Copper species modified carbon nitride as fluorometric detection of nitrate and nitrite ion and as catalyst for reduction of 4- nitrophenol

Abstract

The presence of N-containing compounds such as nitrate (NO3 -), nitrite (NO2 -), and nitrophenol (NP) in industrial wastewater has aroused great interest due to the toxicity of these compounds. Therefore, determination and removal of these compounds are imperative. In this study, copper species modified carbon nitride composites were developed for detection of NO3 - and NO2 - ions and reduction of 4-NP. Bulk carbon nitride (BCN) was synthesized using urea as precursor via thermal polymerization process at 823 K for 4 hours, while mesoporous carbon nitride (MCN) was prepared using the same approach as the preparation of BCN with the addition of silica nanoparticles as a hard template. In order to improve the sensing and catalytic performance of the CN, copper acetylacetonate (Cu(acac)2) was added by impregnation method to produce Cu(II)acac(x)/CN composites (x = 0.1, 0.5, 4, 6, 8, 10, 12 mol%). The composites then underwent thermal oxidation to produce CuO(x)/CN and thermal hydrogenation to produce Cu(x)/CN composites. Based on the Xray diffraction (XRD) and Fourier transform infrared (FTIR) spectra, the structure of BCN and MCN did not change after loading of copper species. The diffuse reflectance ultraviolet-visible (DR UV-Vis) spectra of copper species modified CN indicated the ligand-to-metal charge transfer (LMCT) bands at around 277 and 300 nm and d-d transition of Cu2+ above 400 nm. BCN and MCN exhibited three excitation peaks at 277, 315, and 369 nm owing to the presence of C=N, C=O, and C-N groups, respectively, while there was only one emission peak observed at 450 nm. The emission intensity decreased with increasing copper species loading, suggesting copper species were deposited on the surface of CN and interact with all active sites of the CN. The performances of BCN, MCN, and their composites as fluorometric detection of NO3 - and NO2 - were studied at concentration ranges of 3000-18000 mol and 5-40 mol, respectively. CuO(0.5)/BCN and CuO(0.1)/MCN composites exhibited the highest Ksv values for detection of NO3 - and the NO2 - which were 22 and 2.3 times higher than that of BCN. The catalytic degradation of 4-NP was carried out in the presence of Cu(II)acaca(x)/BCN composites as catalyst and NaBH4 at room temperature. Cu(II)acac(10)/BCN showed the highest catalytic performance with 97% reduction of 4-NP after 6 minutes. This study demonstrated that the copper species modified CN composite is a promising material for fluorometric detection of NO3 - and the NO2 - ions and catalyst for reduction of 4-NP.