Overcoming Electrostatic Interaction via Strong Complexation for Highly Selective Reduction of CN- into N2.

Limited by the electrostatic interaction, the oxidation reaction of cations at the anode and the reduction reaction of anions at the cathode in the electrocatalytic system nearly cannot be achieved. This study proposes a novel strategy to overcome electrostatic interaction via strong complexation, realizing the electrocatalytic reduction of cyanide (CN- ) at the cathode and then converting the generated reduction products into nitrogen (N2 ) at the anode. Theoretical calculations and experimental results confirm that the polarization of the transition metal oxide cathodes under the electric field causes the strong chemisorption between CN- and cathode, inducing the preferential enrichment of CN- to the cathode. CN- is hydrogenated by atomic hydrogen at the cathode to methylamine/ammonia, which are further oxidized into N2 by free chlorine derived from the anode. This paper provides a new idea for realizing the unconventional and unrealizable reactions in the electrocatalytic system.

Shifts of surface-bound •OH to homogeneous •OH in BDD electrochemical system via UV irradiation for enhanced degradation of hydrophilic aromatic compounds.

Indirect electrochemical oxidation by hydroxyl radicals is the predominant degradation mechanism in electrolysis with a boron-doped diamond (BDD) anode. However, this electrochemical method exhibits low reactivity in removal of hydrophilic aromatic pollutants owing to mass transfer limitation. In this study, the combination of ultraviolet light and BDD electrolysis could increase the degradation rate of hydrophilic aromatic pollutants by approximately 8-10 times relative to electrolysis alone. According to the results of the scavenging experiments and identification of benzoic acid oxidation products, surface-bound hydroxyl radical (•OH(surface)) was the primary reactive species degrading aromatic pollutants in the BDD electrolysis process, whereas freely-diffusing homogeneous hydroxyl radical (•OH(free)) was the major reactive species in the UV-assisted BDD electrolysis process. Cyclic voltammetry revealed that UV light decomposed H2O2 formed on the BDD anode surface, thus retarding O2 evolution and facilitating •OH(free) generation. This work also explored the potential application of UV-assisted BDD electrolysis in removing COD from bio-pretreated landfill leachate containing high concentrations of hydrophilic aromatic pollutants. This study shed light on the importance of the existing state of •OH on removal of pollutants during BDD electrolysis, and provided a facile and efficient UV-assisted strategy for promoting degradation of hydrophilic aromatic pollutants.

Mineralization of cyanides via a novel Electro-Fenton system generating •OH and •O2.

Traditional methods of cyanides' (CN-) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO-) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2-. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2- were simultaneously generated and 92.9% of free cyanides were transformed into NO3- within 120 min. No low-toxic CNO- intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN- was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2- via nucleophilic addition to quickly form NO3-, preventing the formation of CNO- and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activation of Peroxymonosulfate to Generate 1 O2 with 100 % Selectivity.

Singlet oxygen (1 O2 ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of 1 O2 . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe1 /CN) containing highly uniform Fe-N4 active sites with a high Fe loading of 11.2 wt %. The Fe1 /CN achieves generation of 100 % 1 O2 by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N4 sites in Fe1 /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO5 .- , and thereafter efficiently generate 1 O2 with 100 % selectivity. In addition, the Fe1 /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of 1 O2 for highly selective and efficient degradation of pollutants.

Silver Single Atom in Carbon Nitride Catalyst for Highly Efficient Photocatalytic Hydrogen Evolution.

Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag-N2 C2 /CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag-N2 C2 configuration have been identified by aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and extended X-ray absorption. Experiments and DFT calculations further verify that Ag-N2 C2 can reduce the H2 evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag-N2 C2 /CN catalyst exhibits much better H2 evolution activity than the N-coordinated Ag single atom in CN (Ag-N4 /CN), and is even superior to the Pt nanoparticle-loaded CN (PtNP /CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.

Highly efficient charge transfer in CdS-covalent organic framework nanocomposites for stable photocatalytic hydrogen evolution under visible light.

