Heterogenous Fenton‐like reactions are frequently proposed for treating persistent pollutants through the generation of reactive radicals. Despite great efforts to optimize catalyst activity, their ...broad application in practical settings has been restricted by the low efficiency of hydrogen peroxide or persulfate decomposition as well as ultrafast self‐quenching of the activated radicals. Theoretical calculations predicted that two‐dimensional (2D) metallic 1T phase MoS2 materials with exposed (001) surfaces and (100) edges should have remarkable affinity towards crucial intermediates in the peroxymonosulfate (PMS) activation process. X‐ray photoelectron spectroscopy and in situ Raman spectroscopy were used to show that the exposed metallic Mo sites accelerate the rate‐limiting step of electron transfer. A lamellar membrane made from a stack of 2D MoS2 with tunable interspacing was then designed as the catalyst. The non‐linear transport between the MoS2 nanolayers leads to high water diffusivity so that the short‐lived reactive radicals efficiently oxidize contaminants.
Organic compounds were efficiently degraded by Fenton‐like reactions. Bisphenol A was removed by generating catalytic peroxymonosulfate (PMS) in a MoS2 membrane with a tunable interspacing. The rapid degradation is enabled by the enhanced generation of radicals and their close proximity to the organic compounds in the nanostructure.
The layered molybdenum chalcogenide MoS2 has attracted wide attention due to its potential electrochemical applications. Based on its unique physical and chemical properties, numerous advances have ...shown that nanostructured MoS2, with the advantages of low cost and outstanding properties, is a promising candidate for environmentally benign energy conversion and storage (ECS) devices. Nowadays, in order to lessen the reliance on fossil fuels, the production of hydrogen from water splitting has become an important issue. Hence, developing catalysts composed of earth-abundant elements that possess activities comparable to those of noble metals is of great urgency. According to DFT calculations in terms of HER free-energy diagrams, MoS2 could be used as an effective substitute for noble metals. Meanwhile, MoS2 with various structures has also been applied in the field of energy storage, including batteries and supercapacitors. Additionally, due to their layer-dependent electrical properties, MoS2-based electrochemical devices have been applied as sensors for a variety of chemicals. In this review, we summarize recent advances in the development of MoS2 with high-performance in various electrochemical domains, and recent progress in discovering the mechanisms underlying the enhanced activity. Moreover, we summarize the critical obstacles facing MoS2, and discuss strategies for further improving its activity. Lastly, we offer some suggestions on the pathways toward achieving high performance competitive with noble metal counterparts, and perspectives on practical applications of MoS2 in the future.
Low‐cost and resourceful transition metal phosphides (TMPs) have gradually received wide acceptance in the energy industry through exhibiting comparable catalytic activity and long‐term stability to ...traditional catalysts (e.g., Pt/C, LiCoO2, LiFePO4, etc.). With the emergence of the research hotspot of TMPs, probing their mechanism of catalytic energy conversion and storage inspired by the superb structure of metal‐phosphorus chelate is of great significance. To this end, recent developments in TMPs with various crystal structures and morphologies have attracted much attention. The design of TMPs ranging from the choice of different transition metals to phosphorus sources has been intensively explored. This research has indicated that multidimensional morphologies of TMPs prominently enrich the patterns of charge storage and electron transportation, and ultra‐nanoscaled TMPs obtained by multiple tools and techniques might challenge the threshold of electrocatalytic reactions. Here, recent developments in synthetic strategies of TMPs from different precursors are classified. The underlying mechanism between the structural and crystallographic characteristics and the tuned properties of TMPs in energy applications is also presented. Additionally, the key trends in structure and morphology characterization of TMPs are highlighted. Future perspectives on the challenges and opportunities facing TMPs catalysts are thereby proposed.
Recent work toward exploring high‐performance TMPs applied in energy conversion and storage is summarized. For each class of TMPs, advances in synthetic mechanisms and methods to the key trends in structure and morphology characterizations in full‐scale energy applications are discussed. Lastly, perspectives on challenges and opportunities facing TMPs are presented to shed light on their promising future.
Application of transition metal phosphide (TMP) catalysts for full water splitting has great potential to help relieve the energy crisis. Various methods have been investigated to obtain high ...catalytic activity, but the use of electronic structure regulation by incorporation of different elements is of particular simplicity and significance for development of a universal TMP synthesis method. We herein describe a novel approach for fabricating a series of TMPs by pyrolyzing phytic acid (PA) cross-linked metal complexes. The introduction of oxygen atoms into TMPs not only enhanced their intrinsic electrical conductivity, facilitating electron transfer, but activated active sites via elongating the M–P bond, favoring the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER). MoP exhibited relative low HER overpotentials of 118 mV and 93 mV while supporting a current density of 20 mA·cm–2 in 0.5 M H2SO4 and 1 M KOH electrolytes, respectively. When CoP was applied as a catalyst for OER, only 280 mV overpotential was required to reach current density of 10 mA·cm–2. Additionally, PA-containing precursors enabled intimate embedding of TMPs onto a flexible substrate surface (carbon cloth), so that electron injection from substrate and transport to the active sites was facilitated. Remarkably, an alkaline electrolyzer was able to achieve a current density of 40 mA·cm–2 at the low voltage of 1.6 V, demonstrating its potential for practical overall water splitting without the use of noble metals.
