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In a global mission to reduce atmospheric concentrations of anthropogenic carbon dioxide, the energy- and carbon-emission-intensive, century-old urea industry has re-captured attention. Today, global urea manufacture from the reaction of ammonia and carbon dioxide, enabled by the Bosch-Meiser process, yields 910 kg of CO2for every ton of urea generated. This amount of CO2is close to the quantity of CO2fixed during its production. Positively, urea utilization as a nitrogen fertilizer facilitates photosynthesis, earth’s largest carbon capture carbon cycle. Negatively, the environmental impact of urea production presents a prime example of one of many global industries that need to be decarbonized to ameliorate climate change in the quest for sustainability. In this perspective, we explore the technical feasibility of green urea production, using system-wide energy efficiency as a key metric, via thermochemistry, electrochemistry, and photochemistry pathways. Baseline parameters for potential green urea industries are benchmarked by comparison with current Bosch-Meiser operations. Quantitative studies of this kind will help define a roadmap for green urea refineries that is consistent with the United Nations Sustainable Development Goals.

Based on classical nucleation and growth theory, the phase evolution of martensite α′ phase of additively manufactured Ti-6.9Al-6.8Zr-2.3Mo-2.2V-0.7Nb alloy under different annealing temperatures (600–960 °C) was systematically investigated. The results show that: Owing to insufficient diffusion of alloy elements during laser deposition, numerous β-stabilizing elements are retained in α′ phase and the microstructure is made up of 95.4% α′ phase and 4.6% β phase. According to TEM, EBSD, SEM/EDX results, the α′ phase can be divided into α′ phase containing more β-stabilizing elements (α′β), α′ phase containing more Al (α′Al). Under annealing condition, martensite decomposition tends to occur at the α′/α' interfaces and the matrix of α′βphase. In the matrix of α′βphase, fine adjacent α′ phase precipitates at β phase because a lot of β-stabilizing elements are consumed by precipitated β phase, thus improving the precipitation of adjacent α′ phase. The decomposition of α′ phase is controlled by diffusion of alloy elements. As the temperature increases, the diffusion of alloy elements and degree of α′ martensitic decomposition become more sufficient. When the Al content in the α′ phase reaches that in equilibrium α phase, the lattice parameters of α′ phase increase from a = 2.97 Å, c = 4.72 Å to a = 3.04 Å, c = 4.77 Å and meanwhile the α′ martensitic decomposition is finished.

Crafting vacancies offers an efficient route to upgrade the selectivity and productivity of nanomaterials for CO2electroreduction. However, defective nanoelectrocatalysts bear catalytically active vacancies mostly on their surface, with the rest of the interior atoms adiaphorous for CO2-to-product conversion. Herein, taking nanosilver as a prototype, we arouse the catalytic ability of internal atoms by creating homogeneous vacancies realized via electrochemical reconstruction of silver halides. The homogeneous vacancies-rich nanosilver, compared to the surface vacancies-dominated counterpart, features a more positive d-band center to trigger an intensified hybridization of the Ag_d orbital with the C_P orbital of the *COOH intermediate, leading to an accelerated CO2-to-CO transformation. These structural and electronic merits allow a large-area (9 cm–2) electrode to generate nearly pure CO with a CO/H2Faradaic efficiency ratio of 6932 at an applied current of 7.5 A. These findings highlight the potential of designing new-type defects in realizing the industrialization of electrocatalytic CO2reduction.

Stable metal nitrides (MN) are promising materials to fit the future “green” ammonia–hydrogen nexus. Either through catalysis or chemical looping, the reductive hydrogenation of MN to MN1–xis a necessary step to generate ammonia. However, encumbered by the formation of kinetically stable M-NH1─3surface species, this reduction step remains challenging under mild conditions. Herein, we discovered that deleterious Ti-NH1─3accumulation on TiN can be circumvented photochemically with supported single atoms and clusters of platinum (Pt1-Ptn) under N2–H2conditions. The photochemistry of TiN selectively promoted Ti-NH formation, while Pt1-Ptneffectively transformed any formed Ti-NH into free ammonia. The generated ammonia was found to originate mainly from TiN reduction with a minor contribution from N2activation. The knowledge accrued from this fundamental study could serve as a springboard for the development of MN materials for more efficient ammonia production to potentially disrupt the century-old fossil-powered Haber–Bosch process.

