Soft Chemical Approach Research Articles

(Invited) From Solid-State Li-S to Polysulfide Flow Batteries: Challenges and Opportunities

Despite several decades of research and development work on Li-S batteries, there are still several fundamental issues that limits their performance and life. Controlling the polysulfide dissolution remains the major bottle neck in liquid electrolyte-based system. To alleviate this issue, there has been a steady progress in transitioning to quasi solid-state gel electrolytes and solid-state sulfur. The talk will cover some recent results on soft-chemistry approach by using a polymer gel electrolyte that has high ionic conductivity at RT and buffers volume changes during electrochemical activity. One example relates to fabrication a gel S-cathode on a carbon nanotube (CNT) matrix coated with a crosslinked network of polyethyleneimine -poly (ethylene oxide) (PEI-PEO), and solvated Li salt (LiTFSI). By optimizing the salt and polymer composition the conductivity of gel electrolyte exceeded 1x10-4 S/cm at RT. Design of high-performance solid-state sulfur cathode relies on effective ionic and electronic wiring with optimal composition of solid- electrolyte and electronic diluent such as carbon nanotube of highly graphitic carbon. Achieving high loading solid-state sulfur cathode is challenging due to limited ion-transport. The talk will cover recent work on catholyte design for sulfur cathodes using sulfide based solid electrolytes. In contrast, RT Li/Na polysulfide flow batteries provide a completely different geometry and architecture where the energy and power density is dictated by the solubility of the polysulfide species in the desired solvent and membrane design and stability. Acknowledgment This research is supported by Asst. Secretary, Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program and Energy Storage Program, Office of Electricity, Department of Energy, USA.

Study of the Photoluminescence Enhancement Observed in ZnO Nanowire Gratings Optimally Grown by the Hydrothermal Method

AbstractAn original ZnO nanowire (NW) architecture has been developed, entirely based on a soft chemistry approach, and thoroughly assessed through optical measurements and electromagnetic simulations. This architecture relies on the photoimprinting of a sol–gel ZnO‐based photosensitive seed layer combined with the subsequent localized hydrothermal growth of ZnO NWs. The optimization of the elaboration protocol has been shown to lead to uniform and reproducible linear and periodic gratings of ZnO NWs with a width/pitch of 2/4 µm. The NW gratings are compared with full‐covered samples (NWs coating) elaborated from a nonimprinted seed layer. A morphological study reveals that NW gratings present a peculiar hedgehog‐like profile. Standard and angle‐resolved photoluminescence studies demonstrate that the ZnO NWs visible emission is strongly modified by the presence of NW gratings and that its red part is directionally extracted and enhanced by a factor of up to 2. The electromagnetic simulations performed for both samples highlight the role of the gratings acting as coupled microcavities that boost the ZnO emission through light localization and diffractive mechanisms. It enables the extraction of the resonant photons at specific angles and wavelengths.

Synthesis of superconducting (Li,Fe)OHFeSe by 2-propanol-assisted solvothermal method

(Li,Fe)OHFeSe superconducting at Tc≃40K has been synthesized by 2-propanol-assisted solvothermal synthetic route. Relatively low-temperature (363–373K) intercalation process gives opportunity to use this method for soft chemistry approaches to the synthesis of iron-based superconductors.

UV Suppression in photoluminescence emission and improved photocatalytic activity under sunlight in nanoassemblies and nanocrystals of ZnO

