Effect of pretreatment of black carbon on electrocatalytic activity of Pt/C catalyst for methanol oxidation

Direct methanol fuel cell (DMFC) has attracted wide attention due to its many advantages. However, its practical application is limited by the low electrocatalytic activity of the anodic Pt/C catalyst usually used for the methanol oxidation. In this paper, in order to increase the electrocatalytic performance of the Pt/C catalyst for the methanol oxidation, the black carbon, usually used as the supporter, was pretreated with CO2, air, HNO3 or H2O2. The cyclic voltarnmetric results indicated that the current densities of the anodic peak of methanol oxidation at the Pt/C catalysts with the black carbon pretreated with CO2,air, HN03, H202 and untreated black carbon were 39, 33, 32, 20 and 18 mA center dot cm(-2), respectively, illustrating that among the above five kinds of the Pt/C catalysts, the Pt/C catalyst with the black carbon pretreated with CO2 shows the best electrocatalytic activity and stability for the methanol oxidation. Its main reason is that the CO2 pretreatment could reduce the content of the oxygen-containing groups on the surface of the black carbon and increase the content of graphite in the black carbon, leading to the low resistance of the black carbon and the increase in the dispersion extent of the Pt particles in the Pt/C catalyst.

Black carbon and polycyclic aromatic hydrocarbons (PAHs) in surface sediments of China's marginal seas

This study investigates the distribution of black carbon (BC) and its correlation with total polycyclic aromatic hydrocarbons (I PAH) pound in the surface sediments of China's marginal seas. BC content ranges from < 0.10 to 2.45 mg/g dw (grams dry weight) in the sediments studied, and varied among the different coastal regions. The Bohai Bay sediments had the highest BC contents (average 2.18 mg/g dw), which comprises a significant fraction (27%-41%) of the total organic carbon (TOC) preserved in the sediments. In comparison, BC in the surface sediments of the North Yellow Sea, Jiaozhou Bay, East China Sea and the South China Sea is less abundant and accounted for an average of 6%, 8%, 14% and 5%, respectively, of the sedimentary organic carbon pool. The concentration of I PAH pound in the surface sediments ranges from 41 to 3 667 ng/g dw and showed large spatial variations among the sampling sites of different costal regions. The Bohai Bay has the highest I PAH pound values, ranging from 79 to 3 667 ng/g dw. This reflects the high anthropogenically contaminated nature of the sediments in the bay. BC is positively correlated to TOC but a strong correlation is not found between BC and I PAH pound in the surface sediments studied, suggesting that BC and PAHs preserved in the sediments are derived from different sources and controlled by different biogeochemical processes. Our study suggests that the abundance of BC preserved in the sediments could represent a significant sink pool of carbon cycling in China's marginal seas.

Preservation of black carbon in the shelf sediments of the East China Sea

Concentrations and carbon isotopic (C-14, C-13) compositions of black carbon (BC) were measured for three sediment cores collected from the Changjiang River estuary and the shelf of the East China Sea. BC concentrations ranged from 0.02 to 0.14 mg/g (dry weight), and accounted for 5% to 26% of the sedimentary total organic carbon (TOC) pool. Among the three sediment cores collected at each site, sediment from the Changjiang River estuary had relatively high BC contents compared with the sediments from the East China Sea shelf, suggesting that the Changjiang River discharge played an important role in the delivery of BC to the coastal region. Radiocarbon measurements indicate that the ages of BC are in the range of 6910 to 12250 years old B. P. (before present), that is in general, 3700 to 9000 years older than the C-14 ages of TOC in the sediments. These variable radiocarbon ages suggest that the BC preserved in the sediments was derived from the products of both biomass fire and fossil fuel combustion, as well as from ancient rock weathering. Based on an isotopic mass balance model, we calculated that fossil fuel combustion contributed most (60%. 80%) of the BC preserved in these sediments and varied with depth and locations. The deposition and burial of this "slow-cycling" BC in the sediments of the East China Sea shelf represent a significant pool of carbon sink and could greatly influence carbon cycling in the region.

