Characterization of the migration of organic contaminants in laboratory-scale groundwater polluted by underground coal gasification.

Underground coal gasification (UCG) is a promising technology, but the groundwater pollution caused by UCG is a potential risk to the environment. The measured results of the stratum in the combustion cavity resulting from UCG had proven that the combustion cavity would be filled with some UCG residues and caving rocks when UCG was finished. The pollutants in underground water around the combustion cavity include organic pollutants, inorganic pollutants, and ammonia nitrogen, and one of the primary organic pollutants is phenol. The migration and diffusion characteristics of organic pollutants (taking phenol as a representative) in the groundwater of the combustion cavity were investigated by breakthrough experiments and numerical simulations. The results show that the hydraulic conductivity of the coarse UCG residues is much higher than that of fine residues, and the hydraulic conductivity of the UCG residues with the size of - 0.15 mm and 0.15-0.3 mm are 4.68 × 10-6 m/s and 1.91 × 10-4 m/s respectively. The dispersivity λ for the migration of organic pollutants will be influenced significantly by the size of UCG residues in fractures of the combustion cavity, while the distribution coefficient Kd will not. The dispersivity of organic pollutants in the fine UCG residues is more significant than that in the coarse residues, and the λ for the two kinds of residues are 3.868 cm and 1.765 cm, respectively. The shape of the migration path slightly affects the pollutant concentration distribution along the path, but the width of a path has a more pronounced influence on the concentration distribution. In this research, the influence was formulated by a new technical term, MPWIT, which is related to transverse dispersion. Specifically, while the transverse dispersion values account for 20% and 10% of the longitudinal dispersion, respectively, the corresponding MPWIT values are 39.48 mm and 33.96 mm.

Recovery of residual carbon from coal gasification fine slag by a combined gravity separation-flotation process.

Recovering inner residual carbon is important for fully utilizing coal gasification fine slag (CGFS) resources. In this study, we adopted a combined gravity-separation and flotation process to efficiently recover residual carbon by considering the characteristics of the CGFS and optimizing the operating factors of the process. CGFS is principally a mixture of residual carbon and ash, with low-density particles containing more of the former. Accordingly, residual carbon is preliminarily enriched by gravity separation, in which gas velocity (vg) and water velocity (vw) significantly impact separation efficiency, followed by feed volume (m). The residual carbon in the initial concentrate was preliminarily enriched (i.e., loss on ignition (LOI): 55.90%; combustible recovery (Ro): 72.36%) under appropriate operating conditions (i.e., vw = 0.04 m/s, vg = 3 m/s, m = 150 g). Moreover, the quality of the flotation concentrate was most influenced by collector dosage (mc), followed by aeration rate (η), frother dosage (mf), stirring speed (w), and grinding time (t) during flotation of the primary concentrate. The flotation concentrate exhibited LOI and Ro values of 90.95% and 50.34%, respectively, under the optimal flotation conditions (i.e., mc = 20 kg/t, mf = 15 kg/t, w = 2600 rad/min, η = 200 L/h, t = 360 s); it has a high residual carbon content and is an ideal raw material for preparing fuels or carbon materials.

Efficient removal of heavy metal and antibiotics from wastewater by phosphate-modified hydrochar.

The preparation, characterization and adsorption performance of the phosphate-modified hydrochar (P-hydrochar) for Pb(II) and ciprofloxacin removal are investigated. Pb(II) and ciprofloxacin adsorption behavior fit well with the Hill model with the adsorption capacity of 119.61 and 98.38 mg/g, respectively. Pb(II) and ciprofloxacin adsorption kinetic process are accurately described by the Pseudo-second-order. Pb(II) and ciprofloxacin have synergy in the binary contaminant system, which reveals that Pb(II) adsorption amount is augmented. While ciprofloxacin adsorption amount is also augmented at low Pb(II) concentration and hindered at high Pb(II) concentration. Pb(II) adsorption mechanisms on P-hydrochar (e.g. precipitation, π-π interaction and complexation) are different from the ciprofloxacin (e.g. hydrogen bonding, pore filling, electrostatic attraction). Pb(II) and ciprofloxacin adsorption process are further analyzed by the density functional theory. The coexisted ions have little influenced on Pb(II) and ciprofloxacin adsorption. P-hydrochar still has large Pb(II) and ciprofloxacin adsorption capacity after five cycles. This result indicates that poplar sawdust waste can be converted into an efficient adsorbent to remove Pb(II) and ciprofloxacin from wastewater,.

