Unusual Electronic Properties of Cellulose Nanocrystals Conjugated to Cobalt Phthalocyanine: Long-Lived Charge Separation and Visible-Light-Driven Photocatalytic Activity

Abstract

Octacarboxylated cobalt phthalocyanine (CoPc) was covalently conjugated to cellulose nanocrystals (CNCs) by employing an esterification protocol. Solid-state NMR, X-ray photoelectron spectroscopy (XPS), Raman, and infrared spectra were used to verify and study the nature of covalent attachment responsible for the immobilization of CoPc on the CNC surface. The covalent attachment was investigated from a theoretical simulation perspective using dispersion-corrected density functional theory (DFT) calculations, which verified the stable bond formation between CNC and CoPc. CoPc is an organic semiconductor with a high exciton binding energy, and CNCs are known to be insulating. Yet, Kelvin probe force microscopy (KPFM) indicated charge carrier generation and long-lived charge separation in the CNC–CoPc conjugate compared to pristine CoPc under visible light illumination. Such behavior is more typical of a semiconductor nanocomposite. The CNC–CoPc conjugate exhibited superior performance in the visible-light-driven surface photocatalytic reduction of 4-nitrobenzenethiol (4-NBT) to p,p′-dimercaptoazobenzene (DMAB) and photodegradation of rhodamine B.

Influence of Carbon Nanotube Support on Electrochemical Nitrate Reduction Catalyzed by Cobalt Phthalocyanine Molecules

“…38−40 Peak fitting shows that the ratio between these two types of N atoms is close to 1 (Figure S2), which is consistent with the molecular structure of CoPc. 27 Two peaks appear in the Co 2p spectra at ∼781 and ∼796 eV, which correspond to the 2p 3/2 and 2p 1/2 signals of the Co 2p electrons, respectively (Figure 1d). 27,41 This observation confirms that Co is in the 2+ oxidation state for both catalysts.…”

“…Additional structural information to support the proper assembly of the CoPc-based catalyst materials was acquired using X-ray photoelectron spectroscopy (XPS). The C 1s spectra of CoPc/CNT and CoPc/OCNT show a peak centered at 284.5 eV, which corresponds to sp 2 -hybridized C (Figure b). , The C 1s signal of CoPc/OCNT is slightly broader than that of CoPc/CNT, suggesting an increase in disorder in the material likely associated with the introduction of functional groups and defects by oxidation. , The N 1s spectra of the CoPc-based catalysts show a peak centered at ∼399 eV and a broad shoulder at ∼401 eV, corresponding to pyridinic N and pyrrolic N, respectively (Figure c). − Peak fitting shows that the ratio between these two types of N atoms is close to 1 (Figure S2), which is consistent with the molecular structure of CoPc . Two peaks appear in the Co 2p spectra at ∼781 and ∼796 eV, which correspond to the 2p 3/2 and 2p 1/2 signals of the Co 2p electrons, respectively (Figure d). , This observation confirms that Co is in the 2+ oxidation state for both catalysts.…”

“…Two main bands are characteristic of the CoPc molecular structure. The first band is a weak band located at ∼594 cm –1 and is associated with Co–N stretching. , The second band is the most intense in the spectra, located at ∼1531 cm –1 , and is assigned to a vibration involving the movement of atoms in the C–N–C bridge bonds between the isoindole units. − Both bands are present in the CoPc hybrid structures. The Raman spectra of CoPc/CNT and CoPc/OCNT also show bands associated with the support materials, in particular, broad D and G bands at ∼1330 and ∼1600 cm –1 , respectively. − The D band represents the disorder or defects in the material, and the G band is attributed to the C–C stretching mode found in all sp 2 -hybridized carbon materials.…”

Isoelectric Substitution Strategy to Construct a Partially Charged MOF for C2H2 Capture and Selective Dye Adsorption

“…However, it poses a great challenge to construct a MOF with partially charged characteristics as only few examples were reported. Meanwhile, it is very difficult for organic dyes to degrade due to their stability to light or oxidants. − Conventional adsorbents such as activated carbon and wood had been used for the adsorption of organic dyes; however, their poor separation selectivity limited their practical application. , Thus, designing and synthesizing multifunctional materials for gas separation and dye adsorption are effective methods to deal with environmental and energy consumption problems. , …”

Molecular Enhancement of Direct Electrolysis of Dilute CO2

“…Figure d shows the spectrum of N 1s X-ray photoelectron spectroscopy (XPS) of the CoPc+P4VP-8 electrode. The N 1s spectrum can be deconvoluted to three peaks which are assigned to the pyrrolic nitrogen atoms (400.0 eV) and bridging nitrogen atoms (399.4 eV) of CoPc molecules and the pyridinic nitrogen atoms (399.0 eV) of P4VP polymer, indicating the successful integration of CoPc and P4VP. The Co 2p XPS peaks of the CoPc+P4VP-8 electrode shift toward lower binding energy by ∼0.2 eV compared to that of the CoPc electrode, indicating a lower Co oxidation state (Figure S1).…”