Surface characteristics and adsorption properties of polypropylene microplastics by ultraviolet irradiation and natural aging.

The vast application and deep integration of plastic commodity with our human lives raise a great concern about the ubiquitous microplastics (MPs) in nature, yet the environmental behavior of MPs remain unclear. As a main type and candidate of MPs, pristine polypropylene MPs (PP-MP-Pris), as well as the influence of ultraviolet (UV) irradiation on the degree of aging and surface characteristics, were characterized quantitatively by Fourier infrared spectroscopy, scanning electron microscopy, contact angle meter, automatic specific surface area and pore analyzer and laser particle analyzer, with natural aged PP-MPs (PP-MP-Age) as comparison. The carbonyl index (CI) of UV aged PP-MPs (PP-MP-U) was increased with extension of exposure time, while biofilm with abundant functional groups and the maximum CI value were the characteristics of PP-MP-Age. Moreover, the adsorption capacity of PP-MP-U for crystal violet (CV) was increased and reached the maximum after 30 days, while that of PP-MP-Age was weakened, probably due to the enhanced hydrophilicity and the shedding of calcium carbonate (CaCO3) during the natural aging process, which was demonstrated by hydrochloric acid treatment, indicating the vital involvement of CaCO3. Moreover, the better fitting to PSO kinetics and Freundlich isotherm models indicated that the multilayered and non-homogeneous surface adsorption was acted as the rate-controlling step. Furthermore, the positive values of ΔGθ, ΔHθ and ΔSθ indicated that the adsorption was a non-spontaneous, endothermic process with increased degree of the freedom on the interface of PP-MPs and CV solution. The presence of divalent salts inhibited CV adsorption, demonstrating that electrostatic attraction played a major role in CV capture. The hydrophobic interaction, micropore filling, hydrogen bonding, and π - π conjugation were possible involved. This study is of great significance for better understanding the complex pollution of MPs and its potential environmental risks in the future.

Aging and adsorption behavior of PP-MPs for methylene blue and tetracycline in unitary and binary systems.

The omnipresence of microplastics (MPs) around the world has attracted extensive attention in the past decade with more focuses on the interactions of standard MPs without additives in regular shapes and individual pollutant, whereas the actual MPs containing various additives in irregular shapes and complex pollutants are often co-occurrence in the environments. In this paper, the adsorption performance of disposable polypropylene (PP) cups-based MPs subjected to ultraviolet irradiation was investigated in unitary and binary water matrices. The surface characteristics were analyzed and the experimental data of adsorption were fitted by various kinetic and isotherm models, and the results indicated that more cracks and oxygen-containing functional groups with decreased hydrophobicity were produced with aging, and electrostatic attraction and hydrogen bonding dominated methylene blue (MB) and tetracycline (TC) capture in the individual system. Moreover, pseudo-second order kinetic model better described the adsorption processes. In the binary system, the co-existence of TC promoted MB uptake, while the presence of MB inhibited TC capture. In addition, TC adsorption was enhanced by Ca2+, maybe due to its complexation effect, while the presence of mono- and divalent inorganic salts inhibited MB capture. This research provides useful insights for the fate of PP-MPs and organic pollutants in the complex environments.

Interfacial interactions of polyethylene terephthalate microplastics and malachite green, tetracycline in aqueous environments.

Polyethylene terephthalate microplastics (PET-MPs) are one of pivotal nondegradable emerging pollutant. Here the variation of the surface physicochemical characteristics of PET-MPs with UV irradiation aging and the adsorption behaviors of PET-MPs in malachite green (MG), tetracycline (TC) solution and the effect of coexisting Cu(II) were comparatively investigated. The yellowing, weakened hydrophobicity, and increased surface negative charge, crystallinity degree and oxygen-containing functional groups were manifested specifically by the aged PET-MPs. Different from the single system, the hydrophobic interaction and metal ion bridging complexation dominated the adsorption of MG and TC, respectively, in the binary solution. While in the ternary solution, cationic ion competition of Cu(II) with MG decreased its capture, and the formation of PET-Cu(II)-TC ternary complexes promoted TC adsorption. Moreover, PET-MPs could serve as an efficient vector for MG and TC in MG/TC/Cu(II) ternary system, indicating PET-MPs tend to carry more varieties in the complex environment, that may increase the environmental risk of PET-MPs.

