Effect of Tube Diameters and Functional Groups on Adsorption and Suspension Behaviors of Carbon Nanotubes in Presence of Humic Acid.

The adsorption and suspension behaviors of carbon nanotubes (CNTs) in the water environment determine the geochemical cycle and ecological risk of CNTs and the compounds attached to them. In this study, CNTs were selected as the research object, and the effect of tube diameters and functional groups (multiwall CNTs (MWNTs) and hydroxylated MWNTs (HMWNTs)) on the adsorption and suspension behaviors of the CNTs in the presence of humic acid (HA) was systematically analyzed. The results indicate that HA adsorption decreased with the increase in the solution pH, and the adsorption amount and rate were negatively correlated with the tube diameter of the CNTs. The surface hydroxylation of the CNTs prevented the adsorption of HA, and the maximum adsorption amounts on the MWNTs and HMWNTs were 195.95 and 74.74 mg g-1, respectively. HA had an important effect on the suspension of the CNTs, especially for the surface hydroxylation, and the suspension of the CNTs increased with the increase in the tube diameter. The characteristics of the CNTs prior to and after adsorbing HA were characterized by transmission electron microscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. The results indicate that surface hydroxylation of the CNTs increased the adsorption of aromatic compounds, and that the CNTs with a smaller diameter and a larger specific surface area had a disordered carbon accumulation microstructure and many defects, where the adsorption of part of the HA would cover the defects on the CNTs' surface. Density functional theory (DFT) calculations demonstrated that HA was more easily adsorbed on the CNTs without surface hydroxylation. This investigation is helpful in providing a theoretical basis for the scientific management of the production and application of CNTs, and the scientific assessment of their geochemical cycle and ecological risk.

Impact of montmorillonite clay on the homo- and heteroaggregation of titanium dioxide nanoparticles (nTiO2) in synthetic and natural waters.

The homoaggregation of titanium dioxide nanoparticles (nTiO2) and their heteroaggregation with ubiquitous natural clay colloids are crucial processes affecting the environmental transport and fate of nTiO2, whereas the latter has received less attention. In this study, the effects of pH, electrolytes, natural organic matter (NOM), and montmorillonite on the homo- and heteroaggregation of nTiO2 were systematically investigated. The isoelectric point of bare nTiO2 was 6.98, whereas TiO2-montmorillonite mixtures remained negative charged due to the reduced particle surface potential by heteroaggregation. Homoaggregation of nTiO2 was mainly affected by anions, whereas heteroaggregation in TiO2-montmorillonite mixtures was mainly affected by cations. Heteroaggregation between nTiO2 and montmorillonite involved the adsorption of CC/CH. Intensive aggregation of nTiO2 was observed with 4 mg/L montmorillonite, whereas with 20 mg/L montmorillonite, the aggregation was significantly inhibited by the over-coverage of montmorillonite. NOM was attached to the surface of nTiO2 with the adsorption of functional groups involving CC/CH and OCO. The addition of NOM effectively reduced the homo- and heteroaggregation of nTiO2, and the stabilizing effect was enhanced with the increased molecular weight and aromatic/aliphatic fraction in NOM. Besides electrostatic repulsion, steric repulsion could also be one of the main stabilization mechanisms of NOM. With Ca2+ in the solutions, the stabilizing effect of NOM was significantly weakened through cation bridging. The addition of montmorillonite could facilitate the aggregation of nTiO2 in the presence of NOM. The homo- and heteroaggregation of nTiO2 were also observed in 7 different types of natural waters. Homoaggregation predominated in waters with high ionic strength and low NOM contents (seawater and groundwater), whereas heteroaggregation predominated in surface freshwater and wastewater systems. The results reflect the instability of nTiO2 in natural aquatic environments and the potential risk they pose to benthic organisms.

Aggregation and stability of sulfate-modified polystyrene nanoplastics in synthetic and natural waters.

