A carbazolide-
bis
(NHC) Ni
II
catalyst (1; NHC,
N
-heterocyclic carbene) for selective CO
2
photoreduction was designed herein by a one-stone-two-birds strategy. The extended π-conjugation and the strong σ/π electron-donation characteristics (two birds) of the carbazolide fragment (one stone) lead to significantly enhanced activity for photoreduction of CO
2
to CO. The turnover number (TON) and turnover frequency (TOF) of 1 were ninefold and eightfold higher than those of the reported pyridinol-
bis
(NHC) Ni
II
complex at the same catalyst concentration using an identical Ir photosensitizer, respectively, with a selectivity of ∼100%. More importantly, an organic dye was applied to displace the Ir photosensitizer to develop a noble-metal-free photocatalytic system, which maintained excellent performance and obtained an outstanding quantum yield of 11.2%. Detailed investigations combining experimental and computational studies revealed the catalytic mechanism, which highlights the potential of the one-stone-two-birds effect.
The electronic effect is crucial for electrocatalytic CO2 reduction. In contrast to previous understanding of the monotonic influence of the electronic effect on the selectivity of CO2 reduction, the dual...
An experimental program concerning 48 specimens of grouted sleeve splices, first heated up to 600°C and then subjected to cyclic loading was presented and discussed in this study. Similar rebar splices were often used in the precast concrete structures designed for seismic regions. The temperature of the splice and the compressive strength of the grout were the main variables considered in this study. It is found that the temperature mainly affected the peak bearing capacity of the grout and the failure pattern of the connection. In fact, the typical failure pattern at room temperature (rebar fracture outside the sleeve) turned to rebar pullout of the sleeve above 400°C, which indicated that below this temperature grout‐to‐rebar bond kept most of its original efficacy. On the contrary, bond failure occurred for all specimens at 600°C because of rebar slip. A calculation method was proposed as well to evaluate the peak bearing capacity of grouted sleeve splice, based on the load transferring mechanisms of the bond between grout‐to‐rebar and sleeve‐to‐grout. The conducted experimental study and analysis provide a better understanding on the bond mechanism of thermally damaged grouted sleeve splices subjected to cyclic loading.
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