Multifunctional interlayer with simultaneously capturing and catalytically converting polysulfides for boosting safety and performance of lithium-sulfur batteries at high-low temperatures

Lithium-sulfur(Li-S) batteries as extremely promising high-density energy storage devices have attracted extensive concern. However, practical applications of Li-S batteries are severely restricted by not only intrinsic polysulfides shuttle resulting from their concentration gradient diffusion and sluggish conversion kinetics but also serious safety issue caused by thermolabile and combustible polymer separators.Herein, it is presented for the first time that a robust and multifunctional separator with urchin-like Co-doped Fe OOH microspheres and multiwalled carbon nanotubes(MWCNTs) as an interlayer simultaneously achieves to suppress polysulfides shuttle as well as improves thermotolerance and nonflammability of commercial PP separator. Accordingly, Li-S batteries with modified separator exhibit remarkable performance in a wide range temperatures of-25–100 ℃. Typically, under 25 ℃, ultrahigh initial capacities of 1441 and 827.29 m A h g-1 at 1 C and 2 C are delivered, and remained capacities of 936 and 663.18 mA h g-1 can be obtained after 500 cycles, respectively. At 0.1 C, the S utilization can reach up to 97%. Significantly, at 1 C, the batteries also deliver an excellent performance with remained capacities of high to862.3, 608.4 and 420.6 m A h g-1 after 100, 300 and 450 cycles under 75, 0 and-25 ℃, respectively. This work provides a new insight for developing stable and safe high-performance Li-S batteries.

Monitoring of PON System Using Compound Surveillance Technique

A passive optical network（PON） monitoring system combined light pulse and frequency sweep techniques is proposed and verified in a field test. The light pulse surveys over the all whole network and the frequency sweep are used to investigate any fault in the link. The field test is performed with 4 PONs. Each PON is monitored at 4 ports, one is the splitter port and the other three are arbitrary chosen multiple optical units（ONUs）. All the tested PONs are monitored in turns once per hour. Faults at the feeder and branch fiber have been observed in this field test and have been analyzed with the monitoring system.

Boosting thermal stability and crystallization of closed-loop-recyclable biodegradable poly(p-dioxanone) by end-group regulation

A chemically closed-loop-recyclable biodegradable polymer,poly(p-dioxanone)(PPDO),is one of the ideal candidates for single-use plastic products due to its suitability for different application scenarios.Fascinatingly,when PPDO wastes can be collected,its monomer p-dioxanone(PDO) will be obtained through chemical recycling of these wastes;when cannot be collected,the wastes are able to be biodegraded into harmless substances.However,unsatisfied thermal stability and low crystallization rate of PPDO restrict its wider applications.Herein,based on end-group regulation,we simultaneously realized the significant enhancement of thermal stability and crystallization of PPDO through the simple melt processing with tributyl phosphite(TBP) or triphenyl phosphite(TPP).The model reactions were conducted to investigate the reaction mechanism and theoretical products during the preparation of PPDO/phosphite compounds.Two kinds of phosphites were proved to act as the end-capped reagent and chain extender in the melt processing,while TBP presented better reactivity.As a result,the activation energy of thermal decomposition was largely elevated,and the unprecedented T_(5%)(the temperature at a weight loss of 5%) and Tmax(the temperature at a maximum rate of weight loss) of PPDO were obtained,i.e.,T_(5%)of ~330 ℃ and Tmaxof ~385 ℃ in N_(2) atmosphere,T_(5%)of ~240 ℃ and Tmaxof ~317 ℃ in air atmosphere,respectively.Furthermore,the increased crystallization rate,crystallinity,crystalline orderliness,and realizable monomer recovery(yield >90%,purity >99.9%) of PPDO/phosphite compounds were confirmed.

利用纳米纤维素调控聚对二氧环己酮纤维的耐水解性

提高可生物降解纤维存储与使用过程中的耐水解性是其应用中的关键问题之一.采用将纤维素纳米纤维(CNF)与聚对二氧环己酮(PPDO)混合纺丝后拉伸热定型处理的方法,制备了耐水解性明显改善的PPDO/CNF纤维.CNF沿拉伸方向取向,进而有序分布于PPDO纤维的无定形区域中,从而有效抑制了水在无定形区中的扩散.放置8周后,PPDO纤维的断裂强度从(146.0±6.4)MPa下降到(27.3±4.8)MPa,并彻底丧失了打结性能;相比之下,PPDO/CNF-2.0 wt%纤维的断裂强度从(162.9±7.0)MPa仅下降到(105.5±12.7)MPa,打结强度从(129.1±19.4)MPa仅下降到(78.0±4.1)MPa,分别相当于降解前纤维的64.8%和60.4%,仍然可满足一定的应用要求.

