Flexible hierarchical Pd/SiO₂-TiO₂ nanofibrous catalytic membrane for complete and continuous reduction of p-nitrophenol

Figures & data

Scheme 1. Schematic illustration of fabrication process of Pd/SiO₂-TiO₂ membranes.

Scheme 2. Reduction of p-nitrophenol to p-aminophenol with NaBH₄.

Scheme 3. Schematic illustration of the flow through catalytic membrane reactor system.

Figure 1. XRD patterns of (a) Pd/SiO₂-TiO₂-0, (b) Pd/SiO₂-TiO₂-0.05, (c) Pd/SiO₂-TiO₂-0.2, (d) Pd/SiO₂-TiO₂-0.5.

Figure 2. FESEM images of (a) Pd/SiO₂-TiO₂-0, (b) Pd/SiO₂-TiO₂-0.05, (c) Pd/SiO₂-TiO₂-0.2, (d) Pd/SiO₂-TiO₂-0.5 with low magnification.

Figure 3. EDS analysis of the catalytic membranes: (a) Pd/SiO₂-TiO₂-0.05, (b) Pd/SiO₂-TiO₂-0.2, (c) Pd/SiO₂-TiO₂-0.5.

Table 1. Pd content and BET analysis of the catalytic membranes.

Samples	Pd content (mg/m^2)	BET surface area (m^2/g)	BJH pore volume (cm^3/g)
Pd/SiO2-TiO2-0	4.05	10.39	0.0122
Pd/SiO2-TiO2-0.05	106.94	14.82	0.0325
Pd/SiO2-TiO2-0.2	389.94	25.89	0.0471
Pd/SiO2-TiO2-0.5	348.95	21.65	0.0396

Figure 4. TEM images of (a, c) Pd/SiO₂-TiO₂-0, (b, d, e) Pd/SiO₂-TiO₂-0.2.

Figure 5. XPS survey spectra of the powder taken from (a) Pd/SiO₂-TiO₂-0, (b) Pd/SiO₂-TiO₂-0.2. The inset is the table of atomic concentration of elements in the catalytic membranes.

Figure 6. Pd 3d XPS spectra of the powder taken from (a) Pd/SiO₂-TiO₂-0, (b) Pd/SiO₂-TiO₂-0.2.

Figure 7. Basic properties of the catalytic membranes: (a) pure water permeability and porosity, (b) pore size distribution.

Figure 8. Tensile stress-strain curves of the catalytic membranes (a), optical images of the catalytic membranes: they can be stretched and folded without damage (b–d).

Figure 9. Catalytic activities of the Pd/SiO₂-TiO₂ catalytic membranes in the hydrogenation of PNP (PNP concentration 12 mM, molar ratio of NaBH₄ to PNP 12.5, temperature 30 °C, rotation rate 30 rpm).

Figure 10. Effects of the reaction conditions on the initial reaction rate: (a) rotation rate of pump, (b) PNP concentration, (c) NaBH₄ concentration, and (d) reaction temperature.

Figure 11. Stability of gravity-driven nanofibrous catalytic membrane reactor: (a) reduction efficiency of PNP over Pd/SiO₂-TiO₂-0.2, the inset is the membrane reactor device driven by gravity; (b) FESEM image of Pd/SiO₂-TiO₂-0.2 after continuous reaction (Reaction conditions: PNP concentration 1.2 mM, molar ratio of NaBH₄ to PNP 50, temperature 25 °C, residence time 3.3 s, permeation flux 153 L·m⁻²·h⁻¹); and (c, d) reduction efficiency of Pd/SiO₂-TiO₂-0.2 for o-nitrophenol (ONP) and m-nitrophenol (MNP), the inset shows the change of the reaction solution.

Figure 12. Proposed mechanism for the reduction of PNP over Pd/SiO₂-TiO₂.

Table 2. Comparison of p-nitrophenol reduction by catalytic membranes.

Samples	Reaction conditions	Reaction time (s)	Pd quantity (mg)	Conversion (%)	Refs.
Pd/BTiO2-CM-AAPTS	PNP 31.3 mM; NaBH4:PNP molar ratio 9.6; 30 ^oC	24	6	100	[13]
Pd/PES-C	PNP 0.53 mM; NaBH4:PNP molar ratio 100;	18000	–	90	[49]
PES-PSS5/Pd	PNP 0.75 mM; NaBH4:PNP molar ratio 100;	1.3	0.086	100	[50]
PSS-PAA8	PNP 0.72 mM; NaBH4:PNP molar ratio 20; RT	0.15	0.33	90	[51]
PVA/PAA/M @Pd	PNP 5 mM; NaBH4:PNP molar ratio 20;	900	–	99	[52]
PY-300-PES	PNP 0.75 mM; NaBH4:PNP molar ratio 20	1740	2.4	100	[53]
Pd/SiO2-TiO2-0.2	PNP 1.2 mM; NaBH4:PNP molar ratio 50; 25 ^oC	3.3	0.62	100	This work

Emin C, Gu Y, Remigy J, et al. Polyethersulfone hollow fibre modified with poly(styrenesulfonate) and Pd nanoparticles for catalytic reaction. Eur Phys J Spec Top. 2015;224(9):1843–1848.

 Web of Science ®Google Scholar

Emin C, Remigy J, Lahitte J. Influence of UV grafting conditions and gel formation on the loading and stabilization of palladium nanoparticles in photografted polyethersulfone membrane for catalytic reactions. J Membr Sci. 2014;455:55–63.

 Web of Science ®Google Scholar

Yin J, Zhan F, Jiao T, et al. Highly efficient catalytic performances of nitro compounds via hierarchical PdNPs-loaded MXene/polymer nanocomposites synthesised through electrospinning strategy for wastewater treatment. Chinese Chem Lett. 2020;31(4):992–995.

 Web of Science ®Google Scholar

Mahdavi H, Heidari A. Chelated palladium nanoparticles on the surface of plasma-treated polyethersulfone membrane for an efficient catalytic reduction of p-nitrophenol. Polym Adv Technol. 2018;29(2):989–1001.

 Web of Science ®Google Scholar