Qiongzhi Gao

Rational Construction of Strongly Coupled Metal–Metal Oxide–Graphene Nanostructure with Excellent Electrocatalytic Activity and Durability

The interaction within heterogeneous nanostructures can provide a great opportunity to radically enhance their electrocatalytic properties and increase their activity and durability. Here a rational, simple, and integrated strategy is reported to construct uniform and strongly coupled metal-metal oxide-graphene nanostructure as an electrocatalyst with high performance. We first simply synthesized the interacted SnO2-prGO (protected and reduced graphene oxide) hybrid with SnO2 nanoparticles (∼4 nm) selectively anchored on the oxygenated defects of rGO using an in situ redox and hydrolysis reaction. After the deposition of Pt, uniform Pt NPs are found to contact intimately and exclusively with the SnO2 phase in the SnO2-prGO hybrid. This constructed nanostructure (Pt-SnO2-prGO) exhibits significantly improved electrocatalytic activity (2.19-fold) and durability (2.08-fold) toward methanol oxidation over that of the state-of-the-art Pt/C catalyst. The detailed explanation of the strong coupling between SnO2 and graphene as well as between Pt and SnO2 is discussed, revealing that such a process can be used to immobilize various metal catalysts on metal-oxide-decorated catalysts for realizing advanced catalytic systems with enhanced performance.

Metal-free carbon nanotube–SiC nanowire heterostructures with enhanced photocatalytic H2 evolution under visible light irradiation

In this report, metal-free multi-walled carbon nanotube (MWCNT)–SiC nanowire 1D–1D nanoheterostructures were successfully synthesized by an in situ chemical reaction between MWCNTs and silicon powder. A vapor–liquid–solid (VLS) mechanism was found to be responsible for in situ growth of SiC nanowires along MWCNTs. The structure, morphology and composition of the as-obtained MWCNT–SiC 1D–1D samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and UV-vis absorption spectroscopy. The H2 evolution photoactivities of the resultant MWCNT–SiC nanoheterostructures under visible light irradiation were also investigated. Results showed that the metal-free MWCNT–SiC 1D–1D nanoheterostructures exhibited the highest H2 evolution rate among all samples, up to 108 μmol g−1 h−1, which was 3.1 times higher than that of pure SiC without MWCNTs. It suggests that the H2 evolution activity enhancement of the MWCNT–SiC 1D–1D nanocomposites under visible light irradiation is mainly attributed to the synergistic effects of enhanced separation efficiency of photogenerated hole–electron pairs at the MWCNT–SiC interfaces, improved crystallinity, unique 1D–1D nanoheterostructures and increased visible light absorption. The present work not only gives new insights into the underlying photocatalysis mechanism of the metal-free MWCNT–SiC 1D–1D nanoheterostructures but also provides a versatile strategy to design 1D–1D nanocomposite photocatalysts, with great potential applications in photocatalytic H2 generation or environmental pollutant degradation.

Ultra-thin SiC layer covered graphene nanosheets as advanced photocatalysts for hydrogen evolution

Herein, for the first time, ultra-thin SiC nanoparticles or ultra-thin layer covered graphene nanosheets were successfully prepared via using a facile in situ vapor–solid reaction. The samples were characterized by X-ray diffraction, UV-visible spectroscopy, photoluminescence spectra analysis, Raman spectra, transient photocurrent responses and transmission electron microscopy. The photocatalytic activities were also evaluated by H2 evolution from pure water or water containing Na2S as an electron donor. The resulting SiC–graphene hybrids show enhanced photocatalytic H2-evolution activities in the presence of an electron donor. Especially, the graphene nanosheet and SiC nanocrystal hybrids show the highest photocatalytic activity in H2 production under visible light, which is about 10 times higher than that of the SiC nanocrystals. The enhanced activities of the SiC–graphene hybrids can be attributed to their 2D nanosheet structures, large surface area, enhanced visible-light absorption and rapid interfacial charge transfer from SiC to graphene. Our results can provide an effective approach to synthesize graphene-based heterogeneous nanocomposites for a wide variety of potential applications in solar energy conversion and storage, separation, and purification processes.

Fabrication and properties of polybutadiene rubber-interpenetrating cross-linking poly(propylene carbonate) network as gel polymer electrolytes for lithium-ion battery

Polybutadiene rubber-interpenetrating cross-linking poly(propylene carbonate) (named as XBRPC) membrane can be readily synthesized from polybutadiene rubber (BR), poly(propylene carbonate) (PPC), polyethylene glycol (PEG), and using benzoyl peroxide (BPO) as cross-linking agent, then activated by absorbing liquid electrolyte to fabricate a novel XBRPC gel polymer electrolyte (GPE) for lithium-ion battery. Electrolyte uptake, mechanical strength, ionic conductivity, electrochemical stability window and charge/discharge performances of the XBRPC membranes were then investigated. The results show that the XBRPC GPEs possess good mechanical strength and high electrolyte uptake. The ionic conductivity was up to 1.25 mS cm−1 at room temperature and 3.51 mS cm−1 at 80 °C for XBRPC70 (70/30 of PPC/BR, w/w) sample. Furthermore, the electrochemical stability window has been established to with stand voltages greater than 4.5 V. The results of charge/discharge tests show that the initial discharge capacity of Li/XBRPC70 GPE/LiFePO4 cell is 119 mA h g−1 at a current rate of 0.1C and in voltage range of 2.5–4.0 V at room temperature. It also exhibited excellent cycling retention performance for high-performance lithium rechargeable battery.

