Mixed-solvent Strategy Research Articles

Phase Engineering of Zirconium MOFs Enables Efficient Osmotic Energy Conversion: Structural Evolution Unveiled by Direct Imaging.

Creating structural defects in a controlled manner within metal-organic frameworks (MOFs) poses a significant challenge for synthesis, and concurrently, identifying the types and distributions of these defects is also a formidable task for characterization. In this study, we demonstrate that by employing 2-sulfonylterephthalic acid as the ligand for synthesizing Zr (or Hf)-based MOFs, a crystal phase transformation from the common fcu topology to the rare jmt topology can be easily facilitated using a straightforward mixed-solvent strategy. The jmt phase, characterized by an extensively open framework, can be considered a derivative of the fcu phase, generated through the introduction of missing-cluster defects. We have explicitly identified both MOF phases, their intermediate states, and the novel core-shell structures they form using ultralow-dose high-resolution transmission electron microscopy. In addition to facilitating phase engineering, the incorporation of sulfonic groups in MOFs imparts ionic selectivity, making them applicable for osmotic energy harvesting through mixed matrix membrane fabrication. The membrane containing the jmt-phase MOF exhibits an exceptionally high peak power density of 10.08 W m-2 under a 50-fold salinity gradient (NaCl: 0.5 M|0.01 M), which surpasses the threshold of 5 W m-2 for commercial applications and can be attributed to the combination of large pore size, extensive porosity, and abundant sulfonic groups in this novel MOF material.

Monodispersed Sub-1nm Inorganic Cluster Chains in Polymers for Solid Electrolytes with Enhanced Li-Ion Transport.

The organic-inorganic interfaces can enhance Li+ transport in composite solid-state electrolytes (CSEs) due to the strong interface interactions. However, Li+ non-conductive areas in CSEs with inert fillers will hinder the construction of efficient Li+ transport channels. Herein, CSEs with fully active Li+ conductive networks are proposed to improve Li+ transport by composing sub-1nm inorganic cluster chains and organic polymer chains. The inorganic cluster chains are monodispersed in polymer matrix by a brief mixed-solvent strategy, their sub-1nm diameter and ultrafine dispersion state eliminate Li+ non-conductive areas in the interior of inert fillers and filler-agglomeration, respectively, providing rich surface areas for interface interactions. Therefore, the 3D networks connected by the monodispersed cluster chains finally construct homogeneous, large-scale, continuous Li+ fast transport channels. Furthermore, a conjecture about 1D oriented distribution of organic polymer chains along the inorganic cluster chains is proposed to optimize Li+ pathways. Consequently, the as-obtained CSEs possess high ionic conductivity at room temperature (0.52mScm-1 ), high Li+ transference number (0.62), and more mobile Li+ (50.7%). The assembled LiFePO4 /Li cell delivers excellent stability of 1000 cycles at 0.5C and 700 cycles at 1C. This research provides a new strategy for enhancing Li+ transport by efficient interfaces.

Phase-pure 2D tin halide perovskite thin flakes for stable lasing.

Ruddlesden-Popper tin halide perovskites are a class of two-dimensional (2D) semiconductors with exceptional optoelectronic properties, high carrier mobility, and low toxicity. However, the synthesis of phase-pure 2D tin perovskites is still challenging, and the fundamental understanding of their optoelectronic properties is deficient compared to their lead counterparts. Here, we report the synthesis of a series of 2D tin perovskite bulk crystals with high phase purity via a mixed-solvent strategy. By engineering the quantum-well thickness (related to n value) and organic ligands, the optoelectronic properties, including photoluminescence emission, exciton-phonon coupling strength, and exciton binding energy, exhibit a wide tunability. In addition, these 2D tin perovskites exhibited excellent lasing performance. Both high-n value tin perovskite (n > 1) and n = 1 tin perovskite thin flakes were successfully optically pumped to lase. Furthermore, the lasing from 2D tin perovskites could be maintained up to room temperature. Our findings highlight the tremendous potential of 2D tin perovskites as promising candidates for high-performance lasers.

