Effective Removal Of Dyes Research Articles

Recyclable copper-decorated magnetic composites as non-precious catalysts for effective removal of 4-nitrophenol and azo dyes

Carbonized lotus leaf (CLL) from agricultural waste is employed as the support to prepare the novel Cu-Fe3O4/carbonized lotus leaf (CuX-FCLL) catalysts. The magnetic catalyst Cu1.5-FCLL demonstrated desirable catalytic activity for the reduction of organic dyes (Congo red, Methyl orange) and nitroaromatic compounds (3- and 4-nitrophenols). The magnetically recoverable catalyst (Cu1.5-FCLL) exhibited ultrafast catalytic activity for 4-nitrophenol reduction with a conversion rate of over 98% within 30 s, which was comparable to those noble metal catalysts widely used. The CLL with unique papillae structures could provide large surface areas and prevent aggregation of metal NPs, and boost the catalytic performance of Cu1.5-FCLL by a synergetic effect. Such a magnetic catalyst was facilely recovered and reused after ten cycles with negligible loss of catalytic performance. This work presents an efficient green catalyst to replace noble metals for wastewater treatment.

Effective removal of cationic dyes from aqueous solutions by using black cumin (Nigella sativa) seed pulp and biochar

Black cumin seed pulp (C), as well as biochar (CC) produced via pyrolysis of black cumin seed pulp were used to remove methylene violet 2B (MV) and basic yellow 28 (BY28) from aqueous solution. Adsorption isotherms and kinetics were applied at 10, 25, and 35 °C. The adsorption of methylene violet 2B and basic yellow 28 on the black cumin seed pulp and biochar surface was exothermic; the heat of adsorption values were lower than 0. The adsorption capacities of BY28-C, BY28-CC, MV-C, and MV-CC were 212.8, 625, 164, and 909 mg g-1 at 25 °C, respectively. The adsorption of black cumin seed pulp and biochar data were examined with the Freundlich, Langmuir, Temkin, Dubinin-Radushkevich (D-R), and Flory-Huggins (F-H) isotherm models. The kinetics of the adsorption were fitted to the pseudo first-order and pseudo second order equations. The pseudo second order equation gave a better fit than the pseudo first-order equation.

Enhanced hybrid hydrogel based on wheat husk lignin-rich nanocellulose for effective dye removal.

Polyvinyl alcohol (PVA) hydrogels were enhanced mechanically through the addition of lignin-rich nanocellulose (LCN), soluble ash (SA) and montmorillonite (MMT) for dye removal. The hybrid hydrogels reinforced with 33.3wt% of LCN had a 163.0% increase in storage modulus as compared to the PVA/0LCN-33.3SM hydrogel. LCN can be added to the PVA hydrogel to alter its rheological properties. Additionally, hybrid hydrogels were highly efficient in removing methylene blue from wastewater, which was attributed to the synergistic effects of the PVA matrix supporting embedded LCN, MMT, and SA. The adsorption time (0-90min) showed that the hydrogels containing MMT and SA had high removal efficiency, and the adsorption of methylene blue (MB) by PVA/20LCN-13.3SM was greater than 95.7% at 30°C. It was found that MB efficiency decreased with a high MMT and SA content. Our study provided a new method for the fabrication of polymers-based eco-friendly, low-cost and robust physical hydrogels for the MB removal.

A novel crosslinking strategy on functional cellulose-based aerogel for effective and selective removal of dye

Motivated by sustainable development, the huge pressure of harmful dyes wastewater treatment has highlighted an urgent need to develop more effective biomass adsorbents for selective removal and separation of dyes. Herein, cellulose-based aerogel adsorbent (CPB) is successfully prepared through a novel crosslinking strategy for static and dynamic dye removal, starting with the fabrication of cellulose acetoacetate (CAA) and β-cyclodextrin acetoacetate (β-CDAA) through transesterification process, followed by the crosslinking of polymer chains using polyethyleneimine (PEI) through the formation of dynamic enamine bonds and the freeze-drying treatment of three-dimensional (3D) network structures. A maximum adsorption capacity toward methyl orange (MO) up to 1013.11 mg g−1 is achieved at 25 °C. Besides, the CPB aerogel has abundant surface positive charge, which can be employed to selectively remove anions dyes from ternary mixed systems and has additional antibacterial activity. More importantly, the CPB material based on the dynamic crosslinking strategy can be regulated by adjusting pH, which greatly facilitates the reprocessing and utilization of the adsorbent. The cellulose-based aerogel presented in this work could be an extremely promising material for dye wastewater treatment.

