Constructing long-cycling crystalline C_(3)N_(4)-based carbonaceous anodes for sodium-ion battery via N configuration control

Carbon nitrides with two-dimensional layered structures and high theoretical capacities are attractive as anode materials for sodium-ion batteries while their low crystallinity and insufficient structural stability strongly restrict their practical applications.Coupling carbon nitrides with conductive carbon may relieve these issues.However,little is known about the influence of nitrogen(N)configurations on the interactions between carbon and C_(3)N_(4),which is fundamentally critical for guiding the precise design of advanced C_(3)N_(4)-related electrodes.Herein,highly crystalline C_(3)N_(4)(poly(triazine imide),PTI)based all-carbon composites were developed by molten salt strategy.More importantly,the vital role of pyrrolic-N for enhancing charge transfer and boosting Na+storage of C_(3)N_(4)-based composites,which was confirmed by both theoretical and experimental evidence,was spot-highlighted for the first time.By elaborately controlling the salt composition,the composite with high pyrrolic-N and minimized graphitic-N content was obtained.Profiting from the formation of highly crystalline PTI and electrochemically favorable pyrrolic-N configurations,the composite delivered an unusual reverse growth and record-level cycling stability even after 5000 cycles along with high reversible capacity and outstanding full-cell capacity retention.This work broadens the energy storage applications of C_(3)N_(4) and provides new prospects for the design of advanced all-carbon electrodes.

Synthesis of crystalline g-C_(3)N_(4) with rock/molten salts for efficient photocatalysis and piezocatalysis

Graphitic carbon nitride(g-C_(3)N_(4))is emerging as a promising visible-light photocatalyst while the low crystallinity with sluggish charge separation/migration dynamics significantly restricts its practical applications.Currently,synthesizing highly crystalline g-C_(3)N_(4) with sufficient surface activities still remains challenging.Herein,different from using alkali molten salts which is commonly reported,we propose an approach for synthesis of highly crystalline g-C_(3)N_(4) with FeCl3/KCl rock/molten mixed salts.The rock salt can serve as the structure-directing template while molten salt provides the required liquid medium for re-condensation.Intriguingly,the synthesized photocatalyst showed further enhanced crystallinity and improved surface area along with high p/p*excitation compared with crystalline C_(3)N_(4) prepared from conventional molten-salt methods.These catalytically advantageous features lead to its superior photocatalytic and piezocatalytic activities with a high reactivity for overall water splitting that is not commonly reported for C_(3)N_(4).This work provides an effective strategy for structural optimization of organic semiconductor based materials and may inspire new ideas for the design of advanced photocatalysts.

Constructing Crystalline g-C_(3)N_(4)/g-C_(3)N_(4-x)S_(x)Isotype Heterostructure for Efficient Photocatalytic and Piezocatalytic Performances

Graphitic carbon nitride(g-C_(3)N_(4))is viewed as a promising visible-light photocatalyst for industrialization due to its low processing temperature and high chemical stability.However,serious charge recombination caused by incomplete polymerization during direct calcination of nitrogen-rich precursors significantly limits its photocatalytic performances.To boost charge separation,herein,we propose a rational strategy by constructing a crystalline g-C_(3)N_(4)/g-C_(3)N_(4-x)S_(x) isotype heterostructure through the molten salt method.Theoretical calculation reveals that apparent charge-transfer channels are formed between g-C_(3)N_(4) and S-doped g-C_(3)N_(4) layers in the heterostructure.Owing to high crystallinity for decreasing charge recombination and isotype heterostructure for efficient charge transfer,the as-prepared g-C_(3)N_(4)/g-C_(3)N_(4-x)S_(x) showed remarkable photocatalytic performances with the hydrogen production rate elevated by up to 12.3 times of its singular components.Another novelty of this work is we investigated for the first time the piezocatalytic activity of crystalline g-C_(3)N_(4) by characterizing its performance for H2O2 generation and KMnO4 reduction.Strikingly,its superior piezocatalytic performance over components can be further improved by NaBH4 treatment,which is uncovered to enhance the asymmetric structure of crystalline g-C_(3)N_(4) by introducing extra cyano groups and removing partial NHx species in its tri-s-triazine layer structure.This work opens up new strategies for the design of highly efficient polymeric photocatalysts and highlights the piezocatalytic studies of g-C_(3)N_(4).

