Graphitic carbon nitride (g-C3N4) has been widely investigated and applied in photocatalysis and catalysis, but its performance is still unsatisfactory. Here, we demonstrated that K-doped g-C3N4 with ...a unique electronic structure possessed highly enhanced visible-light photocatalytic performance for NO removal, which was superior to Na-doped g-C3N4. DFT calculations revealed that K or Na doping can narrow the bandgap of g-C3N4. K atoms, intercalated into the g-C3N4 interlayer via bridging the layers, could decrease the electronic localization and extend the π conjugated system, whereas Na atoms tended to be doped into the CN planes and increased the in-planar electron density. On the basis of theoretical calculation results, we synthesized K-doped g-C3N4 and Na-doped g-C3N4 by a facile thermal polymerization method. Consistent with the theoretical prediction, it was found that K was intercalated into the space between the g-C3N4 layers. The K-intercalated g-C3N4 sample showed increased visible-light absorption, efficient separation of charge carriers, and strong oxidation capability, benefiting from the narrowed band gap, extended π conjugated systems, and positive-shifted valence band position, respectively. Despite that the Na-doped g-C3N4 exhibited narrowed bandgap, the high recombination rate of carriers resulted in the reduced photocatalytic performance. Our discovery provides a promising route to manipulate the photocatalytic activity simply by introducing K atoms in the interlayer and gains a deep understanding of doping chemistry with congeners. The present work could provide new insights into the mechanistic understanding and the design of electronically optimized layered photocatalysts for enhanced solar energy conversion.
Assessment of groundwater quality and health risk was conducted in the Shenfu coal mine area in Ordos basin, northwestern China. Statistical analysis, Piper and Chadha diagrams were used to reveal ...the hydrogeochemical characteristics of groundwater via physicochemical analysis of 44 collected samples. The suitability of groundwater was assessed for domestic and irrigation purposes, and the fuzzy comprehensive method was adopted to assess the overall groundwater quality for further discussion on groundwater management. The model recommended by the USEPA was selected to estimate the non-carcinogenic risks caused by NO
3
−
, NO
2
−
, NH
4
+
, F
−
, Fe and Mn through oral ingestion and direct dermal contact. The results revealed that the predominant hydrochemical types of groundwater were SO
4
∙Cl–Ca∙Mg and HCO
3
–Ca∙Mg types and the major cations and anions followed the orders of Ca
2+
> Na
+
> Mg
2+
>K
+
and HCO
3
−
> SO
4
2−
> Cl
−
, respectively. Groundwater is generally acceptable for irrigation. However, for domestic purposes, 47.73% of the collected samples are of excellent and good quality and are suitable for direct consumption. Both adults and children face non-carcinogenic risks because of exposure to contaminants such as nitrate, nitrite and fluoride. The risk to children is higher than that to adults, which is consistent with other studies. Nitrite contributes most to the risks, followed by nitrate and fluoride. Home-use water quality improvement devices and rainwater harvesting are suggested to enhance the groundwater quality protection and management in this area. The research also indicates that health risk assessment should always accompany general water quality assessment to ensure the reliability of the water quality assessment.
Urban community governance faces unprecedented challenges, but machine learning provides new ideas for it. The objective of this study is to examine the use of machine learning technology in urban ...community governance to enhance governance efficiency and decision-making quality. The study constructs an artificial neural network intelligent decision support model based on genetic algorithm optimization, which is based on the operational requirements of a smart decision support system. A weighted fuzzy inference network is further developed by the fusion of fuzzy logic and neural networks to enhance the system’s ability to deal with uncertainty and ambiguity. Next, prediction tests were conducted on the development levels of six communities to validate the model’s effectiveness. After 1686 training steps, the error squared SSE drops below 0.2%, according to the results. The composite index’s prediction error was 5.12%, while the minimum error was −1.79%. The predicted rankings of the communities did not change from the actual ones, which was in line with the normal trend, and the algorithmic model achieved better prediction results. This study not only provides a new intelligent decision support tool for community governance but also sets a theoretical and practical foundation for the intelligent development of urban community governance in the future.
Hierarchical Co3O4@MnO2 core–shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to ...the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core–shell arrays on Ni foam have exhibited a high specific capacitance (560 F g−1 at a current density of 0.2 A g−1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core–shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg−1 and a maximum power density of 158 kW kg−1. The rational design of the unique core–shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.
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•Hierarchical Co3O4@MnO2 nanowire array was prepared by a facile hydrothermal method.•MnO2 coated on Co3O4 nanowire without carbon coating or electrochemical deposition.•The unique core–shell architecture exhibits a high capacitance of 560 F g−1.•Excellent cycling stability: 95% capacitance retention after 5000 cycles.•The asymmetric supercapacitor yielded a maximum power density of 158 kW kg−1.