Nanoplastics (NPs) are becoming emerging pollutants of global concern. Understanding the environmental behavior of NPs is crucial for their environmental and human risk assessment. In this study, the aggregation and stability of polystyrene (PS) NPs were investigated under different hydrochemical conditions such as pH, salt type (NaCl, CaCl2, Na2SO4), ionic strength (IS), and natural organic matter (NOM). The critical coagulation concentrations of PS NPs were determined to be 158.7 mM NaCl, 12.2 mM CaCl2, and 80.0 mM Na2SO4. Ca2+ was more effective in destabilizing PS NPs, compared to Na+, owing to its stronger charge screening effect. In the presence of monovalent ions, NOM reduced aggregation through steric repulsion, whereas in the case of divalent ions, NOM induced aggregation through cation bridging. Initial and long-term stability studies demonstrated that, in waters with high IS and NOM content, NOM was the most significant factor affecting NPs aggregation. PS NPs would be highly suspended in all freshwaters, and even in wastewater, whereas they would aggregate rapidly and deposit in seawater. Finally, a statistical model was established to evaluate the hydrodynamic diameter of NPs in different waters. The results indicated the stability of PS NPs in natural aquatic environments and their potential for long-term transport.

Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids.

Environmental behavior, bioavailability and risks posed by TiO2, nanomaterials (TiO2 NMs) in surface waters are affected by morphologies of the particles and geochemistry, including pH, inorganic and organic matter. Here, the adsorption, aggregation and sedimentation of TiO2 nanoparticles (TiO2 NPs) and nanotubes (TiO2 NTs) were investigated in the presence of Elliott Soil humic acid (HAE) and Suwannee River humic acids (HAS). The adsorption amount of HA on TiO2 NMs was inversely proportional to pH of solution. Maximum adsorption amount of HA on the surface of TiO2 NMs follows the order TiO2 NPs + HAE (236.05 mg/g) > TiO2 NTs + HAE (146.05 mg/g) > TiO2 NTs + HAS (70.66 mg/g) > TiO2 NPs + HAS (37.48 mg/g). Stability of TiO2 NPs and TiO2 NTs largely depended on their isoelectric point, morphology and solution pH in the absence of HA. Dispersion of TiO2 NMs was enhanced with solution pH deviated from the isoelectric point of nanomaterials due to electrostatic repulsion. Moreover, tubular structures of TiO2 NTs with higher length-diameter ratio seem to aggregate more easily than dose sphere-like TiO2 NPs. This might be due to their spherical structure enhancing steric repulsion. Notably, the adsorption of HA led to disagglomeration and significant stability of TiO2 NPs and TiO2 NTs due to steric hindrance under varying solution pH. In addition, adsorption time, concentration and sources of HA also influenced suspension/sedimentation behavior of TiO2 NPs and TiO2 NTs, and aromatic-rich HAE stabilized TiO2 NMs suspension more aggressively than aliphatic-rich HAS.

Effects of fulvic acid on aggregation, sedimentation, and adsorption of Fe3O4 magnetic nanoparticles.

Environmental behavior, bioavailability, and risks posed by Fe3O4, magnetic nanoparticles (Fe3O4 NPs) in surface waters are affected by complex geochemistry, including pH and inorganic and organic matter. This work provides a systematic analysis of adsorption of fulvic acid (FA) on surfaces of Fe3O4 NPs with adsorption kinetics, adsorption thermodynamic, and adsorption isotherm. Adsorption of FA on surfaces of Fe3O4 NPs is consistent with assumptions of Langmuir and Freundlich adsorption isotherm models. The adsorption amount of FA was inversely proportional to solution pH, and the maximum amount is 128.6 mg g-1. Adsorption of FA on surfaces of Fe3O4 NPs is a spontaneous endothermic process. FA plays an important role in aggregation and suspension/sedimentation behavior of Fe3O4 NPs in aquatic environmental. With continuous adsorption of FA, electrostatic repulsion between the particles and the steric hindrance of FA significantly decreased aggregation and increased suspension of Fe3O4 NPs. The results of FTIR and XPS indicated that FA was adsorbed on Fe3O4 NPs mainly through chemical reactions, and carbohydrates particularly play an important role in adsorption.

