Insights into chemical reactions of graphitic carbon nitride with alkali halides
Insights into chemical reactions of graphitic carbon nitride with alkali halides
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DOI：
10.1088/2515-7655/aca934
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发表时间：
2022-12
期刊：
影响因子：
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通讯作者：
K. Akaike;Ayako Hosokai;K. Tajima;H. Akiyama;H. Nagashima
中科院分区：
文献类型：
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作者：
K. Akaike;Ayako Hosokai;K. Tajima;H. Akiyama;H. Nagashima
富氮分子（如三聚氰胺和尿素）与无机盐的煅烧导致石墨氮化碳（g-CN）的化学改性，这是一种由可见光照射驱动的聚合物光催化剂。碱金属卤化物是用于该目的的丰富且低成本的添加剂，并且增强光催化活性。前体或缩合的氮化碳聚合物与盐反应，甚至低于它们的熔点;然而，g-CN与碱金属卤化物反应的机理理解仍然是未知的。在这项研究中，我们研究了瓜，线性聚合物的heptazine单体，与NaCl的反应，采用傅立叶变换红外（IR）光谱在固相和气相，固态核磁共振光谱，程序升温脱附质谱（TPD-MS），和热重分析。瓜与NaCl在500 °C下的反应用氨腈部分取代一部分氨基，并使桥接七嗪单体的NH基团去质子化。NH_4Cl在煅烧过程中的形成表明，NaCl与作为瓜分子缩合的结果而产生的NH_3反应。TPD-MS和气相IR证实在400 °C以上存在NH3以及H2O和CO2。这些气体分子和NaCl通过Solvay过程反应生成NaHCO 3。NaHCO 3在煅烧温度下分解成Na 2CO 3。碱和气态H2O最终形成OH−。所得到的羟基阴离子将氨腈基团引入到瓜中，使NH基团去质子化，并通过形成作为中间体的氰美尿酸钠将一部分聚合物分解成异氰酸。本研究提出的反应机理将促进对添加剂在g-CN光催化剂化学结构修饰中的作用的分子理解。
The calcination of nitrogen-rich molecules, such as melamine and urea, with inorganic salts, results in chemical modifications of graphitic carbon nitride (g-CN), a polymeric photocatalyst driven by visible-light illumination. Alkali halides are abundant and low-cost additives for that purpose and enhance photocatalytic activity. The precursors or condensed carbon nitride polymer react with the salts, even below their melting point; however, the mechanistic understanding of the reaction of g-CN with alkali halides is still unknown. In this study, we investigated reactions of melon, a linear polymer of heptazine monomers, with NaCl, employing Fourier-transform infrared (IR) spectroscopy in solid and gas phases, solid-state nuclear magnetic resonance spectroscopy, temperature-programmed desorption mass spectrometry (TPD-MS), and thermogravimetry. The reaction of melon with NaCl at 500 °C substitutes a fraction of amino groups with cyanamide moiety and deprotonates NH groups bridging heptazine monomers. The formation of NH4Cl during the calcination implied that NaCl reacted with NH3 that had evolved as a result of the condensation of melon molecules. TPD-MS and gas-phase IR confirmed the presence of NH3 as well as H2O and CO2 above 400 °C. These gaseous molecules and NaCl lead to NaHCO3 via the Solvay process reactions. NaHCO3 is decomposed into Na2CO3 at the calcination temperature. The base and gaseous H2O finally cause OH−. The resultant hydroxyl anion introduces cyanamide groups into the melon, deprotonates the NH groups, and decomposes a fraction of the polymer into isocyanic acid via the formation of sodium cyamelurate as an intermediate. The reaction mechanisms proposed in this study will promote the molecular understanding of the roles of additives in the modification of the chemical structure of g-CN photocatalysts.