Double-Shelled Porous g-C3 N4 Nanotubes Modified with Amorphous Cu-Doped FeOOH Nanoclusters as 0D/3D Non-Homogeneous Photo-Fenton Catalysts for Effective Removal of Organic Dyes.

Graphite phased carbon nitride (g-C3 N4 ) has attracted extensive attention attributed to its non-toxic nature, remarkable physical-chemical stability, and visible light response properties. Nevertheless, the pristine g-C3 N4 suffers from the rapid photogenerated carrier recombination and unfavorable specific surface area, which greatly limit its catalytic performance. Herein, 0D/3D Cu-FeOOH/TCN composites are constructed as photo-Fenton catalysts by assembling amorphous Cu-FeOOH clusters on 3D double-shelled porous tubular g-C3 N4 (TCN) fabricated through one-step calcination. Combined density functional theory (DFT) calculations, the synergistic effect between Cu and Fe species could facilitate the adsorption and activation of H2 O2 , and the separation and transfer of photogenerated charges effectively. Thus, Cu-FeOOH/TCN composites acquire a high removal efficiency of 97.8%, the mineralization rate of 85.5% and a first-order rate constant k= 0.0507 min-1 for methyl orange (MO) (40mg L-1 ) in photo-Fenton reaction system, which is nearly 10 times and 21 times higher than those of FeOOH/TCN (k= 0.0047 min-1 ) and TCN (k= 0.0024 min-1 ), respectively, indicating its universal applicability and desirable cyclic stability. Overall, this work furnishes a novel strategy for developing heterogeneous photo-Fenton catalysts based on g-C3 N4 nanotubes for practical wastewater treatment.

Development of a ZnOS+C Composite as a Potential Adsorbent for the Effective Removal of Fast Green Dye from Real Wastewater.

Wastewater treatment is becoming increasingly important due to the potential shortage of pure drinking water in many parts of the world. Adsorption offers a potential technique for the uptake of contaminants and wastewater purification. In the last two decades, several efforts have been made to remove fast green (FG) dye from wastewater via different adsorbent materials. However, adsorption capacity shown by these adsorbents is low and time-consuming. Herein, we have synthesized for the first time a new powdered adsorbent ZnOS+C, modified zinc peroxide with sulfur and activated carbon to effectively remove FG dye from wastewater. Results of batch adsorption experiments have suggested that ZnOS+C has the maximum adsorption potential of 238.28 mg/g for FG dye within 120 min of adsorption equilibrium for a wide range of pH ranging from 2 to 10 pH. The adsorption process conforms to the Freundlich isotherm model, suggesting a multilayered adsorption process on the outer surface of ZnOS+C. The adsorption kinetics study indicates that the kinetics of the reaction are the intraparticle diffusion model. Briefly, this study shows proof of the application of ZnOS+C powder as a new eco-friendly adsorbent with extremely high efficiency and high surface area for removing FG dye.

Novel Cellulose/Silica Microspheres as Sustainable and Efficient Adsorbents for Methyl Orange Removal

The effective removal of organic dyes from aqueous solutions is essential for environmental protection and remediation. Hence, methods for fabricating efficient and sustainable adsorbents for removing toxic dyes are urgently desired. Here, new cellulose/silica microspheres containing amino groups were prepared and applied as functional materials for capturing anionic pollutants. Tosyl cellulose, which has a high degree of substitution, was prepared from cellulose using an ionic liquid as the solvent. Further, (3-aminopropyl)trimethoxysilane was utilized as a silica precursor to prepare the microhybrids via nucleophilic substitution, followed by the sol–gel process. The fabricated microhybrids exhibited an excellent capacity for methyl orange (MO) adsorption. Furthermore, the effects of different pH values, contact times, and initial dye concentrations on the MO adsorption capacity were evaluated. The Langmuir isotherm and pseudo-second-order kinetic models were effective for modeling the adsorption of MO on the cellulose/silica microspheres. Under the established optimal conditions, the cellulose/silica microspheres exhibited a higher adsorption capacity (588 mg/g) than those in previous reports. Therefore, the proposed cellulose/silica microspheres offer a promising platform for the sustainable development of water-purification systems.Graphical

Green synthesis of photocatalyst hydroxyapatite doped TiO2/GO ternary nanocomposites for removal of methylene blue dye