Triethylamine (TEA) is a flammable and highly toxic gas, and the fast, accurate, and sensitive detection of gas TEA remains greatly challenging. Herein, we report a ZnO nanorod anchored with a single-atom Pt catalyst (Pt1/ZnO) as a gas sensor for TEA detection. The sensor shows high selectivity and high response to gas TEA with a response value of 4170 at 200 °C, which is 92 times higher than that of pure ZnO. Moreover, the Pt1/ZnO sensor has very short response and recovery times of only 34 and 76 s, respectively, and also has a high response to ppb-level TEA gas (100 ppb-21.6). The gas-sensing enhancement mechanism of the Pt1/ZnO sensor to gas TEA was systematically investigated using band structure analysis, in situ diffuse reflectance infrared Fourier transformation spectroscopy, and density functional theory calculations. The results show that the oxygen vacancies on Pt1/ZnO can effectively activate the adsorbed oxygen. Moreover, chemical bonds can be formed between Pt single atoms and N atoms in TEA to achieve effective adsorption and activation of TEA molecules, facilitating the reaction between TEA and the adsorbed oxygen on Pt1/ZnO, and thereby obtaining high gas-sensing performance. This work highlights the crucial role of Pt single-atom in improving the sensing performance for gas TEA detection, paving the way for developing more advanced gas sensors.

Semiconductor-based photocatalytic O2activation is a facile, green, yet versatile strategy to produce reactive oxygen species (ROS) for environmental remediation and pollution control but suffers from low ROS generation rate. Herein, we demonstrate that a simple surface phosphorylation can greatly enhance the O2photoactivation of BiOBr to produce superoxide radical (·O2–) via boosting exciton dissociation. The phosphorylated BiOBr surface establishes an interfacial electrostatic field from the bulk to the surface, and weakens the surface Bi–O bonds to induce oxygen vacancy (VO) generation simultaneously. This interfacial electrostatic field attenuates the exciton binding energy (Eb) from 266 to 89 meV, facilitating the dissociation of excitons to charge carriers, i.e., electrons and holes. Driven by the interfacial electrostatic field, the photoinduced electrons migrate to and are confined by the surface VO, thus activating absorbed O2to the superoxide radical (·O2–). As a result, surface phosphorylated BiOBr could degrade the synthetic chlorobenzene solution with a 6.3 times higher rate (0.69 h–1) than BiOBr (0.11 h–1) under visible light. Impressively, this surface phosphorylated BiOBr was able to decrease the COD value of industrial chlorobenzene wastewater from 153 to 19 mg/L, below the Water Quality Standards Category III of China. This study sheds light on the design and synthesis of high-performance photocatalysts and also provides a green strategy for wastewater treatment with solar energy.

Room-temperature molecular oxygen (O2) dissociation is challenging toward chemical reactions due to its triplet ground-state and spin-forbidden characteristic. Herein, we demonstrate that BiOCl of oxygen and chlorine dual vacancies can photocatalytically dissociate O2into monatomic reactive oxygen (•O–) for the ring opening of aromatic refractory pollutants toward deep oxidation. The electron-rich and geometry-flexible dual vacancies of oxygen and chlorine remarkably lengthen the O–O bond of adsorbed O2from 1.21 to 2.74 Å, resulting in the rapid O2dissociation and the subsequent •O–formation. During the photocatalytic degradation of sulfamethazine, the in situ-formed •O–plays an indispensable role in breaking the critical intermediate of pyrimidine containing a stubborn aromatic heterocyclic ring, thus facilitating the overall mineralization. More importantly, BiOCl of oxygen and chlorine dual vacancies is also superior to its monovacancy counterparts on the degradation of other refractory pollutants containing conjugated six-membered rings, including p-chlorophenol, p-chloronitrobenzene, p-hydroxybenzoic acid, and p-nitrobenzoic acid. This study sheds light on the importance of sophisticated defects for regulating the O2activation manner and deliveries a novel O2activation approach for environmental remediation with solar energy.

