Existence Of Oxygen Vacancies Research Articles

Understanding the synergistic improving adsorbed and catalytic activity of polysulfide by design of oxygen vacancies and Li+ lithiation/delithiation behavior in Titanium Oxide separator

The commercialization of lithium-sulfur (Li-S) battery is hindered by severe shuttle effect and sluggish electrochemical kinetics, which are induced by the high dissolution of intermediate lithium polysulfides (LiPSs) in cathode side. Here, we describe a strategy towards efficient adsorption and conversion of polysulfides by designing a functional TiO2-based separator. The enhanced overall electrochemical performance of cells is highly related to the synergistic effect of mutually transformational of TiO2 and LixTiO2 and the existence of oxygen vacancies (OVs). During the charging and discharging process of Li-S cell, the in-situ formation of LixTiO2 assigned to lithiation of anatase TiO2 plays a pivotal role in reversible adsorption and desorption of LiPSs. In addition, we also discussed the effect of OVs, which can act as active sites to accelerate electrochemical kinetics and exhibit stronger chemical interaction with LiPSs. The synergy of lithiation and delithiation process of TiO2 with OVs not only offers an effective pathway towards the improvement of LiPSs adsorption and catalytic performance but could also inspire new ideas on developing functional metal oxides modified separator for Li-S battery. We anticipate that this work will provide new avenues for Li-S battery commercialization.

Enhanced visible light driven photodegradation of rifampicin and Cr(VI) reduction activity of ultra-thin ZnO nanosheets/CuCo2S4QDs: A mechanistic insights, degradation pathway and toxicity assessment

In this study, we focused on fabrication of porous ultra-thin ZnO nanosheet (PUNs)/CuCo2S4 quantum dots (CCS QDs) for visible light-driven photodegradation of rifampicin (RIF) and Cr(VI) reduction. The morphology, structural, optical and textural properties of fabricated photocatalyst were critically analyzed with different analytical and spectroscopic techniques. An exceptionally high RIF degradation (99.97%) and maximum hexavalent Cr(VI) reduction (96.17%) under visible light was achieved at 10 wt% CCS QDs loaded ZnO, which is 213% and 517% greater than bare ZnO PUNs. This enhancement attributed to the improved visible light absorption, interfacial synergistic effect, and high surface-rich active sites. Extremely high generation of ●OH attributed to the spin-orbit coupling in ZnO PUNs@CCS QDs and the existence of oxygen vacancies. Besides, the ZnOPUNs@CCS QDs, forming Z-scheme heterojunctions, enhanced the separation of photogenerated charge carriers. We investigated the influencing factors such as pH, inorganic ions, catalyst dosage and drug dosage on the degradation process. More impressively, a stable performance of ZnO PUNs@CCS QDs obtained even after six consecutive degradation (85.9%) and Cr(VI) reduction (67.7%) cycles. Furthermore, the toxicity of intermediates produced during the photodegradation process were assessed using ECOSAR program. This work provides a new strategy for ZnO-based photocatalysis as a promising candidate for the treatment of various contaminants present in water bodies.

Surface Transfer Doping in MoO3-x/Hydrogenated Diamond Heterostructure.

Surface transfer doping is proposed to be a potential solution for doping diamond, which is hard to dope for applications in high-power electronics. While MoO3 is found to be an effective surface electron acceptor for hydrogen-terminated diamond with a negative electron affinity, the effects of commonly existing oxygen vacancies remain elusive. We have performed reactive molecular dynamics simulations to study the deposition of MoO3-x on a hydrogenated diamond (111) surface and used first-principles calculations based on density functional theory to investigate the electronic structures and charge transfer mechanisms. We find that MoO3-x is an effective surface electron acceptor and the spatial extent of doped holes in hydrogenated diamond is extended, promoting excellent transport properties. Charge transfer is found to monotonically decrease with the level of oxygen vacancy, providing guidance for engineering of the surface transfer doping process.