Transcatheter arterial chemoembolization monotherapy vs combined transcatheter arterial chemoembolization-percutaneous microwave coagulation therapy for massive hepatocellular carcinoma (≥10 cm).

BACKGROUND: The prognosis of massive hepatocellular carcinomas (MHCCs; ≥10 cm) remains worse. PURPOSE: The aim of this study was to evaluate the clinical benefits of transcatheter arterial chemoembolization (TACE) or TACE combined with percutaneous microwave coagulation therapy (PMCT) and the long-term survival rate of MHCC patients treated with these techniques. PATIENTS AND METHODS: A retrospective study was performed using data involving 102 MHCC patients admitted to the Second Hospital of Nanjing from September 2010 to August 2015. The median interval between treatments and overall survival (OS) was hierarchically analyzed using log-rank tests. Multivariate analysis was done using Cox regression model analysis. RESULTS: The median survival time of MHCC patients was 3 months (range, 1-10 months) in the palliative group, 3 months (range, 1-39 months) in the TACE group, and 7.5 months (range, 3-30 months) in the TACE-PMCT group (P=0.038). The 6-, 12-, and 18-month OS rates for MHCC patients were 15%, 0%, and 0% in the palliative group, 30%, 25.63%, and 17.97% in the TACE group, and 50%, 41.67%, and 16.67% in the TACE-PMCT group, respectively (P=0.0467). In addition, TACE sessions had positive correlation with the survival time of MHCC patients (rho = 0.462, P<0.001). TACE treatment more than three times (HR =0.145, P<0.001) was an independent predictor of the survival of MHCC patients, which was identified by the Cox regression model analysis. CONCLUSIONS: These results indicated that TACE-PMCT treatment in MHCC patients had advantages in prolonging OS and improving liver function. Multiple TACE treatments might be a suitable treatment for the MHCC patients.

Amendment of water quality standards in China: viewpoint on strategic considerations.

Water quality standards (WQS) are the most important tool for protection of quality of aquatic environments in China and play a decisive role in the management of China's aquatic environments. Due to limited scientific information available previously, WQS were developed largely based on water quality criteria (WQC) or WQS recommended by developed countries, which may not be suitable for current circumstances in China. The Chinese government recently initiated the revision of Environmental Quality Standards for Surface Water (EQSSW) (GB3838-2002) to meet the challenge of environmental protection. This review analyzed how the WQS developed and applied in China differ from those of more developed countries and pointed out that the lack of strong scientific bases for China's WQC pose major limitations of current WQS. We focus on discussing the six aspects that require high attention on how to establish a national WQC system to support the revision of WQS (Table 1) such as development of methodology, refining water function zoning, establish priority pollutants list, improving protection drinking water sources, development of site-specific water quality criteria, and field toxicity test. It is essential that China and other developing countries established a relatively mature system for promulgating, applying, and enforcing WQC and to implement a dynamic system to incorporate most recent research results into periodically updated WQS.

Molecular characterization of macrophyte-derived dissolved organic matters and their implications for lakes.

