Search

Platinum (Pt) has found wide use as an electrocatalyst for sustainable energy conversion systems1–3. The activity of Pt is controlled by its electronic structure (typically, the d-band centre), which depends sensitively on lattice strain4,5. This dependence can be exploited for catalyst design4,6–8, and the use of core–shell structures and elastic substrates has resulted in strain-engineered Pt catalysts with drastically improved electrocatalytic performances7,9–13. However, it is challenging to map in detail the strain–activity correlations in Pt-catalysed conversions, which can involve a number of distinct processes, and to identify the optimal strain modification for specific reactions. Here we show that when ultrathin Pt shells are deposited on palladium-based nanocubes, expansion and shrinkage of the nanocubes through phosphorization and dephosphorization induces strain in the Pt(100) lattice that can be adjusted from −5.1 per cent to 5.9 per cent. We use this strain control to tune the electrocatalytic activity of the Pt shells over a wide range, finding that the strain–activity correlation for the methanol oxidation reaction and hydrogen evolution reaction follows an M-shaped curve and a volcano-shaped curve, respectively. We anticipate that our approach can be used to screen out lattice strain that will optimize the performance of Pt catalysts—and potentially other metal catalysts—for a wide range of reactions. By depositing platinum shells on palladium-based nanocubes, the strain can be controlled by through phosphorization and dephosphorization, making it possible to tune the electrocatalytic activity of the platinum shells.

Engineering the nucleation and growth of plasmonic metals (Ag and Au) on their pre-existing seeds is expected to produce nanostructures with unconventional morphologies and plasmonic properties that may find unique applications in sensing, catalysis, and broadband energy harvesting. Typical seed-mediated growth processes take advantage of the perfect lattice match between the deposited metal and seeds to induce conformal coating, leading to either simple size increases (e.g., Au on Au) or the formation of core-shell structures (e.g., Ag on Au) with limited morphology change. In this work, we show that the introduction of a thin layer of metal with considerable lattice mismatch can effectively induce the nucleation of well-defined Au islands on Au nanocrystal seeds. By controlling the interfacial energy between the seed and the deposited material, the oxidative ripening, and the surface diffusion of metal precursors, we can regulate the number of islands on the seeds and produce complex Au nanostructures with morphologies tunable from core-satellites to tetramers, trimers, and dimers. This surface engineering strategy is of great significance in nanomaterial synthesis as it is general and can be used to create secondary structures of many other nanocrystals in a controllable manner.

Nanocomposites containing FeS as catalyst and MoS2 as cocatalyst have been synthesized toward efficient heterogeneous Fenton reaction. The deposition of FeS nanoparticles in situ on the surface of MoS2 nanosheets creates strong contact between the two components and generates a large number of exposed Mo6+ sites and sulfur vacancies, which contribute to the enhanced degradation rate by accelerating Fe3+/Fe2+ cycling and ensuring rapid electron transfer. In addition, the MoS2/FeS nanocomposite catalysts exhibit the best performance at near-neutral conditions (pH 6.5), which solves the challenges in conventional Fenton reactions such as leaching of metal ions, the formation of iron slurry, and the need of adjusting solution pH. Further, the nanocomposite can maintain high efficiency after many recycling experiments. It is believed that the MoS2/FeS nanocomposite represents an efficient heterogeneous Fenton catalyst that can greatly promote the performance of advanced oxidation processes (AOPs) for solving practical environmental issues.

Conventional templating synthesis confines the growth of seeds in rigid spaces to achieve faithful morphological replication. Herein, we explore the use of spherical shape-deformable polymeric nanoshells to regulate the anisotropic growth of Ag nanoplates. The flexible shells deform adaptively to accommodate the initial overgrowth of the seeds but restrict the growth in the directions where the shells are fully stretched, eventually producing nanoplates with an unconventional circular profile. The diameter of the final Ag nanoplates can be precisely predicted by stretching and flattering the nanoshells into a plate-like capsule while retaining their original internal surface area. Furthermore, unlike conventional templates, the polymer shells eventually turn themselves into a conformal coating that binds to the surface of the full-grown Ag nanoplates and significantly enhances their stability against oxidative etching.

Metal nanoparticles have drawn great attention in heterogeneous catalysis. One challenge is that they are easily deactivated by migration-coalescence during the catalysis process because of their high surface energy. With the rapid development of nanoscience, encapsulating metal nanoparticles in nanoshells or nanopores becomes one of the most promising strategies to overcome the stability issue of the metal nanoparticles. Besides, the activity and selectivity could be simultaneously enhanced by taking advantage of the synergy between the metal nanoparticles and the encapsulating materials as well as the molecular sieving property of the encapsulating materials. In this review, we provide a comprehensive summary of the recent progress in the synthesis and catalytic properties of the encapsulated metal nanoparticles. This review begins with an introduction to the synthetic strategies for encapsulating metal nanoparticles with different architectures developed to date, including their encapsulation in nanoshells of inorganic oxides and carbon, porous materials (zeolites, metal-organic frameworks, and covalent organic frameworks), and organic capsules (dendrimers and organic cages). The advantages of the encapsulated metal nanoparticles are then discussed, such as enhanced stability and recyclability, improved selectivity, strong metal-support interactions, and the capability of enabling tandem catalysis, followed by the introduction of some representative applications of the encapsulated metal nanoparticles in thermo-, photo-, and electrocatalysis. At the end of this review, we discuss the remaining challenges associated with the encapsulated metal nanoparticles and provide our perspectives on the future development of the field.

