Lan Cui

Graphene-DNA hybrids: self-assembly and electrochemical detection performance

Graphene combines with single-stranded DNA by a self-assembly process under strong ultrasonication and in the resulting water-dispersible graphene-DNA hybrids, monolayers of globular ss-DNA molecules are adsorbed on both sides of the graphene sheets by a non-covalent π–π stacking. The cyclic voltammetry results of the graphene-DNA hybrids coated electrodes demonstrate a well-defined and nearly symmetrical redox characteristic which means an enhanced electron transfer on the electrode surface as compared to the uncoated glassy carbon electrodes. Accordingly, the coated ones show apparently better sensing performance towards hydrogen peroxide which is characterized by large detection range, rapid response and high sensitivity.

Loosening the DNA wrapping around single-walled carbon nanotubes by increasing the strand length

In this study, we discuss the influence of DNA strand length on DNA wrapping of single-walled carbon nanotubes under high-shear sonication and find that different strand length results in changed DNA-nanotube interaction, which is sensitively probed by the upshift extent of the Raman radial breathing mode bands of nanotubes due to DNA wrapping. The difference in the interaction between nanotubes and DNA strands of various length results in apparently different degrees of wrapping compactness, revealed by atomic force microscopy observations, and nanotube selectivity in wrapping, indicated by both Raman and photoluminescence spectroscopy results. The above findings can be utilized to precisely control the nanotube diameter distribution and modulate the physicochemical properties of the nanotube wrapped by DNA without any direct functionalization of nanotubes. This finding is of considerable interest from both theoretical and practical standpoints.

Modest Oxygen-Defective Amorphous Manganese-Based Nanoparticle Mullite with Superior Overall Electrocatalytic Performance for Oxygen Reduction Reaction

Manganese-based oxides have exhibited high promise as noncoinage alternatives to Pt/C for catalyzing oxygen reduction reaction (ORR) in basic solution and a mix of Mn3+/4+ valence is believed to be vital in achieving optimum ORR performance. Here, it is proposed that, distinct from the most studied perovskites and spinels, Mn-based mullites with equivalent molar ratio of Mn3+ and Mn4+ provide a unique platform to maximize the role of Mn valence in facile ORR kinetics by introducing modest content of oxygen deficiency, which is also beneficial to enhanced catalytic activity. Accordingly, amorphous mullite SmMn2 O5-δ nanoparticles with finely tuned concentration of oxygen vacancies are synthesized via a versatile top-down approach and the modest oxygen-defective sample with an Mn3+ /Mn4+ ratio of 1.78, i.e., Mn valence of 3.36 gives rise to a superior overall ORR activity among the highest reported for the family of Mn-based oxides, comparable to that of Pt/C. Altogether, this study opens up great opportunities for mullite-based catalysts to be a cost-effective alternative to Pt/C in diverse electrochemical energy storage and conversion systems.

Millisecond laser ablation of molybdenum target in reactive gas toward MoS2 fullerene-like nanoparticles with thermally stable photoresponse.

As a promising material for photoelectrical application, MoS2 has attracted extensive attention on its facile synthesis and unique properties. Herein, we explored a novel strategy of laser ablation to synthesize MoS2 fullerene-like nanoparticles (FL-NPs) with stable photoresponse under high temperature. Specifically, we employed a millisecond pulsed laser to ablate the molybdenum target in dimethyl trisulfide gas, and as a result, the molybdenum nanodroplets were ejected from the target and interacted with the highly reactive ambient gas to produce MoS2 FL-NPs. In contrast, the laser ablation in liquid could only produce core-shell nanoparticles. The crucial factors for controlling final nanostructures were found to be laser intensity, cooling rate, and gas reactivity. Finally, the MoS2 FL-NPs were assembled into a simple photoresponse device which exhibited excellent thermal stability, indicating their great potentialities for high-temperature photoelectrical applications.

Porous activated graphene nanoplatelets incorporated in TiO2 photoanodes for high-efficiency dye-sensitized solar cells

Activated graphene nanoplatelets (a-GNPs) were first prepared by a hydrothermal method with KOH as the activating agent. The effects of the preparation conditions on the morphology and structure of the a-GNPs were studied in detail. Morphological observations and N2 adsorption–desorption isotherms indicate that the a-GNPs exhibit a uniform pore size distribution and have a larger specific surface area (113.5 m2 g−1) compared to graphene nanoplatelets (GNPs). The incorporation of a-GNPs (0.02 wt%) into a TiO2 film photoanode in a dye-sensitized solar cell (DSSC) enhances the short circuit current and energy conversion of the cell by 35.8% and 26.8%, respectively. The TiO2/a-GNP composite photoanodes were characterized by UV-vis spectroscopy and electrochemical impedance spectroscopy. The results reveal that the three-dimensional porous structure of a-GNPs serves as an efficient pathway for electrolyte ions and electrons, which accelerates the electron transfer and charge separation, and suppresses the electron recombination and back transport reaction in DSSCs. However, excessive a-GNP incorporation leads to a decrease in the dye adsorption and thus a low energy conversion efficiency of DSSCs.