Chemically recyclable copolyesters from bio-renewable monomers:controlled synthesis and composition-dependent applicable properties

The development of chemically recyclable polymers is a promising solution to address the dual challenges of the environment and resources caused by petroleum-based plastics.Despite recent advancements,it is highly desirable for developing recyclable polymers to meet the requirements of both practical uses and well-performed recyclability.Bio-renewable monomers have been paid great attention recently as promising potential candidates for establishing a sustainable circular polymer economy.Herein,a sequential copolymerization of various bio-renewable n-alkyl substituted δ-valerolactone((R)VLs)and p-dioxanone(PDO)is conducted to synthesize novel chemically recyclable diblock copolymers poly(p-dioxanone)-block-poly(n-alkyl-valerolactones)(PPDO-b-P(R)VLs)with well-defined and controlled structures.The properties of copolymers including thermal property,crystallization,mechanical property,hydrophilicity and transport property can be tuned effectively to meet the requirements of practical uses by alternating the alkyl substituents(R)and the P(R)VLs content.In addition,the high-efficiency and facile chemical recycling of copolymers to PDO and(R)VL comonomers is realized with a high yield of>96.5%and a high purity of 99%.

Unveiling human impacts on pollinators and pollination in the urbanization era

Among the trademarks of global change and the Anthropocene,the relentless trend of urbanization has the most profound impact on driving rapid declines in biodiversity,species interactions,and ecosystem services(Grimm et al.2008).Of particular concern is the decline of pollinators and pollination services,which occurs globally at an unprecedented rate(Kevan&Viana 2003;Tylianakis 2013).

引入δ-内酯疏水取代烷基结构实现聚对二氧环己酮的性能调控

可反复化学循环、可生物降解的聚对二氧环己酮(PPDO),存在水解降解快等问题,不利于其储存和使用.基于此,本文通过将不同正烷基取代的δ-内酯(RVL)分别与对二氧环己酮(PDO)在磷酸二苯酯催化下本体共聚,高效地合成了3种结构和组分可控的PPDO基共聚物(PDRVL).通过热重分析(TGA)、差示扫描量热分析(DSC)、广角X射线衍射分析(WXRD)、拉伸测试研究了共聚物的热稳定性、结晶性能和力学性能.结果表明:PDRVL为半结晶共聚物,固定其分子量和RVL引入量改变取代烷基碳原子数为3、5、7,共聚物初始分解温度、熔融温度、屈服强度和断裂伸长可分别控制在245~251℃、96.5~99.8℃、21.6~24.3 MPa和212.7%~235%范围,能满足加工和使用要求.水接触角(WCA)和吸水率测试表明,随RVL的取代烷基链碳原子数目增加,共聚物可从亲水转变为疏水,且吸水率也随之降低.对比研究了PPDO和PDRVL在纯水中的降解情况,由降解过程中样品的质量保留率、特性黏数保留率、表面微观形貌等变化可以得出,含取代烷基链的疏水RVL单体的引入显著延缓了PPDO的水解降解,从而实现其降解速度在一定范围内的调控.

A Self-supporting,Surface Carbonized Filter Paper Membrane for Efficient Water-in-Oil Emulsion Separation

Due to the important role of oil source in our life,the separation of water-in-oil emulsion is urgent and necessary.Membrane seperation technology has been an efficient and widely used method in separating oil-water separation.Herein,we report a versatile approach to fabricate surface carbonized membranes with self-standing property from biomass-derived precursor by synergistic charring of phytic acid,arginine and filter paper.The obtained membrane exhibited superhydrophobicity in oil,excellent fouling resistance,and self-supporting ability.The membrane can be cycle-used at least 12 times with high permeation flux(up to 1380 L·m^(-2)·h^(-1))and separation efficiency(up to 99.4%).

Reversible photoswitching aggregation and dissolution of spiropyran-functionalized copolymer and light-responsive FRET process

Well-defined, reversibly light-responsive amphiphilic diblock copolymer grafted with spiropyran, was prepared by reversible addition-fragmentation chain transfer （RAFT） polymerization. The copolymer self-assembles into polymeric micelles in water and exhibits reversible dissolution and re-aggregation characteristics upon ultraviolet （UV） and visible （Vis）-light irradiation. The fluorescence response of spiropyran immobilized onto the copolymer was light switchable. When nitrobenzoxadiazolyl derivative （NBD） dyes are encapsulated into the core of the micelles, a reversible, light-responsive, dual-color fluorescence resonance energy transfer （FRET） system is constructed and processed, which is well regulated by alternatively UV/vis irradiation. We anticipate these photoswitchable and FRET lighting up nanoparticles will be useful in drug delivery and cell imaging or tracking synchronously.