Synthesis and characterization of a luminescent diphosphine and aromatic N-heterocyclic copper(I) coordination polymer

Luminescent Cu(I) complexes have drawn considerable attention as alternative materials to precious transition metal complexes due to their low cost and electron configuration. Discrete heteroleptic diamine-diphosphine copper(I) complexes have been investigated owing to their outstanding photophysical features. However, heteroleptic copper(I) coordination polymers remain mostly unexplored. Herein, we report the synthesis and photophysical characterization of a heteroleptic copper(I) coordination polymer by employing bidentate oxybis(2,1-phenylene)bis(diphenylphosphine) (POP) diphosphine and nitrogen heterocyclic 5-[4-(1-imidazolyl)phenyl]-2H-tetrazole (ipt) as ligands. By utilizing the mixed-solvent strategy, a one-dimensional (1D) linear chain was constructed under solvothermal reaction conditions. Temperature-dependent emission spectra combined with decay time measurements demonstrate that emission originated from triplet phosphorescence at ambient temperature.

Tuning of hybrid highly concentrated electrolytes and the interfacial building for lithium-based cells

The mixed solvent strategy was applied to construct optimized highly concentrated electrolytes (HCEs). Hybrid HCEs based on FEC and AN were investigated systematically. The accelerated ion transport and enhanced anions-derived SEI were achieved.

A mixed solvent strategy enabling efficient all-solution-processed perovskite light-emitting diodes

We report a mixed solvent strategy for depositing an electron transport layer of solution-processed perovskite light-emitting diodes (PeLEDs), which achieves a champion external quantum efficiency of 4.76% in all-solution-processed PeLEDs.

Trace oxophilic metal induced surface reconstruction at buried RuRh cluster interfaces possesses extremely fast hydrogen redox kinetics

Developing high-efficiency electrocatalysts is the key to generating and consuming hydrogen by accelerating the reaction kinetics of the hydrogen oxidation and evolution reactions (HOR/HER). Although the kinetics process of the adsorbed intermediates (Had)-water-oxophilic metal has been investigated in the alkaline media, the hydroxyl species (Had or OH- or OHad)-activity relationship for oxophilic metal alloy electrocatalysis during multiple HOR and HER processes is still unclear. In this regard, our density functional theory (DFT) calculation results show that, due to partial substitution of Ru (Rh) clusters at buried interfaces by oxophilic-metal (OM) species, the long-range order of Ru (Rh) clusters surface atoms can be broken, and then the active atom reconstruction at buried interfaces is triggered, which decreases the oxidation intermediates of Ru (Rh) and gives rise to the increased activity for alkaline HER/HOR. At the same time, an OH--adsorption promoter forms, also favorable for OER. Encouraged by the first-principles calculation results, an ultralow-loaded OM species (0.13 wt% Co, 0.23 wt% Mn, 2.4 wt% Cr or 1.3 wt% Fe) incorporated RuRh cluster (RuRh-OM) catalyst is built by a mixed-solvent strategy. Impressively, after incorporating OM (Co; Mn; Cr and Fe), these catalysts exhibit higher HOR activity than pristine RuRh and commercial Pt even at higher potentials in 0.1 M KOH solutions, which outperforms most reported HOR catalysts and ~ 2 times higher than that of commercial Pt. Meanwhile, RuRh-Co also exhibits the highest HER activity among all reported Ru-based HER catalysts, and greatly improved OER and overall water spitting performances in alkaline solutions (1 M KOH for HER and overall water spitting, 0.1 M KOH for OER), exceeding RuRh and commercial noble metal catalysts.

