Theoretical Study on the Structures of Single-Atom M (M=Fe, Co and Ni) Adsorption Outside and Inside the Defect Carbon Nanotubes

Single-atom confinement inside carbon nanotubes has attracted much attention in many fields. This class of materials may not only serve as a catalyst but also as a support material for certain reactions. In this paper, we have studied the single-walled carbon nanotubes (SWCNT), single vacancy defect (SV) and Stone-Wales defect (SW) carbon nanotubes with Fe, Co and Ni atom by both inside and outside adsorption structures in density function theory (DFT). Our results reveal that the binding abilities of atomic Fe, Co, Ni onto the internal and external surfaces of the SWCNT, SV and SW are in following orders by metals: Ni>Co>Fe. The adsorption energies of SV toward Fe, Co and Ni are more stable than those of SWCNT and SW, which can be attributed to the three active carbon sites created by a C atom removing, while the SWCNT and SW demonstrate similar adsorption energy due to the similar structure. Generally, the stability of external adsorption structures is stronger than those of internal adsorption structures, but as for the SW, the stability of internal and external adsorption structures is close, which means that the defects have improved the confinement of carbon nanotubes to M (M=Fe, Co Ni).

Integrated Stirred-Tank Bioreactor with Internal Adsorption for the Removal of Ammonium to Enhance the Cultivation Performance of gdhA Derivative Pasteurella multocida B:2

Growth of mutant gdhA Pasteurella multocida B:2 was inhibited by the accumulation of a by-product, namely ammonium in the culture medium during fermentation. The removal of this by-product during the cultivation of mutant gdhA P. multocida B:2 in a 2 L stirred-tank bioreactor integrated with an internal column using cation-exchange adsorption resin for the improvement of cell viability was studied. Different types of bioreactor system (dispersed and internal) with resins were successfully used for ammonium removal at different agitation speeds. The cultivation in a bioreactor integrated with an internal column demonstrated a significant improvement in growth performance of mutant gdhA P. multocida B:2 (1.05 × 1011 cfu/mL), which was 1.6-fold and 8.4-fold as compared to cultivation with dispersed resin (7.2 × 1010 cfu/mL) and cultivation without resin (1.25 × 1010 cfu/mL), respectively. The accumulation of ammonium in culture medium without resin (801 mg/L) was 1.24-fold and 1.37-fold higher than culture with dispersed resin (642.50 mg/L) and culture in the bioreactor integrated with internal adsorption (586.50 mg/L), respectively. Results from this study demonstrated that cultivation in a bioreactor integrated with the internal adsorption column in order to remove ammonium could reduce the inhibitory effect of this by-product and improve the growth performance of mutant gdhA P. multocida B:2.

Poly(N-isopropylacrylamide-co-acrylic acid) Hydrogel and Its Thermo-responsive Properties for Polymer Enhanced Ultrafiltration

Poly(N-isopropylacrylamide-co-acrylic acid) hydrogel with thermo-responsive properties has been successfully synthesized. The hydrogel functional groups, volume phase transition (VPT) temperature and hydrodynamic size were altered upon copper ion adsorption indicated that the copper ion adsorption had disturbed the hydrogen bonding between the water molecule and the amine/ carboxylic groups present in the hydrogel matrix. It also demonstrates that internal adsorption also play important roles that enhance the copper ion removal. The adsorption process is more favourable at low temperature while the separation process should be carried out at higher temperature to mitigate fouling phenomenon. The hydrophobic behaviour of the hydrogel at temperature higher than the VPT value could minimize its interactions with the hydrophilic membrane.