Enhancing stability and immobilization techniques for graphitic carbon nitride in photocatalytic applications

Abstract

Emerging contaminants from urban and industrial sources require effective water treatment and photocatalysis using graphitic carbon nitride (GCN) is emerging as a promising solution. This graphitic polymer, devoid of metals in its structure, exhibits properties similar to titanium oxide, the quintessential traditional photocatalyst. This work aims to optimize the application of GCN as photocatalysts, emphasizing its role in photocatalytic processes by improving its properties for the visible light-assisted photodegradation process and assessing the removal of a selected pollutant, Rhodamine B. Initially, the role of the catalyst precursor (urea, melamine and a ratio 1:1 of them) in the synthesis was evaluated. GCN obtained from urea as precursor yielded to better properties and higher purity of the catalyst. In addition, through acid treatment, slight improvements in the material properties were verified, such as an increase of the crystallinity and active sites. This acid modified catalyst enhanced the photocatalytic process, achieving complete removal of Rhodamine B in 30 min. A significant improvement in the chemical stability of the material was also observed, maintaining nearly its entire removal efficacy after 10 cycles. However, several operational problems were observed due to the powder form of the GCN, and, thus, requesting the development of efficient immobilized catalysts. Therefore, three techniques (encapsulation, electrospinning, and composite) were evaluated and the variations in GCN distribution and their influence on the photocatalysis process ascertained. From this evaluation, it can be concluded that the electrospinning technique, using polyacrylonitrile polymer (PAN) to form fibres, generated a highly porous, hydrophilic material with excellent floatability. This allowed maximizing radiation exposure during the process, achieving an 85 % reduction of Rhodamine B concentration in 90 min. Among other remarkable properties, GCN exhibits high reusability when incorporated into PAN fibres, as it remained chemically and physically stable, retaining more than 85 % of its dye removal efficiency after 4 cycles.