Single-crystalline CoFe alloy nanoparticles encapsulated in nitrogen-doped carbon nanotubes (CoFe@N–C) were synthesized through a simple heat-treatment in an N2 environment. CoFe@N–C effectively catalyzed the overall water splitting in alkaline media. Specifically, the as-synthesized CoFe@N–C exhibited excellent activity towards the oxygen evolution reaction (OER) with a low overpotential of 292 mV at 10 mA cm−2 and the hydrogen evolution reaction (HER) with a low overpotential of 110 mV at 10 mA cm−2. The good electrocatalytic properties may be attributed to the synergistic electronic coupling between single-crystalline CoFe and highly conductive N-doped CNTs and the enrichment of active sites. Additionally, CoFe@N–C showed excellent stability and durability with no observable deviation in the overpotential for the OER and HER after 1000 cycles of cyclic voltammetry (CV).

Mechanical vibrations and solar energy are ubiquitous in the environment. Hereon, we report the synergic enhancement of the oxidation by simultaneously harvesting solar and mechanical vibrations through flexible piezo and photocatalytic composite nanofiber mats. Surface enriched titanium dioxide nanoparticles incorporated in polyacrylonitrile (PAN/TiO

Creating highly branched plasmonic superparticles can effectively induce broadband light absorption and convert light to heat regardless of the light wavelength, angle, and polarization. However, their direct synthesis in a controllable manner remains a significant challenge. In this work, we propose a strain modulation strategy to produce branched Au nanostructures that promotes the growth of Au on Au seeds in the Volmer-Weber (island) mode instead of the typical Frank-van der Merwe (layer-by-layer) mode. The key to this strategy is to continuously deposit polydopamine formed in situ on the growing surface of the seeds to increase the chemical potential of the subsequent deposition of Au, thus achieving continuous heterogeneous nucleation and growth. The branched Au superparticles exhibit a photothermal conversion efficiency of 91.0% thanks to their small scattering cross-section and direction-independent absorption. Even at a low light power of 0.5 W/cm2 and a low dosage of 25 ppm, these particles show an excellent efficacy in photothermal cancer therapy. This work provides the fundamental basis for designing branched plasmonic nanostructures and expands the application scope of the plasmonic photothermal effect.

Conventional colloidal syntheses typically produce nanostructures with positive curvatures due to thermodynamic preference. Here, we demonstrate the creation of surface concavity in Au nanorods through seed-mediated growth in confined spaces and report their thermochromic responses to temperature changes. The unique surface concavity is created by templating against Fe3O4 nanorods, producing a new concavity-sensitive plasmonic band. Due to the high surface energy, the metastable nanorods can be reconstructed at a moderate temperature, enabling convenient and precise tuning of their plasmonic properties by aging in different solvents. Such structural reconstruction of concave Au nanorods enables the fabrication of thermochromic plasmonic films that can display images with vivid color changes or exhibit encrypted, invisible information upon aging. This templating strategy is universal in creating concave nanostructures, which may open the door to designing new nanostructures with promising applications in sensing, anticounterfeiting, information encryption, and displays.

The fast and reversible switching of plasmonic color holds great promise for many applications, while its realization has been mainly limited to solution phases, achieving solid-state plasmonic color-switching has remained a significant challenge owing to the lack of strategies in dynamically controlling the nanoparticle separation and their plasmonic coupling. Herein, we report a novel strategy to fabricate plasmonic color-switchable silver nanoparticle (AgNP) films. Using poly(acrylic acid) (PAA) as the capping ligand and sodium borate as the salt, the borate hydrolyzes rapidly in response to moisture and produces OH- ions, which subsequently deprotonate the PAA on AgNPs, change the surface charge, and enable reversible tuning of the plasmonic coupling among adjacent AgNPs to exhibit plasmonic color-switching. Such plasmonic films can be printed as high-resolution invisible patterns, which can be readily revealed with high contrast by exposure to trace amounts of water vapor.

The molecule (E)-(5-(3-anthracen-9-yl-allylidene)-2,2-dimethyl-[1,3] dioxane-4,6-dione) (E-AYAD) undergoes E→Z photoisomerization. In the solid state, this photoisomerization process can initiate a physical transformation of the crystal that is accompanied by a large volume expansion (ca. 10 times), loss of crystallinity, and growth of large pores. This physical change requires approximately 10 % conversion of the E isomer to the Z isomer and results in a gel-like solid with decreased stiffness that still retains its mechanical integrity. The induced porosity allows the expanding gel to engulf superparamagnetic nanoparticles from the surrounding liquid. The trapped superparamagnetic nanoparticles impart a magnetic susceptibility to the gel, allowing it to be moved by a magnetic field. The photoinduced phase transition, starting with a compact crystalline solid instead of a dilute solution, provides a new route for in situ production of functional porous materials.