Effects of interfacial buffering layer on imprint and domain switching dynamics in Pb(Zr,Ti)O3 thin-film heterostructures

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO3 (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O3/SrRuO3 (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO3 layer at the Pb(Zr,Ti)O3 surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO3 layer is buffered at the Pb(Zr,Ti)O3/SrRuO3 interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO3 electrodes and the Pb(Zr,Ti)O3 layer associated with the existence of oxygen vacancies in the SrTiO3 layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO3-buffered Pb(Zr,Ti)O3 capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments.

Enhanced photocatalytic performance of ZnO under visible light by co-doping of Ta and C using hydrothermal method.

This study attempted to improve the photocatalytic activity of zinc oxide (ZnO) semiconductors in the visible light region by introducing the co-doping of carbon (C) and tantalum (Ta) to ZnO (ZTC) using a simple hydrothermal method with the respective precursors. The obtained uniform ZTC nanoparticles with an average crystal size of 29.30 nm (according to Scherrer's equation) revealed a redshift with a decrease in bandgap (Eg) from 3.04 eV to 2.88 eV, allowing the obtained photocatalyst to absorb the energy of the visible light for photocatalysis. Furthermore, the Zn 2p and Ta 4f core level spectra confirmed the presence of Zn2+ and Ta5+ in the ZTC sample. In addition, the infrared spectra identified hydrogen-related defects (HRDs), while the O 1s spectra indicated the existence of oxygen vacancies (VO). Electrochemical tests revealed improvement in the electron conductivity and charge separation of the obtained materials. To follow, the photocatalytic performance assessment was conducted by varying the C/Zn2+ ratios (5, 10, and 15 mol%) in ZTC samples, the initial RhB concentration (7, 15, and 30 ppm), and the pH of the RhB solution (3.0-10.0). The photodegradation on ZTC samples showed the most effectiveness for a 7 ppm RhB solution with a C/Zn2+ ratio of 10 mol% in the slightly alkaline medium (pH 9.0). Additionally, ZTC also exhibited commendable durability after being reused several times. The nature of RhB photodegradation was proposed and discussed via a mechanism at the end of this work.

Structural, optical, photoluminescence and sunlight photocatalytic properties of sprayed NiO-ZnO nanocomposite thin films

In this study, the photocatalytic properties of NiO-ZnO nanocomposite thin films were explored towards the degradation of a pollutant model, methylene blue, when exposed to sunlight. The spray pyrolysis technique was used to synthesize nano-sized pristine ZnO and NiO, as well as NiO-ZnO nanocomposites with different molar ratios (Ni:Zn 1:3, 1:1, 3:1). The as-prepared materials' structural and optical characteristics were investigated using different techniques such as XRD, Raman, EDX, SEM, photoluminescence, and UV–visible spectroscopy. Thewetting propertiesof the samples were evaluated using contact angle measurements. The deposited NiO-ZnO nanocomposites were shown to have higher photocatalytic activity than the individual semiconductors. The enhanced activity of nanocomposites might be due to improved charge separation and the existence of oxygen vacancy, which capture these charges to produce active radicals after interacting with adsorbed oxygen. The inherent correlations between photocatalytic activities and PL intensities were investigated in depth.

Superior functionality of niobium pentoxide nano-rod/tripod photocatalyst synthesized using polyethyleneimine as a soft template for the abatement of methylene blue under UV and visible irradiation.

