Hydroxide Adsorption Research Articles

Boosting selectivity for multi-carbon products in electrochemical CO2 reduction via enhanced hydroxide adsorption in ultrafine CuOx/CeOx nanoparticles

The electricity-driven reduction of CO2 presents a unique prospect of mitigating atmospheric CO2 levels and converting renewable energy into chemical fuels. However, the lack of an efficient catalyst that can transform CO2 into desired products with appreciable selectivity at commercially relevant current densities (ID) impedes the practical implications of this technology. This work describes a scalable approach for producing ultrafine nanoparticles of CuOx-CeOx (CuCe) composites via rapid coprecipitation under oxygen-deprived conditions. In this process, Ce(OH)3 acts as a reducing agent converting Cu(OH)2 into ultrafine Cu2O nanoparticles. Thus, the Ce: Cu ratio in composite effectively controls the particle size and bulk structural fixture of the CuCe composites. Despite having lower ECSA, The CuCe composites exhibit superior catalytic performance compared to CuO, with significantly higher selectivity for ethanol production and lower selectivity for CO and H2. The Cu1.5Ce prepared using a Cu: Ce ratio of 1.5:1, demonstrated remarkable catalytic activity with Faradaic efficiencies (F. E.) of 34.2 % for ethanol, 44.1 % for ethylene, and 81.08 % for multi-carbon (C2+) products. Moreover, while operating at the ID of 500 mA cm−2, Cu1.5Ce achieves a single pass CO2 conversion (SPCC) of 19.9 %, and a half-cell energy efficiency (E. E. half-cell) of 31.5 % for the C2+ products. It produces the C2+ products at the partial current density (pID) of 405.4 mA cm−2. The superior performance of Cu1.5Ce can be attributed to the improved hydroxide adsorption and partial retention of oxidized copper species under cathodic bias.

Propensity of hydroxide and hydronium ions for the air-water and graphene-water interfaces from abinitio and force field simulations.

Understanding acids and bases at interfaces is relevant for a range of applications from environmental chemistry to energy storage. We present combined abinitio and force-field molecular dynamics simulations of hydrochloric acid and sodium hydroxide highly concentrated electrolytes at the interface with air and graphene. In agreement with surface tension measurements at the air-water interface, we find that HCl presents an ionic surface excess, while NaOH displays an ionic surface depletion, for both interfaces. We further show that graphene becomes less hydrophilic as the water ions concentration increases, with a transition to being hydrophobic for highly basic solutions. For HCl, we observe that hydronium adsorbs to both interfaces and orients strongly toward the water phase, due to the hydrogen bonding behavior of hydronium ions, which donate three hydrogen bonds to bulk water molecules when adsorbed at the interface. For NaOH, we observe density peaks of strongly oriented hydroxide ions at the interface with air and graphene. To extrapolate our results from concentrated electrolytes to dilute solutions, we perform single ion-pair abinitio simulations, as well as develop force-field parameters for ions and graphene that reproduce the density profiles at high concentrations. We find the behavior of hydronium ions to be rather independent of concentration. For NaOH electrolytes, the force-field simulations of dilute NaOH solutions suggest no hydroxide adsorption but some adsorption at high concentrations. For both interfaces, we predict that the surface potential is positive for HCl and close to neutral for NaOH.

Water-Polymer Slide Electrification in Polyethylene Films Coated with Amphiphilic Compounds and Its Connection to Surface Properties Dependent on Water-Polymer Interactions.

Slide electrification experiments were performed on low-density polyethylene films (PE) and PE sprayed with five amphiphilic compounds, including antistatic and slip additives. Drops of aqueous solutions were delivered on the films and after sliding spontaneously acquired a net electrical charge (Qdrop), which is dependent on the pH and ionic strength. The slide electrification was detected in pristine PE films and those with five additives. An acid-base equilibrium model, based on the adsorption of hydroxides and protons on surface sites, accounted for the dependence of Qdrop on pH, allowing recovery of the acid-base equilibrium constants and the density of adsorption sites. The model was modified to account for ionic strength effects through activity factors. The surface conductivity, wettability, and friction coefficients were strongly modified by the additives. However, the observed trends are different from those observed in slide electrification, which better correlated with zeta potential determinations. This suggests that the interaction mechanisms among surface water, the considered additives, and the polymer, which are involved in slide electrification and the generation of zeta potential, are different from those associated with other surface processes involving surface water. Although additives are required for changing surface resistivity, friction coefficients, and wettability, the generation of sliding electrical charges in polyethylene is a spontaneous and highly effective process. For one specific additive, a simultaneous decrease in friction coefficients, zeta potential, and Qdrop was observed, assigned to the blockade of hydroxide adsorption sites and water repulsion by the compound.

