Immobilization of isolated dimethyltin species on crystalline silicates through surface modification of layered octosilicate

Single metal atoms supported on silica are attractive catalysts, and precise control of the local environment around the metal species is essential. Crystalline silica is useful as an efficient support for the incorporation of well-defined metal sites. Dimethyltin species were regularly grafted onto the layer surfaces of layered octosilicate, a type of two-dimensional (2D) crystalline silica. Dimethyltin dichlorides react with the surface silanol (SiOH) groups of the silicate layers. The formation of Si-O-Sn bonds was confirmed by 29Si magic-angle spinning (MAS) NMR. X-ray absorption fine structure (XAFS) analysis showed the four-coordinated Sn species. These results suggested the presence of well-defined dipodal dimethyltin species on the layer surfaces. The degree of modification of the silanol groups with the dimethyltin groups increased with increasing amounts of dimethyltin dichloride; however, the maximum degree of modification was approximately 50%. This value was interpreted as an alternate modification of the octosilicate reaction sites with dimethyltin groups. These results demonstrate the potential for developing highly active single metal catalysts with a high density of regularly arranged active sites on high surface area supports.

Template-Assisted SnO2: Synthesis, Composition, and Photoelectrocatalytical Properties

A series of tin oxides were synthesized with polystyrene microspheres (250 nm) as the template. It was shown that an increase in the template content led to increasing specific pore volume and to the formation of bimodal pore structure with pores of 9 and 70 nm in diameter. Addition of cetyltrimethylammonium bromide (CTAB) during synthesis led to the formation of friable structures (SEM data), to an increase in the average pore diameter from 19 to 111 nm, and to the formation of macropores of 80–400 nm in size. All materials had similar surface properties and cassiterite structure with 5.9–10.8 nm coherent scattering region (XRD data). Flat-band potentials of the samples were determined and their photoelectrocatalytic properties to oxidation of water and methanol were studied in the potential range of 0.4–1.6 V RHE. It was shown that the sample obtained using CTAB was characterized by lower flat-band potential value, but appeared significantly higher photocurrent in methanol oxidation, which resulted from enhanced macro-meso-porous structure to facilitate methanol pore diffusion.

Visible Light Driven Ultrasensitive and Selective NO2 Detection in Tin Oxide Nanoparticles with Sulfur Doping Assisted by l-Cysteine

In the pandemic era, the development of high-performance indoor air quality monitoring sensors has become more critical than ever. NO₂ is one of the most toxic gases in daily life, which induces severe respiratory diseases. Thus, the real-time monitoring of low concentrations of NO₂ is highly required. Herein, a visible light-driven ultrasensitive and selective chemoresistive NO₂ sensor is presented based on sulfur-doped SnO₂ nanoparticles. Sulfur-doped SnO₂ nanoparticles are synthesized by incorporating l-cysteine as a sulfur doping agent, which also increases the surface area. The cationic and anionic doping of sulfur induces the formation of intermediate states in the band gap, highly contributing to the substantial enhancement of gas sensing performance under visible light illumination. Extraordinary gas sensing performances such as the gas response of 418 to 5 ppm of NO₂ and a detection limit of 0.9 ppt are achieved under blue light illumination. Even under red light illumination, sulfur-doped SnO₂ nanoparticles exhibit stable gas sensing. The endurance to humidity and long-term stability of the sensor are outstanding, which amplify the capability as an indoor air quality monitoring sensor. Overall, this study suggests an innovative strategy for developing the next generation of electronic noses.

Efficient perovskite solar cells via improved carrier management

Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols^1-3, chemical compositions^4,5 and phase stabilization methods^6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage)¹¹. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit¹². Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO₂). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.

