Intercalation Of Molecules Research Articles

Controllable Design of Metal-Organic Framework-Derived Vanadium Oxynitride for High-Capacity and Long-Cycle Aqueous Zn-Ion Batteries.

Introducing N atoms in vanadium oxides (VOx) of aqueous Zn-ion batteries (ZIBs) can reduce their bandgap energy and enhance their electronic conductivity, thereby promoting the diffusion of Zn2+. The close-packed vanadium oxynitride (VON) generated often necessitates the intercalation of water molecules for restructuring, rendering it more conducive for zinc ion intercalation. However, its dense structure often causes structural strain and the formation of by-products during this process, resulting in decreased electrochemical performance. Herein, carbon-coated porous V2O3/VN nanosheets (p-VON@C) are constructed by annealing vanadium metal-organic framework in an ammonia-contained environment. The designed p-VON@C nanosheets are efficiently converted to low-crystalline hydrated N-doped VOx during subsequent activation while maintaining structural stability. This is because the V2O3/VN heterojunction and abundant oxygen vacancies in p-VON@C alleviate the structural strain during water molecule intercalation, and accelerate the intercalation rate. Carbon coating is beneficial to prevent p-VON@C from sliding or falling off during the activation and cycling process. Profiting from these advantages, the activated p-VON@C cathode delivers a high specific capacity of 518 mAh g-1 at 0.2 A g-1 and maintains a capacity retention rate of 80.9% after 2000 cycles at 10 A g-1. This work provides a pathway to designing high-quality aqueous ZIB cathodes.

Heterostructure assembled by organic-molecule intercalated MoS2 and reduced graphene oxide for enhanced interface energy and supercapacitor performance

Organic molecule intercalation and heterostructure construction can optimize the capacitive storage of MoS2. To begin with, we choose MoO3 as the molybdenum source and polypyrrole (PPy) as the intercalation agent to synthesize the enlarged interlayer spacing MoS2 (MoS2-PPy). On this basis, MoS2-PPy@reduced graphene oxide (rGO) heterostructures are eventually fabricated. The electrochemical merits of rGO and MoS2-PPy can be combined through synergistic effects among the heterostructure. What's more, to examine the kinetics storage mechanisms of MoS2 samples, density functional theory (DFT) calculations have been done. It turns out the introduction of rGO enhanced the polarity of MoS2, which lead to stronger interface energy and additional capacitance. Additionally, for the involvement of rGO, the conductivity has been effectually elevated. Moreover, an AC//MoS2-PPy@rGO asymmetric flexible device is assembled, and it have an excellent energy density of 134.4 µWh cm−2 at a power density of 800 µW cm−2. This work paves the way for constructing organic-molecular intercalated-MoS2 based heterostructures in capacitive energy storage.

Intercalation of organosilane in clay mineral for the removal of Procion red MX-5B: Investigational and theoretical studies

Finding new materials with specific characteristics such as eco-friendly, low-cost, sustainable, and efficient in wastewater treatment is still challenging. Thus, the present work combines the surface modification and intercalation of [3-(2-aminoethylamino)propyl]trimethoxysilane (TMSPEDA) of natural montmorillonite (Mmt) and its adsorption performance in the removal of Procion red MX-5B from aqueous solution. The modified clay (Mmt@SPEDA; the hybrid of montmorillonite-[3-(2-aminoethylamino)propyl] silane) was also characterised using XRD, FESEM, EDS, pHpzc, FTIR, N2-adsorption/desorption analyses, elemental analysis, TGA/DTG, hydrophobicity-hydrophilicity balance (HI). In order to improve the comprehension of the process intercalation and adsorption mechanism between Procion red MX-5B and Mmt@SPEDA adsorbent, a theoretical analysis of the adsorption phenomenon was performed based on DFT calculation. As a result, the interlamellar spacing of natural clay increased more than 1.50 times after the intercalation process, corresponding to a 50.33 % expansion. The final geometry of the intercalation process reveals that SPEDA molecules are perpendicular to the surface of montmorillonite with a specific orientation interaction between the oxygen atoms of the silanol group of the intercalating molecules and the atoms on the surface of montmorillonite. These interactions are likely electrostatic or correspond to van der Waals forces and hydrogen bonds. The characterisation data confirms the grafting of SPEDA groups on the clay. The positive adsorption energies indicate the endothermic nature of the adsorption process, suggesting that the system absorbs energy during the adsorption of PRMX-5B dye. The Liu's Qmax values for PRMX-5B dye varied from 171.4 and 318.6 mg g−1 for temperatures ranging from 10°–45 °C, demonstrating the excellent properties of the Mmt@SPEDA hybrid adsorbent.