Aging and characterization of disposable polypropylene plastic cups based microplastics and its adsorption for methylene blue.

Microplastics (MPs) as emerging pollutants are of increasing concern, due to their ubiquitous, uncertain, and complex environmental impacts. Different from the standard spherical MPs without additives, here polypropylene microplastics (PP-MPs) in flake derived from the disposable plastic cup in food-grade in daily life were studied. The characterization of PP-MPs demonstrated that the carbonyl index represented the aging degree was enhanced from 0.26 significantly to 0.82 after 10 days, and the aging process fitted well with pseudo-first-order kinetic. Moreover, the crystallinity degree, polarity and surface negative charges were enhanced, while the hydrophobicity was decreased. The adsorption behavior of PP-MPs toward methylene blue (MB), and the impacts of various pHs, salinities, and humic acid in aquatic environments were also explored. The pseudo-second-order kinetic, Henry and Sips isotherm models provided a good correlation with the experimental data, indicating that the rate-limiting step was closely related with the complex surface adsorption, and the hydrophobic partitioning, polar interaction, electrostatic attraction, and hydrogen bonding were possibly involved in the adsorption. These exhaustive experiments aim to provide a theoretical basis for assessing and better understanding the environmental behavior of disposable PP plastic cups in nature.

Aging, characterization and sorption behavior evaluation of tire wear particles for tetracycline in aquatic environment.

Accounting for more than half of the total primary microplastic (MP) emissions, and one-sixth of the total marine MP pollution in China in 2015, tire wear particles (TWP) are inevitable to age and interact with co-existing species, thus pose a potential risk to the surroundings. The impacts of simulated ultraviolet radiation weathering and liquid-phase potassium persulfate oxidation of TWP on the surface physicochemical properties were comparatively explored. The characterization results demonstrated that the content of carbon black, particle size and specific surface area of the aged TWP all decreased, while the changes of the hydrophobicity and polarity were inconsistent. The interfacial interactions with tetracycline (TC) in aqueous were investigated, the well fitted pseudo-second-order kinetics, Dual-mode Langmuir and Scatchard isotherm models indicated the attachment of TC dominated by surface adsorption at lower concentration, and there's a positive synergistic effect among the main sorption domains. Moreover, the results of the influences of co-existing salts and natural organic matter revealed that the potential risks of TWP elevated by the adjacent media in natural compartment. This work provides new insights into the way that TWP interact with contaminants in the real environment.

Identification of the aged microplastics film and its sorption of antibiotics and bactericides in aqueous and soil compartments.

Here, thin-film microplastics (MPs) from black garbage bags were simulated aged by artificially ultraviolet radiation, and their sorption behavior toward antibiotics and bactericides in water and soil was explored. The chemical structure, surface functional groups, and the aged degree indicators of the identified polyethylene microplastics (PE-MPs) were studied by FT-IR spectra. The decreased crystallinity and hydrophobicity of PE-MPs-16 demonstrated by XRD and contact angle measurements and enhanced carbonyl index (0.0105) were highly related to the enhanced sorption capacities, especially for crystal violet (18.10 mg/g) in water. Moreover, PE-MPs-16 mitigated the adsorption rate and had little influence on the sorption capacity in soil. The sorption data fitted well to Henry (water) or Freundlich (soil) isotherm model, indicating the hydrophobic partition was involved in the sorption. Our research helps to clarify the interaction between MPs and organic pollutants and better understand the fate of virgin and aged PE-MPs in the varied compartments.

Identification of naturally weathering microplastics and their interactions with ion dyes in aquatic environments.