Novel 3-D nanoporous graphitic-C3N4 nanosheets with heterostructured modification for efficient visible-light photocatalytic hydrogen production

Phosphorus-doped g-C3N4 (P-C3N4) nanosheets with unique 3-D nanoporous structures are synthesized for the first time in this work; such functional porous architectures coupled with BiPO4 nanorods can exhibit superior photocatalytic activity for hydrogen production. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffusive reflectance spectroscopy have been employed to characterize the heterostructured photocatalytic materials. The as-prepared composite photocatalyst show outstanding activity for photocatalytic hydrogen production under visible light (λ > 420 nm). The composite photocatalyst with 3.0 wt% BiPO4 shows an optimum photocatalytic activity with a H2-production rate of 1110 μmol h−1 g−1. The enhanced photocatalytic activity for P-C3N4 coupled with BiPO4 comes from the high migration efficiency of photoinduced electrons on the interface of P-C3N4 and BiPO4.

Electrochemical lithium storage of Li4Ti5O12/NiO nanocomposites for high-performance lithium-ion battery anodes

Li4Ti5O12/NiO (LTO/NiO) composites with various NiO contents were prepared successfully as anode materials for high-performance lithium-ion battery. The preparation procedure consisted of high-energy ball milling, high-temperature calcination, and solution coating in succession. Several techniques such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were applied to fully investigate the micromorphology, composition structure, and electrochemical performances of the LTO/NiO composites. It was found that all the LTO/NiO composites showed higher discharge capacity than the pure LTO anode within the representative 20 cycles. The LTO/5 wt.% NiO, which had the largest specific surface area of 2.1229 m2 g−1 among all the LTO/NiO composites, delivered a capacity of 203 mAh g−1 in a voltage window of 0.5–3.0 V at 1 C rate and retained a capacity of 176 mAh g−1 after 100 cycles. The CV and EIS analysis indicated that the charge/discharge processes of LTO/NiO composites included the Li+ diffusion into or out of LTO phase and the redox reaction of NiO phase. The results demonstrate that the surface modification of LTO with small amounts of NiO nanoparticles can decrease the overall charge transfer resistance by forming in situ the electron-conductive Ni, leading to the improved electrochemical behavior of the composites.

Polydopamine as a bridge to decorate monodisperse gold nanoparticles on Fe3O4 nanoclusters for the catalytic reduction of 4-nitrophenol

Herein, gold nanoparticles (Au NPs) were decorated on magnetic Fe3O4 nanoclusters@polydopamine nanocomposites (Fe3O4@PDA NCs) through a direct and green reduction method. The morphology was investigated via transmission electronic microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Results showed that Fe3O4 nanoclusters were successfully coated with a PDA shell layer of 25 nm thickness that could work as a reducing reagent to form Au NPs on the surface of Fe3O4@PDA NCs and prevent the aggregation of Au NPs as well. More interestingly, the concentration of the Au precursor had a great effect on both the size and the dispersion of Au NPs on the surface of Fe3O4@PDA NCs, which directly affected the catalytic activity of Fe3O4@PDA@Au. The catalytic performance of Fe3O4@PDA@Au was determined by reducing 4-nitrophenol to 4-aminophenol in the presence of excessive NaBH4, and the result showed that Fe3O4@PDA@Au prepared from a 130 μM Au precursor exhibited the best catalytic activity with the reaction rate constant of 39.2 s−1 g−1 and a conversion of >99% in ten minutes. After being recycled and reused ten times, the magnetic catalyst still had a conversion of >95%; this suggested that it might have practical applications in the reduction of nitroaromatic compounds.

FABRICATION AND PHOTOCATALYTIC PROPERTIES OF TiO2 NANOFILMS CO-DOPED WITH Fe3+ AND Bi3+ IONS

In this work, the titanium dioxide (TiO2) nanofilms co-doped with Fe3+ and Bi3+ ions were successfully fabricated by the sol–gel method with dip-coating process. Methylene blue was used as the target degradation chemical to study the photocatalytic properties affected by different doping contents of Fe3+ and Bi3+ ions. The samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and infrared (IR) spectroscopy. The results indicated that both pure TiO2 nanofilms and single-doped samples possessed the photocatalytic activity in degradation of methylene blue. However, when the nanofilms co-doped with Fe3+ and Bi3+ ions were fabricated at the molar ratio of 3:1 (Fe3+:Bi3+), they exhibited the best photocatalytic activity after the heat treatment at 500∘C for 2h. The wettability property test indicated that the TiO2 nanofilms co-doped with Fe3+ and Bi3+ ions in the molar ratio 3:1 owned an excellent hydrophilic property.