Effect of montmorillonite and humic acid on cotransport of g-C3N4 and lead: The role of triazine ring in lead adsorption and deposition in soil components

In the past few years, Graphitic carbon nitride (g-C3N4) has been produced on a large scale and has been widely used because of its excellent optical properties and physicochemical stability. It is easy to ignore the risk of g-C3N4 transport in the environment, including soil and groundwater, due to the non-toxicity of metals. Based on this situation, we investigated the effects of pumping flow rate, ionic strength, and the presence of lead (Pb) on the transport behavior of g-C3N4 in quartz sand, montmorillonite, and humic acid-coated sand through column experiments. The retention of g-C3N4 in the media and the adsorption mechanism of Pb onto g-C3N4 were analyzed by FTIR and XPS. The results showed that fast flow rate and low ionic strength were favorable conditions for the transport of g-C3N4. The cotransport experiment results showed that Pb reduced the outflow of g-C3N4 by more than 50%. Contrarily, 6.95%, 0.43%, and 11.01% Pb were hindered in quartz sand, montmorillonite, and humic acid-coated sand due to the presence of g-C3N4. Compared with the uncontaminated media, the recoveries of g-C3N4 in Pb contaminated quartz sand, montmorillonite, and humic acid-coated sand were reduced by 0.34%, 5.86%, and 15.34%, respectively. Concomitantly, which were attributed to the special triazine ring structure and the abundant bonding modes with soil components and Pb, g-C3N4 particles were easier to deposit in montmorillonite and humic acid-coated sand, and could be used as the carrier to release 6.70% and 5.64% Pb from contaminated quartz sand and humic acid-coated sand.& COPY; 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

Graphitic carbon nitride (g-C3N4) has been widely used due to its excellent optical properties and physicochemical stability. The risk of g-C3N4 transport in the environment has been overlooked, but this study investigated its transport behavior in various media. The results showed that flow rate and ionic strength influenced the transport, and the presence of lead (Pb) affected the outflow of g-C3N4. The unique structure of g-C3N4 particles allowed them to deposit in certain media and act as carriers for Pb release.