Potential release pathways, environmental fate, and ecological risks of carbon nanotubes

Carbon nanotubes (CNTs) are currently incorporated into various consumer products, and numerous new applications and products containing CNTs are expected in the future. The potential for negative effects caused by CNT release into the environment is a prominent concern and numerous research projects have investigated possible environmental release pathways, fate, and toxicity. However, this expanding body of literature has not yet been systematically reviewed. Our objective is to critically review this literature to identify emerging trends as well as persistent knowledge gaps on these topics. Specifically, we examine the release of CNTs from polymeric products, removal in wastewater treatment systems, transport through surface and subsurface media, aggregation behaviors, interactions with soil and sediment particles, potential transformations and degradation, and their potential ecotoxicity in soil, sediment, and aquatic ecosystems. One major limitation in the current literature is quantifying CNT masses in relevant media (polymers, tissues, soils, and sediments). Important new directions include developing mechanistic models for CNT release from composites and understanding CNT transport in more complex and environmentally realistic systems such as heteroaggregation with natural colloids and transport of nanoparticles in a range of soils.     

Dispersion state and humic acids concentration-dependent sorption of pyrene to carbon nanotubes

Sonication and humic acids (HA) are known to disperse carbon nanotube (CNT) suspensions, but potential effects on sorption of chemicals to CNTs remain poorly understood. We applied a passive sampling method to investigate the influence of dispersion/aggregation on sorption of pyrene to CNTs. Sonication broke down CNT aggregates and increased pyrene sorption affinity by up to 1.39 orders of magnitude. Sorption surfaces newly exposed by sonication remained available to pyrene even after reaggregation occurred, suggesting an irreversible effect of sonication. The presence of HA decreased sorption of pyrene to CNTs, but at the highest HA concentration investigated (200 mg/L), sorption affinity was still 1.90 orders of magnitude larger than sorption of pyrene to HA alone. Specific interactions between pyrene and CNTs were thus still taking place, in spite of the presence of a HA coating on the CNTs' surface. A greater suppression of sorption by CNTs occurred when the HA addition was combined with a sonication pretreatment. Sorption isotherm fitting indicated that the maximum sorption capacity, sorption affinity, and heterogeneity of the CNT surface were all affected by sonication and the presence of HA at a concentration as low as 1 mg/L. The present results contribute to an improved understanding of the sorption behavior of CNTs in both natural and wastewater systems.     

Electrochemical carbon nanotube filter oxidative performance as a function of surface chemistry

An electrochemical carbon nanotube filter has been reported to be effective for the removal and electrooxidation of aqueous chemicals and microorganisms. Here, we investigate how carbon nanotube (CNT) chemical surface treatments including calcination to remove amorphous carbon, acid treatment to remove internal residual metal oxide, formation of surficial oxy-functional groups, and addition of Sb-doped SnO(2) particles affect the electrooxidative filter performance. The various CNT samples are characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) and electrochemically evaluated by cyclic voltammetry, open circuit potential versus time analysis, and electrochemical impedance spectroscopy. Voltammetry results indicate that the near CNT surface pH is at least two units lower than the bulk pH. The electrooxidative performance of the various CNT samples is evaluated with 1 mM of methyl orange (MO) in 100 mM sodium sulfate at a flow rate of 1.5 mL min(-1). At both 2 and 3 V, the efficacy of electrochemical filtration is observed to be function of CNT surface chemistry. The samples with the greatest electrooxidation were the calcinated then HCl-treated CNTs, i.e., the CNTs with the most surficial sp(2)-bonded carbon, and the Sb-SnO(2)-coated CNTs, i.e., the CNTs with the most electrocatalytic surface area. At 3 V applied voltage, these CNT samples are able to oxidize 95% of the influent MO within the liquid residence time of <1.2 s. The broader applicability of electrochemical filtration is evaluated by challenging the C-CNT-HCl and C-CNT-HNO(3) networks with various organics including methylene blue, phenol, methanol, and formaldehyde. At 3 V applied voltage, both CNTs are able to degrade a fraction of all the organics with the extent organic degradation dependent on both CNT and organic properties. The C-CNT-HCl network generally had the better oxidative performance than the C-CNT-HNO(3) network with an exception being the positively charged methylene blue. The extent of MO degradation, steady-state current, anode potential, effluent pH, and back pressure are also measured as a function of applied voltage (1-3 V) and CNT surface chemistry. Mass spectrometry of electrochemical CNT filter effluent at 2 and 3 V is utilized to evaluate plausible electrooxidation products. Energy consumption as compared to state-of-the-art electrodes and strategies to tailor the CNT surface for a specific target molecule are discussed.     