Preparation of pyrolysis products by catalytic pyrolysis of poplar: Application of biochar in antibiotic wastewater treatment.

Poplar waste is acted as feedstock to produce renewable biofuel and green chemical by catalytic pyrolysis using ferric nitrate and zinc chloride as additive. The additive contributes to the generation of furfural in bio-oil. Additive promotes the generation of H2 and inhibits the generation of CO with bio-gas heating value of 12.16 MJ (Nm3)-1. Biochar exists ZnO and Fe3O4 with large surface area, which could be used as absorbent and photocatalyst for tetracycline and ciprofloxacin removal. The tetracycline and ciprofloxacin adsorption amount of biochar are 316.41 and 255.23 mg g-1 respectively. While the photocatalytic degradation removal of the tetracycline and ciprofloxacin is close to 100%. The adsorption and photocatalytic degradation mechanism are investigate and analyzed using the density functional theory and electron paramagnetic resonance analysis. Biochar can be quickly recycled and regenerated after use. Besides, biochar can be used in lithium ion battery industry for energy storage, which specific capacity is 535 mAh g-1.

Preparation of valuable pyrolysis products from poplar waste under different temperatures by pyrolysis: Evaluation of pyrolysis products.

Poplar waste is used as feedstock to prepare valuable pyrolysis products by pyrolysis under different temperature. The bio-oil is rich in aldehyde with the maximum relative content of 47.15%, which has potential application in chemical industries. Pyrolysis temperature has significantly influenced the composition and heating value of bio-gas. The maximum heating value of bio-gas is 14.56 MJ/Nm3. Biochar is used as an adsorbent to adsorb Ag+ from aqueous solution with the adsorption capacity of 76.09 mg/g. Biochar forms the value-added Ag-Biochar composite by reduction after adsorption Ag+. While, Ag-Biochar composite can be used as catalyst for methyl orange removal with the maximum removal of 94.08%. Ag-Biochar composite is also used as lithium ion battery cathode material for energy storage with the specific capacity of 345 mAh/g. Besides, preliminary economic analysis is used to evaluate the economics of pyrolysis process with the total annual revenue of $115, 725/year.

Flotation purification of waste high-silica phosphogypsum.

High-silica phosphogypsum (PG) is a kind of industrial by-product with great utilization potential. However, it is difficult to reuse PG directly due to the related gangue minerals (e.g., SiO2), and thus efficient purification is required to allow its further applications. Herein, a typical high-silica phosphogypsum waste was purified by a new "reverse-direct flotation" method. The organic matters and fine slimes were removed by reverse flotation, and then, the silica impurity was removed by direct flotation. Via the closed-circuit flotation process, the whiteness of the PG concentrate is improved from 33.23 to 63.42, and the purity of gypsum in the PG concentrate increases from 83.90% to 96.70%, with a gypsum recovery of 85%. Additionally, the content of SiO2 is significantly reduced from 11.11% to 0.07%. In-depth investigations suggest that the difference in the floatability of gypsum and quartz is prominently intensified by flotation reagents at pH = 2-2.5, and thus leads to good desilication performance. Further characteristics of the PG concentrate prove that impurities have been well removed, and the PG concentrate meets the requirement of related standards for gypsum building materials. The flotation method reported here paves the way for the purification of high-silica phosphogypsum, which can be extended to the purification and value-added reutilization of other industrial solid wastes.

High-efficiency removal of lead/cadmium from wastewater by MgO modified biochar derived from crofton weed.

