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Developing anatase/rutile phase-junction in TiO2 to construct Z-scheme system is quite effective to improve its photoelectrochemical activity. In this work, the anatase/rutile phase-junction Ag/TiO2 nanocomposites are developed as photocathodes for hydrogen production. The optimized Ag/TiO2 nanocomposite achieves a high current density of 1.28 mA cm−2, an incident photon-to-current conversion efficiency (IPCE) of 10.8 %, an applied bias photon-to-current efficiency (ABPE) of 0.32 at 390 nm and a charge carriers’ lifetime up to 2000s. Such enhancement on photoelectrochemical activity can be attributed to: (i) the generated Z-scheme system in the anatase/rutile phase-junction Ag/TiO2 photocathode enhances the separation, diffusion and transformation of electron/hole pairs inside the structure, (ii) Ag nanodots modification in the anatase/rutile phases leading to the tuned band gap with enhanced light absorption and (iii) the formed Schottky barrier after Ag nanodots surface modification provides enough electron traps to avoid the recombination of photogenerated electrons and holes. Our results here suggest that developing phase-junction nanocomposite as photocathode will provide a new vision for their enhanced photoelectrochemical generation of hydrogen.

Herein we develop a novel and effective alkoxide hydrolysis approach to in-situ construct the trimanganese tetraoxide (Mn3O4)/graphene nanostructured composite as high-performance anode material for lithium-ion batteries (LIBs). This is the first report on the synthesis of Mn3O4/graphene composite via a facile hydrolysis of the manganese alkoxide (Mn-alkoxide)/graphene precursor. Before hydrolysis, two dimensional (2D) Mn-alkoxide nanoplates are closely adhered to 2D graphene nanosheets via Mn-O chemical bonding. After hydrolysis, the Mn-alkoxide in-situ converts to Mn3O4, while the Mn-O bond is preserved. This leads to a robust Mn3O4/graphene hybrid architecture with 15 nm Mn3O4 nanocrystals homogeneously anchoring on graphene nanosheets. This not only prevents the Mn3O4 nanocrystals agglomeration but also inversely mitigates the graphene nanosheets restacking. Moreover, the flexible and conductive graphene nanosheets can accommodate the volume change. This maintains the structural and electrical integrity of the Mn3O4/graphene electrode during the cycling process. As a result, the Mn3O4/graphene composite displays superior lithium storage performance with high reversible capacity (741 mAh g−1 at 100 mA g−1), excellent rate capability (403 mAh g−1 at 1000 mA g−1) and long cycle life (527 mAg g−1 after 300 cycles at 500 mA g−1). The electrochemical performance highlights the importance of rational design nanocrystals anchoring on graphene nanosheets for high-performance LIBs application.

Lithium-sulfur (Li-S) batteries have attracted significant attention for their high specific capacity, non-toxic and harmless advantages. However, the shuttle effect limits their development. In this work, small-sized tin disulfide (SnS2) nanoparticles are embedded between interlayers of two-dimensional porous carbon nanosheets (PCNs), forming a multi-functional nanocomposite (PCN-SnS2) as a cathode carrier for Li-S batteries. The graphitized carbon nanosheets improve the overall conductivity of the electrode, and the abundant pores not only facilitate ion transfer and electrolyte permeation, but also buffer the volume change during the charge and discharge process to ensure the integrity of the electrode material. More importantly, the physical confinement of PCN, as well as the strong chemical adsorption and catalytic reaction of small SnS2 nanoparticles, synergistically reduce the shuttle effect of polysulfides. The interaction between a porous layered structure and physical-chemical confinement gives the PCN-SnS2-S electrode high electrochemical performance. Even at a high rate of 2 C, a discharge capacity of 650 mA h g−1 is maintained after 150 cycles, underscoring the positive results of SnS2 based materials for Li S batteries. The galvanostatic intermittent titration technique results further confirm that the PCN-SnS2-S electrode has a high Li+ transmission rate, which reduces the activation barrier and improves the electrochemical reaction kinetics. This work provides strong evidence that reducing the size of SnS2 nanostructures is beneficial for capturing and reacting with polysulfides to alleviate their shuttle effect in Li-S batteries.

