Surface Covering Of Gold Nanoarrays And Their SERS Sensing Performances To Trace Benzene-volatile Organic Compounds

Volatile organic compounds(VOCs)are one of the major pollutants in the atmospheric environment,and most of them are toxic and hazardous substances with relatively strong activity,which are extremely harmful to the ecological environment and human health.As the pollution problem of VOCs becomes more and more serious,the rapid and identifiable portable trace detection of them is especially important.Surface-enhanced Raman scattering(SERS)is a new surface-sensitive molecular-level identifiable detection technique with unique advantages in the field of VOCs detection and monitoring,which is expected to develop into a rapid,highly sensitive and identifiable detection technique for VOCs.However,due to the weak binding of VOCs molecules to noble metals,it is difficult to be captured by adsorption on enhanced substrates.And the Raman scattering cross section of most VOCs molecules is small,producing a weak Raman signal.Therefore,to achieve fast and sensitive SERS detection of VOCs,the key is that the substrate needs to have high SERS performance and the ability to capture gas molecules.In this paper,we investigated the surface covering of gold nanoarrays and their SERS sensitive properties for trace VOCs,using toluene and styrene as the main detection molecules and highly reactive Au/Si nanocone arrays as SERS substrates,starting from improving the capture/enrichment ability of the substrate surface for gas molecules.The innovative results achieved are as follows:(1)A strategy of surface porous ZnO covering based on gold nanoarrays to assist VOCs enrichment is proposed:uniform and controlled covering of porous ZnO on Au/Si nanocone arrays is achieved by a one-step chemical growth method.Such composite chip shows highly selective capture of gaseous B-VOCs(benzene,toluene,nitrobenzene,xylene,and chlorobenzene,etc.),which leads to the rapid and sensitive SERS responses to them.Typically,this chip can response to gaseous toluene within 30 s,and the lowest detectable concentration is below 10 ppb.In addition,the SERS response of the composite chip is recoverable and meets the requirement of repeated use.(2)Porous ZnO-induced chemical capture and electromagnetic-chemical dual enhancement mechanisms were proposed:Based on the SERS response results of the ZnO-coated composite chip to benzene VOCs molecules,the enhanced response of the composite chip to benzene VOCs was explained by combining DFT theoretical calculations,and the porous ZnO-coated layer-induced chemical capture effect and electromagnetic-chemical dual enhancement mechanisms were proposed.(3)A concept of Ni-Fe layered double hydroxide covering for efficient styrene capture is proposed:uniform porous covering layers are formed on gold nanoarray substrates by applying pre-synthesized Ni-Fe layered bimetallic hydroxide nanosheets by alternating dropwise addition/drying method.The ultra-sensitive detection of styrene by SERS was achieved by using the efficient structure capture and chemisorption of styrene by the cladding layer.The fastest response time is<10 s and the lowest detection concentration is<10 ppb.The composite chip has good selectivity and anti-interference for styrene,and also has certain response effect for other benzene VOCs.(4)Proposed covering-induced styrene capture and structure-enhanced SERS response mechanisms:The experimental results of styrene SERS response were analyzed and combined with DFT theoretical simulations to propose a structureinduced efficient chemical capture effect and structure-enhanced SERS response mechanism for Ni-Fe layered double hydroxide covering.