Efficient solar light-driven hydrogen generation using an Sn3O4 nanoflake/graphene nanoheterostructure.

Herein, we report Sn3O4 and Sn3O4 nanoflake/graphene for photocatalytic hydrogen generation from H2O and H2S under natural "sunlight" irradiation. The Sn3O4/graphene composites were prepared by a simple hydrothermal method at relatively low temperatures (150 °C). The incorporation of graphene in Sn3O4 exhibits remarkable improvement in solar light absorption, with improved photoinduced charge separation due to formation of the heterostructure. The highest photocatalytic hydrogen production rate for the Sn3O4/graphene nanoheterostructure was observed as 4687 µmol h-1 g-1 from H2O and 7887 µmol h-1 g-1 from H2S under natural sunlight. The observed hydrogen evolution is much higher than that for pure Sn3O4 (5.7 times that from H2O, and 2.2 times from H2S). The improved photocatalytic activity is due to the presence of graphene, which acts as an electron collector and transporter in the heterostructure. More significantly, the Sn3O4 nanoflakes are uniformly and parallel grown on the graphene surface, which accelerates the fast transport of electrons due to the short diffusion distance. Such a unique morphology for the Sn3O4 along with the graphene provides more adsorption sites, which are effective for photocatalytic reactions under solar light. This work suggests an effective strategy towards designing the surfaces of various oxides with graphene nanoheterostructures for high performance of energy-conversion devices.

Unique hierarchical SiO2@ZnIn2S4 marigold flower like nanoheterostructure for solar hydrogen production.

The novel marigold flower like SiO2@ZnIn2S4 nano-heterostructure was fabricated using an in situ hydrothermal method. The nanoheterostructure exhibits hexagonal structure with marigold flower like morphology. The porous marigold flower assembly was constructed using ultrathin nanosheets. Interestingly, the thickness of the nanopetal was observed to be 5-10 nm and tiny SiO2 nanoparticles (5-7 nm) are decorated on the surface of the nanopetals. As the concentration of SiO2 increases the deposition of SiO2 nanoparticles on ZnIn2S4 nanopetals increases in the form of clusters. The optical study revealed that the band gap lies in the visible range of the solar spectrum. Using X-ray photoelectron spectroscopy (XPS), the chemical structure and valence states of the as-synthesized SiO2@ZnIn2S4 nano-heterostructure were confirmed. The photocatalytic activities of the hierarchical SiO2@ZnIn2S4 nano-heterostructure for hydrogen evolution from H2S under natural sunlight have been investigated with regard to the band structure in the visible region. The 0.75% SiO2@ZnIn2S4 showed a higher photocatalytic activity (6730 µmol-1 h-1 g-1) for hydrogen production which is almost double that of pristine ZnIn2S4. Similarly, the hydrogen production from water splitting was observed to be 730 µmol-1 h-1 g-1. The enhanced photocatalytic activity is attributed to the inhibition of charge carrier separation owing to the hierarchical morphology, heterojunction and crystallinity of the SiO2@ZnIn2S4.

Plasmonic Ag decorated CdMoO4 as an efficient photocatalyst for solar hydrogen production.

The synthesis of Ag-nanoparticle-decorated CdMoO4 and its photocatalytic activity towards hydrogen generation under sunlight has been demonstrated. The CdMoO4 samples were synthesized by a simple hydrothermal approach in which Ag nanoparticles were in situ decorated on the surface of CdMoO4. A morphological study showed that 5 nm spherical Ag nanoparticles were homogeneously distributed on the surface of CdMoO4 particles. The UV/DRS spectra show that the band gap of CdMoO4 was narrowed by the incorporation of a small amount of Ag nanoparticles. The surface plasmonic effect of Ag shows broad absorption in the visible region. The enhanced photocatalytic hydrogen production activities of all the samples were evaluated by using methanol as a sacrificial reagent in water under natural sunlight conditions. The results suggest that the rate of photocatalytic hydrogen production using CdMoO4 can be significantly improved by loading 2% Ag nanoparticles: i.e. 2465 µmol h-1 g-1 for a 15 mg catalyst. The strong excitation of surface plasmon resonance (SPR) absorption by the Ag nanoparticles was found in the Ag-loaded samples. In this system, the role of Ag nanoparticles on the surface of CdMoO4 has been discussed. In particular, the SPR effect is responsible for higher hydrogen evolution under natural sunlight because of broad absorption in the visible region. The current study could provide new insights for designing metal/semiconductor interface systems to harvest solar light for solar fuel generation.

