:Na+<K+<Ca2+.(3)Cyclic voltammetry method was applied to investigated the electrochemical behavior of FTMA-Mt.Results indicate that FTMA-Mt is good electrochemical reversibility with the current ratio being approximately one and the difference between anodic and cathodic peak potentials with a peak separation of 50mV.(4)Desorption process of phenol from the phenol-adsorbing FTMA-Mt achieved to equilibrium after 16h and desorption efficiency was positive relation to the phenol concentration.Desorption efficiency of phenol released from the phenol-sorbing FTMA-Mt was more than 60%after electrochemically oxidation..After electrochemical regeneration,FTMA-Mt also have perfect sorption capacity for phenol sorption.As the original phenol concentration was larger,the desorption-sorption efficiency was better.Additionally,FTMA-Mt can be reused for phenol sorption after five cycles of sorption-regeneration.(5)Treatment effect of phenol in coking wastewater on FTMA-Mt was better than that on CTAB-Mt and CPC-Mt.As the concentration of modified montmorillonites was 1.25 g/L,the removal efficiency of phenol on FTMA-Mt,CTAB-Mt and CPC-Mt were 29.1,25.9 and 28.0%,respectively.The electrochemical regeneration of FTMA-Mt can be also appplied in phenol removl from coking wastewater with removal efficiency of 29.5%,which was lower than the origial removal efficiency on unregenerated FTMA-Mt(34.3%). |
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