Highly crystalline acceptor materials based on benzodithiophene with different amount of fluorine substitution on alkoxyphenyl conjugated side chains for organic photovoltaics

Organic solar cells based on narrow bandgap small-molecule acceptors(SMAs)with highly crystalline characteristics have attracted great attentions for their superiority in obtaining high photovoltaic efficiency.Employing highly crystalline SMAs to enhance power conversion efficiencies(PCEs)by regulating and controlling morphology and compatibility of donor and acceptor materials has turned out to be an effective approach.In this study,we synthesized three different crystalline SMAs by using fluorine substitution on alkoxyphenyl conjugated side chains to modulate the relationship of crystallinity and morphologies,namely ZY1(zero F atoms),ZY2(two F atoms),and ZY3(four F atoms).The three SMAs show the broad absorption edges and similar frontier orbital energy levels,generating the analogical(over 0.9 V)open circuit voltage(VOC)of the polymer solar cells(PSCs).As a result,the PM6:ZY2-based PSCs yield a PCE of 10.81%with a VOC of 0.95 V,a short-circuit current density(JSC)of 16.154 mA cm^(-2),and a fill factor(FF)of 0.71,which is higher than that of 9.17%(PM6:ZY1)and 6.37%(PM6:ZY3).And the PCE(17.23%)of the PM6:Y6:ZY2 based ternary PSCs is also higher than that of 16.32%PM6:Y6 based binary device.Obviously,the results demonstrate that adding fluorine atoms on the conjugated side chains to construct high crystalline materials is a positive strategy to effectively increase the efficiencies of binary and ternary PSCs.

Hierarchical loading of CuO on SiO_(2) aerogel@high crystalline TiO_(2) nanofibers for efficiently photocatalytic reduction of CO_(2) without sacrificial agent

Silica aerogel was prepared by a sol-gel method with combination of freeze drying.The aerogel was filled with TiCl4 in autoclave and used to fabricate a hierarchical structure of TiO_(2) nanofiber shell and SiO_(2) aerogel core(SiO_(2)@TiO_(2)).The TiO_(2) nanofibers with a diameter of 10-15 nm were highly crystalline and mainly grew along the(101)or(001)planes,favoring charge migration along the growth axis of the fibers.The photoluminescence(PL)emission spectra show that the TiO_(2) nanofibers exhibited much lower PL intensity than P25.The free standing TiO2 nanofibers loaded with CuO had a band gap of 3.04 eV.When CuO was hierarchically loaded on the nanofiber surface and into the aerogel core(SiO_(2)/CuO@TiO_(2)/CuO),the absorption edge significantly red shifted,and the band gap was further narrowed to 2.66 eV.Meanwhile,Fe^(3+)implanted TiO_(2) nanofibers on the aerogel surface(SiO_(2)@Fe-TiO_(2))were also fabricated in the same strategy.The CuO loaded nanofibers(SiO_(2)/CuO@Fe-TiO_(2)/CuO)had a band gap of 2.62 eV.The photocatalytic reduction of CO_(2) was performed under light irradiation by a 300 W Xe-lamp for 4 h.The methanol yield over the SiO_(2)/CuO@Fe-TiO_(2)/CuO reached~2,400 μmol·gcat^(-1) in the absence of sacrificial agent.