Integrated experimental and DFT-based study on pH-dependent photoelectrochemical performance of Ca2Fe2O5

In this study, photoelectrochemical (PEC) performance of Ca2Fe2O5 nanoflakes were explored to understand corrosion and degradation tendency. Ca2Fe2O5 nanoflakes were synthesized via a modified two step thermochemical method consisting of hydrothermal reaction and chemical conversion. Detailed characterization using SEM, XRD, and TEM confirmed the highly crystalline and (200) faceted Ca2Fe2O5 nanoflake morphologies. PEC measurements, conducted in six distinct electrolyte conditions, revealed significant photocurrent variations with respect to pH change, highlighting pH 11 as the optimal environment. Electrochemical impedance spectroscopy (EIS) was applied to elucidate charge transfer rate depending on the hydrogen evolution reaction (HER) mechanisms. Furthermore, DFT calculations provided insights into the surface interactions of Ca2Fe2O5 with hydrogen and hydroxide absorbates, elucidating the electronic and structural change during PEC reactions. The simulation demonstrated that, while hydrogen adsorption induced Fe-O bond dissociation, hydroxide adsorption showed minimal effect on surface bonds. HER overpotentials were calculated for both Tafel and Volmer step, elucidating the facile and stable HER in OH terminated surface environments. These findings underscore the importance of alkaline electrolyte environment in optimizing the PEC stability and efficiency of Ca2Fe2O5 photocathodes.

(Invited) Efficient Ternary Nicuw Hydrogen Oxidation Catalysts for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) offer prospective approaches to replace proton exchange membrane fuel cells via cost-effective catalysts and membranes. While significant progress has been made in efficient nonnoble electrocatalysts for oxygen reduction reaction in alkaline media, the hydrogen oxidation reaction (HOR) in the alkaline condition still relies on high platinum loadings to compensate for its sluggish kinetics. Therefore, developing efficient non-noble metal electrocatalysts with Pt-like HOR performances in alkaline electrolytes is highly desired but a great challenge.The hydrogen binding energy (HBE) has been identified as the primary descriptor for the HOR. Additionally, an unfavorable hydroxide binding energy (OHBE) is considered the rate-determining step in the Volmer reaction to generate water. Therefore, an ideal catalyst for HOR should achieve a balance between HBE and OHBE. However, despite being a promising non-noble metal, nickel exhibits excessively high HBE and lacks active sites for hydroxide adsorption, which hinders its further application in the real fuel cell.In this work, NiW was successfully deposited onto Cu to form a ternary Ni-Cu-W alloy catalyst by a chemical reduction method. Through XPS spectra, we found the charge transfer from Ni to W to give Ni a higher valence state, contributing to a weakened hydrogen binding energy. Electrochemical measurements observed Ni-Cu-W exhibit an kinetic activity with 117.9 mA/mgNi at η= 50 mV, which is the highest among the reported platinum group metal-free catalysts. Ni-Cu-W alloy showcased robust stability, with no activity degradation during an accelerated long-term durability test between a low overpotential (-0.1 ~ 0.1 V, vs RHE) with 10,000 cyclic voltammetry scans and only a 5.7% activity loss at η= 50 mV when applying more larger overpotential (-0.1 ~ 0.2 V) with the same cycles. When assembled with this catalyst as anode and Pt/C as cathode, it delivered a peak power density of 289 mW/cm2. Both experimental and theoretical studies were conducted to gain insights into the catalyst's enhanced performance. Our findings revealed that the incorporation of Cu into the catalyst significantly weakened the adsorption of hydrogen species, while simultaneously lowering the energy barrier required for the absorption of hydroxide ions. These key observations might shed light on the underlying mechanisms responsible for the catalyst's improved activity and stability.

