Ion-exchange Route Research Articles

Chimie Douce Synthesis of Novel Metastable Cathodes for Potassium-Ion Batteries

The quest for innovative cathode materials is crucial for advancing secondary potassium-ion batteries (KIBs). Dedicated efforts have led to the exploration of broadly four distinct classes of materials, namely layered transition metal oxides, polyanion, Prussian blue analogues and organic materials [1]. However, synthesizing cathodes for KIBs, especially those based on layered 3d-series transition metals, pose significant challenges. These include the low concentration of K-ions due to electrostatic repulsion, hygroscopic instability, and decomposition susceptibility. In our current study, we addressed these complex synthetic challenges by employing the ambient ion-exchange synthesis method to create metastable cathode materials suitable for stationary energy storage applications. Integrating diffraction and spectroscopic techniques, we have elucidated that the ion exchange reaction proceeds via an overlay ordered structure formation (Figure 1) mechanism [2-6]. Additionally, we have conducted comprehensive investigations into the structural, morphological, electronic, and electrochemical characteristics of ion-exchanged materials [4]. To analyze the K+ insertion mechanism, we employed both ex-situ and in-situ X-ray diffraction analysis, along with potentio/galvanostatic titration techniques. Synergizing experimental tools with the theoretical calculations, we have unveiled the efficacy of ambient ion-exchange reactions to prepare promising novel cathode materials. Two case studies will be presented as noted below. Chemical ion-exchange route was employed to obtain a novel P2-type KxCo1/3Mn2/3O2 cathode for KIBs. With due material optimization and usage of suitable electrolytes, this oxide can be harnessed as a high-voltage cathode for KIBs operating at ~ 2.9 V at room and high (40-50 °C) temperatures (Figure 1c) [7-8].Following, two novel compounds analogous to Na2Mn3O7 has been successfully synthesized via ambient chimie douce This discovery reveals the utilization of a cost-effective, scalable, and energy-efficient K-Mn-O ternary mixture as an extensively studied cathode material for KIBs (Figure 1d) [9]. Finally, this work provides a new dimension in obtaining targeted battery material beyond traditional synthetic route for the development of KIBs for next generation stationary energy storage system.

Novel visible-light-driven I− doped Bi2O2CO3 nano-sheets fabricated via an ion exchange route for dye and phenol removal

Here, we report a novel visible-light-driven I− doped Bi2O2CO3 nano-sheet photocatalyst synthesized via a facile ion exchange route at room temperature. This obtained Bi2O2CO3 nano-sheet with I− doping shows several advantages. The specific surface area of I0.875-Bi2O2CO3 is 2.16 times higher than that of Bi2O2CO3, providing more catalytic sites for the degradation reactions. Moreover, a 3.2 times photocurrent enhancement is observed in I0.875-Bi2O2CO3 compared with Bi2O2CO3, producing more photogenerated electron-hole pairs for degradation. The synergistic effect between texture property and photoelectric effect boosts the removal of organic pollutants. Under visible light illumination, I0.875-Bi2O2CO3 displays superior photocatalytic performance for the degradation of methyl orange (MO) and phenol. Notably, a phenol degradation rate, 88%, is achieved by I0.875-Bi2O2CO3 with illuminating for 60 min, which is about 29 times higher than that of pristine Bi2O2CO3. This finding may provide an opportunity to develop a promising I− doped catalyst for organic pollutants removal.

New anode materials for sodium-ion batteries: NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH prepared from dechlorination wastes

