3D nanostructures have attracted much attention because of their unique properties and potential applications. [1][2][3][4][5][6][7][8][9][10][11][12][13] The simplest synthetic route to 3D nanostructures is probably selfassembly, in which ordered aggregates are formed in a spontaneous process.[2] However, it is still a big challenge to develop simple and reliable synthetic methods for hierarchically selfassembled architectures with designed chemical components and controlled morphologies, which strongly affect the properties of nanomaterials. Iron oxides have been extensively studied in diverse fields including catalysis, [14][15][16] environment protection, [17][18][19][20][21][22][23] sensors, [24] magnetic storage media, [25] and clinical diagnosis and treatment. [26] Various iron oxide structures, such as nanocrystals, [27][28][29] particles, [30,31] cubes, [32] spindles, [33] rods, [34,35] wires, [36] tubes, [37] and flakes, [38] have been successfully fabricated by a variety of methods. However, the self-assembly of these low-dimensional building blocks into complex 3D ordered nanostructures is still considerably more difficult. In order to further understand the mechanism of self-organization and expand the applications of iron oxide nanomaterials, self-assembled iron oxide 3D nanostructures need to be explored in more detail. Herein, we report the synthesis of novel 3D flowerlike iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process. Such a method has been adopted previously for the preparation of V 2 O 5 hollow microspheres, [7] SnO 2 nanowires, [39,40] and cobalt alkoxide disk-shaped particles.[41] However, in these previous studies, expensive metal organic compounds including acetates, oxalates, or acetylacetonates were used as metal-ion sources; in this study we used ferric chloride, an inexpensive and nontoxic reagent, as our iron source. By calcination at an elevated temperature, the assynthesized iron oxide precursor was transformed into iron oxide. The phase of the final product could easily be controlled to be either a-Fe 2 O 3 , c-Fe 2 O 3 , or Fe 3 O 4 , three of the most common iron oxides, simply by altering the calcination conditions. All of the products maintained their original flowerlike morphology. The reaction mechanism leading to the iron oxide precursor and the self-assembly process are discussed. As an example of potential applications, the as-obtained iron oxide nanomaterials were used as adsorbent in waste-water treatment, and showed an excellent ability to remove various water pollutants. In a typical procedure, ferric chloride (FeCl 3 ·6 H 2 O), urea, and tetrabutylammonium bromide (TBAB) were dissolved in EG. The solution was refluxed at ca. 195°C for 30 min. After cooling, the as-synthesized iron oxide precursor was collected as a green precipitate by four centrifugation and ethanolwashing cycles. The morphology of the precursor was studied by scanning electron microscopy (SEM). Figure 1a shows the SEM image of a typical sample composed of many un...

Lower olefins-generally referring to ethylene, propylene and butylene-are basic carbon-based building blocks that are widely used in the chemical industry, and are traditionally produced through thermal or catalytic cracking of a range of hydrocarbon feedstocks, such as naphtha, gas oil, condensates and light alkanes. With the rapid depletion of the limited petroleum reserves that serve as the source of these hydrocarbons, there is an urgent need for processes that can produce lower olefins from alternative feedstocks. The 'Fischer-Tropsch to olefins' (FTO) process has long offered a way of producing lower olefins directly from syngas-a mixture of hydrogen and carbon monoxide that is readily derived from coal, biomass and natural gas. But the hydrocarbons obtained with the FTO process typically follow the so-called Anderson-Schulz-Flory distribution, which is characterized by a maximum C-C hydrocarbon fraction of about 56.7 per cent and an undesired methane fraction of about 29.2 per cent (refs 1, 10, 11, 12). Here we show that, under mild reaction conditions, cobalt carbide quadrangular nanoprisms catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (constituting around 60.8 per cent of the carbon products), while generating little methane (about 5.0 per cent), with the ratio of desired unsaturated hydrocarbons to less valuable saturated hydrocarbons amongst the C-C products being as high as 30. Detailed catalyst characterization during the initial reaction stage and theoretical calculations indicate that preferentially exposed {101} and {020} facets play a pivotal role during syngas conversion, in that they favour olefin production and inhibit methane formation, and thereby render cobalt carbide nanoprisms a promising new catalyst system for directly converting syngas into lower olefins.

