| Natural rectorite exhibits electronegativity and strong hydrophilicity,resulting in poor adsorption of anionic dyes,which greatly limit the application range of rectorite to industrial water treatment.In this paper,the changes of rectorite before and after adsorption of typical dyes were studied.The effect of differernt concentrations were compared before and after the experiment combined with characterization of SEM,XRD,FT-IR and BET.Besides,the modified rectorite(M-REC)was prepared with the cationic surfactant cetyl trimethyl ammonium bromide(CTAB).The physical and chemical properties,surface morphology and structure of M-REC were characterized by SEM,XRD,FT-IR,TG and Zeta potential.Based on the positive charge characteristics of M-REC,the adsorption performance of anionic dye acid orange(AO)was studied.For comparison,two kinds of typical cationic dyes methylene blue(MB)and crystal violet(CV)were also selected to explore adsorption behavior by REC and M-REC,the structure changes of M-REC before and after dye adsorption and the migration of dye molecules in the adsorption process were discussed.Through the above research,the main conclusions are as follows:The adsorption capacity of REC to neutral red(NR)and MB is higher than AO.Under different concentration conditions,the adsorption capacity of REC to MB is smaller than that of NR.XRD results showed no change in the crystal structure of REC after adsorption of MB/NR.However,SXRD results indicated that the cationic dye molecule MB/NR entered the layers of REC.It had an effect of swelling and opening between the layers of REC,resulting in an increase in the interlayer spacing.The FT-IR spectra analysis indicated that MB and NR had been adsorbed on the surface of REC,and there was an electrostatic attraction between REC and the positively charged cationic dye MB/NR.However,it had no effect on the basic silicate skeleton of REC.The best conditions for preparing modified rectorite: modifier dosage 1.2 CEC,liquid-solid ratio 10:1,modification temperature 60 °C,oscillation speed 150 r/min,modification time 5 h.According to the characterization results,the modifier CTAB was successfully embedded in the interlayer of REC.The layered structure of M-REC became loose and more pore structures appeared.And the interlayer distance of M-REC was enlarged from 2.57 nm to 3.13 nm.TG analysis indicated that the modifier was almost completely loaded on REC.Zeta potential analysis showed that the surface charge of M-REC was changed from negative to positive after modification.The adsorption equilibrium time of M-REC for AO was 30 min.The uptake of AO increased along with increased the dosage of M-REC,while solution p H was not affected the removal efficiency of AO.The adsorption isotherm was well described by Langmuir model,the calculated AO adsorption capacity was 98.59 mg/g,and the adsorption process belongs to monolayer adsorption.The adsorption kinetic data were fitted by the pseudo-second order model.The removal process was dominated by chemical adsorption.Reusability of the adsorbent is an important parameter in order to consider the practical applicability.The recycling and recyclability of M-REC were good and the adsorption capacity of AO still occupied more than 97% of the initial adsorption capacities after five cycles.By analyzing the distribution mechanism of three dyes adsorbed by M-REC,it was found that the anionic dye molecules AO entered the interlayer of the M-REC,and the electrostatic attraction occurred between positively charged organic chain of the M-REC and AO,which expanded the interlaminar domain volume of the rectorite.However,the electrostatic repulsion existed between the cationic dye MB/CV molecules and the M-REC resulted in the MB/CV molecules simply filled the surface and interlamellar of the rectorite.The adsorption mechanism analysis confirmed that electrostatic attraction between the positively charged M-REC surface and the negatively charged AO played a key role in the high uptake of AO from water. |
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