Layered double hydroxides (LDHs) are considered promising materials in energy storage. Herein, we design a one-step ion-exchange route to prepare two new LDH-based materials, NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH as anode materials for sodium-ion batteries (SIBs), using Ca2Al(OH)6Cl·2H2O (Ca2Al-Cl LDH) generated from disposing of chlorine-containing wastewater as the feed material. The high-electroactive Ni2+ and Co2+ replace a part of low-electroactive Ca2+ in Ca2Al-Cl LDH, forming NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH materials with tunnel-like and defective structure, and abundant active sites. Density functional theory calculations indicate that the incorporation of Ni2+ and Co2+ effectively drives electron transfer and directly influences the charge density surrounding the active center, thereby enhancing the conductivity of NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH. Ex situ XRD and XPS analyses demonstrate a redox reaction between Na+ and NixCa2-xAl-Cl LDH/CoyCa2-yAl-Cl LDH during the discharging/charging process. The NixCa2-xAl-Cl LDH and CoyCa2-yAl-Cl LDH materials exhibit excellent electrochemical performance for SIBs. Among them, Ni0.8Ca1.2Al-Cl LDH and Co0.6Ca1.4Al-Cl LDH deliver discharge capacities of 256.9 and 292.8 mAh g−1 after 200 cycles at 0.2 A g−1 and maintain the discharge capacities of 102 and 118.1 mAh g−1 after 600 cycles at 2 A g−1. This study provides a simple and low-cost method to prepare LDH-based anode materials for SIBs. It also provides a new path for the conversion of low-value dechlorination wastes into high-value-added products.

Decoding Li+/H+ ion exchange route toward low-temperature synthesis of layered oxide cathode materials for lithium-ion batteries

Decoding Li+/H+ ion exchange route toward low-temperature synthesis of layered oxide cathode materials for lithium-ion batteries

Chloride binding behavior and mechanism of phosphoaluminate cement clinker and its hydration products

As one of potential materials for extending the lifetime of reinforced concrete serving in chloride-rich environments, phosphoaluminate cement (PAC) offers excellent chloride binding capacity and superior resistance to chloride penetration. The chloride binding behavior as well as binding routes and mechanisms of the clinker and its hydration products had not been clarified so far. This study revealed that the clinker would preferentially form Friedel's salts through a dissolution-precipitation route in NaCl solutions, thereby binding chloride. This dissolution-precipitation process led to an accumulation of Al3+ in solutions, which negatively affected the subsequent hydration reactivity of the clinker. In the hydration products, the calcium hydroaluminates, mainly as C2(A,P)H8 with minor C(A,P)H10, could bind chloride rapidly via an ion exchange mechanism. Through the ion-exchange route, the chemical binding of calcium hydroaluminates to chloride could be completed in less than 1 hour. In contrast, the unhydrated clinker exhibited a slow chloride binding behavior until 72 hours. All these would provide theoretical guidance for using PAC cementitious materials in reinforced concrete to enhance resistance to chloride attack.

(Invited) Ion-Exchange Route for the Cathode Development of Na-Ion Batteries

Ion-exchange reactions are frequently used to develop novel metastable electrode materials for alkali-ion batteries that cannot be synthesized (or difficult to synthesize) using direct chemical reactions. We have recently demonstrated that potassium (K)-containing compounds can be good Na+-hosting cathode materials that exhibit good electrochemical performance.[1-2] In this presentation, we will discuss, with layered oxide and polyanionic compounds as model systems, how K+-to-Na+ ion exchange occurs and how the K-containing structure benefits the electrochemical Na+ intercalation and deintercalation properties.

Metal-free azo dyes anchored on CdS nanowires: Subtle solar cell exploration through experimental and DFT studies

Herein, as-synthesized azo dye (E)-2-isopropyl-5-methyl-4-((4-(4-nitrophenyl) thiazol-2-yl) diazenyl) phenol (D2) has been anchored on a high surface area one dimensional CdS nanowires (NWs) in thin film form. CdS nanowires have been grown through Cd(OH)2 template formation followed by conversion to CdS by ion-exchange route. The light-electricity conversion efficiency of the CdS-Azo dye-based solar cell has shown about 5-fold remarkable surge (0.159%) compared to the bare CdS (0.03%) with I3−/I− redox mediator under standard AM 1.5 illumination (100 mW cm−2). Albeit, the DFT studies revealed a higher band gap for pristine D2, alluringly it has depicted higher light-electricity conversion efficiency among the fabricated thin film solar cells after sensitization. The relative increase in sensitivity after sensitization is attributable to facile dye regeneration. Furthermore, after the co-sensitization of CdS thin film with equimolar cocktails of as-synthesized dyes and a natural dye Betanin (Bn), less efficiency was depicted ascribable to plausible dye aggregation upon blending.

