Simultaneous Removal Of Heavy Metals And Dyes Pollutants By Adsorb/Photocatalytic Of Mercaptocarboxylic Acid Intercalated Layered Double Hydroxide Composites

The pollution of organic and inorganic mixtures in water body poses a serious threat to human body and ecosystem,which is a global problem to be solved urgently.At present,a large number of technological methods have been applied to the remediation of polluted water,among which,adsorption method is considered as an effective method to remove pollutants in water because of its simple operation and good adsorption effect.However,traditional adsorbent existed in the process,the difficulty of repeated use of low and recycling.As a result,some researchers have proposed by discarded adsorbent transformation strategy,photocatalyst to realize adsorbent recycling and effectively remove mixed pollutants in water.As a kind of anionic layered nanomaterial with adjustable composition and structure,layered double hydroxide（LDH）has both adsorption and catalytic properties,and has potential application value in environmental protection,medical treatment,biology and other fields.In this paper,Mg Al/LDH intercalated by MPA,and highly dispersed metal sulfide nanoparticles（NPs）were generated in situ between layers catalyzed by alkaline centers of LDH laminates during the adsorption of Hg²⁺,Pb²⁺and Cu²⁺to provide good photocatalytic activity for the degradation of dyes,Simultaneous removal of heavy metal/dye mixed pollutants in water.Firstly,the mercaptocarboxylic acid/layered double hydroxide（MPA/LDH）composite was synthesized by coprecipitation method.The structure and properties of the composite were characterized by XRD,FT-IR,SEM,BET and contact Angle,and the interaction mechanism between LDH layer and intercalated anions was investigated by theoretical calculation method.Secondly,MPA/LDH was used in the adsorption experiments of wastewater containing Hg²⁺,Pb²⁺and Cu²⁺,and the effects of different dosages,initial p H of solution and competitive adsorption on MPA/LDH adsorption performance were investigated.The adsorption behaviors of Hg²⁺,Pb²⁺and Cu²⁺on MPA/LDH were described by adsorption isotherms,kinetics and thermodynamic fitting results.The cycling performance of the adsorbent was tested and the adsorption mechanism was revealed.Finally,metal sulfide nanoparticles（NPs）generated in situ between LDH layers after the adsorption of heavy metal ions were used as photocatalysts to degrade methylene blue（MB）dye.Meanwhile,the ability of MPA/LDH to treat organic and inorganic mixed pollutants in wastewater simultaneously under visible light irradiation was investigated.The experimental results show that:MPA can successfully enter the LDH layer,and it demonstrated excellent adsorption capacities for Hg²⁺,Pb²⁺and Cu²⁺.Langmuir adsorption isotherm model and quasi-second-order kinetic model can better describe the adsorption behavior of Hg²⁺,Pb²⁺and Cu²⁺on MPA/LDH.The maximum adsorption capacities for Hg²⁺,Pb²⁺,and Cu²⁺were 250.30,122.10,and 105.33 mg/g at adsorbent dosage of 0.2 g/L and p H of 5.5.The excellent adsorption performance was attributed to the inner-sphere surface complexation between the heavy metal ions and the S-S and COO^-groups in MPA/LDH.In addition,the charge characteristics and wettability of MPA/LDH surface also improve the adsorption capacity of MPA/LDH for heavy metal ions.After the adsorption of Hg²⁺,Pb²⁺,and Cu²⁺,the suitable energy band and high dispersity of highly dispersed metal sulfide NPs which spontaneously formed in the LDH interlayer via confined base catalysis,providing excellent photocatalytic activity for the degradation of organic dyes.MPA/LDH-Hg S showed the best photodegradation performance of 99.2%for methylene blue.Notably,MPA/LDH can be used for the simultaneous removal of heavy metals and organic dyes under visible light irradiation.This work not only provides environmental protection strategy for the transformation of waste adsorbent to photocatalyst,but also realizes the simultaneous removal of organic and inorganic mixed pollutants in water,which has broad industrial application prospects.