Studies On The Adsorption And Catalytic Performance Of Dyes In Water By Nanomaterials Modified Clay Mineral

With the development of society and chemical industry,the dyestuff industry is in a good development situation.However,dyes entering the water bodies will cause serious water pollution problems,and damage the ecosystem and human health as well.Dye wastewater is one of the most visible environmental problems in the world and is difficult to purify.Therefore,it is urgent to explore feasible ways to treat dye wastewater for alleviating the water resource crisis.Clay minerals have been widely used as adsorbents for dye wastewater treatment due to their economic and environmental advantages,but their treatment capacit ies are commonly limited.Their properties and wastewater treatment capacity can be improved by the modification with nanomaterials.According to previous studies,modification of graphene materials can increase the specific surface area of raw materials and thus improve the adsorption performance of materials.Silver nanoparticles need solid carrier materials to improve their stability and catalytic activity.Based on the above viewpoints,graphene materials with strong adsorption capacity and silver nanoparticles with catalytic properties were selected to modify clay minerals,thereby preparing different composite materials as adsorbents and catalysts in this subject,respectively.Meanwhile,the adsorption and catalytic performances of those composite materials for dye removal were investigated through a series of experiments.This study can provide theoretical basis for the development of novel clay mineral composites and the solution of the drawbacks of adsorbents and catalysts.It is also conducive to the development and utilization of clay mineral resources and the expansion of clay minerals for environmental application routes.The specific research work and main experimental results of this paper are as follows:（1）Four sample materials including graphene oxide modified kaolin（GO-kaolin）,graphene hybridized ploydopamine coated kaolin（PDA-rGO-kaolin）,ploydopamine-kaolin supported Ag nanoparticles（PDA-kaolin-Ag）,and lignosulfonate functionalized kaolin-Ag hybrid（LS-kaolin-Ag）were prepared by different facile approaches.The characteristic analyses of transmission electron microscopy（TEM）,X-ray powder diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and BET etc.were used to confirm the successful preparation of samples.（2）The synthesized GO-kaolin composites were named as 2%GK,5%GK,and10%GK based on the different weight ratios of GO/kaolin,respectively.In order to explore the adsorption performance of GO-kaolin samples,batch adsorption experiments were carried out using methylene blue（MB）as a model dye pollutant in various experimental conditions.The adsorption results showed that graphene oxide modification can promote the adsorption efficiency of MB on kaolin from aqueous solution in each experiment condition,and the adsorption affinities of dye to four adsorbents followed the order of kaolin<2%GK<5%GK<10%GK,which was attributed to the increase of graphene oxide content could increase the specific surface area and adsorption sites of the composites.When the concentration of MB was 20mg/L,the removal efficiency of kaolin was only 16.04%,while the removal efficiency of MB by 10%GK could reach 92.00%,increased by 4.74 times.The adsorption of MB on GO-kaolin samples was found to be in accordance with the pseudo-second-order kinetic model,and the Langmuir isotherm model could better explain the adsorption behavior of GO-kaolin samples.Furthermore,graphene oxide modification could change the adsorption process of MB on kaolin.The results show that graphene oxide modification can significantly improve the adsorption capacity of MB dye by changing the surface properties of the kaolin.（3）To explore the approach for further enhancing the dye removal performance of polydopamine（PDA）coated materials,a novel composite of PDA-kaolin with reduced graphene oxide hybridization（PDA-rGO-kaolin）was synthesized.A series of comparative experiments on PDA-kaolin and PDA-rGO-kaolin towards MB removal in various conditions were carried out.The BET characteristic analysis showed that the surface area of PDA-kaolin was 8.65 m²/g,whereas the surface area of PDA-rGO-kaolin reached 35.35 m²/g,increased by 3.1 folds.The adsorption of MB by PDA-rGO-kaolin was more satisfactory than that by PDA-kaolin in various dye solutions,which was ascribed to the introduction of graphene materials that could increase the specific surface of PDA-kaolin and theπ-πinteraction force between materials and dye molecules.Pseudo-second-order kinetic model and Langmuir isotherm model could better describe the adsorption kinetics and adsorption behavior,respectively.Compared with the adsorption of PDA-kaolin,PDA-rGO-kaolin showed higher maximum adsorption capacity towards MB（39.663 mg/g）.Temperature tests showed that the adsorption of MB molecules on adsorbents was spontaneous and endothermic process.Moreover,PDA-rGO-kaolin showed a good regeneration performance for MB removal.These results show that the introduction of graphene is a feasible and efficient method to improve the decontamination performance of PDA coated materials.（4）Silver nanoparticles supported on polydopaminecoated kaolin composite（PDA-kaolin-Ag）was fabricated by an in-situ reduction method with PDA as both reductant.Catalytic reduction tests confirmed that the increase of polydopamine content on modified materials could increase the loading of silver nanoparticles,thus promoting the catalytic reduction efficiency of rhodamine B（RhB）.When the concentration of dopamine was 2 mg/L and the concentration of silver ammonia solution was 10 mg/L,the decolorization reaction of RhB（50 mL,20 mg/L）could be completed within 9 minutes with 10 mg catalyst material in the presence of NaBH₄.The catalytic reduction processes conformed to pseudo-first order kinetics.Meanwhile,PDA-kaolin-Ag catalyst t showed excellent stability and recyclability for dye decoloration.Furthermore,PDA-kaolin-Ag catalyst also exhibited good catalytic performance on methylene blue,methyl orange,and Congo red.These results suggest that PDA-kaolin-Ag composites can be used as efficient and cost-effective catalyst for the decolorization of various organic dyes.（5）Silver nanoparticles were immobilized on lignosulfonate-functionalized kaolin（LS-kaolin-Ag）by a facile reduction method without additional reductant and stabilizer.To investigate the catalytic reduction performance of LS-kaolin-Ag,the catalytic reduction tests on both cationic dye rhodamine B and anionic dye Congo red were carried out.Similar reaction trends on both dyes were observed,and the rapid dye decolorization could be occurred with catalyst at suitable dosage.Meanwhile,this catalyst showed good recyclability for dye decolorization with just a little decrease of conversion percent in five successive reactions.These results suggest that LS-kaolin-Ag composite as catalyst shows possible application potential for dye wastewater treatment.The studies of this paper were carried out from two aspects including dye adsorption and catalysis based on the basic material of kaolin,consequently,understanding the roles of different functional nanomaterials and providing the theoretical basis for enhancing the environmental application modes of nanomaterial modified clay minerals in future.