The adsorption performance and mechanisms of Pb2+ and Cd2+ in wastewater using MgO modified biochar derived from crofton weed (MBCW600) are investigated. The Pb2+ and Cd2+ adsorption capacities of MBCW600 by the Hill model reach 384.08 mg/g and 207.02 mg/g, respectively, which is larger than that of original biochar. Pb2+ could be more easily captured by MBCW600 compared to Cd2+ in the multimetal system. Mg2+ contributes to Pb2+ and Cd2+ adsorption among coexisting cations. The exhausted MBCW600 could be well regenerated by simple method after use. The adsorption mechanism study indicates that Pb2+ and Cd2+ removal are primary contributed to mineral precipitation and ion exchange. The effective treatment volumes of Pb2+ and Cd2+ wastewater achieve 3050 mL and 2150 mL in the fixed-bed column experiment, respectively. Therefore, MBCW600 presents remarkable adsorption capability, excellent recoverability and large throughput, which shows the potential application in future treatment of wastewater containing heavy metal.

Copper recovery from waste printed circuit boards by the flotation-leaching process optimized using response surface methodology.

Recycling of waste printed circuit boards (PCBs) receives increasing attention due to abundant metallic resources and significant environmental threats. This work proposes a process for copper recovery from PCBs by froth flotation and oxidation leaching. Copper grade is improved from 38.70% to 68.34% with the recovery of 88.76% by froth flotation, and froth flotation is significantly influenced by copper liberation and particles dispersion of PCB powders. Process variables of oxidation leaching are examined by response surface methodology (RSM). A reliable mathematical model is obtained to predict the response as a function of independent variables and their interactions. Oxidation leaching is remarkably influenced by experimental variables, and the interactions between sulfuric acid and hydrogen peroxide are significant. Optimum conditions are achieved as sulfuric acid 1.0 mol/L, hydrogen peroxide 17%, temperature 50°C, and time 234 minutes, and the maximum leaching ratio of Cu is up to 99.94%, indicating that oxidation leaching is an effective method for Cu recovery from PCBs.Implications: Recycling of waste printed circuit boards (PCBs) receives increasing attention due to abundant metallic resources and significant environmental threats. This work proposes a novel process for copper recovery from PCBs by froth flotation and oxidation leaching. Froth flotation is efficient to enrich copper in metal fractions. Process variables of oxidation leaching are examined by response surface methodology (RSM). A reliable mathematical model is obtained to predict the response as a function of independent variables and their interactions. The froth flotation-oxidation leaching process is practicable and effective for copper recovery from waste printed circuit boards. This study significantly contributes to recycling metal resources from waste PCBs. We believe that this work will attract a broad readership and lead others to follow our approach.

Magnetic graphene-based nanocomposites as highly efficient absorbents for Cr(VI) removal from wastewater.

Due to the merits of their high adsorption and convenient separation, magnetic graphene-based composites have become a promising adsorbent in terms of wastewater treatment. However, recycling and regeneration properties of magnetic graphene-based composites are still a conundrum, which remains to be resolved. Here, Fe3O4/reduced graphene oxide (RGO) (Fe3O4/RGO) nanocomposites were synthesized by one-step solvent-thermal reduction route and used as adsorbents for water purification. It was encouraging to find that the nanocomposites possessed many intriguing properties in removing of Cr(VI) ions, including high adsorption efficiency and excellent recycling and regeneration property. The results indicated that the magnetic separation process of the Fe3O4/RGO nanocomposites only took less than 5 s and the maximum removal efficiency of Cr(VI) reached 99.9% under the optimum experimental conditions. Most significantly, the adsorption rate of Cr(VI) can still be as high as 98.13% after 10 cycles and the single recycle quality of the nanocomposites can maintain at more than 80%. As a result, the Fe3O4/RGO nanocomposites could be a potential adsorbent for removing heavy metal ions effectively, especially in environmental protection and restoration.

3-Dimensional Porous Carbon with High Nitrogen Content Obtained from Longan Shell and Its Excellent Performance for Aqueous and All-Solid-State Supercapacitors.

