Weiling Sun

Heterogeneous photocatalysis of methylene blue over titanate nanotubes: Effect of adsorption

Titanate nanotubes were synthesized with hydrothermal reaction using TiO(2) and NaOH as the precursors and subsequent calcination at 400°C for 2h. The products were characterized with SEM and XRD. Adsorption and photocatalysis of methylene blue over titanate nanotubes and TiO(2) were investigated. The results indicated that titanate nanotubes exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system than that in equilibrium adsorption followed by a photodegradation system, whereas TiO(2) showed no significant differences in photocatalytic activity in the two systems. The methylene blue overall removal efficiency over TNTs in the first system even exceeded that over TiO(2). The different catalytic performances of titanate nanotubes in the two systems were tentatively attributed to different effects of adsorption of methylene blue, i.e., the promoting effect in the former and the inhibition effect in the latter. Decantation experiments showed that the titanate nanotube photocatalyst could be easily separated from the reaction medium by sedimentation. Thus titanate nanotubes with high sedimentation rates and concurrent adsorption represent a new catalyst system with a strong potential for commercial applications.

Sorption of mercury (II) and atrazine by biochar, modified biochars and biochar based activated carbon in aqueous solution

Corn straw biochar (BC) was used as a precursor to produce Na2S modified biochar (BS), KOH modified biochar (BK) and activated carbon (AC). Experiments were conducted to compare the sorption capacity of these sorbents for aqueous Hg (II) and atrazine existed alone or as a mixture. In comparison to BC, the sorption capacity of BS, BK and AC for single Hg (II) increased by 76.95%, 32.12% and 41.72%, while that for atrazine increased by 38.66%, 46.39% and 47 times, respectively. When Hg (II) and atrazine coexisted in an aqueous solution, competitive sorption was observed on all these sorbents. Sulfur impregnation was an efficient way to enhance the Hg (II) removal due to the formation of HgS precipitate, and oxygen-containing functional groups on the sorbents also contributed to Hg (II) sorption. Activated carbon was the best sorbent for atrazine removal because of its extremely high specific surface area.

Titanium dioxide mediated photocatalytic degradation of 17β-estradiol in aqueous solution

Photocatalytic degradation of 17beta-estradiol (E2) in aqueous medium mediated with titanium dioxide (TiO2) was studied. Moreover, effect of TiO2 dosage on the degradation efficiency was investigated. Particular attention was paid to the identification of intermediates and analysis of photocatalytic degradation mechanism of E2 under neutral and alkaline conditions. The degradation efficiency of E2 increased with increasing concentration of TiO2 but decreased due to light scattering as TiO2 concentration was greater than 0.5mgml(-1). Several intermediates were formed during photocatalytic degradation of E2. However, only a few of the compounds could be identified and confirmed by LC-MS and LC-MS/MS. Six intermediates were observed by photocatalytic oxidation under alkaline conditions, namely 2-hydroxyestradiol, 10epsilon-17beta-dihydroxy-1,4-estradien-3-one (DEO), 10epsilon-hydroperoxide-17beta-hydroxy-1,4-estradien-3-one and three kinds of dicarboxylic acids formed by the opening of aromatic ring. In addition to the six intermediates mentioned above, 17beta-hydroxy-1,4-estradien-3-one (EO) was observed under neutral conditions and in the presence of methanol. Based on these intermediates, which were hardly degraded even after E2 was fully degraded, the mechanism of E2 degradation by TiO2 photocatalysis was elucidated.

Initial photocatalytic degradation intermediates/pathways of 17α-ethynylestradiol: effect of pH and methanol.