The objective of present study is to analyse the impact of alterations in the shape and size of ZnO on PL emission and photocatalytic activity of ZnO nanostructures. The study also aims at addressing the knowledge gap between synthesis approach and its role in governing the optical, morphological and photocatalytic behaviour. Here, we report the facile and controlled synthesis of nanoassemblies (NA) and nanocrystals (NC) of ZnO via soft chemical approach. The synthesized ZnO nanostructures were characterized using TEM, SEM, UV–vis and photoluminescence (PL) measurement. The morphology of ZnO is tuned by adjusting the molar ratio of DEG and water whose impact is also noticed on the PL emission spectra. PL analysis revealed that the UV emission (378 nm) and defect levels attributed to Zn interstitial (Zni) and oxygen interstitial (Oi) are stabilized at ambient condition. However, UV band gap emission peak is significantly reduced making it lesser distinct by introducing appropriate amount of water in diethylene glycol (DEG) solvent during ZnO synthesis. Such controlled nanostructured growth demonstrates potential for sustainable photocatalytic activity under both UV and Sunlight irradiation. The study shows 100% photodegradation efficiency for ZnO NA and it get completely irradiated methylene blue dye within 90 min under UV light, whereas only 70% dye is degraded in 100 min for ZnO NC. Under natural Sunlight, ZnO NA has been achieved 97% degradation efficacy in 75 min; however, ZnO NC has degraded only 89% of dye. Further, the degradation of dye over ZnO was observed to follow pseudo first order reaction kinetic model that is used to determine the rate constant of the reaction.

Synthesis of SiO2@MnCo2O4 core–shell nanorattles using layered double hydroxide precursors and studies on their peroxidase-like activity

The current work demonstrates a simple soft chemical approach to synthesize SiO2@MnCo2O4 core–shell nanorattles using SiO2@MnCo-LDH (layered double hydroxide) precursors.

Natural sunlight driven photocatalytic performance of Ag/ZnO nanocrystals

Herein, spherical-shaped ZnO nanoparticles of an average size of about 10 nm were successfully synthesized through a soft chemical approach. We further prepared the Ag/ZnO nanocrystals by varying the loaded amounts of metallic silver nanoparticles (1, 3, and 5 wt%) without using any reducing and stabilizing agent. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the transformation of Ag ions into metallic Ag and the interaction between Ag and ZnO nanoparticles. High resolution-transmission electron microscopy (HR-TEM) images revealed that Ag nanoparticles of an average size of about 4.6 nm are present on the surface of spherical ZnO nanoparticles. UV-visible absorption spectra showed that the appropriate amount of Ag loading with ZnO shifted the band gap from UV to the visible region. Photoluminescence spectrum reveals the inclusion of Ag in ZnO and minimizes the recombination of electron-hole pairs. These synthesized Ag/ZnO nanocrystals were investigated for its potential applications in photocatalytic degradation of methylene blue dye under UV and sunlight irradiation and compared their efficiency with pure ZnO. Interestingly, it is seen that ZnO nanocrystals that are UV active become visible active when loaded with 1 and 5 wt% of metallic Ag. ZnO loaded with 1 wt% of metallic Ag completely degraded the methylene blue within 3 h under natural sunlight. Under UV light, 3 wt% of Ag in ZnO exhibits higher photocatalytic performance than the others. Thus, incorporating metallic Ag in ZnO nanoparticles shows excellent photocatalyst performance and recycling capability. Furthermore, the participation of different reactive species in the photocatalysis degradation mechanism was studied using four scavengers and the results indicate that superoxide and singlet oxygen are the dominant reactive species. We report heterostructure of Ag/ZnO nanocrystals and explored their efficiency for photocatalytic degradation of dye under visible light irradiation. • Synthesis of Ag/ZnO nanocrystals without any reducing and stabilizing agent. • Transformation of band gap from UV to Visible by incorporation of appropriate amount of Ag in ZnO. • Excellent photocatalytic performance and recycling capability for degradation of dye under UV and natural sunlight. • These nanocatalysts can be for further use for inhibition of bacteria pathogens.

