Data on the catalytic CO oxidation and CO2 reduction durability on gC3N4 nanotubes Co-doped atomically with Pd and Cu

Understanding the fabrication mechanism of graphitic carbon nitride (gC3N4) nanostructures is critical for tailoring their physicochemical properties for various catalytic applications. In this article, we provide deep insights into the optimized parameters for the rational synthesis of one-dimensional gC3N4 atomically doped with Pd and Cu denoted as (Pd/Cu/gC3N4NTs) and its fabrication mechanism. This is in addition to the CO oxidation durability along with the electrochemical and photoelectrochemical CO2 reduction durability of Pd/Cu/gC3N4NTs. The presented herein results are correlated to the research article entitled “Precise Fabrication of Porous One-dimensional gC3N4 Nanotubes Doped with Pd and Cu Atoms for Efficient CO Oxidation and CO2 Reduction (Kamel Eid et al., 2019).


Data
The presented data article is associated with the research article (Kamel Eid et al., 2019 [1]). This includes (i) the SEM and TEM images of metal-free gC 3 N 4 , (ii) the TEM images of Pd/Cu/gC 3 N 4 prepared in different morphologies, (iii) the CO oxidation durability of Pd/Cu/gC 3 N 4 NTs, Pd/gC 3 N 4 NTs, and Cu/ gC 3 N 4 NTs, (iv) the electrocatalytic and photoelectrochemical CO 2 reduction of Pd/Cu/gC 3 N 4 NTs, and (v) the XRD, EDX, and TEM image of Pd/Cu/gC 3 N 4 after the CO durability testes.

CO oxidation
We tested the CO oxidation reaction in a fixed bed quartz tubular reactor connected to an online gas analyzer (IR200, Yokogawa, Japan) in the presence of 50 mg of each catalyst. Initial pretreatment was carried out at 250 C under an O 2 flow of 50 mL min À1 for 1 h, and then H 2 (30 mL min À1 ) for 1 h. Following that, the catalysts were exposed to the gas mixture involving of 4% CO, 20% O 2 , and 76% Ar with a total flow of 50 mL min À1 under continuous heating from 25 C to 400 C (5 min À1 ) [1e5]. The percentage of CO conversion (% CO) was calculated using the following equation: %CO ¼ ½ðCO in À CO out Þ = CO in Â 100 (1) where CO in is, the input quantity and CO Out is the output quantity.

Data format
The obtained data are imaged and analyzed. Experimental factors The thermal CO oxidation stability tests were measured under continuous gas mixture flow while heating (25e300 C). The electrocatalytic CO 2 reduction durability tests were benchmarked at the room temperature in 0. Value of the data Optimization of the fabrication process of gC 3 N 4 nanostructures doped with binary metals is essential in various catalytic applications.
Understanding the fabrication mechanism of Pd/Cu/gC 3 N 4 NTs is essential for tailoring their physicochemical and catalytic properties for various applications. The catalytic CO oxidation and CO 2 reduction durability of Pd/Cu/gC 3 N 4 NTs are central factors in commercial applications.
These data may open new avenues on using gC 3 N 4 -based materials for gas conversion reactions.

