Gradient Adsorption Of Compound Silica Nanosheets Towards Methylene Blue And Rhodamine B From Aqueous Solution

Adsorption is a common waste water treatment method which is environmental,efficient and easy to operate.Silica nanosheets（Si NSs）is an emerging and promising adsorbent precursor owing to its easy preparation,low cost and very low layer charge.The gemini surfactant 1,3-bis（hexadecyldimethylammonio）propane dibromide（16-3-16）was synthesised for switching Si NSs to be organo Si NSs（OSIs）.Characteriation methods,Fourier transform infrared spectroscopy（FT-IR）,thermogravimetric analysis（TG）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）etc.,were used to explore the structural character of gemini surfactant and adsorbents.Methylene blue（MB）and rhodamine B（Rh B）were taken as targets,gradient adsorption was adopted to treat binary system simulate sewage by compound Si NSs（raw Si NSs and OSIs）,the first order derivative spectroscopy method was improved to test the separate dye concentration in binary system.The results of structural characterization showed that the prepared gemini surfactant has a higher purity.The results of elemental analysis（EA）,FT-IR,TG proved the success of modification.And the resultant Si NSs and OSIs known possess layered structure with porous and large surface area as the results of SEM and BET displayed.The results of adsorption showed that,in single system,the adsorptions of MB and Rh B on Si NSs and OSIs were 350.4 mg g^-1（R=91.3%）and 267.5 mg g^-1（R=79.8%）within 15 min,respectively,which was caused by electrostatic or hydrophobic interactions,separately.Therefore,chargeability,hydrophobicity and surface area of the adsorbents also played significant roles in adsorption.In binary-dye system,the total removal efficiency of gradient adsorption reached 99.5%（MB）and 86.4%（Rh B）under the same conditions,the affinity of the adsorbents to MB was stronger than that of Rh B.The results of kinetic,isotherms and thermodynamics researches showed,the calculated kinetic parameters indicating pseudo-second order kinetic model can fit well with the adsorptions of MB and Rh B,and thermodynamics parameters were fitted by the model of R-P adsorption isotherms,negativeΔH°suggests exothermic nature of the adsorption process for the contaminants.Besides,according to the results of regeneration tests,the compound Si NSs could be regenerated by 0.1 mol L^-1 HCl acid picking at least 3 cycles.