Visible-light-induced V2O5 -TiO2 photocatalysts with high photocatalytic ability for degradation of tetracycline

In this contribution, mesoporous V2O5–TiO2 heterojunctions were constructed utilizing a soft-chemistry approach. The photocatalytic ability of the V2O5–TiO2 nanocomposites was assessed for tetracycline degradation under visible exposure compared to bare TiO2 and P-25. TEM images presented the close contact between the tetragonal TiO2 in the anatase phase and orthorhombic V2O5 with particle sizes between 10 and 20 nm. The obtained V2O5–TiO2 photocatalysts indicated higher photocatalytic performance compared to bare TiO2 and P-25 in the photooxidation of tetracycline. It demonstrated that 3%V2O5–TiO2 nanocomposite exhibited a superb photocatalytic ability in the destruction of tetracycline ∼100% after 120 min, owing to its promoted visible harvest ability, large surface area and enhanced separation efficiency of carriers. Meanwhile, the kinetic rate constant of 3%V2O5–TiO2 nanocomposite was about 9.8 and 29.3 times larger than bare TiO2 and P-25. The photocurrent responses and PL spectra measurements are matched well with the photocatalytic efficiency of the V2O5–TiO2 nanocomposites. The reasonably designed heterojunctions V2O5–TiO2 nanocomposites could enhance the photocatalytic performance by reducing the recombination rate of photoinduced carriers.

Lepidocrocite Titanate–Graphene Composites for Sodium-Ion Batteries

To overcome electronic transport issues of layered titanates in sodium-ion batteries, we have designed and synthesized composites of lepidocrocite titanates with reduced graphene oxide through a solution-based self-assembly approach. The parent lepidocrocite titanate (K0.8[Ti1.73Li0.27]O4) was exfoliated by a soft-chemical approach and mechanical shaking. Exfoliated layered titania sheets (LTO) were then combined with reduced graphene oxide (rGO) layers to assemble into composites through flocculation. Countercations (i.e., Mg2+) were used for the self-assembly of negatively charged titania and rGO nanosheets via flocculation. The carbon content in the composites was tuned from 1 to 17% by changing the ratio of titania and rGO sheets in the mixed colloidal suspensions. Electrodes were processed with as-prepared LTO–rGO composites without any carbon additives and tested in sodium half-cell configurations. Mg+-coagulated LTO–rGO composite electrodes deliver higher capacities than electrodes prepared with coagulated titania sheets and 10% acetylene black in sodium half-cells and display good capacity retention after 50 cycles. Electrochemical impedance spectroscopy results indicate lower charge transfer resistance for LTO–14.5%rGO composites than that of coagulated titania sheets with 10% acetylene black. A power law analysis of cells containing the composites indicate a hybrid mechanism consisting of both surface and diffusional processes. A comparison with a similar system, that of dopamine-derived LTO-C heterostructures, reveal significant differences. While capacities showed a strong dependence on carbon content for the dopamine-derived materials, this was not true for the LTO–rGO composites. Instead, the highest capacity was obtained for the 14.5% rGO sample, with a lower value obtained for the 17% rGO sample. A greater proportion of the redox processes were surface rather than diffusional in nature for the LTO–rGO composites as well.

A Brief Review: The Use of L-Ascorbic Acid as a Green Reducing Agent of Graphene Oxide.

The reduced form of graphene oxide (r-GO) represents a versatile precursor to obtain graphene derivatives. Graphene oxide (GO) consists of a layered material based on a carbon skeleton functionalized by different oxygen-containing groups, while r-GO is obtained by the almost complete removal of these oxygen-containing functional groups. The r-GO has mechanical, electrical, and optical properties quite similar to graphene, thus, it proves to be a convenient 2D material useful for many technological applications. Nowadays, the most important aspects to consider in producing r-GO are: (i) the possibility of obtaining the highest reduction grade; (ii) the possibility of improving the dispersion stability of the resulting graphene using surfactants; (iii) the use of environmentally friendly and inexpensive reducing agents. Consequently, the availability of effective soft-chemistry approaches based on a green reducing agent for converting GO to r-GO are strongly needed. Among the green reductants, the most suitable is L-ascorbic acid (L-aa). Different studies have revealed that L-aa can achieve C/O ratio and conductivity values comparable to those obtained by hydrazine, a typical reducing agent. These aspects could promote an effective application strategy, and for this reason, this review summarizes and analyzes, in some detail, the up-to date literature on the reduction of GO by L-aa. The results are organized according to the two most important approaches, which are the reduction in liquid-phase, and the reduction in gel-phase. Reaction mechanisms and different experimental parameters affecting the processes were also compared.

