Strategies for improving the photocatalytic performance of metal-organic frameworks for CO2 reduction: A review

Photocatalytic CO₂ reduction is an appealing strategy for mitigating the environmental effects of greenhouse gases while simultaneously producing valuable carbon-neutral fuels. Numerous attempts have been made to produce effective and efficient photocatalysts for CO₂ reduction. In contrast, the selection of competitive catalysts continues to be a substantial hindrance and a considerable difficulty in the development of photocatalytic CO₂ reduction. It is vital to emphasize different techniques for building effective photocatalysts to improve CO₂ reduction performance in order to achieve a long-term sustainability. Metal-organic frameworks (MOFs) are recently emerging as a new type of photocatalysts for CO₂ reduction due to their excellent CO₂ adsorption capability and unique structural characteristics. This review examines the most recent breakthroughs in various techniques for modifying MOFs in order to improve their efficiency of photocatalytic CO₂ reduction. The advantages of MOFs using as photocatalysts are summarized, followed by different methods for enhancing their effectiveness for photocatalytic CO₂ reduction via partial ion exchange of metal clusters, design of bimetal clusters, the modification of organic linkers, and the embedding of metal complexes. For integrating MOFs with semiconductors, metallic nanoparticles (NPs), and other materials, a number of different approaches have been also reviewed. The final section of this review discusses the existing challenges and future prospects of MOFs as photocatalysts for CO₂ reduction. Hopefully, this review can stimulate intensive research on the rational design and development of more effective MOF-based photocatalysts for visible-light driven CO₂ conversion.     

Heavy metal bioaccumulation in selected medicinal plants collected from Khetri copper mines and comparison with those collected from fertile soil in Haridwar,India

Heavy metal distribution in medicinal plants is gaining importance not only as an alternative medicine, but also for possible concern due to effects of metal toxicity. The present study has been focused on emphasizing the heavy metal status and bioaccumulation factors of V, Mn, Fe, Co, Cu, Zn, Se (essential metals) and Cr, Ni, Cd, As and Pb (potentially toxic metals) in medicinal plants grown under two different environmental conditions e.g., near to Khetri copper mine and those in fertile soils of Haridwar, both in India, using Instrumental Neutron Activation Analysis (relative method) and Atomic Absorption Spectrometry. The copper levels in the medicinal plants from Khetri were found to be 3-4 folds higher (31.6–76.5 mg kg^?1) than those from Haridwar samples (7.40–15.3 mg kg^?1), which is correlated with very high copper levels (763 mg kg^?1) in Khetri soil. Among various heavy metals, Cr (2.60–5.92 mg kg^?1), Cd (1.47–2.97 mg kg^?1) and Pb (3.97–6.63 mg kg^?1) are also higher in concentration in the medicinal plants from Khetri. The essential metals like Mn (36.4–69.3 mg kg^?1), Fe (192–601 mg kg^?1), Zn (24.9–49.9 mg kg^?1) and Se (0.13–0.91 mg kg^?1) and potentially toxic metals like Ni (3.09–9.01 mg kg^?1) and As (0.41–2.09 mg kg^?1) did not show much variations in concentration in the medicinal plants from both Khetri and Haridwar. The medicinal plants from Khetri, e.g., Ocimum sanctum, Cassia fistula, Withania somnifera and Azadirachta Indica were found rich in Ca and Mg contents while Aloe barbadensis showed moderately high Ca and Mg. Higher levels of Ca-Mg were found to correlate with Zn (except Azadirachta Indica). The bioaccumulation factors (BAFS) of the heavy metals were estimated to understand the soil-to-plant transfer pattern of the heavy metals. Significantly lower BAF values of Cu and Cr were found in the medicinal plants from Khetri, indicating majority fraction of these metals are precipitated and were immobilized species unsuitable for plant uptake. Overall, Withania somnifera (Ashwagandha) showed very high metal bioaccumulation.     

Absorption characteristics of new solvent based on a blend of AMP and 1,8-diamino-p-menthane for CO2 absorption

Aqueous 1,8-diamino-p-menthane (KIER-C3) and commercially available amine solutions were tested for CO₂ absorption. A 2-amino- 2-methyl-1-propanol (AMP) solution with an addition of KIER-C3 showed 9.3% and 31.6% higher absorption rate for CO₂ than the AMP solution with an addition of monoethanolamine (MEA) and ammonia (NH₃), respectively. The reaction rate constant for CO₂ absorption by the AMP/KIER-C3 solution was determined by the following equation: k_2,AMP/C3 = 7.702×10⁶ exp (-2248.03/T). A CO₂ loading ratio of the AMP/KIER-C3 solution was also 2 and 3.4-times higher than that of the AMP/NH3 solution and the AMP/MEA solution, respectively. Based on the experimental results, KIER-C3 may be used as an excellent additive to increase CO₂ absorption capability of AMP.     