Electrochemical reduction of CO 2
The cyclic voltammogram (CVs), linear sweep voltammogram (LSV), and electrochemical impedance spectroscopy (EIS) measurements were measured on Gamry electrochemical analyzer (reference 3000, Gamry Co., USA) using a three-electrode system composed of a Pt wire (counter electrode), Ag/ AgCl (reference electrode), and glassy carbon ((5mm) working electrode). The CVs, LSVs, and EIS were measured in a CO 2 -saturated aqueous solution of 0.5 M NaHCO 3 at a sweep rate of 50 mV s À1 . In the photoelectrochemical measurements, the light source was ozone-free xenon lamp (100 W, Abet Technologies, USA) with fluorine-doped tin oxide as a working electrode in a Quartz photo-glass cell (50 mm Â 50 mm). The catalyst loading amount of each catalyst on the working electrode was fixed to 10 mg cm À2 using. After deposition of each catalyst on the working electrodes, a 5 mL of Nafion solution (1 wt %) was added on each electrode and left to dry completely under vacuum at 80 C before the measurements.
Scheme 1 shows the fabrication process of Pd/Cu/gC 3 N 4 NTs, including the initial slow mixing of melamine in an aqueous solution of ethylene glycol solution, contains Pd-and Cu precursors [3]. Then, nitric acid was added dropwise to slowly deprotonate melamine and facilities the polymerization step Scheme 1. Schematic shows the synthesis process of Pd/Cu/gC 3 N 4 NTs. to polymeric gC 3 N 4 , followed by annealing at elevated temperature to allow the carbonization process and formation of gC 3 N 4 NTs doped with Pd and Cu. Fig. 1 shows the histogram chart of Pd/Cu/gC 3 N 4 NTs. The widths of thus obtained Pd/Cu/gC 3 N 4 NTs ranged from 60 to 90 nm. The average width of thus formed nanotubes is nearly 80 nm. Fig. 2 shows the SEM and TEM images of metal-free gC 3 N 4 NTs that were prepared by the same method of Pd/Cu/gC 3 N 4 NTs but in the absence of Pd and Cu precursors. Fig. 2a reveals the SEM image of gC 3 N 4 NTs formed in high yield (nearly 100%) of nanotubes shape. The nanotube shape was uniform and mono distributed with an average width of 78 nm and an average length of 1.4 mm. The TEM image shows the absence of any undesired nanostructures such as spherical nanoparticles or other shapes. Under the same conditions and parameters of nanoflakes, the quick addition of nitric acid produced sheet-like nanostructures. This arose from the quick deprotonation and polymerization process via rapid addition of nitric acid (Fig. 3b). Reducing the concertation of nitric acid to 0.03 M with fixing all other conditions and parameters formed aggregated and non-uniform Pd/Cu/C 3 N 4 nanotubes (Fig. 3c). Using isopropanol solution instated of ethylene glycol led to the production of Pd/Cu/C 3 N 4 nanofibers in line with our previous reports (Fig. 3d) [2]. The as-formed nanofibers were highly uniform with average dimensions of 1.5 ± 0.2 mm in length and 80 ± 3 nm in width. Fig. 3e shows the formation of gC 3 N 4 nanosheets decorated with aggregated Pd/Cu nanoparticles formed through increasing the concertation of Pd/Cu to 60 mM instead of 20 mM with fixing all other conditions. Similarly, decreasing the concertation of Pd/Cu to 40 mM drove the formation of nanosheets decorated with uniform Pd/Cu nanoparticles (Fig. 3f). These results warranted that the formation of Pd/Cu/C 3 N 4 NTs is highly sensitive to the concentration of reactants and their mixing conditions. In particular, the addition of melamine and nitric acid should be sluggish to provide enough time for a consistent polymerization into uniform nanotubes. Nitric acid facilitates the deprotonation of active eNH 2 groups of melamine and allowing the conversion of melamine into melem and then to polymeric gC 3 N 4 composed of triazine-based units after carbonization at an elevated temperature [1e5]. Meanwhile, the concertation of Pd/Cu precursors should be lower to be anchored on the N-