Free radicals exert a significant impact on the fate of redox-active substances and play a crucial role in the surface corrosion of solid in environment. Dynamic visualization on the response of the surface to the free radicals at nanoscale is essential to explore the mechanism. Environmental transmission electron microscopy will be a powerful tool for dynamic changes of the interface redox process of solid surface with electron beams induced free radicals, to simulate the redox process of a solid in the environment. Black phosphorus (BP), an environment-sensitive material, is selected as an example to visualize the degradation pathways with environmental transmission electron microscopy. The distribution of the corrosion initiation points, formation and growth of corrosion areas, and the eventual splintering and disappearance of BP nanoflakes are recorded vividly. In situresults are substantiated by the ex situexperiments and density functional theory (DFT) calculations. Results show that degradation originates at the edges and defect structures when the humidity reaches high enough. The microscopic structural oxidative etching of solid surface with radicals in natural light is simulated with radicals produced by electron beam irradiation on suspending medium O2and H2O for the first time. This method will offer unprecedented details and valuable insights into the mechanism involved in the oxidative etching with natural light.

[Display omitted] • Toughening effects of Mo and Nb on impact toughness and crack resistance of titanium alloys were studied systematically. • Dislocation mobility and deformation twinning were responsible for impact toughness and crack resistance of titanium alloys. • Theoretical models were proposed to explore the mechanisms for improved dislocation mobility and deformation twinning. Ti-6Al, Ti-6Al-2Mo and Ti-6Al-3Nb alloys were prepared to investigate the toughening effects of β stabilizers Mo and Nb on impact toughness and crack resistance of titanium alloys. Instrumented Charpy impact tests showed that the total impact absorbed energy of Ti-6Al-2Mo and Ti-6Al-3Nb (∼64 J) were two times higher than that of Ti-6Al (∼30 J), indicating the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys. Analysis of load-displacement curves revealed the similar crack initiation energy of Ti-6Al, Ti-6Al-2Mo and Ti-6Al-3Nb (15.4 J, 16.1 J and 15.0 J, respectively). However, the higher crack propagation energy of Ti-6Al-2Mo and Ti-6Al-3Nb (46.7 J and 48.3 J, respectively) were about three times higher than that of Ti-6Al (14.4 J), indicating the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb. Post-mortem analysis of impact samples demonstrated that the increased dislocation density and deformation twinning were mainly responsible for the stronger resistance to crack propagation in Ti-6Al-2Mo and Ti-6Al-3Nb. Due to the invisibility of dislocation activation and deformation twinning during the Charpy impact process, a mathematical model has been proposed to evaluate the effects of Al, Mo and Nb elements on dislocation mobility based on the Yu Rui-huang electron theory. Addition of Mo and Nb elements significantly improved the dislocation mobility in Ti-6Al-2Mo and Ti-6Al-3Nb compared to that in Ti-6Al alloy. Therefore, more dislocations were activated in Ti-6Al-2Mo and Ti-6Al-3Nb which supplied the larger plastic deformation under impact loading. A dislocation-based model also has been proposed to interpret the nucleation and propagation of deformation twinning under the impact loading. Dislocation pileup at α/β interfaces provided potential sites for nucleation of deformation twinning in Ti-6Al-2Mo and Ti-6Al-3Nb. Furthermore, deformation twinning facilitated the dislocation motion in α grains with hard orientations. The increased dislocation mobility and deformation twinning were responsible for the stronger crack resistance as well as the higher impact toughness of Ti-6Al-2Mo and Ti-6Al-3Nb alloys. [ABSTRACT FROM AUTHOR]

