دانلود رایگان مقاله تاثیر منشا بار لایه و چگالی بار لایه اسمکتیت بر جذب سطحی آفلاتوکسین

Abstract

The aflatoxin adsorption efficiency of a bentonite depends strongly on the physical, chemical, and mineralogical properties of the smectite, the dominant clay mineral in bentonites. The objective of this study was to determine the effects of the layer charge origin, octahedral cation composition, and layer charge density on the smectites' selectivity and adsorption capacity for aflatoxin. Six smectite samples with different layer charge densities and octahedral cation compositions were evaluated: a montmorillonite (4TX) and a hectorite, which represent smectites with octahedral charge origin; and a beidellite, two saponites from Australia and Spain, and a nontronite, which represent smectites with tetrahedral charge origin. The clay fraction of the smectites was saturated with Na, Ca, and Ba, respectively. Aflatoxin adsorption isotherms were conducted for these smectites. The CEC of one high-charge montmorillonite (5OK) and the nontronite were reduced by Li-saturation and heating. Similar effect of the exchangeable cations was observed in all smectites, but significant differences in the aflatoxin adsorption capacity were observed among the smectites. The octahedrally charged smectites showed higher aflatoxin adsorption than the tetrahedrally charged smectites. The aflatoxin-smectite bonding mechanism was not affected by the layer charge origin or density. Optimal layer charge density was required to have sufficient non-polar sites on the smectite for aflatoxin molecules. High-charge-density smectites had low adsorption capacity and binding affinity for aflatoxin, but aflatoxin adsorption on these smectites can be improved by reducing the layer charge density of the clay mineral. Smectites with octahedral charge increased the interlayer accessibility of aflatoxin molecules. The octahedral cation composition had a negligible effect on the aflatoxin adsorption capacity of smectites.

5. Conclusions

The results corroborated previous observations that the exchangeable cation strongly affected the AfB1 adsorption and demonstrated that the effect was similar on all smectites. The exchangeable cation in- fluenced the size and polarity matching between the adsorbing domains and AfB1 molecules in the interlayer. The adsorption capacity of the smectites was influenced by the layer charge density. As the negative charge sites on the surface increased, the non-polar sites for the sorption of aflatoxin decreased. The results also demonstrated that the low adsorption of high charge smectites can be improved by reducing the CEC. The charge origin had a slight effect on the aflatoxin adsorption. Smectites with octahedral charge adsorbed more AfB1 than the smectites with tetrahedral charge. The CEC reduction treatment demonstrated that octahedral charged smectites were the best adsorbents for aflatoxin. The diffused layer charge in smectites with octahedral charge allowed more accessibility to the interlayer space and less repulsion for AfB1 molecules than the smectites where the charge was of tetrahedral origin. The octahedral structural composition of the smectites had negligible effect on the aflatoxin adsorption. Similar adsorption capacities were observed when comparing di- and tri-octahedral smectites with either octahedral charge origin (montmorillonite and hectorite) or tetrahedral charge origin (beidellite, nontronite, and saponite). The bonding mechanism previously described for montmorillonite remains the same for the other smectites with no effects from the charge origin and the layer charge density