Increased Oxygen Vacancies Research Articles

NiCo2O4/P,N‐doped Carbon with Engineered Interface to Improve the Rechargeability of Zn‐Air Batteries at High Energy Demands

The search for cost‐effective, high‐performance bifunctional catalysts for Zn‐air batteries (ZABs) requires extensive research into precious‐metal‐free materials. This study provides insight into the synergy between nickel cobaltite and P,N‐doped carbon modified through interface engineering by inducing oxygen vacancies in the spinel and non‐metallic heteroatoms in the carbon material. NiCo2O4 with various oxygen vacancy levels was synthesized via an ethylene glycol‐assisted solvothermal route. This resulted in significant changes in the structural and morphological properties, such as reduced crystallite size, lattice distortion, and increased oxygen vacancies, as observed from the physicochemical results. This was further verified by X‐ray photoelectron spectroscopy (XPS) and high‐resolution transmission electron microscopy (HR‐TEM), which showed a homogeneous dispersion of nickel cobaltite nanorods on the carbonaceous matrix, along with an increased concentration of pyridinic nitrogen and the formation of P–N and P–C bonds, both of which enhance electrocatalytic activity. NiCo2O4DI/P,N‐C exhibited superior discharge polarization behavior, achieving power and current densities of 124.4 mW cm−2 and 215.8 mA cm−2. The catalyst presented excellent stability (up to 100 h), while Pt‐IrO2/C lasted near 21 h. These results demonstrate the great potential of tailoring surface defects and heteroatom doping via interface engineering, resulting in high‐performance precious‐metal‐free electrocatalysts for long‐lasting and high‐efficiency ZABs.

Increasing Oxygen Vacancies by Incorporating Co into Nano ZnO for Selective Hydrogenation of CO2 into Methanol

Increasing Oxygen Vacancies by Incorporating Co into Nano ZnO for Selective Hydrogenation of CO₂ into Methanol

Entropy Manipulation of SrTiO3 Perovskite for Enhanced Thermoelectric and Mechanical Properties.

Reducing the thermal conductivity while maintaining excellent electrical transport properties is crucial for enhancing the thermoelectric performance of SrTiO3-based perovskites. Here, we successfully achieved this goal through precisely manipulating the configurational entropy. A series of Ca0.25Nd0.25Sr0.5-x BaxTiO3 (x = 0, 0.05, 0.15, 0.25) ceramics were successfully synthesized using the solid-state reaction combined with graphite burial sintering. It was discovered that structural defects from competing elements in the A-site not only slowed diffusion and hindered grain growth but also increased oxygen vacancies by creating additional gas transmission channels. The gradual decrease in carrier mobility with increasing entropy resulted in the degradation of electrical conductivity, while the Seebeck coefficient experienced a large enhancement due to band modification and increased carrier scattering. Meanwhile, multiscale defects, including point defects, local strain fields, dislocations, and grain boundaries, effectively scatter phonons, leading to a low lattice thermal conductivity of 1.73 W·m-1·K-1. Consequently, the sample with x = 0.15 exhibited a peak ZT of 0.15 at 900 K, reflecting a 148% enhancement compared to that of the matrix. In addition, the hardness increases with configurational entropy because of the chemical disorder, grain refinement, and increased defect concentration. The work emphasizes the importance of precise manipulation of configurational entropy, offering valuable insights for optimizing thermoelectric materials through entropy engineering strategy.

Enhancement effects of Ga-Gd Co-doping on the structure, conductivity, and interfacial polarization of CeO2-based electrolytes