A facile and effective impregnation combined with photo-deposition approach was adopted to deposit cadmium sulfide (CdS) nanoparticles on CTF-1, a covalent triazine-based frameworks (CTFs). In this system, CTF-1 not only acted as supporter but also served as photocatalyst and electron donor. The performance of the obtained CdS deposited CTF-1 (CdS-CTF-1) nanocomposite was evaluated by H2 evolution reaction under visible light irradiation. As a result, CdS-CTF-1 exhibited high H2 production from water, far surpassing the CdS/CTF-1 nanocomposite, in which CdS was deposited via solvothermal method. The high activity of CdS-CTF-1 was attributed to the confined CdS nanoparticles with small size, leading to expose more active sites. In addition, time-resolved spectroscopy indicated that the superior performance of CdS-CTF-1 also can be ascribed to the fast electron transfer rate and injection efficiency (KET = 0.18 × 109 s-1, ηinj = 39.38%) between CdS and CTF-1 layers, which are 3.83 times faster and 4.84 times higher than that of CdS/CTF-1 nanocomposite. This work represents the first example on using covalent organic frameworks (COFs) as a support and electron-donor for fabricating novel CdS-COF nanocomposite system and its potential application in solar energy transformations.

Phthalates in plastic bottled non-alcoholic beverages from China and estimated dietary exposure in adults.

Concentrations of six phthalates were determined in 69 plastic bottled non-alcoholic beverages collected from marketplaces in China. Di-n-butyl phthalate (DBP) and di-(2-ethylhexyl)-phthalate (DEHP) were the most detected compounds with frequencies of 100%. Dimethyl phthalate was found less, with a mean frequency of almost 34%. The samples were divided into seven groups. The frequencies of phthalates in these groups ranged from 6.67% to 100%, which indicated that different types of beverages were differently contaminated by phthalates. DEHP contained the highest mean and median concentrations (1.60 ng g-1 and 0.62 ng g-1), followed by DBP (1.34 ng g-1 and 0.27 ng g-1). For DBP, the highest phthalate concentration of 14.3 ng g-1 was measured. The results of estimated daily intake (EDI) showed that the risk of Chinese adults exposed to these 6 phthalates in beverages examined was lower than the reference doses as suggested by the United States Environmental Protection Agency. The range of EDI values was between 1.77 × 10-4 µg kg-bw-1 day-1 and 0.478 µg kg-bw-1 day-1.

Reaction of antibiotic sulfadiazine with manganese dioxide in aqueous phase: Kinetics, pathways and toxicity assessment.

Sulfonamide antibiotics are often detected in terrestrial and aquatic environment, but little is known about abiotic degradation of these antibiotics. In the present study, the degradation of the sulfonamide antibiotic sulfadiazine by a synthesized δ-MnO2 was investigated. The initial reaction rate of sulfadiazine oxidized by manganese dioxide increased as the solution pH decreased by weakening electrostatic attraction between sulfadiazine and MnO2 and enhancing the reduction potential of MnO2. The presence of metal ions (Mn2+, Na+ and Ca2+), especially Mn2+, decreased the initial reaction rate by competitively adsorbing and reacting with MnO2. Two different products were identified during the reaction of sulfadiazine with MnO2 and the transformation of parent compound started with the formation of sulfadiazine radicals. Furthermore, toxicity assay results showed that the toxicity of products produced by bacteria decreased with elapse of reaction time. Results from the present study indicate that manganese dioxides in environmental matrix could be helpful in dissipation of sulfadiazine released into the environment.

Three-Dimensional Reduced Graphene Oxide Coupled with Mn3O4 for Highly Efficient Removal of Sb(III) and Sb(V) from Water.

Highly porous, three-dimensional (3D) nanostructured composite adsorbents of reduced graphene oxides/Mn3O4 (RGO/Mn3O4) were fabricated by a facile method of a combination of reflux condensation and solvothermal reactions and systemically characterized. The as-prepared RGO/Mn3O4 possesses a mesoporous 3D structure, in which Mn3O4 nanoparticles are uniformly deposited on the surface of the reduced graphene oxide. The adsorption properties of RGO/Mn3O4 to antimonite (Sb(III)) and antimonate (Sb(V)) were investigated using batch experiments of adsorption isotherms and kinetics. Experimental results show that the RGO/Mn3O4 composite has fast liquid transport and superior adsorption capacity toward antimony (Sb) species in comparison to six recent adsorbents reported in the literature and summarized in a table in this paper. Theoretical maximum adsorption capacities of RGO/Mn3O4 toward Sb(III) and Sb(V) are 151.84 and 105.50 mg/g, respectively, modeled by Langmuir isotherms. The application of RGO/Mn3O4 was demonstrated by using drinking water spiked with Sb (320 µg/L). Fixed-bed column adsorption experiments indicate that the effective breakthrough volumes were 859 and 633 mL bed volumes (BVs) for the Sb(III) and Sb(V), respectively, until the maximum contaminant level of 5 ppb was reached, which is below the maximum limits allowed in drinking water according to the most stringent regulations. The advantages of being nontoxic, highly stable, and resistant to acid and alkali and having high adsorption capacity toward Sb(III) and Sb(V) confirm the great potential application of RGO/Mn3O4 in Sb-spiked water treatment.