Hierarchical assembly of NiFe-PB-derived bimetallic phosphides on 3D Ti3C2 MXene ribbon networks for efficient oxygen evolution

The development of MXene-based heterostructures for electrocatalysis has garnered significant attention owing to their potential as high-performance catalysts that play a pivotal role in hydrogen energy. Herein, we present a multistep strategy for the synthesis of a Ti3C2 MXene ribbon/NiFePx @graphitic N-doped carbon (NC) heterostructure that enables the formation of three-dimensional (3D) Ti3C2 MXene ribbon networks and bimetallic phosphide nanoarrays. With the assistance of HF etching and KOH shearing, the MXene sheets were successfully transformed into 3D MXene networks with interlaced MXene ribbons. Notably, a hydrothermal method, ion exchange route, and phosphorization process were used to anchor NiFePx@NC nanocubes derived from Ni(OH)2/NiFe-based Prussian blue (NiFe-PB) onto the MXene ribbon network. The resulting MXene ribbon/NiFePx@NC heterostructure demonstrated enhanced oxygen evolution reaction (OER) activity, characterized by a low overpotential (164 mV at a current density of 10 mA cm−2) and a low Tafel slope (45 mV dec−1). At the same time, the MXene ribbons/NiFePx@NC heterostructure exhibited outstanding long-term stability, with a 12 mV potential decay after 5000 cyclic voltammetry (CV) cycles. This study provides a robust pathway for the design of efficient MXene-based heterostructured electrocatalysts for water splitting.

Recent Progress in Synthesis of Nanostructures through Ion Exchange Route and their Applications

AbstractThe inorganic colloidal nanocrystals (ICNCs) have received a great deal of interest because of their tunable electronic and optical properties with coarse and finely controlled compositions, morphologies and thus, hybrid nanostructures have a wide range of applications in supercapacitor, luminescent solar concentrators (LSCs) and photothermal therapy (PPT). The ion exchange (IEx) process includes great diffusion rates of parent nanoparticles (NPs) ions from their crystal structure and their complete dissociation in specific solvents. The bond dissociation energies (BDEs) of different transition metal atoms with specific p‐block elements have been reviewed to analyze their effect on the IEx process. The alloy and doped and inorganic perovskite ICNCs have been synthesized via different IEx methodologies, showing varied photoluminescence quantum yields (PLQYs), nano‐dimensional morphology, composition, reaction time and temperature, and their performance for a specific application have been tabulated. The perovskite nanocrystals (NCs) are responsible for fast IEx dynamics that drop to homogenization in their composition, leading to NCs emitting in a narrow spectral region acting as an intermediate between those of the model NPs. The nanoscale metal‐organic particles (NMOPs) have opened plausible opportunities for their application in nanomedicine having highly enriched functionalities, well‐designed shapes/sizes, adjustable compositions, and intrinsic biodegradability. The potential to develop well‐designed heterostructures and for the growth of large‐area monocrystalline CsPbBr3 thin films provide a strong base for fundamental investigations of the intrinsic properties of perovskite‐based devices. The Cs3Sb2I9 is an active emitter layer that directs us toward low‐dimensional lead‐free A3B2X9 perovskite optoelectronic materials.

Ion-Exchange Route Induced Heterostructured CoS2/FeS Nanoparticles Confined in Hollow N-Doped Carbon Frameworks for Enhanced Sodium Storage Performance

As a result of the high theoretical capacities, transition metal sulfides have attracted increasing attention as potential anodes for sodium-ion batteries (SIBs), but severely suffer from large volumetric variations, sluggish kinetics, and polysulfide shuttling. Herein, utilizing metal–organic frameworks (MOFs) as functional templates, heterostructured CoS2/FeS nanoparticles confined in a hollow N-doped carbon framework are successfully fabricated via a controlled ion-exchange reaction combined with subsequent carbonization and sulfurization processes. The construction of CoS2/FeS heterointerfaces promotes electron transfer and provides more active sites, while the derived N-doped carbon framework with a unique hollow interior effectively improves the electrical conductivity, alleviates the volumetric variations, and facilitates the sodium storage process with shortened Na+ diffusion paths. As anodes for SIBs, the optimal CoS2/FeS hybrid composite exhibits a high initial Coulombic efficiency (ICE) of 89.3%, a prolonged cycle life with a capacity of 494 mAh g–1 over 500 cycles under a current density of 1.0 A g–1, and an excellent rate capability of 428 mAh g–1 at 5.0 A g–1, showing the great promise for SIBs. This research offers an efficient and feasible approach for exploring and fabricating bimetallic sulfide heterostructures with a unique hollow structure for high-performance metal-ion batteries.