Polyethyleneimine (PEI) capping agent-cum-template-mediated synthesis of niobium oxide nanoparticles is reported to explore its impact on the resultant morphology, porosity, crystallinity, phase complexation, and thus on the photocatalytic activity. The resultant niobium oxides calcined at 800°C and 1000°C crystallized into highly ordered nano-rod/tripod nanostructure with inter-rod angle <120° having orthorhombic phase and heavily agglomerated rod-like nanostructures having monoclinic crystal phase, respectively. Contrary to the expectations, the nano-rod/tripods showed superior photocatalytic degradation kinetics and high adsorption of methylene blue dye in the hydrocolloid than formerly reported monoclinic nanoparticles. The best adsorption capability and photocatalytic activity are observed for the sample calcined at 800°C, resulting in a combined degradation efficiency of 98.8% of methylene blue dye. The adsorption characteristics, stability of the hydrocolloid system, the existence of oxygen vacancies, and the distinct morphology of the photocatalytic nano-rod/tripods are mainly responsible for this behavior. The process and the performance of unique nanostructure over others presents a superior alternative.

High Performance Metal Oxide–Reduced Graphene Oxide Electrocatalyst for All Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is one of the most favorable technologies for large-scale energy storage applications owing to its numerous gorgeous features, such as flexible design, high safety, and long cycle life. In this study, metal oxide (MOx)–reduced graphene oxide (rGO) nanohybrid was successfully synthesized via a facile hydrothermal route followed by annealing and employed as an electrocatalyst to modify the graphite felt (GF) electrode material for all-vanadium redox flow batteries (VRFBs) application. The as-synthesized MOx–rGO nanohybrid reveals good electrocatalytic reversibility and higher anodic and cathodic peak current density for V3+/V2+ and VO2 +/VO2+ redox couples compared with those of rGO and MOx samples. The voltage efficiency of the VRFB using MOx–rGO nanohybrid reaches 84% at 80 mA cm−2, which is 4% and 13% higher than the VRFBs using the rGO-loaded GF electrode and the pristine GF electrode, respectively. It still shows the voltage efficiencies of 76% and 70% at relatively high current densities of 120 mA cm−2 and 140 mA cm−2, respectively, but other samples have no effective discharge. This improvement is accredited to the uniform distribution of MOx nanoparticles on the rGO surfaces, avoiding the restacking of the rGO sheets and conquering nanoparticles aggregation, which might boost the effective active surface area and improve mass transport at the electrode-electrolyte interfaces. Besides, the existence of oxygen vacancies on MOx, the high electrical conductivity of rGO, and the high content of oxygen functional groups play the prodigious roles to facilitate the reversibility of vanadium ions redox reactions.

Copper-doped layered Fe2VO4 nanorods for aqueous zinc-ion batteries

Zinc-ion batteries (ZIBs) have attracted an increasing attention as a potential low-cost, environmentally friendliness, and high-safety energy storage system. Among them, transition metal vanadates with high oxidation state vanadium have great potential in ZIBs cathode research due to their high theoretical capacity. However, many vanadate particles still inevitably suffer from low ion mobility, low electrical conductivity and stability. Cation doping or compositing is an effective pathway capable of enhancing electrical conductivity. In this work, layered Cu-Fe2VO4 porous nanorods are obtained by introducing Cu2+ into MIL-88A(Fe) (a metal–organic framework; MIL stands for materials from Institute Lavoisier) and further ion-exchanged with NH4VO3, exhibiting excellent zinc storage properties as an cathode. The existence of oxygen vacancies and the change of electronic structure caused by Cu2+ substituting part of Fe2+ enhanced the conductivity and electron transfer rate. It delivers a reversible discharge capacity of 237 mAh/g at 0.3 A/g and a satisfactory high rate capacity of 126 mAh/g after 30 cycles at 5 A/g, and stable cycling performance (198 mAh/g after 1000 cycles at 1 A/g). Furthermore, the energy density can reached to 230.97 Wh kg−1 at 208.6 W kg−1. The assembled quasi-solid-state ZIBs maintain a high capacitance retention of 75% after 8000 cycles at 1 A/g.

