Fabrication And Gas Sensing Characteristics Of Colloidal Quantum Dot/MWCNT Nanocomposites

Semiconductor based gas sensors have been widely utilized due to their high sensitivity,rapid response,long lifetime.However,there are still some issues such as high operation temperature and poor selectivity.Current research is mainly focused on the usage in special activities of low-dimensional materials to decrease the operation temperature,thus developing new type semiconductor gas sensor with high performance and low consumption.Carbon nanotubes are often introduced into gas sensors as carrier transport materials or gas adsorbent materials by virtue of their superb surface area,carrier transport capability.They are also used in the fields of flexible devices due to their excellent mechanical properties.And the characteristics of extremely large surface-to-volume ratio,compatibility with various of substrates and excellent film-forming properties at room temperature make CQDs promising sensing materials for gas sensor.Here,PbS/MWCNT nanocomposites were constructed using as-synthesized PbS CQDs,and MWCNT.Through the Raman,HRTEM and UV-vis tests,we confirmed the nano-micro structure which the quantum dots anchored on the surfaces of MWCNTs.The PbS/MWCNT nanocomposites based gas sensor was fabricated by spin coating with ligand exchange treatment at room temperature,which had a response of 178 towards 40 ppm NO₂ at room temperature,the response time and recovery time were 14 s,25 s,respectively.Furthermore,taking into account the CQDs' advantages of the compatibility with the four kinds of substrates,the flexible sensors based on PbS/MWCNT nanocomposites were fabricated on paper substrates.Through the detection and the microscopic characterization of the devices on various paper substrates,it was found that the stone paper was the best substrate for sensor fabrication;A preliminary attempt for optimizing the amount of MWCNTs shown the best MWCNT-to-QD weight ratios was 2:1;We also had tested its flexibility performance at different angles and bent it 600 times at 30° to prove an improvement of flexural bending resistance after introducing MWCNTs.SnO₂ CQD/MWCNT nanocomposites were synthesized to fabricate the gas sensing film using the similar process,which showed a response of 108 towards 50 ppm H2 S at 70 oC,the response time and recovery time were 23 s,44 s,respectively.The interface band structure of PbS / MWCNT nancomposites and SnO₂ / MWCNT nancomposites were established by means of Kelvin probe test and cyclic voltammetry.It was found that both of the nancomposites' interfaces were suitable for the transportation from the surfaces of gasadsorbed quantum dots to MWCNTs,no matter it was p-type PbS/MWCNT or n-type SnO₂.And then,the conductive MWCNTs could serve as the charge transport highway to direct the carriers flow to the electrode for collection,thereby improving the gas sensing response.