Functional Modification Of G-C₃N₄ And Its Application

Cycloaddition of carbon dioxide and epoxides to yield cyclic carbonate under solvent-free conditions is an ecofriendly way to use CO₂ in environmental science and green chemistry.In this work,we report that metal-free,boron doped graphitic carbon nitride?B-g-C₃N₄?can be a potential catalyst for such reactions.B-g-C₃N₄,especially if supported on high-surface-area ordered mesoporous silica SBA-15?i.e.,B-g-C₃N₄/SBA-15?,is highly active for cycloaddition of CO₂ and styrene oxide?SO?to yield styrene carbonate?SC?,with conversion and selectivity above 95%,under solvent-free conditions.The material can be reused for at least 6 cycles,without appreciable loss of activity.That is due to its increased surface area,and especially the Lewis acid-Lewis base duality,induced by the doping of B atoms.A mechanism based on dual active sites is proposed,where the acid site is used for SO activation,and the basic site for CO₂ activation.The metal-free B-g-C₃N₄ with dual active sites provides an effective option for cheap,green and efficient catalysts for CO₂ utilization.Mesoporous graphitic carbon nitride?meso-g-C₃N₄?was synthesized using Ludox HS-40 as template and guanidine hydrochloride?GndCl?as precursor,and used for the first time as adsorbent for adsorption removal of methylene blue?MB?from aqueous solution.X-ray diffraction,Fourier transform infrared spectroscopy,Transmission electron microscopy,N₂ physisorption isotherms,X-ray photoelectron spectroscopy and temperature programmed desorption of CO₂?CO₂-TPD?were used to characterize the materials.Results showed that meso-g-C₃N₄₀.7,obtained at mass ratio of silica to GndCl equals 0.7,exhibit the best ability for adsorption removal of MB,due to its high surface area,large pore size and pore volume.The maximum capacity of meso-g-C₃N₄₀.7 for MB adsorption is 1.2 * 10^-4 mol/g,which is four and two times higher than activated carbon?AC?and silica SBA-15,respectively.Furthermore,the material can be re-used for 5 times with no appreciable loss of activity.The highly efficient and reusable ability suggests that meso-g-C₃N₄₀.7 is a promising industrial adsorbent for adsorption removal of MB from water.As we know,meso-g-C₃N₄ is an effective catalyst for the Friedel–Crafts reaction due to its electronic properties and high surface area.But the Preparation process of mesoporous samples of C₃N₄ is very tedious and the removal of the silica host matrices involves aqueous ammonium bifluoride?NH₄HF₂?or hydrogen fluoride?HF?,which is hazardous and not environmentally friendly.So in order to abandon the tedious prepare program and the toxic aqueous hydrogen fluoride,a reliable and facile strategy to modify g-C₃N₄ is needed without decrease of the activation.So in this work,series of different metal ion?K,Zn and Fe?doped g-C₃N₄ and supported g-C₃N₄ were synthesized via thermal polymerization of dicyandiamide and KCl,ZnCl₂,FeCl₃ and SBA-15 in N2 atmosphere and tested for their catalytic activity for acylation of benzene.For a given catalyst weight,Zn-g-C₃N₄ showed the best catalytic performance among the modified samples tested with close to 100% selectivity to benzoyl in heptane under relatively mild reaction conditions at room temperature.