Development of template methods for the preparation of porous photocatalysts of graphite-like carbon nitride
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摘要: 氮化碳作為一種具有高催化性能的光催化劑,具有無毒無害,自然環境下穩定的性質,在水解制氫氣氧氣以及降解有機污染物領域得到了廣泛的關注. 其中類石墨相氮化碳(g-C3N4)因其特殊的片層結構而具有較高比表面積,常配合孔結構的構造,提供光生載流子及反應物質的運輸通道以及大量活性位點用于氧化還原反應,是具有高光電性能的一種光催化劑.制備該種催化劑孔結構的方法有硬模板法,軟模板法與非模板法,其中硬模板法需要在實驗后除去模板,軟模板法的模板會隨著高溫除去,非模板法的制備過程沒有模板的參與。本文根據近年文獻的整理,著重闡述和比較各制備方法的優劣,結合常用的修飾手段總結各制備方法的變化趨勢和發展方向,并對后續研究中制備方法的使用前景做出判斷.Abstract: As a metal-free photocatalyst with high catalytic performance, carbon nitride is non-toxic, harmless, and stable in the natural environment. Owing to its facile synthesis, stable physical and chemical properties, tunable structure, and suitable band gap, graphite-like carbon nitride (g-C3N4) plays an increasing role in the field of photocatalysis. It has attracted extensive attention in the fields of evolution of hydrogen and oxygen via water-splitting hydrolysis and in the degradation of organic pollutants. In particular, g-C3N4 is identified to have a high specific surface area (SSA) because of its special lamellar structure. Meanwhile, the abundant pores intrinsic in it are able to provide both transporting channels for photogenic carriers or reactive species and a large number of active sites for redox reactions. These merits endow it with high photoelectrical properties. The preparation methods of the pore structures of such catalyst include hard templates, soft templates, and non-template ones. The hard template method enables the preparation of regular pore structures but requires additional removal treatment. However, the soft templates can be decomposed during the high-temperature preparation of g-C3N4, which avoids the use of toxic reagents and consequently is harmless to the environment, and the template-free method does not involve any templates, which will simplify the experimental process from the aspect of sample preparation with reduced cost. In this paper, the advantages and disadvantages of various preparation methods were elaborated and compared based on the literature review in recent years. The developments and applications in the environmental and energy aspects were summarized by combining the commonly used modification methods, which provided the perceptions with respect to the development of metal-free g-C3N4-based photocatalysts in the future. Further, the photocatalytic mechanism was explained, and the four different precursors of g-C3N4 were compared. Finally, the ongoing outlook and perspectives will be covered in this review.
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Key words:
- graphite-like carbon nitride /
- photocatalyst /
- porous structure /
- template method /
- template-free method
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圖 4 (a)圖解說明由不同前體合成的聚合C3N4形成的示意圖;(b)由不同前體合成的C3N4的X射線衍射圖譜;(c)由不同前體合成的C3N4的N2吸附?解吸等溫線;(d)由不同前體合成的C3N4的UV-Vis吸收光譜;(e)使用由不同前體合成的C3N4降解TC的效率圖;(f)由不同前體合成的C3N4對TC的光降解速率[36]
Figure 4. (a) Schematic illustrating the formation of polymeric C3N4 synthesized from different precursors; (b) XRD pattern of C3N4 synthesized from different precursors; (c) nitrogen adsorption?desorption isotherms of C3N4 synthesized from different precursors; (d) UV-Vis absorption spectra of C3N4 synthesized from different precursors; (e) degradation pattern of TC using C3N4 synthesized from different precursors; (f) photodegradation rate of TC using C3N4 synthesized from different precursors [36]