Efficient photocatalytic nitrogen fixation over novel 2D/2D Bi12O17Br2/ZnCr layered double hydroxide heterojunction

Herein, a novel ultrathin 2D/2D heterostructure, Bi12O17Br2 with oxygen vacancies/ZnCr layered double hydroxides (Vo-Bi12O17Br2/ZnCr-LDHs, Vo-BZ) is prepared by solvothermal and coprecipitation methods for photocatalytic reduction of N2 to NH3. The optimal 2D/2D Vo-BZ heterostructure photocatalyst shows production rate of ammonia production of 286.0 μmol·g−1·h−1. It is 12.5 and 3.6 times higher than that of pure ZnCr-LDHs and Vo-Bi12O17Br2. The improved photocatalytic nitrogen reduction performance is attributed to the intimate contact interface, matching bandgap structure, the shortened migration distance, and thus significantly improved separation and transfer efficiency of hole-electron pairs and light adsorption ability. The large number of oxygen vacancies and high specific surface promote the absorption, activation and deionization of N2 molecules. The theoretical simulation calculation indicates that the free energy of nitrogen molecules on the surface of Vo-BZ is favorable for the absorption and activation of N2 molecules. The existence of oxygen vacancies and formation of heterojunctions can dramatically reduce energy barrier of nitrogen molecule hydrogenation process to boost photocatalytic N2 reduction. This study provides a new idea for the development of efficient photocatalytic nitrogen fixing catalysts.

Polypyrrole-decorated ZnO/g-C3N4 S-scheme photocatalyst for rhodamine B dye degradation: Mechanism and antibacterial activity

Polypyrrole (PPy) and graphitic carbon nitride (g-C3N4) nanoparticles are added to the surface of ZnO nanorods to successfully produce a Step-scheme (S-scheme) photocatalytic system known as g-C3N4/PPy/ZnO (GPZ) by a multistep process: hydrothermal and calcination processes, followed by polymerization. During the formation of the heterojunction, the oxygen vacancy (OV) on ZnO promotes effective separation and increases the redox power of the photogenerated excitons via the built-in internal electric field of S-scheme pathways between g-C3N4 and ZnO. The successful construction of the S-scheme heterojunction was substantiated through X-ray photoelectron spectroscopy, experimental calculations, radical trapping experiment, and liquid electron spin resonance (ESR) characterization, whereas the existence of OVs was well confirmed by ESR analysis. Meanwhile, the PPy served as a supporter, and the polaron and bipolaron species of PPy acted as electron and hole acceptors, respectively, which further enhances the charge-carrier transmission and separation in the ternary GPZ photocatalyst. The photocatalytic activity of the PPy-designed ternary photocatalyst g-C3N4/PPy/ZnO is outstanding and is greater than that of other samples like g-C3N4, ZnO, and ZnO/g-C3N4 and remove 99.0% of RhB (50 mg/L) in 60 min. RhB could be degraded most effectively by GPZ-0.75 photocatalysis at a pH of 7, and 1.0 g/L of the photocatalyst was the ideal concentration. Gram-positive (G + ve) and Gram-negative (G-ve) microorganisms were used as test subjects to determine the antibacterial effectiveness of the photocatalysts using the good diffusion approach. Ternary g-C3N4/PPy/ZnO heterostructure outperformed its competitors in terms of antibacterial activity. Additionally, after five cycles, the as-synthesized photocatalyst showed superb stability. By using a photocatalyst with a superior utilization efficiency of visible light energy, this paper offers a clearly promising, highly effective, and simple method to destroy exceedingly harmful and renowned contaminants.

Graphene quantum dots functionalized Ce-ZnO nanofibers with enriched oxygen vacancy sites morphology to improve the efficiency of selective electrochemical detection of Hg (II)