Hydrogen Evolution from Water Coupled with the Oxidation of As(III) in a Photocatalytic System.

A series of heterostructured CdS/Sr2(Nb17/18Zn1/18)2O7-δ composites with excellent photocatalytic ability for simultaneous hydrogen evolution and As(III) oxidation under simulated sunlight were synthesized and characterized. Among them, 30% CdS/Sr2(Nb17/18Zn1/18)2O7-δ (30CSNZO) has the highest in activity, exhibiting a H2 production rate of 1669.1 µmol·h(-1)·g(-1) that is higher than that of many photocatalysts recently reported in the literature. At pH 9, As(III) is completely oxidized to As(V) over 30CSNZO in 30 min of irradiation of simulated sunlight. In the photocatalytic system, H2 production rate decreases with the increase of As(III) concentration, and the recycle experiments show that 30CSNZO exhibits excellent stability, durability, and recyclability for photocatalytic hydrogen evolution and As(III) oxidation. We propose a mechanism in which superoxide radical (·O2(-)) is the active species for As(III) oxidation and the oxidation of As(III) has an effect on hydrogen evolution. For the first time, it is demonstrated that simultaneous hydrogen evolution and arsenite oxidation is possible in a photocatalytic system.

Facile fabrication and enhanced photosensitized degradation performance of the g-C3N4-Bi2O2CO3 composite.

Flower-like Bi2O2CO3 and g-C3N4-Bi2O2CO3 microspheres with a high adsorption ability were synthesized using a facile method, and their dye-induced photosensitized degradation activity under visible light irradiation was evaluated. The as-synthesized samples were characterized by XRD, FT-IR, FESEM, TEM (HRTEM), UV-vis DRS and nitrogen adsorption-desorption techniques. It was found that the activity of Bi2O2CO3 was significantly enhanced due to the generation of g-C3N4-Bi2O2CO3 heterostructures. The dye-sensitization and the presence of g-C3N4 are beneficial for the visible-light excited process. The enhancement of photocatalytic performance is ascribed to the proper matching of the energy levels of the dye, Bi2O2CO3 and g-C3N4 that facilitates the separation and transfer of photogenerated electrons and holes at the heterojunctions. The results of the present study give insights that are beneficial for the design of heterostructured materials.

Room-temperature synthesis of flower-like BiOX (X═Cl, Br, I) hierarchical structures and their visible-light photocatalytic activity.

A simple method for facile synthesis of three-dimensional (3D) bismuth oxyhalide (BiOX, X═Cl, Br, I) hierarchical structures at room temperature has been developed. Under the influence of L-lysine surfactant, the bismuth and halogen (Cl, Br, I) sources hydrolyze and self-assemble into flower-like hierarchical architectures within 10 min. The resulted materials were characterized by XRD, FESEM, TEM, UV-vis DRS, and N2 adsorption-desorption techniques. We found that l-lysine is indispensable for their formation and the amount of HX has great effect on the final morphology. The BiOX (X═Cl, Br, I) hierarchical architectures are composed of single-crystalline nanoplates. We propose an amino-and-carboxyl structure-directing mechanism for the formation of the hierarchical structures. To evaluate the photocatalytic activity of the as-prepared materials, rhodamine-B was employed as a probe dye for degradation under visible light. All of the BiOX (X═Cl, Br, I) with 3D architectures show higher photocatalytic activities than their sheet-like counterparts. The superior activity is ascribed to the better light-harvesting capacity of the 3D hierarchical structures. The adopted method can be applied for large-scale generation of novel structures of similar kinds in a facile manner.

Porous peanut-like Bi2O3-BiVO4 composites with heterojunctions: one-step synthesis and their photocatalytic properties.

For the first time, porous peanut-like Bi(2)O(3)-BiVO(4) composites with heterojunctions have been synthesized by a one-step mixed solvothermal method with the assistance of a l-lysine template. A mixture of ethylene glycol (EG) and H(2)O (volume ratio of EG-H(2)O = 3:1) is used as the solvent. Unlike the traditional methods, no concentrated HNO(3) and/or NaOH are involved in diluting Bi and V sources in the adopted approach. The as-synthesized peanut-like samples are rough and porous on the surface and to some extent are interior-hollow. The degradation of methylene blue (MB) is employed to evaluate the photocatalytic activity of the Bi(2)O(3)-BiVO(4) composite. It is observed that the composite performs much better than Bi(2)O(3) and BiVO(4), plausibly due to heterojunctions formed between Bi(2)O(3) and BiVO(4). To investigate the relationship between structure and performance, the as-synthesized samples are characterized by XRD, XPS, SEM, TEM (HRTEM), UV-vis DRS, PL and nitrogen adsorption-desorption methods. Additionally, a possible growth mechanism of this hollow peanut-like structure and the separation process of photogenerated electron-hole pairs on the heterojunctions have been discussed.

