Significance of Crystal Morphology Controlling in Semiconductor-Based Photocatalysis: A Case Study on BiVO₄ Photocatalyst

Precise control of the morphology and crystalline structure of semiconductor-based photocatalyst is crucial for improving the efficiency of solar energy conversion system. In this work, taking BiVO₄ semiconductor photocatalyst as an example, we investigated the formation process for the regular decahedron BiVO₄ crystals prepared by a convenient hydrothermal method and found that the synthesis is undergoing a dissolution–recrystallization process, concomitantly, the phase was transformed from tetragonal zircon type to monoclinic sheelite-type. By controlling the kinetics of crystal growth for BiVO₄ through regulating acidity of the reaction solution, we rationally tune the morphology of monoclinic BiVO₄ from regular decahedron crystals to short rod-like particles, particularly precisely modulate the proportion of {010}/{011} facets for the decahedron BiVO₄. By tuning the crystalline phase and morphologies of BiVO₄ crystal, we found that the photocatalytic water oxidation activity for the well-defined BiVO₄ crystal with specific configuration of {010} and {011} exposed facets can be 50 times of tetragonal BiVO₄ particles. Our work shows a convenient strategy for precise control of the growth process of semiconductor-based photocatalyst, based on the understanding of the crystal morphology evolution mechanism, which will be instructive for constructing semiconductor-based photocatalysts for solar energy conversion

Photocatalytic Water Oxidation on BiVO₄ with the Electrocatalyst as an Oxidation Cocatalyst: Essential Relations between Electrocatalyst and Photocatalyst

The oxygen evolution is kinetically the key step in the photocatalytic water splitting. Cocatalysts could lower the activation potential for O₂ evolution. However, the cocatalyst for O₂ evolution has been less investigated, and few effective cocatalysts were reported. This paper reports that the O₂ evolution rate of photocatalytic water splitting under visible light irradiation can be significantly enhanced when the electrocatalyst cobalt–phosphate (denoted as CoPi) was deposited on BiVO₄. The photocurrent density is also greatly enhanced by loading CoPi on BiVO₄ electrode, and this enhancement in performance shows the similar trend between the photocatalytic activity and photocurrent density. We also found that this tendency is true for BiVO₄ loaded with a series of different electrocatalysts as the cocatalysts. These results demonstrate that an effective electrocatalyst of water oxidation can be also an effective cocatalyst for O₂ evolution from photocatalytic water oxidation. By depositing the CoPi as the oxidation cocatalyst and Pt as the reduction cocatalyst on an yttrium-doped BiVO₄ (Bi_0.5Y_0.5VO₄), overall water splitting reaction to H₂ and O₂ was realized. Our work also reveals the essential relations between photocatalysis and electrocatalysis in water splitting reaction

Positioning the Water Oxidation Reaction Sites in Plasmonic Photocatalysts

Plasmonic photocatalysis, stemming from the effective light absorbance and confinement of surface plasmons, provides a pathway to enhance solar energy conversion. Although the plasmonic hot electrons in water reduction have been extensively studied, exactly how the plasmonic hot holes participate in the water splitting reaction has not yet been well understood. In particular, where the plasmonic hot holes participate in water oxidation is still illusive. Herein, taking Au/TiO₂ as a plasmonic photocatalyst prototype, we investigated the plasmonic hot holes involved in water oxidation. The reaction sites are positioned by photodeposition together with element mapping by electron microscopy, while the distribution of holes is probed by surface photovoltage imaging with Kelvin probe force microscopy. We demonstrated that the plasmonic holes are mainly concentrated near the gold–semiconductor interface, which is further identified as the reaction site for plasmonic water oxidation. Density functional theory also corroborates these findings by revealing the promotion role of interfacial structure (Ti–O–Au) for oxygen evolution. Furthermore, the interfacial effect on plasmonic water oxidation is validated by other Au–semiconductor photocatalytic systems (Au/SrTiO₃, Au/BaTiO₃, etc.)

Sulfurization-Assisted Cobalt Deposition on Sm₂Ti₂S₂O₅ Photocatalyst for Water Oxidation under Visible Light Irradiation

Deposition of cocatalyst is an efficient way for photocatalytic water splitting to improve solar energy conversion efficiency, and its deposition method has been known to make a great effect. In this work, we introduced a sulfurization-assisted deposition method to load earth-abundant cobalt cocatalyst for the purpose of promoting water oxidation performance of Sm₂Ti₂S₂O₅ oxysulfide that is characterized with wide visible light absorption. The cobalt deposition introduced here undergoes first formation of CoS_<i>x</i> by sulfurization at high temperature and subsequent conversion into CoO_<i>x</i> by calcinations in air. Compared to conventionally impregnated cobalt or IrO₂ colloids, the sulfurization-assisted cobalt deposition well maintains structure of photocatalyst and inhibits the formation of defect sites leading to better separation of photogenerated carriers and water oxidation performance. The apparent quantum efficiency of the optimized sample reaches 5.0% at 420 nm. The sulfurization-assisted deposition actually open a new way to modify the (oxy)­sulfide semiconductors

High-Gravity-Tuned Synthesis of Uniformly Distributed Silver Bismuth Chromate Semiconductor Crystals

The synthesis of semiconductor crystals with controllable size distribution, morphology, and uniformity influences their notable physicochemical properties, thus promoting applications in various fields. Herein, we report the high-gravity-tuned synthesis of a binary metal oxide semiconductor, silver bismuth chromate, AgBi(CrO4)2. The high-gravity effect induces the formation of AgBi(CrO4)2 crystals with uniform size distributions and fusiform-like morphology at room temperature. By tuning the shearing and centrifugal forces of the high-gravity reactor, the aspect ratio of the fusiform-like AgBi(CrO4)2 crystal follows a quasi-quadratic relation with the applied forces. The high-gravity effect makes the local concentration of the solution precursors rapidly approach the supersaturated nucleation concentration, which significantly promotes the nucleation and growth of the AgBi(CrO4)2 crystal. This work demonstrates feasibility to modulate the nucleation and growth kinetics of semiconductor crystals and exhibits the promises of high-gravity-tuned synthesis of semiconductor nanocrystals

Habitat use of GPS-collared giant pandas with respect to elevation over time.

<p>Values shown are the means for each month after randomly selecting one point per day. Chinese names refer to individual pandas.</p

Summary of study pandas and GPS collar performance over the one year period included in this study.

<p>Summary of study pandas and GPS collar performance over the one year period included in this study.</p

Proportion of giant panda utilization distributions occurring in different classes of habitat characteristics.

<p>Chinese names refer to individual pandas.</p

Contribution of habitat variables to predicting giant panda habitat use across their utilization distributions (n = 5).

<p>Only significant variables are shown.</p

Oestrus profiles for Hao Hao_SB741.

<p>Profiles corrected with USpG (A) and creatinine (B): a sharper and significant oestrogen peak without confounding same-level pre-and post- peak peaks demonstrates the superiority of USpG normalisation in breeding management. Progesterone profiles for Hao Hao corrected with USpG (C) and creatinine (D): the irregular skewed progesterone profile with outliers and a two-week earlier onset of secondary rise demonstrates the difficulty in interpreting creatinine-normalised profiles.</p