Reversible Constrained Dissociation and Reassembly of MXene Films.

Enabling materials to undergo reversible dynamic transformations akin to the behaviors of living organisms represents a critical challenge in the field of material assembly. The pursuit of such capabilities using conventional materials has largely been met with limited success. Herein, the discovery of reversible constrained dissociation and reconfiguration in MXene films, offering an effective solution to overcome this obstacle is reported. Specifically, MXene films permit rapid intercalation of water molecules between their distinctive layers, resulting in a significant expansion and exhibiting confined dissociation within constrained spaces. Meanwhile, the process of capillary compression driven by water evaporation reinstates the dissociated MXene film to its original compact state. Further, the adhesive properties emerging from the confined disassociation of MXene films can spontaneously induce fusion between separate films. Utilizing this attribute, complex structures of MXene films can be effortlessly foamed and interlayer porosity precisely controlled, using only water as the inducer. Additionally, a parallel phenomenon has been identified in graphene oxide films. This work not only provides fresh insights into the microscopic mechanisms of 2D materials such as MXene but also paves a transformative path for their macroscopic assembly applications in the future.

Hydrothermal synthesis of layered zirconium phosphates and their intercalation properties

ABSTRACT Layered inorganic materials are widely used as fillers in nanocomposites due to their unique properties such as mechanical performance, thermal properties, flame resistance, barrier properties, corrosion resistance, catalytic activity, and multifunctionality. Among them, layered α-zirconium phosphate (α-ZrP: Zr(HPO4)2H2O) is one of the representative inorganic materials and unique properties with P–O–H groups that can exchange inorganic and organic cations and intercalate basic molecules. This paper deals with the use of this compound as an adsorbent for heavy metal cations in wastewater. Samples were prepared by hydrothermal treatment at various Zr/P ratio, water amounts, and temperatures. Furthermore, an attempt was made to widen the interlayer distance of the sample using n-butylamine. The α- zirconium phosphate prepared at 160°C for 20 h with Zr/P = 1/2 adsorbed the most amount of metal ions. Furthermore, interlayer amine modification was effective. Then, the behaviour of the adsorption process was observed by varying the time of adsorption from 1 h to 50 h, in order to clarify the change in adsorption of the samples over time.

Intercalation of small molecules in the selective layer of polyamide nanofiltration membranes facilitates the separation of Mg2+/Li+

In addressing lithium supply shortages driven by increased energy demand, nanofiltration membrane technology is crucial for recovering lithium from salt lake brines. Overcoming the challenge of achieving high selectivity for Li+ and water permeability in polymer nanofiltration membranes, this study proposes a simple approach using Aminomalononitrile (AMN) intercalation to modify polyamide layers. Density functional theory simulations predict AMN's superior selectivity and enhanced hydrophilicity. Stable intercalation of AMN between polyethyleneimine (PEI) molecules is demonstrated, synergistically enhancing water permeability and Li+ selectivity. The resulting PEI/AMN-TMC membrane exhibits exceptional Li+ selectivity and improved water permeability (13.1 L·m−2·h−1·bar−1), 2.9 times higher than traditional PEI-TMC membranes. Stable performance for over seven days, along with anti-scaling and anti-bacterial properties, underscores its practicality. This investigation sheds light on membrane structure regulation through small-molecule intercalation, offering insights into precise adjustments for enhanced water permeability and ion selectivity.

N-DMBI Doping of Carbon Nanotube Yarns for Achieving High n-Type Thermoelectric Power Factor and Figure of Merit.

