Relating Cd2+binding by humic acids to molecular weight:A modeling and spectroscopic study

Molecular weight（Mw） is a fundamental property of humic acids（HAs）, which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid（HA） extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized.Complexation of cadmium was investigated by titration experiments. For the first time,Langmuir and non-ideal competitive adsorption-Donna（NICA-Donnan） models combined with fluorescence excitation-emission matrix（EEM） quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd2＋ to Mw fractions of HA followed the order UF1（〈 5 kDa） 〉 UF2（5–10 kDa） 〉 UF4（〉 30 kDa） 〉 UF3（10–30 kDa）. Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd2＋ among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd2＋ to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding,which has important implications in the control of heavy metal migration and bio-toxicity.

原位同步辐射红外关联谱学技术研究界面电化学反应过程

电化学界面动力学决定了所有电化学反应性质.从原子和分子水平上多维度原位观察电极的表界面电化学反应动态过程对于典型的电化学储能技术(电解槽、燃料电池)中催化剂的结构设计、合成和筛选具有重要意义,但是复杂的电化学界面以及微量、快速的反应中间态信号给界面电化学反应动态过程研究带来了极大的挑战.同步辐射傅里叶变换红外光谱(SR-FTIR)具有独特的分子指纹识别功能,可以用来确定电化学界面的活性物质,结合对纳米材料的局部原子结构高度敏感的同步辐射X射线吸收精细结构(SR-XAFS)光谱可以开展界面电化学反应过程的实时动态研究,有助于指导设计用于高效高能量密度能源系统的先进电催化剂.本文基于近年来本课题组的研究工作,系统地介绍了获得高质量的电化学反应过程中同步辐射红外关联谱学实验结果的策略,及其应用于电催化反应动态过程研究成果,其中主要选用当前热门的金属有机框架(MOF)纳米材料以及金属单原子催化剂(SACs)作为研究对象.最后,对原位同步辐射实验方法发展及其针对电化学反应动态过程的研究进行了展望,旨在通过揭示电化学反应的动态机理来指导和合成高效稳定的催化材料.

Biomass-derived hard carbon microtubes with tunable apertures for high-performance sodium-ion batteries

Sodium-ion batteries(SIBs)are considered the most up-and-coming complements for large-scale energy storage devices due to the abundance and cheap sodium.However,due to the bigger radius,it is still a great challenge to develop anode materials with suitable space for the intercalation of sodium ions.Herein,we present hard carbon microtubes(HCTs)with tunable apertures derived from low-cost natural kapok fibers via a carbonization process for SIBs.The resulted HCTs feature with smaller surface area and shorter Na+diffusion path benefitting from their unique micro-nano structure.Most importantly,the wall thickness of HCTs could be regulated and controlled by the carbonization temperature.At a high temperature of 1,600℃,the carbonized HCTs possess the smallest wall thickness,which reduces the diffusion barrier of Na+and enhances the reversibility Na+storage.As a result,the 1600HCTs deliver a high initial Coulombic efficiency of 90%,good cycling stability(89.4%of capacity retention over 100 cycles at 100 mA·g^(−1)),and excellent rate capacity.This work not only charts a new path for preparing hard carbon materials with adequate ion channels and novel tubular micro-nano structures but also unravels the mechanism of hard carbon materials for sodium storage.

Interface regulation of Cu_(2)Se via Cu–Se–C bonding for superior lithium-ion batteries

Transition metal selenides have aroused great attention in recent years due to their high theoretical capacity.However,the huge volume fluctuation generated by conversion reaction during the charge/discharge process results in the significant electrochemical performance reduction.Herein,the carbon-regulated copper(I)selenide(Cu_(2)Se@C)is designed to significantly promote the interface stability and ion diffusion for selenide electrodes.The systematic X-ray spectroscopies characterizations and density functional theory(DFT)simulations reveal that the Cu–Se–C bonding forming on the surface of Cu2Se not only improves the electronic conductivity of Cu_(2)Se@C but also retards the volume change during electrochemical cycling,playing a pivotal role in interface regulation.Consequently,the storage kinetics of Cu_(2)Se@C is mainly controlled by the capacitance process diverting from the ion diffusion-controlled process of Cu2Se.When employed this distinctive Cu_(2)Se@C as anode active material in Li coin cell configuration,the ultrahigh specific capacity of 810.3 mA·h·g^(−1)at 0.1 A·g^(−1)and the capacity retention of 83%after 1,500 cycles at 5 A·g^(−1)is achieved,implying the best Cu-based Li^(+)-storage capacity reported so far.This strategy of heterojunction combined with chemical bonding regulation opens up a potential way for the development of advanced electrodes for battery storage systems.