Here, naturally weathering plastics were collected and identified to understand the effect of the weathering conditions on their properties. The adsorption and desorption of crystal Violet (CV), a candidate of cationic organic pollutant, on microplastics (MPs) under various environmental conditions were simultaneously explored. The first type was the aged polyethylene (PE-MPs), which exhibited a fibrous structure with a smoother and uniform surface attached some flaps, while the second type was recognized as the aged polypropylene (PP-MPs), which showed a lamellar structure with less smooth and distorted texture surface attached with fragments and small grains. The experiment data fitted well with the pseudo-second-order kinetic and Freundlich isotherm models. The possible interactions between CV and MPs included electrostatic attraction, hydrogen bonding and hydrophobic interactions. This study demonstrates that the high possibility of transport ionic pollutants from fresh water to ocean by the naturally weathering microplastics, highlighting their potential risk in various environments.

Enhanced adsorption of tetracycline by the modified tea-based biochar with the developed mesoporous and surface alkalinity.

A tea residue-based biochar, Fe-BCK0.5-VB6, was obtained by pyrolysis with KOH activation and alkalization with vitamin B6, to develop the mesopore structure and functionalized surface to improve the adsorption performance on tetracycline (TC). An increased specific surface area of 455 m2·g-1 and expanded mesopore volume of 0.138 cm3·g-1 for Fe-BCK0.5-VB6, were observed. The Avrami-fractional order kinetics and Langmuir isotherm models best fitted the experimental data, indicating the characteristics of multiple kinetic stages and monolayer of TC adsorption process. Several possible interactions, including acid-base reaction, pore filling, electrostatic interactions, π-π interactions, and hydrogen bonding forces, were participated in the attachment of TC. This novel mesoporous biochar with enhanced surface alkalinity is expected with a viable future role as an efficient adsorbent in the remedies of acidic antibiotics wastewater pollution.

Electrospinning of multifunctional cellulose acetate membrane and its adsorption properties for ionic dyes.

Electrospinning of cellulose acetate with appropriated solvent system is the most straightforward method for fabricating micro- and nanofibers. To simultaneously and effectively remove both cationic and anionic dyes, a novel cost-effective multifunctional cellulose acetate (CA) fibers membrane was prepared by electrospinning followed by deacetylation, carboxymethylation and polydopamine (PDA) coating. The adsorption properties of PDA@DCA-COOH membrane were evaluated with methylene blue (MB) and Congo red (CR) as the ionic representatives for their removal. The results indicated that carboxyl, hydroxyl and amine multifunctional groups had been successfully grafted on the surface of the nanofibers with the maximum adsorption capacities of 69.89 and 67.31 mg g-1 for MB and CR, respectively, in the individual systems. The effect of co-existed dyes, inorganic salts and surfactants on the uptake of MB and CR in the simulated real complex system was strongly depended on the initial pH and ionic strength of the solution. The excellent adsorption capacities of the composite membrane were due to strong electrostatic attraction through the abundant functional groups on PDA@DCA-COOH surface. Based on its excellent recycling performance and adsorption property, PDA@DCA-COOH has a promising potential as an effective adsorbent in water treatment.

Adsorption studies of Orange II onto polyaniline/bentonite nanocomposite.

Modification of bentonite is essential for the adsorption of anionic dyes, as its negative surface charge. In this study, polyaniline/bentonite (PAni-Bent) nanocomposite was synthesized by in-situ intercalative polymerization technique and used to remove anionic dye Orange II (ORII) from synthetic wastewater. Its structure was confirmed by X-ray diffraction (XRD), scanning electron microscopy, Fourier-transform infrared spectra and Brunauer-Emmett-Teller specific surface area measurements. The adsorption behaviours of PAni-Bent towards ORII in the single anionic dye wastewater, the cationic/anionic mixture dye wastewater, with or without salt or surfactant, were investigated principally. The results show that cetyl trimethyl ammonium bromide have an obviously suppressing effect on dye removal in the MB/ORII mixture system. The Langmuir and Temkin isotherm models described the adsorption process better than Freundlich or Dubinin-Radushkevich (D-R) model, and the pseudo-second-order and Boyd kinetic models fit better with the experimental data. Considering all these unique characteristics, PAni-Bent can be considered as effective adsorbent material for potential removal of dye from aqueous solution in industry.