Li-Se battery is a promising energy storage candidate owing to its high theoretical volumetric capacity and safe operating condition. In this work, for the first time, we report using the whole organic Melamine-based porous polymer networks (MPNs) as a precursor to synthesize a N, O, S co-doped hierarchically porous carbon nanobelts (HPCNBs) for both Li-ion and Li-Se battery. The N, O, S co-doping resulting in the defect-rich HPCNBs provides fast transport channels for electrolyte, electrons and ions, but also effectively relieve volume change. When used for Li-ion battery, it exhibits an advanced lithium storage performance with a capacity of 345 mAh g−1 at 500 mA g−1 after 150 cycles and a superior rate capacity of 281 mAh g−1 even at 2000 mA g−1. Further density function theory calculations reveal that the carbon atoms adjacent to the doping sites are electron-rich and more effective to anchor active species in Li-Se battery. With the hierarchically porous channels and the strong dual physical–chemical confinement for Li2Se, the Se@ HPCNBs composite delivers an ultra-stable cycle performance even at 2 C after 1000 cycles. Our work here suggests that introduce of heteroatoms and defects in graphite-like anodes is an effective way to improve the electrochemical performance.

We report the well-designed active {1 1 0} and {1 1 1} faceted Cu2O hollow nanospheres (Cu2O-HNs) for the quick removal of the high concentration pollutants in water. For the first time, these Cu2O-HNs combine the advantages of the active facets, hollow structure and nanostructures. The abundance of dangling Cu atoms in two active facets results in positively charged surface to effectively react with the negatively charged pollutants. The hollow structure provides the opportunity to take full use of these active sites. Consequently, the active faceted Cu2O-HNs demonstrate excellent adsorption and photodegradation capacities for high concentrated anionic dyes. The smallest Cu2O-HNs (~100 nm) can adsorb ~90% of methyl blue (MB) (100 mg L−1) in 10 min and degrade ~92% of MB (100 mg L−1) in 10 min under visible-light. In particular, a film consisting of the smallest Cu2O-HNs can quickly remove high concentrated organic dyes and be reused after solar light irradiation for 10 min in air, showing the promising practical application for the removal of organic pollutants.

Lithium-sulfur batteries with high theoretical specific capacity are quite promising in energy storage systems. The application of lithium-sulfur batteries however has mainly been hampered by the severe shuttle effect of polysulfides during the charging/discharging process. Here, we report the in situ self-assembling of ultra-thin flexible polyaniline layer decorated manganese dioxide nanoparticles (PANI-MnO2) to form a three-dimensional hierarchically porous network as a sulfur host for lithium-sulfur batteries. The hierarchically porous PANI-MnO2 network not only provides a porous structure to alleviate the volume expansion, but also offers fast channels to accelerate the transfer of active species, electrons and ions to improve the redox reaction kinetics. The as-fabricated PANI-MnO2-S electrode thus demonstrates excellent electrochemical performance, with a stable capacity up to 1195 mA h g-1 at 0.5C after 100 cycles. In particular, the hierarchically porous PANI-MnO2 network employs an extraordinary chemical process for polysulfides to form active thiosulfates, which are further converted into Li2S. This significantly suppresses the shuttle effect, thus providing the possibility for fast charging. As a result, the PANI-MnO2-S electrode exhibits a discharge capacity of 640 mA h g-1 at 2C after 500 cycles. Even at a high sulfur loading of 4.0 mg cm-2, a stable areal capacity of ∼3.12 mA h cm-2 is achieved at 1C after 200 cycles.

