Preparation of Activated Carbon-Reinforced Composite Beads Based on MnO2/MCM-41@Fe3O4 and Calcium Alginate for Efficient Removal of Tetracycline in Aqueous Solutions.

Tetracycline (TC) is a common antibiotic; when untreated TC enters the environment, it will cause a negative impact on the human body through the food chain. In the present study, MnO2/MCM-41@Fe3O4 (FeMnMCM) prepared using a hydrothermal and redox method and Camellia oleifera shell-activated carbon (COFAC) prepared through alkali activation were encapsulated using alginate (ALG) and calcium chloride as a cross-linking matrix to give the composite beads COFAC-FeMnMCM-ALG. The resultant COFAC-FeMnMCM-ALG composite beads were then carefully characterized, showing a high immobilization of MnO2/MCM-41@Fe3O4, with porous COFAC as an effective bioadsorbent for enriching the pollutants in the treated samples. These bead catalysts were subsequently applied to the oxidative degradation of TC in a Fenton oxidation system. Several parameters affecting the degradation were investigated, including the H2O2 concentration, catalyst dosage, initial TC concentration, and temperature. A very high catalytic activity towards the degradation of TC was demonstrated. The electron paramagnetic resonance (EPR) and quenching results showed that ·OH and ·O2- were generated in the system, with ·OH as the main radical species. In addition, the COFAC-FeMnMCM-ALG catalyst exhibited excellent recyclability/reusability. We conclude that the as-prepared COFAC-FeMnMCM-ALG composite beads, which integrate MnO2 and Fe3O4 with bioadsorbents, provide a new idea for the design of catalysts for advanced oxidation processes (AOPs) and have great potential in the Fenton oxidation system to degrade toxic pollutants.

Insight into the rheological behaviors of a polyanionic collagen fabricated with poly(γ-glutamic acid)-NHS ester.

The rheological behaviors of a polyanionic collagen, fabricated using poly(γ-glutamic acid)-N-hydroxysuccinimide (γ-PGA-NHS) as a novel modifier, were investigated in this study. It was found that both of the native and modified collagen solutions were pseudoplastic fluids, as shown from the steady-shear tests. While the storage modulus and loss modulus of collagen increased with increasing the amount of γ-PGA-NHS, or with increasing the degree of esterification of γ-PGA-NHS; meanwhile, the dynamic denaturation temperature determined by dynamic temperature sweep was also increased, indicating an improved thermal stability of collagen solution modified by γ-PGA-NHS. The creep-recovery measurements showed that the resistance to deformation was enhanced for modified collagen, probably due to the cross-linking occurred between the ε-amino groups of collagen molecules and α-COOH groups of γ-PGA-NHS, as well as the electrostatic interaction and hydrogen-bond interactions between the two molecules. Furthermore, the aggregation of collagen fibers was promoted due to these interactions between collagen and γ-PGA-NHS as observed by atomic force morphology. In addition, the modified collagen exhibited good cytocompatibility as demonstrated by cell growth culturing. The obtained information was expected to give valuable clues to the design and fabrication of controlled stable collagen-based products for applications in various biomedical fields.

Effect of carboxymethylcellulose on fibril formation of collagen in vitro.

The effect of carboxymethylcellulose (CMC) on the fibril formation of collagen in vitro was studied by turbidity measurements and atomic force microscopy (AFM). The kinetics curves of fibril formation indicated that the rate of collagen fibrillogenesis was decreased with the addition of CMC, meanwhile the final turbidity was obviously increased as the CMC/collagen ratio reached 30%. The AFM images of collagen-CMC solutions showed that the number of nucleation sites of collagen fibrillogenesis was significantly increased with the presence of CMC, while the diameter of immature collagen fibrils was obviously decreased. Moreover, the thermal stability of collagen fibril hydrogels was obviously improved with the presence of CMC. In addition, the morphologies of collagen fibrils observed by AFM revealed that the adjacent fibril segments or fibrils were intertwisted and even tightly merged, probably due to the hydrogen bonding and molecular entanglement interactions between CMC and collagen molecules.

Effect of surface modification of cellulose nanocrystal on nonisothermal crystallization of poly(ß-hydroxybutyrate) composites.

Ring-opening polymerization of l-lactide from cellulose nanocrystal (CNC) surface yielded polylactide-grafted CNC (CNC-g-PLA). The structure and chemical composition of the CNC-g-PLA were characterized by FT-IR, 1H NMR, XPS and XRD. The crystallization behavior and lamellar structure of poly(ß-hydroxybutyrate) (PHB) in the presence of pristine CNC and CNC-g-PLA were elucidated via DSC and SAXS, and Babinet's reciprocity theory was applied. Crystallization kinetics were further analyzed using Ozawa, Mo and Kissinger models. In the presence of pristine CNC, nucleation of PHB crystals led to an increase in the crystallization temperature (Tc) of PHB; while CNC-g-PLA acted as antinucleation agent, resulting in a remarkable reduction in Tc of PHB. Accordingly, the composite with pristine CNC possessed a higher crystallization rate than neat PHB, while CNC-g-PLA displayed the lowest crystallization rate. However, the lamellar structure of PHB was not affected by the presence of pristine and modified CNCs, and almost identical crystallization activation energies as the neat PHB were observed, indicating that nucleation is dominant during PHB crystallization, instead of crystal growth. This study offers a promising approach of using pristine and modified CNCs to control the crystallization of biodegradable aliphatic polyesters.

Effect of γ-PGA on the formation of collagen fibrils in vitro.

The effect of γ-poly(glutamic acid) (γ-PGA) on the self-assembly of collagen was studied. Under physiological conditions, the kinetic curves for fibril formation showed that the turbidity of collagen/γ-PGA blends at 313 nm was increased with the addition of γ-PGA. Furthermore, it was shown using both field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) that fibrils with a larger diameter were obtained following the addition of γ-PGA, probably due to the electrostatic and hydrogen bond interactions between collagen and γ-PGA, which promoted the lateral association of collagen molecules. In addition, both the thermal stability and viscoelastic properties of the hybrid hydrogels, which were evaluated by differential scanning calorimetry and rheological measurements, respectively, were improved by the addition of γ-PGA.