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Soil-based Heavy Metal Detection

Tsinghua University and Shenzhen Science Academy Lab

Background

This summer I joined Green Lion’s mangrove conservation project in Hua Hin, Thailand and visited the largest Pranburi Mangrove Forest. Despite human activities and climate change, the forest still retains a relatively good ecological environment through strict royal protection since 1982 and persistent reforestation projects.

In contrast, the Futian Mangrove Forest in southern China’s Shenzhen City suffers severe degradation with 32% of original area vanished to urban expansion since 1988. Water pollution from industrial and domestic wastewater depleted fish/shrimp stocks, reduced bird diversity and weakened its role s as coastal defense.

I enrolled myself in a soil protection research project, provided by Tsinghua University Shenzhen Science Academy Lab.

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During my study in Shenzhen, my research focus shifted from the previous emphasis on inorganic and catalyst synthesis to the synthesis of organic nanomolecules. Moving from the inorganic laboratory to the organic laboratory, I came into contact with many new devices. For instance, rotary evaporators, the chromatographic principle of separating by-products, and nuclear magnetic resonance (NMR) analysis of functional groups.

I participated in and contributed to the development of a patent in a laboratory in Shenzhen. The key innovation of this patent is: we introduced ethylenediamine (an organic solvent and pollutant in seawater) and changed nanopolymer molecules from a twisted spatial configuration to a planar spatial structure.

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After planarization, the coordination sites within the molecule (such as nitrogen, oxygen, etc.) can be fully exposed, and at the same time, the electrons of the conjugated system can more easily interact with the metal ions to form aggregates. Different types of metal ions aggregates generate different fluorescence, resulting in the emission of light at different wavelengths. Additionally, the metal ions aggregates precipitates, thus achieving the removal of metal ions.

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In this patent, my contribution was to propose the idea of integrating the two functions of metal detection and metal removal into one. To achieve this goal, Dr. Pan guided me, using the existing experience and discoveries of their laboratory, and together we designed a new spatially structured nanomolecule.

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The new nanomolecule 1) can detect a wider range of metal ions; 2) can simultaneously detect and remove metal ions; 3) and enables more precise measurements.

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We used the nanomolecules in this patent to detect the soil of Shenzhen Futian mangrove forest. Final detection results shows that Mn2+ (0.094 mg/L) exceeds the hygiene standard for drinking water in daily life and fails to meet the environmental quality standard for surface water; Gd3+ (23 ng/L), Ni2+ (0.011 mg/L) are close to the hygiene standard for drinking water, but may have an impact on the survival of organisms in the mangrove reserve. The main reason for the excessive presence of these heavy metals could be related to the discharge from nearby research institutions and industries.

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(a) and (b) are respectively the emission and absorption spectra of different nanoprobes before and after responding to different metal ions.

(c) The states presented by different nanoprobes under ultraviolet lamp before and after responding to different metal ions.

(d) Specificity verification of different nanoprobes for metal ion detection.

This research has allowed me to have a deeper understanding of organic scientific research, expanded my laboratory skills, and also made me recognize the role of organic molecules in environmental protection in real-life situations.

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