Fully reversible lithium storage of tin oxide enabled by self-doping and partial amorphization

SnO₂ has a high theoretical capacity of 1493 mA h g^-1 as an anode material for Li-ion batteries, but its full reversibility is difficult to achieve upon cycling due to the sluggish kinetics. We for the first time demonstrate a fully reversible SnO₂ anode for Li-ion batteries enabled by self-doping and partial amorphization by anchoring its nanoparticles on a graphene/single walled carbon nanotube hybrid framework. The uniquely structured nanocomposite containing 74% SnO₂ exhibits high reversible capacities together with good rate and cycling capabilities. For instance, the composite anode retains an overall capacity of 1215 mA h g^-1 (1425 mA h g^-1 for SnO₂) after 200 cycles at 0.1 A g^-1, which is very close to its theoretical capacity. Moreover, an overall capacity of 947 mA h g^-1 (1062 mA h g^-1 for SnO₂) can be delivered at a higher rate (1 A g^-1) with 98% capacity retention over 350 cycles. This exceptional performance can be attributed to the formation of highly dispersed metallic Sn in the Li₂O matrix during cycling, which is caused by the unique two-step lithiation mechanism of the self-doped and partially amorphous SnO₂ nanoparticles. A similar strategy can also be applied to develop other high-performance electrodes with conversion reactions.

Steering Charge Kinetics of Tin Niobate Photocatalysts: Key Roles of Phase Structure and Electronic Structure

Tin niobate photocatalysts with the phase structures of froodite (SnNb₂O₆) and pyrochlore (Sn₂Nb₂O₇) were obtained by a facile solvothermal method in order to explore the impact of phase structure and electronic structure on the charge kinetics and photocatalytic performance. By employing tin niobate as a model compound, the effects of phase structure over electronic structure, photocatalytic activity toward methyl orange solution and hydrogen evolution were systematically investigated. It is found that the variation of phase structure from SnNb₂O₆ to Sn₂Nb₂O₇ accompanied with modulation of particle size and band edge potentials that has great consequences on photocatalytic performance. In combination with the electrochemical impedance spectroscopy (EIS), transient photocurrent responses, transient absorption spectroscopy (TAS), and the analysis of the charge-carrier dynamics suggested that variation of electronic structure has great impacts on the charge separation and transfer rate of tin niobate photocatalysts and the subsequent photocatalytic performance. Moreover, the results of the X-ray photoelectron spectroscopy (XPS) indicated that the existent of Sn⁴⁺ species in Sn₂Nb₂O₇ could result in a decrease in photocatalytic activity. Photocatalytic test demonstrated that the SnNb₂O₆ (froodite) catalyst possesses a higher photocatalytic activity toward MO degradation and H₂ evolution compared with the sample of Sn₂Nb₂O₇ (pyrochlore). On the basis of spin resonance measurement and trapping experiment, it is expected that photogenerated holes, O₂^-•, and OH^• active species dominate the photodegradation of methyl orange.

Synthesis and Characterization of Modified BiOCl and Their Application in Adsorption of Low-Concentration Dyes from Aqueous Solution

The synthesis and characterization of BiOCl and Fe³⁺-grafted BiOCl (Fe/BiOCl) is reported that are developed as efficient adsorbents for the removal of cationic dyes rhodamine B (RhB) and methylene blue (MB) as well as anionic dyes methyl orange (MO) and acid orange (AO) from aqueous solutions with low concentration of 0.01~0.04 mmol/L. Characterizations by various techniques indicate that Fe³⁺ grafting induced more open porous structure and higher specific surface area. Both BiOCl and Fe/BiOCl with negatively charged surfaces showed excellent adsorption efficiency toward cationic dyes, which could sharply reach 99.6 and nearly 100% within 3 min on BiOCl and 97.0 and 98.0% within 10 min on Fe/BiOCl for removing RhB and MB, respectively. However, Fe/BiOCl showed higher adsorption capacity than BiOCl toward ionic dyes. The influence of initial dye concentration, temperature, and pH value on the adsorption capacity is comprehensively studied. The adsorption process of RhB conforms to Langmuir adsorption isotherm and pseudo-second-order kinetic feature. The excellent adsorption capacities of as-prepared adsorbents toward cationic dyes are rationalized on the basis of electrostatic attraction as well as open porous structure and high specific surface area. In comparison with Fe/BiOCl, BiOCl displays higher selective efficiency toward cationic dyes in mixed dye solutions.

