DOI: 10.1002/asia.201200781 Synthesis and Photocatalytic Activity of Poly(triazine imide) Yeilin Ham, [a] Kazuhiko Maeda, [a, b] Dongkyu Cha, [c] Kazuhiro Takanabe, [d] and Kazunari Domen* [a] Introduction The existence of carbon nitride C 3 N 4 , a ubiquitous light- weight material, was first predicted by Franklin nearly a cen- tury ago. [1] C 3 N 4 has attracted considerable scientific atten- tion since 1985, when calculations indicated that b-C 3 N 4 should be harder than diamond. [2] Since this report, various attempts to synthesize b-C 3 N 4 have been reported, followed by efforts to identify the structure of the synthesized materi- als. [3–15] One of these studies showed that b-C 3 N 4 is less stable than planar carbon nitride (p-C 3 N 4 ), making p-C 3 N 4 a more likely product than b-C 3 N 4 . [6] The structure of p- C 3 N 4 suggested by Ortega et al. was based on s-triazine units bridged by amine groups. A few other structures of p-C 3 N 4 (or graphitic C 3 N 4 (g-C 3 N 4 ), which has become the more common name) have been suggested as well. [5, 6, 12–14] Later, it was reported that tri-s-triazine was the building block of the most stable form of g-C 3 N 4. [16] Since this report, it became more common for g-C 3 N 4 to represent specifically the most stable form of graphitic carbon nitride, than to represent graphitic carbon nitride in general. Several unique and useful properties of g-C 3 N 4 have since been reported. One conspicuous property of this material is its photocatalytic activity. [17, 18] Since g-C 3 N 4 is one of the few metal-free photocatalysts with suitable band positions to split water under visible light, various modifications have been examined to improve its photocatalytic activity. Some of these modifications include: 1) increased surface area by the introduction of mesoporosity into g-C 3 N 4 , [19, 20] 2) proto- nation of g-C 3 N 4 , [21] 3) inclusion of foreign elements such as sulfur, [22, 23] phosphorous, [24] fluorine, [25] or both boron and fluorine in the structure, [26] 4) variation of the ratio of carbon to nitrogen by copolymerization of the precursor with barbituric acid, [27] and 5) surface functionalization using, for example, 1,2,4,5-benzenetetracarboxylic dianhy- dride. [28] More recently, a crystalline phase of carbon nitride was synthesized from the condensation of dicyandiamide in a salt melt of LiCl–KCl. [29] Further characterization of this material indicated that this crystalline carbon nitride, which was named poly(triazine imide) with intercalation of Li + and Cl  ions (PTI/Li + Cl  ), has a structure based on the s- triazine unit. [30] Since this new type of carbon nitride also has a graphitic structure, PTI/Li + Cl  might also possess a band structure Abstract: Poly(triazine imide) was syn- thesized with incorporation of Li + and Cl  ions (PTI/Li + Cl  ) to form a carbon nitride derivative. The synthesis of this material by the temperature-induced condensation of dicyandiamide was ex- amined both in a eutectic mixture of LiCl–KCl and without KCl. On the basis of X-ray diffraction measure- ments of the synthesized materials, we suggest that a stoichiometric amount of LiCl is necessary to obtain the PTI/Li + Cl  phase without requiring the pres- ence of KCl at 873 K. PTI/Li + Cl  with modification by either Pt or CoO x as cocatalyst photocatalytically produced H 2 or O 2 , respectively, from water. The production of H 2 or O 2 from water in- dicates that the valence and conduction bands of PTI/Li + Cl  were properly lo- cated to achieve overall water splitting. The treatment of PTI/Li + Cl  with [Pt- ACHTUNGTRENNUNG(NH 3 ) 4 ] 2 + cations enabled the deposi- tion of Pt through ion exchange, dem- onstrating photocatalytic activity for H 2 evolution, while treatment with [PtCl 6 ] 2 anions resulted in no Pt depo- sition. This was most likely because of the preferential exchange between Li + ions and [PtACHTUNGTRENNUNG(NH 3 ) 4 ] 2 + cations. Keywords: Carbon nitrides · lithium chloride · photocatalysis · water splitting [a] Y. Ham, Dr. K. Maeda, Prof. Dr. K. Domen Department of Chemical System Engineering The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) Fax: (+ 81) 3-5841-8838 E-mail: domen@chemsys.t.u-tokyo.ac.jp [b] Dr. K. Maeda Precursory Research for Embryonic Science and Technology (PRESTO) (Japan) Science and Technology Agency (JST) 4-1-8 Honcho Kawaguchi Saitama 332-0012 (Japan) [c] Dr. D. Cha Advanced Nanofabrication, Imaging and Characterization Laboratory King Abdullah University of Science and Technology (KAUST) 4700 KAUST, Thuwal 23955-6900 (Saudi Arabia) [d] Dr. K. Takanabe Division of Physical Sciences and Engineering KAUST Catalysis Center (KCC) King Abdullah University of Science and Technology (KAUST) 4700 KAUST, Thuwal 23955-6900 (Saudi Arabia) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201200781. Chem. Asian J. 2013, 8, 218 – 224  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 218 FULL PAPER