Photoreactive TiO2/carbon nanotube composites: synthesis and reactivity

Electron-hole recombination limits the efficiency of TiO2 photocatalysis. We have investigated the efficacy with which anatase/carbon nanotube (CNT) composite materials reduce charge recombination and enhance reactivity. We synthesized nanostructured assemblies composed of different proportions of anatase (5 or 100 nm) and either single-or multi-walled CNTs. The composites were prepared using a simple low temperature process in which CNTs and anatase nanoparticles were dispersed in water, dehydrated at 80 degrees C, and dried at 104 degrees C. The structures of the various TiO2/CNT composites were characterized by scanning electron microscopy (SEM) and their function was tested by phenol oxidation. Charge recombination was compared by measuring the photoluminescence spectra of select composites. We found that a nanostructured composite assembled from the 100 nm anatase and single-walled CNTs (SWCNTs) exhibited enhanced and selective photocatalytic oxidation of phenol in comparison to both pure anatase and Degussa P25. A mechanism for the enhanced reactivity is proposed in which electrons are shuttled from TiO2 particles to the SWCNTs as a result of an optimal TiO2/ CNT arrangement that stabilizes charge separation and reduces charge recombination. In addition, the SWCNT assembly provides better catalyst-support (dispersal and connection) than multi-walled CNTs.     

Tannic acid adsorption and its role for stabilizing carbon nanotube suspensions

Dissolved organic matter (DOM) has been reported to stabilize carbon nanotube (CNT) suspensions, which increases concern over the subsequent transport and behavior of CNTs. However, it is unknown exactly which compounds or functional groups cause the stabilization of CNTs in natural environments. Naturally occurring tannic acid (TA), which has a large number of aromatic functional groups, was used as a surrogate of DOM to investigate its interaction with CNTs. CNT suspendability in TA solution increased with increasing CNT diameter without the aid of sonication. Sorption affinity of CNTs for TA increased with decreasing CNT diameter, positively related to their surface area. A two-stage sorption model was proposed to illustrate the interaction between CNTs and TA. TA molecules may be adsorbed first onto CNTs with aromatic rings binding to the surface carbon rings via pi-pi interactions, until forming a monolayer; the TA monolayer then further sorbed the dissolved TA by hydrogen bonds and other polar interactions. The sorbed TA increased the steric repulsion between individual CNTs, which might disperse the relatively loose CNT aggregates and result in the stabilization of large-diameter CNTs in TA solution. The sorption and suspending processwere also examined bytransmission electron microscopy, providing further evidence for the above proposed CNT-TA interactions. This study implies that widely distributed TA may promote the mobility and transport of CNTs in natural aqueous environments.     

Electrical conductivity of CNT/polysulfonamide composites

Carbon nanotube/polysulfonamide (CNT/PSA) composite spinning solutions with different CNTs contents were prepared using the physical blending method. The corresponding composite fibers were extruded through a set of wet spinning unit and the composite membranes were prepared using a digital spin-coating technique. The distribution of CNTs in PSA matrix and the crystalline structure of composite fibers were investigated by scanning electron microscope (SEM) and X-ray diffraction, respectively. The influences of CNTs on mechanical properties as well as electrical conductivity of PSA composites were also analyzed. In addition, the general effective media equation was chosen to explain the electrical conductivity behavior of the CNT/PSA composites. The experimental results showed that CNTs with low contents can be distributed evenly in PSA; the crystallization in PSA was promoted at low CNTs contents; the mechanical properties of composites can be improved significantly; and the electrical conductivity of composites increased obviously and the percolation threshold of the blending system was at about 3?wt%.     