Solvothermal synthesis of carbonate-type layered double hydroxide monolayer nanosheets: Solvent selection based on characteristic parameter matching criterion

Monolayer nanosheets of CO32−-type layered double hydroxides (LDHs) have many special applications, but their fabrication is challenging. Herein, Co2Al-CO3 and Co2Fe-CO3 LDH nanosheets were synthesized via a solvothermal method. 31 solvents with different characteristic parameters, including the surface free energy (γ) and solubility (δ) parameters were chosen, to explore the correlation between the formation of monolayer LDHs (ML-LDHs) and the characteristic parameters of solvents. The results reveal that when the solvents used have the characteristic parameters matching to those of the LDHs, CO32−-type ML-LDHs with a thickness of ca. 1 nm can be obtained. The mixed-solvent strategy can provide the effective solvents for the synthesis of ML-LDHs. The dispersions of CO32−-type ML-LDHs can be stable for at least six months without obvious precipitation. In addition, it is demonstrated that the δ parameters of LDHs can be calculated from the γ parameters via the molar volume-free γ–δ equations developed previously. Furthermore, a new parameter called “surface free energy distance” is introduced, which can be used for screening effective solvents for the synthesis of ML-LDHs. To the best of our knowledge, this is the first time to investigate the applicable of the characteristic parameter matching principle for the bottom-up synthesis of ML-LDHs. This work deepens the understanding on the feature of CO32−-type LDHs and provides a solvent selection strategy for the synthesis of CO32−-type ML-LDHs.

Facile synthesis and frequency-response behavior of supercapacitor electrode based on surface-etched nanoscaled-graphene platelets

We report on capacitive properties of functionally-graded porous activated nanoscaled-graphene platelets (aNGNS) prepared via reexfoliation of graphite, and high-energy fragmentation through mixed solvent strategy followed by thermochemical etch-away conversion. aNGNS based symmetric supercapacitor demonstrated excellent specific capacitance of 242 F/g at the current density of 0.5A/g with a capacity retention of 97.21 % after 1000 cycles. The device shown remarkable energy density of 27.22 Wh/kg at a power density of 230.56 W/kg at constant current density of 0.5 A/g. Moreover, the enormous amount of porosity created via chemical-assisted etching could facilitate minimal ion-diffusion resistance to achieve exceptional specific capacitance.

Facile synthesis of CuBTC and its graphene oxide composites as efficient adsorbents for CO2 capture

Abstract Easily regenerable adsorbents are highly desirable for CO2 capture. In this regard, a modified synthesis method for preparing CuBTC and its graphene oxide (CuBTC@GO) composites as adsorbents is developed using a mixed solvent strategy at 323 K for the first time. The addition of N, N-Dimethylformamide was vital for the crystallization of CuBTC at low temperature by accelerating the nucleation. The newly synthesized CuBTC showed much higher surface area and total pore volume, compared with CuBTC synthesized by conventional method. As a result, the as-synthesized CuBTC showed a CO2 adsorption capacity of 8.02 mmol/g at 273 K, 1 bar, which was 17–90% higher than the reported CO2 capacity of CuBTC prepared by conventional method. The fabrication of CuBTC@GO composites enhanced the CO2 adsorption capacity mainly through the improved porosity and dispersion force. Compared with CuBTC, an improved CO2/N2 selectivity for CuBTC@1%GO was obtained from the binary breakthrough experiments, which is beneficial to practical gas separations. The partition coefficient of CuBTC and CuBTC@GO composite were evaluated at different breakthrough levels, e.g., 5%, 10% and 100%, with an inlet CO2 partial pressure of 0.15 bar. CuBTC@1%GO displayed higher partition coefficient values than CuBTC at all three breakthrough levels. The cyclic adsorption experiments for regenerability evaluation showed that the CO2 adsorption reversibility for CuBTC@1%GO composite could maintain above 90%, while that of CuBTC dropped to less than 74% after five adsorption-desorption cycles. The CuBTC@GO composite would be a promising CO2 capture adsorbent with both high CO2 adsorption capacity and remarkable regeneration performance.