Lengthy one-dimensional magnetite (Fe3O4) sub-microfibers with excellent electrochemical performance.

One dimensional Fe3O4 sub-microfibers with an average diameter of about 920nm and length of about 25µm were prepared by hydrothermal synthesis in the presence of sodium citrate (Na3cit). The physicochemical properties were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). It was found that Fe3O4 crystal nuclei were generated from different Fe2+-citrate complexes under hydrothermal conditions and Na3cit as a capping agent promoted the formation of Fe3O4 microfibers. The Fe3O4 nanocrystals grew along the (110) axis on the exposed (111) facet, and then further formed microfibers via an oriented attachment mechanism during the collisions. Polyvinylpyrrolidine (PVP) was more conducive to microfibers growth in comparison to polyethyleneglycol 4000 (PEG-4000), cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The electrochemical measurements show that the Fe3O4 sub-microfibers had a specific capacitance of 117.6Fg-1 with good cycling performance.

Synthesis of magnetic epichlorohydrin cross-linked carboxymethyl cellulose microspheres and their adsorption behavior for methylene blue.

Epichlorohydrin cross-linked carboxymethyl cellulose microspheres (ECH/CMC) obtained by inverse suspension method and magnetic Fe3O4 nanoparticles encasing the ECH/CMC microspheres (M-ECH/CMC) obtained by two different methods were successfully prepared and compared. Their structures and morphologies were analyzed using polarizing microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The adsorption behaviors of M1-ECH/CMC for methylene blue (MB) in the single cationic dye wastewater, the cationic/anionic dye mixture in the absence or presence of co-existed additives (salt and surfactant) wastewater, were also investigated with UV-vis spectrometer. The results showed that the magnetic Fe3O4 nanoparticles were loaded readily in situ into ECH/CMC by specific, chemical interactions between COO- groups of ECH/CMC and magnetic responsive Fe3O4. The Langmuir isotherm and pseudo-second-order kinetic model provide best correlation with the experimental data for the adsorption of MB onto ECH/CMC and M1-ECH/CMC microspheres, while the Langmuir isotherm and pseudo-first-order kinetic model for M2-ECH/CMC. These microspheres are easily recyclable and exhibit high desorption and adsorption, which suggests that they can be applied as potential environmental adsorbents.

Adsorption properties of crosslinking carboxymethyl cellulose grafting dimethyldiallylammonium chloride for cationic and anionic dyes.

Novel and efficient microspheres adsorbent (MCA-E0.7/CMC-g- PDMDAAC), based on monochloroacetic acid (MCA) modified epichlorohydrin (ECH) cross-linked carboxymethyl cellulose (CMC), then grafting by dimethyldiallylammonium chloride (DMDAAC), was synthesized and its adsorption properties on cationic and anionic dyes were investigated. The results demonstrated that such MCA-E0.7/CMC-g-PDMDAAC microspheres showed pH-sensitive and could effectively adsorb cationic dye methylene blue (MB) or anionic dye orange II (OR II), at near neutral (pH>4) or acidic (pH<3) condition, respectively. Moreover, it could selectively adsorb the cationic dye MB from the cationic/anionic dye mixture at neutral pH condition. The desorption experiments were mainly performed under acidic (pH 3) or basic (pH 11) condition, over 98.54% of MB and 83.07% of OR II can be desorbed within 20min, respectively. The pseudo-second-order kinetic model and Langmuir isotherm provide better correlation with the experimental data for the adsorption of dyes onto MCA-E0.7/CMC-g-PDMDAAC microspheres.

