Positioning cyanamide defects in g-C3N4: Engineering energy levels and active sites for superior photocatalytic hydrogen evolution
Positioning cyanamide defects in g-C3N4: Engineering energy levels and active sites for superior photocatalytic hydrogen evolution
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DOI：
10.1016/j.apcatb.2018.05.064
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发表时间：
2018-12
期刊：
影响因子：
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通讯作者：
Jili Yuan;Xia Liu;Yanhong Tang;Yunxiong Zeng;Longlu Wang;Shuqu Zhang;T. Cai;Yutang Liu;S. Luo
中科院分区：
文献类型：
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作者：
Jili Yuan;Xia Liu;Yanhong Tang;Yunxiong Zeng;Longlu Wang;Shuqu Zhang;T. Cai;Yutang Liu;S. Luo
g-C3 N4是一种新型的太阳能光催化剂。尽管如此，试图提高其固有的低活性很少基于精确的分子可调性策略。本研究通过硫脲在KCl存在下的热聚合反应制备了两种类型的氨腈缺陷接枝g-C3 N4（CCN）。通过硫脲异构化原位生成稳定的异硫氰酸钾（KSCN），然后与三均三嗪环上的不同氨基（单键NH 2和双键NH）反应，得到两种类型的氨腈缺陷。理论计算和实验结果证实了两种类型的氰胺缺陷的比例可以通过KCl的剂量进行调节，伴随着CCN的能级可调。CCN的载流子转移和分离得到了很大的改善。此外，氨腈缺陷的存在阻碍了g-C3 N4分子间氢键的形成，有利于多孔结构的形成，暴露出更多的光催化析氢活性中心.结果，优化的光催化剂（CCN-0.03）显示出4.0 mmol g−1h−1的高HER速率，这是原始g-C3 N4的0.8 mmol g−1h− 1的5倍。在420 ± 10 nm处，表观量子效率达到14.65%。这些发现加深了对g-C3 N4分子精确调控的理解。
g-C3N4has recently emerged as a promising photocatalyst for solar energy conversion. Nonetheless, attempts to enhance its inherently low activity are rarely based on precise molecular tunability strategy. In this study, two-type cyanamide defects-grafting g-C3N4(CCN) was prepared through the thermal polymerization of thiourea in the presence of KCl. Stable potassium isothiocyanate (KSCN) was in situ generated via thiourea isomerization and then reacted with different amino groups (single bondNH2and double bondNH) in tri-s-triazine rings to obtain two-type cyanamide defects. Theoretical calculations and experiment results confirm that the ratio of the two-type cyanamide defects could be adjusted by KCl dosage, accompanying tunable energy levels of CCN. The charge carrier transfer and separation of CCN was greatly improved. Furthermore, the existence of cyanamide defects hindered the formation of intermolecular hydrogen bonds among g-C3N4, which facilitated the formation of porous structure and exposed more active sites for photocatalytic hydrogen evolution reaction (HER). As a result, the optimized photocatalyst (CCN-0.03) showed a high HER rate of 4.0 mmol g−1h−1, which was 5 times higher than 0.8 mmol g−1h−1for pristine g-C3N4. And the apparent quantum efficiency reached up to 14.65% at 420 ± 10 nm. The findings deepen the understanding on precise molecular tuning of g-C3N4.