Resonance-based Sensor for Detection of Nitrogen Oxide (NOₓ)-polluted Water in Industrial Effluents

Water is a fundamental necessity for human existence. Unfortunately, water quality has been steadily deteriorating due to various pollutants, with industrial contamination being a major contributor. Industrial wastewater often contains hazardous substances among these pollutants, nitrogen-based compounds such as nitrates $\mathrm{NO}_{3}{ }^{-}$ and nitrites NO
2
are of particular concern. In this study, we employ Ti
3
C
2
T
x
-Fe
3
O
4
to achieve this objective.Ti
3
C
2
T
x
, a family of two-dimensional layered compounds, has displayed potential in gas sensing applications due to its unique attributes, including a high surface area, strong metallic conductivity, high hydrophilicity, good mechanical properties, and active surface chemistry. The selectivity of NO
2
gas in Ti
3
C
2
T
X
can be further improved with Fe
3
O
4
nanoparticles. Fe
3
O
4
facilitates the electron transfer from NO
2
to $\mathrm{NO}_{3}{ }^{-}$, while Ti
3
C
2
T
x
offers ample surface area for this reaction to occur, along with providing additional electrons. The properties are studied as a function of variation of dielectric constant of Ti
3
C
2
T
x
-Fe
3
O
4
with gas interaction. Using our earlier studies, a well optimized complementary slit-ring resonator (CSRR) sensor, operating at 430MHz, was used as a unit cell sensor. Separately, Ti
3
C
2
T
x
-Fe
3
O
4
was exposed to NO
x
(ranging from 0 to 106 ppm), and the resulting NO
x
-purged Ti
3
C
2
T
x
-Fe
3
O
4
composite was later exposed to the CSRR device. As the purged gas concentration changed from 0 to 106 ppm, there was a systematic shift in frequency and power. The maximum power shift was ~ 18.4 dB. The frequency shift gave a sensitivity of 400 KHz / ppm with NO
x
-purged Ti
3
C
2
T
x
-Fe
3
O
4
, which was two times higher than the reference Ti
3
C
2
T
x
system. Thus, a two-stage apparatus for detection of hazardous industrial effluents is presented using a novel Ti
3
C
2
T
x
-Fe
3
O
4
composite system.