Silicon boron carbonitride (SiBCN) ceramics have garnered significant attention due to their exceptional high-temperature stability, resistance to creep, and favorable electrical properties. However, the ceramicization mechanism of covalently bonded boron atoms in polyborosilazane (PBSN), which is crucial in determining the structural and crystalline phase evolution of silicon boron carbonitride (SiBCN) ceramics through the polymer-to-ceramic process, still needs further clarification for the design of advanced ceramics. Therefore, PBSN precursors constructed with B–C bonds were systematically investigated in the polymer-to-ceramic conversion process. B–C bonds were transformed into B-N bonds between 300°C and 600°C, ultimately resulting in the formation of h-BN at high temperatures. Meanwhile, higher levels (8.11–14.12%) of B facilitated the formation of SiC at equivalent temperatures but hindered the formation of Si 3 N 4 crystal nuclei. That is due to the formation of B–N and NB 3 units, which inhibited the formation of Si–N bonds and SiN 4 units, thereby interfering with the nucleation process of Si 3 N 4 and facilitating the crystallization of SiC. This study offers valuable insights for regulating the microphase evolution and properties of PDC nanocomposites.
The construction of enzyme-inspired artificial catalysts with enzyme-like active sites and microenvironment remains a great challenge. Herein, we report a single-atomic-site Co catalyst supported by carbon doped boron nitride (BCN) with locally polarized B–N bonds (Co SAs/BCN) to simulate the reductive dehalogenases. Density functional theory analysis suggests that the BCN supports, featured with ionic characteristics, provide additional electric field effect compared with graphitic carbon or N-doped carbon (CN), which could facilitate the adsorption of polarized organochlorides. Consistent with the theoretical results, the Co SAs/BCN catalyst delivers a high activity with nearly complete dechlorination (~98%) at a potential of −0.9 V versus Ag/AgCl for chloramphenicol (CAP), showing that the rate constant ( k ) contributed by unit mass of metal ( k /ratio) is 4 and 19 times more active than those of the Co SAs/CN and state-of-the-art Pd/C catalyst, respectively. We show that Co single atoms coupled with BCN host exhibit high stability and selectivity in CAP dechlorination and suppress the competing hydrogen evolution reaction, endowing the Co SAs/BCN as a candidate for sustainable conversion of organic chloride.
Constructing a chemical bond between the catalysts’ interfaces can establish a fast electron diffusion path and improve interfacial charge transport, thus produce a high efficiency in the catalytic field. We innovatively incorporate the humic acid (HA) and SrBi 2 B 2 O 7 (SBBO) to degrade oxytetracycline (OTC) under ball milling (BM), the degradation efficiency of OTC for SBBO/HA under BM is 93.17 % and its pseudo-first-order kinetic constant is 0.0434 min −1 , being 1.41 times than the sum of rate constant for HA (0.00826 min −1 ) and SBBO (0.0225 min −1 ), and 5.26 times than that for BaTiO 3 (0.00825 min −1 ), illustrating their outstanding synthetic effect of SBBO and HA on piezoelectric degradation of OTC. The mechanism of enhanced piezoelectric activity was attributed to the B-N bond which enhances the local polarized electric field improving electron transfer and contributes to the generation of •O 2 – and •OH. The possible degradation pathways involving bonds cleavage, ring-opening, and dehydroxylation process were proposed based on LC-MS and Fukui index calculation. The toxicity of intermediates generated during the piezoelectric catalysis was predicted and investigated by T.E.S.T. software and mung bean growth. This study provides a new technology of enhancing piezoelectric catalytic activity by combining HA, SBBO and BM and clarifies the mechanism in detail.
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