Synergistic coupling of defective Ru nanoclusters with oxygen-ligand-steered Ru single-atoms modifying interfacial water structure and key intermediates bonding toward efficient hydrogen energy conversion

Constructing highly efficient ruthenium (Ru)-based electrocatalysts and understanding their reaction mechanisms for hydrogen energy conversion are highly desirable, but extremely challenge. Herein, we integrate the well-dispersed defective Ru nanoclusters and oxygen-coordinated Ru single atoms into one electrocatalyst (RuSA-O4/RuNC) toward alkaline hydrogen oxidation and evolution reactions (HOR/HER). Synergistic catalytic mechanism of dual-sites has been revealed by in situ ATR-SEIRAS characterization, EDTA/SCN– poisoning experiments and DFT calculations. Benefiting from the electronic redistribution between RuSA-O4 and RuNC sites, the single-atom RuSA-O4 species can act as Lewis acid sites that display strong affinity toward interfacial water via an O-down (H2O↓) conformation and subsequently promote water dissociation/formation as well as hydroxide adsorption. Meanwhile, adjacent defective Ru sites have around thermoneutral value of H adsorption free energy. RuNC works with RuSA-O4 species, collaboratively reducing reaction barriers. As expected, the RuSA-O4/RuNC achieves 20.3 times mass activity of commercial Pt/C for alkaline HOR at 10 mV overpotential and excellent alkaline HER activity with a low overpotential of 22 mV to deliver 10 mA cm−2, as well as considerable HER mass activity of 17.0-times compared to commercial Pt/C at 50 mV overpotential. Besides, the synergistic dual-sites strategy can also be extended to prepare efficient PtSA-O4/PtNC and IrSA-O4/IrNC electrocatalysts.

Utilizing supercritical fluid for efficient preparation of kaolinite nanosheets to enhance Ga(Ⅲ) adsorption

This study explores the efficient preparation of few-layered or monolayered kaolinite (K) nanosheets using supercritical gasification exfoliation technology, aiming to enhance their adsorption capacity for Ga(III). Crystal structure and morphology analysis indicated that the exfoliated K nanosheets maintained an excellent hexagonal lamellar crystal shape, with significantly reduced thickness (∼10 nm) while maintaining an unchanged lateral dimension (400 ∼ 600 nm). The exfoliation mechanism primarily relies on the considerable impact force generated by the rapid expansion of supercritical carbon dioxide (CO2) volume during fast pressure release, which facilitates exfoliation between K layers where the interlayer hydrogen bonds have been disrupted by potassium acetate. Batch adsorption experiments demonstrated a significant improvement in the removal rate of exfoliated K for Ga(III), increasing from 50.66 % to 80.47 % under the conditions of a Ga(III) concentration of 15 mg/L and an adsorbent dosage of 0.4 g/L, attributed to the exposure of numerous active sites. Kinetic and isotherm fitting results indicated a monomolecular adsorption process primarily controlled by chemical adsorption, with a maximum theoretical adsorption capacity of 32.90 mg/g for Ga(III). In multivariate mixed adsorption experiments, exfoliated K exhibited good adsorption selectivity for Ga(III), primarily through chemical adsorption of aluminum hydroxide (Al–OH) functional groups and electrostatic adsorption of silicon oxide (Si–O). Density functional theory (DFT) calculations further demonstrated that the bidentate adsorption coordination of K with Ga(III) exhibits higher stability compared to monodentate adsorption coordination, indicating that the adsorption process is mainly dominated by bidentate adsorption. Consequently, the supercritical gasification exfoliation technology, as a recyclable green process, offers efficient exfoliation of K, holding significance implications for the high-value and high-efficiency utilization of K resources, as well as for establishing a green, low-carbon, and recycling development economic system.