Developing high-performance electrocatalysts for the ethanol oxidation reaction (EOR) is critical to the commercialization of direct ethanol fuel cells. However, current EOR catalysts suffer from h...

Herein, we show that copper nanostructures, if made anisotropic, can exhibit strong surface plasmon resonance comparable to that of gold and silver counterparts in the near-infrared spectrum. Further, we demonstrate that a robust confined seeded growth strategy allows the production of high-quality samples with excellent control over their size, morphology, and plasmon resonance frequency. As an example, copper nanorods (CuNRs) are successfully grown in a limited space of preformed rod-shaped polymer nanocapsules, thereby avoiding the complex nucleation kinetics involved in the conventional synthesis. The method is unique in that it enables the flexible control and fine-tuning of the aspect ratio and the plasmonic resonance. We also show the high efficiency and stability of the as-synthesized CuNRs in photothermal conversion and demonstrate their incorporation into nanocomposite polymer films that can be used as active components for constructing light-responsive actuators and microrobots.

Oxygen evolution reaction (OER) plays a vital role in green technologies including water splitting and carbon dioxide reduction. As promising alternatives of noble metals–based OER electrocatalysts such as IrO2 and RuO2, the OER performance of nanostructured Co-based materials is far from satisfactory. In this report, a coordination-assisted etching strategy is proposed to incorporate iron into cobalt oxide porous nanoplates, producing composite nanostructures with optimized Co:Fe ratio that manifest significantly enhanced OER performance (an overpotential of 304 mV at 10 mA/cm2 as well as a low Tafel slope of 38 mV/dec). The enhancement can be attributed to the modulated electronic structure of cobalt, favorable absorption energy of OER intermediates, and the formation of more oxygen vacancies. This work highlights the importance of rational integration of iron with cobalt for optimal electrocatalytic performance enabled by the coordination-assisted etching strategy, providing more opportunities for the design and synthesis of mixed metal electrocatalysts for energy conversion and storage.

While creating open nanostructures represents a popular strategy for improving the utilization efficiency of Pt-based catalysts for electrochemical reactions, the exposed facets should be precisely controlled for further enhancement of the catalytic activity. Here, we report a novel strategy for creating regularly shaped nanopores in ultrathin nanotubes of bimetallic noble metals. By templating against Ag nanowires and then applying a thermal ripening process, we have successfully produced ultrathin (with a wall thickness of ∼1 nm) Pt–Ag alloy nanotubes containing high-density well-defined rectangular nanopores and a collapsed double-layer structure. The resulting porous nanotubes expose {100} facets at the basal sides and {110} facets with step sites at the edges of the rectangular nanopores. The particular surface structure and the bimetallic composition enable suppressed CO poisoning of the catalysts and consequently enhanced electrocatalytic activity in the methanol oxidation reaction. The typical spe...

As an excellent electrocatalyst, platinum (Pt) is often deposited as a thin layer on a nanoscale substrate to achieve high utilization efficiency. However, the practical application of the as-designed catalysts has been substantially restricted by the poor durability arising from the leaching of cores. Herein, by employing amorphous palladium phosphide (a-Pd-P) as substrates, we develop a class of leaching-free, ultrastable core-shell Pt catalysts with well-controlled shell thicknesses and surface structures for fuel cell electrocatalysis. When a submonolayer of Pt is deposited on the 6 nm nanocubes, the resulting Pd@a-Pd-P@PtSML core-shell catalyst can deliver a mass activity as high as 4.08 A/mgPt and 1.37 A/mgPd+Pt toward the oxygen reduction reaction at 0.9 V vs the reversible hydrogen electrode and undergoes 50 000 potential cycles with only ∼9% activity loss and negligible structural deformation. As elucidated by the DFT calculations, the superior durability of the catalysts originates from the high corrosion resistance of the disordered a-Pd-P substrates and the strong interfacial Pt-P interactions between the Pt shell and amorphous Pd-P layer.

Summary: Advanced oxidation processes (AOPs) based on sulfate radicals (SO4⋅−) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO2 as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO4⋅−-based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO2, whereas the exposed active sites of Mo(IV) on MoO2 surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO2 as a cocatalyst is a promising technique for large-scale practical environmental remediation. : Inorganic Chemistry; Catalysis; Water Resources Engineering Subject Areas: Inorganic Chemistry, Catalysis, Water Resources Engineering

Summary Advanced oxidation processes (AOPs) based on sulfate radicals (SO4⋅−) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO2 as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO4⋅−-based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO2, whereas the exposed active sites of Mo(IV) on MoO2 surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO2 as a cocatalyst is a promising technique for large-scale practical environmental remediation., Graphical Abstract, Highlights • The degradation rate of PMS/Fe(II)/MoO2 system is 50 times higher than that without MoO2 • Fe(III)/Fe(II) cycle on (110) surface of MoO2 in PMS/Fe(II)/MoO2 system was confirmed • The metal active sites exposed to MoO2 (110) surface are responsible for PMS activation • Compared with MoS2, MoO2 co-catalytic system has less toxicity and no release of H2S, Inorganic Chemistry; Catalysis; Water Resources Engineering