•15 new first-tier cities still had a relatively low smart level.•The gaps among different smart cities were significant.•The performance of smart cities in different dimensions is unbalanced.•Smart ...infrastructure, economy and life had a poor performance.
Overload of infrastructure, shortages in energy resources and environmental pollution constitute the main challenges facing current urban management and development. As the best solution to these challenges, smart cities enjoy increasing attention around the world. As China speeds up the urbanization process, the number of pilot smart cities in China continues to increase. Under such a context, it is of great significance to arrange effective and comprehensive evaluations on the construction level of these smart cities. Based on the development realities of cities in China, this study arranged an in-depth analysis of the current literature and policies and established an evaluation system with five dimensions and 30 indicators. The entropy method and TOPSIS (technique for order preference by similarity to an ideal solution) were comprehensively applied to evaluate 15 new first-tier cities in China. The study results demonstrated that these 15 new first-tier cities still had a relatively low smart level, and the gaps among different cities were significant. Because of the differences in the emphasis of the smart city construction of various cities, their performances under different dimensions were widely divergent. Among the five dimensions, smart infrastructure, economy and life had poor performance compared with smart governance and the environment. In addition, some recommendations were initiated to boost the construction of smart cities in China, including accelerated construction for new infrastructure, more emphasis on the digital economy, acceleration in the development of important mechanisms, etc.
In order to tackle China’s severe air pollution issue, the government has released the “Air Pollution Prevention and Control Action Plan” (known simply as the “Action Plan”) since 2013. A recent ...study reported a decreased trend in PM2.5 concentrations over 2013–2017, but O3 pollution has become more serious. However, the effects of surface O3 on crops are unclear after the implementation of the “Action Plan”. Here, we evaluated the potential negative effects of surface O3 on three main food crops (winter wheat, maize and rice) across China during 2015–2018 using nationwide O3 monitoring data and AOT40-yield response functions. Results suggested that mean O3 concentration, AOT40 and relative yield loss in China showed an overall upward trend from 2015 to 2018. During winter wheat, maize, single rice, double-early rice, and double-late rice growing seasons, mean O3 concentration in recent years ranged from 38.6 to 46.9 ppb, 40.2–43.9 ppb, 39.3–42.2 ppb, 33.8–40.0 ppb, and 35.9–39.1 ppb, respectively, and AOT40 mean values ranged from 8.5 to 14.3 ppm h, 10.5–13.4 ppm h, 9.8–11.9 ppm h, 5.2–9.2 ppm h, and 8.0–9.5 ppm h, respectively. O3-induced yield reductions were estimated to range from 20.1 to 33.3% for winter wheat, 5.0–6.3% for maize, 7.3–8.8% for single rice, 3.9–6.8% for double-early rice and 5.9–7.1% for double-late rice. O3-induced production losses for winter wheat, maize, single rice, double-early rice, and double-late rice totaled 39.5–88.2 million metric tons, 12.6–21.0 million metric tons, 9.5–11.3 million metric tons, 1.2–1.8 million metric tons, and 2.2–2.7 million metric tons, respectively, and the corresponding economic losses totaled 14.3–32.0 billion US$, 3.9–6.5 billion US$, 3.9–4.6 billion US$, 0.5–0.7 billion US$, and 0.9–1.1 billion US$, respectively. Our results suggested that the government should take effective measures to reduce O3 pollution and its effects on agricultural production.
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•Surface O3 is posing an increasingly serious threat to main food crops in China.•The O3-induced yield losses were 20.1–33.3% for wheat, 5.0–6.3% for maize, and 3.9–8.8% for rice.•Annual production losses amounted to 65–124 million metric tons, worth 24–45 billion US$.•Some policies are urgently needed to reduce the risks caused by O3 to agricultural production.
The main finding of this study: This study provides an estimate of O3-induced crop yield losses across China after the implementation of the “Action Plan” using nationwide O3 measurements, suggesting a potential risk for agricultural production in recent years.
Removals of Rhodamine B (RhB) and Acid red 1 using the organic modification of bentonite from aqueous phase were optimized. The organobentonite was synthesized by replacing exchangeable Na+ ions in ...Na-bentonite (Na-Bt) with cetyl trimethylammonium bromide (CTAB) and systematically explored for its adsorption behavior as an efficient adsorbent for the removal of dyes. Batch adsorption studies manifested that the maximum adsorption capacity of dyes were found to be 173.5 mg/g and 157.4 mg/g for RhB and Acid red 1 at the initial concentration of 300 mg/L at 30 °C and pH 9 and 8, respectively. The investigations of adsorption isotherm and kinetics model showed that the adsorption isotherm data were fitted well to the Langmuir isotherm and the adsorption kinetic was better by pseudo-second-order kinetic model. Besides, the thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic. Furthermore, the properties of the obtained samples were characterized by X-ray diffraction (XRD), Scanning electronic microscopy (SEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectrometry (FT-IR) and zeta potential analysis. The results of the characterization provided evidence of the morphological properties and how well the adsorption process performed.
