Data on structural and composition-related merits of gC3N4 nanofibres doped and undoped with Au/Pd at the atomic level for efficient catalytic CO oxidation

Precise design of graphitic carbon nitride (gC3N4) nanostructures is of grand importance in different catalytic applications. This article emphasizes additional data on the fabrication of metal-free gC3N4 nanofibres (gC3N4NFs) and its associated structural and composition analysis compared with Au/Pd co-doped gC3N4 nanofibres (Au/Pd/gC3N4NFs). The data is including the typical fabrication process of metal-free gC3N4 nanofibers and its SEM, TEM, and element mapping analysis beside Raman, and FTIR spectra relative to Au/Pd/gC3N4NFs. We also investigated the catalytic CO oxidation durability testes on Au/Pd/gC3N4NFs compared to Pd/gC3N4NFs and Au/gC3N4NFs. The presented data are associated with the research article entitled “Rational synthesis of one-dimensional carbon nitride-based nanofibers atomically doped with Au/Pd for efficient carbon monoxide oxidation.” [1].


Data
The presented herein data provides deep insights on the rational synthesis of metal-free gC 3 N 4 NFs and its correlated analysis relative to Au/Pd/gC 3 N 4 NFs. This is in addition to the CO oxidation durability of Au/Pd/gC 3 N 4 NFs and its compositional analysis after CO oxidation reaction. Particularly, the data involves the SEM, TEM, and elemental mapping images of gC 3 N 4 NFs (Fig. 1), while the FTIR and Raman spectra of gC 3 N 4 NFs compared to Au/Pd/gC 3 N 4 are represented in Fig. 2 and Fig. 3, respectively. Meanwhile, the CO oxidation stability testes carried out on Au/Pd/gC 3 N 4 NFs, Pd/ gC 3 N 4 NFs, and Au/gC 3 N 4 NFs beside their loss in the complete conversion temperature (T 100 ) are shown in (Fig. 4). This is alongside the Energy Dispersive X-ray Analysis (EDX) analysis of Au/Pd/gC 3 N 4 NFs after the CO oxidation durability testes (Fig. 5) and the schematic reveals the synthetic mechanism process of Au/Pd/gC 3 N 4 NFs in (Fig. 6). Fig. 1 shows the SEM and TEM images of metal-free gC 3 N 4 NFs typically synthesized by the slow dispersion of melamine (1 g) in an aqueous solution of isopropanol (30 mL, 99%) under stirring at 40 C. Then, an aqueous solution of nitric acid (HNO 3 , 60 mL, 0.3 M) was added to the previous solution under stirring at 40 C. The as-formed white precipitate was filtered and washed with isopropanol solution before being dried at 100 C for 12 h. Finally, the obtained powder was subsequently annealed under nitrogen at 550 C for 2 h (5 C min À1 ).

Synthesis of metal-free gC 3 N 4 NFs
Specifications Table   Subject area  Chemistry  More specific subject area  Catalysis  Type of data  Scheme, Tables, Figures  How data was acquired  Transmission electron microscope ((TEM), TecnaiG220, FEI, Hillsboro, OR, USA) equipped with Energy Dispersive X-Ray Analysis (EDX), scanning electron microscope ((SEM), Hitachi S-4800, Hitachi, Tokyo, Japan), Raman spectroscopy (PerkinElmer Raman Station 400 spectrometer), and CO oxidation stability tests (online gas analyzer IR-200, Yokogawa, Japan). Data format The presented raw data are imaged and analyzed.

Experimental factors
The CO oxidation durability tests were carried out under continuous gas mixture gas flow while heating from room temperature to 300 C.

Experimental features
The CO conversion durability tests were benchmarked as a function of temperature and metal dopants. Data source location Center for advanced materials, Qatar University, Doha P.O. Box 2713, Qatar.

Data accessibility
The data are available in this article Related research article Rational synthesis of one-dimensional carbon nitride-based nanofibers atomically doped with Au/Pd for efficient carbon monoxide oxidation." [1] Value of the Data The present data allowed controlling the shape and composition of gC 3 N 4 nanofibers that paves the way for scientists to tailor and decipher the formation mechanism of gC 3 N 4 . This data allowed understanding the architectural and compositional related merits of the gC 3 N 4 -based materials; thus, it is beneficent for controlling their properties for various catalytic applications. Investigating the catalytic CO oxidation stability of Au/Pd/gC 3 N 4 NFs is essential for its scaling up for the commercial applications. These data can serve as a benchmark for further development of new gC 3 N 4 -based nanostructures for CO conversion to CO 2 and other gas conversion reactions.
The fabrication of Au/Pd/gC3N4NFs was done according to the same procedure of metal-free gC3N4NFs but in presence of Au and Pd precursors before the addtion of HNO 3 (see Ref. [1] for more information).
The SEM image clearly shows the formation of uniform one-dimensional fiber-like morphology in high yield (nearly 100%) without resolving any other undesired shapes such as spherical and sheets (Fig. 1a). The average length of thus formed nanofibers obtained from the TEM is about 10 mm. The TEM image further confirmed the formation of a nanofiber structure with smooth surfaces and had an average width of nearly 80 ± 2 nm (Fig. 1b). The element mapping analysis indicated the presence of both C and N with an atomic ratio of 41 and 59, respectively ( Fig. 1c and d).