腐植酸钠对棉织物的吸附性能

采用腐植酸钠对棉织物进行染色,研究了染色pH值、温度、氯化钠用量、浴比和腐植酸钠用量对染色织物色深值△E的影响,探讨了腐植酸钠对棉纤维的吸附动力学和热力学。研究表明,染色pH值对染色织物的色深值影响很小,随着染色温度的升高染色织物的△E值逐渐降低,氯化钠用量为0-15g/L时染色织物色深值逐渐增加,氯化钠用量高于15g/L时染色织物色深值逐渐下降直至平衡,随着染色浴比的增大染色织物的△E值逐渐降低,0-6%o.m.f的腐植酸钠用量范围内,腐植酸钠在棉纤维上具有很好的提升性能。由动力学数据可知,染色温度越高,腐植酸钠在棉纤维上的吸附速率k越快,半染时间t1/2越短,平衡吸附量C∞越低。由热力学数据可知,腐植酸钠在棉纤维上的吸附适合用Freundlich热力学吸附模型描述,其与棉纤维以氢键和范德华力结合为主。     

Cadmium bioavailability and accumulation in the presence of humic acid to the zebra mussel, Dreissena polymorpha

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.     

腐植酸的提取及上染羊毛纱线的工艺

研究了从四川大凉山无土栽培基质中提取的腐植酸,对其组分等进行了测试分析.将所提取的腐植酸用于羊毛纱线的染色,并对染色工艺进行了研究.实验采用单因素对比方法分别对影响羊毛染色的染料用量、染液pH值、染色温度、染色时间等做系列梯度实验.得出最佳染料用量、染液pH值、染色时间、上染温度等工艺条件.实验结果表明:腐植酸作为一种天然环保型染料可用于羊毛纱线(蛋白质纤维)的染色.     

Effect of humic and fulvic acid concentrations and ionic strength on copper and lead binding

We investigated the influence of humic and fulvic acid concentration (in the range of 1-1000 mg/L) on the binding of the two trace metals Cu(II) and Pb(II). The ability of the non-ideal competitive adsorption (NICA)-Donnan model to correctly predict Cu and Pb binding at low humic or fulvic acid concentration and lower ionic strength (0.01 M NaNO3), based on model parameters obtained from experiments conducted at high humic or fulvic acid concentrations (approximately 1000 mg/L) and higher ionic strength (0.1 M NaNO3), was tested. The binding of Cu and Pb to humic and fulvic acid in 0.01 M NaNO3 was determined over wide ranges in proton and metal ion activities using three different methods: ligand exchange-adsorptive differential pulse cathodic stripping voltammetry at low humic or fulvic acid concentrations (1-3 mg/L), differential pulse anodic stripping voltammetry at intermediate humic or fulvic acid concentrations (10-20 mg/L), and ion-selective electrodes at high humic or fulvic acid concentrations (approximately 1000 mg/L). The results demonstrate that binding isotherms for Cu and Pb can be measured at low humic or fulvic acid concentration using suitable voltammetric techniques. The binding isotherms for Cu and Pb to humic and fulvic acid obtained at constant pH values in the range of pH 4-8 are shown to be independent of humic and fulvic acid concentration. The NICA-Donnan model, calibrated for Cu and Pb binding using data measured at high humic and fulvic acid concentrations and an ionic strength of 0.1 M, accurately predicts Cu and Pb binding at low humic and fulvic acid concentrations and lower ionic strength (0.01 M). We conclude that NICA-Donnan parameters obtained by fitting experimental data measured with ion-selective electrodes at high humic or fulvic acid concentrations can be used for geochemical modeling of soils and aquatic environments with much lower concentrations of humic or fulvic acids.     

