No abstract

Dimensional isomers, defined in reticular chemistry as frameworks consisting of identical molecular building blocks but extended in two or three dimensions (2D or 3D), are an important type of framework isomers that have never been isolated. Herein, we report the crystallization of dimensional isomers in covalent organic frameworks (COFs) for the first time. By polymerization of the same molecular building blocks at different temperatures, both 2D and 3D COFs were successfully constructed due to the temperature-induced conformational changes of precursors from planar to tetrahedral. In addition, the nonfluorescent 2D COF can be gradually converted into the fluorescent 3D COF by increasing the temperature under solvothermal conditions. Therefore, it is reasonable to crystallize the dimensional isomers of reticular materials by controlling the conformation of molecular building blocks, and more examples can be expected. Since the obtained dimensional isomers show different properties and functions, this work will definitely motivate us to design reticular materials for target applications in the future.

Three-dimensional covalent organic frameworks (3D COFs) have gained increasing attention for their attractive features.H owever,t he development of 3D COFs is strongly restricted, mainly due to their synthetic difficulty and complicated structure determination. Post-synthetic modification, which can avoid these problems by incorporating functional moieties into ap redetermined framework, provides an alternative way to construct 3D COFs with specific functions. Herein, we report the designed synthesis and characterization of as eries of highly crystalline 3D COFs with different loadings of ethynyl groups.N otably,t hese alkyne-tagged 3D COFs provide ap latform for targeted anchoring various specific groups onto the pore walls via click reactions.M oreover,the pore surface engineering can accordingly change their properties,f or example,t he obtained click products exhibited higher CO 2 /N 2 selectivity.W ed escribe as imple but powerful strategy to build functional 3D COFs,w hich will certainly advance them for ar anging of interesting applications in the future.

Purpose The purpose of this paper was to investigate the corrosion behavior of X65 steel in the CO2/oil/water environment using mass loss method, potentiodynamic polarization technique and characterization of the corroded surface techniques. Design/methodology/approach The weight loss analysis, electrochemical study and surface investigation were carried out on X65 steel that had been immersed in the CO2/oil/water corrosive medium to understand the corrosion behavior of gathering pipeline steel. The weight loss tests were carried out in a 3L autoclave, and effects of flow velocity, CO2 partial pressure and water cut on the CO2 corrosion rate of X65 steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature of 60°C and CO2 partial pressure of 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using X-ray diffraction. Findings The results showed that corrosion rates of X65 steel both increased at first and then decreased with the increase of flow velocity and CO2 partial pressure, and there were critical velocity and critical pressure in the simulated corrosive environment, below the critical value, the corrosion products formed on the steel surface were loose, porous and unstable, higher than the critical value, the corrosion product ?lms were dense, strong adhesion, and had a certain protective effect. Meanwhile, when the flow velocity exceeded the critical value, oil film could be adsorbed on the steel surface more evenly, corrosion reaction active points were reduced and the steel matrix was protected from being corroded and crude oil played a role of inhibitor, thus it influenced the corrosion rate. Above the critical CO2 partial pressure, the solubility of CO2 in crude oil increased, the viscosity of crude oil decreased and its fluidity became better, so that the probability of oil film adsorption increased, these factors led to the corrosion inhibition of X65 steel reinforced. The corrosion characteristics of gathering pipeline steel in the corrosive environment containing CO2 would change due to the presence of crude oil. Originality/value The results can be helpful in selecting the suitable corrosion inhibitors and targeted anti-corrosion measures for CO2/oil/water corrosive environment.