Preparation And Electrochemical Study Of Vertically Oriented Mesoporous-based Silica Film Materials

Vertically oriented mesoporous silica films（VMSF）have many advantages such as uniform pore size,high specific surface area,long-range order,good thermal stability,as well as adjustable pore size,good molecular accessibility and fast mass transfer.At the same time,due to the spatial confinement effect of the pore and the selectivity to molecular size,charge,hydrophobicity,etc,they can be used to construct new devices and sensors.Based on the above background,herein,vertically oriented mesoporous silica nanochannels were firstly used as a hard template to synthesize oriented conducting polymer nanowires by using the sterical confinement effect of nanochannels,and their electrochemical properties were also discussed.In addition,vertically-oriented mesoporous silica films have become a research hotspot in the field of electrochemical sensing due to vertical orientation of the channels allowing fast mass transport from the solution to the electrode and a large number of accessible active sites.Here,VMSF was grown on a conductive substrate with its single-pass nanochannel array was used as a detection platform and the conductive substrate was used as a signal transduction element.The electrochemical detection performance of heavy metal ions was investigated by analyzing the change of the electrochemical signals.The specific researches are as follows:（1）Polyaniline is a kind of conductive polymer with low cost and good stability,and its synthesis methods are simple.One-dimensional（1D）polyaniline nanowires have potential applications in supercapacitors,catalysis and other fields due to their high aspect ratio structure,rapid charge transfer and enhanced conductivity.Herein,a vertically oriented mesoporous silica film（VMSF）was first prepared on the surface of an ITO conductive substrate using octadecyltrimethylammonium bromide as a template by electrochemical-assisted self-assembly（EASA）method.The CV、SEM,HRTEM and 2D-GISAXS characterization techniques were used to characterize the film integrity,channel arrangement order and vertical orientation,respectively,indicating that the mesoporous silica films with highly ordered hexagonal arrangement of channels and perpendicular to the substrate were obtained.Subsequently,using VMSF/ITO as the working electrode,the PANI nanowires were prepared by the potentiostatic deposition method with the vertically oriented mesoporous channels as the hard template,thus the PANI/VMSF/ITO composite electrode material was prepared.The effects of initial sol composition,electropolymerization potential and growth time on the electrochemical deposition of polyaniline were investigated by CV,SEM,HRTEM,FTIR and other characterization methods,and the optimized electrodeposition conditions were obtained.The electrochemical reversibility and capacitive properties of the PANI/VMSF/ITO composite electrode were investigated by comparing with the direct deposition of polyaniline on ITO substrate（PANI/ITO electrode）.The results show that the PANI/VMSF/ITO composite electrode exhibits better electrochemical reversibility and higher specific capacitance（3.00m F/cm²,current density is 20μA/cm²）.Compared with PANI/ITO,the specific capacitance is increased by 152%.At the same time,the specific capacitance of PANI/VMSF/ITO electrode is 3.55 m F/cm² at a current density of 5μA/cm²,and can still maintain 78.9%at a current density of 30μA/cm²,indicating that it has good rate characteristics.The main reason can be attributed to that the spatial constraint of the oriented mesoporous channels can separate the PANI nanowires from each other and avoid the mutual hybridization between chains,which makes the structure of the nanowires orderly and further improves its electrochemical performance.The fast charge transfer and redox reversibility of the composite electrode is expected to improve its performance in catalysis,sensors,energy,or molecular electronics application.（2）At present,heavy metal ions have become common pollutants in water,soil and food.It is of great practical significance to detect heavy metal ions efficiently,quickly and accurately by using a simple,sensitive and low-cost method.Herein,VMSF was prepared on ITO surface by St（?）ber solution growth method,and the surface quality,mesopore channels arrangement order and orientation of VMSF/ITO films were characterized by CV,SEM and HRTEM,and the electrochemical detection performance on Cu²⁺,Cd²⁺and Pb²⁺heavy metal ions was investigated.The electrochemical detection uses differential pulse voltammetry（DPV）method,and the process consists of electrodeposition of metal ions and subsequent anodic stripping in the mesochannels.The relationship between the detection signal and the concentration of each metal ion in different concentration ranges was measured and analyzed,and the sensitivity and detection limits of these various ions in different concentration ranges were also calculated.The results showed that the linear equation for the detection of Cu²⁺ions in the concentration range of 5-35μmol/L was I（μA）=-4.699c（μM）-12.818（R²=0.996）,with a sensitivity of 4.699μA/μM,and I（μA）=-12.041c（μM）-3.745（R²=0.995）in the concentration range of 1-2μmol/L,with a sensitivity of 3.745μA/μM and a detection limit of 16 nmol/L（S/N=3）.The linear equation for the detection of Pb²⁺ions in the concentration range of 5-40μmol/L was I（μA）=-5.147c（μM）-0.736（R²=0.990）with a sensitivity of 5.147μA/μM,and I（μA）=-8.168c（μM）-4.222（R²=0.997）in the concentration range of 1-2μmol/L with a sensitivity of 8.168μA/μM and a detection limit of 27 nmol/L（S/N=3）.The linear equation for the detection of Cd²⁺ions in the concentration range of 5-35μmol/L was I（μA）=-5.655c（μM）+20.381（R²=0.992）with a sensitivity of 5.655μA/μM,and in the concentration range of 1-5μmol/L was I（μA）=-1.144c（μM）-10.323（R²=0.991）,the sensitivity was 1.144μA/μM,and the detection limit of Cd²⁺was 111 nmol/L（S/N=3）.Finally,the interference of each ion and the stability of the working electrode were investigated during the simultaneous testing of multiple ions.The results showed that there was some interference between different heavy metal ions,but the stripping peak current of the VMSF/ITO electrode was almost unchanged when the metal ions were detected at the same concentration for several times,indicating that the VMSF/ITO electrode could be used repeatedly.