Structural Design Of Self-floating Adsorbent Materials And Its Adsorption Performance For Water Pollutants

In recent decades,the rapid development of global industry has brought serious environmental problems,especially the increasing water pollution,which has caused a huge impact on human beings and ecosystems.Typical pollutants in waterbody,such as organic dyes and heavy metals,have characteristics of refractory,strong toxicity,environmental persistence and bioenrichment,etc.Their existence in water will cause“three”harms to human health（carcinogenic,teratogenic and mutagenic）,and cause serious or even irreversible damage to the ecosystem.Therefore,how to rapid,environmental friendly and efficient removal of toxic and harmful pollutants from water has become one of the important research contents in the field of water treatment in China.Adsorption method has been widely used in various wastewater treatment processes because of its advantages of convenient operation,low cost and strong adaptability.Adsorption materials（or adsorbents）are the key and core of adsorption technology.At present,the common adsorbents for wastewater treatment,such as activated carbon,zeolite,cellulose,resin,biomass and so on,have been studied a lot.These adsorbents have the advantages of low cost,easy operation and environmental friendliness,but there are still some shortcomings such as poor adsorption capacity,long treatment cycle,low mechanical strength,lack of targeted adsorption characteristics and stable regeneration performance.How to improve the comprehensive performance of adsorbent（large adsorption capacity,fast adsorption speed,good adsorption selectivity,easy separation,enrichment and recovery,easy regeneration,low cost）to meet the high requirements of industrial wastewater treatment and purification is still the biggest bottleneck restricting the development of adsorbent materials.Based on this,we constructed a series of new adsorbents and explored their adsorption performance.The main studies are summarized is as follows:（1）Chlorine-substituted PZS-Cl microspheres were prepared by precipitation polymerization using hexachlorocyclotriphosphazene（HCCP）and 4,4’-dihydroxydiphenylsulfone（BPS）as comonomers.Then,polyethyleneimine（PEI）was coated on the surface of poly（cyclotriphosphazene-co-4,4’-dihydroxydiphenylsulfone）（PZS-Cl）through grafting reaction to obtain a spherical adsorbent（PZS-PEI）rich in amino/imino groups,which was used to selectively adsorb and separate anionic dyes from water.The adsorption materials were characterized by scanning electron microscopy（SEM）,infrared spectroscopy（FT-IR）and X-ray photoelectric spectroscopy（XPS）.The adsorption experiment results showed that the capture effect of PZS-PEI on the anionic dyes methyl orange（MO）,acid chrome blue k（ACBK）and eosin Y（EY）in water was greatly affected by p H values.The adsorption kinetics suggested that the adsorption of MO,ACBK and EY by PZS-PEI followed a pseudo-second-order kinetic model and the adsorption process was divided into three stages.The adsorption isotherm and thermodynamic studies indicated that Freundlich model can describe the experimental results well and the adsorption reaction was a spontaneous endothermic process,that is,the increase in temperature leads to an increase in the amount of adsorption.Through the selective adsorption experiment in the binary system,it was found that PZS-PEI performed excellently in the selective adsorption of anionic dyes.Adsorption-desorption experiments showed that PZS-PEI has good recycling performance and the superior structural stability.Meanwhile,the adsorption mechanism of MO dye by PZS-PEI was proposed.（2）In order to endow the adsorbent with self-floating separation property,a template-induced assembly technique was used to prepare a self-floating adsorbent（HGM@HCPE）using low-density hollow glass microspheres（HGM）as a hard template.Using acid chrome blue k（ACBK）,Congo red（CR）and hexavalent chromium as model pollutants,the adsorption behavior of HGM@HCPE was systematically studied.Adsorption experiments and floating experiments showed that HGM@HCPE has excellent adsorption performance and self-floating ability.The pseudo-second-order kinetic model and the Langmuir isotherm model can describe the experimental results well.Adsorption thermodynamic studies indicated that the adsorption of dyes by HGM@HCPE was endothermic,while the adsorption process of hexavalent chromium was exothermic.Adsorption-desorption experiments suggested that the adsorbent after six cycles still had good adsorption performance and self-floating ability,which indirectly indicated that the structure of the adsorbent was stable.Meanwhile,the adsorption mechanism of HGM@HCPE for model pollutants was proposed in detail.（3）Hydroxyl-rich self-floating functional adsorbent（HGM@HCTA）was prepared by cross-linking tannic acid（TA）with cyclotriphosphazene using HGM-OH（HGM treated with alkali）as carrier for the removal of cationic dyes MG and Cu²⁺in aqueous solution.Based on a series of characterizations such as SEM,FT-IR and XPS,it was found that TA has been successfully coated on the surface of HGM-OH.The adsorption behavior studies suggested that the pseudo-second-order kinetic model and the Langmuir model can better describe the experimental results,and the adsorption was a spontaneous endothermic process.The adsorption mechanism of MG and Cu²⁺on HGM@HCTA was proposed.（4）With HGM-OH as the carrier and cyclotriphosphazene as the cross-linking agent,a simple chemical synthesis method was used to graft polyethyleneimine（PEI）and p-aminobenzoic acid（PABA）onto the surface of HGM-OH to prepare a self-floating amphoteric adsorbent（HGM@HCPA）.The SEM images showed that the surface of adsorbents were uneven,and there are many wrinkles and contains a large number of uniform spherical small particles,which greatly increases the possibility of contact and adsorption between the adsorbent and the dye.The p H change has a greater effect on the adsorption of MO and MG dyes by HGM@HCPA.Among them,the adsorption capacity of MO was 377.21 mg g^-1 at p H=1,and the adsorption capacity of MG was 386.26 mg g^-1 at p H=10.The adsorption kinetic and isotherm studies indicated that the adsorption process of MO and MG on HGM@HCPA were more in line with the pseudo-second-order kinetic model and the Langmuir model.Meanwhile,the adsorption thermodynamic parameters suggested that the adsorption reaction was a spontaneous endothermic process.The study of the binary system showed that MO can act as a“bridge”between MG and HGM@HCPA to improve the adsorption capacity of MG.The synergistic adsorption mechanism of MO and MG on HGM@HCPA was also proposed.In summary,the work focuses on the construction of a self-floating adsorbent based on cyclotriphosphazene to achieve effective removal and efficient separation of target pollutants in wastewater.A series of as-prepared adsorbents showed high adsorption performance and separation ability.The results will provide important reference for the construction of new advanced adsorbents and the study of their adsorption performance.