Effective Synthesis of Carbon Hybrid Materials Containing Oligothiophene Dyes

Abstract

This paper shows the first study of the synthesis of hybrid materials consisting of commercial Norit carbons and oligothiophenes. The study presents the influence of surface oxidation on dye deposition as well as changes of pore structure and surface chemistry. The hybrid materials were characterised using Raman spectroscopy, and scanning and transmission electron microscopy (SEM and HR-TEM, respectively). Confocal microscopy was employed to confirm the immobilization of oligomers on the surface of the carbons being investigated. Confocal microscopy measurements were additionally used to indicate whether dye molecules covered the entire surface of the selected commercial Norit samples. Specific surface area and pore structure parameters were determined by low-temperature nitrogen adsorption. Additionally, elemental content and surface chemistry were characterised by means of X-ray photoelectron spectroscopy (XPS) and combustion elemental analysis. Experimental results confirmed that oligothiophene dyes were adsorbed onto the internal part of the investigated pores of the carbon materials. The pores were assumed to have a slit-like shape, a set of 82 local adsorption isotherms was modelled for pores from 0.465 nm to 224 nm. Further, XPS data showed promising qualitative results regarding the surface characteristics and chemical composition of the hybrid materials obtained (sulphur content ranged from 1.40 to 1.45 at%). It was shown that the surface chemistry of activated carbon plays a key role in the dye deposition process. High surface heterogeneity after hydrothermal oxidation did not improve dye adsorption due to specific interactions between surface oxygen moieties and local electric charges in the oligothiophene molecules.

Keywords: activated carbon; adsorption; confocal microscopy; hybrid material; oligothiophene dye; porous material.

Figure 1

Nitrogen adsorption isotherms of pristine carbon, oxidized, and hybrid materials for (a) Norit_1, (b) Norit_2, (c) Norit_1_ox, and (d) Norit_2_ox.

Figure 2

Pore size distribution calculated from the adsorption branch using the Nguyen and Do (ND) method [26,27] for (a) Norit_1, (b) Norit_2, (c) Norit_1_ox, and (d) Norit_2_ox.

Figure 3

Morphology of the samples: (a) HRTEM of Norit_2_raw, (b) SEM of Norit_2_raw, (c) SEM/EDX mapping of Norit_2_3T, (d) HRTEM of Norit_2_3T sample, (e) SEM of Norit_2_3T sample and (f) SEM/EDX mapping of Norit_2_ox_3T sample; arrow highlights—evidence of dye adsorption.

Figure 4

XPS spectra for: (a) S2p3 for NORIT_2_6T, (b) S2p3 for Norit_2_ox_6T, (c) C1s for Norit_2_6T, (d) C1s for Norit_2_ox_6T sample, (e) and (f) Raman spectra of hybrid materials modified with 6T-α-sexithiophene.

Figure 5

Confocal microscopy images for Norit_1_6T (a–d) and Norit_2_6T (e–h) samples, (b) and (f) present enlarged details from confocal microscopy images shown in (a) and (e). (c) and (g) provide inverted-colour versions of the studied materials. (d) and (h) show the last recorded images after using the laser beam.