Correction: Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach.

Correction for 'Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach' by Rajendra P. Panmand et al., Nanoscale, 2017, 9, 4801-4809.

Hierarchical CdMoO4 nanowire-graphene composite for photocatalytic hydrogen generation under natural sunlight.

Herein, a facile in situ solvothermal technique for the synthesis of a CdMoO4/graphene composite photocatalyst is reported. Graphene oxide (GO) was synthesised by an improved Hummers' method and was further used for the in situ synthesis of graphene via GO reduction and the formation of a CdMoO4 nanowire/graphene composite. The structural phase formation of tetragonal CdMoO4 was confirmed from X-ray diffraction measurements. The small nanoparticle assembled nanowires, prismatic microsphere morphology and crystalline nature of the synthesized material were investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Due to its unique morphology and stability, the CdMoO4/graphene composite was used as a photocatalyst for H2O splitting. In comparison to pristine CdMoO4, the CdMoO4/graphene composite showed the best hydrogen evolution rate, i.e. 3624 µmole h-1 g-1, with an apparent quantum yield of 30.5%. The CdMoO4/graphene composite has a higher photocatalytic activity due to the inhibition of charge carrier recombination. H2 production measurements showed that the ternary semiconductor/graphene composite has enhanced photocatalytic activity for H2 generation.

Surface modified Li4Ti5O12 by paper templated approach for enhanced interfacial Li+ charge transfer in Li-ion batteries.

The Li4Ti5O12 (LTO) and lithium silicate (LS) surface modified LTO have been demonstrated by a unique paper templated method. Comparative study of structural characterization with electrochemical analysis was demonstrated for pristine and modified Li4Ti5O12. Structural and morphological study shows the existence of the cubic spinel structure with highly crystalline 250-300 nm size particles. The LS modified LTO shows the deposition of 10-20 nm sized LS nanoparticles on cuboidal LTO. Further, X-ray photoelectron spectroscopy (XPS) confirms the existence of Li2SiO3 (LS) in the modified LTO. The electrochemical performance was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge. The modified LTO with 2% LS (LTS2) exhibited excellent rate capability compare to pristine LTO i.e. 182 mA h g-1 specific capacity at a current rate, 50 mA g-1 with remarkable cycling stability up to 1100 cycles at a current rate of 800 mA g-1. The lithium ion full cell of modified LTO with LS as an anode and LiCoO2 as a cathode exhibited a remarkably reversible specific capacity i.e. 110 mA h g-1. Both electronic and ionic conductivities of pristine LTO are observed to be enhanced by incorporation of appropriate amount of LS in LTO due to a larger surface contact at the interface of electrode and electrolyte. More significantly, the versatile paper templated synthesis approach of modified LTO with LS provides densely packed highly crystalline particles. Additionally, it exhibits lower Warburg coefficient and higher Li ion diffusion coefficient which in turn accelerate the interfacial charge transfer process, which is responsible for enhanced stable electrochemical performance. The detailed mechanism is expressed and elaborated for better understanding of enhanced electrochemical performance due to the surface modification.

Nanostructured N-doped orthorhombic Nb2O5 as an efficient stable photocatalyst for hydrogen generation under visible light.