Effects of natural organic matter and solution chemistry on the deposition and reentrainment of colloids in porous media

The role of humic acid in the transport of negatively charged colloids through porous media was examined. Adsorption of humic acid on latex colloids and silica collectors reduced the deposition of suspended particles and enhanced the reentrainment of deposited particles in porous media. These effects are considered to arise from additional electrostatic and steric contributions to the repulsive interaction energy due to the adsorption of negatively charged humic acid on both the suspended particles and the media collectors. At low ionic strength reversible deposition in shallow secondary minima is hypothesized to be the principal attachment mechanism, independent of the presence of humic acid. It is proposed that under these solution conditions, particle deposition and reentrainment are the result of a dynamic process, in which particles are continuously captured and released from secondary minima. At higher ionic strengths, deposition may be regarded as a combination of two mechanisms: capture in the primary well and capture in the secondary minimum. Theoretical calculations of the attachment efficiency were conducted using two existing mathematical models. The first model is based on deposition in the primary well (interaction force boundary layer, IFBL), and the second model is based on the Maxwell kinetic theory and deposition in the secondary minimum (Maxwell model). Simulations conducted with the Maxwell model provide significantly better fits of the experimental results than those conducted with the IFBL model.     

Systematic and Quantitative Investigation of the Mechanism of Carbon Nanotubes' Toxicity toward Algae

Concurrent with the increasing production and application of carbon nanotubes (CNTs) comes an increasing likelihood of CNTs presenting in the aquatic environment, and thereby potentially threatening aquatic organisms via toxic mechanisms that are, at present, poorly understood. This study systematically investigated the toxicity of three multiwalled CNT (MWCNT) samples toward a green alga (Chlorella sp.), focusing on examining and quantifying the contributions of five possible mechanisms to the algal growth inhibition. The results showed that the MWCNTs significantly inhibited the algal growth. The contribution of metal catalyst residues in the MWCNTs to the algal growth inhibition was negligible, as was the contribution from the MWCNTs' adsorption of nutrient elements. The algal toxicity of MWCNTs could mainly be explained by the combined effects of oxidative stress, agglomeration and physical interactions, and shading effects, with the quantitative contributions from these mechanisms depending on the MWCNT size and concentration. At MWCNT concentrations around 96 h IC(50), the oxidative stress accounted for approximately 50% of the algal growth inhibition, whereas the agglomeration and physical interactions, and the shading effects each took approximately 25% of the responsibility.     

Inhibition of humic substances mediated photooxygenation of furfuryl alcohol by 2,4,6-trimethylphenol. Evidence for reactivity of the phenol with humic triplet excited states

To probe the reactivity of 2,4,6-trimethylphenol with humic triplet excited states, we investigated its influence on the humic substances-mediated photooxygenation offurfuryl alcohol. Elliott soil humic and fulvic acids were employed for these experiments. When added in the concentration range of 10(-4) - 10(-3) M, 2,4,6-trimethylphenol inhibited furfuryl alcohol photooxygenation to an extent depending on its concentration. The inhibiting effect decreased as the oxygen concentration was increased. By postulating that 2,4,6-trimethylphenol competes with oxygen for reaction with humic triplet excited states and with furfuryl alcohol for reaction with singlet oxygen, we obtained kinetic laws describing the consumption profiles of furfuryl alcohol and 2,4,6-trimethylphenol. Experimental rates of 2,4,6-trimethylphenol and furfuryl alcohol loss could be satisfactorily fitted with 1.09-1.16 for the ratio k2/k3, where k2 and k3 are the reaction rate constants of humic triplet excited states with oxygen and 2,4,6-trimethylphenol, respectively. These types of experiments could be extended to a variety of substrates to measure their reaction rate constants with humic triplet excited states.     

乳铁蛋白-乳清分离蛋白乳状液微聚集体构建与酶交联对其流变学特性的影响

以乳清分离蛋白（whey protein isolate,WPI）与乳铁蛋白（lactoferrin,LF）乳状液形成微聚集体与转谷氨酰胺酶酶促交联微聚集体,以期提高体系流变特性。通过微射流分别制备WPI和LF乳状液,二者混合后,乳状液微滴之间发生异型聚集效应,通过转谷氨酰胺酶交联结合形成具有特定三维空间网络结构的微聚集体。研究结果表明：WPI与LF乳状液发生异型聚集,最大程度的聚集和最高物理稳定性体系发生在50% LF-50% WPI微滴形成的微聚集体。异型聚集效应改变了乳状液的流变特性,与单一WPI和LF乳状液相比,50% LF-50% WPI微聚集体流变学特性黏度值分别为单一乳状液的3.72?倍和2.2?倍,通过转谷氨酰胺酶交联,乳状液微聚集体的黏度值为原来的11.4?倍。因此,基于异型聚集效应结合酶促交联,可提高食品体系的流变特性,为开发食品脂质替代物提供了一定的理论支持。     