Estimation of surface free energy and solubility parameters of Mg[sbnd]Al layered double hydroxides

The characteristic parameters, surface free energy (γ) and solubility parameters (δ), of Mg2AlNO3, Mg3AlNO3, Mg4AlNO3, Mg3AlCl, and Mg3AlCO3 layered double hydroxides (LDHs) were estimated using contact angle and liquid phase exfoliation (LPE) methods. The γ parameters include total (γst), dispersive (γsd), and polar (γsp) ones. The δ parameters include the Hildebrand parameter (δt,s) and the Hansen dispersive (δd,s), polar (δp,s), and hydrogen-bonding (δh,s) ones. Results show that the γst, γsd, and γsp of the five LDHs are ∼50.9–56.9, 35.2–39.4, and 15.6–18.8 mJ/m2, respectively, and the δt,s, δd,s, δp,s and δh,s of the LDHs except for the Mg3AlCO3 LDH are ∼31.4–32.9, 17.2, 9.5–10.0, and 24.5–26.1 MPa1/2, respectively. The compositions of LDHs have no obvious impact on all the characteristic parameters. In comparison with van de Waals attraction-bonded materials, the electrostatic attraction-bonded LDHs exhibit higher γst and δt,s values and, especially, much larger δh,s values. The characteristic parameter matching principle and the mixed-solvent strategy are suitable for the LPE of LDHs. Non-toxic glycol/PEG200 mixed liquids are found to be a good medium for the direct LPE of LDHs, producing monolayer nanosheets. To the best of our knowledge, this is the first report on the γ and δ parameters of LDHs. This work not only deepens the understanding of the feature of LDHs, but also provides effective liquid media for the direct LPE of LDHs.

Synthesis of amorphous nickel–cobalt–manganese hydroxides for supercapacitor-battery hybrid energy storage system

In this work, amorphous nickel–cobalt–manganese hydroxide (NiCoMn–OH) was hydrothermally synthesized using a mixed solvent strategy and used as positive electrode materials for supercapacitor-battery hybrid energy storage system. The experimental results show that the mixed solvent is indispensable to form the amorphous phase of NiCoMn–OH, which exhibits significantly improved electrochemical activity and rate capability in comparison with the crystalline counterpart because of more grain boundaries and ion diffusion channels in the former phase. A strong synergy between the transition metal ions in the amorphous NiCoMn–OH is found to significantly contribute to the electrochemical activity, rate capability and cycling stability. In addition to battery behavior, the amorphous NiCoMn–OH exhibits pseudocapacitive behavior, which contributes approximately 40% to the total energy storage capacity. The pseudocapacitive property significantly enhances the rate performance. The robust synthesis method described in this paper was also used to fabricate the NiCoMn–OH porous network on Ni foam, which shows a specific capacity close to its theoretical value, indicating a complete utilization of the electroactive material. Furthermore, a supercapacitor-battery hybrid cell fabricated with the amorphous NiCoMn–OH as the positive electrode and reduced graphene oxide (RGO) as the negative electrode exhibits both high-energy and high-power performances with a specific energy of 42.8 Wh kg–1 at a specific power of 749 W kg–1 or a specific energy of 19.9 Wh kg–1 at a specific power of 20.9 kW kg–1.

Humidity Sensing Properties of Coexfoliated Heterogeneous WS2/WSe2 Nanohybrids

To-dimensional-layered Van der Waals nanostructures and their hybrids have been in focus since the discovery of graphene. Transition metal dichalcogenides are an important segment of materials of this class which is analogous to graphene and can be exfoliated to mono and few layers form. Excellent interlayer coupling among these nanomaterials may result in fascinating synergistic properties. In this work, a simple liquid-phase coexfoliation technique was utilized to exfoliate WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> simultaneously by an optimized mixed solvent strategy. The assynthesized nanohybrids were characterized by using different material characterization techniques. The coexfoliated nanomaterial has shown excellent humidity sensing properties including high reproducibility, stability, and low hysteresis. The response from our humidity sensor varies between 15.4 (at 40% RH) to 57 times (at 80% RH), compared to the reference value of the air (at ~25% RH). The response and recovery times were observed to be 40 and 65 s, respectively, for 60% RH. The performance of coexfoliated sensing layer was compared with individual WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheets and nanocomposite prepared by exfoliation separately. Better performance of sensors utilizing coexfoliated nanosheets has been attributed to synergistic interfacial effects and high proton conductivity. A mechanism based on heterogeneous WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanohybrids has been proposed where the interfaces help in creating favorable sites for water adsorption and desorption apart from the sulfur vacancies in the individual WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . This has been attributed to modulation of surface barrier potential through interfacial electron transfer. We believe such sensing mechanism can help in the development of a new generation highly sensitive humidity sensor.

