Carbon nitride materials: impact of synthetic method on photocatalysis and immobilization for photocatalytic pollutant degradation

Isabel Köwitsch,Michael Mehring

doi:10.1007/s10853-021-06405-z

Abstract

Different synthesis routes for carbon nitride materials (CN) and the resulting products were compared to study the photocatalytic activity (pollutant degradation) in dependence on structure and properties. The CN materials were synthesized by thermal decomposition of dicyandiamide in air and under argon as well as in sealed ampoules with or without the use of a salt melt. The as-prepared materials were characterized by IR spectroscopy, nitrogen adsorption measurement, solid-state NMR spectroscopy, diffuse reflectance UV–Vis spectroscopy, elemental analysis and powder X-ray diffraction (PXRD). The surface polarity of the CN materials was estimated by adsorption of the dicyano-bis(1,10-phenanthroline)-iron(II) complex, which allows an evaluation of the degree of condensation. The CN materials were tested with regard to the photocatalytic degradation of rhodamine B (RhB). It is shown that the photocatalytic activity increases with higher surface polarity. Promising CN materials with high RhB degradation of 85% within 25 min and high surface polarity of 0.89 were selected for an immobilization approach to obtain coatings on a silicone substrate using a high-volume low-pressure (HVLP) spray coating technique. To study the photocatalytic activity of the catalyst coatings, the degradation rates of an aqueous RhB solution and solutions of organic pollutants such as triclosan and ethinyl estradiol were examined. Pollutants are decomposed with up to 63% of the initial concentration. Xenon lamps and different LEDs were used as light sources for comparison. Particularly high degradation efficiencies were obtained using LEDs, and the degradation rates are increased by adjusting the emission spectrum of the lamp to the pollutant and absorption edge of the catalyst, which results in a 40 times higher degradation efficiencies of LEDs compared to a Xe lamp.Graphical abstract

Highlights

The use of pharmaceuticals, biocides and dyes increased in the last decades, e.g., the consumption of antibiotics showed an increase by 35% between 2000 and 2010 [1]
The surface polarity and the degree of condensation of differently synthesized carbon nitride materials (CN) materials were determined by the hydrogen bonding donor ability (HBD)
It is shown that the hydrogen bond donor (HBD) has a greater influence on the photocatalytic activity of CN materials than the BET surface area

Summary

Introduction

The use of pharmaceuticals, biocides and dyes increased in the last decades, e.g., the consumption of antibiotics showed an increase by 35% between 2000 and 2010 [1]. Scheme 1 Structures of melamine (1) and different structure models for a melon networks (2a and 2b); structure models for a graphitic carbon nitride based on heptazine building blocks (3a) and triazine building blocks (3b), with lithium ions and X = Cl- or Br- intercalated in triazine-based carbon nitride (4) [26, 29, 32]. Wang et al described that a higher degree of condensation and a high crystallinity was obtained for carbon nitrides that were prepared via thermal decomposition of dicyandiamide in sealed ampoules with and without the use of a salt melt. Selected films were used for the degradation of triclosan and ethinyl estradiol and the influence of different light sources on the degradation mechanism and degradation rates was investigated

Results and discussion

Conclusion

Evaluation of photocatalytic activity