Summary Advanced oxidation processes (AOPs) are widely proposed for treating persistent pollutants by the ⋅ OH radicals generated from H 2 O 2 decomposition. However, their broad applications in practical settings have been hampered by the low efficiency of H 2 O 2 decomposition. Here, we report that metal sulfides (MoS 2 , WS 2 , Cr 2 S 3 , CoS 2 , PbS, or ZnS) can serve as excellent co-catalysts to greatly increase the efficiency of H 2 O 2 decomposition and significantly decrease the required dosage of H 2 O 2 and Fe 2+ in AOPs. Unsaturated S atoms on the surface of metal sulfides can capture protons to form H 2 S and expose metallic active sites with reductive properties to accelerate the rate-limiting step of Fe 3+ /Fe 2+ conversion. The efficiency of AOPs involving co-catalysts can be further enhanced by visible-light illumination thanks to the sensitization of organic pollutants. This discovery is expected to drive great advances in the use of AOPs for large-scale practical applications such as environmental remediation.

Ultrathin Pt nanostructures exposing controlled crystal facets are highly desirable for their superior activity and cost-effectiveness in the electrocatalytic oxygen reduction reaction (ORR), and they are conventionally synthesized by epitaxial growth of Pt on a limited range of templates, such as Pd nanocrystals, resulting in a high cost and less structural diversity of the ultrathin Pt nanostructures. To solve this problem, we demonstrate that ultrathin Pt nanostructures can be synthesized by templating conveniently available Ag nanocrystals without involving galvanic replacement, which enables a much-reduced cost and controllable new morphologies, such as ultrathin Pt nanoplates that expose the {111} facets. The resulting ultrathin Pt nanoplates are ∼1-2 nm in thickness, which show an ∼22-fold increase in specific activity (5.3 mA cm-2), an ∼9.5-fold increase in mass activity (1.62 A mg-1) and significantly enhanced catalytic stability in the ORR, compared with the commercial Pt/C catalyst. We believe this strategy opens a door to a highly extendable family of ultrathin noble metal nanostructures, thus promising excellent activity and stability in a broad range of catalytic applications.

The poor stability of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) has severely impeded their practical applications. Although there are some successful examples on encapsulating multiple CsPbX3 NCs into an oxide or polymer matrix, it has remained a serious challenge for the surface modification/encapsulation using oxides or polymers at a single particle level. In this work, monodisperse CsPbX3/SiO2 and CsPbBr3/Ta2O5 Janus nanoparticles were successfully prepared by combining a water-triggered transformation process and a sol–gel method. The CsPbBr3/SiO2 NCs exhibited a photoluminescence quantum yield of 80% and a lifetime of 19.8 ns. The product showed dramatically improved stability against destruction by air, water, and light irradiation. Upon continuous irradiation by intense UV light for 10 h, a film of the CsPbBr3/SiO2 Janus NCs showed only a slight drop (2%) in the PL intensity, while a control sample of unmodified CsPbBr3 NCs displayed a 35% drop. We further highlighted the advantageous features of t...

The fabrication of ultrathin alloy shells as heterogeneous catalysts to increase the utilization efficiency and enhance the catalytic activity of metal atoms has been recognized as an effective method for the construction of efficient metal nanocatalysts, particularly noble-metal nanocatalysts. In this study, we demonstrate the successful formation of Pd-M (M = Ni, Ag, Cu) alloy shells with a tunable thickness on preformed nanoscale Pd seeds. The success of this synthesis mainly relies on the combination of the slow reduction of “M” ions and the subsequent diffusion of M ad-atoms into the surface lattice of Pd seeds. The composition of the Pd-M alloy shell is easily tuned by changing the type and amount of the added precursor, and the shell thickness is manipulated according to the reaction time. More significantly, the surface structure of these alloy shells is maintained after the reaction, implying that any desired surface structure of Pd-M alloy shells can be prepared by using the appropriate starting materials. Further catalytic evaluation of the hydrogenation of chloronitrobenzenes shows that these alloy surfaces exhibit significantly improved selectivity compared to the Pd seeds. The Pd-Ni alloy surfaces exhibit much better catalytic selectivity (as high as > 99%) than Pd catalysts.

Visible light-responsive reversible color switching systems are attractive to many applications since visible light has superior penetration and causes far less damages to organic molecules than UV. Here we report that self-doping of Sn2+ in SnO2-x nanocrystals red shifts their absorption to visible region and simultaneously produces oxygen vacancies, which can effectively scavenge photogenerated holes and thus enable color switching of redox dyes using visible light. Wavelength selective switching can also be achieved by coupling the photocatalytic activity of the SnO2-x NCs with the color switching kinetics of different redox dyes. The fast light response enables the further fabrication of a solid film that can be repeatedly written freehand using a visible laser pen or projection printing through a photomask. This discovery represents a big step forward towards practical applications, especially in areas with concerns on the safety and photodamage issues of UV light.

