Artificial photoelectrochemistry (PEC) has emerged as a promising and efficient technology for the sustainable conversion of solar energy into chemicals. In this study, we present a refined PEC process that enables the highly selective and stable production of piperonal and other valuable aldehydes through the oxidation of the corresponding alcohols. By employing Fe2O3 or TiO2 as the photoanode material and 2,2,6,6-tetramethylpiperidinooxy (TEMPO) as a redox mediator in an H2O/acetonitrile solution, we achieve 100% selectivity and a >95% Faradaic efficiency for piperonal production from piperonyl alcohol (PA) oxidation. Remarkably, we reveal the enhancing effect on the PA oxidation reactivity of appropriate-amount water in the solvent as it plays a crucial role in inhibiting the photoelectron-hole recombination efficiency and facilitating charge transfer. Mechanistic analysis suggests that TEMPO-mediated PA oxidation involves the formation of â¢O2- radicals by the reduction of oxygen on the cathode, resulting in water as the sole byproduct. Furthermore, our PEC oxidation system exhibits applications on the 100%-selective production of various conjugated aldehydes, including 4-anisaldehyde, cuminaldehyde, and the vitamin B6 derivative. By implementing a TiO2//Fe2O3 dual-photoanode system, we achieve an enhanced piperonal production rate of 31.2 µmol h-1 cm-2 at 1.0 V vs Ag/Ag+ and demonstrate its stability over a 102 h cyclic test, ensuring near-quantitative yield. This research illuminates the potential of the PEC strategy as a generally applicable method for the efficient production of high-value aldehydes.
This study demonstrates Ti and Pt co-doping can synergistically improve the PEC performance of the α-Fe2O3 photoanode. By varying the doping methods, the sample with in-situ Ti ex-situ Pt doping (Tii-Pte) exhibits the best performance. It demonstrates that Ti doping in bulk facilities charge separation and Pt doping on the surface further accelerates charge transfer. In contrast, Ti doping on the surface inhibits charge separation, and Pt doping in bulk hinders charge separation and transfer. HCl treatment is used to minimize the onset potential further, while it is favorable for the ex-situ doped α-Fe2O3, which is more efficient on Tie than the Pte-doped ones. On the ex-situ Ti-doped α-Fe2O3 after HCl treatment, anatase TiO2 is probed, suggesting that Ti-O bonds accumulate when Fe-O bonds are partly removed, which enhances the charge transfer in surface states. Unfortunately, HCl treatment also induces lattice defects that are adverse to charge transport, inhibiting the performance of in-situ doped α-Fe2O3 and excessively treated ex-situ doped ones. Coupled with methanol solvothermal treatment and NiOOH/FeOOH cocatalysts loading, the optimized Ti-Pt/Fe2O3 photoanode exhibits an impressive photocurrent density of 2.81 mA cm-2 at 1.23 V vs. RHE and a low onset potential of 0.60 V vs. RHE.
Fe2O3 is a promising photoanode material used for photoelectrochemical water splitting due to its narrow bandgap and excellent stability in solution. However, because the nanorods shrink and coalesce when annealed under high temperatures, the charge separation and injection efficiencies are suppressed in the conventional nanocoral Fe2O3, resulting in its high bias potential and low photocurrent density. Herein, by improving the radial growth of FeOOH precursor, highly dispersed Fe2O3 nanorods could be prepared. It enabled them to have sufficient light-harvesting and short charge transport distance, high light absorption and charge separation/injection efficiencies, increased photocurrent density and reduced onset potential Von. The optimized Fe2O3 photoanodes obtained a remarkable low-bias photocurrent density of 0.84 mA cm-2 at 1.0 V versus reversible hydrogen electrode (vs. RHE). It was further improved to 1.36 mA cm-2 at 1.0 V vs. RHE with the Von reduced to 0.50 V vs. RHE when post-treated with a solvothermal method and loaded with NiOOH/FeOOH cocatalysts. The applied bias photo-to-current conversion efficiency was maximized to 0.45% at 0.84 V vs. RHE.
Morphology and geometrical dimensions play crucial roles in the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) for water splitting. Decahedral BiVO4 was synthesized through a facile hydrothermal process, which exhibited superior charge injection efficiency to the nanoporous counterpart prepared by the traditional method. More importantly, the crystal size and facet proportion of BiVO4 decahedrons were facilely controlled. The charge separation efficiency can be significantly improved with a reduction in the crystal size and an increase in (040) facet exposure. A new method was developed for rate law analysis: illumination intensity-modulated oxygen evolution reaction rate versus open circuit potential difference, which suggested that the surface reaction kinetics was not affected by facet regulation. Furthermore, after decorating the FeOOH and NiOOH as dual oxygen evolution cocatalysts, an enhanced photocurrent density of 3.2 mA cm-2 at 1.23 V versus reversible hydrogen electrode and interfacial charge injection efficiency of 97.0% can be reached. Our work inspires the development of facet-regulated BiVO4 photoanodes with high charge injection efficiency in the PEC field and provides a feasible route to enhance its charge separation efficiency.
