基于金属纳米材料的雾霾传感器射频放电检测机理研究

Haze is becoming more and more serious in super megacities of our country, seriously damaging humans’ health and threatening lives. Especially, the emissions of power plants are the main source of the haze. However, the existing haze monitoring equipment exhibits easy-interferential property, short life-span and poor stability. In this proposed project radio frequency discharge mechanism is proposed to detect the haze medium the very first time. Radio frequency range will be explored and determined. Then, the bombardment of positive ions on the nanomaterials of the sensor electrodes will be effectively limited, leading to low voltage and low power consumption, consequently extending the life-span of the electrodes. Additionally, metallic nanomaterials will be fabricated as novel cathodes. The both will enable us to overcome the short life-span limitation, induced by carbon nanotubes (CNTs) being not resistant to bombardment from positive ions in our previously reported CNT electrode sensing technology based on dc discharge. The dependence of concentration and species of haze particles on radio frequency, power, and electrode separation, will be studied. Due to the featuring of an extreme sensitivity of gas discharge to ultratrace changes, discharge frequency and power range for the detection of 0.1 μg/m3 micro-haze and ppt order emission gases will be creatively studied. Multiphysics software COMSOL will be used to assist the design and the optimization on the prototype will be realized through the integration of analytical and experimental studies. The discharge structure will be optimized to extract more positive ions away from the cathode and easily clean haze particles out of the collecting electrode, thus the life-span of the electrode will be significantly increased. The exponential dependence of the discharge current on the electrode separation will be used innovatively for selectivity purpose, since the sensors with different interelectrode spacing will exhibit distinct response to the mixed gases and the temperature. Therefore, the sensors with different electrode separations will be fabricated and constructed as an array for simultaneous detection of various haze particles, emission gases and temperature. Radio frequency discharge condition will be explored for interference suppression from the emission gases and temperature and for the decrease of detection error.

我国超特大城市的雾霾日益严重，严重危害人类健康并威胁生命。火电厂排放物是雾霾的主要来源，而现有的雾霾监测设备易受干扰、寿命短、稳定性差。本项目开创性地研究雾霾介质中的射频放电检测机理，研究限制正离子轰击阴极的射频频率范围，延长纳米材料电极的寿命；采用金属纳米材料制做电极；解决直流放电碳纳米管电极不耐正离子轰击造成的寿命短问题。研究频率、功率、电极极间距与雾霾颗粒浓度及种类的对应关系。借助气体放电对超微量极为敏感的特征，创新性地研究可检测0.1 μg/m3微量雾霾以及ppt级烟气的放电频率及功率范围。基于Comsol仿真及实验验证的新方法，创新性地研究传感器电极结构优化以引出更多正离子以及雾霾颗粒的清除机理，延长电极的寿命。创新性地借鉴放电电流与极间距的指数关系，采用极间距不同的传感器构成阵列，研究可同时检测各类雾霾颗粒、烟气及温度的射频放电条件，抑制烟气及温度干扰，减小雾霾的测量误差。

我国超特大城市的雾霾污染问题严重，尤其是火电厂的污染物排放产生的雾霾，严重威胁着人类的健康。而现有的雾霾检测技术存在抗干扰能力差、寿命短、稳定性差的缺点，研究一种新型的雾霾检测技术，对于大气环境的治理具有重要的科学意义。本项目开创性地研究了雾霾介质中的射频放电检测机理，理论及实验研究了射频频率范围。在最优射频频率范围内，射频放电减少了正离子对阴极材料的轰击，延长了纳米材料电极的寿命。基于粒子质量守恒方程、电子能量守恒方程和泊松方程建立了流体模型，仿真分析了雾霾颗粒与烟气混合物的电离过程；阴极发射的高能电子首先电离气体，产生正离子；然后这些正离子被雾霾粒子吸附，电荷从气体分子正离子转移至雾霾颗粒使颗粒物带电；设计并优化了传感器结构，显著提高了传感器的使用寿命。同时，基于深硅刻蚀方法，研究制备了基于金属微纳米材料的电极，增强了传感器电极的发射特性和耐轰击能力，传感器连续工作3个月以上。研究分析了颗粒物浓度、种类与射频频率、功率及传感器极间距之间的关系，获得了传感器的单值敏感特性，灵敏度高出现有技术两个数量级。基于气体放电对超微量变化极为敏感的特征，创新性地检测了0.1 微克/立方米的微量雾霾以及ppt级烟气，检测灵敏度、量程等性能均达到国际领先水平。利用超声波振荡器有效地去除了雾霾颗粒；基于超声波在气体中的传播特性，研究建立了超声波振幅及声压变化与传播时间、传播距离关系的理论模型；仿真优化确定了超声波换能器与传感器之间的距离、超声波频率及功率，去除了98 %的雾霾颗粒。为了提高传感器对不同参量的选择性，研究了放电电流和电极极间距之间的指数关系。制作了8个不同电极间距的传感器，构建了传感器阵列。阵列对不同粒径的雾霾颗粒、混合气体和温度展示出截然不同的敏感特性，可同时检测雾霾、气体和温度。研究了基于粒子群优化的支持向量机技术，基于收集电流与被测参数之间的单值关系，建立了8个被测量的读数模型。被测量的读数结果，最大引用误差均小于3 %。共发表论文5篇，SCI收录2篇（最高影响因子6.393），EI收录1篇，已投论文1篇（大修状态），待投论文3篇（均为SCI收录期刊），授权发明专利7项。