Eco-friendly Facile Fabrication of Novel g-C3N4 nanosheet/Carbon Dots/Ag6Si2O7 Photocatalysts for Photocatalytic Degradation of Congo-Red Dye

Nowadays, textile wastewaters that obtained dyeing industries, which commonly identified through strong color, high levels of chemical oxygen demand, and low biodegradability, are main sources of environmental pollutant. For this aim, considerable attempts have been managed to improve impressive methods for elimination of pollutants from environmental. New treatment procedures have been introduced such as advanced oxidation processes (AOPs) that are identified through the production of O2 reactive species in order that quickly oxidize dye molecules presence in industrial effluents and reach high degradation rates of them [1]. There is more variety of AOPs, which between them heterogeneous photocatalysis strategies have been extensively applied at different treatment stages of water and effluent and have been introduced as an excellent method capable of affecting the removal of effluents contaminants. But visible-light nanocomposites with a narrower energy gap have been receiving an enhancing attention for vast kinds of photocatalytic applications. For this purpose, graphitic carbon nitride (g-C3N4) as a favorable visible-light-induced semiconductor, has been investigated in removal of various pollutions and water splitting, owing to its appropriate band position, supreme biocompatibility, chemical durability, biological activity, and corrosion resistance. Nonetheless, negligible surface area, the weak light harvesting ability, and quick recombination of electron/hole pairs rather restricts its extensive applications [2]. Also, to dominate those limitations, very researchers have proposed several of techniques to improve the photoability of g-C3N4, i.e. through introducing heteroatoms, mixing it with metals, nonmetallic element, controlling morphology, organic dye sensitizers, and coupling with various photocatalysts. In the present work, among these approaches, texture modification is considered as one of the most efficient ways in order to increase specific surface and improve photocatalytic performance of g-C3N4. Nanosheets of g-C3N4 were synthesized by an easy heating method. Also, carbon dots, a novel group of carbonic nano-sized materials are including of quasi-spherical nanoparticles and nowadays have become a rising star. The up-conversion feature of carbon dots develops the light usage region, owing to transfer more photons with higher wavelength to a photon with shorter wavelength by sequential harvesting low energy multi-photon and then emitting light by high energy [3]. Also, since carbon dots is very much imagined for serving as an electron acceptor and donor, so movement of the photo-excited electrons of semiconductors by the carbon dots network can reduce in the recombination of the charges. These parameters caused, we focused on integration carbon dots with the g-C3N4 nanosheets. In addition, in a coupling process, g-C3N4 based heterostructures illustrates a supreme potential to boost the photoability of g-C3N4, due to the photoinduced charges can be impressively separated, and then migrate across the interface of the heterostructure to decrease the recombination. Among the various co-catalysts, silver-based semiconductor photocatalyst, such as Ag6Si2O7 with a entirely little band gap of 1.58 eV can be supreme selection as one of the most favorable visible-light-induced nanocomposite to degrade hazardous contaminates [4].In this work, the fabricated photocatalyst was subsequently characterized by different techniques and it was utilized for photocatalytic removal of Congo-Red dye under visible light. Congo-Red dye is a typical water-soluble anionic pollutant utilized in cellulose and cotton textile industries. This azo dye is dangerous for the aquatic environment even at low concentrations. So the removal of this water pollutant has become a burgeoning field of research. Studies have shown that by depositing both Ag6Si2O7 and carbon dots particles on the g-C3N4 nanosheets, photocatalytic activity was greatly increased; indicating its ability to usage in the water remediation applications.

Keywords:

Visible-light-activity , g-C3N4 nanosheet/Carbon dots/Ag2Si2O7 , Electron–hole separation , Congo-Red , Photocatalysis