[Biological phosphorus removal in intermittent aerated biological filter].

Under intermittent aerated and continuous fed operation where the biofilm system was subjected to alternated anaerobic/aerobic condition, the effect of influent volatile fatty acids (VFAs) concentrations, operation cycle and backwash on the biological phosphorus removal performance of the biofilter was studied. In the experiment, synthetic domestic wastewater was used, and the influent velocity was 5 L x h(-1) with gas versus liquid ratio of 8:1 and hydraulic retention time (HRT) of 1.3 h, resulting in average COD, ammonium and phosphorus load of 4.7, 0.41 and 0.095 g x (L x d) (-1) respectively. Results show that, (1) effective release and uptake of phosphorus was achieved in a operation cycle; (2) when influent VFAs was 100 mg x L(-1) (calculated by COD value) and operation cycle was 6 h the filter performed best in phosphorus removal, the phosphorus loading removal rate can be as much as 0.059 g x (L x d)(-1) at the aerated phase with those of COD and ammonium being 3.8 g x (L x d)(-1) and 0.28 g x (L x d)(-1) respectively, and with average effluent phosphorus, COD and ammonium concentrations being 1.8, 43.6 and 8.7 mg x L(-1), which shows nitrogen loss also happened; (3) the pause of backwash decreased the phosphorus removal performance rapidly with the removal efficiency lower than 40% in two days, but the consequent daily backwash operation gave a short improvement on the phosphorus removal, which disappeared in another two days. Thus, it is shown that biological phosphorus removal achieved with better phosphorus loading removal performance in the biofilter under intermittent aerated and continuous fed operation, and that sufficient and stable influent VFAs concentration, proper operation cycle, and more frequent backwash favored the performance.

Analysis and characterization of cultivable heavy metal-resistant bacterial endophytes isolated from Cd-hyperaccumulator Solanum nigrum L. and their potential use for phytoremediation.

This study investigates the heavy metal-resistant bacterial endophytes of Cd-hyperaccumulator Solanum nigrum L. grown on a mine tailing by using cultivation-dependent technique. Thirty Cd-tolerant bacterial endophytes were isolated from roots, stems, and leaves of S. nigrum L. and classified by amplified ribosomal DNA-restriction analysis into 18 different types. Phylogenetic analysis based on 16S rDNA sequences showed that these isolates belonged to four groups: Actinobacteria (43%), Proteobacteria (23%), Bacteroidetes (27%) and Firmicutes (7%). All the isolates were then characterized for their plant growth promoting traits as well as their resistances to different heavy metals; and the actual plant growth promotion and colonization ability were also assessed. Four isolates were re-introduced into S. nigrum L. under Cd stress and resulted in Cd phytotoxicity decrease, as dry weights of roots increased from 55% to 143% and dry weights of above-ground from 64% to 100% compared to the uninoculated ones. The total Cd accumulation of inoculated plants increased from 66% to 135% (roots) and from 22% to 64% (above-ground) compared to the uninoculated ones. Our research suggests that bacterial endophytes are a most promising resource and may be the excellent candidates of bio-inoculants for enhancing the phytoremediation efficiency.

Towards aqueous gold nanoparticles with buffer resistance and high concentration.

High-concentration gold nanoparticles stabilized by poly(vinylpyrrolindone) (PVP) are prepared through modified citrate-reduction method. The modified approach possesses all the advantages of the popular citrate reduction method. With PVP as weak ligands as well as spatial effects for the metal nanoparticles, the control of the size and size distribution of the gold nanoparticles in the size range between 10 and 30 nm was achieved via maintaining balanced nucleation and growth by tuning the feed ratios of the metal precursors and reducing reagents. As a modified procedure to gold nanoparticles, PVP-stabilized gold nanoparticles are more stable in a broad range of pH and different buffers than conventional gold colloids. Because only PVP are employed in the new synthetic schemes, surface modification and functionalization of the resulting gold nanoparticles through small molecular ligands can be readily carried out.

Green chemistry for large-scale synthesis of semiconductor quantum dots.

Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190-230 degrees C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs.