| Malachite green（MG）dye wastewater mainly come from industry and fishery,with high carcinogenicity,teratogenicity,mutagenicity and enrichment.Because of its low price and high efficiency,MG is irreplaceable now.So it is urgent to find a way to treat MG wastewater.Among the many decontamination methods,adsorption is an efficient method for concentrating wastewater.Nowadays,preparing new adsorbents becomes the key to improving the adsorption performance.In this paper,Hubei halloysite（Hal）was used as raw material,activated by piranha solution,and modified by APTES to prepare a new Hal adsorbent combined with TEM,XRD,FTIR,TG,NMR and other characterization methods,investigating the changes of morphology,structure and surface groups during the preparation.Batch tests were carried out to investigate the efficiency,process and mechanism of removing MG dye contaminants.The research results are expected to provide theoretical and experimental support for the development,preparation and application of modified Hal materials to remove MG dye pollutants.The main research results of this paper are as follows:（1）Piranha solution（20%v/v,H2O2/H2SO4=3/7）had a fast etching speed for Hal at room temperature.When the etching time reached 45minutes,the inner wall of the tube ruptured and collapsed,pilling up to form quartz particles.The following is the mechanism of piranha solution etching Hal:Piranha solution preferentially etches the aluminum oxide layer on the inner surface of the tube,so that the silicon oxide layer collapses to form SiO2particles,and the hydroxyl groups on the inner surface of the tube are retained,while the outer surface,edges and end faces of the tube are stimulated to produce more hydroxyl sites.（2）During the modification process,APTES was successfully grafted to the hydroxy sites on the surface of Hal.Most of the grafting reaction occurred at the silanol sites on the outer surface of Hal,and a few part occurred at the hydroxy sites on the inner surface,edge and end surface of the pipe.At the same time,the contribution of the oligomerization reaction between silanes to the surface modification cannot be ruled out.By comparison,anhydrous toluene（non-polar）solvent was more conducive to the grafting reaction than anhydrous ethanol（polar）solvent.The reason why the addition of water in the ethanol system significantly increased the amount of silane grafted was that the increase of the water content in the solvent promoted the hydrolysis of APTES to produce more silanols,which in turn increased the silane grafting activity.（3）The removal of malachite green dye pollutants in the water by the modified product is significantly affected by the pH of the system.Under the optimized pH value of 7.0,the adsorption equilibrium can be reached after 40 minutes of reaction,and the maximum equilibrium adsorption capacity is 58.01mg/g and the decontamination is self-distributing heat.The process is less disturbed by background ions,the adsorption kinetics process follows the pseudo-first-order model,and the adsorption data fitted well with the Freundlich equation.The removal of pollutants is mainly based on electrostatic physical adsorption.The modified product can be reused many times,and the pollutant removal rate is still higher than 60%after 4 cycles,which has a good practical application prospect. |
