Epitaxial Growth of Flower-Like MoS2 on One-Dimensional Nickel Titanate Nanofibers: A "Sweet Spot" for Efficient Photoreduction of Carbon Dioxide.

Herein, a full spectrum-induced hybrid structure consisting of one-dimensional nickel titanate (NiTiO3) nanofibers (NFs) decorated by petal-like molybdenum disulfide (MoS2) particles was designed through a facile hydrothermal method. The key parameters for tailoring the morphology and chemical, surface, and interfacial properties of the heterostructure were identified for efficient and selective conversion of CO2 into valuable chemicals. Introducing MoS2 layers onto NiTiO3 NFs provided superior CO2 conversion with significantly higher yields. The optimized hybrid structure produced CO and CH4 yields of 130 and 55 µmol g-1 h-1, respectively, which are 3.8- and 3.6-times higher than those from pristine NiTiO3 nanofibers (34 and 15 µmol g-1 h-1, respectively) and 3.6- and 5.5-times higher than those from pristine MoS2 (37 and 10 µmol g-1 h-1, respectively). This improved performance was attributed to efficient absorption of a wider spectrum of light and efficient transfer of electrons across the heterojunction. Effective charge separation and reduced charge carrier recombination were confirmed by photoluminescence and impedance measurements. The performance may also be partly due to enhanced hydrophobicity of the hierarchical surfaces due to MoS2 growth. This strategy contributes to the rational design of perovskite-based photocatalysts for CO2 reduction.

Novel design of hollow g-C3N4 nanofibers decorated with MoS2 and S, N-doped graphene for ternary heterostructures.

Herein, we newly design a ternary structure of 1-dimensional hollow g-C3N4 nanofibers (HGCNF) decorated with molybdenum disulfide (MoS2) and sulfur/nitrogen-doped graphene (SNG) via a one-pot hydrothermal treatment at relatively low temperature. The firstly presented HGCNF are fabricated using electrospinning followed by the thermal sintering method. After that, MoS2 is grown onto HGCNF, while SNG covered the structures during the hydrothermal method. We observed the morphological structures, chemical composition and optical absorbance of this ternary HGCNF/SNG/MoS2 structure. Of the as-prepared catalysts, HGCNF/SNG/MoS2 exhibited a good possibility to produce hydrogen as an electrocatalyst. Furthermore, we evaluated its stability performance using chronoamperometry for 48 hours, as well as by 3000 cycles of cyclic voltammetry. From the double-layer capacitance measurement, HGCNF/SNG/MoS2 proved itself as an electrocatalyst due to the higher value of electrocatalytically active sites to be 6.97 × 10-3 F cm-2 than that of only HGCNF (0.18 × 10-5 F cm-2) and the binary structure of HGCNF/MoS2 (2.54 × 10-3 F cm-2). We believe that our novel 1-dimensional ternary HGCNF/SNG/MoS2 structure has expedited the electron pathways by reducing the resistance at interfaces among HGCNF, SNG and MoS2, to be potentially useful for the hydrogen evolution reaction.

Evaluation of dual layered photoanode for enhancement of visible-light-driven applications.

Ternary structures consisting of hollow g-C3N4 nanofibers/MoS2/sulfur, nitrogen-doped graphene and bulk g-C3N4 (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C3N4 film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron-hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 × 10-3 min-1, which is about four times faster than that of bare TCN film. Furthermore, we estimated the H2 evolution of the dual layered film to be 44.9 µmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (∼50 ohm cm2) compared to the TCN film, the ternary structures and bulk g-C3N4 film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron-hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.

Quantum scale biomimicry of low dimensional growth: An unusual complex amorphous precursor route to TiO2 band confinement by shape adaptive biopolymer-like flexibility for energy applications.

Crystallization via an amorphous pathway is often preferred by biologically driven processes enabling living species to better regulate activation energies to crystal formation that are intrinsically linked to shape and size of dynamically evolving morphologies. Templated ordering of 3-dimensional space around amorphous embedded non-equilibrium phases at heterogeneous polymer─metal interfaces signify important routes for the genesis of low-dimensional materials under stress-induced polymer confinement. We report the surface induced catalytic loss of P=O ligands to bond activated aromatization of C-C C=C and Ti=N resulting in confinement of porphyrin-TiO2 within polymer nanocages via particle attachment. Restricted growth nucleation of TiO2 to the quantum scale (≤2 nm) is synthetically assisted by nitrogen, phosphine and hydrocarbon polymer chemistry via self-assembly. Here, the amorphous arrest phase of TiO2 is reminiscent of biogenic amorphous crystal growth patterns and polymer coordination has both a chemical and biomimetic significance arising from quantum scale confinement which is atomically challenging. The relative ease in adaptability of non-equilibrium phases renders host structures more shape compliant to congruent guests increasing the possibility of geometrical confinement. Here, we provide evidence for synthetic biomimicry akin to bio-polymerization mechanisms to steer disorder-to-order transitions via solvent plasticization-like behaviour. This challenges the rationale of quantum driven confinement processes by conventional processes. Further, we show the change in optoelectronic properties under quantum confinement is intrinsically related to size that affects their optical absorption band energy range in DSSC.

