具有丰富活性位点和高电子传导性的非晶MOF用于高效肼氧化

金属有机框架(MOF)虽然具有完美的结晶性质,但由于其配位不饱和位点数量不足和电子传导性较低,这些特性限制了它在电催化领域的应用.尽管通过去除部分有机配体可以暴露晶体MOF的一些金属位点,但常用的方法涉及高压、高温、强酸、强碱等苛刻的条件,很容易造成MOF的多孔结构完全坍塌.相较于晶态MOF,非晶态MOF具有短程有序而长程无序的结构特征.通过快速组装MOF,有望实现MOF的非晶化,从而创造大量不饱和位点,并优化金属位点的电子结构.因此,开发高效的非晶态MOF合成策略十分必要.本文报道了一种诱导非晶态MOF在碳布上快速组装的电合成方法,制得了具有丰富活性位点和高电子传导性的非晶态MOF(记为aMnFc'/CC).在电合成过程中,有机配体在碳布上迅速去质子化,并与金属离子快速组装,形成具有大量配位不饱和Mn位点的非晶态aMnFc'.X射线衍射和透射电镜选区电子衍射结果表明,aMnFc'为无定形结构.电子顺磁共振和X射线吸收近边结构光谱等表明,aMnFc'比cMnFc'含有更多的不饱和Mn金属中心.随后,利用三电极体系评估催化剂在肼氧化(HzOR)中的催化活性,在0.1 mol L^(−1) PBS+0.4 mol L^(−1) N_(2)H_(4)电解质中,aMnFc'/CC的起始电位为287 mV(1 mA cm^(−2)),在10 mA cm^(−2)下的工作电势为667 mV,其活性远优于晶态MOF 起始电位为540 mV(1 mA cm^(−2)),在10 mA cm^(−2)下的工作电势为(871 mV).aMnFc'/CC在0.1 mol L^(−1) PBS中的HzOR性能优于大多数已报道的Mn/Fe基催化剂和MOFs催化剂.四探针法测定cMnFc'和aMnFc'的电导率分别为1.5×10^(−4)和1.8×10^(−3) S cm^(−2),表明MOF的非晶化可以提高电导率,从而增强其电化学性能.密度泛函理论计算表明,MnFc'-V在费米能级附近的态密度比MnFc'的态密度更强,说明不饱和Mn中心的存在增强了MOF的导电性.进一步通过理论计算研究了肼在MnFc'和MnFc'-V表面的逐步脱氢过程,结果发现,MnFc'和MnFc'-V的决速步都是从*N_(2)H_(3)到*N_(2)H_(2)的脱氢过程,其中MnFc'-V的自由能差(0.22 eV)远小于MnFc'的自由能差(0.65 eV).由此可见,在aMnFc'中,不饱和Mn位点使d带中心更接近费米能级,增强了活性位对N_(x)H_(x)中间体的吸附能,从而提高了HzOR活性.综上,本文提出一种电合成方法,实现了非晶态MOF在碳布上的快速组装,制备出具有丰富活性位点和高电子传导性的非晶态MOF,显著提升了其在肼氧化反应中的催化活性.这一新策略不仅克服了晶态MOF在电催化应用中的局限,而且为工业电流条件下合成用于HzOR的非晶态MOF提供了参考.

Stable ultraviolet ultrafast laser based on all-polarizationmaintaining fiber femtosecond laser

We report a high-stability ultrafast ultraviolet(UV)laser source at 352 nm by exploring an all-fiber,all-polarizationmaintaining(all-PM),Yb-doped femtosecond fiber laser at 1060 nm.The output power,pulse width,and optical spectrum width of the fiber laser are 6 W,244 fs,and 17.5 nm,respectively.The UV ultrashort pulses at a repetition rate of 28.9 MHz are generated by leveraging single-pass second-harmonic generation in a 1.3-mm-long BiB_(3)O_(6)(BIBO)and sum frequency generation in a 5.1-mm-long BIBO.The maximum UV output power is 596 mW.The root mean square error of the output power of UV pulses is 0.54%.This laser,with promising stability,is expected to be a nice source for frontier applications in the UV wavelength window.

Degradation of platinum electrocatalysts for methanol oxidation by lead contamination

Platinum exhibits high electrocatalytic activity toward various reactions but might be poisoned by some species. This communication reports a new finding that the electrocatalytic activity of platinum for methanol oxidation will be largely lost in a lead-contaminated environment. This activity loss is demonstrated in an electrochemical cell using a lead counter electrode for measuring the activity of platinum electrode towards methanol oxidation. The recorded methanol oxidation current in this cell is significantly decreased compared with that using a platinum counter electrode. The possible mechanism is related to the adsorption of trace lead ions from the lead counter electrode, as confirmed by comparing the calculated binding energies of platinum and lead ions with oxygen ion. This report is of great importance for reliably designing and efficiently managing direct methanol fuel cells, because trace lead might be present in various components in the fuel cell systems or in air and attention should be paid to its negative effect.