Heterogenization of biomolecules by immobilizing on a metal oxide support could greatly enhance their catalytic activity and stability, but their interactions are generally weak. Herein, cobalt phthalocyanine (CoPc) molecules were firmly anchored on a Ce-based metal-organic framework (Ce-BTC) due to π-π stacking interaction between CoPc and aromatic frameworks of the BTC linker, which was followed by a calcination treatment to convert Ce-BTC to mesoporous CeO2 and realize a molecular-level dispersion of CoPc on the surface of CeO2. Various characterization results confirm the successful fabrication of molecular-based CoPc/CeO2 catalysts which exhibited good CO oxidation performance. Importantly, we found that the mixing manner of Ce-BTC and CoPc remarkably affects the physicochemical properties which then determined the catalytic performance of the resultant CoPc/CeO2 catalysts. In contrast, the direct physical mixing of CoPc and CeO2 led to poor performance toward CO oxidation, manifesting that the Ce-BTC-mediated CoPc loading strategy is promising for the heterogenization of catalytic biomolecules.
The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted. To increase light absorption in thin-film Fe2O3:Ti, commercial substrates such as Cu foil, Ag foil, and a mirror are adopted acting as back-reflectors and individually integrated with the Fe2O3:Ti electrode. The promotion effect of the commercial back-reflectors on the light absorption efficiency and photoelectrochemical (PEC) performance of the hydrothermally prepared Fe2O3:Ti electrodes with a variety of film thicknesses is investigated. As a result, Ag foil and the mirror show favorable and equal efficacy while the promoting effect of Cu foil is limited. In addition, the photocurrent increment achieved by the Ag back-reflector decreases linearly along with the logarithmic of the film thickness and the optimized film thickness of the Fe2O3:Ti electrode is decreased from 520 to 290 nm. The high durability of Ag foil in the alkaline electrolyte during solar light irradiation is demonstrated. Furthermore, the reflective substrate also shows a promotion effect on the BiVO4 photoanode and CuBi2O4 photocathode, as well as the unbiased photocurrent from a tandem cell constituted by TiO2 and CuBi2O4.
Herein, a series of metal oxide/CeO2 (M/CeO2) nanocomposites derived from Ce-benzene tricarboxylate (Ce-BTC) adsorbing with different metal acetylacetonate complexes were prepared for CO oxidation under four different CO gas atmospheres. It was demonstrated that Cu/CeO2 exhibited the highest catalytic activity and stability in CO oxidation. Remarkably, both O2 selectivity and CO selectivity to CO2 are 100% in most of the investigated conditions. Several analytical tools such as N2 adsorption-desorption and powder X-ray diffraction, were employed to characterize the prepared catalysts. In addition, the excellent catalytic performance of Cu/CeO2 in CO oxidation was revealed by H2 temperature-program reduction experiment, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The result showed that high oxygen vacancy and high CO adsorption capacity (Cu+-CO) caused by the electron exchanges of Cu2+/Cu+ and Ce3+/Ce4+ pairs (Ce4+ + Cu+ â Ce3+ + Cu2+) are two key factors contributing to the high oxidation performance of Cu/CeO2 catalyst.
Biomimetic catalysts have drawn broad research interest owing to both high specificity and excellent catalytic activity. Herein, we report a series of biomimetic catalysts by the integration of biomolecules (hemin or ferrous phthalocyanine) onto well-defined Au/CeO2, which leads to the high-performance CO oxidation catalysts. Strong electronic interactions among the biomolecule, Au, and CeO2 were confirmed, and the CO uptake over hemin-Au/CeO2 was roughly about 8 times greater than Au/CeO2. Based on the Au/CeO2(111) and hemin-Au/CeO2(111) models, the density functional theory calculations reveal the mechanisms of the biomolecules-assisted catalysis process. The theoretical prediction suggests that CO and O2 molecules preferentially bind to the surface of noncontacting Au atoms (low-coordinated sites) rather than the biomolecule sites, and the accelerating oxidation of Au-bound CO occurs via either the Langmuir-Hinshelwood mechanism or the Mars-van Krevelen mechanism. Accordingly, the findings provide useful insights into developing biomimetic catalysts with low cost and high activity.
Three-dimensional (3D) printing technique has received exceptional global attention as it can create a myriad of high-resolution architectures from digital models. In the present study, 3D-printed metal-organic frameworks (MOFs) were shaped into several geometries via direct ink writing, which overcomes the instability and high-pressure drop of powdery MOF during the flow of gas or liquid streams. The inclusion of a blend of calcium alginate and gelatin (CA-GE) as biocompatible binder allowed for easy writing and an enhanced mechanical property. Besides, it was found that the printing geometry (square, hexagon, and circle), MOF loading amount, and MOF size also greatly influenced the adsorptive performance. For instance, the methylene blue adsorption efficiency of CA-GE scaffolds without MOF was only 43.6%, while the printed MOF/CA-GE sample exhibited 99.8% adsorption efficiency at 20 min. Both the inherent microporous structure of MOFs and meso/macroporous structures of the 3D matrix contributed to the excellent adsorption properties towards a variety of organic dyes and their mixtures. Furthermore, the 3D-printed adsorbents can be easily regenerated in dilute acid solution and reused for at least 7 times without performance loss. In contrast, the powdery MOF can only be repeatedly used for at most 2 times.
Coloring Agents/chemistry , Copper/chemistry , Metal-Organic Frameworks/chemistry , Nanoparticles/chemistry , Water Pollutants, Chemical/chemistry , Adsorption , Alginates/chemistry , Gelatin/chemistry , Polymers/chemistry , Printing, Three-Dimensional , Tricarboxylic Acids/chemistry , Water Purification/methods