The application of carbon nanotube (CNT) yarns as thermoelectric materials for harvesting energy from low-grade waste heat including that generated by the human body, is attracting considerable attention. However, the lack of efficient n-type CNT yarns hinders their practical implementation in thermoelectric devices. This study reports efficient n-doping of CNT yarns, employing 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzimidazole-2-yl) phenyl) dimethylamine (N-DMBI) in alternative to conventional n-dopants, with o-dichlorobenzene emerging as the optimal solvent. The small molecular size of N-DMBI enables highly efficient doping within a remarkably short duration (10s) while ensuring prolonged stability in air and at high temperature (150°C). Furthermore, Joule annealing of the yarns significantly improves the n-doping efficiency. Consequently, thermoelectric power factors (PFs) of 2800, 2390, and 1534µWm-1K-2 are achieved at 200, 150, and 30°C, respectively. The intercalation of N-DMBI molecules significantly suppresses the thermal conductivity, resulting in the high figure of merit (ZT) of 1.69×10-2 at 100°C. Additionally, a π-type thermoelectric module is successfully demonstrated incorporating both p- and n-doped CNT yarns. This study offers an efficient doping strategy for achieving CNT yarns with high thermoelectric performance, contributing to the realization of lightweight and mechanically flexible CNT-based thermoelectric devices.

Interlayer manipulation of bio-inspired Ti3C2Tx nanocontainer through intercalation of amino acid molecules to dramatically boosting uranyl hijacking capability from seawater

More than 4.5 billion tons of unconventional uranium resources [UO2(CO3)3]4- are uniformly dissolved in seawater, providing a sustainable and abundant fuel source for the development of nuclear energy. Herein, we presented a rational design and development of Ti3C2Tx nanocontainer inspired by the exceptional selectivity and affinity exhibited by superb-uranyl proteins through amino acid intercalation. The amino acid intercalation of Ti3C2Tx demonstrated exceptional UO22+ capture capacity (Arg-Ti3C2Tx, His-Ti3C2Tx, and Lys-Ti3C2Tx with qmax values of 594.46, 846.04, and 1030.17 mg/g). Furthermore, these intercalated materials exhibited remarkable sequestration efficiency and selectivity (Uinitial = ∼45.2 ∼7636 μg/L; ∼84.45% ∼98.08%; and ∼2.72 ×104 ∼1.28 ×105 KdU value), despite the presence of an overwhelming surplus of Na+, Ca2+, Mg2+, and Co2+ ions. Significantly, even in the 0.3 M NaHCO3 solution and surpassing 103-fold of the Na3VO4 system, the adsorption efficiency of Lys-Ti3C2Tx still achieved a remarkable 63.73% and 65.05%. Moreover, the Lys-Ti3C2Tx can extract ∼30.23 ∼8664.03 μg/g uranium after 24 h contact in ∼13.3 ∼5000 μg/L concentration from uranium-spiked natural seawater. The mechanism analysis revealed that the high binding capability can be attributed to the chelation of carboxyl and amino groups with uranyl ions. This innovative state-of-the-art approach in regulating uranium harvesting capability through intercalation of amino acid molecules provides novel insights for extracting uranium from seawater.

Prominent Nonlinear Optical Absorption in SnS2‐Based Hybrid Inorganic–Organic Superlattice

AbstractNonlinear optical materials hold great promise for applications in advanced opto‐/opto‐electronic devices. However, achieving a substantial nonlinear absorption coefficient and modulation depth concurrently remains challenging. This study proposes an effective strategy for enhancing the nonlinear optical response of materials through the construction of hybrid inorganic–organic superlattices via convenient organic intercalation. Synthesizing SnS2 intercalated with various tetra‐alkylammonium cations, it is revealed that the optimized sample (SnS2/CTA: SnS2 intercalated with cetyltrimethylammonium, CTA+) exhibits a substantial enhancement of nonlinear absorption across a broad wavelength range (from 515 to 1550 nm) and for diverse nonlinear optical processes (saturable absorption, two‐photon absorption, and three‐photon absorption). Specifically, the SnS2/CTA demonstrates a third‐order nonlinear absorption coefficient of (9.847 ± 0.084) × 103 cm GW−1 and a 69% modulation depth under laser excitation at 800 nm. Under 1550 nm excitation, it displays a fifth‐order nonlinear absorption coefficient of (45.3 ± 1.2) cm3 GW−2 and a 62% modulation depth. Notably, these values surpass those of the majority of non‐exfoliated materials. Structural, spectral, and density functional theory calculations indicate no induced structure defects post‐organic intercalation. The observed bandgap reduction is attributed to the electron injection associated with the organic molecule intercalation. The calculated performance enhancement, based on dielectric enhancement and bandgap reduction, qualitatively aligns with experimental findings.

Leveraging ordered voids in microporous perovskites for intercalation and post-synthetic modification.