Thermally-induced tensile strain that remains in perovskite films following annealing results in increased ion migration and is a known factor in the instability of these materials. Previously-reported strain regulation methods for perovskite solar cells (PSCs) have utilized substrates with high thermal expansion coefficients that limits the processing temperature of perovskites and compromises power conversion efficiency. Here we compensate residual tensile strain by introducing an external compressive strain from the hole-transport layer. By using a hole-transport layer with high thermal expansion coefficient, we compensate the tensile strain in PSCs by elevating the processing temperature of hole-transport layer. We find that compressive strain increases the activation energy for ion migration, improving the stability of perovskite films. We achieve an efficiency of 16.4% for compressively-strained PSCs; and these retain 96% of their initial efficiencies after heating at 85°C for 1000 hoursthe most stable wide-bandgap perovskites (above 1.75 eV) reported so far.

A new approach was designed to synthesize tin‐nanoparticles encapsulated in elastic hollow carbon spheres (TNHCs) with uniform size, in which tin nanoparticles with a diameter <100 nm were encapsulated in one thin hollow carbon sphere. The content of tin is up to over 70% by weight, andthe void volume inside the TNHCsis as high as 70–80%, which can accommodate the volume after expansion. This tin‐based nanocomposite exhibits a great potential as an anode materials for lithium‐ion batteries.

The enhancement of power conversion efficiency (PCE) and the development of toxic Cd-, Pb-free quantum dots (QDs) are critical for the prosperity of QD-based solar cells. It is known that the properties (such as light harvesting range, band gap alignment, density of trap state defects, etc.) of QD light harvesters play a crucial effect on the photovoltaic performance of QD based solar cells. Herein, high quality ∼4 nm Cd-, Pb-free Zn-Cu-In-Se alloyed QDs with an absorption onset extending to ∼1000 nm were developed as effective light harvesters to construct quantum dot sensitized solar cells (QDSCs). Due to the small particle size, the developed QD sensitizer can be efficiently immobilized on TiO2 film electrode in less than 0.5 h. An average PCE of 11.66% and a certified PCE of 11.61% have been demonstrated in the QDSCs based on these Zn-Cu-In-Se QDs. The remarkably improved photovoltaic performance for Zn-Cu-In-Se QDSCs vs Cu-In-Se QDSCs (11.66% vs 9.54% in PCE) is mainly derived from the higher conduction band edge, which favors the photogenerated electron extraction and results in higher photocurrent, and the alloyed structure of Zn-Cu-In-Se QD light harvester, which benefits the suppression of charge recombination at photoanode/electrolyte interfaces and thus improves the photovoltage.

As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4 /C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen. Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. The work brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts.

All-inorganic lead halide perovskites demonstrate improved thermal stability over the organic-inorganic halide perovskites, but the cubic α-CsPbI with the most appropriate bandgap for light harvesting is not structurally stable at room temperature and spontaneously transforms into the undesired orthorhombic δ-CsPbI. Here, we present a new member of black-phase thin films of all-inorganic perovskites for high-efficiency photovoltaics, the orthorhombic γ-CsPbI thin films with intrinsic thermodynamic stability and ideal electronic structure. Exempt from introducing organic ligands or incorporating mixed cations/anions into the crystal lattice, we stabilize the γ-CsPbI thin films by a simple solution process in which a small amount of HO manipulates the size-dependent phase formation through a proton transfer reaction. Theoretical calculations coupled with experiments show that γ-CsPbI with a lower surface free energy becomes thermodynamically preferred over δ-CsPbI at surface areas greater than 8600 m/mol and exhibits comparable optoelectronic properties to α-CsPbI. Consequently, γ-CsPbI-based solar cells display a highly reproducible efficiency of 11.3%, among the highest records for CsPbI thin-film solar cells, with robust stability in ambient atmosphere for months and continuous operating conditions for hours. Our study provides a novel and fundamental perspective to overcome the Achilles' heel of the inorganic lead iodide perovskite and opens it up for high-performance optoelectronic devices.

Hierarchically structured metal oxides have two or more levels of structure. Their nanometer‐sized building blocks provide a high surface area, a high surface‐to‐bulk ratio, and surface functional groups that can interact with, e.g., heavy metal ions. Their overall micrometer‐sized structure provides desirable mechanical properties, such as robustness, facile species transportation, easy recovery, and regeneration. In combination these features are suitable for the removal of heavy metal ions from water. Several general synthesis routes for the fabrication of metal oxides with various morphologies and hierarchical structures are discussed including soft and hard template‐assisted routes. These routes are general, reliable, and environmentally friendly methods to prepare transition and rare earth metal oxides, including cobalt oxide, iron oxide, and ceria. As‐prepared hierarchically structured metal oxides show excellent adsorption capacities for AsV and CrVI ions in water.