The development of lithium-ion batteries using transition metal oxides has recently become more attractive, due to their higher specific capacities, better rate capability, and high energy densities. Herein, the in situ growth of advanced mesoporous CuO/O-doped g-C3N4 nanospheres is carried out in a two step hydrothermal process at 180 °C and annealing in air at 300 °C. When used as an anode material, the CuO/O-doped g-C3N4 nanospheres achieve a high reversible discharge specific capacity of 738 mAhg-1 and a capacity retention of ∼75.3% after 100 cycles at a current density 100 mAg-1 compared with the pure CuO (412 mAhg-1, 47%) and O-doped g-C3N4 (66 mAhg-1, 53%). Even at high current density 1 Ag-1, they exhibit a reversible discharge specific capacity of 503 mAhg-1 and capacity retention ∼80% over 500 cycles. The excellent electrochemical performance of the CuO/O-doped g-C3N4 nanocomposite is attributed to the following factors: (I) the in situ growing CuO/O-doped g-C3N4 avoids CuO nanoparticle aggregation, leading to the improved lithium ion transfer and electrolyte penetration inside the CuO/O-doped g-C3N4 anode, thus promoting the utilization of CuO; (II) the porous structure provides efficient space for Li+ transfer during the insertion/extraction process to avoid large volume changes; (III) the O-doping g-C3N4 decreases its band gap, ensuring the increased electrical conductivity of CuO/O-doped g-C3N4; and (IV) the strong interaction between CuO and O-doped g-C3N4 ensures the stability of the structure during cycling.

The hydrogen evolution reaction (HER) achieved via electrochemical and photoelectrochemical measurements in an acid electrolyte (0.5 M H2SO4) was examined on hexagonal WO3 photoanodes of different morphological structures comprised of WO3 nanotubes (NT), nanorods (NR) and nanospheres (NS). The WO3 synthesized using free (NR) and inorganic templates (NS and NT) thru a new sonication/hydrothermal route was comprehensively characterized utilizing XRD, TEM-SAED, photoluminescence, UV–Vis diffuse reflectance, Raman, FTIR and N2 adsorption techniques. Herein, the WO3 NT with an average diameter of 2.9 nm and energy gap of 2.3 eV shows the best HER activity with an overpotential of −500 mV to offer a current density of 8.0 mA cm−2 that strikingly enhanced into 14 mA cm−2; at −410 mV, under visible light illumination (λ > 420). The electrochemical properties determined by cyclic voltammetry, EIS and Tafel plots argued that the activity of WO3 NT is accelerated due to small size, enhanced wettability (WO3.H2O); so as to facilitating the reaction with the electrolyte, together with the 1D assisted electron transfer. It was also emphasized that the HER activity is mainly controlled by the high oxygen vacancies; emphasized via XPS technique, decreased resistances and crystal orientations when using WO3 NTs rather than the high surface texturing properties devoted for the WO3 NRs (SBET = 54.3 m2 g−1, Vp = 0.084 cm3 g−1, pore radius = 6.5 nm). This wok provides a new approach for synthesizing a free Pt WO3 NTs photo-electrocatalyst with excellent stability; towards a remarkable HER, as examined via chronopotentiometry technique for 100 h.

ZnO thin films were prepared by chemical vapour transport method in inductively coupled plasma (ICP). The films were synthesized at different substrate positions and various oxygen/argon ratios. X-ray diffraction (XRD) revealed that all the synthesized films at different positions are mixture of hexagonal ZnO and hexagonal Zn phases. The relative peak integrated intensity (RPII) of the ZnO phase is 83.6, 25.3 and 45.3%, for positions 1, 2 and 3, respectively. Morphology of ZnO films was found to be sensitive to substrate position. Flat flakes, bended nanowires (NWs) and nanoparticles morphologies are observed for positions 1, 2 and 3, respectively. The sample synthesized at 1 is stoichiometric, whereas the samples prepared in positions 2 and 3 are sub-stoichiometric. The films prepared at positions 1 and 3 have relatively high transmittance and low reflectance values, whereas the film prepared at position 2 has low transmittance and high reflectance. The ZnO film prepared at position 2 is hydrophobic with water contact angle of 112.2°, which can be used as self-cleaning coating. For ZnO films prepared with various O2 ratios, the RPII was 83.2, 88.0, 96.4 and 100% for films prepared with 10, 20, 30 and 40%, respectively. With increasing O2 ratio, the nanograins became bigger and the stoichiometry improved. The transmittance and optical bandgap increased, whereas the reflectance and refractive index decreased with increase in O2 ratio. The ZnO film synthesized with 30% O2 ratio has the highest figure of merit (FOM) value; thus, this film may be considered as the best ZnO film for transparent conducting coating applications.

