Zhanqin Wang,Yongzhong Jia,Bing Liu,Yan Jing,Ying Yao
Flotation complexation extraction can effectively extract and separate lithium isotopes. The effects of nitrogen flow rate, bubble size, gas holdup, reaction flow pattern, aeration time, and temperature on the separation process were studied. In addition, the complex relationship and separation mechanism of lithium with 10-hydroxybenzoquinoline were discussed. Results show that nitrogen flow rate and bubble size significantly affected the flotation complexation extraction process. With an appropriate flow rate, we obtained a homogeneous regime pattern containing small and evenly distributed bubbles to achieve better separation efficiency and ensure a smooth extraction process. According to the slope method, lithium and 10-hydroxybenzoquinoline were complexed and extracted at a ratio of 1: 2. Compared with the traditional oscillating extraction, the bubble mass transfer mode in the flotation complexation extraction strengthened the complex extraction process and achieved higher extraction rate and separation efficiency.
Controlled polymerization to synthesize hyperbranched polypeptides (HBPPs) with tunable degree of branching (DB) and molecular weight (MW) is still challenging in synthetic polypeptides and their biomaterials fields. A new photocaged amino acid monomer Nε-(1-(2-nitrophenyl)ethoxycarbonyl)-L-lysine-N-carboxyanhydride (NPE-Lys NCA) was designed. Without the addition of any catalyst/initiator and/or scavenger, lysine-based HBPPs were directly synthesized from the UV phototriggered ring-opening polymerization (ROP) of NPE-Lys NCA by a one-pot method and at room temperature. Their branched structures were fully characterized by means of 1H NMR, 1H,1H-COSY, 1H,13C-HSQC, and quantitative 13C NMR techniques. The effects of irradiation intensity and N2 flow rate on the phototriggered ROP and MWs, DBs, and conformations of the resulting polypeptides were investigated. At a lower irradiation intensity of 0.3 mW cm−2, the actual MWs (Mw,LLS) of P1 to P3 increased from 34.9 kDa to 62.8 kDa when N2 flow rate shifted to 300 mL min−1; DB reduced from 0.43 to 0.21; and the α-helix content rose from 35% to 63%, while the random coil decreased from 50% to 26%. By tuning the UV irradiation intensity and/or the N2 flow rate, this methodology can efficiently produce lysine-based HBPPs with tunable DBs of 0.21–0.54 and higher actual MWs of 13.7–62.8 kDa.
A simple and efficient method was developed to prepare a copper–carbon (Cu–C) catalyst with high oxygen reduction reaction (ORR) activity via direct pyrolysis of a mixture of metal salts (Cu(NO3)2·3H2O and Zn(CH3COO)2) and 1,3,5-benzenetricarbocylic acid at 1010 °C under a N2 stream. It is found that the Cu–C catalyst exhibits superior catalytic activity toward ORR with a half-wave potential of 0.81 V and a four-electron transfer pathway in 0.1 M KOH electrolyte. Generally, it is known that N plays an important role for the high ORR catalytic activities of nonprecious metal-doped carbon materials. Herein, we demonstrate that N is not required for the superior catalytic activity of Cu–C materials. Both the Cu particles and the embedded Cu atoms in the carbon substrate are suggested to provide the ORR active sites. In addition, despite the fact that the Zn is removed during the pyrolysis, the adding of Zn salt in the precursor is important for the enhanced catalytic activity. The evaporation of Zn during the pyrolysis results in the large surface area of the catalyst, which is beneficial to the mass transfer during the catalytic process. Moreover, a large number of carbon defects can be created via the removal of Zn atoms that facilitated the ORR.
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