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A photocatalysis–electro-Fenton (PEF) system was constructed via molybdenum disulfide (MoS2) to remove tetracycline (TC) without an external oxidant supply and solution pH adjustment. In the system, original graphite felt (GF) was used as a cathode, from which H2O2was in situgenerated continuously under power. MoS2was motivated by visible light to facilitate the cycle of Fe2+/Fe3+, enhancing the Fenton process to produce •OH. The experimental results showed that the system can increase the degradation rate of pollutants by more than 5 times. Moreover, the quenching and electron paramagnetic resonance (EPR) tests demonstrated that •OH was the dominant active species. X-ray photoelectron spectroscopy (XPS) characterization, Mo concentration, and cycle experiments proved the excellent catalytic activity and chemical stability of MoS2. It is worth mentioning that the photocatalytic performances of different morphologies of MoS2(flower, flake, and radar) were compared. As a result, flower-like MoS2exhibited a much superior photoresponse than flake and radar, which could accelerate the Fe2+/Fe3+cycle further effectively. These findings highlight the morphology–performance relationship of MoS2under a PEF system and the mechanisms of contaminant degradation, which is of great significance for developing photoelectric Fenton technology.

ABSTRACTThis study assesses the diversity, composition, structure and abundance of urban forests in Adama city, Central Ethiopia to provide baseline information useful for developing a conservation strategy. The urban forest of Adama has an estimated 525,200 trees with a tree cover of 20%. The three most common species are Azadirachta Indica(14.8%), Carica papaya(6.8%), and Acacia abyssinica(5%). The i-Tree Eco model was used to organise output. A total of 214 sample plots were generated directly in the i-Tree Eco application using the random plots’ generator via the Google Maps function. A 0.1acre circular plot was used. A total of 805 trees were sampled across the 214 plots. Among the 86 species encountered in the sample plots, 68 (79%) were introduced and only 18 (21%) were native species. Most introduced trees originated from Asia (22%). The tree diversity calculated using the Shannon Weiner index (H’) was 3.61 and the dominance of Simpson’s value was 0.95. The evenness index of the plots sampled was 0.80. The study indicates the crucial role that urban forests play in maintaining and conserving urban trees and enhancing ecosystem services in urban areas.

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Direct discharge of wastewater from flotation processes can pose a significant threat to environmental protection due to the presence of residual organic surfactants. These surfactants can decrease the surface tension of aqueous solutions and generate stable foam, which can interfere with further purification treatments. To address this issue, sodium oleate (NaOL), one of the most commonly used surfactants, was studied, and the Fenton oxidation process was utilized to degrade NaOL and mitigate foam generation. In this work, the foamability of NaOL before and after Fenton oxidation pretreatment, the optimal conditions for NaOL degradation, and the effect of temperature on the oxidative process were examined. The findings demonstrate that the foamability of NaOL solution is directly proportional to its concentration, and the Fenton oxidation process can significantly reduce the maximum foam volume and half-life period of the foam. Moreover, the activation energy was determined to be 37.60 kJ/mol, indicating that the oxidative reaction proceeds with a low energy barrier.

Based on the strong activation activity and affinity of Co and MoS2for peroxymonosulfate (PMS), respectively, in this study, a CoS2/MoS2@chitosan (CoS2/MoS2@CS) gel with favorable photo responsive behavior was synthetically synthesized for more potent degradation of tetracycline (TC). It was found that CoS2/MoS2@CS had excellent catalytic active for the degradation of TC under visible light irradiation. The presence of CoS2/MoS2interfacial structure improve the electron transfer ability of the MoS2interface, and the degradation rate of TC was increased from 0.0106 min−1to 0.0463 min−1, with a high degradation rate of 97.4 %. CoS2/MoS2can effectively degrade TC within 5 cycles, demonstrating superior cycling stability. In addition, the system degraded different organic pollutants (tetracycline (TC), tetracycline hydrochloride (TCH), crystal violet (CV), and methylene blue (MB)) with a degradation rate higher than 96 %, which supports the ability of the CoS2/MoS2@CS-PMS system to degrade various chemical contaminants. Quenching analysis indicates that SO4•−is the primary reactive chemical free radical for the degradation of TC in the CoS2/MoS2@CS-PMS system. It provides an approach of combining the synergistic action of Co (II) and photogenerated carriers for more efficient activation of PMS that some inspirations of heterojunction catalysts for AOP applications.

