Phenyl-modified carbon nitride based multifunctional gel for the detection, adsorption, photocatalytic reduction and recycling of chromium(VI) in wastewater

It is of vital significance to explore effective and economical multifunctional materials for the detection, remediation and recycling of heavy metal (Cr(VI)). Herein, two-dimensional (2D) phenyl-modified carbon nitride (PCN) polymer was prepared through thermal polymerization of phenylguanidine carbonate. The incorporation of phenyl groups endowed PCN polymer with both strong green fluorescence and high photocatalytic activity for the reduction of Cr(VI). An multifunctional gel for simultaneous detection, adsorption, photo-reduction and recycling of Cr(VI) was further prepared by assembling PCN with polyethyleneimine–N,N’-methylenebisacrylamide (PEI-MBA) gel. PCN-PEI-MBA gel showed a sensitive fluorescence / colorimetric dual-mode detection of Cr(VI). Meanwhile, PCN-PEI-MBA gel displayed preeminent adsorption capacity of 3055.9 mg g−1, surpassing previously reported adsorbents. Under visible-light irradiation, the absorbed Cr(VI) in PCN-PEI-MBA gel was photocatalytically reduced into Cr(III) with visual real-time monitoring the detoxification process and Cr(III) can be further recycled as Cr2O3 by calcination of PCN-PEI-MBA gel. Finally, PCN-PEI-MBA gel was utilize to adsorb and recycle Cr(VI) from the chromium-plating wastewater and detect the concentration of remaining Cr(VI) in the wastewater. This work provides an all-in-one treatment strategy for the detection, remediation and resource recycling of Cr(VI) in practical wastewater.