The synthesis of orthorhombic nitrogen-doped niobium oxide (Nb2O5-xNx) nanostructures was performed and a photocatalytic study carried out in their use in the conversion of toxic H2S and water into hydrogen under UV-Visible light. Nanostructured orthorhombic Nb2O5-xNx was synthesized by a simple solid-state combustion reaction (SSCR). The nanostructural features of Nb2O5-xNx were examined by FESEM and HRTEM, which showed they had a porous chain-like structure, with chains interlocked with each other and with nanoparticles sized less than 10 nm. Diffuse reflectance spectra depicted their extended absorbance in the visible region with a band gap of 2.4 eV. The substitution of nitrogen in place of oxygen atoms as well as Nb-N bond formation were confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. A computational study (DFT) of Nb2O5-xNx was also performed for investigation and conformation of the crystal and electronic structure. N-Substitution clearly showed a narrowing of the band gap due to N 2p bands cascading above the O 2p band. Considering the band gap in the visible region, Nb2O5-xNx exhibited enhanced photocatalytic activity toward hydrogen evolution (3010 µmol h-1 g-1) for water splitting and (9358 µmol h-1 g-1) for H2S splitting under visible light. The enhanced photocatalytic activity of Nb2O5-xNx was attributed to its extended absorbance in the visible region due to its electronic structure being modified upon doping, which in turn generates more electron-hole pairs, which are responsible for higher H2 generation. More significantly, the mesoporous nanostructure accelerated the supression of electron and hole recombination, which also contributed to the enhancement of its activity.

Growth study of hierarchical Ag3PO4/LaCO3OH heterostructures and their efficient photocatalytic activity for RhB degradation.

We have demonstrated the synthesis of Ag3PO4/LaCO3OH (APO/LCO) heterostructured photocatalysts by an in situ wet chemical method. From pre-screening evaluations of photocatalysts with APO/(x wt% LCO) composites with mass ratios of x = 5, 10, 15, 20, 25 and 30 wt%, we found that the APO/LCO (20 wt%) exhibited a superior photocatalytic activity for organic pollutant remediation. Therefore, an optimised photocatalyst APO/LCO (20 wt%) is selected for the present study and we investigate the effect of a mixed solvent system (H2O:THF) on the morphology, which has a direct effect on the photocatalytic performance. Interestingly, a profound effect on the morphological features of APO/LCO20 heterostructures was observed with variation in the ratio of the solvent system. From the FESEM study it is observed that the LCO spherical nanoparticles are transformed into nanorods with the variation of THF into the solvent system. Moreover, these LCO nanorods make intimate contact with the APO microstructures which is helpful for the improvement of the photocatalytic activity. The photocatalytic activities of the APO/LCO composites with different solvent ratios were evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. Excellent photocatalytic activity was observed for the APO/LCO-2 (H2O : THF = 60 : 40) sample. This might be due to uniform covering of the APO microstructures by fine LCO rod-like structures offering intimate contact between the APO and LCO and providing proper channels for the degradation reactions. Furthermore, with an increasing THF volume ratio in the reaction system there was an increase of the dimensions of the LCO rod-like structures and also a loose compactness of their uniform intimate contact between the APO/LCO heterostructures. All in all, the enhanced photocatalytic activity of the APO/LCO heterostructures is attributed to the collective co-catalytic effect of LCO, by providing accelerated charge separation through the heterojunction interface, and THF, by helping to tune the unique morphological features which eventually facilitate the photocatalysis process.

Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach.

Herein, we demonstrated a green approach for the synthesis of high surface area (850 m2 g-1) mesoporous perforated graphene (PG) from Bougainvillea flower for the first time using a template free single-step method. The existence of PG was confirmed by XRD, Raman spectroscopy, FESEM, and FETEM. Surprisingly, FETEM clearly showed 5-10 nm perforation on the graphene sheets. More significantly, these mesoporous perforated graphene sheets can be produced in large scale using the present green approach. Considering high surface area and unique perforated graphene architecture, these PGs were studied for supercapacitor applications in detail without any chemical or physical activation. The nanoporosity and high conductivity of PG derived from Bougainvillea flower exhibited excellent supercapacitive performance. According to the supercapacitor study, the synthesized perforated graphene sheets conferred a very high specific capacitance of 458 F g-1 and an energy density of 63.7 Wh kg-1 at the power density of around 273.2 Wh kg-1 in aqueous 1 M Na2SO4. Significantly, the areal capacitance of PG was observed to be very high, i.e. 67.2 mF cm-2. The cyclability study results showed excellent stability of synthesized perforated graphene sheets up to 10 000 cycles. Note that the specific and areal capacitance and the energy density of the synthesized PGs are much higher than the earlier reported values. The high supercapacitive performance may be due to high surface area and mesoporosity of PG. The present approach has a good potential to produce cheaper and high surface area PG. These PGs are good candidates as an anode material in the lithium-ion battery.