Various kinds of clays occur naturally and are accompanied by particular cations in their interlayer domains. Here we report the reassembled membranes with nanofluidic channel arrays by using the natural clays montmorillonite, mica, and vermiculite, which were imparted with the natural selectivity for realizing precise recognition and directional regulation of the naturally occurring interlayer cations. A typical surface-governed ionic transport behavior was observed in the clay nanofluidic channels. Through asymmetric structural modification, cationic current rectification was realized in montmorillonite channels that performed as a nanofluidic diode. Interestingly, in the mica nanofluidic channel, the K+that was naturally occurring in the interlayer domain of mica showed a reciprocating motion and resulted in a periodically fluctuating current. Electrodialysis demonstrated that such a fluctuating current reflects a directional selectivity for K+, achieving at least a 6000 times permeation rate difference with Li+ions. The specific selectivity for Li+/Mg2+on vermiculite reached up to 856 times with similar cations by the current technique. As-obtained clay membranes possess application prospects in energy conversion, brine resource development, etc. Such a strategy can achieve the designed selectivity through systematic screening of the building blocks, thus imparting them with the inherent characteristics of natural clays, which provides an alternative solution to the present manufacture of selective membranes.

Volumetric solar evaporations by using light-absorbing nanoparticles suspended in liquids (nanofluids) as solar absorbers have been widely regarded as one of the promising solutions for clean water production because of its high efficiency and low capital cost compared to traditional solar distillation systems. Nevertheless, previous solar evaporation systems usually required highly concentrated solar irradiation and high capital cost, limiting the practical application on a large scale. Herein, for the first time in this work, polydopamine (PDA)-capped nano Fe3O4(Fe3O4@PDA) nanofluids were used as solar absorbers in a volumetric system for solar evaporation. The introduction of organic PDA to nano Fe3O4highly contributed to the high light-absorbing capacity of over 85% in wide ranges of 200–2400 nm because of the existence of numerous carbon bonds and pi (π) bonds in PDA. As a result, high evaporation efficiency of 69.93% under low irradiation of 1.0 kW m−2was achieved. Compared to other nanofluids, Fe3O4@PDA nanofluids also provided an advantage in high unit evaporation rates. Moreover, Fe3O4@PDA nanofluids showed excellent reusability and recyclability owing to the preassembled nano Fe3O4, which significantly reduced the material consumptions. These results demonstrated that the Fe3O4@PDA nanofluids held great promising application in highly efficient solar evaporation.

Two-dimensional montmorillonite nanolayers (2D Mnt) are excellent adsorbents for methylene blue due to the fully exposed active sites, but the separation of 2D Mnt from water is difficult. The objective of the present study was to assemble 2D Mnt and graphene oxide sheets into a three-dimensional aerogel (3D Mnt-rGO Gel) to achieve easy solid–liquid separation. Structural characterization demonstrated that the Mnt-rGO Gel has a porous 3D structure with Mnt nanolayers distributed uniformly within; the introduction of 2D Mnt could reduce significantly the degree of restacking of graphene sheets. Adsorption tests indicated that 2D Mnt enhances the methylene blue (MB) removal performance of Mnt-rGO Gel with a large adsorption capacity of 207 mg g–1, which may be attributed to the adsorption of MB onto 2D Mnt and the increased adsorption surface of rGO resulting from the reduced restacking of graphene sheets. The MB was removed completely by 300 mg L–1of Mnt-rGO Gel-3 in 180 min. The adsorption process of MB onto Mnt-rGO Gel followed the pseudo-second order kinetic model and the Langmuir isotherm model. Mnt-rGO Gel also showed good reusability. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results suggested that the adsorption of MB onto Mnt-rGO Gel may be attributed to the π–π interactions between aromatic rings of MB and graphene, hydrogen bonding, and the electrostatic interactions between the nitrogen groups on the MB and oxygen-containing groups on the Mnt-rGO Gel.

Developing earth-abundant, active, and stable electrocatalysts for hydrogen evolution reactions (HERs) at large current densities has remained challenging. Herein, heterostructured nickel foam-supported cobalt carbonate hydroxide nanoarrays embellished with NiCoSxnanoflakes (NiCoSx@CoCH NAs/NF) are designed via room-temperature sulfurization, which can drive 10 and 1000 mA cm–2at low overpotentials of 55 and 438 mV for HER and exhibit impressive long-term stability at the industrial-level current density. Surprisingly, NiCoSx@CoCH NAs/NF after a 500 h stability test at 500 mA cm–2exhibit better catalytic performance than the initial one at high current densities. Simulations showed that NiCoSx@CoCH NAs have an optimized hydrogen adsorption free energy (ΔGH*) of 0.02 eV, owing to the synergistic effect of CoCH (ΔGH*= 1.36 eV) and NiCoSx(ΔGH*= 0.03 eV). The electric field at the heterostructure interface leads to electron transport from CoCH to NiCoSx, which enhances HER dynamics. The hierarchical nanostructure has a large specific area and a superaerophobic surface, which are beneficial to hydrogen generation/release for efficient and stable HER.