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•Microplastic behavior was investigated during drinking water treatment process.•Low microplastic removal efficiency was observed after coagulation.•Al-based salts performed better ...than Fe-based salts.•PAM played an important role in increasing microplastics removal efficiency.•After coagulation, microplastics induced different UF membrane fouling behavior.
Microplastics have garnered much attention worldwide as a new emerging pollutant, especially because of their eco-toxicological effects in marine environments. As they are gradually detected in freshwaters, understanding how microplastics, with their small particle size and low density, will behave during current drinking water treatment processes is urgently needed. In this study, Al- and Fe-based salts were used in the presence of polyethylene (PE), which is suspended/floats easily in water and is the main constituent of microplastics. Results showed that Al-based salts performed better in PE removal efficiency than Fe-based salts. The smaller the PE particle size, the higher the removal efficiency. However, a low removal efficiency was observed, even with a high Al-based salt dosage of 15 mM (below 40%). Additionally, water conditions, such as ionic strength, turbidity level, barely influenced the removal efficiency. In comparison to pH, polyacrylamide (PAM) addition played an important role in removing PE; especially anionic PAM addition, because of the positively charged Al-based flocs it generates under neutral conditions. For ultrafiltration, although PE particles can be completely rejected, slight membrane fouling was induced after coagulation with conventional Al-based salts. With increasing dosage, membrane fouling was gradually aggravated owing to the thick cake layer formed. However, the larger the PE particles, the greater the roughness of the Al-based floc cake layer, leading to less severe membrane fouling. Based on this investigation, the microplastic removal behaviors exhibited during coagulation and ultrafiltration processes have potential application in drinking water treatment.
The development of low cost, durable and efficient nanocatalysts to substitute expensive and rare noble metals (
e.g.
Pt, Au and Pd) in overcoming the sluggish kinetic process of the oxygen reduction ...reaction (ORR) is essential to satisfy the demand for sustainable energy conversion and storage in the future. Graphene based transition metal oxide nanocomposites have extensively been proven to be a type of promising highly efficient and economic nanocatalyst for optimizing the ORR to solve the world-wide energy crisis. Synthesized nanocomposites exhibit synergetic advantages and avoid the respective disadvantages. In this feature article, we concentrate on the recent leading works of different categories of introduced transition metal oxides on graphene: from the commonly-used classes (FeO
x
, MnO
x
, and CoO
x
) to some rare and heat-studied issues (TiO
x
, NiCoO
x
and Co-MnO
x
). Moreover, the morphologies of the supported oxides on graphene with various dimensional nanostructures, such as one dimensional nanocrystals, two dimensional nanosheets/nanoplates and some special multidimensional frameworks are further reviewed. The strategies used to synthesize and characterize these well-designed nanocomposites and their superior properties for the ORR compared to the traditional catalysts are carefully summarized. This work aims to highlight the meaning of the multiphase establishment of graphene-based transition metal oxide nanocomposites and its structural-dependent ORR performance and mechanisms.
Recent advances in the studies of oxygen reduction reaction (ORR) on graphene-based transition metal oxide nanocomposites are reviewed with emphasis on the morphologies and interactions between graphene and the supported component.
In our previous studies, a synthesized Fe–Mn binary oxide was found to be very effective for both As(V) and As(III) removal in aqueous phase, because As(III) could be easily oxidized to As(V). ...As(III) oxidation and As(V) sorption by the Fe–Mn binary oxide may also play an important role in the natural cycling of As, because of its common occurrence in the environment. In the present study, the respective role of Fe and Mn contents present in the Fe–Mn binary oxide on As(III) removal was investigated via a direct in situ determination of arsenic speciation using X-ray absorption spectroscopy. X-ray absorption near edge structure results indicate that Mn atoms exist in a mixed valence state of +3 and +4 and further confirm that MnO x (1.5 < x < 2) content is mainly responsible for oxidizing As(III) to As(V) through a two-step pathway reduction of Mn(IV) to Mn(III) and subsequent Mn(III) to Mn(II) and FeOOH content is dominant for adsorbing the formed As(V). No significant As(III) oxidation by pure FeOOH had been observed during its sorption, when the system was exposed to air. The extended X-ray absorption fine structure results reveal that the As surface complex on both the As(V)- and As(III)-treated sample surfaces is an inner-sphere bidentate binuclear corner-sharing complex with an As–M (M = Fe or Mn) interatomic distance of 3.22–3.24 Å. In addition, the MnO x and FeOOH contents exist only as a mixture, and no solid solution is formed. Because of its high effectiveness, low cost, and environmental friendliness, the Fe–Mn binary oxide would play a beneficial role as both an efficient oxidant of As(III) and a sorbent for As(V) in drinking water treatment and environmental remediation.