Built-in electric field in NiO-CuO heterostructures to regulate the hydroxide adsorption sites for 5-hydroxymethylfurfural electrooxidation assisted hydrogen production

The development of catalysts with suitable adsorption behavior for the reaction molecules and the elucidation of their internal structure-adsorption-catalytic activity relationships are crucial for the electrooxidation of 5-hydroxymethylfurfural (HMF). In this work, NiO-CuO heterostructures with a spontaneous built-in electric field (BEF) are specifically designed and used to regulate the OH− adsorption site for freeing up the active site of HMF for the HMF oxidation reaction (HMFOR). The mechanism driving electron pumping/accumulation of the BEF is examined by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Electrochemical data and theoretical calculations show that BEF modulates the adsorption energy and adsorption site of substrate molecules, thereby enhancing the performance of HMFOR and hydrogen evolution reaction (HER). Notably, the NiO-CuO electrode demonstrates high 2,5-Furandicarboxylic acid (FDCA) selectivity (99.76 %) and generation rate (13.79 mmol gcat−1 h−1). It only requires 1.33 V to obtain a current density of 10 mA cm−2 for HMFOR-coupled H2 evolution. This research introduces a novel approach by regulating the adsorption of reactive molecules for HMFOR-assisted H2 evolution.

Variation of topological surface states of nodal line semimetal MgB2 resulting from adsorption of hydrogen, hydroxide, and water molecules.

Topological semimetals have garnered significant interest due to their intrinsic topological physics and potential applications in devices. A crucial feature shared by all topological materials is the bulk-boundary correspondence, indicating the presence of unique topologically protected conducting states at the edges when non-trivial band topology exists in the bulk. Previous studies on surface states of topological materials predominantly focused on pristine surfaces, leaving the exploration of surface states in topological semimetals with adsorbates relatively uncharted. This work, based on ab initio calculations, examines variations in the topological surface states of MgB2, a well-known conventional superconductor and topological nodal line semimetal. We employ a thick slab model with Mg/B atoms as surface terminations to simulate its topological surface states. Subsequently, we investigate the adsorption of hydrogen (H), hydroxide (OH), and water (H2O) on the surface slabs to observe changes in the surface states. The pristine slab model gives the drumhead-like surface states inside the surface projected nodal lines, while the topological surface states change differently after adsorbing H, OH, and H2O, which can be understood systematically by combining the surface adsorption Gibbs free energy ΔG, surface terminations, and surface charge density distributions. Especially, our findings suggest that the Bader charge transfer value of surface atoms providing topological states is a key indicator for evaluating the variation in topological surface states after adsorption. This study provides a systematic understanding of the topological surface states of MgB2 with different adsorbates, paving the way for future theoretical and experimental investigations in related fields and shedding light on the potential device applications of topological materials.

A highly active and durable NiMoCuCo catalyst with moderated hydroxide adsorption energy for efficient hydrogen evolution reaction

A charge valence state and surface-electronegativity-modulated NiMoCuCo composite is proposed as an active and durable alkaline hydrogen evolution reaction electrocatalyst with moderated hydroxide adsorption energy.

Nickel molybdate/cobalt iron carbonate hydroxide heterojunction with oxygen vacancy enables interfacial synergism to trigger oxygen evolution reaction

The development of electrocatalysts with excellent performance toward oxygen evolution reaction (OER) for the production of hydrogen is of great significance to alleviate energy crisis and environmental pollution. Herein, the heterostructure (NMO/FCHC-0.4) was fabricated by the coupling growth of NiMoO4 (NMO) and cobalt iron carbonate hydroxide (FCHC) on nickel foam as an electrocatalyst for OER. The interfacial synergy on NMO/FCHC-0.4 heterojunction can promote the interfacial electron redistribution, affect the center position of d band, optimize the adsorption of intermediate, and improve the conductivity. Beyond, oxygen defect sites are conducive to the adsorption of intermediates, and increase the number of active sites. Real-time OER kinetic simulation revealed that the interfacial synergism and molybdate could reduce the adsorption of hydroxide, promote the deprotonation step of M-OH, and facilitate the formation of M-OOH (M represents the metal active site). As a result, NMO/FCHC-0.4 displays excellent OER electrocatalytic performance with an overpotential of 250/280 mV at the current density 100/200 mA cm−2 and robust stability at 100 mA cm−2 for 100 h. This work provides deep insights into the roles of interfacial electronic modulation and oxygen vacancy to design high-efficiency electrocatalysts for OER.

