Pilot-Scale Studies of WO3/S-Doped g-C3N4 Heterojunction toward Photocatalytic NOx Removal.

Marta Kowalkińska,Anna Zielińska-Jurek,Marcin Łapiński,Jakub Karczewski,Paweł Głuchowski,Anna Grzegórska,Agnieszka Fiszka Borzyszkowska,Mirosław Sawczak

doi:10.3390/ma15020633

Abstract

Due to the rising concentration of toxic nitrogen oxides (NOx) in the air, effective methods of NOx removal have been extensively studied recently. In the present study, the first developed WO3/S-doped g-C3N4 nanocomposite was synthesized using a facile method to remove NOx in air efficiently. The photocatalytic tests performed in a newly designed continuous-flow photoreactor with an LED array and online monitored NO2 and NO system allowed the investigation of photocatalyst layers at the pilot scale. The WO3/S-doped-g-C3N4 nanocomposite, as well as single components, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area analysis (BET), X-ray fluorescence spectroscopy (XRF), X-ray photoemission spectroscopy method (XPS), UV–vis diffuse reflectance spectroscopy (DR/UV–vis), and photoluminescence spectroscopy with charge carriers’ lifetime measurements. All materials exhibited high efficiency in photocatalytic NO2 conversion, and 100% was reached in less than 5 min of illumination under simulated solar light. The effect of process parameters in the experimental setup together with WO3/S-doped g-C3N4 photocatalysts was studied in detail. Finally, the stability of the composite was tested in five subsequent cycles of photocatalytic degradation. The WO3/S-doped g-C3N4 was stable in time and did not undergo deactivation due to the blocking of active sites on the photocatalyst’s surface.

Highlights

The development of industry and intensified agricultural activities, energy production, and transport has led to increased nitrogen oxides (NOx) concentration in the air and contributed to environmental degradation resulting in acid rain or fog formation
Considering the promising properties of S-doped g-C3N4 compared with un-doped gC3N4, for the first time, we propose WO3/S-doped g-C3N4 nanocomposite for solar-driven photodegradation of NOx
The photocatalytic performance of WO3/S-doped g-C3N4 nanocomposite towards NOx removal was studied for the first time

Summary

Introduction

The development of industry and intensified agricultural activities, energy production, and transport has led to increased NOx concentration in the air and contributed to environmental degradation resulting in acid rain or fog formation. One of the promising methods of nitrogen oxides removal is heterogeneous photocatalysis, in which the combination of semiconductor materials and light allows the generation of reactive oxygen species (ROS) to degrade emerging contaminants [4,5]. Graphitic carbon nitride has unique physicochemical properties such as a suitable bandgap energy (~2.7 eV), corresponding to visible-light absorption [7]. The significant restriction of practical use of graphitic carbon nitride is a fast recombination rate of photoexcited electron-hole pairs, which lowers the photocatalytic efficiency [10]. Various modifications of g-C3N4 have been investigated, including doping to generate electron trapping centers or heterojunction in composites to enhance the charge carriers’ separation and limit the recombination process [10,11]

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