Two dimensional (2D) nanostructures are promising to provide a new hierarchical architecture for transition metal oxides (TMOs) with outstanding lithium storage. In this work, we grew ordered CuO nanorods on 2D Cu/g-C3N4 nanosheets to form the hierarchical CuO@Cu/g-C3N4 nanorods film as freestanding anode for advanced lithium storage. This assembled freestanding film demonstrates a high discharge specific capacity at 726 mAhg−1 after 200 cycles at 0.1C and a discharge specific capacity of 457 mAhg−1 after 625 cycles at 1C, among the best performance in CuO and CuO based nanostructures for lithium storage. Its outstanding stability and cyclic performance are ascribed to the following aspects during the reaction process: (i) the unique 2D nanostructure provides large exposed area for Li+ insertion, (ii) the ordered CuO nanorods provide interior spaces to accommodate the volume change and offer more paths for charges and Li+ transfer, (iii) the existence of Cu nanosheets increases the electrons transport and (iv) the porous g-C3N4 nanosheets endow the prepared structure more active sites for facilitating Li+ transport and accommodating volume change. Our strategy on growing ordered nanostructures on 2D nanosheets will be an effective way to modify TMOs for advanced lithium-ion batteries.

The present work demonstrates the structural and photophysical properties of mixed zinc tin oxide (Zn:SnO2) nanowires (NWs) synthesized via vapor transport technique with Zn content of 10, 25 and 50 wt%. The XRD spectra reveals the tetragonal phase of SnO2 for 10 wt% Zn content, whereas a combination of tetragonal SnO2 and hexagonal ZnO phases were observed for higher Zn ratios. The SEM images reveals the formation of smooth NWs for low Zn content, whereas a combination of NWs along with spherical nanoparticles have been observed for 50 wt% Zn:SnO2 sample. The optical band gap was decreased from 3.21 eV (10% Zn:SnO2) to 2.84 eV (50% Zn:SnO2), whereas the corresponding Urbach energy increased from 971 meV to 1132 meV. The refractive index values increased from 2.28 to 2.64 when Zn content increased from 10 to 50 wt%. The absorption spectra showed a red shift and the appearance of new band with increasing Zn wt.%, signaling the formation of new electronic states below the conduction band. The fabricated films displayed a broad steady state emission with peak around 462 nm, which intensity decreased with the increasing of Zn ratio. The effective life time of charge carrier was decreased from 198 ps for 10 wt% Zn:SnO2 to 172 ps for 50 wt% Zn:SnO2.

Hydrothermal method as a facile bottom-up synthesis technique has many advantages for manufacturing various nanomaterials with controlled properties. In this work, lead telluride nanostructures were synthesized via a simple hydrothermal method at different surfactant concentrations. It was observed that the surfactant concentration has considerable effect on the morphology, and size of the synthesized nanostructures and thus the thermoelectric performance. In the present work, several techniques were used to characterize the structure, morphology, composition and optical properties of the synthesized PbTe nanostructures including XRD, TEM, EDS as well as PL and Raman spectroscopy. The electrical and thermoelectric properties were studied in the temperature range from 300 to 550 K. The results demonstrate that increasing the surfactant concentration improves the power factor due to a significant enhancement in the Seebeck coefficient.