Ti-5321 alloy formed by laser cladding has good mechanical properties. By subsequent heat treatment of the alloy, not only can rich microstructures be obtained, but its strength, toughness, or damage tolerance performance can also be improved. Four typical microstructures, including basket-weave structure, large layer structure, ultrafine needle-like structure, and rod-like structure were constructed through different heat treatments. Basket-weave structure is composed of slender lamellar α, which has the best plasticity and toughness. Due to the large orientation difference between adjacent lamellar α and the susceptibility to multiple slip during crack propagation, this will greatly increase the crack propagation resistance and the curvature of the crack propagation path, which is beneficial for improving the damage tolerance performance of the alloy. Large layer structure is composed of large layer α and ultrafine needle-like α, with the highest strength. The orientation difference between adjacent large layer α is extremely small and prone to {10-11}<1-210> pyramidal slip. The crack propagation resistance is reduced, which in turn damages the damage tolerance performance of the alloy. Ultrafine needle-like structure is entirely composed of ultrafine needle-like α, with high strength and extremely low plasticity and toughness. The orientation difference between adjacent needle-like α is single, making it prone to pyramidal slip and first-order pyramidal slip. The strength of rod-like structure matches well with its plasticity and toughness. There are multiple slip systems in rod-like structure and there is significant difference in orientation between adjacent α. Large orientation differences will have certain hindering effect on crack deflection.

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO2nanoparticulate intermediate layer and a In2O3–x(OH)ynanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO2photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In2O3–x(OH)ynanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO2nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In2O3–x(OH)ynanoparticles and participate in the reactions occurring at the catalyst surface.

Optimizing kinetic barriers of ammonia synthesis to reduce the energy intensity has recently attracted significant research interest. The motivation for the research is to discover means by which activation barriers of N2dissociation and NHz(z= 1–2, surface intermediates) destabilization can be reduced simultaneously, that is, breaking the “scaling relationship”. However, by far only a single success has been reported in 2016 based on the discovery of a strong–weak N-bonding pair: transition metals (nitrides)-LiH. Described herein is a second example that is counterintuitively founded upon a strong–strong N-bonding pair unveiled in a bifunctional nanoscale catalyst TiO2–xHy/Fe (where 0.02 ≤ x≤ 0.03 and 0 < y< 0.03), in which hydrogen spillover (H) from Fe to cascade oxygen vacancies (OV–OV) results in the trapped form of OV-H on the TiO2–xHycomponent. The Fe component thus enables facile activation of N2, while the OV-H in TiO2–xHyhydrogenates the N or NHzto NH3easily.

The limitations of the Haber–Bosch reaction, particularly high-temperature operation, have ignited new interests in low-temperature ammonia-synthesis scenarios. Ambient N2electroreduction is a compelling alternative but is impeded by a low ammonia production rate (mostly <10 mmol gcat–1h–1), a small partial current density (<1 mA cm–2), and a high-selectivity hydrogen-evolving side reaction. Herein, we report that room-temperature nitrate electroreduction catalyzed by strained ruthenium nanoclusters generates ammonia at a higher rate (5.56 mol gcat–1h–1) than the Haber–Bosch process. The primary contributor to such performance is hydrogen radicals, which are generated by suppressing hydrogen–hydrogen dimerization during water splitting enabled by the tensile lattice strains. The radicals expedite nitrate-to-ammonia conversion by hydrogenating intermediates of the rate-limiting steps at lower kinetic barriers. The strained nanostructures can maintain nearly 100% ammonia-evolving selectivity at >120 mA cm–2current densities for 100 h due to the robust subsurface Ru–O coordination. These findings highlight the potential of nitrate electroreduction in real-world, low-temperature ammonia synthesis.