Herein, GQD functionalized Ce-ZnO hybrid nanofibers (GQD/Ce-ZnO NFs) towards selective Hg2+ ion detection through DPV technique was investigated. The hybrid NFs were synthesized via a facile electrospinning process and their physical properties were investigated through XRD, SEM-EDS, HR-TEM with SAED pattern, XPS, UV-DRS, and ESR techniques. Notably, the plane value, phase recognition, and purity of the GQD/Ce-ZnO NFs were examined through XRD analysis. The chemical states, chemical composition, and weight percentage of the elements were examined by the XPS and EDS analysis. Similarly, the width of the hybrid NFs and structural morphology were elucidated through SEM and HR-TEM analysis. The existence of oxygen vacancies (vo) was verified using UV-DRS and ESR techniques. The electrochemical characteristics of GQD/Ce-ZnO NFs-modified glassy carbon electrode (GCE) was investigated using diverse electrochemical methodologies like cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Remarkably, DPV studies depict that GQD/Ce-ZnO NFs modified GCE achieved high anodic peak current 3.48 × 10−4 A upon successive addition of Hg2+ (0.1–100 μM). The anodic peak current was directly proportional to the mercury ions concentration throughout a wide range of 0.1 × 10−6 to 100 × 10−6 M with a LOD of 267 nM in an optimized experimental condition. The GQD/Ce-ZnO NFs modified GCE showed remarkable reproducibility, with an RSD value of 1.81 %. Additionally, it maintained a strong current retention rate of 71.5 % over 12 days, indicating commendable long-term stability.

Pinched hysteresis loop and internal bias field in Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics

A-site high entropy Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics were designed and prepared by a standard solid state sintering process. First-order ferroelectric transition occurs around 240 °C on heating, while around 136 °C on cooling. Pinched and asymmetric P–E hysteresis loops were observed within and below the thermal hysteresis temperature range of the ferroelectric transition. Pinched P–E hysteresis loops were attributed to the coupling between the ferroelectric transition and the commensurate/incommensurate modulation transition. The reason for the asymmetry of the hysteresis loop was the presence of an internal bias electric field. Different measuring procedures were designed to clarify the evolution of hysteresis loop asymmetry. The existence of oxygen vacancy and Eu3+/Eu2+ was identified by x-ray photoemission spectroscopy. The electric field cycling with elevated temperatures caused defect dipoles incline to align along the direction of spontaneous polarization leading to the internal bias electric field. Due to the A-site high entropy effect, dielectric strength of Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 ceramics is up to 300 kV/cm, which is increased by more than 50% than that with the single element in the A1-site.

Degradation mechanism differences between TiN- and TaN-electrode HZO-based FeRAMs analyzed by current mechanism fitting

This paper investigates the difference in electrical performance and reliability arising from using either titanium nitride (TiN) or tantalum nitride (TaN) as the electrode in ferroelectric random access memories. Because the lattice constant of TaN is better matched to HZO, the TaN-electrode device exhibits better characteristic. However, the leakage of TaN-electrode device increases significantly after wake up. To figure out this phenomenon, current fitting is implemented. According to the fitting results of conduction mechanisms, the existence of oxygen vacancies in the TaN-electrode device provides a reliable explanation to propose models to clarify the degradation mechanisms observed from the TiN- and TaN-electode devices.

Anchoring cobalt molybdenum nickel alloy nanoparticles on molybdenum dioxide nanosheets as efficient and stable self-supported catalyst for overall water splitting at high current density

Developing bifunctional electrocatalysts with efficient and stable catalytic performance at high current density to improve the productivity of water splitting is important for relieving the environmental pollution and energy crisis. Herein, the Ni4Mo and Co3Mo alloy nanoparticles were anchored on MoO2 nanosheets (H-NMO/CMO/CF-450) by annealing the NiMoO4/CoMoO4/CF (CF: self-made cobalt foam) under Ar/H2 atmosphere. Benefitting from the nanosheets structure, synergistic effect of the alloys, existence of oxygen vacancy and the cobalt foam with smaller pore sizes as conductive substrate, the self-supported H-NMO/CMO/CF-450 catalyst demonstrates outstanding electrocatalytic performance, which delivers small overpotential of 87 (270) mV at 100 (1000) mA·cm−2 for HER and 281 (336) mV at 100 (500) mA·cm−2 for OER in 1 M KOH. Meanwhile, the H-NMO/CMO/CF-450 catalyst is used as working electrodes for overall water splitting, which just require 1.46 V @ 10 mA·cm−2 and 1.71 V @ 100 mA·cm−2, respectively. More importantly, the H-NMO/CMO/CF-450 catalyst can stabilize for 300 h at 100 mA·cm−2 in both HER and OER. This research provides an idea for the preparation of stable and efficient catalysts at high current density.