Hexavalent chromium Cr(VI), a highly toxic oxyanion, widely occurs in drinking water supplies. This study designed and synthesized a new type of highly reductive TiO2 nanocrystals for photochemical Cr(VI) removal, via the thermal hydrolysis of TiCl4 in the presence of diethylene glycol (DEG). Surface analyses and hydroxyl radical measurements suggested that DEG was chemically bonded on TiO2 surface that resulted in an internal hole-scavenging effect and a high electron-releasing capacity, making it advantageous to conventional TiO2 materials. Upon UV irradiation, the synthesized TiO2 photocatalyst exhibited fast Cr(VI) reduction kinetics in diverse water chemical conditions. Fast elimination of Cr(VI) was achieved on a time scale of seconds in drinking water matrices. The removal of Cr(VI) by reductive TiO2 exhibited a three-stage kinetic behavior: an initial fast-reaction phase, a lag phase resulting from surface precipitation of Cr(OH)3(s), and a final reaction phase due to surface regeneration from oxidation-reduction induced ripening process. The lag phase disappeared in acidic conditions that prevented the formation of Cr(OH)3(s). The catalyst exhibited extremely high electron-releasing capacity that can be reused for multiple cycles of Cr(VI) removal in drinking water treatment.

This communication reports an efficient bimetallic catalyst by incorporating Au atoms onto the surface of palladium nanocrystals via a simple solution phase surface alloying process. While retaining the original surface structure of Pd, the surface alloy catalyst shows the highest activity and the best selectivity toward alkyne semihydrogenation reactions in comparison to commercial Pd/C and Lindlar catalysts. This simple surface alloying process could be easily extended to the optimization of commercial Pd/C catalysts to significantly improve their catalytic performance. The surface modification approach proposed in this work not only provides a new direction in engineering efficient metal nanocatalysts for fine chemical industries, but also improves our understanding of bimetallic nanocrystal surfaces.

In this work, we carried out both theoretical calculation and experimental studies to reveal the contribution of hollow geometry to the light utilization efficiency of the TiO2 photocatalysts in diluted aqueous solution. It is found that the single or multi-shelled hollow structures do not induce significant multiple reflections within the shells as widely believed in previous reports, and therefore the geometric factor has minimal contribution to the improvement of the light utilization efficiency of the photocatalyst. To design TiO2 photocatalysts with higher activity, it is more appropriate to focus on the improvement of the crystallinity, diffusion, surface area, and dispersity of the catalysts, rather than their geometric shapes.

Photoinduced syntheses offer significant advantages over conventional thermal strategies, including improved control over reaction kinetics and low synthesis temperatures, affording nanoparticles with nontrivial and thermodynamically unstable structures. However, the photoinduced syntheses of non-metallic nanocrystalline products (such as metal sulfides) have not yet been reported. Herein, we demonstrate the first photoinduced synthesis of ultrafine (sub-2 nm) Ag2S quantum dots (QDs) from Ag nanoparticles at 10 °C. By thorough investigation of the mechanism for the transformation, a fundamental link was established between the intrinsic structures of the molecular intermediates and the final Ag2S products. Our results confirm the viability of low-temperature photochemical approaches in metal sulfide synthesis, and demonstrate a new rule which could be followed in it.

Although electrocatalysts based on transition metal phosphides (TMPs) with cationic/anionic doping have been widely studied for hydrogen evolution reaction (HER), the origin of performance enhancement still remains elusive mainly due to the random dispersion of dopants. Herein, we report a controllable partial phosphorization strategy to generate CoP species within the Co-based metal-organic framework (Co-MOF). Density functional theory calculations and experimental results reveal that the electron transfer from CoP to Co-MOF through N-P/N-Co bonds could lead to the optimized adsorption energy of H2 O (ΔG H 2 O * ) and hydrogen (ΔGH* ), which, together with the unique porous structure of Co-MOF, contributes to the remarkable HER performance with an overpotential of 49 mV at a current density of 10 mA cm-2 in 1 m phosphate buffer solution (PBS, pH 7.0). The excellent catalytic performance exceeds almost all the documented TMP-based and non-noble-metal-based electrocatalysts. In addition, the CoP/Co-MOF hybrid also displays Pt-like performance in 0.5 m H2 SO4 and 1 m KOH, with the overpotentials of 27 and 34 mV, respectively, at a current density of 10 mA cm-2 .

Noble metal nanocrystals have been widely used as active components in catalysis and chemical/bio-sensing. The sizes, structures, and shapes of noble metal nanocrystals are crucial to their electronic, optical, and catalytic properties. However, metal nanocrystals tend to lose their structural and morphological properties when they are subjected to thermal and chemical treatment. Therefore, stabilization of noble metal nanostructures remains a challenge. In this feature article, we present our recent efforts on the stabilization of noble metal nanocrystals, i.e., using inorganic and non-metal solids as supports and physical barriers, protecting the nanocrystal surface by a metal coating, and forming alloys with other metals. At the end of this review, we provide our perspectives on the future development of effective methods for nanocrystal stabilization.

