One of the crucial challenges to enhance the photoelectrochemical water‐splitting performance of hematite (α‐Fe2O3) is to resolve its very fast charge recombination in bulk. Herein, we describe the ...design and fabrication of dual‐axial gradient‐doping on 1D Fe2O3 nanorod arrays with Zr doping for x‐axial and Sn doping for y‐axial directions to promote the charge separation. This dual‐axial gradient‐doping structure fulfills the requirements of a greater electron‐carrier concentration for increasing conductivity as well as a higher charge‐separation efficiency across the dual‐axial direction of Fe2O3 nanorods, ultimately showing an excellent photocurrent density of 1.64 mA cm−2 at 1.23 V vs. RHE, which is 26.3 times more than that of the bare Fe2O3. Furthermore, the remarkably improved photocurrent density, when comparing the uniform Zr‐doped Fe2O3 nanorod arrays (1.0 mA cm−2 at 1.23 V vs. RHE) with dual‐axial gradient‐doped (Zr and Sn) Fe2O3 nanorod arrays, highlights the additional charge‐separation effect resulting from gradient codoping of Zr and Sn. Hence, this promising design may provide guidelines for dual‐axial gradient doping into photoelectrodes to realize efficient PEC water splitting.
Solar energy: The dual‐axial gradient doping (Zr and Sn) on hematite with Zr doping for x‐axial and Sn doping for y‐axial directions fulfills the requirements of a greater electron‐carrier concentration for increasing conductivity and a higher charge‐separation efficiency across the dual‐axial direction of Fe2O3 nanorods.
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•Homogeneous and heterogeneous iron species activation of PS and PMS are presented.•Synthetic ways for heterogeneous iron catalysts for PS/PMS activation are reviewed.•Influencing ...factors and synergistic methods for PS/PMS activation are introduced.•Further efforts related to iron-mediated activation of PS and PMS are proposed.
Various organic contaminants accumulated in the environment pose great threat to ecosystems and human health. Sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted increasing attention for the removal of these contaminants in recent years. Iron species, including ferrous and ferric iron, zero-valent iron, iron oxides and oxyhydroxides, iron sulfides and various supported iron catalysts, are known to be effective in activating persulfate (PS) or peroxymonosulfate (PMS) to generate sulfate radicals. This review is dedicated to summarize the up-to-date research progresses of iron-mediated activation of PS and PMS mediated by these iron-based species in both homogeneous and heterogeneous ways. The activators are categorized based on their chemistry, and the up-to-date knowledge regarding the activation mechanisms are summarized and discussed. Then, a summary of frequently-used synthesis methods of heterogeneous iron catalysts is presented. In addition, the effects of anions, solution pH, dissolved oxygen, and external energy on the activation processes are discussed. Finally, future research perspectives on the iron-based PS/PMS activation method are proposed and how to further improve such a technology for practical application are also discussed.
Photoelectrochemical water splitting to produce hydrogen using solar energy can capture and directly convert solar energy into chemical energy, which is an effective way to deal with the current ...energy and environmental problems. The conversion efficiency of solar energy depends on the performance of semiconductor photoelectrodes in photoelectrochemical water splitting. This article presents our recent advances in the design and performance control of high-efficiency photoelectrocatalytic materials, followed by the discussion of the strategies employed for improving the performances of photoelectrodes in terms of photon absorption, charge separation and migration, as well as surface chemical reactions.
A summary of the design strategies for promoting the efficiency of photoelectrocatalytic water splitting is presented in this article.
We report the fabrication of tungsten trioxide (WO3) with different morphologies applied in photoelectrochemical (PEC) water splitting. The antimony sulfide (Sb2S3) was incorporated onto WO3 for the ...first time with the aim of improving its photoelectrocatalytic activity under visible-light illumination. In the present work, WO3 of different morphologies were fabricated on FTO glass via adjusting the pH value via a facile hydrothermal method and the morphological effect on the photoelectrocatalytic activity of the obtained samples has been discussed. WO3/Sb2S3 heterojunction photoelectrocatalysts were subsequently synthesized successfully to further improve the photoelectrocatalytic activity. Among them, WO3/Sb2S3 heterojunction photoelectrocatalyst based on WO3 micro crystals achieved an enhanced photocurrent of 1.79 mA/cm2 at 0.8 V versus RHE under simulated sunlight, compared to 0.45 mA/cm2 of pristine WO3 micro crystals. This excellent PEC performance benefits from the enhanced light absorbance, construction of suitable energy band gap, the improved photogenerated electron–hole pairs separation and transfer efficiency, which potentially provides new insights into PEC water splitting systems.
Urbanization and climate change are together exacerbating water scarcity-where water demand exceeds availability-for the world's cities. We quantify global urban water scarcity in 2016 and 2050 under ...four socioeconomic and climate change scenarios, and explored potential solutions. Here we show the global urban population facing water scarcity is projected to increase from 933 million (one third of global urban population) in 2016 to 1.693-2.373 billion people (one third to nearly half of global urban population) in 2050, with India projected to be most severely affected in terms of growth in water-scarce urban population (increase of 153-422 million people). The number of large cities exposed to water scarcity is projected to increase from 193 to 193-284, including 10-20 megacities. More than two thirds of water-scarce cities can relieve water scarcity by infrastructure investment, but the potentially significant environmental trade-offs associated with large-scale water scarcity solutions must be guarded against.
