Synthesis And Photoelectric Catalysis Properties Of Doped Graphene Quantum Dots

In recent decades,increasing environmental pollution has attracted more and more attention,especially the discharge of dye wastewater from factories.It is therefore appropriate to find an effective,low-cost and pollution-free replacement for traditional energy sources.Photoelectrocatalysis could be one of the most effective measures to solve the problems of energy shortage and environmental pollution.However,the photocatalysts commonly used at present,such as titanium dioxide?TiO₂?,zinc oxide?ZnO?,all have the disadvantages of wide band gap and too fast combination of photo-generated electron hole pairs,resulting in too low photocatalytic efficiency.Therefore,it is of great significance to find efficient,simple and environmentally friendly auxiliary catalysts for improving the photocatalytic performance of catalysts.Platinum?Pt?is often used as a catalyst for batteries,its catalytic efficiency is low due to some effects in the reaction process.Pt is a precious metal and its use cost is very high,so it is an irresistible trend to look for a kind of efficient and low-cost catalyst.Graphene quantum dots?GQDs?is a novel kind of 0D carbon nanomaterial with the dimensions below 100 nm.GQDs are environmentally friendly materials with strong anti-chemical corrosion and anti-ultraviolet?UV?irradiation capabilities.Based on the excellent performance of GQDs,this paper adopts a simple hydrothermal method to modify GQDs with nitrogen and sulfur doping,studies its role in photocatalytic and electrocatalytic performance,and studies the difference in optical performance of GQDs with different sizes.The details are as follows:?1?GQDs were prepared by a simple hydrothermal method.In order to obtain the GQDs of different sizes,we dialyzed the solution in different sizes with 14000 Da,7000 Da,3500 Da and 1000 Da dialysis bags successively to study its PL performance.The results show that the intensity of GQDs peak varies with the different size of GQDs.With the decrease of size,the intensity of luminescence peak increases.In our work,the GQDs in the 1000 Da dialysis bag showed the strongest PL strength.?2?Synthesis of nitrogen-doped graphene quantum dots?N-GQDs?by hydrothermal method using the prepared GQDs and ammonia water.Different volumes of ammonia?50ml,100ml?were compounded with GQDs and characterized by X-ray photoelectron spectroscopy?XPS?.It was calculated that when 50 ml of ammonia was added,the nitrogen doping rate reached 10.64%,of which the doping rates of pyridine nitrogen and graphite nitrogen were as high as 22.47% and 31.44% respectively.The result shows that the photocatalytic effect of N-GQDs-50 was the best,with the degradation rate reaching 95% within 12 minutes through the photocatalytic experiment of degradation of methyl orange?MO?.After the cyclic experiment,the catalytic effect of N-GQDs-50 was still as high as 90%.The higher the content of pyridine nitrogen and graphite nitrogen,the better the catalytic effect.These results show that pyridine nitrogen and graphite nitrogen play a significant role in the photocatalytic performance.?3?In this study,a novel and simple hydrothermal method was developed to synthesize sulfur-doped graphene quantum dots?S-GQDs?with a diameter of 1–6 nm and S-GQD/reduced graphene oxide?S-GQDs/rGO?hybrids.The results indicated that an increase in the sulfur content led to superior ORR electrocatalytic activity.Moreover,it is found that thiophene S plays a significant role in the electrocatalytic activity.In addition,the average electron transfer number depends on the content of thiophene S.It is believed that the proposed synthesis strategy is a general and effective method for designing high-performance metal-free electrocatalytic materials.