This study investigated the photocatalytic degradation of the synthetic oral contraceptive 17alpha-ethynylestradiol (EE2). Particular attention was paid on the effects of pH and the co-solvent methanol on the degradation intermediates of EE2. Twelve intermediates were identified, and several intermediates reported herein have not been found in previous studies. The degradation efficiency of EE2 and the number of identified intermediates decreased evidently at pH 3 and in the presence of methanol at pH 7. Three photocatalytic degradation pathways were proposed: The transformation of the phenolic moiety (pathway I) is the primary initial reaction pathway; the initial photocatalytic degradation in the aliphatic carbon linked to the aromatic ring (pathway II) only took place at pH 7; the isomerization of EE2 (pathway III) could occur only in the presence of methanol at pH 7. Results from this study underscore the importance of photocatalytic degradation on the removal of estrogenic activity mainly expressed by the phenol moiety of EE2.

Effect of inorganic nanoparticles on 17β-estradiol and 17α-ethynylestradiol adsorption by multi-walled carbon nanotubes.

With extensive application of diverse engineered nanoparticles (NPs), multiple NPs would inevitably be released into the environment. However, much emphasis in most previous studies on the interactions of pollutants with NPs has been placed on only one type of NPs at a time. This study investigated the impact of inorganic NPs (I-NPs) on the adsorption of 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) by multi-walled carbon nanotubes (CNTs). The presence of I-NPs inhibited the adsorption and increased the equilibrium time of E2 and EE2 by CNTs. Moreover, the effect of Al2O3 was stronger than that of SiO2, because electrostatic attraction enhanced the interaction between oppositely charged Al2O3 and CNTs. The addition sequence of I-NPs and pollutant also influences adsorption. This is among the first studies investigating the effect of I-NPs on pollutants adsorption by CNTs, which is useful for understanding the transport and fate of CNTs and contaminants in natural aquatic systems.

A duodecennial national synthesis of antibiotics in China's major rivers and seas (2005–2016)

The occurrence of 94 antibiotics in water and sediments from seven major rivers and four seas in China during 2005-2016 was reviewed. Twelve antibiotics were most frequently detected in both water and sediment samples, including 3 sulfonamides (SAs), 2 tetracyclines (TCs), 4 fluoroquinolones (FQs), and 3 macrolides (MLs). Their median concentrations were below 100ng/L and 100ng/g in river water and sediments, respectively. The highest median concentrations were found in water (1.30-176ng/L) and sediments (0.15-110ng/g) in the Hai River, due to its larger population density, higher consumption of antibiotics, and lower water flow. The concentrations of TCs and FQs were higher in the Pearl River sediments, due to their extensive use in aquaculture. The Yangtze River showed lower median concentrations of antibiotics in both water (1.33-17.3ng/L) and sediments (0.31-14.8ng/g), resulting from its larger catchment size, and higher precipitation and water flow. The Yellow River exhibited lower median concentrations of antibiotics in sediments (0.04-9.04ng/g), probably due to low organic matter content in sediments and high suspended particle content in water. Organic carbon normalized distribution coefficients (Koc) of antibiotics were positively correlated with the octanol/water partition coefficients (Kow) of antibiotics, and the correlation for MLs with a macrocyclic lactone ring was different from that of SAs, FQs, and TCs, likely due to their much larger molecular size. Among Chinas major rivers, the Hai River had the highest ecotoxicological risk from antibiotics to algae, invertebrate, fish, and plant.

FLUORESCENCE EVOLUTION OF LEACHATES DURING TREATMENT PROCESSES FROM TWO CONTRASTING LANDFILLS

Abstract Landfill leachates are composed of a complex mixture of organic matter, including a wide range of potentially fluorescent organic compounds. The fluorescence excitation–emission matrix (FEEM) of leachates during treatment processes is investigated. Particular attention is paid to the fluorescence evolution of leachates during treatment processes. Two typical types of landfill, landfill A (a direct municipal solid waste (MSW) landfill) and landfill B (disposal of bottom ashes from MSW incinerators), in a city in Southern China were selected. The results show that two characteristic and intense excitation–emission peaks located at Ex/Em = 310–330 nm/395–410 nm (peak α) and Ex/Em = 250–260 nm/450–460 nm (peak α′) are observed. As the aromatic chemicals, capable of emitting fluorescence, are more recalcitrant to biodegradation than aliphatic chemicals, enhancement of the dissolved organic carbon normalized fluorescence intensities is demonstrated during treatment processes of leachate A and leachate B. This is confirmed by the variation of ultraviolet absorptivity of leachates at 254 nm. Peak α′ and peak α are attributed to a mixture of xenobiotic organic compounds with low molecular weight and relatively stable aromatic fulvic‐like matters with high molecular weight, respectively. Humic substances are more resistant to biodegradation than xenobiotic organic compounds, so a significant reduction in the Iα′ /Iα values (fluorescence intensity ratios of peak α′ and peak α) of leachate A was observed during treatment processes. However, no evident variation for the Iα′ /Iα values of leachate B was found during treatment processes owing to the low concentrations of xenobiotic organic compounds in leachate B after incineration.