Three-dimensional porous carbon is considered as an ideal electrode material for supercapacitors (SCs) applications owing to its good conductivity, developed pore structure, and excellent connectivity. Herein, using longan shell as precursor, 3-dimensional porous carbon with abundant and interconnected pores and moderate heteroatoms were obtained via simple carbonization and potassium hydroxide (KOH) activation treatment. The electrochemical performances of obtained 3-dimensional porous carbon were investigated as electrode materials in symmetric SCs with aqueous and solid electrolytes. The optimized material that is named after longan shell 3-dimensional porous carbon 800 (LSPC800) possesses high porosity (1.644 cm3 g-1) and N content (1.14 at %). In the three-electrode measurement, the LSPC800 displays an excellent capacitance value of 359 F g-1. Besides, the LSPC800 also achieves splendid specific capacitance (254 F g-1) in the two electrode system, while the fabricated SC employing 1 M Li2SO4 as electrolyte acquires ultrahigh power density (15930.38 W kg-1). Most importantly, LSPC800 electrodes are further applied into the SC adopting the KOH/polyvinyl alcohol (PVA) gel electrolyte, which reaches up to an outstanding capacitance of 313 F g-1 at 0.5 A g-1. In addition, for the all-solid-state SC, its rate capability at 50 A g-1 is 72.73% and retention at the 10,000th run is 93.64%. Evidently, this work is of great significance to the simple fabrication of 3-dimensional porous carbon and further opens up a way of improving the value-added utilization of biomass materials, as well as proving that the biomass porous carbons have immense potential for high-performance SCs application.

Facile and Efficient Fabrication of Bandgap Tunable Carbon Quantum Dots Derived From Anthracite and Their Photoluminescence Properties.

Low-cost and earth-abundant coal has been considered to have a unique structural superiority as carbon sources of carbon quantum dots (CQDs). However, it is still difficult to obtain CQDs from raw coal due to its compactibility and lower reactivity, and the majority of the current coal-based CQDs usually emit green or blue fluorescence. Herein, a facile two-step oxidation approach (K2FeO4 pre-oxidation and H2O2 oxidation) was proposed to fabricate bandgap tunable CQDs from anthracite. The K2FeO4 pre-oxidation can not only weaken the non-bonding forces among coal molecules which cause the expansion of coal particles, but also form a large number of active sites on the surface of coal particles. The above effects make the bandgap tunable CQDs (blue, green, or yellow fluorescence) can be quickly obtained from anthracite within 1 h in the following H2O2 oxidation by simply adjusting the concentration of H2O2. All the as-prepared CQDs contain more than 30 at% oxygen, and the average diameters of which are <10 nm. The results also indicate that the high oxygen content only can create new energy states inside the band gap of CQDs with average diameter more than 3.2 ± 0.9 nm, which make the as-prepared CQDs emit green or yellow fluorescence.

Hydrothermal-template synthesis and electrochemical properties of Co3O4/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure.

Despite the high capacity of Co3O4 employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of Co3O4 during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, Co3O4/nitrogen-doped hemisphere-porous graphene composite (Co3O4/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that Co3O4 nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g-1), but also shows significantly improved rate performance (1188 mA h g-1 at 0.1 A g-1, 344 mA h g-1 at 5 A g-1) and enhanced cycling stability (683 mA h g-1 after 500 cycles at 1 A g-1). The enhanced electrochemical properties of Co3O4/N-HPGC nanocomposites can be ascribed to the synergistic effects of Co3O4 nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.

Nitrogen-Doped Porous Co3O4/Graphene Nanocomposite for Advanced Lithium-Ion Batteries.

A novel approach is developed to synthesize a nitrogen-doped porous Co3O4/anthracite-derived graphene (Co3O4/AG) nanocomposite through a combined self-assembly and heat treatment process using resource-rich anthracite as a carbonaceous precursor. The nanocomposite contains uniformly distributed Co3O4 nanoparticles with a size smaller than 8 nm on the surface of porous graphene, and exhibits a specific surface area (120 m2·g-1), well-developed mesopores distributed at 3~10 nm, and a high level of nitrogen doping (5.4 at. %). These unique microstructure features of the nanocomposite can offer extra active sites and efficient pathways during the electrochemical reaction, which are conducive to improvement of the electrochemical performance for the anode material. The Co3O4/AG electrode possesses a high reversible capacity of 845 mAh·g-1 and an excellent rate capacity of 587 mAh·g-1. Furthermore, a good cyclic stability of 510 mAh·g-1 after 100 cycles at 500 mA·g-1 is maintained. Therefore, this work could provide an economical and effective route for the large-scale application of a Co3O4/AG nanocomposite as an excellent anode material in lithium-ion batteries.