Urbanization results in habitat loss and habitat fragmentation concurrently, both influencing biodiversity and ecological processes. To evaluate these impacts, it is important to understand the ...relationships between habitat loss and habitat fragmentation per se (HLHF) during urbanization. The objectives of this study were two-fold: 1) to quantify the different forms of the HLHF relationship during urbanization using multiple landscape metrics, and 2) to test the validity of the HLHF relations reported in the literature. Our analysis was based on a long-term urbanization dataset (1800-2000) of 16 large cities from around the world. Habitat area was represented as the percentage of non-built-up area in the landscape, while habitat fragmentation was measured using several landscape metrics. Our results show that the relationship between habitat loss and habitat fragmentation during urbanization is commonly monotonic-linear, exponential, or logarithmic, indicating that the degree of habitat fragmentation per se increases with habitat loss in general. We compared our results with 14 hypothesized HLHF relationships based on simulated landscapes found in the literature, and found that four of them were consistent with those of urbanization, whereas the other ten were not. Also, we identified six new HLHF relationships when fragmentation was measured by total core area, normalized total core area, patch density, edge density and landscape shape index, respectively. In addition, our study demonstrated that the "space-for-time" approach, frequently used in ecology and geography, generated specious HLHF relationships, suggesting that this approach is largely inappropriate for analyses of urban landscapes that are highly heterogeneous in space and unusually contingent in dynamics. Our results show both generalities and idiosyncrasies of the HLHF relationship, providing new insights for assessing ecological effects of urbanization.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Localized SSPs were used to assess the effects of urban expansion on NHQ.•Localized SSPs can better describe the actual situation of socioeconomic development.•The effects of future urban expansion ...on NHQ can be simulated more effectively.•The error of simulated results was reduced by about 50%.•This approach will provide more reliable guidance for improving sustainability.
Effectively evaluating the effects of future urban expansion on natural habitat quality (NHQ) is critical for improving the sustainability of regional and even global cities. However, because of the difficulties in simulating spatiotemporal distribution of future urban expansion and the uncertainties in future socioeconomic development, effectively evaluating the effects of future urban expansion on NHQ is still challenging. Using the Hohhot-Baotou-Ordos-Yulin (HBOY) urban agglomeration in China as an example, this study simulated future urban expansion and evaluated its effects on NHQ. We first quantified the NHQ spatial patterns in HBOY using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Second, we simulated urban expansion in HBOY from 2017 to 2050 by coupling localized Shared Socioeconomic Pathways (SSPs) and the Land Use Scenario Dynamics-urban (LUSD-urban) model. Finally, we evaluated the effects of future urban expansion on NHQ by calculating the degradation rate of NHQ in the entire region and in different types of cities. We found that coupling localized SSPs and the LUSD-urban model can effectively evaluate the effects of future urban expansion on NHQ. Compared with coupling original SSPs and the LUSD-urban model, in HBOY case study, our method reduced the absolute of the evaluation error from 5.17 to 11.43% to 2.86–5.17%. The results showed that under all localized SSPs, the urban expansion from 2017 to 2050 in large cities will lead to the most obvious decrease in regional NHQ of 4.85–7.32%, while that in medium cities and small cities will be 1.23–2.37% and 0.19–0.35%, respectively. Therefore, we suggest that SSPs should be localized when used to simulate the effects of future urban expansion on NHQ. In addition, in order to achieve the sustainable development goals, the HBOY urban agglomeration should control the urban size and optimize the urban spatial pattern, especially for large cities, in the future to reduce the impacts of urban expansion on NHQ.
Adequate light absorption and effective charge separation and transfer are deemed to be the contributing factors to achieve high photoelectrochemical (PEC) water splitting on photoanodes. Herein, in ...this work, a Mo-WO3/Fe-WO3 homojunction was fabricated firstly by coating Fe doped WO3 (Fe-WO3) on Mo doped WO3 (Mo-WO3) via a two-step hydrothermal method, and then Bi2S3 nanoparticles (NPs) were further introduced onto the surface of Mo-WO3/Fe-WO3 to construct a multi-junction structure. In this Mo-WO3/Fe-WO3/Bi2S3 photoanode, the Bi2S3 NPs as the primary light absorber improve the light utilization efficiency. Moreover, the Fe-WO3/Bi2S3 heterojunction is formed due to their well-matched bands, which could facilitate charge separation and transfer; meanwhile, the internal built-in electric field at the interface of the Mo-WO3/Fe-WO3 homojunction would hinder the recombination of electron–hole pairs. Notably, the homojunction can further promote carrier transfer because of its unique property of eliminating the lattice mismatch. As expected, the Mo-WO3/Fe-WO3/Bi2S3 photoanode yields a significantly enhanced photocurrent of 2.55 mA cm−2 at 1.23 V vs. RHE, which is 8.23 times that of the WO3 photoanode. Thus, constructing a multi-junction structure with a ladder staggered alignment by integrating a homojunction and a heterojunction is believed to be an effective strategy to improve the PEC performance of WO3 photoanodes.
In spintronics, it is highly desirable to find new materials that can simultaneously possess complete spin-polarization, high-speed conduction electrons, large Curie temperature, and robust ...ferromagnetic ground states. Using first-principles calculations, we demonstrate that the stable YN2 monolayer with octahedral coordination is a novel p-state Dirac half metal （DHM）, which not only has a fully spin-polarized Dirac state, but also the highest Fermi velocity （3.74×10^5 m/s） of the DHMs reported to date. In addition, its half-metallic gap of 1.53 eV is large enough to prevent the spin-flip transition. Because of the strong nonlocal p orbitals of N atoms （N-p） direct exchange interaction, the Curie temperature reaches over 332 K. Moreover, its ferromagnetic ground state can be well preserved under carrier doping or external strain. Therefore, the YN2 monolayer is a promising DHM for high-speed spintronic devices and would lead to new opportunities in designing other p-state DHMs.
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