Oxygen vacancies and tailored redox activity encountered with NiCo2O4 nanostructures for promising applications in supercapacitor and water oxidation

It is well known that transition metal oxides play a significant role in the development of efficient electrochemical energy storage and conversion systems. However, their application is limited by low electrical conductivity, a limited number of electroactive sites, and limited stability. In this study, nickel‑cobalt bimetallic oxide (NiCo2O4) nanostructures were prepared using orange peel extract and its fruit juice during hydrothermal method. The use of green chemical components from orange peel extract and its fruit juice was to demonstrate their ability to manipulate NiCo2O4's structural and functional properties. For this reason, the optimized 1 mL of orange peel extract and its fruit juice was found highly active for improving the electrochemical properties of NiCo2O4 nanostructures. The electrochemical supercapacitor performance of optimized NiCo2O4 nanostructures showed a specific capacitance of 997.50 Fg−1 with a cycling stability of more than thirty thousand cycles, resulting in a capacitance retention rate of almost 100 % at 1.5 Ag−1. In addition, during the oxygen evolution reaction (OER), the overpotential was 120 mV at 20 mA/cm2 and the Tafel slope was 110 mVdec−1, with a prolonged stability exceeding 45 h were observed for optimized NiCo2O4 nanostructures. With an electrode material comprising NiCo2O4 nanostructures and an orange peel extract, outstanding electrochemical performance was obtained. This could be explained by several factors, including high electroactive site exposure, rapid charge transfer kinetics, high hydroxide adsorption, oxygen vacancies on the surface, and abundance of Co(III). The approach described here can be used for the facile synthesis of a wide range of nanostructured functional materials that exhibit impressive electrochemical properties, particularly for energy storage and conversion applications.

Controlled synthesis of sulfur-vacancy-enriched sheet-like Ni3S2@ZnS composites for asymmetric supercapacitors with ultralong cycle life

To improve the electrochemical performance of supercapacitors, pseudocapacitive electrode materials must be synthesized with high surface activity, high electrical conductivity, and ultralong cycle life, which presents a significant challenge. In this study, we reported on the synthesis of sulfur-vacancy-enriched sheet-like Ni3S2 @ZnS composites based on 3D network porous nickel foam (NF) using a two-step electrodeposition protocol. The Ni3S2 @ZnS/NF exhibited a specific capacitance of 1141.9 C g−1 (241.0 mC cm−2) at a current density of 19 A g−1 (5 mA cm−2). The Ni3S2 @ZnS/NF positive electrode was used to fabricate an all-solid asymmetric supercapacitor, which demonstrated an ultrahigh energy density of 12.0 μWh cm−2 at a power density of 7.2 mW cm−2, as well as an ultrahigh capacitance retention rate of 86.7% after 50,000 cycles. Experimental and theoretical results indicated that the introduction of sulfur vacancies could improve the surface activity of the electrode, as well as its hydroxide diffusion and adsorption ability by adjusting the surrounding local electron concentration of cations around them. This accelerated the interfacial redox reaction and resulted in remarkable electrochemical performance for the Ni3S2 @ZnS/NF electrode. This research provides a pathway for the controlled synthesis of 2D nanosheets with vacancy-rich structures and their potential electrochemical applications.

Lattice tensile strain cobalt phosphate with modulated hydroxide adsorption and structure transformation towards improved oxygen evolution reaction

The adsorption energy of oxygen-containing intermediates for the oxygen evolution reaction (OER) electrocatalysts plays a key role on their electrocatalytic performances. Rational optimization and regulation of the binding energy of intermediates can effectively improve the catalytic activities. Herein, the binding strength of Co phosphate to *OH was weakened by generating lattice tensile strain via Mn replacement, which modulated the electronic structure and optimized the reactive intermediates adsorption with active sites. The tensile-strained lattice structure and stretched interatomic distance were confirmed by X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectra measurements. The as-obtained Mn-doped Co phosphate exhibits excellent OER activity with an overpotential of 335 mV at 10 mA cm−2, which is much higher than pristine Co phosphate. In-situ Raman spectra and methanol oxidation reaction experiments demonstrated that Mn-doped Co phosphate with lattice tensile strain shows optimized *OH adsorption strength, and is favorable to structure reconstruction and form highly active Co oxyhydroxide intermediate during OER process. Our work provides insight into the effects of the lattice strain on the OER activity from the standpoint of intermediate adsorption and structure transformation.

