The Nanjing Soil Institute has made progress in the preparation of remediation materials based on nonlinear optical materials for efficient mercury removal

Mercury is a non-degradable toxic heavy metal derived mainly from natural and man-made pollution
.
It occurs in a variety of forms, with methylmercury being the most toxic, with its bioconcentration and biomagnification properties causing severe damage
to the nervous system.
In anaerobic environments, mercury ions are converted to the more toxic methylmercury
.
The treatment of mercury ion pollution is conducive to reducing the formation of methylmercury and achieving the remediation
of mercury pollution.
The repair of mercury ions mainly includes adsorption fixation and reduction removal
.

Jiang Xin's research team from Nanjing Institute of Soil Science, Chinese Academy of Sciences recently selected the nonlinear optical substance DMABR (p-dimethylaminobenzyl Rhodenin), using silicate mineral sepiolite as the carrier, bromobutane and bromodecane as quaternary ammonium salt modification raw materials, and successfully prepared silicon substrate materials (SD, SD-BB and SD-DB) with high efficiency to remove mercury pollution through a green method of hydrothermal synthesis, realizing the adsorption, fixation and reduction removal
of mercury ions by organic source electron donors 。 Sepiolite loading can increase the polarity and stability of DMABR; The quaternary ammonium salt modification of the sepiolite carrier was realized by the direct addition of quaternary ammonium raw materials atypical tertiary amine DMABR and bromoalkanes
.
As a typical nonlinear optical material, DMABR contains a functional group structure with high affinity for mercury ions, which is conducive to strong adsorption and complexation
of mercury ions.
Its large molecular polarizability and the presence of intramolecular electron transfer (ICT) give non-localized electrons in nonlinear optical materials the ability to transfer non-localized electrons to the main complexing functional groups, and realize the complexation and reduction
of mercury ion adsorption.
Based on infrared spectroscopy, scanning electron microscopy, UV/VIS absorption spectroscopy and Raman spectroscopy, DMABR is loaded on sepiolite with hydrogen bonds and N-Si covalent bonds after a one-step hydrothermal synthesis process, and is uniformly dispersed
by the debundled sepiolite fibers.
The SD material exhibits high removal of mercury and has very good cycle stability
.
The SD material still exhibits excellent removal results
under the influence of interfering metal ions and organic components (humic acid).
Based on X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy and Raman spectroscopy, the research team further revealed the mechanism of mercury pollution remediation of the material: mercury ions are first complexed with C, -COO- and N to form satellite peaks with peak types; With the increase of mercury ion concentration, the long-chain polysulfur (L-S_x, S 6~8 or S_6~8 n-) of SD material decomposes into S 2₂- under mercury ion stress, further forming^α-HgS, and the coordination number on N increases, resulting in asymmetric complexation products.
Elemental mercury is produced with the reduction, and the reduction repair
is realized.
Finally, based on the optical properties of DMABR itself, the research team further explained the kinetic mechanism
of mercury ion remediation and removal by gradually increasing the mercury ion concentration.
The SD material enables mercury adsorption fixation and reduction removal, while its fluorescence signal indicates the end point
of adsorption.
This study provides a theoretical basis for the adsorption and reduction and remediation of mercury pollution based on organic source electron donors, and also provides a reference
for the biochemical earth cycle of pollutants in which nonlinear optical materials may participate.

The relevant results were recently published in the Chemical Engineering Journal, with master student Wang Yuncheng as the first author and senior engineer Bian Yongrong as the corresponding author
of the paper.
The research work was supported
by the National Key Research and Development Project and the National Natural Science Foundation of China.

Links to papers