Chemical structure and composition analysis
The chemical bonds and the functional groups of both Au/Pd/gC 3 N 4 NFs and gC 3 N 4 NFs were evaluated using the Fourier transform infrared (FTIR) analysis. Both Au/Pd/gC 3 N 4 NFs and gC 3 N 4 NFs revealed the peaks attributed to the stretching vibration of triazine at 810 cm À1 and several peaks for CeN heterocycles from 1000 to 1750 cm À1 (Fig. 2) [2]. The weak bands observed between 2900 and 3300 cm À1 are assigned to the NeH vibrations at the edges of gC 3 N 4 -based material. The anchoring of  Fig. 3a shows the Raman spectra of gC 3 N 4 NFs, compared to Au/Pd/gC 3 N 4 NFs. Both materials revealed a sharp peak at 1555 cm À1 of graphitic (G) band, which indicates the high degree of graphitization of the as-obtained materials [4,5]. The G band of Au/Pd/gC 3 N 4 NFs was slightly positively shifted relative to that of gC 3 N 4 NFs, implying its higher strained effect. Additionally, both materials     displayed a small spectrum at 2690 cm À1 of (Gˋpeak), resulting from the disordered surface. Fig. 3b shows the typical spectrum of melamine starting from 500 until 3000 cm À1 , which are dissimilar to those recorded for Au/Pd/gC 3 N 4 NFs and gC 3 N 4 NFs [1e3]. Table 1 summarizes the identification and position for Raman spectra of Au/Pd/gC 3 N 4 NFs and gC 3 N 4 NFs.

CO oxidation stability tests
The CO oxidation is of particular interest in wide varieties of industrial, biological, and environmental remediation applications [2,6e8]. Thus, it is essential to develop efficient and durable catalysts for CO oxidation reaction to convert highly toxic CO gas into less toxic gasses or other fuels [1e4,8e11]. After determination, the complete CO conversion temperature (T 100 ) on the as-synthesized Au/Pd/ gC 3 N 4 NFs, Pd/gC 3 N 4 NFs, and Au/gC 3 N 4 NFs, the long-term durability tests were investigated at their T 100 for 48 h. In particular, the catalysts were exposed to the gas mixture consisting of CO (4%), O 2 (20%), and Ar (76%) with a total flow of 50 mL min À1 and the temperature was increased steadily (5 C min À1 ) until the T 100 of each catalyst. Then, the percentage of CO conversion was monitored through an online multichannel infrared gas analyzer (IR200, Yokogawa, Japan). Following the durability tests, the CO conversion efficiencies were measured again through the pretreatment at 250 C under an O 2 flow of 50 mL min À1 , and H 2 (30 mL min À1 ) for 1 h. Then, each catalyst was exposed to a gas mixture of CO (4%), O 2 (20%), and Ar (76%) with a total flow of 50 mL min À1 , while heating from the room temperature till the complete CO conversion occurred. Fig. 4 shows the CO oxidation durability of Au/Pd/gC 3 N 4 NFs compared to Pd/gC 3 N 4 NFs, and Au/ gC 3 N 4 NFs. In particular, after the accelerated durability tests, Au/Pd/gC 3 N 4 NFs reserved its initial CO oxidation activity without any noticed loss (Fig. 4a); meanwhile, Pd/gC 3 N 4 NFs loss is around 7% (Fig. 4b) and Au/gC 3 N 4 NFs lose about 11% (Fig. 4c). However, from the light-off curves for the CO conversion durability expressed as a function of time, all materials did not show any noticed change in the CO oxidation kinetics. To this end, the estimated T 100 after the stability cycles on Au/Pd/gC 3 N 4 NFs, Pd/gC 3 N 4 NFs, and Au/Pd/gC 3 N 4 NFs were about 146 C, 203 C, and 246.4 C, respectively (Fig. 4d).

Compositional stability
After the CO oxidation durability tests, the elemental composition of Au/Pd/gC 3 N 4 NFs was carried out using the EDX analysis to examine any changes in the composition. Fig. 5 shows the EDX analysis of Au/Pd/gC 3 N 4 NFs, which revealed the presence of C, N, Au, and Pd without any changes or undesired phases. The detailed atomic ratios of C/N/Au/Pd are about with 39/60/0.51/0.44, respectively.
Chemically speaking, and looking deeply to the formation mechanism, Au/Pd/gC 3 N 4 NFs combine between the unique physicochemical properties of gC 3 N 4 and catalytic merts of Au/Pd atomic dopants [1e4,12e15]. Particularly, the strong binding affinity between N-atoms of melamine and metal atoms Au/Pd led to their chemical bonding in the form of -N-Au and -N-Pd during the polymerization step resulting in a coherent distribution through the skeletal structure of gC 3 N 4 NFs (Fig. 6) [1e4]. These chemical legends not only allow the homogenous distribution of Au/Pd inside the nanofibers but also stabilize them against the detachment and agglomeration, during the CO oxidation reaction.

Acknowledgments
This publication was supported by Qatar University Internal Grant No. IRCC-179. The findings achieved herein are solely the responsibility of the authors. Table 1 The position of the resolved Raman spectra of the as-prepared materials.