Formation of transition metal dichalcogenides thin films with liquid phase exfoliation technique and photovoltaic applications

We report on the production of transition metal dichalcogenides (TMDCs) dispersion with high–concentration mixed-solvent strategy. The MoS2 and WS2 thin films are processed by liquid exfoliation which has advantages for residue-free, large-scale, and low-cost in TMDCs film fabrication. Various thicknesses of TMDCs films are prepared and controlled by a centrifuge process for the photovoltaic applications (5 × 5 mm scale) with gold/TMDCs/silicon/indium geometry. Based on ultraviolet photoelectron spectroscopy measurement results, the energy band diagram of the devices using MoS2 and WS2 films can be constructed. The external quantum efficiency and power conversion efficiency (PCE) of MoS2 and WS2 devices are measured with different film thicknesses. The 126–nm-thick MoS2 and 132–nm-thick WS2 film devices show the maximum PCEs of 3.55% and 2.98%, respectively, under 100 mW cm−2 solar illumination. Thus, we demonstrate potential of MoS2 and WS2 films in photovoltaic applications.

Investigations on the role of mixed-solvent for improved efficiency in perovskite solar cell

The morphology of the spin-coated photoactive layer is one of the major factors affecting the performance of perovskite solar cells. In this work, we have employed a mixed-solvent strategy to obtain a high quality MAPbI3 (MA = CH3NH3) perovskite film, without pinholes and reduced grain boundaries. Perovskite films formed with single and mixed-solvents are systematically characterized for their optical, structural, and morphological properties using UV-vis absorption, photoluminescence (PL), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) tools. The power conversion efficiency (PCE) of the devices fabricated using the mixed-solvent showed better performance than the devices made using the single solvent. The best-optimized mixed-solvent perovskite film exhibited a PCE of 15.2% with uniform film coverage on the substrate, better charge generation, and a high hole mobility of 1.16 × 10−4cm2/V s. The disparities in photovoltaic properties have been analyzed with the intensity dependent current density-voltage (J-V), transient photovoltage (TPV), and relationship between photocurrent (Jph) and effective voltage (Veff).

Efficient mixed-solvent exfoliation of few-quintuple layer Bi2S3 and its photoelectric response

A scalable liquid exfoliation of layered Bi2S3 employing a mixed-solvent strategy was used for the fabrication of Bi2S3 nanosheets. We found that 10% deionized water in 90% isopropyl alcohol is the best mixed solvent for the efficient and effective exfoliation of layered Bi2S3. These results are consistent with the absorbance spectra and enthalpy of mixing theory. The obtained Bi2S3 nanosheets had few-quintuple layers and were investigated by transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. These Bi2S3 nanosheets can be used to fabricate large-scale thin films by filtration method; the films demonstrated sensitive photoelectric response with the rise and decay response of photocurrent on the sub-second scale under visible light excitation. The electronic structures of bulk and one-quintuple layer Bi2S3 are calculated by first-principle calculation for better understanding of the photoelectric response. A green mixed-solvent processing of Bi2S3 opens up the potential application of Bi2S3 optoelectric films to photoelectric detection and solar energy conversion devices.

A mixed-solvent route to unique PtAuCu ternary nanotubes templated from Cu nanowires as efficient dual electrocatalysts

Forming alloys with transition metal remarkably decreases the u sage of noble metal and offers benefits for electrocatalysis. Here we introduced a mixed-solvent strategy to synthesize unique PtAuCu ternary nanotubes (NTs) with porous and rough surface, using high quality Cu nanowires (NWs) as the partial sacrificial templates. We found that Au plays a key role in the enhancement of e lectrocatalytic performance for both methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR). The mass activities of PtAuCu NTs after acid leaching for MOR and FAOR reach 1698.8 mA mg-1Pt at 0.9 V and 1170 mA mg-1Pt at 0.65 V, respectively. Such ternary NTs show impressive stability due to the irreversibly adsorption of CO* on the Au surface instead of the active Pt surface and the excellent structure stability. The present method could be extended to prepare other new multi-functional electrocatalysts.