Gd0.1Ce0.9-xGaxO2-δ (x = 0, 0.04,0.07, 0.12) are synthesized via the citric acid-EDTA combustion method as an electrolyte material for intermediate-temperature solid oxide fuel cells. XRD and Rietveld refinement revealed that the material exhibits a single-phase cubic fluorite structure. SEM and EDS analyses demonstrated that the incorporation of Ga ions improved the sample's density, increased the grain size, and provided better element dispersion. XPS analysis confirms that Ga-Gd co-doping leads to increased oxygen vacancy concentration and modifies the oxidation states of Ce. Impedance spectroscopy results indicated that Ga-Gd co-doped ceria has higher ionic conductivity and lower activation energy compared to Gd single-doped ceria. In comparison to Gd0.1Ce0.9O1.95, the best-performing Gd0.1Ce0.83Ga0.07O2-δ achieved nearly a 26-fold increase in ionic conductivity and a 66 % reduction in activation energy. The clearance coefficient of Gd0.1Ce0.83Ga0.07O2-δ reached 100.95, while the blocking factor decreased by nearly 73 % compared to Gd0.1Ce0.9O1.95. The incorporation of Ga ions led to a nearly one order of magnitude reduction in the dissipation of oxygen vacancy concentration in the space charge layer, with the potential decreasing from 0.3971V (Gd0.1Ce0.9O1.95) to 0.3117V (Gd0.1Ce0.83Ga0.07O2-δ). Dielectric studies clarified the contribution of the Gd-Ga synergistic effect on interfacial polarization. In terms of single-cell performance, the NiO-GDC| Gd0.1Ce0.83Ga0.07O2-δ|LSCF cell exhibited higher power density and current density, particularly showing a 42.9 % performance improvement at 650 °C compared to NiO-GDC|Gd0.1Ce0.9O1.95|LSCF. Density functional theory calculations indicated that the incorporation of Ga ions effectively suppresses the electronic conductivity of CeO2 and significantly reduces the formation energy, binding energy, and migration barrier of oxygen vacancies. Therefore, Ga-Gd co-doping can be regarded as an effective strategy for enhancing the performance of ceria-based electrolytes in IT-SOFCs.

Oxygen‐Vacancy‐Rich Heterostructured CeO2‐CuO Nanowires for Urea Electrosynthesis via Co‐Reduction of Nitrate and CO2

AbstractThe mild electrosynthesis of urea presents a promising approach to replace the energy‐intensive conventional manufacturing processes, and identifying highly active and selective electrocatalysts is of paramount importance. Herein, the synthesis of oxygen‐vacancy‐rich CeO2‐CuO heterostructure nanowires on copper foam (CeO2‐CuO/CF) are reported. The CuO‐CeO2 heterostructure notably enhances electron transfer and quickens reaction dynamics, and the increased oxygen vacancies greatly promote the C‐N coupling of nitrate and CO2 to urea. As such, the CeO2‐CuO/CF achieves a remarkable faraday efficiency of 31.96% and urea yield of 720.9 µg cm−2 h−1, along with outstanding stability. This research offers a promising electrocatalyst for the sustainable on‐site production of urea.

Carbon-carbon coupling and hydrodeoxygenation during beechwood hydropyrolysis gas upgrading on TiO2: Oxygen vacancies, lewis acidity and basicity

Anatase TiO2 (TiO2-A) has been utilized for biomass upgrading processes such as hydrodeoxygenation (HDO) and Carbon-Carbon (C-C) coupling reactions (ketonisation and aldol condensation), where Ti-O Lewis acid-base pairs (LABPs) serve as active sites. Altering the metal oxide’s reduction state can modify its acid-base properties, yet the effects of oxygen vacancy coverage on TiO2 during biomass vapor upgrading remain unclear. This study investigates the dynamics between C-C coupling and HDO reactions in the ex-situ upgrading of beechwood pyrolysis vapors at 600 °C and 1 atm. LABPs properties were tuned by varying degrees of oxygen vacancy on TiO2, and the catalyst was characterized by BET, XRD, NH3-TPD, CO2-TPD, H2-TPR, Raman, UV–vis, SEM-EDX, and FTIR. Our study demonstrated that decreasing the O/Ti ratio (i.e., increasing oxygen vacancies) promotes C–C coupling and HDO reactions. The highest C-C coupling and moderate HDO observed on an O/Ti ratio of 1.7 produced the highest jet-fuel fraction (56.5%) compared to other TiO2 variants. The C2+ selectivity shifted from 85.2% of hydropyrolysis oil to 99.2 wt%, while the O/C and H/C ratios changed from 0.45 and 1.55 of hydropyrolysis oil to 0.06 and 1.39, respectively, on TiO2 with an O/Ti ratio of 1.7. The adsorption behavior of the acetone, furan, and guaiacol on LABPs was evaluated on the (1 0 1) plane of A-TiO2 by DFT, which corroborated the experimental findings. This is the first time a deep correlation has been provided on the influence of oxygen vacancies on the vapor phase upgrading of real biomass feedstock.

