Basic Research On Adsorption Of Malachite Green By Activated Carbons

Water pollution was caused by dyes,which is not only will reduce the consumption of global water but also bring about a series of related negative impacts.According to the survey of the Ecology and Toxicology Association of Dye and Organic Pigments Manufactures?ETAD?,triphenylmethane dyes,azo dyes and anthraquinone dyes have high toxicity according to the chemical structure classification and basic dyes have the highest toxicity according to the application classification.Therefore,the representative of the basic dyes and the triphenylmethane dyes of the malachite green was selected as the adsorbate in the experiment.It was found that activated carbons have well-developed pore structures and abundant surface functional groups,which is promised to be an effective adsorbent for removing malachite green dye from wastewater.However,the different preparation materials and preparation conditions of activated carbons make their different adsorption capacity.This work aims to find out the common law of adsorption of activated carbons,which provides theoretical support for the efficient adsorption of activated carbons.1.Four types of commercial activated carbon termed coconut-AC,coal-AC,apricot-AC and peach-AC were selected.The elemental analyzer,CO₂ adsorption,N₂ adsorption-desorption,FTIR,X-ray photoelectron spectrometer and thermogravimetric were used to analyze their physicochemical properties.The results showed that pore structure of four activated carbons are significantly different;they have the same surface chemistry and elemental composition,but the content is different,which facilitates the study of their differences in adsorption performance.2.The adsorption capacities of four activated carbons adsorbing MG from solution with an initial concentration of 60²00 mg/L at 25⁴5°C was studied.The results showed that the adsorption reached equilibrium within 48 hours.The kinetic model fitting resultes showed that the adsorption behavior of MG contains three processes:the rate-controlling factor in the first 12 h is related to the adsorption mechanism.Pseudo-second-order equation could well fit the data in the process.Diffusion control is the main rate-determining step from 12 to 35 h.Pseudo-first-order equation provided good correlation for the process.The adsorption process approaches equilibrium over 35 h.The adsorption of MG on activated carbons can be fitted by Langmuir adsorption isotherm model.Thermodynamics indicated that the adsorption is the typical physisorption process.It indicated that the adsorption of malachite green on activated carbon is a single layer physical adsorption.Different pore size parameters?micropore volume,mesopore volume and macropore volume and specific surface area?were correlated with the adsorption properties of activated carbons.We found that the total specific surface area could be used as a key parameter to determine the adsorption performance.3.The effect of surface chemistry properties and ash on the adsorption of MG by activated carbons were studied.The results showed that the strong acidic groups would have the negative influence on the MG adsorption and the weak acid and basic functional groups would have no obvious effect on the adsorption.The values of point of zero charge(pH_pzc)of four activated carbons are between 4.5 and 6.The removal rate of MG eliminated the influence of pH on MG is kept to the minimum at pH values less than 4.However,when the pH values are in the range of 5 and 9,the removal rate is increasing with the increase of pH value.When the pH values are greater than 9,the removal rate reaches the maximum.The maximum and minimum variation of removal is about 43%for four activated carbons though they have different maximum and minimum values.The adsorption behavior of MG before and after deashing of activated carbons were measured.The data showed that the adsorption capacities of activated carbons without deashing were less than the deashing ones.It showed the ash has the detrimental influence on the MG adsorption.