Dielectrophoresis Applications In Removing Cadmium (?) From Wastewater And Manipulating Multi-wall Carbon Nanotubes Gas Sensors

Dielectrophoresis?DEP?was a phenomenon that polarizable particlescan migrate in non-uniform electric field.Nowadays,the dielectrophoresis technology has been applied in the fields of environmental protection,mineral,biology for separating,concentratting and capturing particles and cell.In this thesis,the dielectrophoresis method was employed in the treatement of heavy metals in waste water and the detection of harmful gases in the air,viz:the removal of cadmium?II?in wastewater by dielectrophoresis process combined with the adsorption method and the gas sensing performances of gas sensors based on the dielectrophoretically manipulated multi-wall carbon nanotubes with various functionalized groups towards SO₂ and NH₃.In the research on the removal of cadmium?II?in wastewater by dielectrophoresis process combined with the adsorption,biopottery powders,camellia seed powders,pristine multi-walled carbon nanotubes and modified multi-walled carbon nanotubes were selected as the adsorbent.Under the same adsorption conditions,the removal rate of cadmium?II?for various adsorbents was investigated.It is shown that biopottery was the most efficient in removing cadmium?II?,thus the biopottery powder was determined as the optimum adsorbent herein.The influence of biopottery amount,pH value,solution temperature on the removal rate of cadmium?II?was studied in detail.The results show that when the solution temperature was 293.15 K,biopottery powder amount was 1 g·L^-1,p H value was 5.5 and the adsorption time was 24 h,the removal rate of cadmium?II?was the highest and reached 95.30%.Further,the influence of dielectrophoresis voltage,adsorption time,stainless steel screen electrod mesh,residence time on the removal rate of cadmium?II?was explored by means of dielectrophoresis combined with adsorption.It was found that the highest removal rate of cadmium?II?was 99.27% at 8V of the dielectrophoresis voltage,12h of the adsorption time,100 of the stainless steel wire mesh and 30min of the residence time.Compared with the adsorption method,after using dielectrophoresis combined with adsorption,the removal rate of cadmium?II?was increased by 63.73% under the same experimental conditions,whereas the adsorption time was cut by 12 h.The dielectrophoresis combined with adsorption could enhance the removal rate of cadmium?II?and shorten the adsorption time.In the research on the gas sensing performances of gas sensors based on the dielectrophoretically manipulated multi-wall carbon nanotubes with various functionalized groups towards SO₂ and NH₃,gas sensors of pristine multi-wall carbon nanotubes?MWNTs?and functionalized multi-wall carbon nanotubes?MWNTs-x x: NH₂,OH,COOH?were fabricated on the chromium–silver-gold microelectrode chips by dielectrophoresis process.The dielectric response behavior of MWNTs and MWNTs-x were investigated.The dielectrophoresis parameters of 2 MHz and 8 V were determined as the fabrication condition of MWNTs gas sensors.The particles of MWNTs and MWNTs-x were captured to the electrode tip under the dielectrophoretic force,which was the positive dielectrophoresis?p-DEP?.The gas sensing performances of the fabricated gas sensors towards different concentrations of SO₂ and NH₃ were tested at room temperature.It was found that the response time,recovery time and sensitivity of gas sensors towards SO₂ and NH₃ were increased with the increase of SO₂ and NH₃ concentrations.The functionalized MWNTs gas sensors showed remarkably higher sensitivity than pristine MWNTs gas sensors toward SO₂.The sensitivity of the aminoated MWNTs?MWNTs-NH₂?gas sensors was the highest and 17²3 times higher than that of pristine MWNTs.We conclude that the interactions between carbon tubes and SO₂ such as capillary forces,surface tensions,hydrogen bonding and chemical bonds are influential factors for the gas sensing performances of these gas sensors.