Microbial electrosynthesis of acetate from CO_(2)under hypersaline conditions

Microbial electrosynthesis(MES)enables the bioproduction of multicarbon compounds from CO_(2)using electricity as the driver.Although high salinity can improve the energetic performance of bioelectrochemical systems,acetogenic processes under elevated salinity are poorly known.Here MES under 35e60 g L^(-1)salinity was evaluated.Acetate production in two-chamber MES systems at 35 g L^(-1)salinity(seawater composition)gradually decreased within 60 days,both under-1.2 V cathode potential(vs.Ag/AgCl)and^(-1).56 A m^(-2)reductive current.Carbonate precipitation on cathodes(mostly CaCO3)likely declined the production through inhibiting CO_(2)supply,the direct electrode contact for acetogens and H2 production.Upon decreasing Ca2t and Mg2t levels in three-chamber reactors,acetate was stably produced over 137 days along with a low cathode apparent resistance at 1.9±0.6 mU m^(2)and an average production rate at 3.80±0.21 g m^(-2)d^(-1).Increasing the salinity step-wise from 35 to 60 g L^(-1)gave the most efficient acetate production at 40 g L^(-1)salinity with average rates of acetate production and CO_(2)consumption at 4.56±3.09 and 7.02±4.75 g m^(-2)d^(-1),respectively.The instantaneous coulombic efficiency for VFA averaged 55.1±31.4%.Acetate production dropped at higher salinity likely due to the inhibited CO_(2)dissolution and acetogenic metabolism.Acetobacterium up to 78%was enriched on cathodes as the main acetogen at 35 g L^(-1).Under high-salinity selection,96.5%Acetobacterium dominated on the cathode along with 34.0%Sphaerochaeta in catholyte.This research provides a first proof of concept that MES starting from CO_(2)reduction can be achieved at elevated salinity.

Enhancing both selectivity and coking-resistance of a single-atom Pd1/C3N4 catalyst for acetylene hydrogenation

Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride （g-C3N4） using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy （HAADF-STEM） confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle （NP） formation. During selective hydrogenation of acetylene in excess ethylene, the g-C3N4-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al2O3 and Pd/SiO2 catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C3N4 likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd1/C3N4 catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.

Single atom accelerates ammonia photosynthesis

Atomically dispersed metal has gained much attention because of the new opportunities they offer in catalysis. However, it is still crucial to understand the mechanism of single-atom catalysis at molecular level for expanding them to other more difficult catalytic reactions, such as ammonia synthesis from nitrogen. In fact, developing ammonia synthesis under ambient conditions to overcome the high energy consumption in well-established Haber-Bosch process has fascinated scientists for many years.Herein, we demonstrate that single Cu atom yields facile valence-electron isolation from the conjugated π electron cloud of p-CN. Electron spin resonance measurements reveal that these isolated valence electrons can be easily excited to generate free electrons under photo-illumination, thus inducing high efficient photo-induced ammonia synthesis under ambient conditions.The NH_3 producing rate of copper modified carbon nitride(Cu-CN) reached 186 μmol g^(-1) h^(-1) under visible light irradiation with the quantum efficiency achieved 1.01% at 420 nm monochromatic light. This finding surely offers a model to open up a new vista for the ammonia synthesis at gentle conditions. The introduction of single atom to isolate the valence electron also represents a new paradigm for many other photocatalytic reactions, since the most photoinduced processes have been successfully exploited sharing the same origin.

Preliminary investigation of phosphorus adsorption onto two types of iron oxide-organic matter complexes

Iron oxide（FeO）coated by natural organic matter（NOM）is ubiquitous.The associations of minerals with organic matter（OM）significantly changes their surface properties and reactivity,and thus affect the environmental fate of pollutants,including nutrients（e.g.,phosphorus（P））.In this study,ferrihydrite/goethite-humic acid（FH/GE–HA）complexes were prepared and their adsorption characteristics on P at various p H and ionic strength were investigated.The results indicated that the Fe O–OM complexes showed a decreased P adsorption capacity in comparison with bare Fe O.The maximum adsorption capacity（Q（max））decreased in the order of FH（22.17 mg/g）〉FH-HA（5.43 mg/g）〉GE（4.67 mg/g）〉GE-HA（3.27 mg/g）.After coating with HA,the amorphous FH–HA complex still showed higher P adsorption than the crystalline GE–HA complex.The decreased P adsorption observed might be attributed to changes of the Fe O surface charges caused by OM association.The dependence of P adsorption on the specific surface area of adsorbents suggests that the Fe O component in the complexes is still the main contributor for the adsorption surfaces.The P adsorptions on Fe O–HA complexes decreased with increasing initial p H or decreasing initial ionic strength.A strong dependence of P adsorption on ionic strength and p H may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the Fe O component and P.Therefore,previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils,especially in humic-rich areas.

