Pyrolysis characteristics and product distribution of oil sludge based on radiant heating.

It needs to be improved the conversion efficiency and stable operation of conventional pyrolysis with high-temperature flue gas heating (HFH). Herein, a new radiative heating (RH) pyrolysis method is proposed. Experimental studies are carried out on a self-made radiation pyrolysis pilot plant to investigate the effects of different factors (pyrolysis final temperature, residence time, and carrier gas volume) on product distribution. The results show that with the increase of pyrolysis temperature, the yield of the gas phase consistently increases, and the proportion of CH4 and H2 in the pyrolysis gas reaches 62.31% at 700 °C. The yield of the liquid phase increases and then decreases. The recovery rate of pyrolysis oil achieves 68.07% when the pyrolysis temperature is 600 °C with main components of ketones and unsaturated hydrocarbon compounds. The yield of the solid phase consistently decreases. The RH in this work generates more pyrolysis gas in the pyrolysis process and alleviates the effects of fouling layers on the continuous operation of the equipment which has guiding significance for the efficient resource utilization of oil sludge.

Co/Mon Invigorated Bilateral Kinetics Modulation for Advanced Lithium-Sulfur Batteries.

Sluggish sulfur redox kinetics and Li-dendrite growth are the main bottlenecks for lithium-sulfur (Li-S) batteries. Separator modification serves as a dual-purpose approach to address both of these challenges. In this study, the Co/MoN composite is rationally designed and applied as the modifier to modulate the electrochemical kinetics on both sides of the sulfur cathode and lithium anode. Benefiting from its adsorption-catalysis function, the decorated separators (Co/MoN@PP) not only effectively inhibit polysulfides (LiPSs) shuttle and accelerate their electrochemical conversion but also boost Li+ flux, realizing uniform Li plating/stripping. The accelerated LiPSs conversion kinetics and excellent sulfur redox reversibility triggered by Co/MoN modified separators are evidenced by performance, in-situ Raman detection and theoretical calculations. The batteries with Co/MoN@PP achieve a high initial discharge capacity of 1570 mAh g-1 at 0.2 C with a low decay rate of 0.39%, uniform Li+ transportation at 1 mA cm-2 over 800 h. Moreover, the areal capacity of 4.62 mAh cm-2 is achieved under high mass loadings of 4.92 mg cm-2. This study provides a feasible strategy for the rational utilization of the synergistic effect of composite with multifunctional microdomains to solve the problems of Li anode and S cathode toward long-cycling Li-S batteries.

Co-Doped Ni3V2O8 Nanofibers Achieving d-d Orbital Coupling for Electrocatalytic Oxygen Reduction.

Efficient and robust non-platinum-group metal electrocatalysts for O2 reduction are a prerequisite for practical high-performance fuel cells and metal-air batteries. Herein, we reported an integrated principle of gradient electrospinning and controllable pyrolysis to fabricate various Co-doped Ni3V2O8 nanofibers with high oxygen reduction reaction (ORR) activity. The representative Co1.3Ni1.7V2O8 nanofibers showed outstanding ORR performance in an alkaline solution with a half-wave potential (E1/2) of 0.874 V vs RHE, along with high long-term stability. Furthermore, the introduction of Co could effectively restrain the growth of nanoparticles and change the electronic structure of Ni3V2O8. Control experiments and theoretical calculations demonstrated that upon Co-doping, the hybridization between the 3d orbital for both Co and Ni guaranteed the stable adsorption interaction with O2 over Ni and Co metal centers. Meanwhile, the weakened binding ability of Ni3V2O8 to OH* reduced the ORR free energy. Overall, the synergistic effect of Co and Ni metal cations essentially reflected the origin of ORR activity on the Co-doped Ni3V2O8 nanofibers. This work offers new insights and practical guidance for designing highly active ORR catalysts for electrochemical clean energy conversion and storage.

Emerging two-dimensional nanomaterials for electrochemical nitrogen reduction.

Ammonia (NH3) is essential to serve as the biological building blocks for maintaining organism function, and as the indispensable nitrogenous fertilizers for increasing the yield of nutritious crops. The current Haber-Bosch process for industrial NH3 production is highly energy- and capital-intensive. In light of this, the electroreduction of nitrogen (N2) into valuable NH3, as an alternative, offers a sustainable pathway for the Haber-Bosch transition, because it utilizes renewable electricity and operates under ambient conditions. Identifying highly efficient electrocatalysts remains the priority in the electrochemical nitrogen reduction reaction (NRR), marking superior selectivity, activity, and stability. Two-dimensional (2D) nanomaterials with sufficient exposed active sites, high specific surface area, good conductivity, rich surface defects, and easily tunable electronic properties hold great promise for the adsorption and activation of nitrogen towards sustainable NRR. Therefore, this Review focuses on the fundamental principles and the key metrics being pursued in NRR. Based on the fundamental understanding, the recent efforts devoted to engineering protocols for constructing 2D electrocatalysts towards NRR are presented. Then, the state-of-the-art 2D electrocatalysts for N2 reduction to NH3 are summarized, aiming at providing a comprehensive overview of the structure-performance relationships of 2D electrocatalysts towards NRR. Finally, we propose the challenges and future outlook in this prospective area.

