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以殼聚糖-奈米碳管新穎複合顆粒吸附水中六價鉻之研究：材料特性、吸附平衡、貫穿曲線之分析

為了解決Stud tire的問題，作者歐米安 這樣論述：

Hexavalent chromium (CrVI) is one of highly toxic heavy metals of concerns in water systems even at parts-per-billion levels. Chromate (CrO42-), hydrogen chromate (HCrO4-) and dichromate (Cr2O72-) are common CrVI forms found in aqueous phase with strong solubility and diffusivity allowing the compo

unds to penetrate tissue membrane. Among different well-established options, adsorption technology continues to be the most viable method to remove such hazardous heavy metal ions from impaired water. This work demonstrates the synthesis of an adsorbent in the form of CN/MWCNTs/Fe beads by combining

chitosan and sodium alginate with iron doped MWCNTs. The physicochemical properties of CN/MWCNTs/Fe beads were characterized in detail by using FE-SEM, FTIR, XRD, XPS, TGA and EDS. During the adsorption experiments, CN/MWCNTs/Fe beads showed robust performance in CrVI removal having the initial con

centration, solution pH and temperature as critical factors to control their removal performance. The beads showed a high CrVI removal performance with an optimized chitosan and alginate contents. The Langmuir isotherm with a maximum adsorptive capacity of 119 mg/g characterized the CrVI removal beh

avior. The pseudo-second-order model exhibited the best fit with experimental results. The intra-particle diffusion model further elucidated the film mass transfer and intra-particle diffusion as multiphasic rate-limiting factors during the adsorption of CrVI ions. Further confirmed by XPS analysis,

the evolution of CrIII indicates a possible charge transfer effect of FeII/FeIII mediated through conductive carbon nanotubes, leading to the reduction of CrVI ions. In case of coexisting anions, the CrVI uptake capacity of composites beads remained in the order of Cl- > NO3- > SO32- > PO43- Moreov

er, the composite beads showed up to 80% of CrVI removal efficiency after five cycles of adsorption.This study also evaluates the CrVI breakthrough behaviors of a continuous-flow column packed with composite beads under various operating conditions, such as water flow rate, feed CrVI concentration,

packed bed height and pH value. The dynamics of the adsorption process and breakthrough curves were characterized by fitting various semi-empirical models namely the Thomas model (TH-model), Yoon-Nelson model (YN-model), and Adams-Bohart model (AB-model). The TH-model and YN-model were found suitabl

e to describe the whole breakthrough curves under all experimental conditions. The AB-model was applicable only to the initial portion of the breakthrough curves (Ct/C0≤0.5) suggesting film mass transfer was dominant during the mass transport of CrVI ions. In addition, fitting mass transfer factor m

odel (MTF-model) to the experimental breakthrough data under varying bed heights revealed a superior global mass transfer rate for the column with shorter bed height. The bed depth service time (BDST) model predicted the service time of the adsorbent bed at various outflow concentrations. The scaled

-up study was executed to estimate an amount of adsorbent required to pack in the column of higher dimensions and throughputs. The higher selectivity of CrVI uptake in simulated wastewater in the presence of other heavy metal ions (copper and cadmium) and background anion (phosphate) suggests the ap

plicability of CN/MWCNTs/Fe beads in the removal of CrVI from industrial wastewater.Finally, a homogeneous surface diffusion model (HSDM) involving convection-dispersion and diffusion equations was formulated, numerically solved, and experimentally validated to elucidate the mass transport of CVI io

ns on to the composite beads. The model (mass transfer) parameters including axial dispersion DL, (1.30×10-8 to 1.56×10-7 m2/s) and surface diffusion Ds, (7.28×10-11 to 1.80×10-10 m2/s) were acquired via an error minimizing approach. The DL value was a function of molecular diffusion, which varied w

ith the flow velocity, mass loading, and bed height. The Ds values were slightly higher than those previously reported, owing to the heterogeneous nature of the adsorbent. The external film diffusion coefficient (kf) was also determined by using Wilson-Geankoplis empirical correlation, which was rec

ognized as a rate-controlling factor during CrVI mass transfer to the adsorbent beads. Furthermore, sensitivity analysis showed that a transition from diffuse- to shock-front occurred with a decreasing DL, while a decrease in the slope of breakthrough curves was observed by decreasing Ds and bed por

osity, and increasing kf and Langmuir parameters. Lastly, the study demonstrated a high correlation between utilization of fractional bed capacity and axial Peclet number (Peax). This method is suitable for optimizing operating conditions to maximize the utilization of a fixed-bed columns. Overall,

this study demonstrated that CN/MWCNT/Fe beads are potential adsorbents with synergistic effects for the treatment of CrVI polluted water, and their reusability is of significance for field applications to remove contaminants from water bodies.