It is widely acknowledged that clay minerals have detrimental effects on the process of flotation, but the mechanisms involved are still not fully understood. In this work, the effects of montmorillonite, kaolinite, and illite on pyrite flotation were investigated from the perspective of various structures of clay minerals. Flotation tests suggested that the detrimental effect of clay minerals on the flotation of pyrite increased as follows: montmorillonite > kaolinite > illite. With the help of rheology measurements, it was found that montmorillonite significantly increased pulp viscosity, which in turn substantially reduced pyrite recovery and grade. Scanning electron microscopy (SEM) images suggested that montmorillonite formed the “house-of-cards” structure by edge-to-edge and edge-to-face contact, while kaolinite and illite platelets were associated mainly in the face-to-face mode. In addition, it was clearly observed by SEM–energy dispersive spectrometry that montmorillonite and kaolinite coat on the pyrite surfaces, which would lower the surface hydrophobicity of pyrite. Kaolinite covered much larger area of pyrite surface than montmorillonite owing to the positive charge occurring at the exposed aluminum–oxygen octahedral sheet of kaolinite. Although illite has a similar 2:1 structure to montmorillonite, it showed little or no effect on pyrite flotation, which was attributed to its poor swelling nature. These findings shed light on the root cause of the adverse effect of clay minerals on pyrite flotation and are expected to provide theoretical guidance for mitigating the negative effects on flotation caused by clays.

Alkali-activated binders based on metakaolin, fly ash and slag without curing were exposed directly in air, Na2SO4and MgSO4solutions for studying the evolution in mechanical strength and microstructure. A series of binders were synthesized and characterized on 7, 21, 45, 60, 75 and 90 days, respectively. Compressive strength measurement, scanning electron microscope (SEM) mapping, X-ray diffraction (XRD) and unclear magnetic resonance (NMR) were applied in the study. It is found that the exposure in sulfate solutions leaded to the deterioration of the binders by the dissolution of alkalis. In Na2SO4solution, a higher percentage of zeolite was formed in the binders. While in MgSO4, a precipitate layer (e.g., brucite and gypsum), forming on the binder surface plays an important role in protecting the formation of gel, promoting the compressive strength improvement of alkali-activated slag, and compensating the decrease in compressive strength of alkali-activated metakaolin. These results provide clues for the direct preparation of alkali-activated concrete in aggressive sulfate environment.

Aerogels, with porous channels for water supply and vapor escape, can provide many inherent advantages in solar desalination and wastewater treatment. For the first time, this work demonstrates the preparation of a novel three-dimensional (3D) MoS2-based aerogel with high porosity and mechanical stability by a facile strategy for solar desalination. This 3D MoS2aerogel has an excellent light-absorbing efficiency of over 95% within the whole solar spectrum range, enabling a high evaporation efficiency of 88.0% under a low solar irradiation of 1.0 kW m–2and superhigh evaporation efficiencies of over 90% under a slightly enhanced solar irradiation of 1.5–3.0 kW m–2as well as a remarkable desalination performance. In addition, the excellent mechanical stability of this MoS2aerogel renders it to be reused for at least 10 cycles with stable water productivity. Because of its 3D architectures with high porosity and easy separation, this MoS2-based aerogel also provides promising applications in solar-driven water purification, sterilization, and so forth.

This work attempts to investigate the effects of aluminum dosage on the immobilization of heavy metals in alkali-activated municipal solid waste incineration fly ash-based pastes to manage hazardous threats in it. A variable proportion of metakaolin is used to achieve different aluminum dosages in the synthesized pastes. Structure, composition, morphology, and mechanical property of the prepared pastes are studied by employing X-ray diffraction, 29Si NMR, scanning electron microscopy, and compressive strength measurements. The results showed that a 5% metakaolin-composed paste exhibited the highest compressive strength (10.94 MPa). The addition of the aluminum dosage-converted soluble chloride salt into Friedel’s salt, subsequently, improved the immobilization of heavy metals. The toxic characteristic leaching procedure test showed that a small amount of aluminum can improve immobilization dominantly because of the effective encapsulation ability of the pastes. The molecular modeling and simulation analysis illustrated that because of the presence of Na+in it, sodium–alumino–silicate–hydrate (N–A–S–H) gel possesses the most stable molecular orientation.

