Studies On Gradient Interlayer Spacing Control Of Twodimensional Electroactive α-ZrP/PANI And Selective Separation Of Heavy Metal Ions Using ESIX

The discharge of industrial wastewater containing lead and silver ions from electroplating,metallurgy,chemical industry and mining has caused serious contamination to the natural water environment.It threatens the healthy operation of the biosphere,as well as affects the lives of millions.The continuous pollution of water resources,especially the pollution of drinking water,has become one of the foremost global risk factors for illness,diseases and death due to the substandard discharge or even untreated discharge of industrial wastewater.It is difficult to achieve efficient and selective separation by existing technologies,due to the complexity and low concentration of toxic and harmful ions in water.In this context,trying to change the idea of"heavy metal wastewater"to"metal resources"has become a hot issue to be considered urgently.Electrochemically switched ion exchange（ESIX）,which is an environment-friendly ion separation technology,has become an emerging hot technology for the separation and recovery of heavy metal ions from wastewater.This technology mainly relies on the great advantages of efficient cleaning without secondary pollution and electronic control selective separation of low concentration of target heavy metal ions.In this paper,a series ofα-ZrP/PANI composite films with gradient layer spacing were prepared by Unipolar Pulse electrodeposition method（UPED）.The precise regulation of layer spacing was characterized by XRD.Adsorption experiments showed that:（1）The gradient layer spacing ofα-ZrP/PANI films was precisely controlled by adjusting the amount of intercalated polyaniline content.（2）Theα-ZrP/PANI film electrode showed different adsorption selectivity for Ag⁺,Pb²⁺,Ni²⁺,Co²⁺and Zn²⁺with increased distribution of hydration ion radii.When ANI:α-ZrP is 2:1,the spacing betweenα-ZrP layers is regulated at about 15.28（?）.The composite film electrodes for Ag⁺showed good adsorption selectivity and distribution coefficient of 144.44 L·g^-1,the order of selectivity was found to be Ag⁺>Pb²⁺>Ni²⁺>Zn²⁺>Co²⁺.The adsorption capacity of 2:1-α-ZrP/PANI film for Ag⁺is462.71mg·g^-1.When ANI:α-ZrP is 4:1,he spacing betweenα-ZrP layers is regulated at about19.34（?）.The composite film electrodes for Pb²⁺showed good adsorption selectivity and distribution coefficient of 80.579 L·g^-1,the order of selectivity was found to be Pb²⁺>Ag⁺>Ni²⁺>Co²⁺>Zn²⁺.The adsorption capacity of 4:1-α-ZrP/PANI film for Pb²⁺is458.70mg·g^-1.Subsequently,under the support of the first principles of quantum chemistry,this paper also through the theoretical calculation tool,to further explore the adsorption mechanism of Pb²⁺-（α-ZrP/ANI）.Theα-ZrP/ANI system was firstly established and the relaxation of this complex system was completed.The optimal K-points grid can achieve the balance between computing power and accuracy.First of all,compared with the aniline monomer and dimer,the aniline monomer and dimer with H⁺removed are more likely to form a stable structure of Pb²⁺,which is consistent with the experimental mechanism of ESIX.And then,The calculation shows that this kind of amazing adsorption properties ofα-ZrP/ANI system for Pb²⁺is derived from orbital hybridization of the O sites and Pb²⁺by calculating binding energy and analyzing density of states（DOS）and partial density of states（PDOS）.The interaction force they produce is responsible for the good adsorption properties.The O sites is mainly divided into the bridging oxygen（Zr-O-P）and the terminal oxygen（P-OH）.In comparison,the interaction force between bridging oxygen and Pb²⁺is stronger.The DFT theoretical calculation results agree with the experimental results,which explains the good adsorption performance ofα-ZrP/PANI composite film electrode for Pb²⁺.In addition,by comparing the binding energies of five heavy metal ions in theα-ZrP/ANI model,the same adsorption rule was obtained as the selective adsorption experiment of 4:1-（α-ZrP/PANI）film.To further build a more perfectα-ZrP/PANI model,the energy difference between cis-aniline and trans-aniline polymers was compared.The results show that:（1）With the increase of the number of aniline monomers,the energy difference between cis-aniline and trans-aniline polymers increased gradually.（2）Compared with trans-aniline octamer,cis-aniline octamer has more negative energy and is more consistent with the actual electrochemical and optical properties of PANI.This indicates that cis-aniline octamer can be used for the next step ofα-ZrP intercalation.The results of computational simulation have important reference significance to the experimental guidance and evidence.This work also lays a solid foundation for the further design ofα-ZrP as the main body and electrically controlled separation of heavy metal ions composite materials.