Unveiling photochemical CO2 reduction processes on PbBiO2I/GO surfaces: Insights from in-situ Raman spectroscopy

Bismuth-based materials are increasingly valued for their dual capability in catalyzing the photochemical CO2 reduction reaction (CO2RR) and enhancing the selectivity towards multi-carbon (C2+) products. This study introduces a novel PbBiO2I/graphene oxide (PbBiO2I/GO) composite, synthesized to leverage the unique properties of both components for improving catalytic performance. The physical and chemical properties of these composites were characterized to delineate their functionality and interaction mechanisms. The heterojunction structure in the composites significantly facilitated the CO2RR, with a noted CH4 conversion rate of 0.8376 µmolg−1h−1. This rate is significantly higher ∼1.78 times that of standalone PbBiO2I under similar conditions. Advanced X-ray photoelectron spectroscopy (XPS) analysis indicated that the incorporation of graphene oxide enhances the electronic environment around Pb2+ and Bi3+ ions, reducing their charge states and increasing oxygen vacancies. This modification likely contributes to the observed catalytic enhancement. Furthermore, in-situ Raman spectroscopy provided insights into the dynamic formation of key intermediates during the CO2RR. Under targeted light irradiation, distinct intermediates such as *COO−, *CO, H*CO/H*COH, OC*C*O, O*CCHO, and C–H were detected, facilitating a deeper understanding of the mechanistic pathways involved in C1 and C2 product formation. This comprehensive analysis not only elucidates the enhanced catalytic pathways facilitated by the composite structure but also sets a foundation for future optimizations in bismuth-based photocatalytic systems.

Application of CeO2 catalyst derived from alkaline-etched MOF-808 (Ce) for DMC synthesis from CO2

To achieve higher yields of dimethyl carbonate (DMC), it is crucial to have precise control of reaction conditions and to develop advanced catalysts with synergistic interactions at active sites. In this work, we synthesized a series of alkali-modified MOF-808 (Ce) catalysts by varying NaOH concentrations (0–1.0 M), followed by carbonation to yield the advanced catalysts—M-CeO₂-CX. Our evaluations of catalytic performance revealed that a 0.5 M NaOH alkaline environment (M-CeO₂-C0.5) was the most effective in breaking the non-covalent interactions within Ce-BTC ligands. Comprehensive characterization further confirmed that M-CeO₂-C0.5 exhibited markedly increased oxygen vacancies and higher densities of basic sites. Both of them are pivotal for enhancing CO₂ activation, leading to superior catalytic performance. Particularly, it was also applied, for the first time, in the direct synthesis of DMC from methanol and CO₂ without a dehydrating agent. Using Plackett-Burman (PB) and Box–Behnken Design (BBD) experimental techniques, we demonstrated that thermodynamic forces significantly outweighed kinetic effects in driving the reaction. Additionally, predictive yield models were developed and rigorously validated, identifying optimal conditions that resulted in a DMC yield of 24.61 mmol/g cat•h. Remarkably, the catalyst retained 97.88 % of its initial activity after 12 cycles, underscoring its exceptional stability and promising industrial scalability.

Unraveling the Effects of Strain-Induced Defect Engineering on the Visible-Light-Driven Photodynamic Performance of Zn2SnO4 Nanoparticles Modified by Larger Barium Cations.

