Study On The Reversible Adsorption Mechanism Of Acid-base Regulated Switch Organic Bentonite

As a common adsorbent,organic bentonite is widely used in the treatment of organic wastewater.However,the lack of economical and effective regeneration methods for organic bentonite adsorbed organic pollutants restricts its application in organic wastewater treatment.On-off surfactants are a class of substances that can reversibly control the viscosity,surface activity and micelle morphology of the system through external stimulation.Among them,acid-base responsive on-off surfactants use the p H of the system as a means of regulation.The acid-base regulation system is mature,and the acid-base responsive on-off surfactant raw materials are easy to obtain,which provides new ideas for the regeneration of organic bentonite adsorbents and the desorption of adsorbed organic pollutants.In this paper,acid-base-responsive switchable surfactant dodecyl dimethyl amine oxide(C₁₂DMAO)was used as a modifier to modify sodium bentonite to prepare acid-base-regulated switchable organic bentonite(C₁₂DMAO-Mt)adsorbent.After C₁₂DMAO-Mt adsorbs pollutants in wastewater,C₁₂DMAO-Mt is regulated by changing the p H value of the system to release pollutants from C₁₂DMAO-Mt adsorbent,realizing the regeneration of C₁₂DMAO-Mt saturated with adsorption,so that C₁₂DMAO-Mt can be used again for the adsorption of pollutants.In this study,phenol and catechol were selected as the target pollutants,and the structural properties of modified bentonite,the adsorption and desorption regeneration mechanism and law of phenol and catechol on acid-base controlled switch organic bentonite were studied.The main results and conclusions are as follows:（1）The results showed that the addition of C₁₂DMAO changed the original morphological characteristics of bentonite and the size of the bottom layer spacing,and the layer spacing increased with the increase of C₁₂DMAO dosage.In the range of 60%CEC～150%CEC,the actual loading ratio of surfactant is more than 80%.According to the d₀₀₁ value,it can be inferred that the arrangement mode of C₁₂DMAO in the interlayer of bentonite is flat monolayer.XRD and TOC analysis showed that the intercalation mechanism of C₁₂DMAO on bentonite was ion exchange and hydrophobic interaction between long carbon chains.FT-IR results showed that the addition of C₁₂DMAO basically did not destroy the basic skeleton structure of the original soil.Thermogravimetric analysis results show that the decomposition law of C₁₂DMAO-Mt is consistent with that of conventional organic bentonite,and the thermal stability is good.（2）The adsorption isotherms showed that the adsorption capacity of C₁₂DMAO-Mt increased with the increase of C₁₂DMAO content.The adsorption of phenol and catechol by C₁₂DMAO-Mt showed a good linear law,and the adsorption was dominated by distribution.The adsorption capacity of organic bentonite modified by C₁₂DMAO and common zwitterionic surfactant BS-12 to phenol is not much different,and the adsorption of organic pollutants by C₁₂DMAO-Mt is feasible.The adsorption kinetics showed that the pseudo-second-order kinetic fitting could better describe the related adsorption behavior of phenol and catechol on C₁₂DMAO-Mt,and chemical adsorption was the main rate-controlling step.The adsorption experiments under different system p H showed that the optimum adsorption p H of C₁₂DMAO-Mt for phenol and catechol was between 6 and 7.The adsorption thermodynamics showed that the adsorption of phenol and catechol by C₁₂DMAO-Mt was spontaneous.In a certain range of ionic strength,the adsorption of phenol and catechol by C₁₂DMAO-Mt generally increased with the increase of ionic strength.At the same ion concentration,Na⁺will promote the adsorption of phenol by C₁₂DMAO-Mt,and Ca²⁺will promote the adsorption of catechol by C₁₂DMAO-Mt.（3）Zeta potential and viscosity measurements confirmed that C₁₂DMAO can undergo reversible transition under the condition of p H change,which has the reversible characteristics of switching surfactants.The desorption experiments at different p H showed that the optimum desorption p H was between 8 and 9,and the desorption effect of catechol and phenol was the best at p H=9.The desorption equilibrium time of phenol and catechol was about 90 min.The desorption effect of catechol on100C₁₂DMAO-Mt was better,while the desorption of phenol on 60C₁₂DMAO-Mt and100C₁₂DMAO-Mt showed a good trend.The increase of temperature is beneficial to the desorption process.Among the coexisting cations,Ca²⁺had the greatest inhibitory effect on the desorption of catechol,while Na⁺had the greatest inhibitory effect on the desorption of phenol.Different ionic strength systems have a strong inhibitory effect on the desorption process of phenol and catechol.C₁₂DMAO-Mt still has adsorption capacity for phenol and catechol after regeneration.