Table 1. Results of Previous Work.
| refs | materials | sensitivity | response/recovery time | limit | year |
|---|---|---|---|---|---|
| (32) | amine-functionalized SBA-15 | not given | 11/15 s | not given | 2007 |
| (26) | PEI/PVA | 0.5 Hz/ppm | not given | not given | 2010 |
| (33) | PEI/PS | 1.7 Hz/ppm | not given | 3 ppm | 2011 |
| (27) | PEI/BC | 3.15 Hz/ppm | not given | 10 ppm | 2011 |
| (28) | PEI-functionalized TiO2 fibers | 0.014 Hz/ppm | <120 s | 1.2 ppm | 2012 |
| (34) | PAN/PVA | not given | not given | 0.5 ppm | 2013 |
| (29) | chitosan + PEI | 0.172 Hz/ppm | not given | not given | 2014 |
| (35) | PEI/MWCNTs | 0.82 Hz/ppm | 114/127 s | 0.6 ppm | 2015 |
| (36) | graphene oxide | 22.9 Hz/ppm | 60 s | 0.06 ppm | 2016 |
| (30) | Cu(DDS)2Cl2(MeOH2) | not given | 50 s | 50 ppb | 2017 |
| (37) | diamino diphenyl sulfone (DDS) | 3.68–5.94 Hz/ppm | 60 s (1.7 ppm) | 1 ppm | 2017 |
| (38) | PDA/PODS | 10 Hz/ppm | not given | not given | 2018 |
| (39) | copper manganese composite oxide | 167 Hz/ppm | 60 s | 0.3 ppm | 2018 |
| (40) | PDA/HMSSs | 21.4–51.8 Hz/ppm | 5–9/3–15 s | 100 ppb | 2018 |
| (31) | CuO/ZnO nanofiber | 0.743 Hz/ppm | not given | 41 ppb | 2019 |
| (3) | calix[4]arene cage (SCC) | 18.324 Hz/ppm | not given | 0.67 ppb | 2020 |