Novel rhombus-shaped cerium oxide sheets as a highly durable methanol oxidation electrocatalyst and high-performance supercapacitor electrode material

In this work, novel rhombus-shaped cerium oxide sheets (RCOS) were prepared using a facile, soft-chemical approach that was low cost, scalable, eco-friendly, and industrially viable. The structural and surface chemical properties were studied using spectroscopic and electron microscopic techniques. The synthesized RCOSs were used for the methanol oxidation reaction and supercapacitor studies. The RCOSs showed a current density of ∼227 mA cm–2 with an onset potential of ∼0.37 V. The electrocatalyst activity retention was 92% of the initial activity after 500 CV cycles. A specific capacitance of 481 F g–1 at a scan rate of 5 mV s–1 was observed for supercapacitor application. The specific capacitance retention was ∼83% after 500 cycles. The huge specific surface area and conductivity associated with cerium oxide sheets were responsible for the enhanced electrochemical properties. This is the first report on the synthesis of rhombus-shaped cerium oxide sheets, which leads to new avenues for synthesizing novel cerium-based electrode materials.

Highly efficient ZnO nanostructures for enhanced photocatalytic degradation of organic contaminants under simulated solar light: An efficient industrial approach

The increasing demand for uncontaminated and affordable water is now the biggest challenge worldwide. Therefore, there is an urgent need to remove the soluble organic effluents from wastewater and make water reusable. In this aspect, two different morphologies of ZnO nanostructures (NPs and NRs) were developed by a soft-chemical approach and their photocatalytic activity for degradation of organic dyes were investigated. TEM micrographs confirm the formation of nanoparticles (NPs: 20 ± 3 nm) and nanorods (NRs: length of 60 ± 5 nm and width of ∼ 10 nm) of ZnO. XRD and Raman spectra show the formation of single-phase hexagonal wurtzite for both the ZnO nanostructures. The UV–visible absorption and photoluminescence studies confirm that ZnO nanostructures show a change in bandgap and defect concentration as morphology changes from particles to rods. Both the morphologies of ZnO nanostructures show the excellent photocatalytic degradation of methylene blue (MB), rhodamine B (RhB), methyl orange (MO) (under UV and simulated solar light) as well as an industrial dye (under simulated solar light). TheZnO NPs and NRs degrade MB, RhB and MO with 100 % efficiency under UV and solar light at the appropriate time. Moreover, ZnO nanostructures show good photostability and reusability which make them useful for industrial applications.

Chiral plasmonic nanostructures: recent advances in their synthesis and applications

This review presents the main techniques employed to construct chiral plasmonic materials and metasurfaces, in particular using soft-chemistry approaches, and discusses some applications of these nanostructures.

Nanocomposite of SnO2 quantum dots and Au nanoparticles as a battery-like supercapacitor electrode material

Quantum dot-based nanocomposite materials have gained huge attention in electrochemical energy storage devices due to their extremely high surface-to-volume ratio and enhanced conductivity. In this work, nanocomposites of SnO2 quantum dots and Au nanoparticles (SQD-Au) has been prepared by an in-situ soft-chemical approach. The structural and charge storage properties of the prepared material were investigated. The prepared composite material coated on the nickel foam and used as working electrode for supercapacitor applications. Results show that the SQD-Au electrode material exhibits an excellent specific capacity of 87 mAh g−1 at the current density of 1A g−1. The columbic efficiency of the electrode was found be 98 % after 5000 GCD cycles. Some of the factors responsible for the observed superior charge storage properties of SQD-Au composite compared pristine SQDs are enhanced conductivity and fast electron transport.

