Synthesis Of Ordered Large-pore Mesoporous(W And Mo)-based Oxide With High Specific Surface Area For Detecting Hazardous Gases In Mine

Hazardous gases in mine such as hydrogen sulfide,nitrogen dioxide,methane,carbon monoxide,are usually dangerous to underground workers,which should be carefully monitored.Therefore,it is necessary to develop advanced gas sensors with high sensitivity,good selectivity,low detection limit and good stability,where excellent gas sensing materials are particularly critical.In this paper,a series of ordered large-pore mesoporous(W and Mo)-based oxides with high specific surface area were synthesized and their gas-sensing properties were also studied.A series of ordered mesoporous tungsten oxide materials were synthesized via the nanocasting method by using mesoporous silica KIT-6 as hard template and silicotungstic acid as precursor.Pore size and interconnectivity of mesoporous silica template KIT-6 were decreased by changing the hydrothermal aging temperature from 140 to 40? and the framework thickness of the resultant mesoporous tungsten oxide reduced from 9.1 to 3.4 nm,accompanied with the increase of the specific surface area from 64 to 163 m2/g and pore size from 3 to 12 nm.The gas sensing properties of those mesoporous tungsten oxides toward hydrogen sulfide(H2S)were evaluated and the response significantly increased with the specific surface area,and the response and recovery time were shortened with the increase of the pore size.Especially,the ordered mesoporous tungsten oxide with both high specific surface area of 163 m2/g and large pores size of 12 nm exhibited a highest response(Rgas/Rsir=313)toward 1000 ppb H2S,a quite low limit of detection(<2 ppb)and good selectivity at a relatively low operating temperature of 100?.Similarly,a series of ordered mesoporous molybdenum dioxides were also synthesized by using KIT-6 as hard template and ammonium molybdate tetrahydrate as precursor.Among of them,ordered mesoporous molybdenum dioxide with both large mesopores(12 nm)and high specific surface area(169 m2/g)as well as thin frameworks(7.1 nm)was found to possess 3.2 times higher response toward 10 ppm ethanol than that for its counterpart with both small pore(4 nm)and low specific surface area(109 m2/g)as well as thick framework(9.9 nm)at an operating temperature of 300?,213 and 67 respectively.In addition,a series of ordered mesoporous nickel molybdate/nickel oxide composite with specific surface area of 115?133 m2/g,pore size of 3?12 nm,and framework thickness of 6.3?9.5 nm were synthesized by using KIT-6 as hard template and ammonium molybdate tetrahydrate and nickel nitrate hexahydrate as mixed precursor.The gas sensing testing results exhibit that large-pore mesoporous(12 nm)nickel molybdate/nickel oxide composites with high specific surface area(133 m2/g)and thin framework(6.3 nm)is sensitive to nitrogen dioxide at the optimum operating temperature of 150 0C,whose response toward 1000 ppb nitrogen dioxide is 8.5 times higher than that of the small-pore mesoporous(3 nm)nickel molybdate/nickel oxide composites with low specific surface area(115 m2/g)and thick framework(9.5 nm),59.6 and 8.5 respectively.