Waterborne infections caused by pathogenic microorganisms represent serious health risks for humans. Ternary zinc-tin oxide nanoparticles have great potential as a cost-effective, environmentally friendly, and efficient candidate for waterborne infections; however, their photocatalytic and antibacterial effects are quite limited due to insufficient visible light absorption and rapid electron-hole recombination. Herein, barium-doped zinc stannate (Ba@ZTO) nanoparticles were synthesized by the hydrothermal method and used for the first time not only as antibacterial agents to prevent the spread of the harmful bacteria S. aureus and E. coli but also as photocatalysts to degrade the organic pollutant rhodamine B. Unexpectedly, Ba2+ ions exhibited compressive stress behavior instead of the predicted tensile stress when inserted into the ZTO crystal lattice, playing an active role in increasing oxygen vacancies within the crystal lattice and in the formation of hydroxyl radicals in the bulk solution and hydrogen peroxide (H2O2) radicals, significantly improving the photocatalytic and antibacterial properties. Strain-induced defects created by the insertion of larger barium ions into the ZTO lattice promote the increase of shallow traps for boosting photocatalytic/disinfection properties while suppressing deep-level traps that encourage nonradiative recombination. In essence, defect and strain engineering opens a promising route to achieve high disinfection efficiency by inducing larger cation ions under visible light in oxide-based materials.

Role of perovskites phase in Ni-based catalysts for low temperature CO2 methanation

CO2 methanation is considered as a promising reaction in the context of mitigating climate change by reducing CO2 emissions and providing a renewable source of methane fuel. The CeNiO3 and LaNiO3 perovskite catalysts were synthesized using the sol-gel method. The effect of perovskite structure on the catalytic activity was studied. The results were compared with Ce-supported and La-supported Ni catalysts (Ni/CeO2 & Ni/La2O3). Different methods including XRD, N2 adsorption-desorption, H2-TPR, FE-SEM, and CO2-TPD, were employed for the characterization of the catalysts. The perovskite catalysts are more active than the corresponding supported catalysts. Among all prepared catalysts CeNiO3 perovskite catalyst showed highest activity 80% conversion and 98% selectivity at 300 °C. Weak basicity, high active metal reducibility and the synergy between Ni and Ce due to perovskite structure are the responsible factors for high activity of CeNiO3 catalyst. The CeNiO3 catalyst showed excellent stability for CO2 methanation during 24 h of time on study with different GHSVs. The effect of calcination temperature was also studied on CeNiO3 catalyst at 650, 750 and 850 °C temperatures. Raman spectra concluded that the oxygen vacancy sites increased with rise of calcination temperature from 650 to 750 °C and decreased with further increase in temperature. The CeNiO3 calcined at 750 °C (CeNiO3-750) showed highest activity among all other catalysts. The increased activity is due to increased oxygen vacancies which ensures that Ni nanoparticles are highly dispersed.

Electrochemically assisted preparation of defect-rich Co3O4 electrocatalysts in a water-modified deep eutectic solvent for enhanced oxygen evolution in acid

Co3O4-based electrode materials exhibit great potential for utilization as efficient catalysts for the oxygen evolution reaction (OER), especially in acidic media. However, enhancing their catalytic stability remains a crucial challenge. Herein, we present a facile electrochemical deposition approach coupled with calcination treatment to achieve in-situ growth of active Co3O4 films from a deep eutectic solvent with water as the modifier. The incorporation of water optimizes the structure of fabricated Co3O4 by increasing oxygen vacancies and elevating the Co2+/Co3+ ratio, enabling it to sustain the OER in 0.5 M H2SO4. Impressively, the catalyst grown on Pt/Ti substrate exhibits stable operation over 125 h at 10 mA cm−2. Attenuated total reflection-fourier transform infrared (ATR-FTIR) spectroscopy reveals that OER on the defect-rich Co3O4 catalyst occurs through both lattice oxygen mediated mechanism (LOM) and adsorption evolution mechanism (AEM).

Achieving nearly 70 cm2/V·s field-effect mobility in single amorphous Ga-In-ZnO thin-film transistors deposited by sputtering process via intermediate patterned metal layer insertion

