Studies Of Activated Carbon Adsotption On Amoxicillin In Water

In this paper, the granular activated carbons (GAC-0) were modified with nitric acid and high temperature reduction to prepare the modified activated carbons (GAC-1, GAC-2). The removal of amoxicillin from aqueous solution was investigated in batch mode using the modified activated carbons. The surface structure and surface chemical properties of the modified activated carbons were characterized by scanning electron microscopy, pHpzc, and Boehm titration method. The specific surface areas (SBET) of the activated carbons were obtained from N2adsorption-desorption isotherms at77K using a surface area analyzer. Batch adsorption experiments were conducted to determine the effect of contact time, dosages, pH and temperature and initial concentration of amoxicillin. Langmuir and Freundlich isotherms were used to analyze the amoxicillin adsorption by the modified activated carbons. The adsorption mechanism was discussed. The experimental results showed that:(1) The active carbon modified with oxidation can increase the surface acid group and reduce zero electric point pH (pHpzc) value, meanwhile the oxidation process also can lead to the specific surface area reduced. But after thermal treatment, it can remove the oxygen atoms of activated carbon surface, and produce the electron-rich lewis base sites and increase pHpzc. Therefore, activated carbon after thermal modification can remove effectively amoxicillin from water.(2) Effects of reaction time, doses and pH were studied. The results showed that the removal rate of amoxicillin increased with increasing amount of the modified activated carbons. The optimum pH was4.0,3.0respectively for GAC-1and GAC-2. For GAC-2, appropriate dosage was5.0g/L, optimum pH was3.0and the removal rate reached maximum at12h. Amoxicillin removal rate was up to97.42%.(3) Form adsorption kinetics study, It can be seen that the pseudo-second-order model is the most suitable in describing the adsorption kinetics of amoxicillin, which can be demonstrated by higher R2(>0.99). The pseudo-first-order equation and Elovich model can also be very fitting the test data except the low concentration (100mg/L).(4) The isotherm data was consistent with both the Freundlich and Langmuir models, and the correlation coefficients suggested that a better fit was obtained using the Freundlich model than the Langmuir model. The adsorption process was spontaneous with negative values of A G. The positive value of⊿H confirms the exothermic nature of adsorption, so adsorption capacity of modified activated carbon increased with temperature increasing. The positive⊿S indicates that the degrees of freedom increased at the solid-liquid interface. Compared with the initial activated carbon, GAC-2showed beter adsorption performance than GAC-1.