A chemically etched CuCo-oxide (CE-CCO) electrode prepared by electrodeposition was used for oxygen evolution reaction electrocatalyst. Surface chemical etching of CuCo-oxide (CCO) introduced oxygen vacancies and thus increased electrical conductivity to promote oxygen generation. During practical applicability testing, when CE-CCO was used as the anode of an anion-exchange membrane water electrolyzer, enhanced oxygen evolution performance was observed (current density = 1390 mA/cm2 at 1.8 Vcell), which, among other reactions, was ascribed to the easy removal of O2 from the aerophobic electrode surface. In addition to featuring low mass transfer resistance even at high current density with substantial gas generation, the CE-CCO electrode featured remarkable durability, exhibiting stable performance over 3600 h under the conditions of continuous O2 evolution. Thus, this work shows that the performance of electrodeposited oxide catalysts can be enhanced by introducing oxygen vacancies, while the energy conversion efficiency of the corresponding water electrolysis systems can be increased by lowering mass transfer resistance via efficient gas removal and reactant supply.

Structural defects have been proven to determine many of the materials' properties. Here, we demonstrate a unique approach to the creation of Ag nanowires with high-density defects through controllable nanoparticles coalescence in one-dimensional pores of mesoporous silica. The density of defects can be easily adjusted by tuning the annealing temperature during synthetic process. The high-density defects promote the adsorption and activation of more reactants on the surface of Ag nanowires during catalytic reactions. As a result, the as-prepared Ag nanowires exhibit enhanced activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and turnover frequency (TOF). We show further that the silane conversion rate can be enhanced by maximizing the defect density and thus the number of active sites on the Ag nanowires, reaching a remarkable TOF of 8288 h(-1), which represents the highest TOF that has been achieved by far on Ag catalysts. This work not only proves the important role of structural defects in catalysis but also provides a new and general strategy for constructing high-density defects in metal catalysts.

A new gold–titania catalyst has been developed for cryogenic oxidations based on a yolk–shell nanoarchitecture. The synthesis of those structures involves the sequential deposition of a sacrificial silica layer and a titania shell around well-defined gold nanoparticles followed by removal of the silica via NaOH etching. The resulting catalyst contains an amorphous titania shell with sodium titanate and silicon impurities that proved critical for the cryogenic activity; removal of those via HCl treatment kills most of the catalytic conversion. Oxidation of carbon monoxide is possible with this Au@Void@TiO 2 catalyst at temperatures as low as 120 K, by a mechanism different than the one operative at room temperature that involves a weakly-adsorbed CO species with a C O stretching frequency of 2162 cm − 1 , possibly at Au–TiO 2 interfacial sites.

Composite nanostructures with well-defined characteristics are often advantageous catalysts for highly efficient photocatalytic processes. Here, we report the tailored synthesis of C@TiO2 yolk–shell nanostructures and their photocatalytic applications in the degradation of organic dyes. The conductive carbon core serves as an electron-sink to promote the separation of electron–hole pairs photo-excited in the TiO2 shell, improve their lifetime, and enhance the photocatalytic performance of the system. The yolk–shell nanostructures were synthesized through a sol–gel coating of TiO2 on resorcinol-formaldehyde (RF) resin spheres followed by silica-protected calcination and ultimately NaOH etching to remove the silica layer and produce C@TiO2 yolk–shell nanostructures. In order to improve the crystallinity of the TiO2 shell, post-processing including acid treatment and re-calcination was also carried out. The resulting yolk–shell structures have many desirable properties for photocatalytic applications including the existence of a conductive core, well-maintained structural integrity, uniform particle dimensions, favorable mesoscale porosity, tunable crystallinity, and controllable crystalline phase of TiO2. As a result, we have been able to optimize the structure and property of the composite photocatalysts and achieve superior photocatalytic performance to commercial P25-TiO2 catalysts.

We communicate an unconventional synthesis of Au nanoplates with high yield and excellent reproducibility through polyvinylpyrrolidone (PVP)-assisted H2O2 reduction. Unlike the ones prepared using halide-based surfactants, the PVP-capped Au nanoplates are found to afford fairly easy bio-functionalization, suggesting a vastly expanded spectrum of applications in bio-related fields.

We report a "ligand stripping" method for the creation of secondary structures of colloidal nanocrystals. Using iron oxide as an example, we demonstrate that the use of diols as "stripping agents" allows the controllable removal of the original capping ligands and induces aggregation of nanocrystals into well-defined clusters.

Noble metal/transition metal (hydr)oxide interfaces are often highly active catalytic sites for many oxidation reactions. One of the challenges in such catalyst systems especially in high-temperature reactions is the lack of an effective mechanism to stabilize the catalysts against sintering over time and to maintain the metal/oxide interfaces. Herein, we report an alloying–dealloying process for the production of ultrafine Pt/FeOx nanoconjugates (∼1.8 nm) with confinement in silica nanoshells for effective stabilization. The synthesis started with coating of ultrasmall Pt/Fe precursor nanoparticles in reverse micelles by a microporous silica shell, which served as a nanoreactor to allow the subsequent transformation of the precursor nanoparticles into the target Pt/FeOx nanoconjugates. Thanks to the ultrasmall size of the nanoconjugates and their effective protection by the silica shells, the resulting Pt/FeOx@SiO2 yolk/shell nanospheres showed high catalytic activity and remarkable durability in preferential CO oxidation in H2 (PROX). This synthesis strategy may represent a general approach in rational design of highly stable catalysts with complex nanostructures for a broad range of catalysis.

