| Soil erosion is the driving force for the non-point source pollution in water environment.The aggravation of soil erosion causes millions of tons of pollutants into the water every year,which pollutes the water in rivers,reservoirs,lakes,coastal waters seriously.In a wide variety of non-point source pollutants,hexavalent chromium and phosphate pose serious threats to the ecological environment and human health due to their high toxicity,extensive contamination and difficulty of the treatment.The pollution of hexavalent chromium and phosphate in water does severe harm to the ecological environment and human health.Currently,some main technologies are used to treat Cr(VI)and phosphate in water,including chemical precipitation,ion exchange method,electrolytic process,crystallization method,biological method and adsorption method.However,those processes have some disadvantages,such as complex operation,consuming a large amount of chemical reagents,high cost,producing sludge sedimentation,instable reaction,poor performance,short service life,strict requirement for waste water environment and causing the secondary pollution.In this study,two new improved methods were used to synthesize two kinds of new type nanocomposites,respectively.The optimum conditions to synthesize these new type nanocomposites were determined by changing the reaction conditions in the process of preparation.Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),Field emission scanning electron microscopy(FESEM),Energy-dispersive(EDS),Thermogravimetric differential thermal analysis(TG),Ultraviolet-visible spectroscopy(UV-Vis)and Brunauer Emmett Teller(BET)were applied for comparison on the microscopic appearance and structure characterization of two nanocomposites.The performance of nanocomposites on Cr(VI)and phosphate removal was studied as well.The novel Zn(II)dithiocarbamate/ZnS nanocomposite was synthesized through an improved method.Its optimum preparation technology was discussed by modifying the parameters such as the ratio of amine and sulfur,the ratio of amine and zinc,reaction temperature and reaction time.The results showed that the Zn(II)dithiocarbamate/ZnS with better performance could be obtained when the mole ratio of amine and sulfur was 2:1,the mole ratio of amine and zinc was 1:1,the reaction temperature was 70℃ and the reaction time was 3h.Zn(II)dithiocarbamate/ZnS nanocomposite was characterized as a small particle with uniform distribution which consist of zinc dithiocarbamate and zinc sulfide.The vibrational characteristics of DTC and ZnS were observed through the absorption spectrum.the presence of Zn,S,C,N elements and N-C=S group in nanocomposite were proved.The effects of dosage,initial concentration of solution,pH value,reaction time and reaction temperature on adsorption were investigated.The results indicated that Zn(Ⅱ)dithiocarbamate/ZnS nanocomposite had outstanding performance on Cr(Ⅵ)removal from aqueous solutions.It could reach 96.5%of removal efficiency at a reaction time of lmin.Additionally,the nanocomposite showed high removal ability under all pH conditions.Kinetic and thermodynamic study suggested that the adsorption process for Cr(Ⅵ)or phosphate was fitted with pseudo-second-order kinetics and Freundlich models.It was naturally spontaneous and endothermic,and could be facilitated at high temperature.The maximum adsorption capacity for Cr(Ⅵ)was 75.30 mg/g at 50℃.The results of phosphate removal were similar to that of Cr(Ⅵ)removal.Based on performance studies and characterization tests,the Cr(Ⅵ)or phosphate removal by nanocomposites included two steps.Firstly,the Cr(Ⅵ)or pnosphate were chelated by the functional group of HNC(=S)S—in the Zn(Ⅱ)dithiocarbamate with a certain molecular ratio.The Zn(Ⅵ)dithiocarbamate was bonded to the Cr(VI)or phosphate and formed a complex agent ring surrounding the Cr(VI)or phosphate.Meanwhile,the Cr(Ⅵ)or phosphate were adsorbed to the ZnS nanocomposite having open ends with only sulphur atoms.It catalyzed adsorption of nanocomposite for metal cations due to negative polarization.The nano titanic acid was synthesized through an improved organic deposition method.The optimum preparation technology of nano titanic acid was discussed by modifying the the types of doped metal ions and the ratio of metal ion.The results showed that the performance of Fe-doped nano titanic acid on Cr(Ⅵ)removal was better than that with other metal doped.Furthermore,the nano titanic acid showed the best performance with the doping percentage of Fe element at 10%.Characterization showed that the Fe-doped nano titanic acid had the flower ball structure which composed of nanosheet with small particles distributed on the surface uniformly.This nanocomposite included characteristic function groups of titanic oxide,Ti.O and Fe elements.The effects of dosage,initial concentration of solution,pH value,reaction time and reaction temperature on adsorption were investigated.The results showed that the Fe-doped nano titanic acid exhibited outstanding performance on Cr(Ⅵ)removal from aqueous solutions and that the removal efficiency could reach 87.5%just in 1 min.The adsorption quantity firstly increased dramatically and then decreased with the increase of dosage.There appeared the adsorption peak of 36.08 mg/g at the dosage of 0.03 g.Except for strong acid and strong alkaline conditions,the nanocomposites showed high removal ability under all pH conditions.Kinetic and thermodynamic study suggested that the adsorption of Fe-doped nano titanic acid for Cr(Ⅵ)and phosphate was fitted with pseudo-second-order and Langmuir models.It was a naturally spontaneous and exothermic process,and could be facilitated at low temperature.The maximum adsorption capacity for Cr(Ⅵ)and phosphate at 20℃ were 30.15 and 291.55 mg/g,respectively.Compared with the other adsorbents,such as activated carbon and phosphor-free activated carbon,the Zn(Ⅱ)dithiocarbamate/ZnS and Fe-doped nano titanic acid synthesized in this study demonstrated excellent adsorption capacity on Cr(Ⅵ)and phosphate.The two kinds of nanocomposites have potentially broad application in the fields of water treatment due to their advantages such as simple preparation process,high reaction rate,good adsorption capacity and great performance under a wide range of reaction conditions.Especially,they are very suitable for treatment of the sudden water pollution incident caused by factory leakage,and can quickly remove high concentrations of Cr(Ⅵ)and phosphate in water preventing the spread of pollution effectively.Most importantly,the chelate formed during the removal process of Cr(Ⅵ)and phosphate by nanocomposites can be further used in the fields of electricity,magnetism and light catalysis.There is no need to treat them through regeneration or stacking and no secondary pollution to the environment.The reuse of chromium and phosphorus is also realized,which makes two kinds of nanocomposites of extremely good research value and application prospect in treatment of the non-point source pollution in water environment. |
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