Dominant Polar Surfaces of Colloidal II-VI Wurtzite Semiconductor Nanocrystals Enabled by Cation Exchange.

Polar surfaces of ionic crystals are of growing technological importance, with implications for the efficiency of photocatalysts, gas sensors, and electronic devices. The creation of ionic nanocrystals with high percentages of polar surfaces is an option for improving their efficiency in the aforementioned applications but is hard to accomplish because they are less thermodynamically stable and prone to vanish during the growth process. Herein, we develop a strategy that is capable of producing polar surface-dominated II-VI semiconductor nanocrystals, including ZnS and CdS, from copper sulfide hexagonal nanoplates through cation exchange reactions. The obtained wurtzite ZnS hexagonal nanoplates have dominant {002} polar surfaces, occupying up to 97.8% of all surfaces. Density functional theory calculations reveal the polar surfaces can be stabilized by a charge transfer of 0.25 eV/formula from the anion-terminated surface to the cation-terminated surface, which also explains the presence of polar surfaces in the initial Cu1.75S hexagonal nanoplates with cation deficiency prior to cation exchange reactions. Experimental results showed that the HER activity could be boosted by the surface polarization of polar surface-dominated ZnS hexagonal nanoplates. We anticipate this strategy is general and could be used with other systems to prepare nanocrystals with dominant polar surfaces. Furthermore, the availability of colloidal semiconductor nanocrystals with dominant polar surfaces produced through this strategy opens a new avenue for improving their efficiency in catalysis, photocatalysis, gas sensing, and other applications.

Nonepitaxial Gold-Tipped ZnSe Hybrid Nanorods for Efficient Photocatalytic Hydrogen Production.

For the first time, colloidal gold (Au)-ZnSe hybrid nanorods (NRs) with controlled size and location of Au domains are synthesized and used for hydrogen production by photocatalytic water splitting. Au tips are found to grow on the apices of ZnSe NRs nonepitaxially to form an interface with no preference of orientation between Au(111) and ZnSe(001). Density functional theory calculations reveal that the Au tips on ZnSe hybrid NRs gain enhanced adsorption of H compared to pristine Au, which favors the hydrogen evolution reaction. Photocatalytic tests reveal that the Au tips on ZnSe NRs effectively enhance the photocatalytic performance in hydrogen generation, in which the single Au-tipped ZnSe hybrid NRs show the highest photocatalytic hydrogen production rate of 437.8 µmol h-1 g-1 in comparison with a rate of 51.5 µmol h-1 g-1 for pristine ZnSe NRs. An apparent quantum efficiency of 1.3% for hydrogen evolution reaction for single Au-tipped ZnSe hybrid NRs is obtained, showing the potential application of this type of cadmium (Cd)-free metal-semiconductor hybrid nanoparticles (NPs) in solar hydrogen production. This work opens an avenue toward Cd-free hybrid NP-based photocatalysis for clean fuel production.

Colloidal Single-Layer Photocatalysts for Methanol-Storable Solar H2 Fuel.

Molecular surfactants are widely used to control low-dimensional morphologies, including 2D nanomaterials in colloidal chemical synthesis, but it is still highly challenging to accurately control single-layer growth for 2D materials. A scalable stacking-hinderable strategy to not only enable exclusive single-layer growth mode for transition metal dichalcogenides (TMDs) selectively sandwiched by surfactant molecules but also retain sandwiched single-layer TMDs' photoredox activities is developed. The single-layer growth mechanism is well explained by theoretical calculation. Three types of single-layer TMDs, including MoS2 , WS2 , and ReS2 , are successfully synthesized and demonstrated in solar H2 fuel production from hydrogen-stored liquid carrier-methanol. Such H2 fuel production from single-layer MoS2 nanosheets is COx -free and reliably workable under room temperature and normal pressure with the generation rate reaching ≈617 µmole g-1 h-1 and excellent photoredox endurability. This strategy opens up the feasible avenue to develop methanol-storable solar H2 fuel with facile chemical rebonding actualized by 2D single-layer photocatalysts.

Why Do Colloidal Wurtzite Semiconductor Nanoplatelets Have an Atomically Uniform Thickness of Eight Monolayers?

Herein we employed a first-principles method based on density functional theory to investigate the surface energy and growth kinetics of wurtzite nanoplatelets to elucidate why nanoplatelets exhibit a uniform thickness of eight monolayers. We synthesized a series of wurtzite nanoplatelets (ZnSe, ZnS, ZnTe, and CdSe) with an atomically uniform thickness of eight monolayers. As a representative example, the growth mechanism of 1.39 nm thick (eight monolayers) wurtzite ZnSe nanoplatelets was studied to substantiate the proposed growth kinetics. The results show that the growth of the seventh and eighth layers along the [112̅0] direction of 0.99 nm (six monolayers) ZnSe magic-size nanoclusters is accessible, whereas the growth of the ninth layer is unlikely to occur because the formation energy is large. This work not only gives insights into the synthesis of atomically uniform thick wurtzite semiconductor nanoplatelets but also opens up new avenues to their applications in light-emitting diodes, catalysis, detectors, and lasers.