Molecular dynamics of adsorption of hydroxide, sulfate and calcium ions at the interface between C-S-H and carbonate crystals

This paper presents a systematical study of the adsorption mechanism of ions in the interface between calcium silicate hydrate(C-S-H) and carbonate crystals using molecular dynamics simulation. By constructing molecular dynamics models of C-S-H and different carbonate crystals, the diffusion behaviors of ions and water molecules in Ca(SO)4 and Ca(OH)2 solutions between C-S-H and carbonate crystals are simulated. The motion trajectory of ions is tracked to analyze the distribution characteristics of cations and anions. The adsorption mechanism of ions at the interface between C-S-H and carbonate crystals is investigated by calculating the density, mean square displacement, and radial distribution functions of water molecules and ions. The results show that the calcite interface has an extremely strong adsorption capacity on calcium ions, while the dolomite and magnesite interface adsorb anions. On the other hand, magnesite has a weaker adsorption capacity for anions, but a stronger repulsion capacity for calcium ions than dolomite. This study reveals the mechanism of adsorption of ions at C-S-H and carbonate crystals at the nanoscale and will have great significance for the investigation of the durability of cement-based materials.

Identifying the Local Atomic Environment of the "Cu3+" State in Alkaline Electrochemical Systems.

CuO-based catalysts are active for the oxygen evolution reaction (OER), although the active form of copper for the OER is still unknown. We combine operando Raman experiments and density functional theory (DFT) electronic structure calculations to determine the form of Cu(O)xOHy present under OER conditions. Raman spectra show a distinct feature related to the active "Cu3+" species, which is only present under highly oxidizing conditions. DFT is used to produce theoretical Raman standards and match the unique Raman feature of copper under OER potentials. This method identifies a range of Cu3+-containing compounds which match the distinct Raman feature. We then integrate experimental electrochemistry to progressively eliminate possible structures and determine the stoichiometry of the active form as CuOOH, which likely takes the form of a surface-adsorbed hydroxide on a CuO surface. Bader charge analysis, site-projected wavefunctions, and density of states analysis show that electron density is removed from O 2p orbitals upon hydroxide adsorption, suggesting that the electronic structure exhibits d9L Cu2+ behavior rather than the local electronic structure of a formal Cu3+.

Enhancing the Surface-Active Sites of Bimetallic 2D Hydroxide Materials by Introducing Fe2+ Ions toward Effective Hydroxide Adsorption for the Water Oxidation Reaction

Here, in this work, via a simple wet chemical method, we have modified the CoFe layered double hydroxide (LDH) surface by doping active Fe2+ ions which function as an excellent electrocatalyst for the oxygen evolution reaction (OER) in 1 M KOH. Variations in the amount of Fe2+ ions show a noteworthy concentration dependency on the electrochemical performance of the catalyst. The catalyst shows an interesting Fe2+ ion dependency toward the OER, and a volcanic relationship between accumulated electronic charge and thermoneutral current densities is observed. This volcanic relation shows that with an optimum concentration of Fe2+ ions, the catalyst could effectively catalyze the OER by following the Sabatier principle of ion adsorption. The LDH having an intermediate amount of Fe2+ loading {FeII-LDH (0.04 M)} shows the highest OER activity, and it demands just a 268 mV overpotential to drive a 10 mA/cm2 current density, whereas the pristine CoFe-LDH displays an overpotential of 345 mV. Also, as a result of introducing Fe2+ ions, a 4-fold increase in the turnover frequency (TOF) value was noticed. Operando in situ impedance analysis reveals that the introduction of Fe2+ ions in the pristine CoFe-LDH lattice largely improvises the charge transfer kinetics at the interface by providing a greater number of surface-active sites toward OH– adsorption. Overall, this study shows an interesting Fe2+ ion loading dependency over the LDH surface toward the water oxidation reaction.