An outstanding hydrogen evolution electrocatalyst should have a free energy of adsorbed atomic hydrogen of approximately zero, which enables not only a fast proton/electron‐transfer step but also ...rapid hydrogen release. An economic and industrially viable alternative approach for the optimization of atomic hydrogen binding energy is urgently needed. Herein, guided by density functional theory (DFT) calculations, it is theoretically demonstrated that oxygen doping in NiCoP can indeed optimize the atomic hydrogen binding energy (e.g., |ΔGH*| = 0.08, 0.12 eV on Co, P sites). To confirm this, NiCoP electrodes with controllable oxygen doping are designed and fabricated via alteration of the reducing atmosphere. Accordingly, an optimal oxygen‐doped NiCoP (≈0.98% oxygen) nanowire array is found to exhibit the remarkably low hydrogen evolution reaction (HER) overpotential of 44 mV to drive 10 mA cm−2 and a small Tafel slope of 38.6 mV dec−1, and long‐term stability of 30 h in an alkaline medium. In neutral solution, only a 51 mV overpotential (@10 mA cm−2) is required, and the Tafel slope is 79.2 mV dec−1. Meanwhile, in situ Raman spectra confirm the low formation overpotential (−30 mV) of NiCo‐phosphate at the surface of ≈0.98% oxygen‐doped NiCoP, which enables the material to show better HER performance.
Based on density functional theory calculations, it is found that atomic hydrogen binding energy can be optimized on NiCoP via oxygen doping. Accordingly, an optimal oxygen‐doped porous NiCoP NWAs/NF (≈0.98% oxygen) is achieved by altering reducing atmosphere, exhibiting low overpotentials of 44, 51 mV (@10 mA∙cm−2), and Tafel slopes of 38.6, 79.2 mV∙dec−1 in alkaline and neutral medium, respectively.
Microplastics have caused great concern worldwide recently due to their ubiquitous presence within the marine environment. Up to now, most attention has been paid to their sources, distributions, ...measurement methods, and especially their eco-toxicological effects. With microplastics being increasingly detected in freshwater, it is urgently necessary to evaluate their behaviors during coagulation and ultrafiltration (UF) processes. Herein, the removal behavior of polyethylene (PE), which is easily suspended in water and is the main component of microplastics, was investigated with commonly used Fe-based salts. Results showed that although higher removal efficiency was induced for smaller PE particles, low PE removal efficiency (below 15%) was observed using the traditional coagulation process, and was little influenced by water characteristics. In comparison to solution pH, PAM addition played a more important role in increasing the removal efficiency, especially anionic PAM at high dosage (with efficiency up to 90.9%). The main reason was ascribed to the dense floc formation and high adsorption ability because of the positively charged Fe-based flocs under neutral conditions. For ultrafiltration, although PE particles could be completely rejected, slight membrane fouling was caused owing to their large particle size. The membrane flux decreased after coagulation; however, the membrane fouling was less severe than that induced by flocs alone due to the heterogeneous nature of the cake layer caused by PE, even at high dosages of Fe-based salts. Based on the behavior exhibited during coagulation and ultrafiltration, we believe these findings will have potential application in drinking water treatment.
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Adsorption isotherm of phosphate by Fe–Mn binary oxide adsorbent fitted with Langmuir and Freundlich models, which demonstrated a relatively high P adsorption capacity.
Phosphate removal is important ...in the control of eutrophication of water bodies and adsorption is one of the promising approaches for this purpose. A Fe–Mn binary oxide adsorbent with a Fe/Mn molar ratio of 6:1 for phosphate removal was synthesized by a simultaneous oxidation and coprecipitation process. Laboratory experiments were carried out to investigate adsorption kinetics and equilibrium, in batch mode. The effects of different experimental parameters, namely contact time, initial phosphate concentration, solution pH, and ionic strength on the phosphate adsorption were investigated. The adsorption data were analyzed by both Freundlich and Langmuir isotherm models and the data were well fit by the Freundlich isotherm model. Kinetic data correlated well with the pseudo-second-order kinetic model, suggesting that the adsorption process might be chemical sorption. The maximal adsorption capacity was 36
mg/g at pH 5.6. The phosphate adsorption was highly pH dependent. The effects of anions such as
Cl
-
,
SO
4
2
-
, and
CO
3
2
-
on phosphate removal were also investigated. The results suggest that the presence of these ions had no significant effect on phosphate removal. The phosphate removal was mainly achieved by the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. In addition, the adsorbed phosphate ions can be effectively desorbed by dilute NaOH solutions. This adsorbent, with large adsorption capacity and high selectivity, is therefore a very promising adsorbent for the removal of phosphate ions from aqueous solutions.
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