This communication reports a remarkably simple method for the deposition of ultrathin Pt layers on second metal nanocrystals based on the fine control of the deposition rate by the coordination effect. Compared with commercial Pt/C catalysts, the as-prepared ultrathin Pt layers exhibit significantly enhanced catalytic properties toward the oxygen reduction reaction.

We report a facile water-assisted crystallization process for the conversion of amorphous sol-gel derived TiO2 into mesoporous anatase nanostructures with a high surface area and well-controlled porosity and crystallinity. As an alternative to conventional calcination methods, this approach works under very mild conditions and is therefore much desired for broad biological, environmental and catalytic applications.

Although aqueous synthesis of nanocrystals is advantageous in terms of the cost, convenience, environmental friendliness, and surface cleanness of the product, nanocrystals of Pt and non-noble metal alloys are difficult to obtain with controlled morphology and composition from this synthesis owing to a huge gap between the reduction potentials of respective metal salts. This huge gap could now be remedied by introducing a sulfite into the aqueous synthesis, which is believed to resemble an electroless plating mechanism, giving rise to a colloid of Pt-M (M=Ni, Co, Fe) alloy nanowires with an ultrasmall thickness (ca. 2.6 nm) in a high yield. The sulfite also leads to the formation of surface M-S bonds and thus atomic-level Pt/M-S(OH) interfaces for greatly boosted hydrogen evolution kinetics under alkaline conditions. An activity of 75.3 mA cm-2 has been achieved with 3 μg of Pt in 1 m KOH at an overpotential of 70 mV, which is superior to previously reported catalysts.

We demonstrate that anatase TiO2 nanocrystals composed of a nanocrystal core and nanorod antennas can be produced via a nonaqueous colloidal seed-mediated growth method. Anatase TiO2 nanocrystals with defined morphologies were first prepared as seeds, and then secondary anatase TiO2 nanorods were grown on the defined facets of the seeds under appropriate conditions. Systematic studies on the growth mechanism reveal that the formation of core-antenna nanocrystals involves an epitaxial growth process with specific orientational preference governed by both thermodynamic and kinetic factors. By manipulating the reaction conditions including the precursor amount and introduction rate, the epitaxial growth behavior can be well controlled. By further varying the morphology of seed nanocrystals, we have also been able to produce core-antenna anatase TiO2 nanocrystals with complex spatial configurations in a highly predictable manner. The high structural configurability and predictability offered by this seed-mediated growth method may provide great opportunities in enhancing the performance of TiO2-based nanostructures in many energy-related applications. As a demonstration, we show by simply manipulating the core-antenna structures that the photocatalytic activity of the anatase nanocrystals can be improved from the relatively less active seed nanocrystals or pure nanorods to the extent that exceeds the activity of the commercial P25 titania.

Anisotropic nanostructures provide an additional degree of freedom for tailoring the collective properties of their ensembles. Using Fe@SiO2 nanoellipsoids as anisotropic building blocks, herein we demonstrate a new class of magnetically responsive photonic structures whose photonic properties can be dynamically tuned by controlling the direction of the magnetic fields they are exposed to. These novel photonic structures diffract at a minimum wavelength when the field direction is perpendicular to the incident angle, and a maximum wavelength when the field is switched to parallel direction; and the diffraction intensity reaches maximum values when the fields are either parallel or perpendicular to the incident light, and decreases when the field direction is moved off-angle.

Colloidal barium-doped TiO2 nanocrystals have been developed that enable the highly reversible light-responsive color switching of redox dyes with excellent cycling performance and high switching rates. Oxygen vacancies resulting from the Ba doping serve as effective sacrificial electron donors (SEDs) to scavenge the holes photogenerated in TiO2 nanocrystals under UV irradiation and subsequently promote the reduction of methylene blue to its colorless leuco form. Effective color switching can therefore be realized without relying on external SEDs, thus greatly increasing the number of switching cycles. Ba doping can also accelerate the recoloration under visible-light irradiation by shifting the absorption edge of TiO2 nanocrystals to a shorter wavelength. Such a system can be further casted into a solid film to produce a rewritable paper on which letters and patters can be repeatedly printed using UV light and then erased by heating; this process can be repeated for many cycles and does not require additional inks.

Plasmonic noble metal nanoparticles have emerged as a promising material in sensitizing wide-bandgap semiconductors for visible-light photocatalysis. Conventional methods in constructing such heterocatalysts suffer from either poor control over the size of the metal nanoparticles or inefficient charge transfer through the metal/semiconductor interface, which limit their photocatalytic activity. To solve this problem, in this work we construct Au/TiO2 photocatalysts by depositing presynthesized colloidal Au nanoparticles with well-controlled sizes to TiO2 nanocrystals and then removing capping ligands on the Au surface through a delicately designed ligand-exchange method, which leads to close Au/TiO2 Schottky contact after a mild annealing process. Benefiting from this unique synthesis strategy, the obtained photocatalysts show superior activity to conventionally prepared photocatalysts in dye decomposition and water-reduction hydrogen production under visible-light illumination. This study not only opens up new opportunities in designing photoactive materials with high stability and enhanced performance for solar energy conversion but also provides a potential solution for the well-recognized challenge in cleaning capping ligands from the surface of colloidal catalyst nanoparticles.

