Preparation Of Rare Earth Oxides Doped SnO₂ Material And Study On Their Sensitive Properties To Trimethylamine

Trimethylamine (TMA) gas is the main gas come from deterioration of fish and one of the major odor gases existing in urban sewer. In this paper, a SnO₂ based gas sensor with lower power consuming, high sensitivity and high selectivity to detect TMA gas with lower concentration existing in urban sewer has been studied.Having summarized the related references, the author reviewed the research background of SnO₂ and rare earth oxides doped gas sensor and the research actuality of gas sensor of detecting TMA. This study is made up of the three parts as follows:SnO₂ ultra-fine grain and La₂O₃, Y₂O₃and CeO₂ doped SnO₂ ultra-fine grain are prepared by the homogeneous precipitated method with carbamide as the initiator and citric acid as the dispersant by controlling experiment condition accuratly. Preparation conditions are researched through experiment of SnO₂ particles precursor and the prepared materials are characterized by analytical method of TG-DTA, XRD, SEM and Zeta potential. We can draw conlusions as follows: The best calcined tempreture of SnO₂ particles precursor is 450℃and La₂O₃ doped SnO₂ particles precursor is 500℃.The average particle diameters of SnO₂, La₂O₃/SnO₂, Y₂O₃/SnO₂, CeO₂/SnO₂ particles are about 8.9nm, 4.3nm, 10.1nm and 9.8nm respectively. Rare earth oxides doped SnO₂ powers contain La₂Sn₂O₇ and Y₂Sn₂O₇ and other conformation of La, Y and Ce. SnO₂ particle in water solution is with negative charges and the isoelectric points of 5wt% La₂O₃, Y₂O₃ and CeO₂ doped SnO₂ are about 3.45, 5.08, 6.34 and 5.57 respectively. The isoelectric points of SnO₂ with rare earth oxides doped are between pure SnO₂ and rare earth oxides. The results show that rare earth oxides have doped into the surface of SnO₂.This experiment has confected TMA gas, ammonia, acetone, and formaldehyde. The conductivity ion chromatography method was used to determine concentration of trimethylamine gas. The lateral-heating sense organs are made and put in the gas sensitive testing system separately to test response sensitivity for trimethylamine gas between 5ppm and 65ppm when work voltage is between 3 V and 6 V. Through sense-testing experiment, the sensitivity and selectivity of sense organs for detecting TMA gas are studied and analyzed, the optimum concentration of rare earth oxides doped and the optimum work conditions of SnO₂ gas sensor are determined. We can draw conclusions as follows: Compared with bad sensitivity of pure SnO₂ to TMA of low concentration, the sensitivity of SnO₂ to TMA of low concentration improved dramatically with La₂O₃, Y₂O₃ and CeO₂ doped and their lowest detection limits can reach 5ppm.The optimum heating voltages of SnO₂ with rare earth oxides doped sense organs are all lower than that of SnO₂ sense organ. The sensitivity of SnO₂ with La₂O₃ doped is superior to SnO₂with Y₂O₃ doped and SnO₂with CeO₂ doped at the same experimental conditions and the resolving rates have reached 6.7, 12, 9.4 for detecting ammonia,acetone and formaldehyde respectively. Also the optimum doping of La₂O₃ mass concentration is 5% and the optimum heating voltage is 5V. Last sensing mechanism of pure SnO₂ and rare earth oxide doped SnO₂ for detecting TMA gas was studied in this paper according to adsorption chemistry and analytical results of experimental data.The sensitivity for detecting three interference gases - ammonia, acetone and formaldehyde and selectivity for TMA have been studied at the optimum work voltage. The results show that 5% La₂O₃ doped SnO₂ sense organ has perfect selectivity for TMA gas. Also 5% La₂O₃ doped SnO₂ sense organ is applied to detection of sewage and polluted mud. The detection results keep the same for three times and repetition property of SnO₂ with 5% La₂O₃ doped sense organ is favorable. It has actual application value and significance to a certain extent.