磷掺杂碳负载Zn_(x)P_(y)O_(z)常温常压下高效电催化合成氨

合成氨(NH_(3))的发展是现代工业进程和人类生存的基石。受氮气(N_(2))化学惰性的限制,当前的合成氨工业能源消耗高并且排放大量的二氧化碳。电化学氮气还原反应(NRR),是有望取代高能耗的Haber-Bosch(HB)合成法的一种绿色可持续的合成氨工艺。然而,因氮气以及析氢竞争富反应(HER)导致电催化氮气还原极低的NH_(3)产率和能量转换效率一直是目前人工固氮领域面临的挑战。在本文中,我们报道了一种具有丰富孔结构的磷掺杂碳(PC)负载Zn_(3)(PO_(4))_(2)/Zn_(2)P_(2)O_(7)纳米复合材料(h-PC/Zn_(3)(PO_(4))_(2)/Zn_(2)P_(2)O_(7)),在酸性和中性介质中将N_(2)高效催化转化为NH_(3)。其独特的分级多孔结构提高了表面粗糙度并加快了氮气在催化剂体相中的扩散,这有利于延长氮气在催化剂表面的停留时间以及提高活性位点的利用效率。而多组分的均匀分布可以调节电子结构并优化反应中间体的吸附行为,进而提高活性位点的本征活性。在0.1mol·L^(-1)HCI电解液中,h-PC/Zn_(3)(PO_(4))_(2)/Zn_(2)P_(2)O_(7)在-0.2 V vs.可逆氢电极(RHE)电位下NH_(3)的产率可以达到38.7±1.2μg·h^(-1)·mgcat^(-1),法拉第效率为19.8%±0.9%。此外;h-PC/Zn_(3)(PO_(4))_(2)/Zn_(2)P_(2)O_(7)在0.1 mol·L^(-1)Na_(2)SO_(4)溶液中同样展现出优异的电催化氮气还原合成氨性能,NH_(3)产率及法拉第效率分别为17.1±0.8μg·h^(-1)·mgcat^(-1)和15.g%±0.6%,明显优于PC/Zn_(3)P_(2)、C/ZnO和大多数报道的非贵金属电催化剂。这种优异的性能主要归因于多孔结构有利于传质及多组分活性位点协同效应。此外,我们采用非原位X射线光电子能谱(XPS)、透射电子显微镜(TEM)和X射线衍射(XRD)等表征手段对NRR测试前后h-PC/Zn_(3)(PO_(4))_(2)/Zn_(2)P_(2)O_(7)的组成和结构变化进行了剖析。在反应后检测到了新增的N物种信号,证明催化剂确实发生了氮气还原反应。本研究提供了一种通过同步构建传质通道并耦合不同的活性位点以协同增强NRR活性和选择性的新思路,这对加快绿色制氨工业化具有重大意义。

Cost-benefit and discriminant validity of a stepwise dementia case-finding approach in an Asian older adult community

Background Case-finding is a recommended approach for dementia early detection in the community.Aims To investigate the discriminant validity and cost-effectiveness of a stepwise dementia case-finding approach in a Singaporean older adult community.Methods The two-phase study was conducted in the community from 2009 to 2015 in Singapore.A total of 3780 participants(age≥60 years)completed phase I(a brief cognitive screening);918 completed phase II and were included in the final analysis.In phase I,all participants were administered the Abbreviated Mental Test(AMT)and the Progressive Forgetfulness Question(PFQ).Those who screened positive on either test were invited to phase II,whereby the Mini-Mental State Examination(MMSE),Montreal Cognitive Assessment(MoCA)and a formal neuropsychological battery were administered,followed by the research diagnosis of no cognitive impairment,cognitive impairment no dementia(CIND)-Mild(≤2 impaired cognitive domains),CIND-Moderate(>2 impaired domains)or dementia.Receiver operating characteristic curve analyses were conducted for the different cognitive instruments.All discriminant indices were calculated,including sensitivity,specificity,positive and negative predictive values(NPV)and accuracy.Cost-effectiveness analysis was conducted by estimating the amount of screening time needed and the number of older adults requiring re-evaluation in two case-finding scenarios,ie,with or without preselection by the PFQ.Results The stepwise case-finding approach(preselection by the PFQ,then MMSE or MoCA or AMT)showed an excellent NPV(>99%)and accuracy(>86%)for excluding dementia-free cases.Without preselection by the PFQ,screening time for the three cognitive tools were 317.5,317.5 and 254 hours,with 159,302 and 175 screen-positive older adults involved in further evaluation.By adopting the stepwise case-finding approach,total screening time were 156.5,156.5 and 126.2 hours,which decreased by 50.7%,50.7% and 50.3% as compared with those without preselection.Furthermore,after preselection,only 98,167 and 145 screen-positive older adults required further evaluation,corresponding to a reduction of 38.4%,44.7% and 17.1% in the numbers compared with those without preselection.Conclusions A stepwise approach for dementia case-finding should be implemented in the community to minimise the time and resources needed for large-scale early detection of dementia.

生物燃气净化提纯制备生物天然气技术研究进展

生物天然气是由生物燃气经过脱硫、脱碳、脱水等工艺手段净化提纯后得到的一种可再生燃气,其成分和热值与常规天然气无异,是我国重点发展的生物能源。传统生物燃气中高含量的H2S和CO2限制了其应用,因此生物燃气净化提纯技术是生物天然气实现商业化生产的关键。本工作综述了国内外生物天然气制备过程中的脱硫和脱碳技术,对各项技术的工艺流程、原理及工业化应用情况进行了详细介绍,阐述了各技术的关键环节和优缺点,指出了生物燃气净化提纯技术当前面临的挑战,讨论了脱硫和脱碳技术未来的发展趋势,旨在为生物天然气的研究和工业发展提供工艺参考。要点:(1)归纳分析了生物天然气制备过程中各种脱硫和脱碳技术的原理、工艺流程及关键技术。(2)对比了不同脱硫和脱碳技术的关键性能参数和各自的优缺点。(3)指出了生物燃气脱硫脱碳技术当前面临的挑战,展望了未来的发展方向。

高效液相色谱法测定生物脱硫系统中的含硫化合物

生物脱硫是利用微生物脱除气体和石油中的含硫化合物,具有操作条件温和、工艺流程简单、脱硫效率高、能量消耗低和环境污染少等优点。但是,当前仍然缺乏简单高效的分析方法来定量分析生物脱硫过程中的含硫化合物。针对这个问题,建立了柱前荧光衍生高效液相色谱法同时测定生物脱硫溶液中的亚硫酸盐、硫代硫酸盐和硫化物的分析方法。该分析方法中含硫化合物的标准曲线具有良好的线性关系,亚硫酸盐、硫代硫酸盐和硫化物相关系数分别为0.99946、0.99967和0.99965,其检测限分别为0.0006μmol/L、0.0007μmol/L和0.0011μmol/L;含硫化合物的加标回收率范围分别为98.17%–101.92%、100.90%–102.60%和101.11%–104.22%;并具有良好的重复性和稳定性。实验证明,该分析方法预处理简单、分析快速、结果准确,可用于同时测定不同生物脱硫系统中的含硫化合物。