发酵乳杆菌的生长限制性因素分析及高密度培养工艺优化

为提高发酵乳杆菌的增殖浓度,对其高密度发酵培养基成分及培养工艺进行优化以提高其活菌数。结果表明,酵母粉复合大分子肽的蛋白胨是发酵乳杆菌的最适氮源,缓冲盐在恒pH培养时对菌株生长无促进作用,Mn²⁺和Mg²⁺均是发酵乳杆菌的限制性微量元素。另外,中性条件下酸根的积累不会对发酵乳杆菌有特异性毒害作用,其生长主要是受到渗透压的抑制。以菌株生长速率被抑制时的碳氮消耗比作为培养基中的碳氮源比例,基于菌株生长速率被抑制时的渗透压确定碳氮源的添加量。进一步优化恒pH分批培养和恒pH自动反馈补糖培养工艺,得到各菌株的最优培养策略:发酵乳杆菌FXJCJ6-1、发酵乳杆菌FGDLZR161、发酵乳杆菌CCFM422分别在恒pH 6.0、5.5、5.5分批培养时,活菌数分别达到(1.3±0.1)×10¹⁰、(1.1±0.1)×10¹⁰、(9.5±0.5)×10^(9 )CFU/mL,较在MRS培养基静置培养时的活菌数提高了3.1、3.8和4.6倍。该研究结果的应用将显著提高发酵乳杆菌的工业化生产效率。     

Role of humic acid and ouinone model compounds in bromate reduction by zerovalent iron

Experiments were conducted to examine the role of humic acid and quinone model compounds in bromate reduction by Fe(0). The reactivity of Fe(0) toward bromate declined by a factor of 1.3-2.0 in the presence of humic acid. Evidence was obtained that the quick complexation of humic acid with iron species and its adsorption passivated the iron surface and decreased the rate of bromate reduction by Fe(0). On the other hand, in the long run, the reduced functional groups present in humic acid were observed to regenerate Fe(II) and reduce bromate abiotically. Compared with the case of humic acid only, the simultaneous presence of Fe(II) and humic acid significantly increased the bromate removal rate. Fe(III)/Fe(II) acted as a catalyst in the oxidation of humic acid by bromate. Anthraquinone-2,6-disulfonate (AQDS) and lawsone did not cause any significant effect on the bromate reduction rate by Fe(0). However, the redox reactivity of lawsone in the presence of Fe(III) was evident, while AQDS did not show any under the tested conditions. The difference was attributable to the presence/ absence of reducing functional groups in the model compounds. The electron spin resonance further demonstrated that the redox functional groups in humic acid are most likely quinone-phenol moieties. Although the bromate reduction rate by regenerated Fe(II) is a few times slower than that by Fe(0), the reactive Fe(II) can be, alternatively, reductively formed to maintain iron surface activation and bromate reduction to prolong the lifetime of the zerovalent iron.     

Involvement of humic substances in regrowth

There appear to be interactions in the distribution system that complicate the ability to use AOC/BDOC as an independent assessment of regrowth potential. Two such complications are the limitation of the assays themselves and the potential interaction between the organic carbon concentration with the presence of disinfectants and pipe materials. To address these interactions, a series of experiments spanning several years have been conducted in model distribution systems at the Center for Biofilm Engineering (CBE) using soil-derived humics. When compared to easily utilized organics, humic substances supported the same order of magnitude of biofilm organisms. As carbon concentration was increased from 500 to 1000 to 2000 ppb, there was no increase in growth rate of the organisms, suggesting zero-order kinetics. If the system was chlorinated, there was less biomass, but growth rates were higher. In the presence of corrosion products, humic-fed systems supported more organisms than a control system fed biologically treated water. When free chlorine was maintained at a residual of about 0.2 mg/l, biofilm numbers on the surfaces were reduced. Phosphate alone did not result in fewer bacteria, while a combination of chorine and phosphate had the best results (lowest biofilm numbers). Adjustment to pH 9 was not effective. Recently completed work compared increasing levels of humic substances in the presence of free chlorine and monochloramine on biofilm growth on a number of surfaces (PVC, epoxy, cement, ductile iron). As the concentration of humic substances was increased from 0, 0.5 to 2 mg/l, there was an increase in biofilm numbers on all surfaces. This effect was the most pronounced on iron surfaces. These results illustrate that carbon compounds not measured by the BDOC or AOC tests may profoundly influence biofilm numbers. In addition, iron surfaces are at much higher risk for elevated biofilm counts in the presence of humic substances, even if disinfection is practiced. However, corrosion control may mitigate this interaction.     