• Synthesized a novel photocatalyst: MoS 2 @MMTNS-HMS; • Featured with the unique-morphological hollow structure and vertically-aligned MoS 2 nanosheets; • Had higher light-utilization efficiency, edge active sites density and stronger photoelectrons separation; • Leading to excellent photocatalytic activity and cycle stability. In this work, MoS 2 @montmorillonite nanosheets hollow microspheres (MoS 2 @MMTNS-HMS) with a novel morphology structure was successfully synthesized through loading MoS 2 to the surface of MMTNS-HMS via hydrothermal method. The novel material has been characterized through the measurements of SEM, TEM, Raman spectra and UV–vis absorption spectra. The results have shown that MoS 2 @MMTNS-HMS emerges higher light-utilization efficiency, density of edge active sites and separation of photoelectrons, owing to its unique hollow structure, vertically-aligned MoS 2 nanosheets, which greatly enhances its photocatalytic activity. Furthermore, the cycle stability of MoS 2 @MMTNS-HMS is much higher than that of pristine MoS 2 , which is attributed to that MMTNS-HMS greatly inhibits the oxidation of MoS 2 during photocatalytic. MoS 2 @MMTNS-HMS could be a promising photocatalyst for the applications in the elimination of organic pollutants. [ABSTRACT FROM AUTHOR]

ABSTRACTFew studies have focused on the effect of mineral composition on the mechanical behaviour and evolution of a geopolymer binder in artificial seawater environment. In this study, a geothermal clay-based geopolymer rich in micron-size cristobalite and metakaolin was compared with a metakaolin-based geopolymer in artificial seawater. The effects of the cristobalite on the mechanical behaviour and microstructure of geopolymers were characterised through compressive strength measurements, x-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The micro-size cristobalite enhanced the compressive strength of the geothermal clay-based geopolymer. Without cristobalite, zeolite formed in metakaolin-based geopolymer and led to compressive strength decrease obviously first then increase slightly. The formation of the geothermal clay-based geopolymer gel was delayed in seawater. The cristobalite in the geothermal clay-based geopolymer hindered the formation of Q4(4Al), Q4(3Al) and Q4(2Al).

Microwave-assisted leaching as a green and efficient method for leaching chalcopyrite has attracted increasing attention. Researchers have actively explored the reasons why microwaves have a positive impact on copper extraction. In this work, X-ray diffraction (XRD), an optical microscope, electron probe micro-analyzer (EPMA) and field emission scanning electron microscope with energy dispersive spectrometer (SEM-EDS) were employed to investigate the surface structure modification of chalcopyrite by microwave during leaching. The modified chalcopyrite had a positive effect on better mineral leachability, higher effective surface for leaching, and the fewer passivation layer. The superior mineral leachability was related to the surplus intermediate products of covellite, while microwave promoted the conversion of chalcopyrite to covellite. In addition, microwave is capable of increasing active sites upon the removal of the passivation layer and the enlargement of the effective reaction surface. This work summarized the relationship between the high copper recovery and the surface structure modification of chalcopyrite systematically.

Few studies have focused on the effect of mineral composition on the mechanical behaviour and evolution of a geopolymer binder in artificial seawater environment. In this study, a geothermal clay-based geopolymer rich in micron-size cristobalite and metakaolin was compared with a metakaolin-based geopolymer in artificial seawater. The effects of the cristobalite on the mechanical behaviour and microstructure of geopolymers were characterised through compressive strength measurements, x-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The micro-size cristobalite enhanced the compressive strength of the geothermal clay-based geopolymer. Without cristobalite, zeolite formed in metakaolin-based geopolymer and led to compressive strength decrease obviously first then increase slightly. The formation of the geothermal clay-based geopolymer gel was delayed in seawater. The cristobalite in the geothermal clay-based geopolymer hindered the formation of Q4(4Al), Q4(3Al) and Q4(2Al).

N-rich nano-activated carbon/montmorillonite nanosheet with high ability for PMS activation and TC degradation was prepared via in-situ polymerization of ANI and calcination, creating open access for PMS to react with the fully exposed active sites. The prepared catalyst exhibited comparable catalytic ability to metal-based catalysts, achieving 86% degradation of TC (40 mg/L) in just 10 min using 0.3 g/L catalyzer and 0.3 g/L PMS. The degradation rate of TC reached 0.35 min−1, which was higher than that of most catalyst. The reason was attributed to the abundant active sites of graphitic N, pyridinic N, pyrrolic N, nitric oxide, and defects, improving the charge distribution and electron transfer of catalyst, and promoting the self-decomposition of PMS into the radical (•OH, •SO4−) and non-radical (1O2, predominant) species for TC degradation. Such catalyzer provided a novel design of metal-free catalysts with significant improvements, achieving the efficient bio-safety disposal of antibiotics from wastewater.

