Nb_2O_5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(Ⅵ)

Niobium oxide nanowire-deposited carbon fiber(CF) samples were prepared using a hydrothermal method with amorphous Nb_2O_5·nH_2O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction(XRD), energy-dispersive spectroscopy(EDS), scanning electron microscopy(SEM), transmission electron microscopy(TEM), selected-area electron diffraction(SAED), UV–visible spectroscopy(UV–vis), N_2 adsorption–desorption, Fourier transform infrared spectroscopy(FT-IR), and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr(VI) was determined.Parameters such as pH value and initial Cr(VI) concentration could influence the Cr(VI) removal efficiency or adsorption capacity of the Nb_2O_5/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14 hr. The maximal Cr(VI) adsorption capacity of the Nb_2O_5 nanowire/CF sample was 115 mg/g. This Nb_2O_5/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr(VI) under UV-light irradiation: the Cr(VI) removal efficiency reached 99.9% after UV-light irradiation for 1 hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr(VI) adsorption capacity and photocatalytic performance was related to its high surface area,abundant surface hydroxyl groups, and good UV-light absorption ability.     

浅埋富水软岩隧道大变形机理与控制研究∗

针对洞口段富水浅埋软弱围岩隧道易发生挤压性大变形的特点,依托某隧道,通过监控量测、室内试验、数值模拟等手段分析隧道的变形特征、影响因素及其致灾机制与力学破坏模式。结果表明,隧洞开挖后变形具有流变特性,且持续时间长、变形量大;此外,上、中台阶开挖造成的拱顶沉降、围岩收敛分别占总变形的 61.16%、63.34%, 是大变形产生的主要阶段;洞内大变形是在多种影响因素的耦合作用下产生的,地下水是造成该软岩隧道大变形的主要控制因素,地下水的软化、渗流是大变形的主要变形机理,破坏力学模式主要有软岩塑流和累进性松脱扩展两种,软岩塑流造成侧墙鼓出、顶压以及钢拱架扭曲等现象,累进性松脱扩展造成垮塌、地表裂缝等现象。数值模拟验证了大变形力学机理的正确性并反演了大变形发展趋势。最终针对该隧道大变形产生的主要原因,提出并实践形成了“内外结合”的主动控制技术：洞外掌子面动态跟进超前降水,洞内“中管棚+小导管”超前支护、上台阶 “核心土+扩大拱脚”、中台阶“临时仰拱+大锁脚”、下台阶“短进短衬,快速支护”,成功穿越 300 m 浅埋富水极软岩段,研究成果可为类似工程提供借鉴。     

柴油环卫车电动化替代环境效益分析及可行性评估

以环卫车为研究对象,通过使用阶段柴油环卫车和电动环卫车污染排放强度对比,分析电动化替代所产生的环境效益。应用模糊数学模型方法从技术、经济、配套设施、污染减排效益方面,综合评估环卫车电动化替代可行性。结果表明:电动环卫车较柴油环卫车具有显著的减排效果,主要大气污染物排放可减少95.5%。影响柴油环卫车电动化替代的关键因素在电池动力性能、续航能力、经济成本和配套设施充电时长等方面。模糊数学模型的评估结果表明,50%柴油环卫车进行电动化替代是最佳方案,能较好地平衡经济性和大气环境保护的公共利益。未来提高电动化替代比例,还需依靠科技创新改进电动环卫车电池技术和动力等性能,降低购置成本,加强充电桩等配套基础设施的完善。     

Concurrent adsorption and reduction of chromium(VI) to chromium(III) using nitrogen-doped porous carbon adsorbent derived from loofah sponge

• A high-efficiency N-doped porous carbon adsorbent for Cr(VI) was synthesized. • The maximum adsorption capacity of Cr(VI) reached up to 285.71 mg/g at 318K. • The potential mechanism for Cr(VI) adsorption by NHPC was put forward. • DFT analyzed the adsorption energy and interaction between NHPC and Cr(VI). To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m²/g), and pore volume (1.18 cm³/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R²≥0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (−0.84 eV) was lower than that of HPC (−0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI).     

中国生态文明建设试点政策评估研究

生态文明建设是关系中华民族永续发展的千年大计。近年来,为加强我国生态文明建设,国家层面制定了一系列生态文明建设试点政策,发挥了对全局性改革的示范、突破和带动作用,但也存在部分试点政策执行进展偏慢、效果不如预期等问题,亟待进行系统评估。本研究基于政策过程理论,从政策制定与政策执行两个维度遴选26项评估指标,通过定量分析与定性分析相结合,对我国的生态文明试点政策体系(共9大类、53项)进行系统评估。研究发现:(1)政策目标有待完善,考核机制尚需健全;(2)改革任务交叉重复且分工不明,存在部门利益导向;(3)试点的空间、类型分布不均衡,试点选择科学性不足;(4)立法、市场、社会参与等管理手段有待进一步完善。在此基础上,本研究从目标设置、任务优化、试点布局以及管理机制运用等四个方面提出了若干对策建议,以期对完善我国生态文明建设制度体系提供决策参考。     

Are there differences in the forces driving the conversion of different non-urban lands into urban use? A case study of Beijing

Environmental Science and Pollution Research - Examining the heterogeneous factors behind the conversion of various types of non-urban land into urban use is of great significance for controlling...     

The interactive influence of personal norm and policy measures on urban resident waste separation behaviour

Journal of Material Cycles and Waste Management - To explore the factors that influence residents’ waste separation intention (WSI) and the interaction mechanism among different influencing...     

Time-varying spillovers among pilot carbon emission trading markets in China

Environmental Science and Pollution Research - Clarifying the time-varying spillovers among pilot carbon emission permit trading markets in China is an important foundation for building the...