Heavy-Metal-Free Colloidal Semiconductor Nanorods: Recent Advances and Future Perspectives.

Quasi-1D colloidal semiconductor nanorods (NRs) are at the forefront of nanoparticle (NP) research owing to their intriguing size-dependent and shape-dependent optical and electronic properties. The past decade has witnessed significant advances in both fundamental understanding of the growth mechanisms and applications of these stimulating materials. Herein, the state-of-the-art of colloidal semiconductor NRs is reviewed, with special emphasis on heavy-metal-free materials. The main growth mechanisms of heavy-metal-free colloidal semiconductor NRs are first elaborated, including anisotropic-controlled growth, oriented attachment, solution-liquid-solid method, and cation exchange. Then, structural engineering and properties of semiconductor NRs are discussed, with a comprehensive overview of core/shell structures, alloying, and doping, as well as semiconductor-metal hybrid nanostructures, followed by highlighted practical applications in terms of photocatalysis, photodetectors, solar cells, and biomedicine. Finally, challenges and future opportunities in this fascinating research area are proposed.

Spontaneous Formation of Noble- and Heavy-Metal-Free Alloyed Semiconductor Quantum Rods for Efficient Photocatalysis.

Quasi-1D cadmium chalcogenide quantum rods (QRs) are benchmark semiconductor materials that are combined with noble metals to constitute QR heterostructures for efficient photocatalysis. However, the high toxicity of cadmium and cost of noble metals are the main obstacles to their widespread use. Herein, a facile colloidal synthetic approach is reported that leads to the spontaneous formation of cadmium-free alloyed ZnSx Se1-x QRs from polydisperse ZnSe nanowires by alkylthiol etching. The obtained non-noble-metal ZnSx Se1-x QRs can not only be directly adopted as efficient photocatalysts for water oxidation, showing a striking oxygen evolution capability of 3000 µmol g-1 h-1 , but also be utilized to prepare QR-sensitized TiO2 photoanodes which present enhanced photo-electrochemical (PEC) activity. Density functional theory (DFT) simulations reveal that alloyed ZnSx Se1-x QRs have highly active Zn sites on the (100) surface and reduced energy barrier for oxygen evolution, which in turn, are beneficial to their outstanding photocatalytic and PEC activities.

Hollow Ag/MnO2 Nanostructures with Controllable Shells: Synthesis and Oxygen Reduction Reaction Catalytic Performance.

Novel hollow Ag/MnO2 nanostructures with controlled shell composition and structure were designed and synthesized. In the present synthetic procedure, silver nanocrystals were oxidized by KMnO4 , and MnO2 was heterogeneously formed on the surface of silver nanocrystals, then released Ag+ was photoreduced to silver adjacent to MnO2 . By simply changing the photoreduction moment, simultaneously with or after the addition of KMnO4 , hollow Ag/MnO2 structures with different shell architectures-a monolayered shell composed of evenly mixed silver and MnO2 and a double-layered shell composed of an inner MnO2 layer and an outer silver layer-can be obtained. Furthermore, the morphology of the hollow structure can be tuned by selecting different silver precursors, and the ratio of silver to MnO2 in the shell can also be controlled by adjusting the ratio in the original reaction mixture. Electrochemical measurements revealed significantly enhanced catalytic performance in the oxygen reduction reaction for the prepared hollow structures. Compared with the Ag/MnO2 composite, the onset potentials positively shift by about 50.0 mV and limiting current densities are nearly 2.0 times higher.

Enhanced Catalytic Activity in Liquid-Exfoliated FeOCl Nanosheets as a Fenton-Like Catalyst.

A facile liquid-phase exfoliation method to prepare few-layer FeOCl nanosheets in acetonitrile by ultrasonication is reported. The detailed exfoliation mechanism and generated products were investigated by combining first-principle calculations and experimental approaches. The similar cleavage energies of FeOCl (340 mJ m(-2) ) and graphite (320 mJ m(-2) ) confirm the experimental exfoliation feasibility. As a Fenton reagent, FeOCl nanosheets showed outstanding properties in the catalytic degradation of phenol in water at room temperature, under neutral pH conditions, and with sunlight irradiation. Apart from the increased surface area of the nanosheets, the surface state change of the nanosheets also plays a key role in improving the catalytic performance. The changes of charge density, density of states (DOS), and valence state of Fe atoms in the exfoliated FeOCl nanosheets versus plates illustrated that surface atomistic relationships made the few-layer nanosheets higher activity, indicating the exfoliation process of the FeOCl nanosheets also brought about surface state changes.