Promoting the activation of H2O via vacancy defects over metal-organic framework-derived cobalt oxide for enhanced oxygen evolution

Engineering the electronic structures of transition metal oxides via vacancy defects is an efficient approach to enhance their catalytic performances, while facilely creating vacancy defects and deeply exploring the effects still remain challenging. Herein, a facile reduction method was applied to introduce oxygen vacancy defects into metal-organic frameworks (MOFs)-derived cobalt oxide (Co3O4) polyhedron. Using zeolitic imidazolate framework-67 (ZIF-67) as Co source and self-sacrificial template, Co3O4 with polyhedron morphology and porous structure was synthesized, and then oxygen vacancy defects were introduced into the as-prepared Co3O4 through one-step NaBH4 reduction treatment. Strikingly, the obtained electrocatalyst (denoted as Co3O4-x) exhibited a larger current density (112.9 mA cm−2 vs. 1.75 V), a lower overpotential (335 mV at 10 mA cm−2) and a smaller Tafel slope (83 mV dec−1) than the Co3O4, which is even superior to the state-of-the-art IrO2 catalyst. Moreover, experiment results combined with density-functional theory (DFT) calculations revealed that the existence of oxygen vacancies could improve the conductivity, promote the activation of H2O and reduce the potential of potential-limited step (PLS), thus greatly boosting electrocatalytic oxygen evolution reaction (OER) performances. This work reported a strategy for preparing defect-rich OER electrocatalysts, and also provided a deep understanding of the defect effects on catalytic performances.

Improved visible-light photocatalytic degradation of pollutants under the synergistic effect of BiOI/BiFeWO6 p-n heterojunction and oxygen vacancies

The construction of p-n heterojunctions has become an effective way to develop high performance photocatalysts to remove pollutants from water. Herein, the BiOI/BiFeWO6 composites abundant in oxygen vacancies (OVs) was rationally designed by combining calcination and solvothermal methods to remove different kinds of pollutants, including rhodamine B (RhB), tetracycline (TC), ciprofloxacin (CIP) and hexavalent chromium (Cr(VI)). The surface properties, structural characterizations and photocatalytic activity of BiOI/BiFeWO6 were investigated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that the morphology of BiOI/BiFeWO6 was BiFeWO6 nanoparticles loaded on BiOI sheet structure. The formation of BiOI/BiFeWO6 heterojunction was demonstrated by the shift of the peaks of Bi and I elements in X-ray photoelectron spectroscopy (XPS). Moreover, the existence of OVs was confirmed by the O 1 s spectrum and electron spin resonance (ESR). By comparison with neat BiOI and BiFeWO6, the BiOI/BiFeWO6 composite showed excellent photocatalytic properties under visible light. The strategy that the p-n heterojunction and OVs work together opens up new avenues to fabricate future high-efficiency photocatalysts.

Enhanced Adsorption and Dissociation of H2O Facilitates Photocatalytic CO2 Reduction on Defective BiSbO4

The dissociation of H2O molecules plays an important role in producing protons for promoting hydrogenation reduction of CO2. Therefore, developing excellent photocatalysts to promote the dissociation of H2O molecules and reveal the effect mechanism is the key research direction to enhance CO2 reduction efficiency. In this work, we synthesized BiSbO4 with oxygen vacancies (OVs) to investigate the photocatalytic mechanism of CO2 conversion and H2O dissociation. Experimental results indicate that the introduction of OVs into BiSbO4 can enhance the absorption capacity of light, narrowing band gaps and impeding the recombination of photogenerated carriers. Importantly, the existence of OVs in BiSbO4 can promote the adsorption and activation of H2O molecules via the stronger covalent interaction, which facilitates the dissociation of H2O molecules to generate more protons and lowers the energy barriers of •COOH to improve the efficiency of CO2 reduction. This study reinforces our understanding of the principle of photocatalytic CO2 reduction and the important role of H2O dissociation in photocatalytic CO2 conversion.

