SYNTHESIS, CHARACTERIZATION, AND PHOTOCATALYTIC EFFICIENCY OF A NEW SMART PdO OXIDE NANOMATERIALS FOR USING IN THE RECYCLING AND SUSTAINABLE WASTEWATER TREATMENT

Nanostructured PdO materials with promising catalytic properties were successfully synthesized by the controlled thermal decomposition in air of three Pd(II) complexes containing Pd(II) ion, ofloxacin drug and amino acid. The Pd(II) complexes which were used as precursors were [Pd(OFL)(Gly)]Cl, [Pd(OFL)(Ala)]Cl, and [Pd(OFL)2]Cl2, where Gly is glycine amino acid, Ala is alanine amino acid, and OFL is ofloxacin. Structural and morphological properties of the synthesized PdO materials were obtained using FTIR, XRD, SEM, and EDX techniques. The XRD results confirm the tetragonal structure of PdO. The obtained PdO materials were tested as a catalyst for the heterogeneous degradation of H2O2 solution. The results revealed that PdO could effectively degrade H2O2.

In this work, nanostructured PdO materials were prepared via the controlled thermal decomposition at low temperatures in air of three Pd(II) complexes containing Pd(II) ion, 108 ofloxacin drug, and amino acid, and these materials were analyzed for their structural and morphological properties using the Shimadzu FT-IR spectrophotometer, XRD, SEM, and EDX techniques. The three complexes which were used as precursors were complex I ([Pd(OFL)(Gly)]Cl), complex II ([Pd(OFL)(Ala)]Cl), and complex III ([Pd(OFL) 2 ]Cl 2 ), where Gly is glycine amino acid, Ala is alanine amino acid, and OFL is ofloxacin. The heterogeneous catalytic degradation of the prepared PdO materials as catalysts toward H 2 O 2 was examined at room temperature in water.

General
The chemicals were of analytical grades and were bought from BDH (UK) and Sigma-Aldrich (USA) chemical companies. The instruments X'Pert Philips X-ray powder diffractometer and Shimadzu FT-IR spectrophotometer were used to collect the XRD and IR spectra of the PdO materials, respectively. Their XRD spectra were scanned from 2 of 105 to 20, where their IR spectra were scanned from wavenumber of 400 cm -1 to 4000 cm -1 .
The SEM and EDX profiles for the PdO materials were obtained using the instruments Joel JSM-639OLV scanning electron microscope (SEM) and Noran six 200 energy dispersive X-ray (EDX) analyzer, respectively.

Synthesis of the PdO materials
Three Pd(II) complexes containing Pd(II) ion, ofloxacin drug, and amino acid (glycine or alanine) where synthesized according to the literature method [40]. These complexes are: I: Complex I, [Pd(OFL)(Gly)]Cl was prepared by adding a hot methanolic solution (2 mmol, 40 mL, 0.722 g) of OFL to an aqueous solution (2 mmol, 25 mL, 0.354 g) of PdCl 2 and glycine (2 mmol, 5 mL, 0.150 g). The reaction mixtures were neutralized at pH = 8-9 and then refluxed for 6-7 h at ~70-80 °C. The solution was filtered off and left to slowly evaporate. Then, they were dried in an oven to dispose of the solvent after 615 h. Yellow color product was deposited and collected in a glass bottle for the chemical analyses.
Complex II, [Pd(OFL)(Ala)]Cl was prepared by adding a hot methanolic solution (2 mmol, 40 mL, 0.722 g) of OFL to an aqueous solution (2 mmol, 25 mL, 0.354 g) of PdCl 2 and alanine (2 mmol, 5 mL, 0.178 g). The reaction mixtures were neutralized at pH = 8-9 and then refluxed for 6-7 h at ~70-80 °C. The solution was filtered off and left to slowly evaporate. Then, it was dried in a drying oven to dispose of the solvent after 615 h. Yellowish white color product deposited and was collected a in glass bottle for the chemical analyses.
Complex III, [Pd(OFL) 2 ]Cl 2 was prepared by adding a hot methanolic solution (4 mmol, 40 mL, 1.445 g) of OFL ligand to an aqueous solution (2 mmol, 15 mL, 0.354 g) of PdCl 2 . The reaction mixture was neutralized at pH = 89 and then refluxed for 6-7 h at ~70-80 °C. The colored solution was filtered off and left to slowly evaporate. Afterwards, it was dried in an oven to dispose of the remaining solvent, and yellowish white color products deposited and were collected in a glass bottle for the chemical analyses.
The Gly in these complexes is glycine amino acid, Ala is alanine amino acid, and OFL is ofloxacin drug. The chemical structures of I, II and III are presented in Figure 1. Nanostructured PdO materials were prepared by the controlled thermal decomposition of I, II and III as precursors in air at temperatures of 600 °C for 3 h using electric furnace. The obtained PdO products were ground into fine powder (2-3 mm), and then characterized by the FTIR, XRD, SEM, and EDX methods.