渤海湾海岸带表层沉积物中黑炭和多环芳烃的分布特征

黑碳（BC）是生物质和化石燃料不完全燃烧产生的高度聚合的碳质混合物，包括木炭 （char/charcoal）和烟炱碳（soot）等形式。黑碳产生后大部分储存在燃烧原地，而烟炱碳 由于粒径较小，易进入大气，滞留一到数周后回到地表。部分土壤黑碳随河流和大气的搬 运作用进入海洋环境，主要汇集在海岸带沉积物中。由于黑碳涉及到气候变化、碳循环、 环境危害、人体健康等诸多问题而成为当前气候与环境领域的研究热点。黑碳在环境介质 中比较稳定，因而可以较好的指示人类能源使用及其对环境质量的影响；同时黑碳具有很 强的吸附性，能显著影响周围介质中持久性有机污染物(如多环芳烃等)的赋存状态和生态 毒理效应。 多环芳烃（PAHs）是指两个或两个以上的苯环以稠环形式结合的芳香族化合物，主要 来源于含碳物质的不完全燃烧过程，在环境中广泛存在。由于PAHs 具有潜在的致癌性、 致畸性和致突变性（“三致”效应）而在环境研究领域中备受关注。另外由于具有主体的 同源性，PAHs 可以指示BC 的来源和环境过程。 海岸带沉积物是包括BC 和PAHs 在内的众多污染物在环境地球化学迁移过程中的主 要载体和归宿，由于受到陆地和海洋双重作用，海岸带对环境污染物尤其敏感。环渤海地 区是我国北方的社会经济中心，工业、农业和交通发达、人口稠密，污染严重。前人的研 究表明渤海湾的BC 和PAHs 污染程度明显高于我国其他海岸带，但受限制于采样区域和 样品数量，不能全面地反应BC 和PAHs 在渤海湾海岸带的分布状况及人类活动对海岸带 环境质量的影响。 本次研究在渤海湾海岸带潮间带、近海及主要入海河流系统布设了多条采样剖面，采 集表层沉积物样品85 个。首先，对国际上较为常用的化学热氧化法（CTO-375）处理沉积 物黑碳样品的方法进行了比对实验和优化，然后对全部样品进行黑碳分析；利用GC-MS 方法对样品中的PAHs（USEPA 的16 种优控物）进行了定量检测；对全部沉积物样品还进 行了粒度分析。 结果表明，该区域内黑碳的含量为0.09 到22.8 mg/g dw，其中，潮间带样品的BC 平 均含量为0.52 ± 0.39 mg/g dw，近海样品为0.84 ± 0.38 mg/g dw，河流样品（海河样品除外） 为1.88 ± 0.89 mg/g dw。BC占总有机碳的比例在潮间带、近海、河流区域分别为18.4 ± 8.3%、 14.5 ± 5.3%、14.2 ± 4.1%。潮间带黑碳存在明显的“北高南低”的趋势（以天津港码头和 海河为界），与近海和河流样品的BC 浓度有相似的变化趋势，反映了BC 在海岸带的运移 扩散具有一定的继承性；河流输入可能是近岸沉积物BC 的主要来源。同时，潮间带沉积 物粒度分析结果表明“北区细”(以粘土质粉砂主)而“南区粗”(以砂为主)，反映了两个区 域不同的水动力条件和沉积环境，可能是造成BC 浓度空间分异的主要原因。 摘要 II 多环芳烃的含量分布为33.1-7658.7 ng/g dw，其中，潮间带样品的PAHs 平均含量为 147.0 ng/g dw，近海样品为170.9 ng/g dw，河流样品（海河样品除外）为1228.5 ng/g dw。 主要成分均为三环和四环多环芳烃。PAHs 也呈现出了与BC 相似的“北高南低”的趋势， 多环芳烃与黑碳的相关性研究表明两者相关性较好（R2=0.59），表明多环芳烃和黑碳的同 源性和继承性。运用比值法（菲/蒽，荧蒽/芘，低环/高环等）对多环芳烃的来源解析显示， 整个研究区域内多环芳烃主要为燃烧源。

Characteristics of clay minerals in the northern South China Sea and its implications for evolution of East Asian monsoon since Miocene

Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.

