Amine Functionalized Metal–Organic Framework Coordinated with Transition Metal Ions: d–d Transition Enhanced Optical Absorption and Role of Transition Metal Sites on Solar Light Driven H₂ Production

Abstract

Design and development of efficient photocatalysts for H2 production from water and sunlight have gained significant attention as the solar assisted approach is considered to be a promising approach for the generation of clean fuel. However, the poor charge carrier separation and light harvesting ability of existing photocatalysts limits the efficiency of photoconversion of water. In this work, the synthesis of transition metal ions (M2+ = Co2+, Cu2+, and Ni2+) coordinated with Ti‐metal organic frameworks (Ti‐MOFs) through a simple post‐synthetic coordination method for efficient solar light‐driven H2 production is reported. Notably, coordination of M2+ ions with Ti‐MOF significantly improves the optical absorption by d–d transitions and the multimetal sites facilitate the fast charge carrier separation, thereby enhancing the solar light‐driven H2 production activity. Very interestingly, the rate of solar light‐driven H2 production is varied with respect to different metal ions coordination due to the position of d–d bands absorption in the solar spectrum, and the complexing tendency of M2+ ions with sacrificial electron donors. A maximum solar H2 production rate of 1583.55 µmol h−1 g−1 is achieved with a Cu2+ coordinated Ti‐MOF, which is ≈13 fold higher than that of the pristine Ti‐MOF.

Bimetal–organic framework derived multi-heterostructured TiO2/CuxO/C nanocomposites with superior photocatalytic H2generation performance

“…56 While the strong peak at 1385 cm À1 can be ascribed to C]O bond stretching, the C-N bond vibration at around 1240 cm À1 arises from the N species decorated on the carbon matrix. 34,58 As demonstrated in Fig. S6 in the ESI, † the CH x bond stretching at around 2900 and 1400 cm À1 is negligible, 59 and C-O, N-O, O]C-OH and C-N bonds are clearly presented between 1700 and 1200 cm À1 as surface functional groups in these as-prepared TiO 2 /Cu x O/C composites.…”

“…The emergence of the shoulder peak can be attributed to the donation of non-bonded lone pair electrons of the -NH 2 group to the Cu 2+ ions resulting in the formation of quaternary valence -NH 2 + . 34 Pyrolysis of bi-MOF NH 2 -MIL-125(Ti/Cu) at 550, 700 and 800 C in water vapor, resulted in the decomposition of NH 2 -MIL-125(Ti/Cu) into TiO 2 , Cu x O and Cu species embedded in a porous carbon matrix. The PXRD patterns (Fig.…”

“…S8a and b, ESI †) for NH 2 -MIL-125(Ti) from yellow to greenish for NH 2 -MIL-125(Ti/Cu) is consistent with the redshi towards the visible region. 34,63 The energy band gaps of NH 2 -MIL-125(Ti/Cu) derived nanocomposites were estimated from the UV-Vis absorption spectra (inset in Fig. 2c).…”

“…8,[30][31][32][33] For instance, Karthik et al recently reported that Cu 2+ coordinated Ti-MOF exhibited much higher photocatalytic H 2 evolution performance than the pristine Ti-MOF under sunlight due to dd transition and enhanced absorption of visible light. 34 Despite their fascinating morphology, promising textural and chemical properties, these photoactive MOFs suffer from poor charge generation, and low charge transfer as well as structural instability, as the photocatalytic H 2 evolution reaction is carried out in aqueous media, which makes the pristine MOFs less favorable materials to be directly used as photocatalysts. 9,33,[35][36][37] However, in recent years MOFs have been proven to be excellent precursors and sacricial templates to derive metal oxide/ carbon nanocomposites.…”

Complete and Versatile Post‐Synthetic Modification on Iron‐Triazole Spin Crossover Complexes: A Relevant Material Elaboration Method

“…[2,17,19,[28][29][30][31][32][33] This strategy allows to have better control in the final material; two important examples of this are: 1) in the biological area; once the protein is biosynthesized, it can be covalently modified on the amino acid side chain or in the backbone of the protein, the phosphorylation being the most common post-translational modification (PTM). [34] 2) in coordination chemistry, to generate co-catalysts associating MOF with multimetal sites to avoid competition between the metal sites, [22,29,35] for example, Neppolian et al [35] synthesized Ti-MOF complexes and then associated them by the coordination of the amino functional group on the Ti-MOF to transition metals such as Ni or Cu. In addition to the advantages on chemical transformations, PSM reactions can provide a template for the solid state structure, in other words, main features of solid-state structures present in the "parent" materials can be preserved in the functionalized material in contrast with direct methods.…”