Design three-dimensional CoFe2O4 nanocage via ion exchange route for ultra-sensitive electrochemical sensing of nitrobenzene

Bimetallic transition metal oxide materials have rich valence states, good biocompatibility, conductivity, high stability, and satisfactory catalytic performance, and stand out among many materials. Therefore, we develop a simple synthesis method of CoFe2O4 nanocage by ion exchange for the detection of nitrobenzene (NB) in this work, which uses the zeolitic imidazolate framework-67 (ZIF-67) as cobalt source and three-dimensional hollow organic framework Co-Fe PBA as precursor. The continuous conversion between ionic valence states in CoFe2O4 enhances the conductivity of the material, showing a good synergistic coupling effect. The low-density hollow structure of nanocage offers various types of sites for adsorbing reactants, and the thin shell structures provide more channels for ion migration and electron transport, facilitate charge transfer, and further improve their electrical sensing ability. Electrochemical tests proved that the material demonstrated excellent electrocatalytic activity for NB, with the limit of detection as low as 0.038 μM, a wide linear response (0.05–1664.55 μM), higher sensitivity, good repeatability, long-term stability and selectivity. More importantly, the sensor has been successfully applied to the determination of trace NB in water samples with satisfactory recovery (98.7%–104.7%). This work provides a novel idea for the detection of low content of NB and expands the application of bimetallic oxide materials in the sensing field.

MOF-Derived CoNi Nanoalloy Particles Encapsulated in Nitrogen-Doped Carbon as Superdurable Bifunctional Oxygen Electrocatalyst

Carbon-encapsulated transition metal catalysts have caught the interest of researchers in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) due to their distinctive architectures and highly tunable electronic structures. In this work, we synthesized N-doped carbon encapsulated with CoNi nanoalloy particles (CoNi@NC) as the electrocatalysts. The metal-organic skeleton ZIF-67 nanocubes were first synthesized, and then Ni2+ ions were inserted to generate CoNi-ZIF precursors by a simple ion-exchange route, which was followed by pyrolysis and with urea for the introduction of nitrogen (N) at a low temperature to synthesize CoNi@NC composites. The results reveal that ZIF-67 pyrolysis can dope more N atoms in the carbon skeleton and that the pyrolysis temperature influences the ORR and OER performances. The sample prepared by CoNi@NC pyrolysis at 650 °C has a high N content (9.70%) and a large specific surface area (167 m2 g-1), with a positive ORR onset potential (Eonset) of 0.89 V vs. RHE and half-wave potential (E1/2) of 0.81 V vs. RHE in 0.1 M KOH, and the overpotential of the OER measured in 1 M KOH was only 286 mV at 10 mA cm-2. The highly efficient bifunctional ORR/OER electrocatalysts synthesized by this method can offer some insights into the design and synthesis of complex metal-organic frameworks (MOFs) hybrid structures and their derivatives as functional materials in energy storage.

Synthesis of cuprous oxide via ion exchange route for photocatalytic degradation of methylene blue

Abstract Cuprous oxide (Cu2O) nanoparticles were successfully synthesized using cupric hydroxide gel as a precursor and glucose as a reductant. A well-dispersed cupric hydroxide gel was prepared by treatment of aqueous cuprous chloride with anion exchange resin. The average diameter of the Cu2O nanoparticles was 780 nm. Attenuated total reflectance Fourier transform infrared spectroscopy showed that polyethylene from the anion exchange resin was present in the Cu2O powder, explaining how the ion exchange route reduces agglomeration of the Cu2O nanoparticles. Addition of hydrogen peroxide during the photocatalytic degradation of methylene blue significantly reduced photocorrosion of the Cu2O nanoparticles. The mechanism by which hydrogen peroxide participates in the photocatalytic process and inhibits photocorrosion was investigated.

