气相二氧化硅物理吸附水测定及与表面硅羟基含量之间关系

热重分析法测定气相二氧化硅表面硅羟基含量操作简便、无化学试剂、误差小,近年来越来越受到关注。但是,其中物理吸附水脱除的条件还存在争议。文中选用国内外2家代表性公司生产的相同比表面积的气相二氧化硅为对象,详细地研究了升温模式、升温速率、等温温度和等温时间对其表面物理吸附水脱除的影响。确定了物理吸附水脱除的最优测试条件:10℃/min升温至200℃等温5 min。对比发现,相同条件下,国外产品的脱水量高于国内产品,这可能是由于国外产品具有更高的硅羟基含量所致。本工作不但找到了国内外产品关键性能的差距,而且完善了热重分析法测定气相二氧化硅表面羟基含量,并为相关测试标准的发展提供技术支撑。

水热时间和低温热处理对δ-MnO_2电容性能的影响

以高锰酸钾(KMnO4)为原料,在不同反应时间下水热法制备δ-MnO_2,同时对不同反应时间制备的δ-MnO_2进行300℃低温热处理。通过SEM揭示δ-MnO_2的生长机理,采用SEM、TEM和XRD对δ-MnO_2的形貌和结晶度进行表征,利用N2吸附-脱附法表征δ-MnO_2的比表面积,通过恒电流充放电、循环伏安法和交流阻抗法对δ-MnO_2的电化学性能进行测试。实验结果表明:随着水热时间的延长,δ-MnO_2的结晶度依次增加,比电容逐渐增大;当电流密度为0.1A/g时,10h的样品在1 M Na2SO4电解液中比电容高达264F/g,展现出最优的比电容。进一步对水热样品进行300℃低温热处理,结晶度进一步提高的同时物理吸附水大量丢失,导致比电容均出现下降。结果证实了δ-MnO_2的结晶度和表面的物理吸附水对电容性能都具有贡献作用,二者缺一不可。δ-MnO_2随着结晶度的提高,层状结构越趋稳定,存储离子电荷的能力不断增强,同时材料表面的物理吸附水有助于提高电解液与电极材料之间的浸润性,降低电荷转移电阻,产生较大的赝电容。

结合水对二氧化铅还原反应的影响

采用循环伏安、恒流放电以及差热分析等方法分析了物理吸附水和化学结构水对于α-PbO2和β-PbO2在放电过程中的还原反应所起的作用。实验证明水的损失直接导致了PbO2容量和电导的下降。当只有物理吸附水被除去时,α-PbO2和β-PbO2的容量损失不大;而化学结构水被除去时,α-PbO2和β-PbO2的容量都衰减很大,而且α-PbO2所受影响更大。对于扩散系数而言,当只有物理吸附水被除去时,β-PbO2的扩散系数变化很小,而α-PbO2的扩散系数下降很大;化学结构水的损失使得β-PbO2的扩散系数变化很大,而α-PbO2的扩散系数变化很小。

Biosorption and desorption of Cd^(2+) from wastewater by dehydrated shreds of Cladophora fascicularis

The adsorption and desorption of algae Cladophora fascicularis and their relation with initial Cd2+ concentration, initial pH, and co-existing ions were studied. Adsorption equilibrium and biosorption kinetics were established from batch experiments. The adsorption equilibrium was adequately described by the Langmuir isotherm, and biosorption kinetics was in pseudo-second order model. The experiment on co-existing ions showed that the biosorption capacity of biomass decreased with an increasing concentration of competing ions. Desorption experiments indicated that EDTA was efficient desorbent for recovery from Cd2+. With high capacities of metal biosorption and desorption, the biomass of Cladophora fascicularis is promising as a cost-effective biosorbent for the removal of Cd2+ from wastewater.

Removal of Heavy Metal Ions from Wastewater by Using Biosorbents from Marine Algae-A Cost Effective New Technology

Heavy metal pollution from industrial wastewater is a worldwide environmental issue. Biosorption of heavy metals by using biosorbents derived from various types of biomass has been shown to be effective for the uptake of heavy metal ions. In this study, biosorbents derived from the biomass of a group of marine macroalgae were used for the removal and recovery of heavy metal ions from aqueous solutions. Results indicated that the biosorbents have high uptake capacities and affinities for a number of heavy metal ions. The uptake capacities of the biosorbents were in the range of 1.0 to 1.5mmol·g-1 for divalent heavy metal ions. The kinetics of the uptake process was fast and the process can be used in both batch and fixed-bed operations. It appears that the biosorption process by using biosorbents from marine macroalgae can be an efficient and cost effective technology for the treatment of heavy metal containing wastewater.

