Molecular Dynamics Simulation of the Adsorption and Diffusion of C8 Aromatic Isomers in MIL-47(V).

The separation of C8 aromatic isomers (oX: o-xylene, pX: p-xylene, mX: m-xylene, and EB: ethylbenzene) remains an enormous challenge in industrial production due to their similar molecular structures and physical properties. Porous materials with suitable pore structures and selective recognition sites to discriminate the slight structural differences of isomers are imminently needed. In this paper, MIL-47(V) with a three-dimensional (3D) grid structure of 10.5 × 10.5 Å2 and a one-dimensional (1D) diamond channel was selected as the adsorbent. However, the mechanism of the adsorption and separation of C8 aromatic isomers in porous materials still needs to be understood. Given the importance of C8 aromatic isomers' confinement in MIL-47(V) for adsorption and diffusion applications, it is important to understand C8 aromatic isomers' behavior in MIL-47(V). Here, we demonstrated from a simulation perspective that metal-organic frameworks MIL-47(V) with one-dimensional (1D) diamond channels can identify C8 aromatic isomers. Molecular dynamics (MD) simulations have shown that organic ligands with guest response sites of MIL-47(V) can effectively distinguish between C8 aromatic isomers by adaptation to the shape of a specific isomer. MIL-47(V) has high adsorption and an excellent separation sequence between C8 aromatic isomers: oX > pX ≈ mX > EB. Significant differences exist in π-π superposition interactions between C8 aromatic isomers and between C8 aromatic isomers and the skeletons. This phenomenon is mainly caused by the unique pore structure and guest response characteristics of MIL-47(V). This work is identified as a supplementary instruction to experimental research and is expected to provide profound insights into research on developing C8 aromatic isomers' adsorption and separation and theoretical support.

Anaerobic starvation realizes partial nitrification and starts anammox bacteria self-enrichment in mainstream municipal sewage treatment in a low filling ratio sequencing batch reactor.

The initiating and stable preservation of partial nitrification (PN) and achievement of anammox bacteria self-enrichment in domestic sewage is a purposeful subject. In this article, an originality tactics of anaerobic starvation for 100 days was adopted for rapidly achieving PN in actual wastewater, the nitrite accumulation rate (NAR) improved from 4.95% to 81.73% in 18 days. After anaerobic starvation was stopped, the stable PN effect furnished enough stroma for the growth of anammox bacteria. The abundance of Candidatus Brocadia grew from 0% to 0.42% in floc sludge and 0.43% in blank biofilm, which promoted nitrogen removal effect. Anaerobic starvation continuing 74 days generated further decrease in the abundance of Nitrobacter and Nitrospira of nitrite-oxidizing bacteria (NOB), indicating that anaerobic starvation can restore the destroyed partial nitrification. In conclusion, this article furnished a low-cost method for achieving anammox bacteria self-enrichment in mainstream municipal wastewater in 10% filling ratio without chemicals addition.