The interface design of (0D/2D/1D) AgI/BiOI/C3N5 dual Z-scheme heterostructures with efficient visible-light-driven photocatalytic activity

Given the present synthesis method of constructing a dual Z-scheme photocatalytic system, the accurate interface structure design remains a challenge. In this work, 0D/2D/1D AgI/BiOI/C3N5 dual Z-scheme heterojunctions with confined interface structures were fabricated by combining a room-temperature precipitation strategy with an ion-exchange route. Tetracycline hydrochloride (TCH) photodegradation under simulated visible light illumination was conducted to evaluate the photocatalytic activity of the as-prepared dual Z-scheme heterojunctions. Compared with the single component as well as the counterpart single Z-scheme heterojunctions, the constructed dual Z-scheme heterojunctions displayed superior catalytic activity. The apparent kinetic constant of the optimized AgI/BiOI/C3N5 nanocomposite was 410.2, 3.2 and 2.1 times as high as the bare C3N5, BiOI and AgI. The enhanced photocatalytic activity was attributed to the efficient charge separation of dual Z-scheme photocatalytic mechanism supported by systematical characterizations. It is anticipated this work can be a guide for the construction of a dual Z-scheme photocatalytic system.

Stepwise conversion of methane to methanol over Cu-mordenite prepared by supercritical and aqueous ion exchange routes and quantification of active Cu species by H2-TPR

Copper-exchanged mordenite prepared by supercritical ion exchange (SCIE) and aqueous ion exchange (AIE) were investigated in stepwise conversion of methane to methanol. Increasing the oxygen activation temperature and methane reaction time enhances the methanol yield of copper-exchanged mordenite prepared by SCIE (Cu-MORS). The reducibility of Cu-MORS was compared with those of Cu-MORA prepared by aqueous ion exchange (AIE) using H2-TPR. It was demonstrated for the first time that deconvoluted H2-TPR profile coupled with effects of Cu loading and oxygen activation temperature on methanol yield data can be used to distinguish the active Cu sites from inactive ones based on their reduction temperature. The copper species responsible for methane activation were found to be reduced below 150 °C by H2 in both Cu-MORS and Cu-MORA. From the stoichiometry of the reaction of H2 with Cu2+ species, the average number of copper atoms of active sites were calculated as 2.07 and 2.80 for Cu-MORS and Cu-MORA, respectively. Differences in structure of copper species caused by the synthesis routes were also detected by in-situ FTIR upon NO adsorption indicating a higher susceptibility of Cu-MORS towards autoreduction. The results demonstrated the potential of TPR based methods to identify copper active sites and suggested the importance of site selective ion exchange in order to controllably synthesize active Cu species in zeolites.

Stepwise Direct Conversion of Methane to Methanol Over Cu-Mordenite Prepared by Supercritical and Aqueous Ion Exchange Routes and Quantification of Active Cu Species by H2-Tpr

Stepwise Direct Conversion of Methane to Methanol Over Cu-Mordenite Prepared by Supercritical and Aqueous Ion Exchange Routes and Quantification of Active Cu Species by H2-Tpr

Heavy Fluorination via Ion Exchange Achieves High-Performance Li-Mn-O-F Layered Cathode for Li-Ion Batteries.

Lithium-excess manganese layered oxide Li2 MnO3 , attracts much attention as a cathode in Li-ion batteries, due to the low cost and the ultrahigh theoretical capacity (≈460mA h g-1 ). However, it delivers a low reversible practical capacity (<200mA h g-1 ) due to the irreversible oxygen redox at high potentials (>4.5V). Herein, heavy fluorination (9.5%) is successfully implemented in the layered anionic framework of a Li-Mn-O-F (LMOF) cathode through a unique ion-exchange route. F substitution with O stabilizes the layered anionic framework, completely inhibits the O2 evolution during the first cycle, and greatly enhances the reversibility of oxygen redox, delivering an ultrahigh reversible capacity of 389mA h g-1 , which is 85% of the theoretical capacity of Li2 MnO3 . Moreover, it also induces a thin spinel shell coherently forming on the particle surface, which greatly improves the surface structure stability, making LMOF exhibit a superior cycling stability (a capacity retention of 91.8% after 120 cycles at 50mA g-1 ) and excellent rate capability. These findings stress the importance of stabilizing the anionic framework in developing high-performance low-cost cathodes for next-generation Li-ion batteries.