Developing of thin film technologies is promising to enhance the efficiency and the stability of photocatalyst materials for hydrogen production, owing to their low cost production for large-scale photocatalytic applications, large surface areas for light harvesting and good electronic properties for charge transfer. Herein, cadmium sulfide (CdS) films supported on ITO glass have prepared by using chemical bath deposition (CBD) technique at different times (3–12 h) at 60 °C, then annealed up to 300 °C for 2 h. When developed as photoanode for water splitting, ITO/CdS/Au electrode successfully achieve high current density Jph,(0.54 mA cm-2), IPCE efficiency(2.34%) and ABPE efficiency (0.42%) compared with ITO/CdS electrode (0.22 mA cm-2,1.35% and 0.10%),respectively. Moreover, the stability of the current density for the prepared films has been prolonged up to 2000 s. The improvement in PEC behavior of the prepared electrodes could be attributed to (i) control the growth mechanism of the prepared CdS thin films which can enhance the light harvesting,(ii) the existence of the Au layer which can facilitate the electron transport. The obtained results endow the prepared CdS ITO/CdS/Au electrode a promising strategy for hydrogen evaluation.

The aim of this work was to examine the influence of radio frequency (rf) power on ZnO films synthesized by means of chemical vapor transport technique in inductively coupled plasma (ICP). As the rf power increased, with a fixed processing time of only 8 min, the temperature inside the reactor tube, the thickness and surface roughness of the formed polycrystalline ZnO films increased. The morphology of the ZnO films changed to oblate, webby like cloud-grains, nanoslices, and a mixture of nanorods and nanograins with changing the rf power from 300 to 500 W. Mixed phases of hexagonal ZnO and hexagonal Zn were found for samples synthesized at 300 and 500 W whereas single hexagonal ZnO was synthesized at 350, 400 and 450 W. The optical band gap decreased from 3.35 eV to 3.05 eV with increasing the rf power from 300 W to 500 W. The refractive index and extinction coefficient values were mainly increased with increasing the rf power. The electrical resistivity was generally decreased with increasing rf power and has values between 1.38 × 10−2 - 2.83 × 10−3 Ωcm. The obtained results might be important for useful applications of ZnO films grown by chemical vapor transport with the assistance of ICP.

In this research, stoichiometric Pb1-xSmxTe (x = 0, 0.02, 0.04, 0.06, 0.08) nanostructures were synthesized using the hydrothermal technique. The synthesized nanostructures were examined using X-ray diffraction, Raman spectroscopy, scanning and high-resolution transmission electron microscope and photoluminescence spectroscope. The results revealed that the samples were crystallized mainly in a cubic phase characterizing the PbTe compounds. However, the samples containing Sm content above x ≥ 0.06 exhibited small minor peaks correspond to the Pb phase. The PL spectra show a strong quantum confinement effectand exhibit a strong peak around 400 nm at room temperature that might be ascribed to the high level transition in the PbTe semiconductor. The thermoelectric measurements verified the domination of p-type semiconducting behavior. The reduction in the thermal conductivity through nanostructuring gives a high ZT of 0.7 at 398 K when Sm content reaches x = 0.06. The value is comparable to that of previously reported best PbTe-based thermoelectric materials.