Structural and Compositional Characteristics of Ball-Milled Lepidocrocite Alkali Titanate and the Correlation to Its Surface Acidic-Basic Properties.

The studies on mechanical treatments of layered alkali metal oxides are limited despite their diverse compositions/structures and potential for property tuning. In this work, we vibratory mill Cs0.7Zn0.35Ti1.65O4, K0.8Zn0.4Ti1.6O4, and Cs2Ti6O13 for up to 4 h, during which the lepidocrocite-type structure and the plate-like morphology are well preserved. X-ray diffraction (XRD) indicates a tiny (≤0.6 Å) interlayer expansion accompanied by the enhancement of the preferred orientation along the stacking direction. Chemical analyses across multiple length scales suggest Cs deintercalation, elemental redistributions, and bulk-to-surface (or crystal edge) Cs migration. This ball-milling-induced Cs-rich moiety partially blocks the surface acid sites, although the solids still show a dominating acidic character. The ball-milled samples Cs0.7-pZn0.35-qTi1.65O4-δ contain vacancies between the sheets (p) and at the sheets (q and δ). It is deduced from Sanderson's electronegativity equalization principle and experimentally verified by X-ray photoelectron spectroscopy (XPS) that ball milling increases (decreases) the partial charge at the surface acidic Ti4+/Zn2+ (basic O2-) sites. These nonporous solids (≤20 m2·g-1) contain water sorbed on the external surface as high as 1.1 mol·mol-1, which is comparable to that in a water-intercalated sample. Our work expands the current understanding of the reactivity vs robustness in layered alkali titanates under physically demanding conditions, complementing knowledge gathered via the soft chemistry approach.

Synthesis of [formula omitted]-FeSe by 2-propanol solvothermal method

Using elemental iron and selenium as well as NH4Cl and 2-propanol as starting materials, a low temperature (473 K) method of solvothermal synthesis of β–FeSe superconducting at Tc≃8K has been successfully applied. This method may result in new possibilities for soft chemistry approaches to the synthesis and modification of iron-based superconductors.

Effect of annealing environment on the photoelectrochemical water oxidation and electrochemical supercapacitor performance of SnO2 quantum dots

SnO2 quantum dots (SQD) were prepared by utilizing the soft-chemical approach. The formed SQD's were annealed in two kinds of environments: air and nitrogen (N2). Each annealing environment resulted in significant improvement in the performance of water oxidation and electrochemical supercapacitor performance. The specific capacitance of the SQD's under the N2 annealing process (SQD-N2) shows significantly better electrochemical performance. A specific capacitance of 79.13 F/g was achieved for SQD-N2 sample by applying a current of 1 mA, which was approximately 1.5 times greater than that of the pristine SQD's. A cycle stability of 99.4% over 5000 cycles was achieved by SQD-N2. The process of nitrogen annealing environment brings down the bandgap from 3.37 to 1.9 eV. The SQD-N2 sample shows the highest photocurrent over SQD and SQD-Air samples. From the LSV study, SQD-N2 shows the photocurrent density of 4.82 mA/cm2, which is 1.43 times greater than pristine SQD sample. The nitrogen-annealing environment provides the optimal environment to tune the average crystallite size and crystallinity nature of SQD's to improve the optical properties like bandgap to enhance the water oxidation and also electrochemical performance.