Revisited Ti2Nb2O9 as an Anode Material for Advanced Li-Ion Batteries.

Ti2Nb2O9 with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g-1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g-1 has been observed practically. In this work, highly reversible capacity of 200 mAh g-1 with the average (de)lithiation potential of 1.5 V vs Li/Li+ is achieved for Ti2Nb2O9 with pseudo-2D layered morphology obtained via thermal decomposition of the NH4TiNbO5 intermediate prepared by K+→ H+→ NH4+ cation exchange from KTiNbO5. Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti4+/Ti3+ and Nb5+/Nb4+ reduction/oxidation within the whole voltage range. Li+ migration barriers for Ti2Nb2O9 along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti2Nb2O9 synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li4Ti5O12 in the next generation of high-performance LIBs.

Interface optimization and fast ion exchange route construction in CoS2 electrode by decorated with dielectric Al2O3 nanoparticles for high temperature primary lithium batteries

As the most investigated cathode of thermal batteries, the electrochemical performance of CoS 2 is limited by a big polarization at high current density and low working temperature, which is ascribed to the poor wettability of molten salt on CoS 2 surface and low exchange current density. In this contribution, Al 2 O 3 is selected as a modifier to improve the wettability of molten salt on CoS 2 surface and exchange current density at the same time, by adjusting the dielectric polarization field of CoS 2 surface. The discharge capacity (V ≥ 1.7 V) of CoS 2 increases by ~11% at 500 °C with a discharge current of 300 mA cm −2 , and 55% at 450 °C with a discharge current of 100 mA cm −2 , by the decoration of Al 2 O 3 nanoparticles. Moreover, the influence of decorated Al 2 O 3 nanoparticles on the electrochemical performance of CoS 2 are discussed. • CoS 2 decorated with Al 2 O 3 nanoparticles can be synthesized via a simple way. • Optimized interface is able to boost the discharge ability of thermal batteries. • Influence mechanisms of Al 2 O 3 on electrochemical behavior of CoS 2 are studied.

Insight into solid-state ion-exchanged Cu-based zeolite (SSZ-13, SAPO-18, and SAPO-34) catalysts for the NH3-SCR reaction: The promoting role of NH4-form zeolite substrates

In this paper, Cu-exchanged SSZ-13, SAPO-18, and SAPO-34 were synthesized via a novel green and sustainable solid-state ion-exchange (SSIE) route with excellent NH3-SCR activities, which could simplify the preparation process and reduce the wastewater production in comparison to conventional aqueous ion-exchange route. The results also proved that Cu-exchanged zeolites synthesized by SSIE technology presented higher Cu ion-exchange (IE) levels and better SCR activities than those prepared via the traditional incipient impregnation route. In the case of SSIE, the usage of NH4-form substrates could achieve more Cu2+ ions and fewer CuOx than those H-form substrates since the formation of Cu(NH3)x2+ intermediate could promote the Cu2+ mobility to facilitate Cu2+ occupying IE sites, which was favorable for the SCR reaction. The combined DFT data confirmed the SSIE reaction energy barriers between Cu(NO3)2 and the NH4-form substrates were almost identical, whereas the higher reaction energy was required for H-form substrates. In-situ DRIFTS results manifested the labile species like NH4+, –NH2, NO2–, NO3–, NO2, etc were the reaction intermediates over the catalysts prepared from NH4-form substrates. The Langmuir-Hinshelwood (“L-H”) and Eley-Rideal (“E-R”) mechanisms contributed collectively over both Cu-SSZ-13 and Cu-SAPO-18 in the SCR reaction, however, the “L-H” mechanism dominated over Cu-SAPO-34.