A multi-technique comparison of the electronic properties of pristine and nitrogen-doped polycrystalline SnO2

Nitrogen doped tin(iv) oxide (SnO2) materials in the form of nanometric powders have been prepared by precipitation with ammonia. Their properties have been compared with those of undoped materials obtained in a similar way using various physical techniques such as photoelectron spectroscopies (XPS and UPS), UV-Vis-NIR spectroscopy and electron paramagnetic resonance (EPR). Nitrogen doping leads to the formation of various nitrogen containing species, the more relevant of which is a nitride-type ionic species, based on the substitution of a lattice oxygen atom with a nitrogen atom. This species exists in two forms, paramagnetic (hole centre, formally N(2-)) and diamagnetic (N(3-)). The mutual ratio of the two species varies according to the oxidation state of the material. The doped solid, like most of the semiconducting oxides, tends to lose oxygen forming oxygen vacancies upon annealing under vacuum and leaving an excess of electrons in the solid. The stoichiometry of the solid can thus be markedly changed depending on the external conditions. Excess electrons are present both as itinerant electrons in the conduction band and as Sn(ii) states lying close to the valence band maximum. The presence of nitride-type centres, which are low energy states located below the top of the valence band, decreases the energy cost for the formation of oxygen vacancies by O2 release from the lattice. This particular feature of the doped system represents a severe limit to the preparation of a p-type SnO2via nitrogen doping.

Facile Synthesis of Wormhole-Like Mesoporous Tin Oxide via Evaporation-Induced Self-Assembly and the Enhanced Gas-Sensing Properties

Wormhole-like mesoporous tin oxide was synthesized via a facile evaporation-induced self-assembly (EISA) method, and the gas-sensing properties were evaluated for different target gases. The effect of calcination temperature on gas-sensing properties of mesoporous tin oxide was investigated. The results demonstrate that the mesoporous tin oxide sensor calcined at 400 °C exhibits remarkable selectivity to ethanol vapors comparison with other target gases and has a good performance in the operating temperature and response/recovery time. This might be attributed to their high specific surface area and porous structure, which can provide more active sites and generate more chemisorbed oxygen spices to promote the diffusion and adsorption of gas molecules on the surface of the gas-sensing material. A possible formation mechanism of the mesoporous tin oxide and the enhanced gas-sensing mechanism are proposed. The mesoporous tin oxide shows prospective detecting application in the gas sensor fields.

Composite Photocatalysts Containing BiVO4 for Degradation of Cationic Dyes

The creation of composite structures is a commonly employed approach towards enhanced photocatalytic performance, with one of the key rationales for doing this being to separate photoexcited charges, affording them longer lifetimes in which to react with adsorbed species. Here we examine three composite photocatalysts using either WO₃, TiO₂ or CeO₂ with BiVO₄ for the degradation of model dyes Methylene Blue and Rhodamine B. Each of these materials (WO₃, TiO₂ or CeO₂) has a different band edge energy offset with respect to BiVO₄, allowing for a systematic comparison of these different arrangements. It is seen that while these offsets can afford beneficial charge transfer (CT) processes, they can also result in the deactivation of certain reactions. We also observed the importance of localized dye concentrations, resulting from a strong affinity between it and the surface, in attaining high overall photocatalytic performance, a factor not often acknowledged. It is hoped in the future that these observations will assist in the judicious selection of semiconductors for use as composite photocatalysts.

The first synthesis of Bi self-doped Bi2MoO6–Bi2Mo3O12 composites and their excellent photocatalytic performance for selective oxidation of aromatic alkanes under visible light irradiation

Bi self-doped Bi₂MoO₆–Bi₂Mo₃O₁₂ composites were first synthesized by a one-step method and they showed excellent photocatalytic performance in the selective oxidation of aromatic alkanes under visible light irradiation.

Non-stoichiometric SnS microspheres with highly enhanced photoreduction efficiency for Cr(vi) ions

Sn²⁺ self-doped SnS microparticles were synthesized via a simple template-free hydrothermal route. The ability to tune the band structure while minimizing defect generation makes self-doped SnS an efficient photocatalyst for treating waste water.

Dendrimer-based preparation and luminescence studies of SiO2 fibers doping Eu3+ activator in interstitial sites

The formation mechanism of SiO₂:Eu³⁺ fibers.

Enhanced visible light photocatalytic activity in BiOCl/SnO2: heterojunction of two wide band-gap semiconductors

A series of BiOCl/SnO₂ heterojunctions exhibiting exceptional visible light photocatalytic performance has been successfully prepared using a two-step solution route.