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The electrocatalytic oxygen evolution reaction from H2O (OER) is essential in a number of areas like electrocatalytic hydrogen production from H2O. A Ni oxyhydroxide nanosheet (NiNS) is among the most widely studied OER catalysts but still suffers from low activity, sluggish kinetics, and poor stability. Herein, we incorporate MoO3 patches into NiNS to form a nanosheet with an intimate Ni-Mo interface (NiMoNS) for the OER. The overpotential at 10 mA cm-2 and Tafel slope on NiMoNS (260 mV, 54.7 mV dec-1) are lower than those on NiNS (296 mV, 89.3 mV dec-1), implying that higher activity and faster kinetics are achieved on NiMoNS. There is no change in electrocatalytic efficiency of NiMoNS after 18 h of OER, but the electrocatalytic efficiency of NiNS decreases by 56% after only 8 h of OER. Thus, NiMoNS has better stability. The intimate Ni-Mo interface promotes two-dimensional lateral growth of NiMoNS to form a surface area 1.5 times larger than that of NiNS, and facilitates electron transfer from Ni to Mo. This makes the Ni3+/Ni2+ ratio on the NiMoNS surface (1.32) higher than that on the NiNS surface (0.68). Moreover, the Ni3+/Ni2+ ratio on NiMoNS surface increases to 1.81 after 18 h of OER but the Ni3+/Ni2+ ratio on the NiNS surface decreases to 0.51 after 8 h of OER. Therefore, the NiMoNS surface has more abundant and stable Ni3+ sites which are catalytically active toward OER. This could be the reason for the enhanced activity, kinetics, and stability of NiMoNS. The results are very valuable for fabricating more efficient catalysts for electrocatalysis.

Solar-energy-driven photocatalysis, such as photocatalytic reduction of CO2, is promising simultaneously for the energy and environmental issues. Coating thin carbon layers with the thickness less than 10 nm on photocatalysts has been developed as an efficient strategy for enhancing the photocatalytic efficiency in recent years. In the present review, we summarize the crucial progress on carbon-coated photocatalysts. Origins for the improved light absorption, charge separation, reactant adsorption and photocatalytic stability on carbon-coated photocatalysts as well as the applications of carbon-coated photocatalysts are discussed. Future opportunities and challenges associated with carbon-coated photocatalysts are shown at the end of the review. We hope that the present review can trigger more deep insights on carbon-coated photocatalysts and provide new opportunities for developing low-cost but efficient photocatalysts.

Electrocatalytic oxidation of water (i.e., oxygen evolution reaction, OER) plays crucial roles in energy, environment, and biomedicine. It is a key factor affecting the efficiencies of electrocatalytic reactions conducted in aqueous solution, e.g., electrocatalytic water splitting and glucose oxidation reaction (GOR). However, electrocatalytic OER still suffers from problems like high overpotential, sluggish kinetics, and over-reliance on expensive noble-metal-based catalysts. Herein, 15 nm thick carbon-based shell coated tungsten oxide (CTO) nanospheres are loaded on nickel foam to form CTO/NF. An enhanced electrocatalytic OER is triggered on CTO/NF, with the overpotential at 50 mA cm-2 (317 mV) and the Tafel slope (70 mV dec-1) on CTO/NF lower than those on pure tungsten oxide (360 mV, 117 mV dec-1) and noble-metal-based IrO2 catalysts (328 mV, 96 mV dec-1). A promoted electrocatalytic GOR is also achieved on CTO/NF, with efficiency as high as 189 μA mM-1 cm-2. The carbon-based shell on CTO is flexible for electron transfer between catalyst and reactants and provides catalytically active sites. This improves reactant adsorption and O-H bond dissociation on the catalyst, which are key steps in OER and GOR. The carbon-based shell on CTO retains the catalyst as nanospheres with a higher surface area, which facilitates OER and GOR. It is the multiple roles of the carbon-based shell that increases the electrocatalytic efficiency. These results are helpful for fabricating more efficient noble-metal-free electrocatalysts.

Organolead halide and mixed halide perovskites (CH3NH3PbX3, CH3NH3PbX3–nYn, X and Y = Cl–, Br–, or I–) are promising materials for photovoltaics and optoelectronic devices. 207Pb solid-state NMR spectroscopy has previously been applied to characterize phase segregation and halide ion speciation in mixed halide perovskites. However, NMR spectroscopy is an insensitive technique that often requires large sample volumes and long signal averaging periods. This is especially true for mixed halide perovskites, which give rise to extremely broad 207Pb solid-state NMR spectra. Here, we quantitatively compare the sensitivity of the various solid-state NMR techniques on pure and mixed halide organolead perovskites and demonstrate that both fast MAS and DNP can provide substantial gains in NMR sensitivity for these materials. With fast MAS and proton detection, high signal-to-noise ratio two-dimensional (2D) 207Pb–1H heteronuclear correlation (HETCOR) NMR spectra can be acquired in less than half an hour from only ca...