Adsorption of catechol from aqueous solution by aminated hypercrosslinked polymers

Adsorption of catechol from aqueous solution with the hypercrosslinked polymeric adsorbent NDA-100 and its derivatives AH-1, AH-2 and AH-3 aminated by dimethylamine, the commercial resin Amberlite XAD-4 and weakly basic anion exchanger resin D301 was compared. It was found that the aminated hypercrosslinked resins had the highest adsorption capacities among the tested polymers. The empirical Freundlich equation was successfully employed to describe the adsorption process. Specific surface area and micropore structure of the adsorbent, in company with tertiary amino groups on matrix affected the adsorption performance towards catechol. In addition, thermodynamic study was carried out to interpret the adsorption mechanism. Kinetic study testified that the tertiary amino groups on the polymer matrix could decrease the adsorption rate and increase the adsorption apparent activation energy.

Biosorption mechanism of Cr (Ⅵ) onto cells of Synechococcus sp.

The biosorption mechanism of Cr （Ⅳ） ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr （Ⅳ） consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-LR spectra of K2Cr2O7, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp show that the speciation of chromium that binds to the cells ofSynechococcus sp. is Cr （Ⅲ）, instead of Cr （Ⅳ）, and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr （Ⅲ）. Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr （Ⅵ）, and the results of FT-IR show that the biosorption of Cr （Ⅵ） follows two subsequent steps, biosorption of Cr2O7 ^2- by electrostatical force at the protonated active sites and reduction of Cr2O7^2- to Cr^3＋ by the reductive groups on the surface of the biosorbents.

Fabrication and adsorption property of novel adsorbent for potential application to wastewater with Fe(Ⅲ) ions

The spherical macroporous cellulose(SMC) was fabricated using medical absorbent cotton as raw material and nano CaCO3 as porogenic agents.And then,the phenylglycine was grafted onto the SMC to obtain the novel spherical macroporous cellulose derivative adsorbent(PSMC).FT-IR and scanning electron microscope(SEM) were employed to characterize the adsorbents and Fe3+ ions served as model solute to evaluate the adsorption property of the adsorbents.The experimental results show that the amount of porogenic agents and the value of pH have obvious influence on adsorption capacity of the adsorbents.The data of adsorption kinetic and isotherm display that the adsorbents possess excellent equilibrium adsorption capacity(348.94 mg/g) and have a bright prospect and considerable potential in the treatment of Fe3+ ions in wastewater.

掺膨胀剂水泥净浆膨胀变形的低场磁共振原状解析

应用膨胀剂补偿水泥基材料干燥收缩时,其补偿效果的发挥与化学结合水和物理吸附水的演化密切相关,多数细微观测试分析手段都要求对试件进行干燥预处理,难以辅助分析补偿收缩的时间发展历程。利用原位无损的低场磁共振弛豫技术,结合宏观质量和长度测试,对持续水养和高湿度空养的掺膨胀剂净浆进行长期监测,从水分状态和含量角度,定量分析化学结合水与物理吸附水的演化规律,进而解析净浆的补偿收缩变形。结果表明:在持续水养过程中,从水养第3 d起算,净浆质量、膨胀变形、可蒸发水含量均持续增大,但增加速率逐渐降低。掺硫铝酸钙类或氧化镁类膨胀剂可明显增大净浆化学结合水增量及其单位增量导致的膨胀变形,但几乎不影响物理吸附水的演变规律及其单位增量导致的膨胀变形。在高湿度(98%相对湿度)空养过程中,从空养第0d(水养第56d)起算,净浆质量先降低、后升高;净浆先收缩、后膨胀;可蒸发水含量在前28 d内迅速降低,后保持稳定。掺硫铝酸钙类或氧化镁类膨胀剂会增大净浆前期可蒸发水含量降幅,也会增大后期膨胀变形以补偿收缩。掺膨胀剂水泥基材料的膨胀过程极其复杂,利用低场磁共振技术并结合其它测试方法实现膨胀变形的精确解析,有助于完善膨胀机理,并协助选用膨胀剂。