In this study, we introduce a novel method for enhancing the mobility of amorphous Ga-In-Zn-O (a-GIZO) thin-film transistors (TFTs) by incorporating a patterned metal layer within the a-GIZO single channel. The patterned metal layer comprises either a single layer of aluminum or a combination of aluminum and gold as the bottom and top layers, respectively. TFTs with a single aluminum layer achieved a field-effect mobility of 40.15 cm2/V∙s, significantly higher than the 16.22 cm2/V∙s of standard a-GIZO TFTs. This enhancement is attributed to aluminum’s low Gibbs free energy, which increases oxygen vacancies in the a-GIZO layer and thus improves carrier mobility. Furthermore, when a patterned dual-metal layer consisting of aluminum as the bottom layer and gold as the top layer is used, a field-effect mobility of 69.46 cm2/V∙s is achieved. This improvement is attributed to the low electrical resistivity of gold, which prevents oxidation between the upper gold layer and the a-GIZO layer deposited by sputtering process. Furthermore, this mechanism facilitates the enhancement of the reaction with a lower a-GIZO layer. The unique characteristics of gold prevent oxidation between the a-GIZO and gold interface, thereby promoting favorable interactions between Al and the underlying a-GIZO layer. Our findings demonstrate that strategically inserted patterned metal layers can significantly boost mobility of a single a-GIZO TFT while maintaining device stability, offering a promising approach for advanced display technologies.

Selective CO2 hydrogenation to methanol over a novel ternary In-Co-Zr catalyst

To address the challenges of global warming and energy shortages, the technology to convert CO2 into methanol is of great significance. Indium-cobalt catalysts have attracted widespread attention due to their significant activity and excellent stability. Herein, In-Co and In-Co-Zr catalyst rich in In2O3 were prepared through a citric acid-assisted co-precipitation method. The results show that the In-Co-Zr catalyst can significantly enhance the activity for hydrogenating CO2 to methanol, achieving a CO2 conversion rate of 17.4 % and a methanol selectivity of 77.7 % under the conditions (5.0 MPa, 310 °C, GHSV = 10.28 l·gcat-1·h-1, H2/CO2 ratio of 4). At a GHSV of 48 l·gcat-1·h-1, the space–time yield of methanol was 0.79 gMeOH·gcat-1·h-1, and the catalyst exhibited stable catalytic activity over a continuous reaction period of 120 h. It was revealed that the incorporation of ZrO2 could significantly improve methanol selectivity of In-Co catalyst. Moreover, an increased oxygen vacancy and strong interaction of the In-Co-Zr catalysts are conducive to improving the CO2 adsorption strength and capacity. It is expected that this novel ternary In-Co-Zr catalyst could inspire new opportunities for designing and developing multi-component hybrid catalysts for highly active, stable and selective CO2 hydrogenation to methanol.

Suppression of structural distortion in Vanadium-doped nickel MOFs for enhanced stability and activity in oxygen evolution reactions

Metal-organic framework (MOF)-based electrocatalysts often undergo structural distortion during the oxygen evolution reaction (OER), which can affect their original structure and stability, and poses challenges for theoretical analysis and mechanistic exploration. Herein, vanadium (V) was doped to construct a V–Ni MOF/NF (1.0: 10) that combines structural stability with excellent catalytic activity. The introduction of V significantly suppressed the structural distortion tendency of Ni MOF during the OER process. Additionally, V doping promoted charge redistribution, which enhanced the overall oxidation state of Ni sites and increased oxygen vacancies, providing more active sites and faster electron transport capabilities, boosting the intrinsic activity. As a result, V–Ni MOF/NF (1.0: 10) can be used as a “real catalyst” directly in alkaline OER testing and further applied to seawater splitting and Zinc-air batteries. This work is the first to propose an inhibition strategy for structural distortion of MOF-based OER catalyst, offering new insights into the development of high-activity and stable MOF-based “real catalysts".

Improving thermoelectric properties of high-entropy (Ca0.27Sr0.27Ba0.27La0.19)TiO3-δ ceramics through defect engineering by controlling the oxygen vacancy content