We report the use of porous organic layers in two-dimensional hybrid organic-inorganic perovskites (HOIPs) to facilitate permanent small molecule intercalation and new post-synthetic modifications. While HOIPs are well-studied for a variety of optoelectronic applications, the ability to manipulate their structure after synthesis is another handle for control of physical properties and could even enable use in future applications. If designed properly, a porous interlayer could facilitate these post-synthetic transformations. We show that for a series of copper-halide perovskites, a crystalline arrangement of designer ammonium groups allows for permanently porous interlayer space to be accessed at room temperature. Intercalation of the electroactive molecules ferrocene and tetracyanoethylene into this void space can be performed with tunable loadings, and these intercalated perovskites are stable for months. The porosity also enables reactivity at the copper-halide layer, allowing for facile halide replacement. Through this, we access previously unobserved reactivity with halogens to perform halide substitution, and even replace halides with pseudohalides. In the latter case, the porous structure allows for stabilization of new phases, specifically a novel copper-thiocyanate perovskite phase, only accessible through post-synthetic modification. We envision that this broad design strategy can be expanded to other industrially relevant HOIPs to create a new class of highly adjustable perovskites.

OXIDE-REDUCED MECHANISM OF Fe(ІІІ) OXIDE REMOVAL FROM MONTMORILLONITE

The article proposes a redox mechanism for the bleaching of bentonite lump red clay and produces fillers for white paints and varnishes. Nanostructures of different types have been studied: intercalation compounds, delaminated nanocomposites, and mixed-type nanocomposites. Using the methods of IR spectroscopy, XRF analysis, laser diffraction, and DTA analysis, samples of synthesized organomodified bentonite were studied and the fact of intercalation of alkylbenzyldiethylamonium chloride molecules into the interlayer galleries of the crystalline inorganic matrix was established. A basic technological scheme for the production of bentonite fillers and organobentonite is presented. Nanocomposite hybrid paints and varnishes with the participation of new fillers and organobentonite have been obtained, and the physical and mechanical properties of new materials and coatings have been established.

Structure, electronic, and magnetic properties of 3d transition metal intercalated borophene/BP heterostructures

AbstractThe intercalation of various atoms or molecules has become one promising way to manipulate the electronic and magnetic properties of layered materials. Using density functional calculations, we explored the 3d transition metal (TM) intercalated α‐borophene/black phosphorus (α‐B/BP) heterostructure, TM@(α‐B/BP) (TM = Sc‐Ni), on their structure, electronic and magnetic properties. Our results demonstrate that TM@(α‐B/BP)s can be ferromagnetic (FM), antiferromagnetic (AFM) and nonmagnetic depending on the choice of TM atoms, and most systems have large magnetic anisotropic energy. Particularly, Ti@(α‐B/BP) is AFM semiconductor with Néel temperature of 470 K, which is much higher than room temperature. Moreover, the electronic and magnetic properties of TM@(α‐B/BP)s can be further altered by the TM intercalation concentration. Our results provide a feasible way to design promising candidates for applications in electronic and information storage devices.

Stepless IR Chromism in Ti3 C2 Tx MXene Tuned by Interlayer Water Molecules.

Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3 C2 Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3 C2 Tx . This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3 C2 Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Effect of the pH on the interaction of hydrotalcite with dyes from textile wastewater

AbstractThe increase in textile fibre production volume is expected to result in a corresponding rise in untreated wastewater, highlighting the need for effective and affordable wastewater treatment methods. This study explored the potential of hydrotalcite, a product in cement hydration, which can be used as a low‐cost adsorbent, in treating wastewater containing Reactive Blue 19 or Acid Green 1 dyes. The effect of pH on the decolourization properties was studied using HCl, HNO3, H2SO4, NaOH, KOH, Ca(OH)2, and Ba(OH)2. The results showed that both dyes had significantly different decolourization properties with hydrotalcite in acidic and basic dye solutions, with acidic environments enhancing dye uptake. The ions present in the dye solution have no significant impact on the decolourization properties. Zeta potential analysis supported these findings, with acidic dye solutions exhibiting higher zeta potential. An intercalation of dye molecules into the layered structure of the hydrotalcite could not be detected. The study shows that hydrotalcite is most effective as an adsorbent in acidic environments.

