Supporting Information. Nature-Inspired Design of Artificial Solar-to-Fuel. Conversion Systems based on Copper Phosphate. Microflowers. Jing Wang,[a] Ting ...
Supporting Information Nature-Inspired Design of Artificial Solar-to-Fuel Conversion Systems based on Copper Phosphate Microflowers Jing Wang,[a] Ting Zhu,[a] and Ghim Wei Ho*[a, b, c] cssc_201600481_sm_miscellaneous_information.pdf
Experimental Materials Copper foils (purity: 99.99%) were purchased from standard sources. Prior to use, the foils were cut into pieces (1 cm × 1 cm), washed successively with acetone, ethanol and deionized (DI) water by ultrasonication, and finally blown dry with nitrogen gas. Phosphoric acid (H3PO4, 85 wt% solution in water), titanium tetraisopropoxide (TTIP), isopropanol (IPA) and methanol were purchased from Sigma-Aldrich Corporation. All the chemicals were used as received without purification. Fabrication of copper phosphates 100 μL of H3PO4 aqueous solution (concentrations: 0.5%, 5% and 10%) was dropped onto a piece of copper foil and left dry at 20 oC under the humidity of 60%. After 24 h, a series of thin layers were formed on the foil surfaces, which were rinsed with DI water several times and then dried under vacuum at 50 oC for 2 h for further use. The as-obtained products are noted as copper phosphates. Fabrication of TiO2/copper phosphate nanocomposites 0.3 g of TTIP, 25 mL of IPA and 6 mL of DI water were mixed in a 50 mL autoclave and magnetically stirred under ambient conditions to form a uniform precursor suspension. A piece of corroded copper foil was added in to the above suspension, which was transferred into an oven and maintained at 180 oC for 12 h. After cooling down to room temperature, the product was collected, centrifuged, washed by DI water and dried under vacuum at 60 oC for 2 h, which was then calcinated at 450 oC in air for 2 h. The as-obtained powder samples are noted as TiO2/copper phosphate nanocomposites. For comparison, bare TiO2 nanoparticles was synthesized similarly without the addition of copper phosphates. Photocatalytic water splitting 5 mg TiO2/copper phosphate nanocomposites was dispersed in a mixed solution of 9 mL DI water and 1 mL methanol in a quartz vial, and stirred until the formation of a homogeneous suspension. Prior to the photocatalytic water splitting, the suspension was purged with argon gas for 10 min. The measurements of H2 generation were performed by magnetically stirring under the illumination of a 300 W xenon lamp with an intensity of 1000 W m-2 (Excelitas, PE300BFM), in which the readings were taken every 30 min within 2 h.
Characterizations Scanning electron microscopy (SEM) images were taken on a JEOL JSM7001F field-emission scanning electron microscope. Element analysis was performed on an Oxford Instruments energy dispersive X-ray (EDX) spectroscopy. X-ray photoelectron spectroscopy (XPS) spectra were attained on a VG Thermo Escalab 220i-XL X-ray photoelectron spectroscopy system. X-ray diffraction (XRD) spectra were achieved on a Philips X-ray diffractometer with Cu Kα radiation (λ = 1.541Å). Transmission electron microscopy (TEM) images were obtained on a JEOL JEM-2100 electron microscope. H2 uptake was measured using pressure composition isotherm measurement on a Shimadzu GC-2014AT gas chromatographer. Brunauer-Emmett-Teller (BET) measurements were conducted on a Nova 2200e surface area & pore size analyzer (Quantachrome Instruments), with nitrogen as the adsorbate at liquid nitrogen temperature. Ultraviolet-visible (UV-vis) absorption spectra were acquired on a Shimadzu UV-3600 UV-vis spectrophotometer. Photoluminescence (PL) emission spectra were recorded on a Shimazu RF-5301PC under the excitation of 300 nm. Linear sweep voltammetry (LSV) curves were evaluated on a CHI 660D electrochemical work station, which was performed in 0.1 M KOH electrolyte at a scanning rate of 5 mV/s. Three-electrode cell was used, with samples-coated FTO glasses as the working electrode, Pt foil as the counter electrode and a standard calomel electrode as the reference electrode. The apparent quantum efficiency (AQE) of the sample was measured with a light emitting diode (LED) of 365 nm as the illumination source, which was determined based on the following equation: output of hydrogen per second input power no. of hydrogen generated per second 2 no. of incident photons per second AQE
Figure S1 EDX spectrum of copper phosphate (5%).
Figure S2 (a) Low- and (b) high-magnification SEM images and (c) EDX spectrum of copper phosphate (5%) after annealing at 450 oC.
Figure S3 (a) SEM image, (b) particle size distribution and (c) XRD spectrum of bare TiO2 NPs.
Figure S4 EDX spectrum of TiO2/copper phosphate nanocomposite (TCP-2).
Figure S5 (a) SEM image and (b-e) elemental mapping images of TiO2/copper phosphate nanocomposite (TCP-3). Scale bar: 5 µm.
Figure S6 P 2p high-resolution XPS spectrum of TiO2/copper phosphate nanocomposite (TCP-2).
Figure S7 Typical nitrogen adsorption-desorption isotherm of TCP-2. Inset shows the corresponding pore size distribution obtained from the desorption isotherm.
As shown in the nitrogen adsorption-desorption isotherm of TCP-2, hysteresis loops of type III are observed, suggesting the presence of mesoporous structures in TiO2/copper phosphate nanocomposites. Based on the obtained isotherms, the specific surface area of TCP-2 is calculated to be 152.3 m2 g-1 with a narrow pore size distribution centred at 8 nm (shown in the inset). The other samples (TCP-1 and TCP-3) also show specific surface areas in the range of 120-140 m2 g-1. As compared to the ~50 m2 g-1 of bare TiO2 NPs, the larger specific surface areas of the nanocomposites indicate more active surface sites for improved photocatalytic hydrogen generation.
Figure S8 Hydrogen generation performance of physically mixed TiO2 and copper phosphates (5%).