表 1 不同模板法調控g-C3N4孔結構總括
Table 1. Summary of the different template methods in adjusting the pore structure of g-C3N4
Sample Reaction precursor, temperature, time, heating rate, & atmosphere Template type& requirement Removal reagents& requirement Specific surface
area/(m2?g?1)Pore volume/
(cm3?g?1)Average pore
size/nmRefs. Porous-C3N4 Dicyandiamide, 500 °C, 4.5 h 7?40 nm SiO2 hard template 20% HF, 4 h ~109 — ~20 [20] MCN1.0 Cyanamide, 550 °C, 4 h, 2 °C?min?1, N2 12 nm SiO2 nanosphere hard template 4.0 mol?L?1
NH4HF2, 24 h~190.7 ~0.52 ~10.9 [22] CLBM?SBA-15 Cyanamide, stirring at room temperature, 1 h, 550 °C, 6 h, air 9.5 nm SBA-15 hard template 4.0 mol?L?1
NH4HF2~145 ~0.43 ~44 [23] C3N4?MCF Melamine, 300 °C, 1 h, 600 °C, 2 h, Ar MCF hard template 15% HF, 12 h ~70 ~0.3 — [24] Bulk-g-C3N4 Dicyandiamide, 560 °C, 2 h, N2 12 nm PSB hard template NH4HF2 ~37 ~0.28 ~36 [25] TiO2 trapped g-C3N4 Dicyandiamide, 560 °C, 2 h, N2 12 nm PSB hard template NH4HF2 ~63 ~0.29 ~20 [25] OCS/gCN Melamine, 550 °C, 2 h, 2 °C?min?1, air 260?320 nm SiO2 nanosphere hard template HF ~105 ~0.123 ~260?320 [26] Meso-g-C3N4/WP/Meso-g-C3N4 Cyanamide, 550 °C, 4 h, 3 °C?min?1, N2 8?15 nm SiO2 hard template 0.5 mol?L?1 HF ~82 — ~8?15 [27] CN?MCF-0.4 Carbon tetrachloride, ethylenediamine,
90 °C, 6 h, 600 °C, 5 h, 3 °C?min?1, Ar35.7 nm MCF hard template 4.0 mol?L?1
NH4HF2~498 ~1.36 ~5.3 [29] mpg?C3N4-δ Dicyandiamide, 550 °C, 4 h,
2.3 °C?min?1, N212 nm SiO2 hard template 4.0 mol?L?1
NH4HF2, 24 h~218.15 ~0.69 ~12.57 [30] PCNCs?ANTa Melamine, 550 °C, 2 h, 2 °C?min?1 6.7 nm ZnO hard template 4.0 mol?L?1 NaOH ~32 ~0.103 ~16.8 [31] g-C3N4 Melamine, 500 °C, 2 h, air P123 soft template ~90 — — [34] Bulk-g-C3N4 Melamine, 600 °C, 2 h, Ar P123 soft template ~90 — ~15 [34] g-C3N4/SnO2 Thiourea, SnCl4, 550 °C, 2 h, 10 °C?min?1 HCl, H2O soft template ~44.3 2.638 ~100?430 [35] C3N4@TiO2 Melamine, 400 °C, 2 h, N2, 2 h, air Melamine soft template ~44.7 ~0.11 ~10.7 [37] N-RGO Graphene oxide, melamine, 900 °C,
30 min, 5 °C?min?1Ice soft template ~190 ~0.99 ~20?200 [38] CNF-0.005 Melamine, 550 °C, 4 h, 3 °C?min?1, N2 Cyanuric acid-melamine supramolcular aggregates & ionic liquid soft template ~381 ~0.85 ~15 [39] PCNM Melamine, urea, 550 °C, 4 h, N2 Melamine soft template ~78 ~0.76 — [40] g-C3N4 ultrathin nanosheet Melamine, glutaraldehyde, 800 °C,
2 h, ArCyanuric acid soft template ~84 — ~3 [48] g-C3N4 bundles Melamine, 500 °C, 4 h, N2 PEG-PPG-PEG soft template ~40.974 — ~100 [49] g-C3N4 beads Dicyandiamide, 530?600 °C, 2 h, N2 PSB soft template ~58 ~0.15 ~30?90 [50] P-C3N4 Melamine, 550 °C, 4 h Free ~40.89 ~0.2 — [43] 2MCN/2UCN Melamine, urea, 550 °C, 1.5 h,
5 °C?min?1, N2Free ~41 ~0.24 ~23 [44] 5% La/g-CNT Melamine, 550 °C, 2 h, air Free ~4 ~0.0623 ~2.8 [45] CN/Fe-1 Urea, 600 °C, 4 h, 5 °C?min?1 Free ~48.19 — — [46] g-C3N4 NS/TMC Melamine, 550 °C, 3 h, 2.3 °C?min?1, air Free ~57.4 — — [47] g-C3N4/Ag3PO4 Urea, 550 °C, 4 h, Ar Free ~20.84 ~0.083 ~16 [51] Brookite/anatase TiO2/g-C3N4 Hexadecylamine, 550 °C, 4 h,
3 °C?min?1, N2Free ~37 ~0.2 ~18 [52] g-C3N4 nanosheet Melamine, 550 °C, 4 h, 500 °C, 2 h, Ar Free ~190.1 ~0.61 ~5?25 [53] Fe2O3(6.6)/CNSb Thiourea, 535 °C, 3 h, 3 °C?min?1, air Free ~33.5 ~0.195 ~25 [54] g-C3N4/MoS2 Thiourea, 500 °C, 2 h, 2 °C?min?1 Free ~45 — — [55] 259luxu-164 -
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