Design of metastable oxychalcogenide phases by topochemical (de)intercalation of sulfur in La2O2S2

Designing and synthesising new metastable compounds is a major challenge of today’s material science. While exploration of metastable oxides has seen decades-long advancement thanks to the topochemical deintercalation of oxygen as recently spotlighted with the discovery of nickelate superconductor, such unique synthetic pathway has not yet been found for chalcogenide compounds. Here we combine an original soft chemistry approach, structure prediction calculations and advanced electron microscopy techniques to demonstrate the topochemical deintercalation/reintercalation of sulfur in a layered oxychalcogenide leading to the design of novel metastable phases. We demonstrate that La2O2S2 may react with monovalent metals to produce sulfur-deintercalated metastable phases La2O2S1.5 and oA-La2O2S whose lamellar structures were predicted thanks to an evolutionary structure-prediction algorithm. This study paves the way to unexplored topochemistry of mobile chalcogen anions.

Soft chemical processing approach for the valorization of seafood waste by-products as a source of bioactive polymers

Abstract Chitin and chitosan as green and active biomacromolecules were extracted from local seafood waste (shrimp shells). The extraction was carried out by a soft chemical process, followed by structural characterization (FTIR, XRD, viscosity average molecular weight M̅v), thermal stability by TGA, and antibacterial tests. FTIR and XRD spectra confirmed the chemical structures of the extracted chitin and chitosan which were similar to the commercial ones. The chitin and chitosan had an average viscosimetric molar weight of 232.21 kDa and 41 kDa, respectively. The chitosan had a high deacetylation degree (DD = 71 %) and low cristallinity index (Icr = 68.3 %); compared to chitin, which exhibited a lower deacetylation degree (DD = 24.27 %), higher thermal stability and higher cristallinity index (Icr = 87.55 %). A bacteriostatic effect of chitin was observed in the gram-negative bacteria, Escherichia coli, Salmonella typhimurium. Chitosan exhibited a bacteriostatic effect on all bacteria tested, except Salmonella typhimurium.

Core-shell Fe3O4@ZnO nanoparticles for magnetic hyperthermia and bio-imaging applications

Combining two materials having different functional properties has become a current research area for biomedical applications. The progress of nanoplatforms brings new non-invasive imaging and therapeutic tools for cancer treatment. Here, multifunctional magnetic Fe3O4@ZnO core-shell nanoparticles (Fe3O4@ZnO CSNPs) have been developed by using a soft-chemical approach. Fe3O4@ZnO CSNPs is well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), physical properties measurement system (PPMS), and photoluminescence spectroscopy. XRD and XPS analyses confirm the presence of both Fe3O4 and ZnO phases. TEM micrograph reveals that Fe3O4@ZnO CSNPs are spherical in shape and an average size of 10 nm. Fe3O4@ZnO CSNPs conserve the intrinsic superparamagnetic behavior of its constituent Fe3O4 with a magnetization value of ∼ 31.2 emu/g. These CSNPs exhibit good heating efficacy under the applied AC magnetic field (ACMF). Further, they show a significant reduction in viability of human cervical cancer cells (HeLa) under ACMF and good fluoresecent based cellular imaging capability. Therefore, these results suggested that the multifunctional Fe3O4@ZnO CSNPs could be used as a promising material for image-guided magnetic hyperthermia.

Soft chemistry of metastable metal chalcogenide nanomaterials.

The metastable nature of metal chalcogenide nanomaterials (MCNs) provides us with fresh perspectives and plentiful grounds in the search of new strategies for physicochemical tuning. In the past decade, numerous efforts have been devoted to synthesizing and modifying diverse emerging MCNs based on their "soft chemistry", that is, gently regulating the composition, structure, phase, and interface while not entirely disrupting the original features. This tutorial review focuses on design principles based on the metastability of MCNs, such as ion mobility and vacancy, thermal and structural instability, chemical reactivity, and phase transition, together with corresponding soft chemical approaches, including ion-exchange, catalytic growth, segregation or coupling, template grafting or transformation, and crystal-phase engineering, and summarizes recent advances in their preparation and modification. Finally, prospects for the future development of soft chemistry-directed synthetic guidelines and metastable metal chalcogenide-derived nanomaterials are proposed and highlighted.