Effects of suspended sediment content on biodegradation of three common endocrine disruptors in river water.

Bisphenol A (BPA), 17β-oestradiol (E2) and 17α-ethynylestradiol (EE2) are common endocrine disruptors (EDs) in river water, and biodegradation is regarded as an important process for their removal from river water. The suspended sediment (SS) content is very high in some rivers, which may affect the biodegradation of these EDs. In this study, the degradation of BPA, E2 and EE2 in river water with different SS contents was investigated using batch experiments. The results show that the biodegradation rates of BPA, E2 and EE2 increase with the SS content in water samples. The half-lives of BPA, E2 and EE2 are 2.44–52.51 days, 0.40–6.38 days and 3.47–25.77 days, respectively, at SS contents ranging from 0 g L–1 to 15 g L–1. Micrographs demonstrate more bacteria in the SS than in the water phase. Higher SS concentrations provide greater surface areas for bacterial attachment and these bacteria apparently accelerate the biodegradation of common EDs.

Sediments inhibit adsorption of 17β-estradiol and 17α-ethinylestradiol to carbon nanotubes and graphene oxide

Increasing use of carbonaceous nanomaterials (CNMs) in many industrial and commercial applications has raised concern over their potential environmental impacts. However, little is known about how the released CNMs could interact with other contaminants in aquatic environments. In this study, the effects of sediment particle size (<1 μm, 1–2 μm, 2–5 μm, 5–10 μm, and 10–63 μm) and organic matter (OM) on adsorption of 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) to carboxylated multi-walled carbon nanotubes (CNTs) and graphene oxide (GO) were investigated using batch adsorption experiments in combination with microscopic, spectroscopic, and computational techniques. The adsorption of E2 and EE2 to CNMs was much stronger than that to the sediments, resulting from π–π interactions and hydrogen bonding, as confirmed with density functional theory calculations. Nonetheless, the presence of sediments inhibited E2/EE2 adsorption to CNTs or GO, and the inhibition effect increased with decreasing sediment particle size. This inhibition effect resulted from the attachment of CNMs to the sediment surface and subsequent blockage of the adsorption sites on CNMs. The removal of OM in the sediments enhanced the inhibition effect, likely due to stronger attachment of CNMs on OM-free sediments. These observations were corroborated by microscopic visualization and DLVO calculations. Our results provided new insights into the effect of sediments on contaminant adsorption by CNMs, as modulated by sediment particle size and OM.

Bio-Source of di-n-butyl phthalate production by filamentous fungi

Although DBP (di-n-butyl phthalate) is commonly encountered as an artificially-synthesized plasticizer with potential to impair fertility, we confirm that it can also be biosynthesized as microbial secondary metabolites from naturally occurring filamentous fungi strains cultured either in an artificial medium or natural water. Using the excreted crude enzyme from the fungi for catalyzing a variety of substrates, we found that the fungal generation of DBP was largely through shikimic acid pathway, which was assembled by phthalic acid with butyl alcohol through esterification. The DBP production ability of the fungi was primarily influenced by fungal spore density and incubation temperature. This study indicates an important alternative natural waterborne source of DBP in addition to artificial synthesis, which implied fungal contribution must be highlighted for future source control and risk management of DBP.