A selective CO evolution from photoreduction of CO2 in water was achieved on a noble-metal-free, carbide-based composite catalyst, as demonstrated by a CO selectivity of 98.3% among all carbon-containing products and a CO evolution rate of 29.2 μmol h–1, showing superiority to noble-metal-based catalyst. A rapid separation of the photogenerated electron–hole pairs and improved CO2 adsorption on the surface of the carbide component are responsible for the excellent performance of the catalyst. The high CO selectivity is accompanied by a predominant H2 evolution, which is believed to provide a proton-deficient environment around the catalyst to favor the formation of hydrogen-deficient carbon products. The present work provides general insights into the design of a catalyst with a high product selectivity and also the carbon evolution chemistry during a photocatalytic reaction.

Developing noble-metal-free photocatalysts highly flexible for separating the photogenerated electron-hole pairs is crucial for the solar-energy-driven photocatalysis, but still remains an open question. Herein, we fabricated two dimensional Co3S4 nanosheets with a thickness of about 10 nm, and applied the nanosheets to support CdS nanoparticles (∼5 nm) to form a noble-metal-free CdS/Co3S4 photocatalyst with a higher ability in charge separation. In the visible-light-driven photocatalytic H2O splitting, an enhanced H2 evolution (1083.9 μmol h−1) was achieved on CdS/Co3S4, as compared with those on the CdS-nanoparticle-loaded Co3S4 nanoparticles (775.5 μmol h−1) and noble-metal-based CdS/Pt photocatalyst (566.3 μmol h−1). The enhanced photocatalytic performance is the result of the multiple roles of the Co3S4 nanosheets in the photocatalytic reaction, including promoting electron-hole separation, providing catalytically active sites and suppressing the aggregation of the CdS nanoparticles responsible for light absorption.

Lead halide perovskites have attracted significant attention in the past few years due to their outstanding performance in photovoltaic devices. Nanoscale versions of these materials are also good candidates for light emitting devices. In this work, we synthesize perovskite nanocrystals using a surfactant-free method by introducing antimony iodide in the perovskite precursor. Surface-bound (CH3NH3)3Sb2I9 layers restrict the growth of CH3NH3PbI3, resulting in CH3NH3PbI3 nanocrystals of about 50 nm in size. Compared to the bulk perovskites, the nanocrystals show stronger photoluminescence. As there are no long-chain organic ligands on the surface that will inhibit the charge transport, these surfactant-free nanocrystals may have better performance in photoelectronic devices.

The ability to produce large-scale, reversible structural changes in a variety of materials by photoexcitation of a wide variety of azobenzene derivatives has been recognized for almost two decades. Because photoexcitation of trans-azobenzene produces the cis-isomer in solution, it has generally been inferred that the macroscopic structural changes occurring in materials are also initiated by a similar large-amplitude trans-to-cis isomerization. This work provides the first demonstration that a trans-to-cis photoisomerization occurs in polycrystalline azobenzene, and is consistent with the previously hypothesized nature of the trigger in the photoactuated mechanisms of the materials in question. It is also demonstrated that under low irradiance, trans-to-cis isomerization occurs in the solid (not via a pre-melted phase); and the presence of the cis-isomer thus lowers the melting point of the sample, providing a liquid phase. A variety of experimental techniques were employed, including X-ray diffraction measurements of polycrystalline azobenzene during exposure to laser irradiation and fluorescence measurements of the solid sample. A practical consequence of this work is that it establishes trans-azobenzene as an easily obtainable and well-defined control for monitoring photoinduced structural changes in X-ray diffraction experiments, using easily accessible laser wavelengths.