A new insight into the generation of hydrogen peroxide from carmine degradation by cryptomelane as a catalyst, oxidant, and adsorbent

Carmine, as a widely used dye, is one kind of refractory organic pollutants that endanger the water environment. Finding an efficient and environmentally friendly degradation method is a crucial step to treat dye-containing wastewater. Using a one-step hydrothermal synthetic method, cryptomelane was synthesized, characterized, and investigated for its ability to degrade carmine in an aqueous solution. Under the optimum conditions of a 2 g/L cryptomelane dosage and an initial pH of 6.8, 97.87% of 100 mg/L carmine degraded within 240 mins. Cryptomelane exhibited excellent reusability after three cycles, with a decolorization efficiency of 85.39%. Cryptomelane accommodated a board working pH range. The carmine was efficiently decolorized via an interaction of oxidation, catalysis, and adsorption of cryptomelane in a ratio of 46.85:47.11:3.90, respectively. The existence of oxygen vacancies on cryptomelane was responsible for H2O2 generation, and O2•- and 1O2 active species were involved in the carmine degradation by cryptomelane. A low reaction activation energy (Ea = 6.36 kJ/mol) caused efficient removal of carmine by cryptomelane at ambient temperature. These findings notably distinguish three roles of cryptomelane as an adsorbent, oxidant, and catalyst in a pollutant removal system, and prove that cryptomelane may have extensive and promising utilization on refractory organic wastewater treatment without the need to add extra oxidants.

New Insights into Cu/Cu2O/CuO Nanocomposite Heterojunction Facilitating Photocatalytic Generation of Green Fuel and Detoxification of Organic Pollutants

Cu/Cu2O/CuO nanocomposites were synthesized using the simple wet chemical approach for the production of dihydrogen as a potential fuel source and for the detoxification of dyes. The formation of Cu/Cu2O/CuO nanocomposites is confirmed by powder X-ray diffraction, whereas the W-H plot revealed the average particle size of nanocomposite approximately 17 nm, which is in good agreement with the Scherrer method and transmission electron microscopy analysis. The uniform distribution of Cu and O elements was supported by the elemental mapping of the nanocomposite. Band gaps of CuO and Cu2O were found to be 1.71 and 1.92 eV, respectively, using diffuse reflectance spectroscopy spectra and Kubelka–Munk functions. The oxygen vacancies in the nanocomposite are confirmed by various analytical spectroscopic techniques, such as electron paramagnetic resonance, Raman, photoluminescence, and X-ray photoelectron spectroscopy (XPS) spectra. The significant boost in the performance of the fabricated nanocomposite was observed and is attributed to the formation of a heterojunction and existence of oxygen vacancy. The nanocomposite demonstrated proficiency in the photocatalytic splitting of water for the production of hydrogen. The maximum hydrogen generation yield (68 μmol g–1) was observed for Cu/Cu2O/CuO nanocomposites along with NiO (co-catalyst) and methanol as a hole scavenger as well as an electron donor. Moreover, the degradation of congo red (CR) and malachite green (MG) dyes was also investigated and the efficiency of the nanocomposite was found to be 80 and 60%, respectively, after 120 min of light irradiation. The stability of nanocomposites after photocatalysis was investigated by the XPS spectrum of the nanocomposite. Explicitly, the area and broadening of the O 1s XPS spectrum demonstrated higher degradation of CR dye as compared to MG dye.