Band Structure Engineering of Schiff‐Base Microporous Organic Polymers for Enhanced Visible‐Light Photocatalytic Performance

Abstract

Recently, microporous organic polymers (MOPs) such as hypercrosslinked polymers, [1,2] polymers of intrinsic microporosity (PIMs), [3,4] and covalent organic frameworks (COFs) [5,6] have attracted increasing scientific and practical interest. The structures and properties of these materials, which are synthesized by bottom-up methods, can be adjusted via the rational choice of the aromatic units with a range of functional groups. For example, a series of poly(aryleneethynylene) MOPs were prepared by varying the "strut" length in the network through a Sonogashira-Hagihara crosscoupling route, [7,8] and it was demonstrated that the average micropore size, the micropore volume, and the BET surface area could be finely tuned. On account of the well-defined porosities and large surface areas, MOPs demonstrate excellent performance for gas storage and gas separation. [9][10][11][12] Moreover, MOPs with incorporated heteroatoms such as S, N, O have unique physical and Schiff-base networks (SBNs), as typical examples of nitrogen-doped microporous organic polymers (MOPs), exhibit promising application prospects owing to their stable properties and tunable chemical structures. However, their band structure engineering, which plays a key role in optical properties, remains elusive due to the complicated mechanisms behind energy level adjustment. In this work, a series of SBNs are fabricated by tailoring the ratio of p-phthalaldehyde and o-phthalaldehyde in the Schiff-base chemistry reaction with melamine, resulting in a straightforward as well as continuous tuning of their band gaps ranging from 4. 4 to 1.4 eV. Consequently, SBNs can be successfully used as photocatalysts with excellent visible-light photocatalytic activity even under metal-free conditions. Significantly, electronic structures of SBNs are systematically studied by electrochemical and spectroscopic characterizations, demonstrating that the enhanced performance is ascribed to proper band structure and improved charge separation ability. More importantly, in combination with theoretical calculations, the band structure regulation mechanism and band structure-photocatalytic property relationship are deeply disclosed. The results obtained from this study will not only furnish SBN materials with excellent performance for solar energy conversion, but also open up elegant protocols for the molecular engineering of MOPs with desirable band structures.

Encapsulation of Pd Nanoparticles in Covalent Triazine Frameworks for Enhanced Photocatalytic CO2 Conversion

“…In addition, isotope-labeling experiments were also conducted to ascertain the carbon source. As shown in gas chromatography--mass spectrometry (Figure S10), signals with an m/z value of 29 ( 13 CO) and 17 ( 13 CH 4 ) can be clearly observed when 13 CO 2 was used as a substrate under identical conditions. The above results robustly verify that the produced CO and CH 4 evolved from CO 2 photoreduction over Pd@Imine-CTF, rather than the decomposition of organic impurities.…”

“…31 The residual peaks located at 122, 131, 143, and 156 ppm were assigned to aromatic carbons in the backbone. 32 After loading of Pd nanoparticles, these features are also observed in the FT-IR and solid-state 13 C NMR spectra of Pd@Imine-CTF, indicating the chemical structure of Imine-CTF is well retained. The thermogravimetric analysis (TGA) results indicated that Imine-CTF and Pd@Imine-CTF possessed high thermal stability up to 350 °C (Figure S2).…”

“…Imine-CTF was synthesized by a Schiff-base condensation reaction between 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 4′4-biphenyldicarboxaldehyde (BDA). The chemical structure of the Imine-CTF is obtained from the Fourier transform infrared (FT-IR) spectroscopy and solid-state 13 C cross-polarization/magic angle spinning (CP/MAS) NMR analyses. In the FT-IR spectra (Figure S1), the two distinct peaks at 1700 and 1202 cm −1 correspond to the characteristic stretching of the imine group.…”

“…Recently, polymer semiconductors have emerged as promising alternatives to inorganic photocatalysts for their multiple advantageous properties, such as high specific surface area, good chemical stability, and molecularly adjustable optoelectronic properties. − Particularly, covalent triazine frameworks (CTFs) have been widely explored as visible-light-responsive photocatalysts for water splitting, − chemical synthesis, − and hydrogen peroxide generation . Moreover, the nitrogen-containing groups embedded in CTFs could intensify the capture and activation of CO 2 molecules, − which makes them good candidates for photocatalytic CO 2 reduction.…”

High special surface area and “warm light” responsive ZnO: Synthesis mechanism, application and optimization

“…ZnO has attracted enormous attention for its unique chemical and physical properties [ [1] , [2] , [3] ]. As an important semiconductor material, ZnO exhibits excellent optical [ 4 ], magnetic [ 5 , 6 ], and piezoresistive properties [ 7 ], which has been widely used in catalysis [ 8 , 9 ], ceramics [ 10 ], sensors [ 11 , 12 ], and optoelectronic devices [ [13] , [14] , [15] ]. It's well known that ZnO has been approved by the U.S. Food and Drug Administration (FDA) as a material with good biocompatibility [ 16 ].…”