Underestimation of phosphorus fraction change in the supernatant after phosphorus adsorption onto iron oxides and iron oxide–natural organic matter complexes

The phosphorus（P） fraction distribution and formation mechanism in the supernatant after P adsorption onto iron oxides and iron oxide-humic acid（HA） complexes were analyzed using the ultrafiltration method in this study.With an initial P concentration of 20 mg/L（I =0.01 mol/L and pH = 7）,it was shown that the colloid（1 kDa-0.45 μm） component of P accounted for 10.6%,11.6%,6.5%,and 4.0%of remaining total P concentration in the supernatant after P adsorption onto ferrihydrite（FH）,goethite（GE）,ferrihydrite-humic acid complex（FH-HA）,goethite-humic acid complex（GE-HA）,respectively.The 〈1 kDa component of P was still the predominant fraction in the supernatant,and underestimated colloidal P accounted for 2.2%,55.1%,45.5%,and 38.7%of P adsorption onto the solid surface of FH,FH-HA,GE and GE-HA,respectively.Thus,the colloid P could not be neglected.Notably,it could be interpreted that Fe3＋ hydrolysis from the adsorbents followed by the formation of colloidal hydrous ferric oxide aggregates was the main mechanism for the formation of the colloid P in the supernatant.And colloidal adsorbent particles co-existing in the supernatant were another important reason for it.Additionally,dissolve organic matter dissolved from iron oxide-HA complexes could occupy large adsorption sites of colloidal iron causing less colloid P in the supernatant.Ultimately,we believe that the findings can provide a new way to deeply interpret the geochemical cycling of P,even when considering other contaminants such as organic pollutants,heavy metal ions,and arsenate at the sediment/soil-water interface in the real environment.

奇异的硫酸根离子(SO_(4)^(2-))自优化促进氧气析出反应

析氧反应(OER)作为能源转化、贮存的重要过程已被广泛研究,有意思的是其阴离子因为种种原因(惰性位点,易溶解,氧化等)长久以来一直被忽视.本文制备了模型催化剂s-Ni(OH)2来捕获催化剂中的阴离子在电化学过程中的行为以填补相关研究空白.尖端的原位同步辐射傅立叶变换红外光谱(SR-FTIR)、同步辐射光电子能谱(SRPES)深度探测和X射线吸收精细结构(Δ-XAFS)差分谱共同指出催化剂中的部分阴离子(SO_(4)^(2-))将在OER过程中发生自优化过程形成新的Ni-S键.像这种奇异的阴离子自优化行为之前从未被观察到.随后的电化学测试表明,自优化之后衍生的真正催化剂相比于参比催化剂Ni(OH)_(2)表现出显著提高的电化学性能(催化活性、稳定性等).理论计算进一步表明,阴离子自优化过程确实会衍生一个热力学稳定的结构相作为真正的催化剂,该催化剂通过优化OER的热力学和动力学过程赋予其优异的催化性能.本工作直观证明了阴离子在电化学过程中的重要作用,将为理解OER开辟新的视角,并对相关领域,尤其是催化和化学领域产生一些启发.

Vacancy manipulating of molybdenum carbide MXenes to enhance Faraday reaction for high performance lithium-ion batteries

“Intrinsic”strategies for manipulating the local electronic structure and coordination environment of defect-regulated materials can optimize electrochemical storage performance.Nevertheless,the structure–activity relationship between defects and charge storage is ambiguous,which may be revealed by constructing highly ordered vacancy structures.Herein,we demonstrate molybdenum carbide MXene nanosheets with customized in-plane chemical ordered vacancies(Mo_(1.33)CT_(x)),by utilizing selective etching strategies.Synchrotron-based X-ray characterizations reveal that Mo atoms in Mo1.33CTx show increased average valence of+4.44 compared with the control Mo_(2)CT_(x).Benefited from the introduced atomic active sites and high valence of Mo,Mo_(1.33)CT_(x)achieves an outstanding capacity of 603 mAh·g^(−1)at 0.2 A·g^(−1),superior to most original MXenes.Li+storage kinetics analysis and density functional theory(DFT)simulations show that this optimized performance ensues from the more charge compensation during charge–discharge process,which enhances Faraday reaction compared with pure Mo_(2)CT_(x).This vacancy manipulation provides an efficient way to realize MXene’s potential as promising electrodes.

Cation-intercalated engineering and X-ray absorption spectroscopic characterizations of two dimensional MXenes

The geometrically multiplied development of 2D MXenes has already promoted the prosperity of various fields of scientific researches especially but not limited in energy storage and conversion.Notably,cation intercalation can improve the interlayer spacing of MXenes resulting in tunable physical and chemical properties.Moreover,the synchrotron radiation X-ray characterizations have also shown high potential on exploring the property and structu re of cation intercalated MXe nes.This review is mainly focused on the recent achievements of cation intercalated MXenes through different methods on energy storage systems.Synchrotron-based X-ray absorption spectroscopic characterizations are emphasized to probe the local coordination and electronic structure in intercalated MXenes.The outlook of cation intercalation on MXenes and their applications are also discus sed.