Solubility of Cefotaxime Sodium in Ethanol + Water Mixtures under Acetic Acid Conditions

Aimed at exploring the influence of acetic acid on crystallization thermodynamics of cefotaxime sodium (CTX), the solubility of CTX in ethanol + water mixtures under acetic acid conditions at various temperatures are measured by a gravimetrical method. Different from the solubility curve when acetic acid is absent, the solubility curves of CTX under acetic acid conditions have a maximum value. The maximum solubility drifts as temperature varies, which is related to the dielectric constants of solvent mixtures. A combination of the Jouyban–Acree model and Apelblat equation is used to correlate the solubility data, and the correlation precision is improved when compared with that of the Jouyban–Acree model. By using the Wilson model, the activity coefficients of CTX and the mixing Gibbs free energies, enthalpies, and entropies of CTX solution are also predicted. The data presented in this study explain why the crystallization of CTX in ethanol + water mixtures is difficult and are helpful for guiding the industrial reaction and crystallization process of CTX

Gelation Phenomenon during Antisolvent Crystallization of Cefotaxime Sodium

In this paper, gelation phenomenon during the crystallization process of cefotaxime sodium (CTX) is systematically studied. First, the gelation process is monitored using a nanoparticle size analyzer; the gel and xerogel are studied by different characterization tools to speculate the gelation mechanism. It is found that the gelation is driven by the crystallization of CTX and the nanoparticles act as gelators before they can be seen by the naked eye. Moreover, the solid-solution interfacial tension used to predict the rate of crystal growth is calculated using the induction periods and solvents are classified using the Hansen solubility parameters method, according to whether it can be gelated by CTX. It is shown that the strong polar interaction between solvent molecules and the carboxyl, amine, or acyl groups exposed on the CTX crystal surface is the key factor for gelation

Facilitating Proton Transport in Nafion-Based Membranes at Low Humidity by Incorporating Multifunctional Graphene Oxide Nanosheets

Nafion, as a state-of-the-art solid electrolyte for proton exchange membrane fuel cells (PEMFCs), suffers from drastic decline in proton conductivity with decreasing humidity, which significantly restricts the efficient and stable operation of the fuel cell system. In this study, the proton conductivity of Nafion at low relative humidity (RH) was remarkably enhanced by incorporating multifunctional graphene oxide (GO) nanosheets as multifunctional fillers. Through surface-initiated atom transfer radical polymerization of sulfopropyl methacrylate (SPM) and poly­(ethylene glycol) methyl ether methacrylate, the copolymer-grafted GO was synthesized and incorporated into the Nafion matrix, generating efficient paths at the Nafion–GO interface for proton conduction. The Lewis basic oxygen atoms of ethylene oxide (EO) units and sulfonated acid groups of SPM monomers served as additional proton binding and release sites to facilitate the proton hopping through the membrane. Meanwhile, the hygroscopic EO units enhanced the water retention property of the composite membrane, conferring a dramatic increase in proton conductivity under low humidity. With 1 wt % filler loading, the composite membrane displayed the highest proton conductivity of 2.98 × 10^–2 S cm^–1 at 80 °C and 40% RH, which was 10 times higher than that of recast Nafion. Meanwhile, the Nafion composite exhibited a 135.5% increase in peak power density at 60 °C and 50% RH, indicating its great application potential in PEMFCs