Nanostructured CdS sensitized CdWO4 nanorods for hydrogen generation from hydrogen sulfide and dye degradation under sunlight.

In this report, CdS nanoparticles have been grown on the surface of CdWO4 nanorods via an in-situ approach and their high photocatalytic ability toward dye degradation and H2 evolution from H2S splitting under visible light has been demonstrated. The structural and optical properties as well as morphologies with varying amount of CdS to form CdS@CdWO4 have been investigated. Elemental mapping and high resolution transmission electron microscopy (HRTEM) analysis proved the sensitization of CdWO4 nanorods by CdS nanoparticles. A decrease in the PL emission of CdWO4 was observed with increasing amount of CdS nanoparticles loading possibly due to the formation of trap states. Considering the band gap in visible region, the photocatalytic study has been performed for H2 production from H2S and dye degradation under natural sunlight. The steady evolution of H2 was observed from an aqueous H2S solution even without noble metal. Moreover, the rate of photocatalytic H2 evolution over CdS modified CdWO4 is ca. 5.6 times higher than that of sole CdWO4 under visible light. CdS modified CdWO4 showed a good ability toward the photo-degradation of methylene Blue. The rate of dye degradation over CdS modified CdWO4 is ca. 7.4 times higher than that of pristine CdWO4 under natural sunlight. With increase in amount of CdS nanoparticle loading on CdWO4 nanorods the hydrogen generation was observed to be decreased where as dye degradation rate is increased. Such nano-heterostructures may have potential in other photocatalytic reactions.

Growth of Bi2Te3 quantum dots/rods in glass: a unique highly stable nanosystem with novel functionality for high performance magneto optical devices.

Magneto optical materials are currently of great interest, primarily for modern applications in optical isolation, modulation and switching in telecommunication. However, single crystals are the benchmark materials still used in these devices which are rather expensive and very difficult to fabricate. In this context, we are reporting herewith a stable and novel Bi(2)Te(3) quantum dot-glass nanosystem obtained using a controlled thermo-chemical method. The Q-dots of hexagonal Bi(2)Te(3) of size 4 to 14 nm were grown along the <1 1 3> direction. Surprisingly, we obtained quantum rods of Bi(2)Te(3) of size 6 × 10 nm for the first time. The strong quantum confinement in the nanosystem is clearly shown by the optical study. The band gap of the host glass was drastically reduced (from 4.00 to 1.88 eV) due to the growth of Bi(2)Te(3) quantum dots whereas photoluminescence showed a Stokes shift ~175 meV. Faraday Rotation (FR) investigations of the Bi(2)Te(3) quantum dot-glass nanosystem show a nonlinear response in Verdet constant with a decrease in the Bi(2)Te(3) dot sizes. The Bi(2)Te(3) Q-dot-glass nanosystem with ~4 nm dots shows significant enhancement (70 times) in Verdet constant compared to the host glass and more radically better than conventional single crystal (TGG). This is the first time that such a type of unique nanosystem has been architectured and has given extremely good magneto-optical performance. We strongly feel that this novel nanosystem has tremendous applications in magneto-optical devices. It is noteworthy that expensive single crystals can be replaced with this cost effective novel glass nanosystem. Interestingly, the present quantum dot-glass nanosystem can be transformed into optical fibers very easily, which will have an exceptionally high impact on the fabrication of high performance magneto optical devices.