Occurrence, seasonal variation and inhalation exposure of atmospheric organophosphate and pyrethroid pesticides in an urban community in South China.

The shift in pesticide usage patterns demands a better understanding of the occurrence, fate and exposure risk of atmospheric current-use pesticides (CUPs). Air samples collected in different seasons from an urban community in Guangzhou, China were analyzed to investigate seasonal variation, gas-particle partitioning and inhalation exposure of atmospheric organophosphate and pyrethroid pesticides. Chlorpyrifos and eight pyrethroids were detected in the air samples and the total concentrations of the nine CUPs ranged from 150 to 3816 pg m(-3). Chlorpyrifos and cypermethrin were the most dominant CUPs detected in the atmosphere, accounting for 68% and 15% of the total CUPs, respectively. Seasonal variation in concentration was observed for most CUPs, with peak concentrations occurring in summer and fall, which was consistent with their application patterns. Partitioning of chlorpyrifos between gas and particle phases was also seasonally-dependent, with more chlorpyrifos found in the gas phase in summer and fall. Additionally, gas-particle partitioning analysis suggested that chlorpyrifos might experience long-range transport. Evaluation of potential exposure from inhalation of atmospheric CUPs suggested that children, toddlers and infants had the highest exposure, but the risk quotients were low for all age groups when annual average concentrations were used as exposure metrics. Exposure risk was higher in summer and fall than the annual average level due to higher atmospheric pesticide concentrations, longer exposure times and more pesticides being in the gaseous form.

Feasibility of fly ash-based composite coagulant for coal washing wastewater treatment.

In this study, several fly ash (FA)-based composite coagulants, leached by hydrochloric acid, were prepared to treat coal washing wastewater. The concentrations of Al(3+) and Fe(2+)/Fe(3+) in the leachates and coagulants were analyzed, and optimal experimental conditions, including coagulant dosage and initial pH, were determined using various analytical techniques (scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction (XRD), X-ray fluorescence (XRF), particle-size analysis, zeta potential, pH and conductivity measurements). A suspended solids (SS) and chemical oxygen demand (COD) removal efficiency from the effluent treated by one of the coagulants reached 99.61% and 96.48%, respectively, at dosages of 10 g l(-1) (initial pH of 9, adjusted by CaO). This indicates that the coagulant was an effective agent for coal washing wastewater treatment, and that the leached Al(3+) and Fe(3+) and introduced Ca(2+) may have improved the coagulation process. Analysis of the dry sludge composition and slurry particle size distribution of the coal washing wastewater showed that charged colloidal particles and the fine particle distribution in the coal washing wastewater make the wastewater treatment a difficult process. Results from this study could provide a novel approach for the treatment of coal washing wastewater and coal fly ash utilization.

Advanced purification of petroleum refinery wastewater by catalytic vacuum distillation.

In our work, a new process, catalytic vacuum distillation (CVD) was utilized for purification of petroleum refinery wastewater that was characteristic of high chemical oxygen demand (COD) and salinity. Moreover, various common promoters, like FeCl(3), kaolin, H(2)SO(4) and NaOH were investigated to improve the purification efficiency of CVD. Here, the purification efficiency was estimated by COD testing, electrolytic conductivity, UV-vis spectrum, gas chromatography-mass spectrometry (GC-MS) and pH value. The results showed that NaOH promoted CVD displayed higher efficiency in purification of refinery wastewater than other systems, where the pellucid effluents with low salinity and high COD removal efficiency (99%) were obtained after treatment, and the corresponding pH values of effluents varied from 7 to 9. Furthermore, environment estimation was also tested and the results showed that the effluent had no influence on plant growth. Thus, based on satisfied removal efficiency of COD and salinity achieved simultaneously, NaOH promoted CVD process is an effective approach to purify petroleum refinery wastewater.

Mild ring-opening coupling of liquid-phase cyclohexane to diesel components using sulfated metal oxides.