Green Preparation of High Yield Fluorescent Graphene Quantum Dots from Coal-Tar-Pitch by Mild Oxidation.

Coal tar pitch (CTP), a by-product of coking industry, has a unique molecule structure comprising an aromatic nucleus and several side chains bonding on this graphene-like nucleus, which is very similar to the structure of graphene quantum dots (GQDs). Based on this perception, we develop a facile approach to convert CTP to GQDs only by oxidation with hydrogen peroxide under mild conditions. One to three graphene layers, monodisperse GQDs with a narrow size distribution of 1.7 ± 0.4 nm, are obtained at high yield (more than 80 wt. %) from CTP. The as-produced GQDs are highly soluble and strongly fluorescent in aqueous solution. This simple strategy provides a feasible route towards the commercial synthesis of GQDs for its cheap material source, green reagent, mild condition, and high yield.

Hydrothermal Synthesis of Ultra-Light Coal-Based Graphene Oxide Aerogel for Efficient Removal of Dyes from Aqueous Solutions.

A novel carboxymethyl cellulose (CMC)-supported graphene oxide aerogel (CGOA) was fabricated from a cost-effective and abundant bituminous coal by a mild hydrothermal process and freeze-drying treatment. Such an aerogel has cross-linked graphene oxide layers supported by CMC, and therefore, displays high mechanical strength while having ultra-low density (8.257 mg·cm-3). The CGOA has a 3D interconnected porous structure, beneficial graphene framework defects and abundant oxygen-containing functional groups, which offer favorable diffusion channels and effective adsorption sites for the transport and adsorption of dye molecules. The adsorption performance of rhodamine B by an optimized CGOA shows a maximum monolayer adsorption capacity of 312.50 mg·g-1, as determined by Langmuir isotherm parameters. This CGOA exhibited a better adsorption efficiency (99.99%) in alkaline solution, and satisfactory stability (90.60%) after three cycles. In addition, adsorption experiments on various dyes have revealed that CGOA have better adsorption capacities for cationic dyes than anionic dyes.

One-Step Green Hydrothermal Synthesis of Few-Layer Graphene Oxide from Humic Acid.

The conventional synthesis route of graphene oxide (GOG), based on Hummers method, suffers from explosion risk, environmental concerns and a tedious synthesis process, which increases production costs and hinders its practical applications. Herein, we report a novel strategy for preparing few-layer graphene oxide (GOH) from humic acid via simple hydrothermal treatment. The formation of GOH is mainly attributed to the hydrolysis, oxidation and aromatization of humic acid under hydrothermal conditions. The as-prepared few-layer GOH has typical morphology (thin and crumpled sheets with the thickness of ~3.2 nm), crystal structure (a Raman ID/IG ratio of 1.09) and chemical composition (an X-ray Photoelectron Spectroscopy (XPS) O/C atomic ratio of 0.36) of few-layer GOG. The thermally reduced GOH (r-GOH) delivers considerable area capacitance of 28 µF·cm-2, high rate capability and low electrochemical resistance as supercapacitor electrodes. The described hydrothermal process shows great promise for the cheap, green and efficient synthesis of few-layer graphene oxide for advanced applications.

Estrogen receptor-regulated microRNAs contribute to the BCL2/BAX imbalance in endometrial adenocarcinoma and precancerous lesions.

Uncontrolled estrogen exposure can induce an imbalance in BCL2/BAX expression in endometrial cells, leading to precancerous lesions and type I endometrial adenocarcinoma. This study aimed to explore the mechanism underlying this phenomenon. We show that the activated estrogen receptor can suppress the expression of BAX by upregulating a group of microRNAs including hsa-let-7 family members and hsa-miR-27a, thereby promoting an increased BCL2/BAX ratio as well as enhanced survival and proliferation in the affected cells. These ER-regulated hsa-let-7 microRNAs can be detected in most hyperplastic endometria, suggesting their potential utility as indicators of estrogen over-exposure.