Inverse opal hydrogels with adjustable band gaps tuned by polyethylene glycol

Inverse opal hydrogels of polyacrylamide (PAM) with adjustable band gaps (P-IOHspam) were fabricated by changing the molecular weight of polyethylene glycol (PEG), and the amount of PEG and N,N′-methylenebisarcylamide (BIS) in the monomer precursors. After the PEG was removed, mesopores were left in the PAM hydrogels and these caused changes in the band gap of the P-IOHspam. Compared with inverse opal hydrogels of PAM (IOHspam) that were prepared without PEG, the reflection peaks shifted to a longer wavelength which provides a wider usable visible wavelength range. P-IOHspam show rapid shifts in the reflection peak in response to chemicals, such as PEG, glycol, glucose and L-lysine. The shift of the reflection peak is greater for the P-IOHspam made from monomer precursors containing more PEG and for higher molecular weights of PEG. The shifts are caused by changes in two factors: the average refractive index of the P-IOHpam material and the degree of equilibrium swelling of the PAM hydrogel, both of which are sensitive to chemicals. Such sensitive materials could be used as chemical sensors.

CdTe nanoflake arrays on a conductive substrate: template synthesis and photoresponse property

CdTe nanoflake arrays were fabricated directly on a conductive substrate via gas-phase tellurization of a cadmium nanoflake template. A put-in-heating technique was developed to prevent the fusion and collapse of the cadmium template, as a result, the nanoflake morphology was well preserved during high temperature tellurization. A simple photoresponse device based on CdTe nanoflake arrays was assembled and exhibited high performance, indicating that CdTe nanoflake arrays are promising for photoelectrical applications.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

Strongly Coupled CoO Nanoclusters/CoFe LDHs Hybrid as a Synergistic Catalyst for Electrochemical Water Oxidation

Exploiting high-performance, robust, and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is crucial for electrochemical energy storage and conversion technologies. Engineering the interfacial structure of hybrid catalysts often induces synergistically enhanced electrocatalytic performance. Herein, a new strongly coupled heterogeneous catalyst with proper interfacial structures, i.e., CoO nanoclusters decorated on CoFe layered double hydroxides (LDHs) nanosheets, is prepared via a simple one-step pulsed laser ablation in liquid method. Thorough spectroscopic characterizations reveal that strong chemical couplings at the hybrid interface trigger charge transfer from CoII in the oxide to FeIII in the LDHs through the interfacial Feuf8ffOuf8ffCo bond, leading to considerable amounts of high oxidation state CoIII sites present in the hybrid. Interestingly, the CoO/CoFe LDHs exhibit pronounced synergistic effects in electrocatalytic water oxidation, with substantially enhanced intrinsic catalytic activity and stability relative to both components. The hybrid catalyst achieves remarkably low OER overpotential and Tafel slope in alkaline medium, outperforming that of Ru/C and manifesting itself among the most active Co-based OER catalysts.

Multiscale Structural Engineering of Ni‐Doped CoO Nanosheets for Zinc–Air Batteries with High Power Density

Zinc-air batteries offer a possible solution for large-scale energy storage due to their superhigh theoretical energy density, reliable safety, low cost, and long durability. However, their widespread application is hindered by low power density. Herein, a multiscale structural engineering of Ni-doped CoO nanosheets (NSs) for zinc-air batteries with superior high power density/energy density and durability is reported for the first time. In micro- and nanoscale, robust 2D architecture together with numerous nanopores inside the nanosheets provides an advantageous micro/nanostructured surface for O2 diffusion and a high electrocatalytic active surface area. In atomic scale, Ni doping significantly enhances the intrinsic oxygen reduction reaction activity per active site. As a result of controlled multiscale structure, the primary zinc-air battery with engineered Ni-doped CoO NSs electrode shows excellent performance with a record-high discharge peak power density of 377xa0mW cm-2 , and works stable for >400 h at 5xa0mA cm-2 . Rechargeable zinc-air battery based on Ni-doped CoO NSs affords an unprecedented small charge-discharge voltage of 0.63xa0V, outperforming state-of-the-art Pt/C catalyst-based device. Moreover, it is shown that Ni-doped CoO NSs assembled into all-solid-state coin cells can power 17 light-emitting diodes and charge an iPhone 7 mobile phone.