Hydrothermal Formation of Lath-Shaped Trioctahedral Smectite with High Crystallinity

Lath-shaped and highly crystalline trioctahedral smectites were synthesized under hydrothermal conditions. The quenched glasses with stoichiometrically dehydrated Na-smectite compositions were treated at （a） 500℃ and 100 MPa for 1 and 11 days; and （b） 300℃ and 100 MPa for 7 days. The crystallinity and particle size of products were dependent on the chemical composition of the starting glass, synthetic temperature and duration of hydrothermal treatment. The high structural ordering and large dimensions of the products were confirmed from the sharpness of XRD peaks; and hydration behavior under controlled relative humidity. Transmission electron microscopy was also performed for the characterization of the particle size of product. Particle sizes vary from ca. 10 nm to a few pm by changing the chemical compositions of the starting materials. The product with the highest structural ordering and largest dimension was obtained from Nao.33（Mg1.83Al0.67）Si4O11 glass treated at 500℃ and 100 MPa for 1 day. The obtained results also confirmed the metastability and compositional dependency in the formation of highly crystalline trioctahedral smectite at hydrothermal conditions.

Effectively Inhibit Phase Separation to Improve Efficiency and Stability of All-Inorganic Planar CsPbIBr2 Perovskite Solar Cells

The advancement in a power conversion efficiency(PCE)to reach 25%,the inorganic perovskites are being explored intensively as promising optoelectronic materials due to their excellent photovoltaic performance,i.e.,thermal stability and efficiency.Lately,the inorganic cesium lead halide perovskite is studied to show enhanced light absorption,however,it suffers from the phase separate into I-rich and Br-rich phase which leads to poor film quality due to difference of electronegativity.Herein,we propose a unique solution of controlling the rate of solvent volatilization followed by gel method to inhibit phase separation effectively to obtain the homogenous and pinhole-free CsPbIBr2 films with high crystalline quality.In this study,an inverted planar device based on a light absorber of CsPbIBr2 is prepared to achieve a power conversion efficiency of 8.8%(maintain a stabilized value of 8%in ambient air conditions).Surprisingly,the optimized cell without encapsulation shows excellent long-term stability,as it maintained 90%initial efficiency over 500 h and controlled storage at around 45%relative humidity and 25℃.

Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO_2 crystals

Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.

Realizing the highly reversible Zn^(2+)and Na^(+) dual ions storage in high-crystallinity nickel hexacyanoferrate microcubes for aqueous zinc-ion batteries

Prussian blue analogues(PBAs)with the 3D open framework are regarded as promising cathode candidates for aqueous Zinc ion batteries(ZIBs).Among various PBAs,nickel hexacyanoferrate(NiHCF)has attracted considerable attention because of its high operating voltage and economic merit.However,the cyclability of NiHCF is unsatisfactory due to poor structural stability during Zn^(2+) ions insertion/deinsertion.Moreover,the ion storage mechanism of NiHCF in aqueous electrolytes has not been fully revealed yet.Herein,high-crystallinity NiHCF(HC-NiHCF)microcubes with improved structural stability and larger crystal plane spacing are synthesized.For the first time,highly reversible Zn2+ions and Na+ions co-insertion/extraction are achieved for the HC-NiHCF microcubes in mixed aqueous electrolyte,as evidenced by various observations including two separated discharge plateaus and sequential changes of Na 1s and Zn 2p signals in ex-situ X-ray photoelectron spectroscopy(XPS).As a result,a high specific capacity of 73.9 mAh g^(−1) is obtained for the HC-NiHCF microcubes at 0.1 A g−1,combined with enhanced cycle stability(75%vs.16.4%)over 1000 cycles at 2 A g^(−1).The reversible Zn^(2+) ions and Na+ions co-insertion in HC-NiHCF microcubes reveals a new ion storage mechanism of Ni-based PBAs in aqueous electrolytes.

