UV/VIS spectroelectrochemical monitoring of 4-nitrophenol degradation

Importance of the Topic

UV/Vis spectroelectrochemistry merges electrochemical and spectroscopic measurements into a single, in situ experiment, delivering simultaneous qualitative and quantitative insights into redox processes. Monitoring the degradation of hazardous compounds such as 4-nitrophenol is essential for environmental protection and water treatment strategies.

Objectives and Overview of the Study

This application note demonstrates the use of the SPELEC spectroelectrochemical instrument to track the degradation kinetics of 4-nitrophenol (4-NP) in aqueous solution. The study aims to obtain synchronized electrochemical and UV/Vis data to characterize reaction pathways and quantify degradation efficiency.

Methodology and Experimental Procedures

The degradation of 4-NP was induced by irreversible reduction in 0.5 M Na₂SO₄ solution. Linear sweep voltammetry (LSV) was performed from –0.30 V to –1.00 V at 0.01 V/s; simultaneous UV/Vis spectra were recorded using the initial 4-NP solution as reference. Chronoamperometry at –1.00 V for 150 s provided time-resolved data, yielding 750 spectra to follow absorbance changes at 400 nm.

Used Instrumentation

• SPELEC: Integrated UV/Vis spectroelectrochemical system (200–900 nm) with bipotentiostat/galvanostat, light source, detector, and Dropview SPELEC software for synchronized data acquisition.
• RPROBE-VIS-UV: Bifurcated reflection probe for near-normal reflection geometry with screen-printed electrodes.
• REFLECELL: Teflon reflection cell designed for standard screen-printed electrodes, featuring magnetic closure.
• 220AT Screen-Printed Gold Electrodes: Three-electrode system on ceramic strip with 4 mm gold working electrode, silver pseudoreference, and carbon counter electrode.

Main Results and Discussion

LSV experiments revealed two UV/Vis absorption bands at 320 nm (4-NP consumption) and 400 nm (degradation products). Time-resolved chronoamperometry showed a progressive increase in absorbance at 400 nm, indicating product formation. Using Lambert–Beer law (ε = 17 357 L mol⁻¹ cm⁻¹, path length 0.36 cm, C = 2×10⁻⁵ M), the theoretical maximum absorbance was 0.125 a.u.; the experimental maximum was 0.095 a.u., corresponding to a 76.0% degradation efficiency. Efficiency profiles over time:

• 25 s: 21.6%
• 50 s: 39.4%
• 75 s: 45.6%
• 100 s: 53.2%
• 125 s: 61.4%
• 150 s: 76.0%

Benefits and Practical Applications of the Method

Real-time UV/Vis spectroelectrochemistry provides comprehensive monitoring of electrochemical reactions, enabling kinetic analysis and quantification of pollutant degradation. The compact SPELEC setup streamlines workflows, offering rapid feedback for environmental monitoring, sensor development, and process optimization.

Future Trends and Potential Applications

Emerging directions include integration with microfluidic platforms, extension to other spectral regions (e.g., near-IR), and coupling with complementary techniques such as mass spectrometry. This approach can be applied to diverse contaminants, mechanistic studies in electrocatalysis, and in situ sensor calibration.

Conclusion

The SPELEC spectroelectrochemical system successfully monitored 4-nitrophenol degradation, delivering synchronized electrochemical and spectroscopic data. Quantitative analysis demonstrated a 76% degradation efficiency, highlighting the technique’s value for environmental analytics.

References

1. US Environmental Protection Agency, Federal Register 44 (1979) 233.
2. US Environmental Protection Agency, Federal Register 52 (1989) 131.
3. D. Chaara et al., Appl. Clay Sci. 50 (2010) 292–298.
4. S. Laha, K.P. Petrova, Biodegradation 8 (1998) 349–356.
5. D. Ibañez et al., Electrochim. Acta 280 (2018) 17–24.