CO oxidation stability tests
The CO oxidation durability is an important factor in large-scale environmental and industrial applications [1e4]. Fig. 4 shows the accelerated durability tests of Pd/Cu/gC 3 N 4 NTs, Pd/gC 3 N 4 NTs, and Cu/gC 3 N 4 NTs measured for ten cycles at their complete CO conversion temperature (T 100 ). The results show that Pd/Cu/gC 3 N 4 NTs is more durable than both Pd/gC 3 N 4 NTs and Cu/gC 3 N 4 NTs. Particularly, the CO oxidation kinetics and T 100 of Pd/Cu/gC 3 N 4 NTs were almost maintained without any significant changes (Fig. 4a). Meanwhile, the T 100 of Pd/gC 3 N 4 NTs, and Cu/gC 3 N 4 NTs increased only by around 11 C (Fig. 4b) and 25 C (Fig. 4c), respectively. However, the CO oxidation kinetics did not decrease substantially on both Pd/gC 3 N 4 NTs and Cu/gC 3 N 4 NTs, as shown in their light-off curves (Fig. 4b and c).
The sample was dispersed in ethanol and sonicated for 3 min and then mounted on a carbon-coated TEM grid. Fig. 5 reveals the TEM images of Pd/Cu/gC 3 N 4 NTs before (Fig. 5a) and after the CO oxidation stability tets (Fig. 5b). Comparing the TEM image of Pd/Cu/gC 3 N 4 NTs before and after the CO oxidation durability testes, we found that the structural stability of nanotube shape is fully maintained without any changes. Therefore, the nanotube morphology did not change after ten durability cycles. Fig. 6a shows the XRD analysis of Pd/Cu/gC 3 N 4 NTs after the CO durability tests, which displayed the one diffraction peak at 27.01 assigned to {002} facet and one peak at 13.15 attributes to{100} facet of gC 3 N 4 nanostructure similar to those obtained for Pd/Cu/gC 3 N 4 NTs before the CO durability tests. Thus,  the XRD result indicates that Pd/Cu/gC 3 N 4 NTs reserved its crystallinity after the CO oxidation durability tests. The EDX analyses after CO stability testes is carried out to confirm the compositional durability of Pd/Cu/gC 3 N 4 NTs (Fig. 6b). The results showed the presence of C, N, Pd, and Cu with atomic contents of 58, 40.9, 0.5, and 0.6, respectively (Fig. 6b). Thus, the EDX result implies that Pd/Cu/gC 3 N 4 NTs kept its composition without any deterioration, owing to the homogenous distribution of Pd and Cu inside the carbon matrix. Table 1 shows the comparison between the catalytic CO oxidation activity of our newly designed Pd/ Cu/gC 3 N 4 NTs and the previously reported catalysts such as Pd-based, Au-based Cu-based, Pt-based, and Mn-based. The complete conversion temperature of our obtained Pd/Cu/gC 3 N 4 NTs was significantly lower than that of all the catalysts reported in the literature as shwon in Table 1 in addition to the low cost of our catalyst that was made of nearly 99% gC 3 N 4 NTs and 1% Pd/Cu.
The TEM, XRD, and EDX results confirmed the structural and compositional stability of the assynthesized Pd/Cu/gC 3 N 4 NTs after the CO oxidation stability tests. This probably originates from coupling between the unique physicochemical properties of 1D gC 3 N 4 nanotubes (e.g., stability, massive accessible active sites, thermal stability nearly up to 600 C, and chemical stability in various solvents) and the inherent catalytic merits of Pd/Cu (eg., electronic effect, synergetic effect, strong adsorption/activation/dissociation for CO/O 2 , and high tolerance for CO 2 product) [1e5,13e16]. Chemically speaking, the atomic doping of gC 3 N 4 NTs with Pd and Cu stabilizes them against aggregation as well as protecting their active catalytic sites from the blocking by the reaction intermediates or products. Scheme 2 shows the formation process and mechanism of typically prepared Pd/Cu/gC 3 N 4 . The strong binding affinity between N-atoms of melamine and Pd/Cu facilitate adsorption and anchoring of both Pd and Cu on N-atoms during the polymerization step that led to the homogenous atomic distribution of Pd, and Cu on the N-atoms of gC 3 N 4 . Fig. 7a shows the CVs for CO 2 reduction measured under various sweeping rates ranged from 25 to 200 mV s À1 , which showed the steady enhancement in the current density with increasing the scan rate. The relationship between the obtained current densities and the square root of scan rates is linear (Fig. 7b).
The electrocatalytic and photo-electrochemical CO 2 reduction durability tests were carried out on Pd/Cu/gC 3 N 4 NTs via measuring the chronoamperometric test (I-T) for 30 min in CO 2saturated an aqueous solution of 0.5 NaHCO 3 at 50 mV s À1 . Then the CVs curve were measured again in CO 2 -saturated an aqueous solution of 0.5 NaHCO 3 at 50 mV s À1 . The CVs curves showed that Pd/Cu/gC 3 N 4 NTs kept its initial electrocatalytic CO 2 reduction activity (Fig. 7c) without any significant deterioration in the current density, reduction kinetics, and reduction potential (Fig. 7d), [17]. Fig. 8 depicts the gas chromatography result that was obtained after calibration relative to pure formic acid and methanol under the same conditions. The results demonstrated the presence of formic acid as the main product as well as methanol as an inferior product (Fig. 8). Therefore, the gas chromatography indicates the ability of Pd/Cu/gC 3 N 4 NTs to reduce CO 2 electrochemically to formic acid at room temperature.