Solidification/stabilization (S/S) of a zinc mine tailing through geopolymerization has been studied. The mechanical property and microstructure of the mine tailings based-geopolymers were investigated through compressive strength measurements, FTIR, NMR and SEM characterizations. The stabilization of zinc in the geopolymers was analyzed through toxicity characteristic leaching procedure (TCLP) and the immobilization forms were characterized through XPS. With the content of metakaolin in raw materials increased from 0 to 50%, the amount of geopolymer gel in the binders and the compressive strength of geopolymer increased. As a ratio of metakaolin to mine tailings of 1:1, the mine tailings promoted the formation of silica-rich gel and the compressive strength of geopolymer was 30.1 MPa which was similar to pure metakaolin-based geopolymer. The immobilization efficiency of Zn in the geopolymers is correlated to their mechanical property. Zinc is immobilized in the geopolymers through physical encapsulation and adsorption of the leached Zn2+by geopolymer gel.

In order to develop a facile and precisely controlled approach to synthesize hierarchical mesoporous materials with tailored property, in this work, a novel study was carried out to fabricate montmorillonite-chitosan hollow and hierarchical mesoporous spheres (MMTNS@CS-HMPHS) based on single-template layer-by-layer (LbL) assembly. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area analysis and X-ray photoelectron spectroscopy (XPS) analyses were carried out to characterize the morphology and surface properties of MMTNS@CS-HMPHS. Benefitting from the unique lamellar structure of MMTNS, mesoporous channels are formed on the shell of MMTNS@CS hollow spheres, resulting in high surface area. Moreover, the surface functionalization and pore size of MMTNS@CS-HMPHS can be easily tuned, due to the tailored property through LbL assembly method. Besides the unique microstructure, MMTNS@CS-HMPHS also possesses the active sites generated from both MMT and chitosan, which greatly promotes its performance in fields of adsorption, drug delivery and catalyst supports, etc. [ABSTRACT FROM AUTHOR]

In this research, metakaolin-based geopolymers were synthesized to study their deterioration in marine environment. The geopolymers were exposed in air, seawater, dry-wet and heat-cool cycles of seawater for 30, 60 and 90 days. The mechanical property of the geopolymers was characterized through compressive strength measurements, and their microstructures were measured by X-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) apparatus. It was found that seawater environment inhibited the geopolymerization reactions, so that a low amount of tetrahedral silicon of Q4(4Al), Q4(3Al) and Q4(2Al) were formed.

Since human daily demands for fresh water have been increased significantly, the supply of fresh water for the mining industry, especially froth flotation, should be considerably reduced. In addition, stricter environmental standards have been implemented in many countries to reduce the risks due to the disposal of wastewater, many flotation operators have to seek more efficient ways to utilize the limited fresh water sources. Recycling water with high concentrations of impurities is a normal strategy for most of the mineral processing plants; however, water quality should be carefully considered to guarantee a smooth flotation process. Recently, the application of seawater in flotation has attracted much attention due to its availability and abundance rather than fresh water. However, the influencing mechanisms due to the application of seawater in flotation have not been fully understood especially the reactions between mineral particles and bubbles in the presence of high concentrations of cations and anions. This would impede the application of alternatives to fresh water in the flotation. Therefore, this paper reviews the current water sources and the technologies for water recycling in the flotation process. Specifically, the life cycle of water in flotation was proposed. In addition, the strategies including high pulp density flotation as well as the most promising alternatives to fresh water have been discussed in details, with the related mechanisms being demonstrated.

The exfoliation of layered montmorillonite (MMT) into mono- or few-layer sheets is of significance for both fundamental studies and potential applications. In this report, exfoliated MMT nanosheets with different aspect ratios have been prepared via a new freezing/thawing–ultrasonic exfoliation method. Freezing/thawing processing can exfoliate MMT tactoids with low efficiency while virtually retaining the original lateral size. The ultrasonic method has better exfoliation efficiency but tends to damage the nanosheets. By combining them and reasonably controlling the cycle index of freezing/thawing and ultrasonic power, the MMT nanosheets with different aspect ratios have been prepared efficiently. Such a unique exfoliation method has broad applicability for layered materials to produce monolayer nanosheets on a large scale.