Preparation Of Superfine Carbon Fiber And Study Of Its Cr(Ⅵ) Removal Performance In Water

Heavy metal pollution has become one of the worst water pollution problemsnowadays. Chromium was considered as a complicated pollutant which possessed twoforms in water body: trivalent chromium and hexavalent chromium. Cr(III), which isone of the essential elements for human body, has much less toxicity compaired toCr(VI). Cr(VI), which mainly exists as CrO42-and Cr2O72-, is highly toxic, easilytransformable, and commonly found in the industrial waste water. Cr(VI) can alsoenter human body through the food chain, causing liver failure, nausea, severe diarrhea,atopic dermatitis, eczema, chrome ulcer and other health problems. Chromiumnormally comes from the waste water from electroplating, metal finishing, coating,leather tanning, textile and chemical industry.Current methods of removing chromium ions from industrial wastewater includechemical precipitation, chemical oxidation reduction, electrolysis, filtration, ionexchange, membrane separation. However, there are some issues about these methods,such as high capital, chemical and energy cost, toxic sludge and secondary pollution,which have limited their application. Whereas adsorption compared to other methodshas fewer advantages, including high removal efficiency, low cost, simple system andlow energy requirement. The key issue in Chromium removal is turn Cr(VI) to Cr(III).Current researches have been drawn to find novel highly efficient adsorbents.In this study, five kinds of superfine carbon fiber (SCF) was prepared ofpolyacrylonitrile-basednanofiber (PANNF) by pre-oxidation and carbonization, then named SCF750-15, SCF850-15, SCF950-15, SCF950-30and SCF950-45. In theSCF’s application of removal of Cr(VI), the adsoption kinetics, isotherms, pHinfluence and coexisting ions influence was carried out. Then, characterization andanalysis of materials was conducted by using SEM and XPS. After the experimentalstudy, draw the following conclusions:1) To explore and study the spinnability from viscosity and electrospinningprocess of single solvent spinning solution and different proportions solventspinning solution. Successfully prepared PANNF which diameter was about350nm, and suitable for superfine carbon fiber (SCF) precursor material.2) Through analysis of the TGA curves of PANNF, determined the temperatureand time of pre-oxidation and carbonization stages. Successfuly prepared fivekinds of SCF, named SCF750-15, SCF850-15, SCF950-15, SCF950-30andSCF950-45. In order to investigate the changing of functional groups ofPANNF after pre-oxidation and carbonization, pre-oxidation PANNF andSCF950-15were characterized and analysis by FTIR.3) Through hexavalent chromium adsorption kinetics of SCF at pH2,screened SCF950-15which had the fastest kinetic and largest Cr(VI)adsorption capacity (44.62mg/g), to carry out the detailed adsorptionprocesses and study.4) The obtained results of adsorption kinetics and isotherms showed, theadsorption kinetics data were well described by the pseudo-second-ordermodel, the isotherm data was well fitted to Redlich-Peterson model. Withinthe set of experimental conditions, pH2was the best to the removal of Cr(VI)from water. The analysis results of XPS spectra and surface charge densityshowed， there not only had physical adsorption such as electrostaticadsorption, but also accompanied with chemical adsorption.5) The obtained results of desorption studies showed, at100rpm shaking rate,the adsorption ratio of Cr onto SCF950-15could be89.21%by3mol/LNaOH. This indicating that SCF950-15could be efficiently regenerated, washigh efficent, affordable adsorbent.