Nonlinear chirped pulse amplification for a 100-W-class GHz femtosecond all-fiber laser system at 1.5μm

In this work,we present a high-power,high-repetition-rate,all-fiber femtosecond laser system operating at 1.5μm.This all-fiber laser system can deliver femtosecond pulses at a fundamental repetition rate of 10.6 GHz with an average output power of 106.4 W–the highest average power reported so far from an all-fiber femtosecond laser at 1.5μm,to the best of our knowledge.By utilizing the soliton-effect-based pulse compression effect with optimized pre-chirping dispersion,the amplified pulses are compressed to 239 fs in an all-fiber configuration.Empowered by such a high-power ultrafast fiber laser system,we further explore the nonlinear interaction among transverse modes LP01,LP11 and LP21 that are expected to potentially exist in fiber laser systems using large-mode-area fibers.The intermodal modulational instability is theoretically investigated and subsequently identified in our experiments.Such a high-power all-fiber ultrafast laser without bulky free-space optics is anticipated to be a promising laser source for applications that specifically require compact and robust operation.

Spectral manipulation in a high-power ultrafast fiber laser system generating ultrashort pulses with GHz repetition rate

In this work,we demonstrate the spectral manipulation in an ultrafast fiber laser system that generates ultrashort pulses with a repetition rate of 1.2 GHz and two switchable modes—a 1064-nm fundamental laser mode with a maximum output power of 66.6 W,and a 1125-nm Raman laser mode with a maximum output power of 17.23 W.The pulse width,beam quality,and power stability are carefully characterized.We also investigate a method to switch between the two modes by manipulating the duty cycle of the modulation signal.It is anticipated that this bi-mode ultrafast fiber laser system can be a promising ultrafast laser source for frontier applications,such as micromachining,bioimaging,and spectroscopy.

Aggregated carbon dots-loaded macrophages treat sepsis by eliminating multidrug-resistant bacteria and attenuating inflammation

Sepsis,caused by uncontrollable infection and inflammatory response,leads to more than 30 million infected patients and results in high morbidity worldwide every year.Currently,no efficient approaches have been developed for sepsis therapy due to antimicrobial resistance and inflammatory storm.Here,we report macrophages loaded with aggregated carbon dots(ACDs)in the lysosome,termed MCDs,to treat sepsis in immunosuppressive mice.The ACDs are constructed by negative CDs and amine-abundant polyethyleneimine(PEI),enabling them to bear the strong antibacterial ability and enhanced photoluminescent efficacy.The ACDs are specifically located in the macrophage lysosomes,efficiently enhancing the multidrug-resistant bacteria-killing ability of MCDs.More importantly,the MCDs possess superior anti-inflammatory effects such as reducing the number of pro-inflammatory(M1)and stimulating anti-inflammatory(M2)macrophages.These effects upregulate the inflammatory cytokines(TNF-α,IL-1β,IL-4,and IL-10),ultimately resulting in increased sepsis survival.Our work provides an intelligent approach to overcoming multidrug-resistant bacteria-induced infection from sepsis patients and paves a new avenue on employing nanoparticle-loaded cells for combating inflammation-related infection.

Manganese salts function as potent adjuvants

Aluminum-containing adjuvants have been used for nearly 100 years to enhance immune responses in billions of doses of vaccines.To date,only a few adjuvants have been approved for use in humans,among which aluminum-containing adjuvants are the only ones widely used.However,the medical need for potent and safe adjuvants is currently continuously increasing,especially those triggering cellular immune responses for cytotoxic T lymphocyte activation,which are urgently needed for the development of efficient virus and cancer vaccines.Manganese is an essential micronutrient required for diverse biological activities,but its functions in immunity remain undefined.We previously reported that Mn^(2+) is important in the host defense against cytosolic dsDNA by facilitating cGAS-STING activation and that Mn^(2+)alone directly activates cGAS independent of dsDNA,leading to an unconventional catalytic synthesis of 2′3′-cGAMP.Herein,we found that Mn^(2+) strongly promoted immune responses by facilitating antigen uptake,presentation,and germinal center formation via both cGAS-STING and NLRP3 activation.Accordingly,a colloidal manganese salt(Mn jelly,MnJ)was formulated to act not only as an immune potentiator but also as a delivery system to stimulate humoral and cellular immune responses,inducing antibody production and CD4^(+)/CD8^(+)T-cell proliferation and activation by either intramuscular or intranasal immunization.When administered intranasally,MnJ also worked as a mucosal adjuvant,inducing high levels of secretory IgA.MnJ showed good adjuvant effects for all tested antigens,including T cell-dependent and T cell-independent antigens,such as bacterial capsular polysaccharides,thus indicating that it is a promising adjuvant candidate.