Vertical orientation of solvent cast nanofilled PS-b-PEO block copolymer thin films at high nanoparticle loading

We demonstrate selective dispersion of photosensitive electron acceptor phenyl-C61-butyric acid methyl ester (PCBM) in cylinder forming polystyrene-b-poly (ethylene oxide) (PS-b-PEO) block copolymer (BCP). Neat PS-b-PEO is structurally robust to forming vertically oriented nanoscale morphology of PEO cylinders in the PS matrix directly after solvent casting. Varying amounts of PCBM nanoparticles were mixed with PS-b-PEO BCP in solvent mixtures and films were spin cast on UV/ozone treated clean silicon wafers. We studied in detail the BCP morphology orientation effect of different solvents and solvent mixtures for varying PCBM loading (ϕPCBM) in the films, range from 0 to 50 weight percent relative to the BCP. The key accomplishments of this work include vertical orientation control even at large concentration of PCBM ∼30% (w/w) particles relative to polymer mass and preferential segregation of PCBM in PS block via mixed solvent strategy which otherwise is difficult to realize due to segregation of PCBM on polar substrate. We explain the preferential dispersion of particles in films by demarcating limits in terms of critical Hansen solubility parameter. This value is close to the percolation threshold of PCBM, so a conducting polymer matrix can be expected, especially when it is partitioned preferentially in the matrix PS domain. We report changes in PEO cylinder diameter, cylinder center-to-center distance with PCBM incorporation into PS matrix, change of film thickness with overall PCBM incorporation and root mean square roughness of the film surface, for a range of casting solvents, solvent mixture compositions and ϕPCBM. Notably, the film thickness increased as the PCBM content in film was increased for same processing condition, so that domain swelling by nanoparticles was self-adjusting with film thickness increment.

Solution-processed yellow-white light-emitting diodes based on mixed-solvent dispersed luminescent ZnO nanocrystals

Yellow-white light emitting diodes (LEDs) using ZnO nanocrystals (NCs) as the active materials have been fabricated based on a solution-processed technology. By utilizing a polar-nonpolar mixed-solvent dispersion strategy, uniform dispersion of ZnO NCs with enhanced emission properties has been achieved. The ZnO NCs based LED devices prepared from the mixed-solvent strategy show much improved electroluminescence properties that exhibit a broad yellow-white emission peaks at ∼555 nm with a maximum brightness of 100 cd/m2 and a color rendering index of 77.25. The device mechanism of the LED device was discussed in terms of energy band diagram and current-voltage characteristics.

Efficient synthesis of monolayer carbon nitride 2D nanosheet with tunable concentration and enhanced visible-light photocatalytic activities

A versatile and scalable mixed solvent strategy was developed to prepare monolayer C3N4 nanosheets with tunable concentration for the first time. This approach could also be used to prepare other 2D nanosheets from their layered materials (such as MoS2, BN, WS2 etc.). The structural features and intrinsic semiconductor properties of the as-prepared C3N4 nanosheets have been investigated in detailed. The photocatalytic activities were evaluated by photocatalytic oxidation of both benzyl alcohol and rhodamine B (RhB) under visible light irradiation. Results showed that the as-prepared monolayer C3N4 nanosheets with thickness of 0.4nm still retained the structural features of g-C3N4 layer. The functionalities of C3N4 nanosheets well inherited from the layered parent counterpart. Furthermore, due to the exceptionally high 2D anisotropy, C3N4 nanosheets showed the distinctive physicochemical properties and unique electronic structures, such as high surface area, lower surface defects, stronger reduction ability of the photogenerated electrons, increased photoelectric response, and promoted the charge-carrier migration and separation. All of these favorable factors co-contributed to the greatly improved photocatalytic activities over C3N4 nanosheets compared with those of its bulk counterpart.