图 Schematic diagram of organic modified bentonite and adsorption dyes. Display omitted
•Adsorption ability of different types of dyes onto CTAB-bentonite was investigated.•The relationship of structures and adsorption properties of adsorbent was explored.•The influence of different factors on the properties of the adsorbent was revealed.
Purpose/significance In order to effectively solve the traffic congestion problem in megacities, it is important to explore the effective application of digital twin technology in urban ...transportation planning. Method/process This article begins by providing an overview of the main content of digital twin technology. Secondly, it analyzes the spatial distribution of urban transportation facilities using the POI data from Amap, with Chengdu City as an example. Methods such as kernel density estimation are employed to examine the spatial distribution of urban transportation facilities in 2016 and 2022, aiming to grasp the current status and existing problems in the planning layout of transportation facilities in megacities. Finally, it explores the path for megacities to achieve digital twin smart transportation planning. Result/conclusion Chengdu has focused on alleviating the traffic congestion problem in the central urban area over the past four years. However, due to high land utilization in the centr
·We explored the pollution characters of metals in street dust of Beijing.·Area-source pollution and point-source pollution exist simultaneously.·We identified the spatial autocorrelation intensities ...and ranges of metals.·Metal pollution anomalies were identified by cluster and outlier analyses.·Urban activities strongly influence the distributions of metals.
The components and concentrations of metals in street dust are indictors of environmental pollution. To explore the pollution levels of Cd, Cr, Cu, Mn, Ni and Pb in street dust and their spatial distribution characteristics, 220 dust samples were collected in a grid pattern from urban street surfaces in Beijing. Multivariate statistics and spatial analyses were adopted to investigate the associations between metals and to identify their pollution patterns. In comparison with the soil background values, elevated metal concentrations were found, except those for Mn and Ni. The results of the geo-accumulation index (Igeo) and the potential ecological risk index (Eri) of the metals revealed the following orders: Cd>Cu>Cr>Pb>Ni>Mn and Cd>Cu>Pb>Cr>Ni. Levels of Igeo ranging from 0 to 5 were found and about 80% of the samples were below the moderately polluted level. The Eri values of single elements were within the low ecological risk level in most sampling sites. Most of the metals in the street dust of Beijing were statistically significantly correlated. It is hard to clearly identify the sources of each metal in the street dust since local environments are very complex. Cadmium, Cu, Cr, Mn and Pb showed medium spatial autocorrelations within the sampling region. Similar spatial distribution patterns were observed for Cu, Cr and Pb, and these metals had relatively high spatial variabilities and were enriched in the center of the city with several peaks scattered in the suburbs. Metal pollution anomalies were identified by using cluster and outlier analyses. Locations identified as clusters with high values indicated non-point source pollution, while locations identified as outliers with high values indicated point source pollution. Traffic, construction, and other human activities influenced these high values. In addition, the locations identified as outliers with low values in urban areas might benefit from less transportation and better management.
The future of islands has been the subject of international concern, scientific debate and media interest in the last decade. As a result of global warming and sea level rise, increasingly more ...research and speculations about the morphology and positions of island coastlines have been produced. However, some assumptions are not well documented due to the lack of large-scale research and data support. This paper contributes to filling this gap by extracting and assessing coastline changes on Southeast Asian islands overall during 2000–2015 based on Landsat remote sensing images. The results are as follows: ① the coastline, defined by the mean high water line (MHWL), of Southeast Asia remained relatively stable but showed considerable variability in space, especially in estuaries, bays and straits. ② A total of 9035 islands were extracted, among which approximately 10% of islands witnessed locational changes in coastlines, resulting in net reductions of nearly 86 km2 in area and 50,000 km in centroid displacement. Additionally, the coastline length increased by 532 km from 2000 (148,508 km) to 2015 (149,040 km). Natural coastlines decreased by 2503 km, while artificial coastlines increased by 3035 km. Among the total coastlines, 11% changed: 5% exhibited deposition, while 6% experienced retreat. ③ The temporal and spatial changes in coastlines were the result of interactions between natural processes and human activities. Climatic and environmental changes had wide impacts, while human activities caused more dramatic local changes. In addition, the sizes, shapes and landforms of the islands played significant roles in coastline changes. ④ Coastal erosion and expansion often coexisted in dynamic equilibrium under the influence of coastal hydrodynamics, such as cyclical tides and near-shore sediment transport. Our findings reveal spatial–temporal variations in island coastlines in Southeast Asia from 2000–2015 and provide critical information for the current study of islands. This work has great significance for the study of global climate change impacts and the integrated management of island coastal zones.
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