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The slow charge reactions at the semiconductor surface severely encumber the photocatalysis applications, which are elusive and complicated in a serial charge excitation-separation-reaction process. Both experimental and theoretical studies are essential in this area. Here, a classical numerical calculation of the charge reaction microkinetic is developed based on a simple consecutive charge separation and reaction model, a conservation law of photogenerated charges, and differential analysis. Several reaction conditions have been discussed to elucidate how a fast charge separation and reaction rate constant influence the apparent reaction kinetics. It is shown that a slower charge separation rate strongly limits the detection of higher-order reaction rates, and higher-order kinetics can be detected with all other processes faster than the reactions. This numerical calculation projects the possible limitations of kinetics study by transient techniques. [ABSTRACT FROM AUTHOR]

Multiple-step mechanisms have been extensively proposed in many electrocatalytic and/or photocatalytic oxygen evolution reactions. But the surface charge reaction is less studied quantitatively. More difficultly, the verification methods for new multiple-step photocatalytic reactions are rarely found, which could be one of the main reasons for the insufficient reaction mechanism study. In this work, we aim to elucidate the rate-law relationship of the multiple-charge reactions, which is derived based on the microkinetics calculation on the photophysical redox reactions using pre-equilibrium approximation and steady-state approximation. The numerical analysis demonstrates that an nth-order feature could be observed when the nth-step is a rate-determined step in a multiple-step reaction. Likely, the 4th-order charge transfer could be possibly found for oxygen evolution reaction, suggesting the analytical methods and results could further boost the fundamental studies in photocatalysts and multiple-step reactions. [ABSTRACT FROM AUTHOR]

For artificial photosynthesis, the lower photon conversion efficiencies of the photogenerated charges hinder the practical application in solar energy harvesting. The challenges are commonly ascribed to the sluggish surface redox reactions and significant surface charge recombination. Although there are several transient techniques applied for monitoring the surface charges evolution, how the experimental spectroscopy data is interpreted still involves ambiguous explanations on the complicated reactions. Here, we firstly developed a parallel 1st–nth order reaction model, which could be applied to quantitatively analyze the surface charge reactions. The microkinetic calculations were carried out by varying the reaction order, rate constants as well as the contribution of the competitive ones. Interestingly, the simplified reaction model can successfully demonstrate the charges react rate changes, which can be further applied in mechanism study complementary with those experimental methods. [ABSTRACT FROM AUTHOR]

In this work, a novel and high-efficiency scavenger based on amino-functionalized cellulose was designed for sodium cholate sorption in vitro. To estimate the adsorption performance of the amino-functionalized cellulose for sodium cholate, various factors including sodium cholate concentration, contact time and electrolyte were investigated. The results suggested that amino-functionalization for cellulose regarding to hyperbranched polyethylenimine not only induce positive charge surface of cellulose but also provide abundant and special binding sites for sodium cholate sorption. The amino-functionalized cellulose displayed an excellent performance to sodium cholate sorption with a maximum adsorption capacity of 569.7 mg/g, higher than cholestyramine, a synthetic lipid-lowering drug in clinic. And the adsorption behavior was well fitted into the Langmuir isotherm model and pseudo-second-order kinetic model, suggesting a homogeneous monolayer chemisorption. Furthermore, the amino-functionalized cellulose presented the features of excellent anti-interferences, cytocompatibility and facile preparation process. All these results support amino-functionalized cellulose as a promising prospect for cholesterol elimination. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-organic polymers (MOPs) can enhance the photoelectrochemical (PEC) water oxidation performance of BiVO 4 photoanodes, but their PEC mechanisms have yet to be comprehended. In this work, we constructed an active and stable composite photoelectrode by overlaying a uniform MOP on the BiVO 4 surface using Fe2+ as the metal ions and 2,5-dihydroxyterephthalic acid (DHTA) as ligand. Such modification on the BiVO 4 surface yielded a core-shell structure that could effectively enhance the PEC water oxidation activity of the BiVO 4 photoanode. Our intensity-modulated photocurrent spectroscopy analysis revealed that the MOP overlayer could concurrently reduce the surface charge recombination rate constant (k sr) and enhance the charge transfer rate constant (k tr), thus accelerating water oxidation activity. These phenomena can be ascribed to the passivation of the surface that inhibits the recombination of the charge carrier and the MOP catalytic layer that improves the hole transfer. Our rate law analysis also demonstrated that the MOP coverage shifted the reaction order of the BiVO 4 photoanode from the third-order to the first-order, resulting in a more favorable rate-determining step where only one hole accumulation is required to overcome water oxidation. This work provides new insights into the reaction mechanism of MOP-modified semiconductor photoanodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced photoelectrochemical water oxidation on Bi 2 WO 6 photoanodes by heterojunction and facet-engineering. • The heterojunction of WO 3 /Bi 2 WO 6 improved charge separation and transfer. • Crystalline {2 0 0} and {1 3 1} orientations on WO 3 /Bi 2 WO 6 and Bi 2 WO 6 films, respectively. • A 1st-order and a 2nd-order charge reaction kinetics were discovered on {2 0 0} and {1 3 1} facets, respectively. Charge separation and transfer kinetics play a significant role in photocatalytic water oxidation, which is sensitive to the crystal facets. Herein, the bismuth tungstate (Bi 2 WO 6) films were used as a model photoanode to investigate how the photogenerated charges react on {1 3 1} and {2 0 0} facets under constantly applied bias in a photoelectrochemical (PEC) cell. On the WO 3 electron transport layer, the Bi 2 WO 6 films have a {2 0 0} orientation while possessing a {1 3 1} orientation on the fluorine-doped tin oxide substrate. It is discovered that {2 0 0} facets on the WO 3 /Bi 2 WO 6 heterojunction display a low overpotential of PEC water oxidation, showing a 1st-order reaction behavior and faster charge transfer rate constant. Differently, water oxidation on the {1 3 1} facet on Bi 2 WO 6 displays a 2nd-order reaction behavior. Further, density functional theory calculations were applied to demonstrate how the rate-determining step and the major formed intermediate correlate with the charge accumulation and reaction orders. The findings of this work shed fundamental light on how to rationally design and precisely modulate surface charge density and reaction kinetics for efficient (photo)electrocatalysts. [ABSTRACT FROM AUTHOR]