Redox-controlled differential weathering of andesitic pumice: Possible catalytic effects of ferrous/ferric iron on rapid halloysite accumulation in a Holocene tephra layer

Differential weathering process of Holocene andesitic tephra in Atsuma, Hokkaido, northern Japan, were investigated with a specific focus on the flame-like occurrence of halloysite bands and their formation mechanism. The parent material was coarse-grained pumice (Ta-d2) deposited 9 ka to form a highly permeable metre-thick layer atop fine-grained impervious periglacial loam, which is covered by humic soil–tephra sequences. The shallower part of the Ta-d2 layer was weathered to a reddish or yellowish brown colour, which is characterized by intensive leaching of Si and Al, with abundant precipitation of iron (hydr)oxide and amorphous secondary minerals in an oxidizing environment. A reductive grey colour was observed only at the Ta-d2 bottom below the halloysite band, where pumice grains survived significant elemental leaching and contained ferrous iron in the solid phase with abundant dissolved Fe in the liquid phase. Between these oxidized and preserved zones, an irregularly shaped, fine-grained, white iron-rich halloysite layer with a decimetre-scale thickness developed. In this clay band, the molar ratio of Si to (Al + Fe) was nearly 1:1, with a small amount of remnant Ca. Mössbauer analysis revealed that Fe2+ was initially incorporated into the aluminosilicate sheet via Al3+ substitution and transformed into Fe3+ within the structure. The halloysite band was formed at depths in the tephra layer corresponding to the redox front. The abundance of Si and Al in pore water in any zone of the tephra layer meets the stability requirements of halloysite, indicating that the redox condition controls the rapid local accumulation of halloysite through the isomorphous substitution followed by valence change of iron. We propose a new hypothesis stating that iron catalyses halloysite nucleation via a stepwise function, including layer charging to absorb hydrated cations and subsequent charge loss resulting in cation desorption and passive intercalation of water molecules within the 1:1 layer.

Chiral Van Der Waals Superlattices for Enhanced Spin-Selective Transport and Spin-Dependent Electrocatalytic Performance.

The emergence of the chiral-induced spin-selectivity (CISS) effect offers a new avenue for chiral organic molecules to autonomously manipulate spin configurations, thereby opening up possibilities in spintronics and spin-dependent electrochemical applications. Despite extensive exploration of various chiral systems as spin filters, one often encounters challenges in achieving simultaneously high conductivity and high spin polarization (SP). In this study, a promising chiral van der Waals superlattice, specifically the chiral TiS2 crystal, is synthesized via electrochemical intercalation of chiral molecules into a metallic TiS2 single crystal. Multiple tunneling processes within the highly ordered chiral layered structure of chiral TiS2 superlattices result in an exceptionally high SP exceeding 90%. This remarkable observation of significantly high SP within the linear transport regime is unprecedented. Furthermore, the chiral TiS2 electrode exhibits enhanced catalytic activity for oxygen evolution reaction (OER) due to its remarkable spin-selectivity for triplet oxygen evolution. The OER performance of chiral TiS2 superlattice crystals presented here exhibits superior characteristics to previously reported chiral MoS2 catalysts, with an approximately tenfold increase in current density. The combination of metallic conductivity and high SP sets the stage for the development of a new generation of CISS materials, enabling a wide range of electron spin-based applications.

High-pressure Raman scattering and X-ray diffraction study of kaolinite, Al2Si2O5(OH)4

Kaolinite is formed by weathering of continental crustal rocks and is also found in marine sediments in the tropical region. Kaolinite and other layered hydrous silicate minerals are likely to play a vital role in transporting water into the Earth's interior via subducting slabs. Recent studies have experimentally documented the expansion of the interlayer region by intercalation of water molecules at high pressures i.e., pressure-induced hydration. This is counter-intuitive since the interlayer region in the layered silicates is quite compressible, so it is important to understand the underlying mechanism that causes intercalation and expansion of the interlayer region.To address this, we explore the high-pressure behavior of natural kaolinite from Keokuk, Iowa. This sample is free of anatase impurities and thus helps to examine both low-energy (0–1200 cm−1) and high-energy hydroxyl (3000–4000 cm−1) regions using Raman spectroscopy and synchrotron-based powder X-ray diffraction.Our results show that the pressure dependence of the hydroxyl modes exhibits discontinuities at ∼3 GPa and ∼ 6.5 GPa. This is related to the polytypic transformation of Kaolinite from K-1 to K-II and K-II to K-III phase. Several low-energy Raman modes' pressure dependence also exhibits similar discontinuous behavior. The synchrotron-based powder X-ray diffraction results also indicate discontinuous behavior in the pressure dependence of the unit-cell volume and lattice parameters. The analysis of the bulk and the linear compressibility reveals that kaolinite is extremely anisotropic and is likely to aid its geophysical detectability in subduction zone settings. The K-I to K-II polytypic transition is marked by the snapping of hydrogen bonds, thus at conditions relevant to the Earth's interior, water molecules intercalate in the interlayer region and stabilize the crystal structure and help form the super-hydrated kaolinite which can transport significantly more water into the Earth's interior.