Harnessing a multi-dimensional fibre laser using genetic wavefront shaping

The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higherdimensional coherent lightwaves but also for the frontier study of the complex three-dimensional(3D)nonlinear dynamics and solitary waves widely involved in physics,chemistry,biology and materials science.Systemically controlling coherent lightwave oscillation in multi-dimensional lasers,however,is challenging and has largely been unexplored;yet,it is crucial for both designing 3D coherent light fields and unveiling any underlying nonlinear complexities.Here,for the first time,we genetically harness a multi-dimensional fibre laser using intracavity wavefront shaping technology such that versatile lasing characteristics can be manipulated.We demonstrate that the output power,mode profile,optical spectrum and mode-locking operation can be genetically optimized by appropriately designing the objective function of the genetic algorithm.It is anticipated that this genetic and systematic intracavity control technology for multi-dimensional lasers will be an important step for obtaining high-performance 3D lasing and presents many possibilities for exploring multi-dimensional nonlinear dynamics and solitary waves that may enable new applications.

High-contrast,fast chemical imaging by coherent Raman scattering using a self-synchronized two-colour fibre laser

Coherent Raman scattering(CRS)microscopy is widely recognized as a powerful tool for tackling biomedical problems based on its chemically specific label-free contrast,high spatial and spectral resolution,and high sensitivity.However,the clinical translation of CRS imaging technologies has long been hindered by traditional solid-state lasers with environmentally sensitive operations and large footprints.Ultrafast fibre lasers can potentially overcome these shortcomings but have not yet been fully exploited for CRS imaging,as previous implementations have suffered from high intensity noise,a narrow tuning range and low power,resulting in low image qualities and slow imaging speeds.Here,we present a novel high-power self-synchronized two-colour pulsed fibre laser that achieves excellent performance in terms of intensity stability(improved by 50 dB),timing jitter(24.3 fs),average power fluctuation(<0.5%),modulation depth(>20 dB)and pulse width variation(<1.8%)over an extended wavenumber range(2700-3550 cm^(−1)).The versatility of the laser source enables,for the first time,high-contrast,fast CRS imaging without complicated noise reduction via balanced detection schemes.These capabilities are demonstrated in this work by imaging a wide range of species such as living human cells and mouse arterial tissues and performing multimodal nonlinear imaging of mouse tail,kidney and brain tissue sections by utilizing second-harmonic generation and twophoton excited fluorescence,which provides multiple optical contrast mechanisms simultaneously and maximizes the gathered information content for biological visualization and medical diagnosis.This work also establishes a general scenario for remodelling existing lasers into synchronized two-colour lasers and thus promotes a wider popularization and application of CRS imaging technologies.

Investigation of a root zone heating system for greenhouse seedling and its effects on micro-environment

Under the extremely cold climatic condition,crops have to survive severe heat stress conditions,even if they are being kept in greenhouses.In the winter and spring of North China,the air and soil temperature is low inside the greenhouse,and when using a traditional heating system,the energy consumption is high.This paper reports on a study of different design solutions for a root zone heating system based on a kind of low temperature radiation material.Root zone heating systems offer increasing crop quality and productivity.A novel type of heat preservation and root zone heating system was applied in greenhouse seedling.And through multiple experiments,the effect of the root zone heating system on the ambient environment and seedbed surface was studied,and the heat preservation effect and heating uniformity were discussed.Results show that single-layer film covering on the root zone heating system can make the average temperature at night increase 1°C.And the average seedbed surface and substrate temperature can increase 11.3°C and 5.2°C,respectively.In conclusion,the root zone heating system can effectively improve the environmental temperature of seedling and the uniformity of heating is high,which provides a strong guarantee for high-quality seedling cultivation.

Highly stabilized and lowly polarized Li anodes using a hybrid surface film with inner Li–Zn nucleation sites and outer LiF-rich protection texture

Lithium(Li)metal is the most promising anode for improving the energy density of currently commercialized Li-ion batteries.However,its practical application is limited due to its high reactivity to electrolytes,which induces severe electrolyte decomposition and Li-dendrite growth.Interphases are usually constructed on Li anode to address the above issue.Meanwhile,it is a big challenge to balance the stability and plating/stripping overpotential of Li anode.In this work,we report a novel strategy for constructing a highly stable and lowly polarized surface film on Li anode.A chemically and structurally unique film is formed by simply dropping a zinc trifluoromethanesulfonate[Zn(OTF)_(2)]and fluoroethylene carbonate(FEC)-containing solution onto Li anode.This unique film consists of inner nucleation sites and outer protection textures,mainly containing Li–Zn alloy and LiF/polymer,respectively.The former results from the preferential reduction of Zn(OTF)_(2),providing nucleation sites with low polarization for Li plating/stripping.In contrast,the latter arises from the subsequent reduction of FEC,providing protection for the underneath Li–Zn alloy and Li metal and ensuring the stability of Li anode.The Li anode with such a unique surface film exhibits excellent cycling stability and low plating/stripping overpotentials,which have been demonstrated using Li//Li symmetric and Li//LiFePO_(4)full cells.