RESUMO
Magnetic chitosan microspheres (Al@CTS@Fe3O4) were prepared for haem separation via chemical cross-linking of chitosan, Fe3O4 and AlCl3·6H2O. The properties of the Al@CTS@Fe3O4 microspheres were investigated through techniques including XRD, TEM, FTIR, BET analysis, SEM, TG, VSM, XPS and pHpzc analysis. The haem adsorption of Al@CTS@Fe3O4 was optimized via a Box-Behnken design (BBD) with three operating factors: Fe3O4 dose (0.5-1.3 g), AlCl3·6H2O concentration (0.25-1.25 mol/L) and glutaraldehyde dose (2-6 mL). The optimal haem adsorption effect was achieved with 1.1 g of Fe3O4, 0.75 mol/L AlCl3·6H2O, and 3 mL of glutaraldehyde. The adsorption kinetics and isotherms demonstrated that haem adsorption by the Al@CTS@Fe3O4 microspheres was best described by the pseudo-second-order model. The maximum adsorption capacity is 33.875 mg/g at pH 6. After six adsorption-desorption cycles, the removal of haem still reached 53.83 %. The surface adsorption mechanism of haem on Al@CTS@Fe3O4 can be attributed to electrostatic, hydrogen bonding, and n-π interactions. Thermodynamic calculations indicated that the adsorption process is spontaneous, with the microspheres preferentially accepting electrons and haem preferentially providing electrons. Consequently, the Al@CTS@Fe3O4 microspheres exhibit considerable potential as adsorbents for haem separation.
RESUMO
Polybenzoxazines with molecular design flexibility have excellent properties by using suitable raw materials. A new benzoxazine monomer terephthalic acid bis-[2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)]ethyl ester (TMBE) with bis-ester groups has been synthesized from the simple esterification reaction of terephthaloyl chloride and 2-(6-methyl-4H-benzo[e][1,3]oxazin-3-yl)-ethanol (MB-OH). The chemical structure of TMBE was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H-NMR, 13C-NMR). Polymerization behavior of TMBE was studied by differential scanning calorimetry (DSC) and FT-IR after each cure stage. The cross-linked polybenzoxazine (PTMBE) gave a transparent film through the thermal casting method. The dynamic mechanical analysis of PTMBE showed that the T g was 110 °C. Thermogravimetric analysis reveals better thermal stability as evidenced by the 5% and 10% weight-loss temperatures (T d5 and T d10) of PTMBE, which were 263 and 289 °C, respectively, with a char yield of 27% at 800 °C. The tensile test of the film revealed that the elongation at break was up to 14.2%.
RESUMO
Computational studies have been applied to gain insight into the mechanism of Pd(ii) catalyzed α-C-H functionalization of N-methoxy cinnamamide. The results show that the whole catalytic cycle proceeds via sequential six steps, including (i) catalyst Pd(t-BuNC)2 oxidation with O2, (ii) O-H deprotonation, (iii) t-BuNC migratory insertion to the Pd-C bond, (iv) acyl migration, (v) C-H activation and (vi) reductive elimination. The regioselectivity for different C-H activation sites depends on the coordination structures of α-C or ß-C to the palladium(ii) center. The coordination of α-C to the palladium(ii) center shows a regular planar quadrilateral structure, which is stable. However, the ß-C coordinating to the palladium(ii) center mainly exhibits a distorted quadrilateral structure, which is relatively unstable. Thus, the barrier of α-C-H activation is much lower than that of ß-C-H activation. The present results provide a deep understanding of the site-selectivity of C-H activation.