Elucidating the Mechanism of Large Phosphate Molecule Intercalation Through Graphene-Substrate Heterointerfaces.

Intercalation is the process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on the intercalation of metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains challenging. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5 at the graphene-substrate heterointerface using various techniques. Density functional theory (DFT) corroborates the experimental results and reveals the intercalation mechanism, whereby P2O5 dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5 intercalation, the possibility of intercalation from predissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This in-depth study advances our understanding of intercalation routes of large molecules via the basal plane of graphene as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds.

Surface chemistry engineering and the applications of MXenes

MXenes have captured extensive attention in various fields by virtue of unique hydrophilicity, high conductivity and tunable surface terminations. In this review, the state-of-the-art progresses of designing functional MXenes have been summarized. Firstly, the synthesis methods of MXenes are summarized and classified into HF etching, in-situ HF etching and fluoride-free etching approaches based on the effect on the surface chemistry of MXenes. Secondly, the factors that affect the surface termination groups are discussed, including synthesis methods, heat treatment temperature and atmosphere. Thirdly, this review gives an overview of the synthetic routes of functional MXenes including termination modification by synthesis methods and heat treatment, heteroatom (N, S, or P) doping, cation and organic molecule intercalation and hybridization with polymer, which inhibit restacking and increase active sites for intrinsically enhancing the inherent physical and chemical properties of MXenes. Finally, the applications with respect to energy storage and conversion, catalysis, sensors, electromagnetic interference shielding and microwave absorption of functional MXenes are introduced. Additionally, the critical challenges and development prospects of functional MXenes are also highlighted.

Effect of water intercalation into tungsten trioxide structure (WO3·xH2O) (x = 0,1,2): Correlation between structure and photocatalytic performances

Tungsten oxide (WO3) is a potential photoanode material for water oxidation, however, its employment is still restricted by its limited light absorption (Eg ∼ 2.75 eV). A particular interest was devoted to tuning its electronic structure and optical bandgap in order to enhance its photocatalytic performance in hydrogen production as well as in advanced oxidation process. One of the promising alternatives for the enhancement of these photocatalytic performances, is the introduction of guest molecules into the tungsten oxide structure. In this paper, the photocatalytic performances of tungsten trioxide were highly improved by the intercalation of water into its structure. The intercalated compounds of chemical formula WO3·xH2O were prepared and characterized by TGA-DSC, PXRD, FT-IR, Raman spectroscopy, SEM-EDS and XPS. The structures of intercalated materials were refined using Rietveld method and the electronic proprieties including bandgap energy, CB and VB edges were estimated using UV–visible reflectance spectroscopy. The obtained results show that the intercalation of water molecules into tungsten oxide structure reduces the gap energy of the WO3 (2.4 eV) to 2.16 eV for WO3∙H2O and to 2.31 eV for WO3∙2H2O. The photocatalytic efficiency of the obtained materials was studied through oxygen evolution reaction tests in the presence of an electron acceptor (Ag+) and the oxidative photodegradation of the orange G dye pollutant. We found that intercalated samples exhibit the highest efficiencies compared with anhydrous samples. These findings are correlated with the increase in the average W-O-W tilt angle in WO3∙2H2O and WO3∙H2O compared to that of WO3. This improvement in the tilt angle induces the shrinkage of the energy bandgap and increases the photocatalytic performance. Furthermore, the stability of the investigated materials was studied as a function of pH, the results reveal that the intercalation of water molecules is beneficial for the chemical stability of the hydrated tungsten oxides. These findings shed light on new alternatives for band-gap engineering and improvement of materials stability through intercalation with water molecules.