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Photocatalytic oxygen reduction reactions and water oxidation reactions are extremely promising green approaches for massive H2O2 production. Nonetheless, constructing effective photocatalysts for H2O2 generation is critical and still challenging. Since the network topology has significant impacts on the electronic properties of two dimensional (2D) polymers, herein, for the first time, we regulated the H2O2 photosynthetic activity of 2D covalent organic frameworks (COFs) by topology. Through designing the linking sites of the monomers, we synthesized a pair of novel COFs with similar chemical components on the backbones but distinct topologies. Without sacrificial agents, TBD‐COF with cpt topology exhibited superior H2O2 photoproduction performance (6085 and 5448 μmol g−1 h−1 in O2 and air) than TBC‐COF with hcb topology through the O2‐O2⋅−‐H2O2, O2‐O2⋅−‐O21‐H2O2, and H2O‐H2O2 three paths. Further experimental and theoretical investigations confirmed that during the H2O2 photosynthetic process, the charge carrier separation efficiency, O2⋅− generation and conversion, and the energy barrier of the rate determination steps in the three channels, related to the formation of *OOH, *O21, and *OH, can be well tuned by the topology of COFs. The current study enlightens the fabrication of high‐performance photocatalysts for H2O2 production by topological structure modulation. [ABSTRACT FROM AUTHOR]

As the power‐conversion efficiency (PCE) of organic–inorganic lead halide perovskite solar cells (PSCs) is approaching the theoretical maximum, the most crucial issue concerns long‐term ambient stability. Here, the application of PCN‐224 quantum dots (QDs) is reported, a typical Zr‐based porphyrinic metal–organic framework (MOF), to enhance the ambient stability of PSCs. PCN‐224 QDs with abundant Lewis‐base groups (e.g., CO, C−N, CN) contribute to high‐quality perovskite films with enlarged grain size and reduced defect density by interaction with under‐coordinated Pb2+. Meanwhile, PCN‐224 QDs enable the well‐matched energy level at the perovskite/hole transport layer (HTL) interface, thereby facilitating hole extraction and transport. More importantly, PCN‐224 QDs‐treated HTL can capture Li+ from bis(trifluoromethanesulfonyl)imide additive, leading to the reduced aggregation and less direct contact with moisture for hygroscopic Li‐TFSI. Moreover, PCN‐224 QDs mitigated Li+ ion migration into the perovskite layer, thus avoiding the formation of deleterious defects. The resultant devices yield a champion PCE of 22.51%, along with substantially improved durability, including humidity, thermal and light soaking stabilities. The findings provide a new approach toward efficient and stable PSCs by applying MOF QDs. [ABSTRACT FROM AUTHOR]

High‐entropy carbides (HECs) are of great interest as they are promising candidates for ultra‐high‐temperature and high‐hardness applications. To discover carbides with enhanced yield strength and hardness, mechanism‐based design approaches are needed. In this study, dislocation core atomic randomness as a mechanism for hardness enhancement is proposed, in which the random interactions between different elements at a dislocation core make it more difficult for the dislocation to slip. The Peierls stress of an a/2⟨11¯0⟩{110} edge dislocation is calculated based on density functional theory, in which atomic randomness is increased by increasing the number of elements at the dislocation core. The results show that the Peierls stress statistically increases with increasing number of elements, indicating that incorporating more elements is likely to produce higher hardness. Based on this guiding principle, three eight‐cation HECs are fabricated (Ti,Zr,Hf,V,Nb,Ta,X,Y)C (X,Y = Mo,W, Cr,Mo, or Cr,W), the composition of which is guided by ab initio calculations of their formation enthalpy and entropy forming ability. The single‐phase dense ceramics all show high nanoindentation hardness of around 40 GPa. The random interactions between different elements at a dislocation core provide a mechanism for improving the hardness of structural ceramics. [ABSTRACT FROM AUTHOR]

Energy filtering effect is usually utilized in composites to enhance the thermoelectric performance, and a reliable theoretical approach is needed to predict the optimum parameters related to this effect. By taking Bi2Te3 as an example, we show that first principles calculations and Boltzmann transport equations can be used to evaluate energy filtering effect, and the optimal values for the maximum power factor of interfacial potential barrier height ( Eb) and carrier scattering probability ( p) can be calculated precisely. The calculation results show that the power factor can be greatly enhanced at high carrier concentrations by energy filtering. This enhancement is sensitive to Eb and p: to achieve 40% power factor enhancement, Eb must be in the range 0.06-0.10 eV, and p should be greater than 60%. The optimal Eb also shows weak dependence on p. Our approach can be easily applied to other materials due to the generality of first principles calculations, and will aid high throughput screening for new thermoelectric composites. [ABSTRACT FROM AUTHOR]

Dioxins emission is a serious problem during thermal utilization of municipal solid waste (MSW). The key structure in dioxins is CACl bond, so controlling the formation of chlorinated hydrocarbons, which contain CACl bond, is very important. PVC, a main source of chlorine in MSW, was used as fuel in this work. Chlorinated hydrocarbons were released from PVC pyrolysis process. A hot-rod reactor combined with a homogeneous conversion stage was established in an attempt to realize the concept of utilizing the hydrogen, which was also released from PVC pyrolysis process, to control the formation of chlorinated hydrocarbons. In the experiments, the influences of temperature, concentration of hydrogen and residence time in the homogeneous conversion stage on the formation of chlorinated hydrocarbons were investigated. Some results were concluded as follows, first, during PVC pyrolysis progress, H2, Cl2, HCl, hydrocarbons and chlorinated hydrocarbons would be released so that the dechlorination reaction and the chlorination reaction occurred in the homogeneous conversion stage. Second, the concentration of hydrogen released during PVC pyrolysis process was enough as opposed to the release of chlorine. Third, elevating the temperature of homogeneous conversion could promote the dechlorination reaction. Increasing the concentration of hydrogen had the same effect. Fourth, enough residence time in the homogeneous conversion stage could ensure the dechlorination reaction completely to occur. In a word, the results suggested that utilizing hydrogen released from PVC pyrolysis could control the formation of chlorinated hydrocarbons effectively when the temperature of the homogeneous conversion stage was over 7008C with residence time more than 1.5 s. [ABSTRACT FROM AUTHOR]

Experiments of nitric oxide reduction by the tar-included syngas from a small biomass updraft gasifier have been carried out on a tubular reactor under a temperature range of 900 to 1200°C. The initial mole fraction of NO was 1000 ppm and that of the oxygen and gasification syngas were varied. Comparison of the reburning results of the present syngas with other fuels clarified the influence of tar. Under the conditions of this work, the participation of tar compounds in NO reduction mainly begins with cracking into light hydrocarbons which is sensitive to both the oxygen concentration and the temperature. Tar leads to a satisfactory NO-reduction improvement under relative oxygen-rich conditions, supplying extra hydrocarbon radicals and creating a more appropriate atmosphere for reburning reactions. As for a reductive environment, little benefit was gained from the presence of tar. The rise of temperature brings a clear promotion only to NO reduction with a high oxygen flow rate, while polymerization should be concerned for a low oxygen flow rate. It is believed that a substantial portion of tar converts to acetylene through cracking under suitable reburning conditions, resulting in an active NO-reduction reaction pathway. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 602-608, 2014 [ABSTRACT FROM AUTHOR]