Preparation Of Novel Adsorbents And Their Application In DGT Technology

With the rapid development of industrial economy,water pollution caused by heavy metal ions has become the main factor which threatened human health.Therefore,it is urgent to monitor the trace heavy metal ions in water.Diffusive gradients in thin-films?DGT?technology can effective enrich and monitor trace heavy metal ions in solution.The binding phase is the key part of the diffusive gradients in thin-films technique for accumulating heavy metal ions.In this paper,we fabricated novel adsorbents and investigated their adsorption properties.Then,utilized them as the binding phase in DGT devices to monitor trace heavy metal ions in water.?1?Zeolite-imidazolate frameworks?ZIF-8?materials have advantages of large specific surface area,high porosity,high thermal stability,chemical stability.Therefore,could be a promising candidate for adsorption of heavy metals,organic pollutants in aqueous system.In this paper,ZIF-8 nanocrystals were synthesized at room temperature.We studied their selective adsorption properties towards Cr?VI?,methyl orange?MO?and phenol in water environment.The equilibrium adsorption capacity at pH=7 is 0.40,0.23 and 0.09 mmol·g-1,respectively,which indicated that ZIF-8 exhibited selective adsorption performance towards Cr?VI?.The adsorption behaviors fit well with pseudo-second-order kinetics model and Langmuir isotherm model,implying the chemical related adsorption process.The selective adsorption mechanism were probably relate to electrostatic interaction and size selectivity.?2?The conventional DGT binding phase is usually prepared by adding adsorbent powder to the diffusion binder.However,some adsorbent powders are not easy to gel which greatly limited the application of DGT.In this chapter,MnOOH film directly used in DGT as a binding phase.MnOOH membrane consists of MnOOH fibers which have10-20?m in length and 20-50 nm in width.The adsorption properties of As?V?and Cu?II?were studied and the results showed that the capacity of As?V?and Cu?II?was 76 mg·g-1,107 mg·g-1 at pH = 5,respectively.All the adsorption processes fitted well with pseudo-second-order kinetics model.At the same time,the adsorption mechanism of As?V?and Cu?II?was not only related to the function of electrostatic attraction but also relate to the oxidation reduction reaction.Utilized MnOOH film as the new the binding phase in DGT to enrich and measure trace As?V?and Cu?II?in aqueous solution.The results showed that MnOOH-DGT can selective accumulation and monitoring of As?V?especially for low concentration?²0ppb?.The site experiments showed that MnOOH-DGT canselective measurement of As.?3?Micro-nanostructured oxides have low cost,stability structural,and high removal capacity for contamination.Therefore,micro-nanostructured oxides has good prospective application in adsorption.We prepared MgO by hydrothermal process and subsequent calcination.The MgO were used to removal the fluoride from wastewater.The results showed that the adsorbent has excellent adsorption capacity for fluoride removal.The adsorption behaviors were investigated to fit well with pseudo-second-order kinetics model.Furthermore,the adsrption isotherms can be well described by the Langmuir isotherm model.The effects of pH and various co-existing ionic on kinetic adsorption of fluoride on MgO were investigated.The results show that MgO has good adsorption performance to remove fluoride ion and the fluoride adsorption capacity can reach 130 mg·g-1 at pH = 3.It has good adsorption capacity in pH=3⁸.The effects of co-existing anions indicated that the anions of NO₃^-had effect on fluoride removal.The adsorption mechanism was analyzed,and it was found that the adsorption of fluoride ions was achieved by exchanging OH-ions on the surface of the adsorbent.