中国近海沉积物中黑碳和多环芳烃的研究

黑碳和多环芳烃都是燃烧产生的污染物，并广泛存在于土壤及海洋特别是近海沉积物中。由于黑碳和多环芳烃对环境及生态系统具有不同的影响途径和危害，多年来一直受到环境研究者的极大重视。本文对我国近海几个海区（渤海湾、北黄海、胶州湾、南海珠江口及其邻近海区）沉积物中黑碳和多环芳烃的含量、分布及来源进行了研究，并首次对各海区表层沉积物中黑碳和多环芳烃的相关性进行了分析。 数据显示，中国近海各海区（渤海湾、北黄海、胶州湾、南海珠江口及其邻近海区）表层沉积物中黑碳的浓度范围为0.1 - 2.45 mg/gdw，占总有机碳浓度的1 - 41%，具有较大的空间差异。渤海湾表层沉积物中黑碳浓度最高（平均为2.18 mg/gdw），占沉积物中总有机碳浓度的27 - 41%。相比之下，北黄海、胶州湾和南海珠江口及其邻近海区表层沉积物中黑碳浓度较低，分别占沉积物中总有机碳浓度的6%、8%和5%。黑碳的分布主要受其来源的影响，陆地来源和河流输入是中国近岸海区表层沉积物中黑碳的重要来源。该研究显示黑碳在沉积物中的埋藏可能代表我国近海各海区碳循环中的一个重要碳汇。 中国近海各海区（渤海湾、北黄海、南海珠江口及其邻近海区）表层沉积物中多环芳烃的浓度范围为47.5 – 3673.5 ng/g（均为干重），亦具有很大的空间差异。渤海湾中多环芳烃的浓度最高（82.9 – 3673.5 ng/g），反映了该地区受人类污染严重的特征。在三个海区表层沉积物中，单组分多环芳烃的分布也具有明显不同的特征，渤海湾主要以5、6环的多环芳烃为主，而北黄海和南海珠江口及其邻近海区3、4环多环芳烃的浓度较高。基于多环芳烃的单组分分布特征和一些特殊指数，可以得到渤海湾表层沉积物中的多环芳烃以木材、煤的不完全燃烧来源为主，而北黄海海区和南海珠江口及其邻近海区的多环芳烃显示出木材、煤的燃烧和石油燃烧的混合来源。 中国近海表层沉积物中黑碳浓度与多环芳烃的浓度并不存在很好的相关性，这说明中国近海表层沉积物中的黑碳和多环芳烃具有不同的来源，且在沉积物中的埋藏受控于不同的地球化学作用。

中国西部大气和雪冰黑碳及其传输过程研究

Glaciers in west China are the sources of the major great rivers in Asia, and the solid water resources are crucial to China and South Asia. Black carbon (BC) results in very complex climate effects not only in the atmosphere, but accelerates the melting after its deposit on the surface of snow/ice. As the main distributed area of glaciers in China, the Tibetan Plateau (TP) and Xinjiang region are abutted by South Asia, Central Asia, and Russia, and east China, and the atmospheric environment would be influenced by the BC emitted from these regions. Whereas, the BC’s temporal and spatial distributions for concentration in the mid and top troposphere in west China, its transport, and its radiative forcing after deposited on the snow/ice surface are not well understood at the present. In the field, we collected samples from surface snow, snow pits, ice core, and aerosol in the glaciers, analyzed BC content mainly by the thermo-oxidized method in the laboratory, and discussed temporal and spatial distributions for BC concentrations in glaciers, the transport, and its impacts on the environment. Several conclusions were derived as follows: 1_Spatial distribution and the impact on albedos for BC concentrations in snow/ice: the BC concentrations in the surface snow for the investigated glaciers could be placed in areas, the Tianshan Mountains ＞ the central TP ＞ the Pamirs ＞ the Qilian Mountians ＞ the Himalayas. This distribution could be attributed to the elevation of the glaciers, the topography of the TP, and more regional emissions. Probably significant impacts on the albedos of the glacier surface could be caused by BC deposits, and the estimated reduced albedos on the glaciers are 9.8% (the Zhadang glacier), 8.7% (the Miao’ergou Riverhead No.3 glacier), and 6.8% (the Kuitun River Haxilegen No.48 glacier), and 6.2% (the Dongkemadi glacier), and 5.3% (the La’nong glacier), and 4.2% (the Muztagata glacier), etc. 2_The temporal variance of BC concentrations in ice of the East Rongbuk Glacier (ERG) and its climatic implications: major cations and anions (e.g., SO42- and Ca2+) concentrations in aerosols during summer monsoon seasons showed their close relationships with the sources of air masses, in which the variance of SO42- concentrations suggested the atmospheric environment over the ERG was significantly influenced by the aerosols from South Asia. BC record based on an ice core suggested its deposit was dominantly transported by monsoons in summers and by westerlies in other seasons, and the BC from South Asia in summers dominated the varying trend of its concentrations in the ice core and caused higher concentrations in summers than those in other seasons. In the past 50 yrs, BC concentrations showed fluctuations, whereas showed an increasing tread in the most recent decade, and exceeded 50 μg kg-1 in the summer of 2001; correspondingly, the radiative forcing caused by BC showed an increasing trend since 1990s, and exceeded 4.5 W m-2 in the summer of 2001. 3_Cabonaceous aerosols in the Nam Co region: organic carbon (OC) concentration accounted for ～95% and BC for ～5% in the total carbonaceous aerosol concentration, which was significantly influenced by summer precipitations. OC was dominantly derived from fossil fuel burning and BC from both fossil fuel and biomass burning. Trajectory analysis and aerosol optical depth suggested the atmospheric environment in the Nam Co region was most probably influenced by the emissions from South Asia. The potential source regions of air pollutants in the Nam Co regions in summers might be Bangladesh and east India, and in winters might be the Indo-gangetic basin. The scavenging ratio of atmospheric BC by rainfalls was less than those at other sites. West China is a less-developed region for industry, where BC concentrations in the atmosphere and snow/ice could be significantly influenced by the emissions from the abutted regions with rising industries (South Asia, Central Asia, and Russia). For example, snow/ice BC concentrations in the glaciers of the Parmirs, the Tianshan Mountains, and the Qilian Mountains in the northeast margin of the TP might be more influenced by the emissions from Centrial Asia (transported by the westerlies), those in the glaciers of the Himalayas might be more influenced by the emissions from South Asia (transported by the monsoons and the westerlies), and atmospheric carbonaceous aerosols might also be more influenced by the emissions from South Asia (transported by the monsoons and the westerlies). The BC concentrations in some glaciers might cause significant impacts on the albedos for the glaciers, and therefore enhanced the radiative forcings, for example, the ERG. The research on the relationships among atmospheric and snow/ice BC and its radiative forcing, variance of snow cover, mass balance of glaciers, and climate forcing would be needed in future.