Geochemical Characteristics of Trace Elements and REEs and their Geological Significance for Uranium Mineralization within the Qianjiadian Sandstone-Hosted Uranium Deposit, Songliao Basin

The Qianjiadian uranium deposit is a typical interstratified oxidized zone sandstone-hosted uranium deposit hosted in the Upper Cretaceous Yaojia Formation of the southern Songliao Basin. Despite its significance, little research has been conducted on the relationship between trace elements, REEs, and uranium mineralization in this deposit. This study presents new geochemical data from sandstones in the oxidation, transition, and reduction zones. The sandstones in the transition zone are highly enriched in U and moderately enriched in Mo, Cd, and V compared to those in the oxidation and reduction zones. They are also weakly enriched in Co, Ni, and Zn. The oxidation and transition zone sandstones have higher ∑LREE and ∑HREE contents than those in the reduction zone. However, the oxidation zone sandstones are characterized by LREE enrichment and flat HRRE distribution, while the transition zone sandstones show HRRE enrichment and flat LREE distribution. These trace element and REE differentiation characteristics within each subzone are closely related to the geological process of interstratified oxygenation. Oxygenated uranium-bearing fluids from southwestern provenance areas carried multiple trace elements and REEs and infiltrated along the oxidation sandstones to reach the Yaojia Formation’s transition zone. During this process, a certain amount of Mo, V, Cd, and LREE from the oxygenated ore-forming fluids was precipitated by Fe-Mn hydroxide adsorption or calcite and siderite cementation. Meanwhile, about 20.33% of preexisting U in the oxidation zone sandstones was continuously extracted and entered into the oxygenated ore-forming fluids. In the transition zone, where dissolved oxygen was exhausted and hydrocarbons were continuously injected, U, Mo, Cd, V, Co, Ni, Zn, and REEs were unloaded and precipitated as uranium minerals, sulfide minerals, or carbonate minerals. The enrichment of Mo, Cd, V, and HREEs in the sandstones can serve as new prospecting indicators for the Qianjiadian uranium deposit.

Simultaneous Phosphate Removal and Power Generation by the Aluminum–Air Fuel Cell for Energy Self-Sufficient Electrocoagulation

A self-powered electrocoagulation system with a single-chamber aluminum–air fuel cell was employed for phosphate removal in this study. Electricity production and aluminum hydroxides in solution were also investigated. When the NaCl concentration increased from 2 mmol/L to 10 mmol/L, the phosphate removal increased from 86.9% to 97.8% in 60 min. An electrolyte composed of 10 mmol/L of NaCl was shown to obtain a maximum power density generation of 265.7 mW/m2. When the initial solution pH ranged from 5.0 to 9.0, 98.5% phosphate removal and a maximum power density of 338.1 mW/m2 were obtained at pH 6.0. Phosphate was mainly removed by aluminum hydroxide adsorption. These results demonstrate that the aluminum–air fuel cell can be applied as electricity-producing electrocoagulation equipment. Aluminum–air fuel cells provide an alternative method to meet the goal of carbon neutrality in wastewater treatment compared with traditional energy-consuming electrocoagulation systems.

New insights into the sphalerite activated by copper sulfate in lime systems

The mechanism of how copper sulfate (CuSO4) activates sphalerite under lime-inhibiting sphalerite conditions has not been fully specified. In the paper, the activation mechanism of CuSO4 for sphalerite surfaces depressed with lime (pH=12) was investigated through micro-flotation experiments, solution chemical analysis, zeta potential measurement, and X-ray photoelectron spectroscopy. The solution chemical analysis and micro-flotation experiments indicated that the Cu2+ ions have produced copper hydroxide (Cu(OH)2) precipitation under alkaline conditions (pH=12); however, the activation effect of sphalerite by Cu(OH)2 is weak. Zeta potential measurement and X-ray photoelectron spectroscopy showed that the inhibition effect on sphalerite in the lime system was attributed to the adsorption of zinc hydroxide and calcium hydroxide on the sphalerite surface. After the treatment with CuSO4, not all of the Cu2+ ions in the lime system (pH=12) will immediately combine with hydroxide and convert to Cu(OH)2. A certain concentration of Cu2+ ions is still present in the lime system (pH=12). This part of the Cu2+ ions will eliminate zinc hydroxide (all) and calcium hydroxide (part) from the sphalerite surface in the lime system, and activate sphalerite by forming a cuprous sulfide film. Therefore, the activation of sphalerite by CuSO4 in the lime system can be explained as the activation process of sphalerite by Cu2+ ions, not copper hydroxide. These results provide a theoretical basis for improving the flotation separation of sphalerite and pyrite in the lime system.