The photocatalytic reduction of methylene blue was recognized as an economical and effective way for dye removal. To enhance photocatalytic activity under visible-light condition, fluorine and graphene synergistically modified TiO2 (F-TiO2/rGO) nanocomposites were successfully prepared by sol–gel method. Characterization results showed F ions played an essential role in the formation of TiO2 nanoparticles. Between the fluorine sources selected, NH4F was more optimal than NaF doping on the grounds that the existence of Na+ ion was an inevitable factor for the production of brookite. F-TiO2/rGO nanocomposite obtained by adding 5%at NH4F significantly narrowed the bandgap energy from approximately 3.17 to 2.41 eV. Box–Behnken design was adopted to optimize the MB photo-degradation process by F(5%NH4F)-TiO2/rGO nanocomposites under different reaction conditions. Moreover, the antibacterial behaviour of this novel material was also investigated by Escherichia coli (E. coli) bacteria under visible light. The morphology changes of E. coli cells were directly observed by field emission scanning electron microscope and further confirmed that the excellent sterilization of F-TiO2/rGO nanocomposites resulted from the active species. The outstanding photocatalytic performance and antibacterial behaviour of F-TiO2/rGO nanocomposite was attributed to the synergistic effect of photocatalytic redox reaction and adsorption. These results indicated F(5%NH4F)-TiO2/rGO nanocomposite was a promising antibacterial photo-adsorbent for wastewater treatment improvement.
Ziqiang Xu,Hang He,Shuyuan Zhang,Beibei Wang,Jiancheng Jin,Cao Li,Xueqin Chen,Bingbing Jiang,Yi Liu
In this work, carboxylated carbon dots (C-CDs) with higher oxidation degrees or hydroxylated CDs (H-CDs) with lower oxidation degrees were applied to fabricate CDs capped silver nanoparticles (denoted as C-CDs@AgNPs and H-CDs@AgNPs, respectively) via a one-step strategy. These two types of as-prepared AgNPs have similar size, morphology and surface charge. Interestingly, both AgNPs exhibit a higher toxicity against Gram-negative bacteria Escherichia coli (E. coli) than against Gram-positive bacteria Staphylococcus aureus (S. aureus), and the AgNPs decorated with H-CDs with lower oxidation degrees can eliminate both bacteria more effectively. Subsequently, the possible reason for this fascinating phenomenon has been explored clearly in the perspective of nano/cell interface interactions, which has rarely been considered in detail in previous work. The species specific antibacterial activity can be understood by the typical structural difference of the two bacteria, i.e. the presence of hydrophilic lipopolysaccharides (LPS) which facilitate the adsorption of AgNPs onto the surface of E. coli and the absence of hydrophilic LPS and the existence of thicker peptidoglycan (PG) on S. aureus which prevent the adsorption of AgNPs. Interestingly, the adsorption capacity of H-CDs@AgNPs towards E. coli is also much larger than that of C-CDs@AgNPs, while their different abilities to eliminate S. aureus can be interpreted by the faster leakage rate of Ag+ from the H-CDs@AgNPs. The above adsorption capacity has been quantified through the association constants between AgNPs and LPS or PG determined by UV-vis absorption spectroscopy. The above mechanism can also be illustrated by the microscopic analysis and permeability changes of the two bacteria induced by the AgNPs. Our results may provide valuable insights into optimization of other AgNPs for security and practical disinfection application.
Qian Zhang,Hui Li,Yuetong Kang,Qianling Cui,Hean Zhang,Lidong Li
Host–guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 ‘head-to-tail’ binding patterns with cucurbit[8]uril (CB[8]) to form host–guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host–guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).
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