Semiconductor photocatalytic technology has great potential for the removal of dilute gaseous NO in indoor and outdoor atmospheres but suffers from unsatisfactory NO-removal selectivity due to undesirable NO2byproduct generation. In this study, we demonstrate that the 99% selectivity of photocatalytic NO oxidation toward nitrate can be achieved over blue TiO2bearing oxygen vacancies (OVs) under visible-light irradiation. First-principles density functional theory calculation and experimental results suggested that the OVs of blue TiO2with localized electrons could facilitate the molecular oxygen activation through single-electron pathways to generate ·O2–and simultaneously promote the photogenerated hole annihilation. The generated ·O2–directly converted NO to nitrate, while the hole annihilation inhibited the side-reaction between holes and NO to avoid toxic NO2byproduct formation, resulting in the highly selective removal of NO. This study reveals the dual functions of OVs in defective photocatalysts and also provides fundamental guidance for the selective purification of NO with photocatalytic technology.

Light-driven heterogeneous catalysis provides a promising way to accomplish chemical reactions by the use of light energy, which reduces the consumption of chemical energy sources. Here, we show that Ru/CeO2catalysts exhibit high activity for the hydrogenation of CO2to methane under illumination only, reaching high CO2conversion (over 99.9%) and selectivity of methane (∼100%) at low temperature. In sharp contrast, less CO2is converted at the same temperature when a traditional heating model is used. As revealed by the results, the enhanced conversion rate under illumination should not only be attributed to the light-induced thermo-heating. Further investigations by in situIR analysis and theoretical calculation provide comprehensive understanding of the reaction mechanism, and the important role of light is revealed. It is expected that the combination of catalysts and light may afford new perspectives for CO2hydrogenation.

Semiconductor nanowires that have been extensively studied are typically in a crystalline phase. Much less studied are amorphous semiconductor nanowires due to the difficulty for their synthesis, despite a set of characteristics desirable for photoelectric devices, such as higher surface area, higher surface activity, and higher light harvesting. In this work of combined experiment and computation, taking Zn2GeO4(ZGO) as an example, we propose a site-specific heteroatom substitution strategy through a solution-phase ions–alternative-deposition route to prepare amorphous/crystalline Si-incorporated ZGO nanowires with tunable band structures. The substitution of Si atoms for the Zn or Ge atoms distorts the bonding network to a different extent, leading to the formation of amorphous Zn1.7Si0.3GeO4(ZSGO) or crystalline Zn2(GeO4)0.88(SiO4)0.12(ZGSO) nanowires, respectively, with different bandgaps. The amorphous ZSGO nanowire arrays exhibit significantly enhanced performance in photoelectrochemical water splitting, such as higher and more stable photocurrent, and faster photoresponse and recovery, relative to crystalline ZGSO and ZGO nanowires in this work, as well as ZGO photocatalysts reported previously. The remarkable performance highlights the advantages of the ZSGO amorphous nanowires for photoelectric devices, such as higher light harvesting capability, faster charge separation, lower charge recombination, and higher surface catalytic activity.

Metamaterials are a new class of artificial materials that can achieve electromagnetic properties that do not occur naturally, and as such they can also be a new class of photocatalytic structures. We show that metal-based catalysts can achieve electromagnetic field amplification and broadband absorption by decoupling optical properties from the material composition as exemplified with a ZnO/Cu metamaterial surface comprising periodically arranged nanocubes. Through refractive index engineering close to the index of air, the metamaterial exhibits near-perfect 98% absorption. The combination of plasmonics and broadband absorption elevates the weak electric field intensities across the nonplasmonic absorption range. This feedback between optical excitation and plasmonic excitation dramatically enhances light-to-dark catalytic rates by up to a factor of 181 times, compared to a 3 times photoenhancement of ZnO/Cu nanoparticles or films, and with angular invariance. These results show that metamaterial catalysts can act as a singular light harvesting device that substantially enhances photocatalysis of important reactions.