We have investigated a mild simple synthesis method for ring-opening coupling of liquid-phase cyclohexane to diesel components using various sulfated metal oxides [SO(4)(2-)/Fe(2)O(3) (SF), SO(4)(2-)/TiO(2) (ST) and SO(4)(2-)/ZrO(2) (SZ)] under low temperature (333K) and atmospheric pressure. Neither solvent nor promoters are needed in the reaction system so as to be a clean approach. Operating under these reaction conditions, a maximum activity of 6% was obtained with SF as catalyst, and a significantly high selectivity of 74.5% for nicer diesel components (n-C(14)-C(18)) was obtained simultaneously. Whereas, ST and SZ displayed low activity for cyclohexane reaction. By utilization of the temperature-programmed desorption of ammonia (NH(3)-TPD) measurement and the N(2) adsorption method, the results suggested that a satisfied acid strength distribution and high density of acid sites appeared in SF catalyst in comparison with other catalysts, which may play an important role in the reaction.

A clean method for solvent-free nitration of toluene over sulfated titania promoted by ceria catalysts.

A mild simple method for nitration of aromatic compounds, various solid acids as catalysts, the air treated with the corona discharge generator as nitrating agent, the liquid-phase nitration of toluene, at ambient temperature and atmospheric pressure without solvent has been investigated. The results show that SO(4)(2-)/TiO(2) (ST) and SO(4)(2-)/TiO(2) doped with CeO(2) (STC) catalysts displayed good nitration activity in the experiments. It is an attractive method for the environmentally friendly synthesis of nitroaromatic compounds. Moreover, only mononitrotoluenes were detected in the products, and the ratio of para-nitrotoluene and ortho-nitrotoluene was approximately 1:1 with various catalysts. A maximum yield of about 11.4% was achieved for mononitrotoluenes in STC reaction system in 3h.

Environmentally friendly efficient coupling of n-heptane by sulfated tri-component metal oxides in slurry bubble column reactor.

SO(4)(2-)/M(x)O(y) is of the greatest interest in solid catalysts and green catalysts. Slurry bubble column reactors are of considerable interest in industrial processes and various biochemical processes. The cetane number (CN) has widely used diesel fuel quality parameter related to the ignition delay time (and combustion quality) of a fuel. CN improvement of diesel fuels is a difficult task that refiners will face in the near future. For that purpose, the tests were designed in which n-heptane is used as the reactant in the air or ozone atmosphere at room temperature (RT) and local atmospheric pressure (LAP) using different catalysts of sulfated tri-component metal oxides SO(4)(2-)/Fe(2)O(3)-TiO2-SnO(2) (SFTSn) and SO(4)(2-)/MnO(2)-TiO2-SnO(2) (SMTSn) in slurry bubble column reactor. The products distribution was analyzed by gas chromatography-mass spectrometry (GC-MS) method and the results show that the relative selectivity of long linear alkane (C(12)-C(28)) reaches the maximum (87.330%) when SMTSn is used as catalyst in flow air at 60 min. Diesel fuel components with higher cetane numbers can be easily obtained from this study.

Novel synthesis of methoxymethyl benzene by electrochemical coupling reaction of toluene with methanol in ionic liquid media.

An ionic liquid (1-butyl-3-methylimidazolium dibutyl phosphate) was prepared and characterized by cyclic voltammogram (CV) and Fourier transform infrared spectrometer (FT-IR). The ionic liquid exhibited good catalytic activity for the electrochemical reaction of toluene with methanol assisted with a pair of porous graphite plane electrodes and product yield higher than 56% was observed. In addition, the electrochemical process was detected by UV-vis spectrum and the products were analyzed by gas chromatography/mass spectrometry (GC/MS). According to the experimental results, a possible free radical reaction mechanism was proposed. It may be concluded that a simply and feasible electrochemical coupling reaction at room temperature and atmospheric pressure may be possible. Compared with methyl tert-butyl ether (MTBE), the main product (methoxymethyl benzene) used as booster to improve fuel combustion was also studied.