Direct coating of a g-C3N4 layer onto one-dimensional TiO2 nanocluster/nanorod films for photoactive applications.

We report the coating of metal-free graphitic carbon nitride (g-C3N4) onto titanium dioxide (TiO2) nanorods via a thermal evaporation method. Prior to g-C3N4 coating, TiO2 nanoclusters were grown on TiO2 nanorods to enhance the surface area by dipping in a TiCl3 solution for 12, 24 and 36 h. The prepared films were analyzed to assess the improvement in absorbance and reduction in recombination losses. Nanoclustered TiO2 grown for 24 h and then coated with a g-C3N4 film (i.e., TC_24h_CN) had the highest photocurrent of 235 and 290 µA, respectively, when measured by transient photocurrent and linear sweep voltammetry techniques. The enhanced performance resulted from a reduced recombination of electron-hole pairs. The TC_24h_CN film displayed an excellent photoresponse over 15 h of exposure to visible light and hence could potentially be used in water purification device technology.

Low temperature fabrication of Fe2O3 nanorod film coated with ultra-thin g-C3N4 for a direct z-scheme exerting photocatalytic activities.

We engineered high aspect ratio Fe2O3 nanorods (with an aspect ratio of 17 : 1) coated with g-C3N4 using a sequential solvothermal method at very low temperature followed by a thermal evaporation method. Here, the high aspect ratio Fe2O3 nanorods were directly grown onto the FTO substrate under relatively low pressure conditions. The g-C3N4 was coated onto a uniform Fe2O3 nanorod film as the heterostructure, exhibiting rational band conduction and a valence band that engaged in surface photoredox reactions by a direct z-scheme mechanism. The heterostructures, particularly 0.75g-C3N4@Fe2O3 nanorods, exhibited outstanding photocatalytic activities compared to those of bare Fe2O3 nanorods. In terms of 4-nitrophenol degradation, 0.75g-C3N4@Fe2O3 nanorods degraded all of the organic pollutant within 6 h under visible irradiation at a kinetic constant of 12.71 × 10-3 min-1, about 15-fold more rapidly than bare Fe2O3. Further, the hydrogen evolution rate was 37.06 µmol h-1 g-1, 39-fold higher than that of bare Fe2O3. We suggest that electron and hole pairs are efficiently separated in g-C3N4@Fe2O3 nanorods, thus accelerating surface photoreaction via a direct z-scheme under visible illumination.

Room-temperature synthesis of nanoporous 1D microrods of graphitic carbon nitride (g-C3N4) with highly enhanced photocatalytic activity and stability.

A one-dimensional (1D) nanostructure having a porous network is an exceptional photocatalytic material to generate hydrogen (H2) and decontaminate wastewater using solar energy. In this report, we synthesized nanoporous 1D microrods of graphitic carbon nitride (g-C3N4) via a facile and template-free chemical approach at room temperature. The use of concentrated acids induced etching and lift-off because of strong oxidation and protonation. Compared with the bulk g-C3N4, the porous 1D microrod structure showed five times higher photocatalytic degradation performance toward methylene blue dye (MB) under visible light irradiation. The photocatalytic H2 evolution of the 1D nanostructure (34 µmol g(-1)) was almost 26 times higher than that of the bulk g-C3N4 structure (1.26 µmol g(-1)). Additionally, the photocurrent stability of this nanoporous 1D morphology over 24 h indicated remarkable photocorrosion resistance. The improved photocatalytic activities were attributed to prolonged carrier lifetime because of its quantum confinement effect, effective separation and transport of charge carriers, and increased number of active sites from interconnected nanopores throughout the microrods. The present 1D nanostructure would be highly suited for photocatalytic water purification as well as water splitting devices. Finally, this facile and room temperature strategy to fabricate the nanostructures is very cost-effective.