An interfacial self-assembly strategy was developed to synthesize sub-100 nm noble metal colloidosomes, showing intriguing collective optical and catalytic properties., Self-assembly at the nanoscale represents a powerful tool for creating materials with new structures and intriguing collective properties. Here, we report a novel strategy to synthesize nanoscale colloidosomes of noble metals by assembling primary metal nanoparticles at the interface of emulsion droplets formed by their capping agent. This strategy produces noble metal colloidosomes of unprecedentedly small sizes (

Identification of active sites for oxygen evolution reaction (OER) plays a key role in the design and fabrication of high-performance cobalt-based electrocatalysts. Herein, we report the synthesis of two types of two-dimensional monometallic cobalt hydroxide nanoplates in aqueous solution for OER: α-Co(OH)2 with both Co2+Td and Co2+Oh sites and β-Co(OH)2 with Co2+Oh sites. Electrochemical characterization reveals that α-Co(OH)2 is more active than β-Co(OH)2 towards OER. The better activity can be attributed to the presence of Co2+Td sites in α-Co(OH)2, which are more active than Co2+Oh sites. Our finding clarifies the contribution of the two catalytic sites and helps future rational design of high-performance OER electrocatalysts.

A template-mediated process for the preparation of mesoporous carbon shells with high surface area, dual-pore structure, and excellent performance in the adsorption of humic acid is reported. Their synthesis involves templating phenolic resin against wrinkled silica nanospheres, subsequent carbonization under Ar atmosphere, and final release of dual-pore mesoporous carbon shells by etching the silica templates. An additional silica layer was used to protect the phenolic resin from aggregation during carbonization, and its subsequent removal gives the carbon shells a hydrophilic surface, which significantly improves their dispersity in aqueous media. When used as adsorbents for humic acid removal, the as-prepared dual-pore mesoporous carbon shells show superior adsorption performance to activated carbon.

Synthesis of metal nanoframes has been of great interest for their open structures and high fractions of active surface sites, which gives rise to outstanding performance in catalysis. In this work, Pd nanoframes with well-defined structures have been successfully prepared by directly excavating solid nanocrystals. The success of this synthesis mainly relies on the fine control over the oxidative etching and regrowth rates. Due to the different regrowth rates at three typical types of surface sites (e.g., corners, edges, and faces), the removal of Pd atoms can be controlled at a certain site by carefully tuning the rates of the oxidative etching and regrowth. Without the presence of the reducing agent, etching dominates the process, resulting in the shape transformation of nanocrystals with well-defined shapes (e.g., octahedra) to cuboctahedra. In contrast, when a certain amount of the reducing agent (e.g., HCHO) is added, the regrowth rate at the corner and edge sites can be controlled to be equivalent to the etching rate, while the regrowth rate at the face sites is still smaller than the etching rate. In this case, the etching can only take place at the faces; thus, Pd nanoframes could be obtained. On the basis of this approach, solid Pd nanocrystals with different shapes, including cubes, cuboctahedra, octahedra, and concave cubes, have been successfully excavated to the corresponding nanoframes. These nanoframes can unambiguously exhibit much enhanced catalytic activity and improved durability toward formic acid oxidation reaction due to their three-dimensional (3D) open frameworks compared with solid Pd octahedra catalysts.

We report that fully alloyed Ag/Au nanospheres with high compositional homogeneity ensured by annealing at elevated temperatures show large extinction cross sections, extremely narrow bandwidths, and remarkable stability in harsh chemical environments. Nanostructures of Ag are known to have much stronger surface plasmon resonance than Au, but their applications in many areas have been very limited by their poor chemical stability against nonideal chemical environments. Here we address this issue by producing fully alloyed Ag/Au nanospheres through a surface-protected annealing process. A critical temperature has been found to be around 930 °C, below which the resulting alloy nanospheres, although significantly more stable than pure silver nanoparticles, can still gradually decay upon extended exposure to a harsh etchant. Nanospheres annealed above the critical temperature show a homogeneous distribution of Ag and Au, minimal crystallographic defects, and the absence of structural and compositional interfaces, which account for the extremely narrow bandwidths of the surface plasmon resonance and may enable many plasmonic applications with high performance and long lifetime, especially for those involving corrosive species.

A controlled sol–gel process has been developed to coat gold nanoparticles with a thin layer of titanium dioxide to produce Au@TiO 2 core–shell catalyst particles, which can be rendered crystalline via calcination at high temperatures. The Au weight percent can be controlled by repeating the coating process while decreasing the water content and core concentration, making it possible to systematically tune the shell thickness over a large range without the need for an excessive number of coating steps. The encapsulating TiO 2 shells protect the Au cores from sintering during processing, which makes it possible to investigate the effect of varying the processing conditions for the catalyst without altering the Au particle size. Catalysts with varying Au weight percents and corresponding shell thicknesses, as well as various calcination temperatures, were tested for their efficacy in the UV-driven reforming of ethanol to produce hydrogen. It was found that an Au weight percent of 0.731% was optimal, along with a calcination temperature of 600 °C, as these conditions produced a sufficiently low Au loading percent while still enabling diffusion of the solution to the core.