Detection And Catalytic Reduction Of P-nitrophenol With Carbon Quantum Dots From Cuttlefish Juice

Carbon quantum dots(CQDs)are a new type of carbon-based zero-dimensional nano-functional materials,which have attracted extensive attention due to their good water solubility,fluorescence stability,low toxicity and biocompatibility.The preparation materials such as garlic,tomato and other non-polluting renewable resources can be used to prepare CQDs.The prepared CQDs have different characteristics form different resources.At present,CQDs are widely used in bioimaging,sensors,drug delivery,and catalysis.p-nitrophenol(PNP)is one of the main environmental pollutants widely distributed in the aquatic environment and soil.It is carcinogenic and genotoxic to humans and wild animals even at low concentration.Devloping a faster,sensitive and convenient assay is beneficial for the effective monitoring of PNP.4-aminophenol is an important intermediate for the synthesis of pharmaceuticals and also has great market demand for medical applications.Reduction of PNP is one of the main ways to synthesize 4-aminophenol.High-efficiency catalyst is an important factor to improve the reduction efficiency,which is a research hotspot of catalytic reduction.In this paper,water-soluble fluorescent CQDs were prepared by hydrothermal method using cuttlefish juice which is rich in protein and melanin spherical particles.The CQDs were characterized and their applications in the detection and reduction of PNP were investigated.The main research contents and results are as follows:1.Preparation and characterization of cuttlefish juice CQDs.New CQDs were prepared by hydrothermal method using cuttlefish juice as the carbon source.The fluorescence properties were investigated using an ultraviolet spectrophotometer and fluorescence spectrophotometer.The elements and functional groups of CQDs were analyzed by XPS and FTIR.The morphology and particle size were analyzed by TEM.The effects of NaCl,pH and metal ions on the fluorescence intensity of CQDs were studied.The results show that the quantum yield of the CQDs is 3.25 %.The CQDs were mainly composed of C,H,N and O elements.The maximum emission peak can be observed between 300 nm and 450 nm and between 450 nm and 600 nm.The CQDs have a uniformly dispersed spherical shape with a particle size ranging from 2 to 5 nm.The average particle diameter is 3.47 nm.It is pale yellow under natural light and can emit blue fluorescence under 365 nm UV light.2.A detection method of PNP was established based on the fluorescence characteristics of cuttlefish juice CQDs.At the excitation wavelengths of 320 and 390 nm,the linear equation and the linearity range of PNP detection were founded according to the variation of fluorescence intensity of CQDs with the concentrations of PNP.The method selectivity for PNP from phenol,hydroquinone,2-nitrophenol,4-aminophenol,3-nitrophenol and 4-nitrobenzoic acid was discussed.The fluorescence quenching mechanism was proposed by single photon counting and cyclic voltammetry.The developed method was applied to actual water detection.The results show that the linearity range of PNP detection at excitation wavelengths of 320 nm and 390 nm is 1.25-50 ?M and 1.25-27.50 ?M,respectively.The detection limit is 0.05 ?M.The developed method has higher sensitivity and wider detection range than the reported method PNP detection.The electron transfer and internal filtering effects between CQDs and PNP lead to fluorescence quenching of CQDs.The recovery rate for water detection is between 88.06 % and 108.71 % with good repeatability.3.Ag@CQDs/MXene as a new catalyst for the reduction reaction of PNP was synthesized and evaluated.Ag@CQD was synthesized with the CQDs as a reducing agent and loaded on the new two-dimensional material MXene to obtain Ag@CQD/MXene.TEM,SEM were used for Ag@CQD and Ag@CQD/MXene for morphology analysis.XRD and XPS are for elemental composition and group analysis.The reduction effect of nano-silver,MXene,Ag@CQD and Ag@CQD/MXene was compared.The addition amount of MXene was further discussed.The mechanism of catalytic reduction reaction was analyzed by electron spin resonance test and adsorption experiment.The results show that Ag@CQD and Ag@CQD/MXene have the catalytic activity for the reduction of PNP.Due to the addition of MXene,Ag@CQD/MXene can exhibit better catalytic performance.It can catalyze the reduction reaction of PNP to complete within 2 min and can still maintain excellent catalytic activity after 10 cycles of the reaction.In conclusion,the obtained CQDs with cuttlefish juice as the carbon source have wavelength tunability,high quantum yield and fluorescence up-conversion properties.Due to electron transfer and internal filtration effects between the CQDs and PNP,a highly sensitive and selective detection method of PNP was established on the basis of the dual-wavelength fluorescence characteristics of the CQDs.This work provides a Ag@CQD/MXene has been tested as an efficient catalyst for the reduction of PNP.