Characterization of the PdO materials
The PdO materials were generated from the solid-state thermal decomposition of I, II and III at 600 °C. The composition, crystallinity, and surface morphology of the obtained PdO materials were investigated using XRD, SEM, EDX and FTIR methods. Figure 2 a-c depicts the IR spectra of the prepared PdO materials. Generally, metal oxides showed IR absorption bands in the fingerprint region below 1000 cm -1 appeared from inter-atomic vibrations. The prepared PdO materials showed weak bands around 1200 cm -1 and 3000 cm -1 , which may be assigned to the OH deformation and stretching vibrations, respectively. These bans arise from the water adsorption on the PdO surface. Bands located at 580 cm -1 and 650 cm -1 were attributed to the PdO stretching vibrations [41]. Peroxo groups stretching vibrations showed that the absorption band appeared at 1365 cm -1 [42].  [43]. Based on the Debye-Scherrer equation, the average particle size for the PdO materials was estimated to be  40 nm. The XRD spectra of the PdO materials showed some minor peaks, which could be due to the presence of trace of impurities presented in PdO. Figure 4 a-c presents the SEM micrographs of the prepared PdO materials taken with different scales from 1 to 50 μm and various magnifications (1,000x to 20,000x). These micrographs indicate that the particles of PdO were agglomerated with nondefined structural morphology. The non-defined shaped of the particles could be due to the high surface energy of the particles and the strong tendency to form agglomerates.     Elementals analysis of the prepared PdO materials has been verified using the EDX technique, and their EDX spectra are illustrated in Figure 5 a-c. These spectra confirmed the successful preparation of the PdO products by the formation of the major emission energies of palladium and oxygen peaks. Table 1 lists the catalytic activity data for the decomposition of H 2 O 2 at a constant weight of PdO and a constant concentration of H 2 O 2 (0.01 N) at room temperature. Figure 6 shows that the rate of decomposition of H 2 O 2 increased with time, which after 50 min were 1.810 -3 < 2.010 -3 < 7.810 -3 for the synthesized PdO products from the thermal decomposition of I, II and III, respectively. The catalytic decomposition of H 2 O 2 tends to be associated with an intermediate radical species, which can bind to the surfaces where H 2 O 2 undergoes decomposition [44,45]. The degree of decomposition of H 2 O 2 showed inverse dependent on the surface area, pore volume and mean pore dimensions. The chemical nature of the surface, rather than the porosity characterizations, was the principal factor in enhancing the disproportionation of H 2 O 2 on the prepared PdO oxides.

CONCLUSION
In this work, nanostructured PdO oxide nanomaterials were synthesized by the calcination of three Pd(II) complexes. These complexes contained ofloxacin drug, amino acid (alanine or glycine), and Pd(II) ions. The structure and morphology of the synthesized PdO nanomaterials were characterized using FTIR, XRD, SEM, and EDX techniques. The PdO nano oxides were tested as a catalyst for the heterogeneous catalytic activity degradation of H 2 O 2 solution at room temperature.