博斯腾湖夏季水下光场特征分析及影响因素探讨

2011年8月,在新疆博斯腾湖17个站点进行水样采集,同步对11个站点进行水下光场原位测定.结果发现,博斯腾湖夏季总颗粒物吸收系数光谱表现出明显的浮游植物吸收特征,而浮游植物光谱曲线有明显的硅藻吸收光谱特征.在光合有效辐射波段,有色可溶性有机物（CDOM）吸收系数与浮游植物吸收系数对总吸收的贡献相当,而非色素颗粒物对总吸收的贡献最低.水下光谱衰减系数的最小值出现在580nm左右的绿光波段,PAR漫射衰减系数平均值为0.53m-1,平均真光层深度约为9.69m,大于湖水平均深度.在博斯腾湖虽然纯水和CDOM在总吸收中占有很重要的部分,但主导漫射衰减的因子仍为颗粒物.通过本文研究,以期能为干旱地区湖泊环境保护和水质遥感监测提供数据和理论基础.     

改进测定水中氨氮分子吸收光谱法的试验研究

水中氨氮含量是反应水质状况的重要指标。文章对测定水中氨氮气相分子吸收光谱法(标准号HJ/T195-2005)进行了改进试验研究。第一,对氧化剂的配比进行了改进,使氨氮的测定范围扩展至100μg。第二,对标准HJ/T195-2005中直接使用亚硝酸钠标准溶液做标准曲线的处理方式也做了探讨。通过一系列对比实验认为,应用硫酸铵标准溶液做工作曲线更加准确合理。最后应用改进后的气相分子吸收光谱法和纳氏比色法或滴定法对多种实际废水样品进行同时测定。结果表明,改进后的气相分子吸收光谱法测定氨氮的范围更宽,灵敏度更高和准确度更好。     

浅水富营养湖泊生态修复效应时间序列与诊断研究

2008年3月至2009年9月对紫阳湖生态修复效应进行了全程跟踪监测及诊断指示研究。研究表明,通过水生生物群落构建,水生态环境有了明显改善,全湖水质达到地表水IV标准,透明度上升到100 cm左右,叶绿素a下降到10 mg/m3以下。生态修复后各指标50%的效应时间序列为Chla、DO、SD、TP、NH3-N、TN和COD。研究认为,Chla/SD作为湖泊水质指数(LQI)是检验生态修复效果较敏感的指标,可用于浅水富营养湖泊生态修复后水质的诊断和评价。     

复合吸收技术净化复杂工业有机废气

以低浓度、大风量、含无机物、尘粒和油分等成分的复杂工业有机废气为对象,进行复合吸收净化技术的研究,从吸收机制初步探索,对净化设备、工艺流程及工程应用分别进行了探讨.分别以3种不同的表面活性剂溶液为复合吸收剂,考察其处理含甲苯和醋酸丁酯废气的净化效果,结果表明降低复合吸收剂的表面张力,有利于甲苯和醋酸丁酯的去除率.针对复杂工业有机废气,开发高效吸收设备,集合了水膜、旋流板和填料3种吸收净化装置的优点于一体,具有结构简单、体积小、防堵塞及多级高效吸收传质的优势.工艺流程以吸收技术为主,整合了加热吹脱、燃烧和厌氧等工艺,最终使废气和吸收尾液达标排放.该技术已在制造、喷涂等多家企业的工程上应用.     

广东南水水库富营养化与浮游植物群落动态

南水水库是广东省第三大水库,属饮用水源一级保护区。于2011年1~12月对该水库的水文、水质和浮游植物进行了每月一次、为期一年的调查,采用营养状态指数(TSI)进行了水质综合评价,分析了浮游植物群落的动态变化规律,选择冗余分析(RDA)研究了影响浮游植物群落结构的环境因素。结果表明:南水水库现为贫营养型,全年浮游植物的种类变化不大,共鉴定出浮游植物6门50属(种),优势种以适应贫营养的种类为主,且浮游植物的丰度、生物量及叶绿素a浓度都较低,其均值分别为8.72×104～2.51×105cells/L、0.031～0.423 mg/L和0.83～2.80 mg/L。浮游植物群落主要以硅藻、甲藻和绿藻种群为主,硅藻种群全年占优势,甲藻和绿藻在不同季节优势度有变化,体现出从硅藻型到硅藻-甲藻型,到硅藻-绿藻型,再到硅藻-甲藻型的变化过程。温度、氮磷比和水体稳定性的季节变化是影响上述浮游植物群落动态的主要因子。     

