Surface Engineering of MoS2 via Laser-Induced Exfoliation in Protic Solvents.

With excellent performance in the hydrogen evolution reaction (HER), molybdenum disulfide (MoS2 ) is considered a promising nonprecious candidate to substitute Pt-based catalysts. Herein, pulsed laser irradiation in liquid is used to realize one-step exfoliation of bulk 2H-MoS2 to ultrastable few-layer MoS2 nanosheets. Such prepared MoS2 nanosheets are rich in S vacancies and metallic 1T phase, which significantly contribute to the boosted catalytic HER activity. Protic solvents play a pivotal role in the production of S vacancies and 2H-to-1T phase transition under laser irradiation. MoS2 exfoliated in an optimal solvent of formic acid exhibits outstanding HER activity with an overpotential of 180 mV at 10 mA cm-2 and Tafel slope of 54 mV dec-1 .

Highly Enhanced Pseudocapacitive Performance of Vanadium-Doped MXenes in Neutral Electrolytes.

2D titanium carbide (Ti3 C2 Tx MXene) is recognized as a promising material for pseudocapacitor electrodes in acidic solutions, while the current studies in neutral electrolytes show much poorer performances. By a simple hydrothermal method, vanadium-doped Ti3 C2 Tx 2D nanosheets are prepared to tune the interaction between MXene and alkali metal adsorbates (Li+ , Na+ , and K+ ) in the neutral electrolyte. Maintaining the 2D morphology of MXene, the coexisting V3+ and V4+ are confirmed to form surface V-C and V-O species. At a medium doping level of V:Ti = 0.17:1, the V-doped MXene exhibits the highest capacitance of 365.9 F g-1 in 2 m KCl (10 mV s-1 ) and excellent stability (5% loss after 5000 cycles), compared to only 115.7 F g-1 of pristine MXene. Density functional theory calculations reveal the stronger alkali metal ion-O interaction on V-doped MXene surface than unmodified MXene and a further capacitance boost to 404.9 F g-1 using Li+ -containing neutral electrolyte is reported, which is comparable to the performance under acidic conditions.

Engineering NiO/NiFe LDH Intersection to Bypass Scaling Relationship for Oxygen Evolution Reaction via Dynamic Tridimensional Adsorption of Intermediates.

Oxygen evolution reaction (OER) is a pivotal reaction in many technologies for renewable energy, such as water splitting, metal-air batteries, and regenerative fuel cells. However, this reaction is known to be kinetically sluggish and proceeds at rather high overpotential due to the universal scaling relationship, namely, the adsorption energies of intermediates are linearly correlated and cannot be optimized simultaneously. Several approaches have been proposed to break the scaling relationship by introducing additional active sites; however, positive experimental results are still absent. Herein, a different solution is suggested on the basis of dynamic tridimensional adsorption of the OER intermediates at NiO/NiFe layered double hydroxide intersection, by which the adsorption energy of each intermediate can be adjusted independently, so as to bypass the scaling relationship and achieve high catalytic performance. Experimentally, the OER overpotential is reduced to ≈205 mV at current density of 30 mA cm-2 , which represents the best performance achieved by state-of-the-art OER catalysts.

Laser-assisted in situ synthesis of graphene-based magnetic-responsive hybrids for multimodal imaging-guided chemo/photothermal synergistic therapy.

Magnetic graphene-based hybrids are being increasing recognized as an effective nanotheranostic agent in biomedicine. Conventional technologies for their synthesis have drawbacks not only from a synthetic standpoint, mainly requiring high temperatures and multi-step processes, but also from a biological perspective, chemical precursors or surfactants involved in the chemical process are toxic to cells. Herein, we report a novel approach for one-step fabricating magnetic graphene hybrid nanocomposites based on laser irradiation of an Fe target in GO-PEG aqueous solution at room temperature without using any other chemical reagent. TEM, XPS, FT-IR, XRD, Mossbauer spectrum and VSM observation reveal that γ-Fe2O3 nanoparticles were directly grown on the surface of GO-PEG with uniform morphology and superior dispersibility. These GO-PEG-γ-Fe2O3 nanocomposites (labeled as GPF) showed low cytotoxicity in vitro compared to chemically synthesized nanoparticles since the pulsed-laser-ablation-in-liquid (PLAL) process is free of toxic agents. After tail vein injection of the nanotheranostics, the tumor was clearly mapped by T2-weighted magnetic resonance of γ-Fe2O3, photothermal imaging of graphene and fluorescence imaging of loaded antitumor DOX. Meanwhile the tumor cells both in vitro and in vivo achieved highly superior inhibition by the synergistic chemo/photothermal therapeutic effect which provided an intense heating effect and enhanced DOX release upon 808 nm NIR light exposure. The results revealed that the magnetic graphene-based hybrids prepared by PLAL is competent for future multi-modal imaging assisted tumor targeted chemo/photothermal synergistic therapy of cancer.

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 FeOCo 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.

[Short-term monitoring of methane emission regulation from a municipal solid waste landfill].

To understand the regulation and influencing factors of methane emission from landfills in China, rates of methane emission from Hangzhou Tianziling municipal solid waste landfill were measured by static chamber technique. The emission rates ranged from 3.67 to 36.65 mmol x (m2 x h)(-1) on average of the two tested points (No. 1 and No. 2) during 24-hour cycle. The max ratio of emission rates between the two tested points was 625. The difference with the rates of the two tested points could be explained by the depth of the cover soils. Rate of methane emission from each point correlated with atmospheric pressure and water content of landfill cover soils, and the result from stepwise regression was r2 = 0.89 for point No. 1, r2 = 0.76 for point No. 2. Rates of methane emission varied from -0.23 to 0.32 mmol (m2 x h)(-1) on average in 40-day test (points with same depth of cover soils). The low correlation (r2 = 0.15) with atmospheric pressure showed that atmospheric pressure was not the decisive factor. For some time, emission rates correlated with water content or temperature of the landfill cover soils significantly, but not obvious (r2 < 0.4) during the whole monitoring time. When atmospheric pressure was included, the results of stepwise regression were improved significantly, which showed that methane emission rates were influenced by different factors, but the effect of each factor was not the same at a different time.