快速微波还原电化学衍生氧化石墨烯制备高结晶石墨烯膜

电化学氧化石墨,可用于大规模合成氧化石墨烯,是一种可持续且直接的方法.然而,关于电化学衍生氧化石墨烯(EGO)进一步还原的研究却很缺少.本文中,我们报道了EGO膜的快速微波还原过程.化学法合成的氧化石墨烯膜需要数分钟微波辐射才能被还原,但是我们制备的EGO膜经3秒微波辐射即可转化为高结晶石墨烯膜(HCGM),并且该过程无需对膜进行预处理或添加微波增敏剂.与以前报道的微波法制备的石墨烯相比,本文制备的HCGM具有大尺寸芳香区(约100 nm)、高碳/氧原子比(约33)和高电导率(约5×10^(4)S m^(−1)).EGO的高微波还原效率可以归因于其独特分子结构,EGO中丰富的芳香区可高效吸收微波,引发EGO膜实现瞬时体相加热.该研究加深了对氧化石墨烯微波还原机理的理解,并为HCGM的生产提供了一条便捷途径.

Regulating crystallinity in linear conjugated polymer to boost the internal electric field for remarkable visible-light-driven disinfection

Conjugated linear polymers are promising metal-free photocatalysts for visible-light-driven photocatalytic water disinfection,but it was still bottlenecked by the insufficient photogenerated charge separation and transport(CST)process.Herein,we obtained the highly crystalline imine-linked conjugated linear poly-mer(ODA-BPAH)with a greatly enhanced CST process.The highly crystalline ODA-BPAH exhibited excel-lent broad-spectrum water disinfection efficiency up to 99.99999%in 1 h,which is among the reported highest of state-of-the-art photocatalysts.The crystallinity of ODA-BPAH was regulated by simply turn-ing the solvent and the experiment results revealed that the ODA-BPAH with high crystallinity exhibited higher internal electric field strength and photocatalytic performance than that with low crystallinity,which indicates that higher crystallinity in linear conjugated polymers contributes to superior CST ef-ficiency as well as the generation of reactive oxygen species.This work highlights the impact of poly-mer crystallinity on the internal electric field and proves that linear poly-imine could be a new type of promising metal-free photocatalyst for water treatment.

Non-Equlibrium Doping,Phase Selection and Fuctionalization in TiO_2 Nanoparticls Prepared by RF Thermal Plasma Methods

1 Results Control of dispersion in synthesized nano-size powders is crucial to the realization of nanoparticles application,such as the fabrication of functional nano-strucured bodies.Dispersion of plasma-synthesized TiO2 nanoparticles,which are formed in-flight in the high temperature thermal plasma,should be superior to those prepared by ordinal wet processes,as the particles have no surface residual groups.RF thermal plasma is characterized by extremely high temperatures,and rapid heating and cooling...

A two-step solvothermal procedure to improve crystallinity of covalent organic frameworks and achieve scale-up preparation

Covalent organic frameworks(COFs),as a novel class of functional polymers,exhibit versatile applica-tions due to their crystalline porous structures and conjugated skeletons.However,synthesis of COFs with high crystallinity still faces great challenges,especially for scale-up preparation.Herein we report a two-step solvothermal process to improve crystallinity of COFs.The first step focuses on polycondensa-tion of monomers with no need for optimizing crystallization conditions.In the second step,appropriate solvothermal conditions are used to facilitate crystallization of the COFs through defects correction and structural repairing.Furthermore,this strategy could also be applicable to scale-up synthesis of high qual-ity COFs,which lays a foundation for their practical applications.

Promoting condensation kinetics of polymeric carbon nitride for enhanced photocatalytic activities

Polymeric carbon nitride(CN)semiconductor by thermal condensation of N-rich precursors has attracted much attention for its capability ranging from photocatalytic and photoelectrochemical energy conversion to biosensing.However,the influence of condensation process on the final structure of CN was rarely studied,making the condensation kinetic far from be fully optimized.Herein,we report the preparation of CN by a simple condensation kinetics modulation using a faster ramping rate during the polymerization process.The modified condensation recipe was even simpler than the conventional one,but led to an improved photocatalytic H2 evolution up to 3 times without any additional chemicals or other complements.Detailed mechanism studies revealed the increase of crystallinity and surface area due to the rapid condensation played the key roles.This work would offer a more facile and effective way to prepare bulk CN for large-scale industrial applications of bulk CN with higher photocatalytic actives for sustainable energy,environmental and biosensing.