查干湖和新立城水库秋季水体悬浮颗粒物和CDOM吸收特性

分别于2012年9月对不同盐度水体的查干湖和新立城水进行水体野外采样和室内实验分析,通过测定颗粒物、CDOM等光学活性物质的吸收系数来对比分析两种水体的光学活性物质的吸收特性、来源及其在400~700 nm范围内对总吸收系数的贡献.结果表明,综合营养状态评价指数显示秋季查干湖、新立城水库水体属于中等富营养化,总悬浮颗粒物的吸收光谱表现均与色素类颗粒物吸收光谱相似.对于盐度较大的查干湖水体(EC=988.87μS·cm~(-1)),非藻类颗粒物占主导地位,各组分贡献率为非藻类颗粒物色素颗粒物CDOM;而盐度较低的新立城水库水体(EC=311.67μS·cm~(-1)),色素颗粒物贡献率略大于非藻类颗粒物贡献,各组分贡献率依次为:色素颗粒物非藻类颗粒物CDOM.查干湖总悬浮颗粒物吸收系数α_p(440)、α_p(675)和非藻类颗粒物吸收系数α_d(440)分别与TSM(总悬浮颗粒物)、ISM(无机悬浮颗粒物)和OSM(有机悬浮颗粒物)、Chl-a(叶绿素a)相关性均较好,相关系数在0.55以上;新立城水库α_p(440)、α_p(675)与Chl-a相关性较好(0.77和0.85,P0.05),α_d(440)与ISM具有相关性(0.74,P0.01),与OSM表现为负相关(-0.63,P0.05).查干湖CDOM吸收系数a_g(440)仅与OSM表现为负相关性(-0.54,P0.05),而新立城水库α_g(440)与其他参数均无相关性.通过对CDOM吸收曲线在250~400 nm的拟合所得到的S_g以及相对分子量M_r发现,查干湖的S_g[(0.021±0.001)m~(-1)]大于新立城的S_g[(0.017 6±0.001)m~(-1)],而CDOM的相对分子量M_r值分别为11.44±2.00(7.5~15.09)、7.53±0.79(6.17~8.89),查干湖M_r值高于新立城水库水体,表明查干湖CDOM组成较新立城水体中CDOM的分子量小,组成更趋向于小分子.查干湖受风速和湖岸坍塌的影响产生矿物悬浮、沉积微粒,水体颗粒物以非藻类为主,部分来自于浮游植物降解产物;新立城水库水体不仅有径流携带的陆源性无机物的输入,同时水体浮游植物生长减弱且微生物分解活动加强,降解有机颗粒物与非藻类吸收系数呈现负相关.     

黑麦草、丛枝菌根对番茄Cd吸收、土壤Cd形态的影响

采用大田试验研究了在重金属Cd(5.943 mg·kg~(-1)污染下,黑麦草和丛枝菌根对2个品种番茄("德福mm-8"和"洛贝琪")生长、Cd含量以及对土壤微生物、酶活性、p H和Cd形态的影响.结果表明,黑麦草和丛枝菌根单一或复合处理显著提高了2个品种番茄果实、根、茎、叶和植株总干重,增幅分别为14.1%~38.4%和4.2%~18.3%、20.9%~31.5%和8.4%~10.3%、13.0%~16.8%和3.0%~9.5%、10.7%~16.8%和2.7%~7.6%、14.3%~36.6%和4.5%~16.8%.黑麦草和丛枝菌根单一或复合处理增加了土壤中细菌、真菌、放线菌数量及土壤脲酶、转化酶、磷酸酶、过氧化氢酶活性,且土壤微生物数量及土壤酶活性在不同品种和处理间的差异达到显著性水平(P0.05).与番茄套种黑麦草或接种丛枝菌根提高了土壤p H值,降低了土壤中可交换态(EXC-Cd)、碳酸盐态(CAB-Cd)和铁锰氧化态(Fe-Mn-Cd)和土壤中Cd总量,土壤中Cd总量降幅为16.9%~27.8%.2个番茄品种果实、叶、茎和根中的Cd含量分别显著下降了6.9%~40.9%、5.7%~40.1%、4.6%~34.7%和9.8%~42.4%.Cd主要积累在番茄的叶、根和茎中,果实积累较少.比较供试的2个番茄品种,果实Cd含量和积累量及植株Cd总积累量以"洛贝琪""德福mm-8".