Developing efficient noble-metal-free catalysts for photocatalysis under the irradiation of visible light, which is the main part of sunlight (44%), would represent a significant step toward making photocatalysis a more competitive strategy for solar energy utilization. Herein, nanospheres (∼200 nm) containing dimolybdenum carbide and carbon (Mo2C@C) were used to support CdS nanoparticles (∼5 nm) to form a noble-metal-free CdS/Mo2C@C photocatalyst. CdS/Mo2C@C shows an enhanced visible-light-driven photocatalytic H2 evolution from water, with a H2 evolution rate of 554.3 μmol h–1, which is about 2 times higher than that on the widely used noble-metal-based CdS/Pt photocatalyst. Improved absorption of the visible light and separation of the photogenerated electron–hole pairs could be the origins for the enhanced photocatalytic activity of CdS/Mo2C@C. The findings of this work will open a new door for fabricating efficient noble-metal-free photocatalysts for visible-light-driven photocatalysis.

We present the time-correlated luminescence of isolated nanocrystals of five methylammonium lead mixed-halide perovskite compositions (CH3NH3PbBr3−xIx) that were synthesized with varying iodide and bromide anion loading. All analyzed nanocrystals had a spherical morphology with diameters in the range of 2 to 32 nm. The luminescence maxima of CH3NH3PbBr3−xIx nanocrystals were tuned to wavelengths ranging between 498 and 740 nm by varying the halide loading. Both CH3NH3PbI3 and CH3NH3PbBr3 nanocrystals exhibited no luminescence intermittency for more than 90% of the 250 s analysis time, as defined by a luminescence intensity three standard deviations above the background. The mixed halide CH3NH3PbBr0.75I0.25, CH3NH3PbBr0.50I0.50, and CH3NH3PbBr0.25I0.75 nanocrystals exhibited luminescence intermittency in 18%, 4% and 26% of the nanocrystals, respectively. Irrespective of luminescence intermittency, luminescence intensities were classified for each nanocrystal as: (a) constant, (b) multimodal, (c) photobrightening, and (d) photobleaching. Based on their photophysics, the CH3NH3PbBr3−xIx nanocrystals can be expected to be useful in a wide-range of applications where low and non-intermittent luminescence is desirable, for example as imaging probes and in films for energy conversion devices.

Metal–semiconductor nanohybrids (or heterostructures), such as Au–CdS, have become an important class of materials because of their role in photochemical hydrogen production and in other catalytic reactions. Here we report the results of photophysical studies of the interactions of these particles with ATTO dyes (ATTO 590 and 655), which are used as fluorescent probes in a wide range of spectroscopic techniques, most notably super-resolution microscopies. The most important feature of the Au–CdS particles is that they provide the possibility of selective excitation at either their CdS or their Au domains, which absorb preferentially at wavelengths shorter or longer than 500 nm, respectively, thus making possible an excited-state charge transfer reaction from ATTO. Fluorescence quenching of ATTO is dominated by charge transfer to either the CdS domain (λex = 400 nm) or the Au domain (λex = 570 nm). This quenching is quantified by steady-state and time-resolved absorption and fluorescence measurements, and ...

In this invited paper, we highlight some of our most recent work on the synthesis of low dimensional nanomaterials. Current graduate students and members of our group present four specific case systems: Nowotny–Juza phases, nickel phosphides, germanium-based core/shells, and organolead mixed-halide perovskites. Each system is accompanied by commentary from the student involved, which explains the motivation behind their work, as well as a protocol detailing the key experimental considerations involved in their synthesis. We trust these and similar efforts will help further advance our understanding of the broader field of synthetic nanomaterials chemistry, while, at the same time, highlighting how important this area is to the development of new materials for technologically relevant applications.

Organolead mixed-halide perovskites such as CH3NH3PbX3–aX′a (X, X′ = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the true chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples ma...

Photocatalytic CO2 reduction on metal-oxide-based catalysts is promising for solving the energy and environmental crises faced by mankind. The oxygen vacancy (V o) on metal oxides is expected to be a key factor affecting the efficiency of photocatalytic CO2 reduction on metal-oxide-based catalysts. Yet, to date, the question of how an V o influences photocatalytic CO2 reduction is still unanswered. Herein, we report that, on V o-rich gallium oxide coated with Pt nanoparticles (V o-rich Pt/Ga2O3), CO2 is photocatalytically reduced to CO, with a highly enhanced CO evolution rate (21.0 μmol·h−1) compared to those on V o-poor Pt/Ga2O3 (3.9 μmol·h−1) and Pt/TiO2(P25) (6.7 μmol·h−1). We demonstrate that the V o leads to improved CO2 adsorption and separation of the photoinduced charges on Pt/Ga2O3, thus enhancing the photocatalytic activity of Pt/Ga2O3. Rational fabrication of an V o is thereby an attractive strategy for developing efficient catalysts for photocatalytic CO2 reduction.