| In recent years,terrorist attacks have occurred frequently and various forms of explosives threaten the security of the country and the people.Relevant compounds and residual explosives in the process of explosion have caused serious environmental pollution and have great harm to people and nature.Therefore,the on-site and real-time detection of explosives can not only prevent terrorist attacks and maintain social stability,but also play a vital role in environmental protection and the harmonious development of human and nature.Surface-enhanced Raman scattering（SERS）as a high sensitivity,label-free and rapid detection method,has been widely employed in the detection of explosives.However,restricted by the structure of the detection substrate,the detection performance still cannot be satisfied in the practical application.Therefore,it is urgent to prepare a new SERS substrate with excellent performance.The single-atom layer sp2 carbon hybrid material represented by graphene was considered to be a kind of SERS substrate material with potential application,due to its large specific surface area and unique physical/chemical properties.However,its maximum SERS detection performance was limited by its two-dimensional（2D）structure.Herein,microwave plasma chemical vapor deposition（MPCVD）method was used to prepare3 D porous carbon-based composite film with large specific surface area,diamond-multilayer graphene nanohybrid（DMGN）film.Firstly,the common dye molecule Rhodamine B（Rh B）was used as the probe molecule,and showed excellent SERS detection performance.Then,based on the chemical enhancement（CM）mechanism,SERS detection of intrinsic composite films and surface modified films on different configurations of explosive molecules was studied,and the influence of excitation light sources of different wavelengths on the detection was investigated.The rules of SERS detection for different configurations of explosives molecules were obtained,meanwhile the mechanism of CM was analyzed.Finally,based on the electromagnetic enhancement（EM）mechanism,Ag nanoparticles（Ag NPs）were loaded into the 3D pore structure of the carbon-based composite films,and the SERS detection performance of explosive was studied,and the EM mechanism was discussed.The specific research contents are as follows:（1）The carbon-based composite films（DMGN）prepared by MPCVD method,had a novel3 D porous morphology.Using a dye molecule（Rh B）as probe,the DMGN substrate exhibited low LOD（ 10-9 mol/L）,large enhancement factor（EF 4.2 × 104）,good uniformity and excellent long-term stability（about 17.5% degradation over 45 days）.However,the hydrophobic surface of the film limits the effective utilization area of the probe molecule to the substrate.The hydrophilicity of the film surface after H2O2 oxidation further improves the detection performance of Rh B molecule（LOD 10-11 mol/L;EF 3.9 × 106;stability > 45days）.The results show that DMGN film can be used SERS substrate with excellent performance,and oxidation treatment can further improve the detection performance.（2）Based on the CM mechanism,the SERS detection performance（detection sensitivity enhancement capability）of intrinsic DMGN substrates for ammonium nitrate（FOX-7）,aromatic hydrocarbons（TATB）and nitro explosives（RDX,HMX,CL-20）and the influence of Raman excitation light sources of different wavelengths on the detection performance were studied.The selectivity of substrates for explosive detection was further explored.The results show that the SERS effect of DMGN film on explosives is not obvious,and the DMGN substrate is more suitable for the detection of TATB molecules under 532 nm excitation.（3）In order to further improve the detection ability of carbon-based composite films for different configurations of explosives,hydroxylated DMGN-OH substrates were obtained by oxidizing films with H2O2.The performance of DMGN-OH substrates for different configurations of explosives and the influence of different light sources on the performance of detection were investigated.The results show that the 3D porous morphology of the DMGNOH film after oxidation was unchanged,and the surface contains a large amount of-OH.Excited by 514.5 nm wavelength,the DMGN-OH substrate exhibits excellent performance(low LOD 10-6mol/L,high EF value 527)and long-term stability（60 days signal reduction rate is 11.3%）.However,DMGN-OH substrates have no significant enhancement effect on aromatic hydrocarbon（TATB）,nitro（RDX,HMX,CL-20）explosives,and even inhibits the generation of signal.（4）In order to further improve the molecular detection ability of explosives on carbon-based composite substrates,carboxylated DMGN1-COOH substrates were prepared by treated the films with HCOOH.The performance of DMGN1-COOH substrates in the detection of explosives with different configurations and the influence of different light sources on the detection performance were investigated.The results show that a large number of-COOH and-OH functional groups were grafted onto the surface of DMGN1-COOH film,and the film still maintains 3D porous structure.DMGN1-COOH substrates show excellent performance for TATB detection under 785 nm laser(low LOD 10-6mol/L,high EF 9.3 × 103).The detection of nitro explosive molecules was improved,but the enhancement was not significant.（5）The introduction of-COOH on the film surface can improve the detection performance of nitro explosives.Therefore,after 12 h and 24 h of mixed acid oxidation treatment with H2SO4: HNO3 = 3:1,the-COOH functional groups on the surface of DMGN2-COOH and DMGN3-COOH films increased,and more active sites were exposed,the films were still porous morphology.The detection ability of DMGN3-COOH for RDX(EF 859;LOD 10-6mol/L),HMX(EF 753;LOD 10-6mol/L)and CL-20(EF 47;LOD 10-4 mol/L)showed excellent performance.（6）Based on the EM mechanism,the uniformity of Ag NPs loaded on carbon-based composite films（DMGN,DMGN-OH）prepared by different methods（chemical reduction and electrochemical）,the effect of the presence of-OH on the SERS detection of TATB were studied.These results indicated that Ag NPs prepared by chemical reduction method are more uniform;the-OH functional group can promote the adsorption of Ag NPs in the 3D structure of the film through electrostatic interaction;1-Ag NPs@DMGN-OH substrate showed good performance in detecting TATB(LOD 10-12mol/L;EF 8.5 × 103;stability > 40 days and uniformity).In this paper,the effect of different surface modified carbon-based composite films on the SERS detection performance of explosives with different configurations was systematically studied,and the detection sensitivity,selectivity,stability,uniformity and other indicators were comprehensively evaluated.From CM mechanism,explosives with different configurations can be detected directionally,and trace detection of explosives can be realized.The ultra-trace detection of TATB explosives has realized from the EM mechanism.This study will provide a new base material,experimental data and theoretical guidance for the practical application of SERS detection of explosives. |
