Abstract
Three types of graphitic carbon nitride (gCN) nanosheets were derived from direct thermal condensation of urea, melamine, and dicyandiamide, respectively. As the sample (uCN) synthesized from urea exhibited porous morphology and highest surface area among other gCN, anatase TiO2 nanoparticles were then in-situ deposited on uCN via solvothermal process without further calcination. The resultant Ti/uCN_x samples remained with higher surface area and exhibited visible-light activity. The derived band structure of each sample also confirmed its ability to photoreduce CO2. XPS results revealed surface compositions of each sample. Those functional groups governed adsorption of reactant, interfacial interaction, electron transfer rate, and consequently influenced the yield of products. Carbon monoxide and methanol were detected from LED-lamp illuminated samples under appropriate moisture content. Samples with higher ratio of terminal amine groups produced more CO. The presence of hydroxyl groups promoted the initial conversion of methanol. The obtained Ti/uCN_0.5 and Ti/uCN_1.5 samples exhibited better quantum efficiency toward CO2 conversion and demonstrated stability to consistently produce CO under cycling photoreaction.
Highlights
The polymeric semiconductor, graphitic carbon nitride, has attracted much attention due to its narrow and tunable bandgap for various photocatalytic applications [1,2,3,4,5]
The characteristic (002) peak at around 27.5◦ is ascribed to the stacking of conjugated aromatic structure of graphitic carbon nitride (gCN) with the interlayer distance of 0.324 nm [2,5,19]
The decorated anatase TiO2 nanoparticles on each gCN nanosheets can be observed from the following TEM images
Summary
The polymeric semiconductor, graphitic carbon nitride (gCN), has attracted much attention due to its narrow and tunable bandgap for various photocatalytic applications [1,2,3,4,5]. To improve its photocatalytic activity, the morphology of gCN has been modified or various heterojunctions have been developed to increase surface area of gCN or to more effectively separate photoinduced charge carriers on gCN. The product yield or selectivity was tunable by changing the relative ratio of gCN and TiO2 [16,17]. Even a relatively porous gCN with larger surface area showed higher photoactivity on CO2 conversion under visible light [18]
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