Chemical properties of whole organic matter (OM) and its dissolved organic matter (DOM) extracted from three types of dominant macrophytes in Lake Dianchi were comparatively characterized using elemental analysis, UV, 3D-EEM and 13C NMR spectroscopy and their implications for lakes were discussed. Ratios of C/N and C/P were least in the floating water hyacinth and submerged sago pondweed, while total dissolved nitrogen (TDN) and phosphorus (TDP), dissolved organic nitrogen (DON) and phosphorus (DOP) were greatest in those species. In emergent species, C/N, C/P, DON and DON/TDN were less in leaves than in their corresponding shoots. The specific UV absorbance at 254nm (SUVA254) and 280nm (SUVA280) of extracts were in the range of 0.50-1.96L/mgC·m and 0.40-1.48L/mgC·m. Both SUVA values were greater in leaves than those in shoots. 3D-EEM spectra showed only a single fulvic-like fluorescence in leaves of emergent macrophytes. In contrast, protein-like peak were observed in spectra of floating and submerged species, as well as the shoot DOM of emergent species. Solid-state 13C NMR demonstrated that leaves had greater percentage of recalcitrant alkyl C and aromatic C, while shoots were rich in labile carbohydrates. The overall characterization works suggested that macrophyte-derived DOM has less aromatic constituents than do DOM in natural waters and soil leachates. Also OM and DOM derived from shoots had greater contents of protein-like and carbohydrate materials, while leaves were rich in aromatics. Floating and submerged plants possessed potential to not only accumulate excess N and P, but also for returning them to the lake. Shoots of riparian and emergent species were also an important source of nutrients. Thus, macrophyte biomass should be a great concern in nutrient regulation in Lake Dianchi.

Comparative study of species sensitivity distributions based on non-parametric kernel density estimation for some transition metals.

Transition metals in the fourth period of the periodic table of the elements are widely widespread in aquatic environments. They could often occur at certain concentrations to cause adverse effects on aquatic life and human health. Generally, parametric models are mostly used to construct species sensitivity distributions (SSDs), which result in comparison for water quality criteria (WQC) of elements in the same period or group of the periodic table might be inaccurate and the results could be biased. To address this inadequacy, the non-parametric kernel density estimation (NPKDE) with its optimal bandwidths and testing methods were developed for establishing SSDs. The NPKDE was better fit, more robustness and better predicted than conventional normal and logistic parametric density estimations for constructing SSDs and deriving acute HC5 and WQC for transition metals in the fourth period of the periodic table. The decreasing sequence of HC5 values for the transition metals in the fourth period was Ti > Mn > V > Ni > Zn > Cu > Fe > Co > Cr(VI), which were not proportional to atomic number in the periodic table, and for different metals the relatively sensitive species were also different. The results indicated that except for physical and chemical properties there are other factors affecting toxicity mechanisms of transition metals. The proposed method enriched the methodological foundation for WQC. Meanwhile, it also provided a relatively innovative, accurate approach for the WQC derivation and risk assessment of the same group and period metals in aquatic environments to support protection of aquatic organisms.

Magnetic Nanoparticles Interaction with Humic Acid: In the Presence of Surfactants.

Adsorbed humic acid (HA) on surfaces of nanoparticles (NPs) will affect their transport, transfer, and fate in the aquatic environment, especially in the presence of surfactants, and thereby potentially alter exposures and bioavailable fractions of NPs and surfactants. This study investigated adsorption of HA on Fe3O4 NPs in the presence or absence of surfactant. Surfactant established a bridge connecting HA and Fe3O4 NPs, and significantly changed adsorption behavior of HA on NPs. Adsorption of HA in the absence of surfactant was 120.3 mg/g, but 350.0 mg/g and 146.5 mg/g in the present of CTAB (hexadecyl trimethylammonium bromide) and SDS (sodium dodecyl sulfate), respectively. Surfactants can form different stages (hemimicelles, mixed hemimicelles and admicelles) on Fe3O4 NPs by electrostatic and hydrophobic interactions, adsorption of HA was different for each of those stages. Adsorption of HA on surface of Fe3O4 NPs/CTAB was codetermined by hydrophobic, electrostatic interactions and ligand exchange. The presence of CTAB or SDS changed mechanisms for adsorption and effects of functional groups. Results of Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that carbohydrate carbon was important in adsorption of HA on Fe3O4 NPs in the presence of surfactants.