The current dependence on a singular optimization approach has severely impeded the further enhancement of the performance characteristics of strontium titanate-based thermoelectric materials, thereby significantly hindering their development and practical applications. This study integrates entropy engineering with defect engineering to explore the influence of increased oxygen vacancy concentrations and their interactions with other defects on the microstructure, electrical, and thermal transport properties of high-entropy (Ca0.27Sr0.27Ba0.27La0.19)TiO3-δ ceramics. These ceramics were synthesized using spark plasma sintering (SPS) and subsequently subjected to varying degrees of annealing in a reducing atmosphere. The enhancement of oxygen vacancy concentration within the ceramic did not alter its intrinsic phase structure; however, it had a significant and observable effect on grain growth, porosity, and the formation of dislocation bands. Additionally, the reduction of Ti4+ to Ti3+ was facilitated. These modifications substantially improved the electrical conductivity of the ceramics and accelerated the reduction in thermal conductivity with temperature, thereby promoting the achievement of high ZT values at elevated temperatures. Ultimately, the thermoelectric ceramic demonstrated an impressive power factor of 492 μW/(m·K2) at 1073 K, coupled with a notably low thermal conductivity of 0.31 W/(m·K) and a ZT value of 0.2. This investigation also confirms the existence of an optimal oxygen vacancy concentration that maximizes the thermoelectric performance of the ceramic material. This research underscores the capacity of the combined application of entropy engineering and defect engineering to transcend the confines of conventional single-optimization methodologies, resulting in a marked improvement in the thermoelectric performance of the material across diverse parameters.

Iron (III)-Facilitated reconstruction in NiMn layered double hydroxides for initiating rapid oxygen evolution reaction

Layered double hydroxides (LDHs) are emerging as efficient oxygen evolution reaction (OER) electrocatalysts due to their structural advantages and compositional flexibility. Despite their promise, Mn-based LDHs are hampered by poor conductivity, limiting their OER efficacy. This research introduces a hydrothermal and chemical etching technique to fabricate NF/NiMn LDH@NiMnFe(OH)x structures, significantly improving OER performance. The study reveals that integrating Fe3+ into the NiMn LDH fosters a synergistic Ni–Fe interaction, markedly boosting electrocatalytic efficiency. The NF/NiMn LDH@NiMnFe(OH)x-90 shows a low overpotential of 250 mV at 10 mA cm−2 and a Tafel slope of 49.9 mV dec−1 in 1 M KOH, surpassing both its NM precursor and other Ni-based LDH catalysts, including commercial RuO2. In situ, Raman spectroscopy indicates a pivotal phase transition in NF/NiMn LDH@NiMnFe(OH)x to NiOOH at elevated potentials, essential for OER activity. Raman peaks at 463 and 585 cm−1 confirm this structural evolution. The OER activity boost is attributed to increased oxygen vacancies and enhanced conductivity. Moreover, NF/NiMn LDH@NiMnFe(OH)x-90 maintains stability with negligible degradation after 24 h, underscoring its durability. These findings offer a strategic approach to designing high-performance OER electrocatalysts, leveraging nickel-based layered double-metal oxides for potential water-splitting applications, and emphasize the significance of surface engineering and compositional tuning.

The influence of Rh-doped SnO2 microspheres on the sensitivity of benzene detection

In this article, Rh-doped SnO2 microspheres were prepared by a convenient hydrothermal treatment. Compared with the non-doped SnO2 microspheres, the Rh-doped SnO2 microspheres had larger specific surface area, faster electron transfer rate and increased oxygen vacancies, which is beneficial to improve the gas sensitivity of the material. The optimal sensitivity was observed of Rh-0.1 at 250 °C, and the response-recovery time of Rh-0.1 were 46 and 25 s, respectively. Besides, the Rh-doped SnO2 microspheres exhibited excellent gas selectivity and stability to benzene vapor. The novel Rh-doped SnO2 microspheres are potential gas detection materials for accessing benzene vapor.

Amorphous/crystalline Ni-Fe based electrodes with rich oxygen vacancies enable highly active oxygen evolution in seawater electrolysis

