| The coal chemical industry (CCI) is an important pillar of our national chemical industries due to the "rich coal, deficient oil, lean gas"energy structure of China. However, CaC2 industry, as an important branch of CCI, suffers from high energy consumption in preparation process, singleness of downstream products, and high pollution of relative crafts, and therefore adversely affects the long-term and benign development of CCI in China. Thus, the studies for CaC2, especially for its reactive activation and new applications, have very important strategic significance for the development of CCI and the national economy.Recently, most researches about the reactive activation of CaC2 were done through trace water addation or high temperature giving. The mechanism of trace water activation method is to contral the reaction between CaC2 and H20, and essentially is the acetylene route. However,this method is under researching, and its practical application is under consideration. On the other hand, although few CaC2 reactions can be activated by high temperature, this activation method can not conform to the concept of the "energy-saving and emission-reduction" theroty and green chemical industry due to its high requirements in equipments,safety, and energy. This makes the reactive activation of CaC2 has become an urgent research subject. This work studies the limiting factors of CaC2 reactions, and then explores several reaction routes about CaC2,including efficient catalysis of CaC2 for the synthesis of isophorone,efficient mechanochemical activation of CaC2 for the synthesis of alkynyl carbon materials, and ionic exchange of CaC2 for the synthesis of metal acetylides or metal elements. Besides, their reactive influential factors,mechanisms, and relative applications are deeply investigated and synthetically analysed.Firstly, the limiting factors of CaC2 reactions were studied in this work through the comprison of the reactions between CaC2/NaC2H and polyhalogenated hydrocarbons (PHHCs), as well as the properities and structures of their as-prepared carbon materials (CMs). The results show that NaC2H has much higher reactivity than CaC2 in these reactions under similar conditions, but the as-prepared CMs are amorphous due to the unidirectionality of the terminal alkynyl. In contrast, although the reactivity of CaC2 is poor, the as-prepared CM has unique structures, and therefore shows great application potentials and research value. This indicates the structural advantage of CaC2 in advanced CM synthesis.Most importantly, the results indicate that the reactivity difference between CaC2 and NaC2H can mainly attribute to the difference in their aggregation structures. For CaC2, its reactivity is extremely limited by its lattice structure, so, its relative reactions are difficult to carry out.Therefore, we believe that the key to the reactive activation of CaC2 is to destroy its lattice structure. Besides, in consideration of the inefficiency under general solvothermal conditions, unique and targeted technical means should be seeked and used for the lattice structure destruction of CaC2.Secondly, the strong Lewis basicity and dehydrating ability of CaC2 were used for the synthesis of isophorone (IP) through the liquid-phase catalytic aldol condensation of acetone for the first time. This process combines the hydrolysis of CaC2 and the aldol condensation of acetone into a one-pot reaction. The aldol condensation of acetone was initiated via the induction effect of alkynyl in CaC2 on acidic a-proton of the acetone, and IP was efficiently synthesized. At the same time, CaC2 is converted to Ca(OH)2 and acetylene by the resulting water, and its lattice structure is simultaneously destroyed, which is benefit for the basic induction effect of alkynyl. Moreover, the aldol condensation of acetone is further accelerated by dehydrolysis of CaC2. Furthermore, the results show that higher temperature, smaller CaC2 size, and higher CaC2 mass ratio are beneficial to the IP synthesis. This process not only achieves a high catalytic efficiency under mild conditions, but also overcomes the disadvantages of the traditional vapor-phase aldol condensation, and also along with the quantitative reclamation of acetylene. Thus, this process can be thought of as a green, cost-effective, and efficient route for the synthesis of IP and provides a valuable use of CaC2.Thirdly, a series of alkynyl carbon materials (ACMs) were synthesized in this study by the mechanochemical reaction of CaC2 with six typical PHHCs for the first time. The results show that these mechanochemical reactions can reach a deep level after three reaction stages, viz., pulverization and initiation, fast interfacial reaction, and deep degradation. The high ACM yields are achieved along with the formation of the nonhazardous CaCl2. The results, which are from the investigation for the influence factors of rotation speed, reactant ratio, and milling time,show that these reactions can proceed in a rapid, comprehensive manner under mild conditions. The as-prepared ACMs are micro-mesoporous materials with distinct layered structure, specific graphitization degree,and clear sp-C existence, and thus can be a new carbon allotrope.Furthermore, their structures and compositions can be modulated via choosing the different PHHC precursors. Furthermore, the lattice structure destruction of CaC2 under strong mechanical stress is deemed as the key to these mechanochemical reactions, viz., the nucleophilic substitution of halogens on PHHC by highly reactive alkynyl. Besides,for the ACMs made from only sp3-C contented PHHCs, the grapheme-like structure can be achieved due to the partial structural rearrangement caused by the high energy density and unstability of their intermediate monomers. While for the ACMs made from the sp2-C dominant PHHCs, their formed structure are stable because of their highly conjugated structures, and thus can be remained.For the as-prepared ACMs, their electrochemical performances in supercapacitors and adsorptivity of mercury are investigated, respectively.The results obtained from their cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests show that all the six ACM electrodes exhibit representative capacitive behavior and excellent charge-discharge reversibility, as well as favorable scan rate and current density capabilities. In addition, their specific capacitances are in the range of 57～133 F/g, which is highly comparable to those of other CMs reported previously. Furthermore, the results obtained from their long cycling performance and electrochemical impedance spectroscopy (EIS)tests show that they have excellent cycling stability, as well as high electrical conductivity and charge-discharge rate. Therefore, the as-prepared ACMs can be ideal candidates for active materials used in supercapacitors. On the other hand, the adsorptivity of Hg(Ⅱ) on ACMs is found to be closely related to their specific surface area and alkynyl content, which is primary for the former and secondary for the latter. In addition, the solution pH exerts a strong influence on their Hg(Ⅱ)adsorption. Most importantly, the adsorption kinetics and the adsorption isotherm can be satisfactorily correlated by the pseudosecond-order model and the Langmuir equation, respectively, indicating that Hg(Ⅱ)adsorption is mainly a chemisorption process due to the specific soft acid-soft base interactions between Hg(Ⅱ) and alkynyl groups.Furthermore, the results show that their saturated adsorption capacity can reach 191.9 mg/g, which is superior compared to the gerenal carbon-based adsorbents, and close to the S-modified ones. The activation energy and thermodynamic calculation indicates that the Hg(Ⅱ)adsorption on ACMs is a rapid, endothermic, entropy-driven, and spontaneous process. Therefore, we believe that the as-prepared ACMs can be used as efficient sorbents for the removal of Hg(Ⅱ) from aquatic ecosystems.Finally, the exchangeability of Ca2+ in CaC2 is investigated, and the Ca2+ exchange reaction can be achieved under high temperature or ultrasonic conditions, respectively. The results indicate that promote the formation of the instantaneous lattice defects is the prerequisite for these ionic exchange reactions, and the strong soft base-soft acid affinity between C2+ and metal ions is the internal impetus, and thus the Ca2+exchange capacity of the metal ions depends on the softness of the metalions. In other words, the more softness of the metal ions, the higher Ca2+exchange capacity it has. Specifically, the order for the Ca2+ exchange capacities of the metal ions in the periodic table can be as follows:ds>d>p>s≈0 and high periods>low periods. |
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