Preparation, Characterization, And Adsorption Properties Of A Chitosan Composite And Hollow α-Fe₂O₃Nanospheres

With the increasing development of industrialization, there are more and moretoxic heavy metal ions and organic dyes emitting into the environment, whichconstitutes a major threat to global ecosystem and human health. Therefore it is ofgreat environmental and economical importance to prepare novel materials that havethe capability to adsorb heavy metal ions and organic dyes from wastewater.According to the characteristics of Ag （I）, As （V）, Cr （VI） and Congo red, whichare common pollutants from industry, two new adsorbent materials were synthesized.First, a novel thiourea-modified chitosan/bentonite （TMCB） composite wassynthesized to crosslink the linear chitosan molecules into interconnected networkswhile introducing heteroatoms and inorganic bentonite. Second, hollow α-Fe₂O₃nanospheres with uniform morphology, large surface area, and fine pore distributionwere fabricated by a microwave-assisted, template-free method. These two materialswere thoroughly characterized and confirmed by SEM, TEM, FTIR, TGA, elementalanalysis, XRD, XPS, etc..The adsorption properties of the prepared materials towards corresponding heavymetal ions and organic dye and their adsorption mechanisms were systematicallystudied, and the results show that:（1） when the pH of the system was5.0, TMCBexhibits good adsorption performance towards Ag （I） with a maximum adsorptioncapacity of385mg g-1and a maximum removal ratio of99%(which is still as high as90%when TMCB was used for5times; the adsorption process fits the Freundlichisothermal equation and the pseudo-second-order model well.（2） hydroxyl andheteroatom groups in the surface of the organic layer of TMCB offer sufficientbonding sites for Ag （I）, and the negatively charged TMCB is inclined to adsorb thepositively charged Ag （I） due to electrostatic attraction.（3） an equilibrium of hollowα-Fe₂O₃nanospheres adsorbing As （V） and Cr （VI） can be established within120min,and the removal ratios are88%for As （V） and67%for Cr （VI）; the adsorption processfits the Langmuir isothermal equation well with relevance coefficient as high as98%,the maximum adsorption capacites of hollow α-Fe₂O₃nanospheres are75.3mg g-1for As （V） and58.6mg g-1for Cr （VI）.（4） newly prepared hollow α-Fe₂O₃nanospherescan absorb approximately90%Congo red within50min, and the final removal ratiocan be as high as96%within300min while the maximum adsorption capacity ofCongo red is160mg g-1. Besides, the adsorption performance of hollow α-Fe₂O₃nanospheres towards Congo red is better than that of commercial α-Fe₂O₃even it isused for many times.Due to their advantages of low cost, facile fabrication, high adsorption capacity,and good reusability, the two materials studied in this paper have the potential to beused as novel efficient adsorbents for practical water treatment.