Optical Spectroscopy of Hydrothermally Treated Soil for Organic Matter Monitoring

ABSTRACT

Hydrothermal treatment is popular in reforming biomass for light-emitting carbon dots for multiple applications, but until now no work has been done on the hydrothermal treatment of soil organic matter (SOM) for this transformation. This work translates the knowledge from the chemical synthesis of carbon dots to the monitoring of SOM by a facile hydrothermal treatment of soils without the usage of toxic chromate chemicals: hydrothermally treated soils produce light-emitting carbon dots whose light absorbance and photoluminescence (PL) was attempted to correlate with the content of SOM. The light absorbance of the carbon dots was found to be correlated very well (R² around 0.7) with the SOM by Walkley-Black acid digestion, but the PL was poor in describing the SOM. The absorbance at 250 nm related to the π-π* transition was less affected by pH or but can be reduced by high concentration ammonia. While the absorbance at wavelengths longer than 300 nm was variable, but it still can be used for SOM quantification. The fundamental optical properties are explored via PL and PL excitation spectroscopies to provide an overview of the monitoring of SOM using facile light-absorbance method.

KEYWORDS:

• SOM
• carbon dots
• UV-Vis
• Walkley-Black method
• photoluminescence

Acknowledgments

C.N. also thanks the support from the merit of Chongqing Bayu Young Scholar.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author Contribution

Lei Liu and Chengsheng Ni conceptualized the work and performed the experiment with Wenxuan Lu. Zhongyi Li, Deti Xie and Jiupai Ni involved in the data analysis. All the authors were involved in the writing and revision of the manuscript.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

The support from the National Key Research and Development Program of China (no. 2018FYD0200701) and Research Funding for Central Universities (no. XDJK2020B066).