To develop a new technology to remediate pollution sites stably and effectively, hydrothermal conversion of polluted soil (model soil) into zeolite P for in situ immobilization of Heavy Metals (HM) was carried out. Zeolite P could be synthesized from soil hydrothermally with a large range of Al/Si ratio (0.33–1.0) in 48 h at 200 °C. With immobilizing heavy metals (Cr, Zn and Cd), the crystallization of Zeolite P (Cr-ZP, Zn-ZP and Cd-ZP) was delayed with the order of Cr >Zn >Cd because the stronger the ligand effect of heavy metals have, the more heavily the nucleation and growth were influenced. During immobilization via zeolitization, a self-adaptive structuring behavior was confirmed by EDAX, BET and Rietveld refinement analyses: zeolite P structured more [AlO4]− to immobilize HM because the flexible 8-member-Ring channels (8 mRs) with higher Al/Si ratio could complex with more HM readily. The encapsulated HM occupied the original Na positions (Na1 and Na2) of zeolite P competitively because of their different cation size, e.g., the smallest Cr3+ could substitute all Na1 because Na1 is closer to the Framework Oxygen (FO); the largest Cd2+, however, substituted Na1 (9%) and Na2 (14%) evenly. The shrunken 8 mRs due to heavy metal immobilization also caused different chemical environments for different heavy metals immobilized because the smaller heavy metal cation could get closer to the framework, and also coordinated with more FO.
Zhang XiaoNan,Yang Zhongxin,Xu Wenqin,Li Xing,Pan Guanghua,Chen Nan-Chun,Xie Qing-Lin,Wang Xiu Li
Potassium diformate (KDF) has broad prospects in replacing common antibiotics in animal feed; however, the utilization rate of KDF in the animal intestine is low. Therefore, it is necessary to construct a drug delivery system for its targeted release in the colon. When Zeolite P was used as a drug-binding effector, KDF was uniformly dispersed in the pectin matrix, and the pectin bacteriostatic microspheres loaded with KDF were prepared using the emulsion cross-linking method. The optimized pectin bacteriostatic microspheres were systematically characterized, we observed that the drug loading rate and stability of pectin bacteriostatic microspheres improved significantly after adding Zeolite P and the utilization rate of KDF in the simulated intestine was higher than that in the stomach. The pectin bacteriostatic microspheres exerted significant bacteriostatic effect on Escherichia coli and Staphylococcus aureus , indicating that they may be widely used in livestock feed as bacteriostatic agents. Graphical Abstract In order to improve the antibacterial effect of KDF in intestinal tract, W/O emulsion microcapsules were prepared by emulsification method. When Zeolite P was used as a drug-binding effector, KDF was uniformly dispersed in the pectin matrix, and the pectin bacteriostatic microspheres loaded with KDF were prepared using the emulsion cross-linking method. Moreover, the bacteriostatic microspheres possessed significant growth inhibitory effects on E. coli, S. aureus and Bacillus subtilis.
Potassium diformate (KDF) is a novel substitute for antibiotics. To achieve controlled release of KDF and extend its antibacterial effect, composite hydrogel antibacterial microspheres of sodium alginate (ALG)/konjac glucomannan (KGM)/ethyl cellulose (EC)/zeolite P were prepared using a sharp-hole coagulation bath. Considering the swelling rate of hydrogel as the response value, the Plackett Burman (PB) design experiment was performed to show that ALG , KGM, zeolite P, and calcium chloride (CA) were the most important influencing factors. Then, the steepest ascent test was performed to approach the maximum response area, and the response surface analysis method was used to establish the continuous variable surface model and investigate the structure-activity relationship and swelling property of the hydrogel microspheres. The results showed that the four factors in descending order of influence were zeolite P > ALG > KGM > CA, and that ALG/CA, KGM/ALG, and zeolite P/ALG interacted. In vitro drug release behavior showed that microspheres improved the drug loading rate and encapsulation efficiency, and prevented the premature release of KDF in gastric juice. The release kinetics also followed the Ritger-Peppas model. Under simulated gastrointestinal environment, in vitro antibacterial tests showed that the minimum inhibitory concentrations (MIC) of the antibacterial agents against Escherichia coli , Staphylococcus aureus, and Bacillus subtilis were 12 mg/mL, 12 mg/mL, and 24 mg/mL, respectively, indicating that the microspheres effectively inhibited the growth of bacteria in the intestine. Our results indicated that hydrogel microspheres can be used as potential drug delivery systems.
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