To realize large-scale production of hydrogen through seawater electrolysis, it is highly crucial to engineer high-activity and robustly stable catalytic materials for oxygen evolution reaction (OER). Here, a facile etching growth strategy based on Ni foam (NF) is employed to fabricate an amorphous/crystalline Ni-Fe based electrode with rich oxygen vacancies as a promising OER electrocatalyst (a/c-NiFeOxHy@NF). Of note, the introduction of Fe induces the generation of plentiful Ni(Fe)OOH species, which can contribute to the remarkable OER behavior. Profiting from the favorable geometric microstructure of ultrathin nanosheets coupled with 3D open-pore architecture and regulated electronic state by increased oxygen vacancies and abundant crystalline-amorphous boundaries, the resulting a/c-NiFeOxHy@NF displays prominent electrocatalytic OER activity in pure alkaline solution and seawater, achieving impressive overpotentials of only 219 and 233 mV to reach 100 mA cm−2, respectively. More significantly, the electrode can keep stable operation without obvious attenuation for over 1200 h at 100 mA cm−2, demonstrating its exceptional corrosion resistance. Such robustness of this electrode surpasses those of almost all reported OER electrocatalysts. Furthermore, in a self-assembled seawater electrolyzer with a/c-NiFeOxHy@NF as the anode and l-RuP@NF as the cathode, a large current density of 500 mA cm−2 is easily achieved at the voltage of 1.795 V at 65 °C. The work offers a novel paradigm for constructing low-cost, high-efficiency, and ultra-stable OER catalysts, which shows huge promise for industrial seawater electrolysis applications.

Homojunction-Incorporated Oxygen Vacancy Functionalized Spherical TiO2 Nanocrystals for the Electrochemical Detection of Chemical Oxygen Demand.

Chemical oxygen demand (COD) is a critical criterion for the analytical assessment of the degree of organic contaminants in an aqueous system. Typically, toxic and expensive reagents are employed in standardized COD analysis methods, leading to secondary pollution. In this work, we developed a rapid electrochemical method for COD detection based on the oxidation of hydroxyl radicals for organics in water by using oxygen vacancy doped anatase/rutile-TiO2 nanoparticles as electrooxidation catalysts. Homojunction interface generated increasing oxygen vacancies for enhancing electron-transfer rate and accelerating H2O oxidation to substantially improve ·OH yield. Oxygen vacancy further increased the oxygen evolution potential of the material. Initially, glucose was chosen as a standard analyte to evaluate electrochemical responses, and water from urban wastewater treatment plants was assessed as real samples subsequently. Excellent analytical characteristics were achieved with the A/R-TiO2 sensor under the optimal conditions, exhibiting a linear range from 1 to 300 mg L-1 and detection limit of 0.1 mg L-1 COD. The estimated COD values obtained from the samples were highly consistent with those determined using the conventional standard dichromate method. We have presented a fast, cost-effective, and ecologically sustainable method that outperforms the standard COD analysis method and holds great potential for the accurate determination of COD and boasts high detection sensitivity and a broad linear range.

Facile Preparation of Cross-Linked Moringa oleifera Seed Hulls Powder/Hydroxyapatite Framework Composite for Efficient Removal of Toluidine Blue and Methyl Violet 2B from Aqueous Solution

AbstractIn this study, adsorption of two cationic dyes, Toluidine Blue (TB) and Methyl violet 2B (MV 2B) from an aqueous solution was achieved by using multifunctional composite material. The formulation of the composite (MO@HA) was obtained by using Moringa oleifera seed hull powder, calcium chloride (CaCl2), and ammonium hydrogenophosphate (NH4)2HPO4 salts. Surface morphology, functional groups, specific surface area, and surface charge of the composite were explored using Scanning electron microscopy (SEM), Fourier Transform infrared spectroscopy (FTIR), BET analysis, and point of zero charge (PZC), respectively. The composite material resulted in a structural change in the surface of the adsorbents, increased oxygen vacancies, enhancement of active sites, and a specific surface area of 735.55 m2 g−1. Different adsorption parameters such as pH, contact time, adsorbent dosage, and initial concentration were evaluated. The adsorption study showed that equilibrium was reached after 60 min, and the optimum adsorption pH for both dyes (TB and MV 2B) was 6. Langmuir, Freundlich, Liu, and Temkin were fitted to describe the adsorption isotherm, both TB and MV 2B had best correlation with Liu isotherm. The maximum adsorption capacity of TB and MV 2B were 341.488 and 182.453 mg g−1, respectively. Adsorption-desorption cycling studies on the adsorbent confirmed its regeneration and reusability after 5 cycles. A possible adsorption mechanism involving electrostatic interactions, n-π bonding, and hydrogen bonding was suggested. These findings highlight a new direction in the development of efficient and sustainable adsorbent in environmental remediation, specifically in the removal of dyes from aqueous solution.