Preparation and characterization of expanded g-C3N4 via rapid microwave-assisted synthesis

Abstract

Microwave assisted heating was successfully employed in significantly accelerated preparation of expanded g-C3N4 via thermal condensation of urea. Comparing to typical synthesis route, rapid microwave assisted heating enables not only shorten synthesis time from hours to few minutes but obtain reasonable yield of the product also. Use of ceramic kiln “hotpot” with intern covered with absorbing layer plays the key role in transformation of the microwave energy into heat. Heat energy in form of radiation from the glowing inner layer surface is focused into the internal volume of the kiln resulting in extremely fast temperature increase. Thus, microwave non-absorbing starting material is extremely fast heated. The effects of reaction conditions on the structural, morphological, optical and photocatalytic properties of prepared g-C3N4 were investigated in detail. Having similar specific surface area but much larger particles than its conventionally prepared analogue, the microwave prepared material can be classified as expanded g-C3N4. Moreover, by simply changing the reaction time, photoluminescence emission of the material can be continuously tuned covering the blue to green light region of visible light. The photocatalytic degradation of Methyl Violet 2B reveal that the adsorption capacity of samples increases with processing time while the rate constant slightly decreases. It can be ascribed to the expansion of the internal surface which results in its worse availability to the diffusion transport of the dye to active sites. It also impedes photodegradation products removal. The synthesis technique described here could be considered applicable to starting materials, which cannot be sufficiently heated by microwave absorption directly.