黄土高原22万年来的黑碳记录和古火灾害历史重建

The term black carbon is used to describe a relatively inert and ubiquitous form of carbon, comprising a range of materials from char and charcoal to element or graphite carbon produced by the incomplete combustion of fossil fuels and biomass. Due to its inertness, the BC in soils, lacustrine and marine sediments and ice can persist over a long period of time. So BC signatures in geological deposits can be used as evidence of natural fires happened in their surroundings. To study the temporal and spatial changes in paleofires over the Chinese Loess Plateau, black carbon concentrations were analyzed on the loess-paleosol samples from three sections including Lijiayuan, Lingtai and Weinan along a north-south transect. Using the orbitally-tuned time-scales of the sections, the black carbon sedimentation rates (BCSR) were calculated. Meanwhile, with objective to document fine resolution fire history during late Pleistocene and Holocene periods, we measured BC concentrations of loess-paleosol samples at dense sampling intervals since 28 ka BP. in Lijiayuan section. The BCSR of the samples were also calculated. In addition, we also conducted observation on black carbon morphologies to examine their sources. Based on the results, the following remarks can be concluded: 1. In the last two glacial cycles, the BCSR values in glacial periods are 2-3 times higher than in interglacial periods, and the BCSR variability has a relatively strong precession-associated 23 kyr period, suggesting that the glacial cold-dry climate conditions were apt to induce natural fires over the Loess Plateau, 2. Comparison of the BCSR records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern and interglacial periods. 3. Pollen records and carbon isotope analyses of organic matter have shown that the Loess Plateau was covered by an Artemisia-dominated grassland vegetation both during glacial and interglacial periods, So grassland fires were the dominant fire types in the Plateau, which is also corroborated by the observation of black carbon morphology. In addition, statistics and comparison of BC particle sizes among the sections demonstrated that BC records probably reflected local fires. 4. According to previous studies about the effect of fires on vegetation changes, we considered that the fires might play an important role in the expansion of grassland during glacial periods, besides the control of climate changes. 5. The high resolution black carbon record in Lijiayuan section has shown that the BCSR series well documented Younger dryas (YD) and Heinrich (HI和H2) events, suggesting that natural fires in the northwestern part of Chinese Loess Plateau could regularly respond to the millennial scale climate oscillation.