Titanium oxynitride (TiOxNy) films capped with 10 nm titanium oxide (TiO2) layer were prepared using reactive direct current magnetron sputtering from pure Ti target. Part of the samples was annealed. Energy dispersive analysis of X-ray revealed that all the samples contain nitrogen and the incorporation of nitrogen into the oxynitrides is not linear. Phase investigation by X-ray diffraction showed structural variation with changing oxygen and nitrogen gas flow rates as well as annealing. Anatase, brookite, rutile and titanium nitride were detected individually or mixed in the as-prepared and annealed samples. The optical properties were found to be controlled by a structure and chemical composition. Transmittance and reflectance measurements were carried out by a high performance double beam ultraviolet-visible-near infrared spectrophotometer. Based on that, the energy band gap, refractive index and extinction coefficient were derived. The obvious difference between the dark and light currents indicated the validity of the TiO2/TiOxNy bilayer samples to act as photoanodes. All the annealed samples have photoelectrochemical water splitting response better than the as-prepared samples. The as-prepared TiO2/TiOxNy bilayer films were hydrophobic (contact angels, 81° - 93°) and their contact angles were independent from the nitrogen content. The annealed samples have lower contact angles than the as-prepared samples. The wettability of the as-prepared and annealed samples was changed from hydrophobic to more hydrophilic with increasing illumination time. These results are of important interest for the self-cleaning surfaces.

TiN/TiOxNy bilayer films with various TiN thicknesses were prepared using direct current (d.c.) reactive magnetron sputtering. The ratio of N/O in the bilayer films increased with increasing TiN top layer thickness. The observed crystalline peaks for the bilayer films, for different TiN layer thicknesses, were indexed to anatase TiO2 with tetragonal structure. Only 0.31° peak shift, to lower 2θ angles was detected. FESEM indicated that the morphology of TiOxNy single layer is consisted of elongated nanocrystals with diameters in the range of 27.9–46.8 nm and the diameters of the nanocrystallites changed slightly with increasing the thickness of TiN layer. The transmittance, absorbance, reflectance spectra and the optical constants of the bilayer films were presented. The photoelectrochemical performance for water splitting of TiN/TiOxNy bilayer films was studied by examination both the continuous and chopped photocurrent density under light illumination. The photocurrent density increases with increasing TiN top layer up to a thickness of 9 nm, after which a reduction in photocurrent is observed. The wettability of TiN/TiOxNy bilayer films could be transformed by UV illumination from hydrophobic to hydrophilic.

Herein, we report the synthesis of MoO3−x nanorods via an environmentally solvothermal/annealing route, which involves refluxing of an ethanolic solution of (NH4)6Mo7O24.4H2O for 5 h at 70 °C followed by drying and calcination at 350 °C for 2 h. Graphene oxide (GO) incorporation at 1% ratio into MoO3 increases the oxygen deficient ratio (20.6%) compared to GO free MoO3 catalyst (17.3%), as emphasized by XPS results. A comprehensive characterization using XRD, TEM-SAED, UV–vis, FTIR, Raman, photoluminescence and N2 sorptiometry was illustrated. The irregular circular shape of 1%GO.MoO3−x; of Eg equal 2.7 eV, and an average diameter of 40 nm has shown higher photocatalytic action towards MB degradation (20 ppm) under visible light illumination (160 W, >420 nm) giving a rate constant of 0.016 min−1 exceeding that of MoO3−x by 18 times. Although 1%GO.MoO3−x exhibits lower surface area and pore volume than those in GO free MoO3−x, the potentiality of the former is mainly dependent on the strong linkage formed between MoO3−x and graphene sheets. Based on increasing the oxygen deficiency in 1%GO.MoO3−x, powerful oxidizing moieties are depicted to affect the MB degradation including in situ generated H2O2, O2¯ and O H species. The gas sensing property of 1%GO.MoO3−x towards 100 ppm NH3 at 200 °C was increased by 6.4 times that of GO free MoO3−x nanorods. This was mainly due to the hetero-junction formed between n-(MoO3−x) and p-type (partially reduced GO) conducting channels; affirmed via Mott-schottky plot, and the facile electron transfer from GO into MoO3−x. The mechanism of the oxygen deficit 1%GO.MoO3−x structure is also discussed, exploring that this type of sensor has a promising application to other reducing gases. The 1%GO.MoO3−x sensor exhibited long-term stability at different NH3 concentrations as well as high selectivity exceeding the corresponding pure counterparts.