Preparation Of Water-soluble Carbon Quantum Dots From Petroleum Coke And Detection Of Cu²⁺

High value-added utilization of heavy oil has become a key focus for one of the major concerned problems of petroleum and petrochemical industry.Petroleum coke is a by-product of oil refining as well as a promising raw material to prepare functionalized carbon nanomaterials.In this work,carbon quantum dots（CQDs）were directly prepared from petroleum coke by ultrasonic-assisted chemical oxidation for the first time.A simple but effective yellow-visual fluorescent CQDs probe for Cu²⁺ detection was developed.Then,CQDs were functionalized by hydrothermal ammonia treatment to improve their fluorescent performance.Finally,electrochemical method was also used to prepare CQDs.The structure and surface chemical property of petroleum coke and obtained CQDs were characterized by transmission electron microscope,X-ray powder diffractomter,X-ray photoelectron spectroscope,Raman spectrometer,Fourier transform infrared spectrophotometer and so on.UV-Vis absorption spectroscope and fluorescence spectroscope were used to evaluate the fluorescent performance of CQDs prepared from petroleum coke.The main results are as following.1.Based on the yields of CQDs prepared from different petroleum coke spicies and different calcination temperatures,Japanese needle coke was selected as the desired raw material.2.CQDs were successfully used for Cu²⁺ detection.Several detecting effect factors were investigated to determine the proper detecting condition.The CQDs is fluorescence turn-off probe for reliable detection of Cu²⁺ in water with a response time as fast as 3 s,which is unprecedentedly rapid response than reported CQDs.The reusable as well as “mix-and-detect” CQDs probe is highly selective and hardly interfered by other coexisted metal ions.The fluorescence intensity of CQDs versus the concentration of Cu²⁺ is of very good linearity from 0.25 to 10 μM,and the detection limit is as low as 0.0295 μM.Theoretically,the detection mechanism of Cu²⁺ via CQDs probe is basically originated from photoinduced electron transfer.Petroleum coke-based CQDs hold a great promise for real-world sensor applications.3.CQDs have been functionalized by hydrothermal ammonia treatment,which is a simple pathway to produce high quality and enhanced photoluminescent CQDs from petroleum coke.The results show that the quantum yield（QY）of CQDs increased greatly from 8.7% of CQDs to 15.8% of N-doped CQDs（N-CQDs）.The fluorescent lifetime of N-CQDs is 6.21 ns,much higher than 3.86 ns of CQDs.The as-made CQDs and N-CQDs with graphene-like structures are rich of oxygen-containing functional groups,and good dispersion.Both CQDs and N-CQDs are water-soluble,and have uniform particle distribution,strong fluorescence,and highly fluorescent sensitivity to pH value in a range of 2.0-12.0.The improved fluorescent mechanism was also illustrated.The uniform size distribution and nitrogen-doping of N-CQDs help to lead to the high yield of radiative recombination,resulting in improved fluorescence properties.4.CQDs were also prepared by the electrochemical method.The preparation parameters of CQDs with superior fluorescent performance were investigated.The QY of CQDs prepared under the optimized condition is 1.6%,and the fluorescent lifetime is 4.74 ns.The as-made CQDs are water-soluble,and have uniform particle distribution,strong fluorescence,and highly fluorescent sensitivity to pH value in a range of 1.0-13.0.The electrochemical preparation mechanism was also studied.