Synthesis of fluorescent carbon dots doped graphitic carbon nitride and its application as Fe3+ sensors

Abstract

Carbon dots (C-dots) have better water solubility, biocompatibility, environmental friendliness, and non-blinking fluorescence than any other materials [1]. Due to the numerous advantages of carbon quantum dots (CQDs) over semiconductor quantum dots, studies on synthesis and fluorescence-based sensing in biocompatible carbon quantum dots (CQDs) have recently become a frequently discussed field of research.  In this work, photoluminescent small sized Carbon dots doped graphitic carbon nitride have been synthesised through hydrothermal method as well as their potential application in sensing of Fe³⁺ selectively [4]. Water-soluble carbon quantum dots (CQDs) are synthesized via citric acid and urea, graphitic carbon nitride is simply synthesised through melamine. The photoluminescence properties of Carbon Dot, graphitic carbon nitride (g-C₃N₄), Carbon dots doped (g-C₃N₄), have been studied, and the results show that they have a strong blue luminescence with excitation wavelength independent, pH sensitive, and ionic strength dependent luminescence features. The as-prepared CQDs generated a vivid blue fluorescence with a strong emission at 450nm and a 335 nm excitation. The fluorescent carbon dots and composite not only exhibit good photoluminescence capabilities and water solubility, but they also demonstrated an extraordinary multifunctional fluorescence sensor for pH probing and (Fe3+) ion detecting applications. Various spectroscopic techniques were used to analyse the morphological structure, optical characteristics, and chemical compositions of Carbon dots, graphitic carbon nitride and carbon dots doped graphitic carbon nitride composites, including fluorescence spectrometer, X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR).  Metal ion pollution has become a pressing concern in the environmental field due to the grave harm they pose to our natural environment and human health. iron is one of the hazardous metal ions, and its stability causes significant damage to our environment and health. A wide range of analytical methods, including atomic absorption and emission spectroscopy (AAS, AES) [3], inductively coupled plasma mass spectrometry, have been developed in recent years for the detection of with excellent sensitivity and precision. In comparison to other methods, fluorescence spectroscopy is preferred because of its great sensitivity, superior selectivity, ease of operation, and low cost.

The obtained CQDs have higher photoluminescence of quantum yield (QY = 54.8%, quinine sulphate as standard).  At room temperature, the fluorescence of C-dots doped graphitic carbon nitride could selectively quenched by Fe³⁺ within seconds than the graphitic carbon nitride alone. Only the addition of Fe ³⁺ caused the fluorescence quenching by destroying the surface imperfections of C-dots. Surface flaws are unaffected by the presence of other common interfering metal ions documented in earlier research like Ag⁺, Cu²⁺ etc. The detection mechanism is based on the inner filter effect (IFE) and it shows excellent linear static quenching [2]. By the addition of ascorbic acid as a reducing agent, the reversible switching in the fluorescence was examined, and a very good recovery in fluorescence was observed for up to three consecutive cycles.[3]. Carbon dots showing higher fluorescence is already reported in several papers, but carbon dots doped graphitic carbon nitride showing fluorescence is the first time studying. Carbon dots doped graphitic carbon nitride showing slightly higher fluorescence intensity than graphitic carbon nitride.