Crystallization induced micellization of poly(p-dioxanone)-block-polyethylene glycol diblock copolymer functionalized with pyrene moiety

Poly（p-dioxanone）-block-polyethylene glycol diblock copolymers functionalized with pyrene moieties（Py-PPDO-b-PEG） at the chain ends of PPDO blocks were synthesized for preparing anisotropic micelles with improved stability.The micellization and crystallization of the copolymers were investigated by nano differential scanning calorimetry（Nano DSC）,transmission electron microscopy（TEM）,UV-vis spectrophotometery,fluorophotometer,and dynamic light scattering（DLS）,respectively.The results indicated that the aggregation of pyrene induced by intermolecular interaction lead to micellization of Py-PPDO-b-PEG at much lower concentrations than those of PPDO-b-PEG copolymers without pyrene moieties.The aggregation of pyrene moieties may also serve as nucleation agent and therefore enhance the crystallization rate of PPDO blocks.Fluorescence measurements by using Nile Red as the fluorescent agent indicated that the micelles of Py-PPDO-b-PEG have high stability and load capacity for hydrophobic molecules.

Controlled synthesis and closed-loop chemical recycling of biodegradable copolymers with composition-dependent properties

The closed-loop recycling concept of the polymer wastes into building-block chemicals is attractive,but the closed-loop recycling of copolymers enabled by energy-efficient chemical recycling and cost-effective separations is still facing great challenges.Herein,for the first time,a one-pot sequential copolymerization of γ-butyrolactone(γ-BL) and p-dioxanone(PDO)using an economical ureas/alkoxides catalytic system is conducted to synthesize biodegradable and chemically recyclable poly-(γ-butyrolactone)-block-poly(p-dioxanone)(PγBL-b-PPDO) diblock copolymers with well-defined and controlled structures.The composition-dependent properties of PγBL-b-PPDO copolymers,including thermal properties and crystallization behavior,are investigated.The results show that the thermal stability and crystalline ability of PγBL are enhanced observably by introducing the PPDO block.Significantly,the PγBL-b-PPDO copolymers can be depolymerized efficiently into the corresponding co-monomers with a yield of over 95% by simply low-temperature pyrolysis under vacuum.Moreover,γ-BL and PDO monomers are selectively separated with an isolated purity of about 99% based on the difference in their physicochemical properties.Subsequently,their repolymerization is realized to obtain the copolymers with nearly identical structures and thermostability,demonstrating the closed-loop recycling of copolymers,i.e.,polymerization-depolymerization-repolymerization.This research provides important guidance for the design of novel sustainable polymers towards more efficient chemical recycling,separation and regeneration.

Synthesis and characterization of poly(p-dioxanone)-based degradable copolymers with enhanced thermal and hydrolytic stabilities

Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(pdioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate)(PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate(HDI) as a chain extender. The structures and molecular weight of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy(1 H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU is much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.

Preparation of polymer nanocomposites with enhanced mechanical properties using hybrid of graphene and partially wrapped multi-wall carbon nanotube as nanofiller

Triblock copolymer of poly（p-dioxanone） and polyethylene glycol end-capped with pyrene moieties（（Py-PPDO）_2-b-PEG） was synthesized and used as modifier for multi-wall carbon nanotubes（MWCNTs）.Nano-aggregates（（Py-PPDO）_2-b-PEG@MWCNTs） with shish-kebab like partially wrapped morphology and very good stability were obtained by incorporating the copolymer with MWCNTs.The bare MWCNT sections of（Py-PPDO）_2-b-PEG@MWCNTs were able to induce n-n interactions with graphene（GE） and resulted in a novel GE/（Py-PPDO）_2-b-PEG@MWCNTs hybrid.The dispersity of GE in solution or polymer matrix was therefore greatly improved.The PCL nanocomposite films using GE/（Py-PPDO）_2-bPEG@MWCNTs as hybrid nanofiller exhibited obviously improved mechanical properties especially at very low hybrid nanofiller content.The influence of the nanofiller content and feed ratio of GE/MWCNTs on the mechanical properties of composites films was evaluated.When the feed ratio of GE to MWCNTs is 2：8 and the total loading of nanofiller is only 0.01 wt%,the tensile strength of the composite film increased by 163%and the elongation at break increased by 17% compared to those of neat PCL These results can be attributed to fine dispersion of the nanofillers in PCL matrix and the hybrid interactions between GE and MWCNTs.Therefore,this work provides a novel method for preparing polymer nanocomposites with high mechanical performance and low nanofiller loading.