15N NMR investigation of the covalent binding of reduced TNT amines to soil humic acid,model compounds,and lignocellulose

The five major reductive degradation products of TNT-4ADNT (4-amino-2,6-dinitrotoluene), 2ADNT (2-amino-4,6-dinitrotoluene), 2,4DANT (2,4-diamino-6-nitrotoluene), 2,6DANT (2,6-diamino-4-nitrotoluene), and TAT (2,4,6-triaminotoluene)-labeled with 15N in the amine positions, were reacted with the IHSS soil humic acid and analyzed by 15N NMR spectrometry. In the absence of catalysts, all five amines underwent nucleophilic addition reactions with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and nonheterocyclic condensation products. Imine formation via 1,2-addition of the amines to quinone groups in the soil humic acid was significant with the diamines and TAT but not the monoamines. Horseradish peroxidase (HRP) catalyzed an increase in the incorporation of all five amines into the humic acid. In the case of the diamines and TAT, HRP also shifted the binding away from heterocyclic condensation product toward imine formation. A comparison of quantitative liquid phase with solid-state CP/MAS 15N NMR indicated that the CP experiment underestimated imine and heterocyclic nitrogens in humic acid, even with contact times optimal for observation of these nitrogens. Covalent binding of the mono- and diamines to 4-methylcatechol, the HRP catalyzed condensation of 4ADNT and 2,4DANT to coniferyl alcohol, and the binding of 2,4DANT to lignocellulose with and without birnessite were also examined.     

Competitive sorption of pyrene, phenanthrene, and naphthalene on multiwalled carbon nanotubes

Knowledge of toxic chemical sorption by carbon nanotubes (CNTs) is critical for environmental application of CNTs as superior sorbents and for environmental risk assessment of both CNTs and toxic chemicals. Single-solute sorption results were reported in the literature, however, they cannot be used for predicting pollutant sorption by CNTs in wastewater and natural water systems where multiple organic contaminants are present. In this study, competitive sorption of pyrene, phenanthrene, and naphthalene on a multiwalled CNT material was investigated. All isotherms in single-, bi-, and tri-solute systems were fitted well by the Dubinin-Ashtakhov (DA) model. The isotherm of a given primary solute changed from being significantly nonlinear to nearly linear when competitors were added. The observed competitive sorption depended on the relative equilibrium concentrations of both primary and cosolutes. Significant competition was observed at relatively low concentrations of primary solute and high concentrations of competitors, while competition was much weaker in the case of relatively high concentrations of primary solute and low competitor concentrations. When the relative concentration of primary solute (Ce/Cs) approached 1, competition by other solutes seemed to disappear. Sorption and competition of three polycyclic aromatic hydrocarbons (PAHs) on CNTs could not be explained with either pore-filling or partition-adsorption mechanisms. A Polanyi-based surface adsorption mechanism was proposed to interpret the observed sorption and competition.     

熊果酸纯化工艺优化

为了将熊果酸的纯度自25%提取纯化到98%以上,以熊果酸提取率及其纯度为评价指标,综合考虑乙醇体积分数、溶解温度、料液比及料炭比(原料质量与活性炭质量的比值)对熊果酸提取纯化的影响,并对其提取纯化工艺进行优化。结果表明：熊果酸纯化的最佳工艺条件为乙醇体积分数95%、提取温度80℃、料液比1:20(g/mL)、料炭比2:1,在此条件下熊果酸的提取率为45.68%,纯度达98.55%。