高温合成がグラファイト系窒化炭素の構造と水素発生能に及ぼす影響

Influence of High Temperature Synthesis on the Structure of Graphitic Carbon Nitride and Its Hydrogen Generation Ability.

• Emilia Alwin
• Kamila Kočí
• Robert Wojcieszak
• Michał Zieliński
• Miroslava Edelmannová
• Mariusz Pietrowski

抄録

ジシアンジアミド,チオ尿素またはメラミンを高温(550,600℃)で熱重合し、加熱速度(2,10℃以上)と合成時間(0,4時間)を変化させて窒化黒鉛型炭素(g-CN)を得た。合成条件と前駆体の種類がg-CNの効率に及ぼす影響を調べた。最も効率が良かったのはジシアンジアミドからの合成で53%であったが、メラミンとチオ尿素からの合成の効率はそれぞれ26%と11%とかなり小さかった。X線回折(XRD),X線光電子分光(XPS),赤外分光(FTIR),紫外可視分光(UV-vis),熱重量分析(TGA),元素分析(EA)の結果に基づいて、最も安定な構造、最も高い構造秩序と縮合度、そして最も高い光触媒活性を有する生成物を得るための最適な前駆体とg-CNの合成条件を特定した。プロトン濃度を下げて縮合度を上げると、水-メタノール溶液の光触媒分解時の水素収率が著しく向上することがわかった。水素発生量は1200μmol g、水素に対する選択性は98%以上であった。

Graphitic carbon nitride (g-CN) was obtained by thermal polymerization of dicyandiamide, thiourea or melamine at high temperatures (550 and 600 °C), using different heating rates (2 or 10 °C min) and synthesis times (0 or 4 h). The effects of the synthesis conditions and type of the precursor on the efficiency of g-CN were studied. The most efficient was the synthesis from dicyandiamide, 53%, while the efficiency in the process of synthesis from melamine and thiourea were much smaller, 26% and 11%, respectively. On the basis of the results provided by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), thermogravimetric analysis (TGA), elemental analysis (EA), the best precursor and the optimum conditions of synthesis of g-CN were identified to get the product of the most stable structure, the highest degree of ordering and condensation of structure and finally the highest photocatalytic activity. It was found that as the proton concentration decreased and the degree of condensation increased, the hydrogen yields during the photocatalytic decomposition of water-methanol solution were significantly enhanced. The generation of hydrogen was 1200 µmol g and the selectivity towards hydrogen of more than 98%.