Waste water treatment due to dyes is always a challenge. The present work focuses on nano Hydroxyapatite (nHAp) synthesis from waste oyster shells, a biogenic source composed of calcium carbonate. nHAp is used in various biomedical fields because of its bioactive and biocompatible material, as well as in the field of waste water treatment. On the other hand, semiconductor metal oxide like Titanium dioxide (TiO2) and Graphene oxide (GO) were chosen to show an effective photocatalytic performance with a synergistic effect. nHAp alone has poor adsorption for dye removal and its efficiency was increased by doping it with TiO2 and forming a composite with GO to treat Methylene Blue (MB) dye which is a common effluent. The synthesized composites were characterized by using Fourier Transform Infra Red (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques to identify the purity and size of the composites. Ultra Violet (UV)-visible studies indicates that nHAp/TiO2/GO composites act as ternary nano photocatalyst and degrades the dye present in waste water at different time intervals from 30 mins to 360 mins. From the absorbance values, it was observed that 98% effective removal of MB dye and the first order rate constant is calculated. Highly interesting fact that prepared ternary nanocomposites compared with other individual species and metal oxides; it exhibits an increased affinity for dye removal by adsorption along with improved photocatalytic performance. The ternary composites exhibited a moderate inhibition zone, at the concentration 500 µg of strain E. coli and S. aureus which are gram negative and positive bacteria respectively.

Electrokinetic Remediation for Textile Wastewater Contaminated Soil

<p>Soil contamination due to industrial activities is very common and discharging of partially treated or untreated textile wastewater into nearby environment in developing countries contaminated soils. The remediation of textile wastewater contaminated soils containing residual organic dyes and inorganic salts is risky. It is required to identify an economic and eco-friendly in-situ remediation technique for the textile wastewater contaminated soil. This paper investigates the effective removal of residual textile dyes and inorganic salts from the soil using electrokinetic remediation. Laboratory scale acrylic reactors were utilized and the soil was collected from the contaminated agricultural site. The experiment was optimized for different electrode combination (Iron-iron, Iron-stainless steel, Iron-aluminium, Iron-graphite), electrode distance (3 cm, 5.5 cm, and 10.5 cm) and electrical potential gradient (3V/cm, 4V/cm, and 5V/cm). Tap water was used as electrolytes in order to prevent further contamination during remediation process. An electroosmotic flow of 256 mL was observed at cathode reservoir for Iron-graphite electrodes and these electrodes removed 93% electrical conductivity and 82% of total organic carbon from soil. It is found that electroosmosis is the dominant mechanism by which residual textile dyes were removed. The proposed remediation technique is found efficient, economic and eco-friendly compared to the existing technologies.</p>

Fabrication of porous polymer particles containing BiVO4 and Fe3O4 nanoparticles using block copolymer as porogen for effective dye removal

Hybrid porous particles (HPPs) of poly(methyl methacrylate-divinylbenzene) P(MMA-DVB) containing a visible light-photocatalyst bismuth vanadate (BiVO4) and magnetite (Fe3O4) nanoparticles (NPs) were synthesized and employed as a reusable material for effective dye removal. The porous structure increasing the surface to volume ratio and high water diffusivity of HPPs, prepared via the microsuspension iodine transfer polymerization, was generated by using poly(methacrylic acid)-block-poly(MMA-3-[trimethoxysilyl] propyl methacrylate) (PMAA-b-P(MMA-MPS)) as porogen. The block copolymer also acting as a surface modifier of BiVO4 NPs allowed the encapsulation of this photocatalyst together with oleic acid coated Fe3O4 NPs in spherical HPPs. The fabricated HPPs could efficiently remove methylene blue (MB) up to 235 mg/g-BiVO4 based on the adsorption and photocatalytic degradation mechanism caused by the particle porosity and BiVO4 NPs, respectively. Moreover, the incorporated Fe3O4 NPs provided the magnetic separation ability of the HPPs for their reusability up to 5 cycles with a high MB removal performance of > 86. These HPPs would be good candidates for effective dye removal in contaminated water

Rheological, morphological and swelling properties of dysprosium-based composite hydrogel beads of alginate and chitosan: A promising material for the effective cationic and anionic dye removal

An alginate (Alg) and Alginate-chitosan (Alg-Ch) based novel hydrogel beads were fabricated by ionotropic gelation method using trivalent lanthanide dysprosium (Dy3+) ion as crosslinking agent. The chemical components, morphology and viscoelasticity of the as-prepared hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM) and rheology. The hydrogels beads with high content of Alginate were smooth but with increase in chitosan in the hybrid beads, significant macro-porous structure was observed by FE-SEM. The Dy-Alg beads possess higher viscoelasticity compared to Dy-Alg-Ch hybrid beads along with the higher breaking strain and structure recovery as revealed by rheology. However, the hydrogel beads of 1:1 and 2:1 Dy-Alg-Ch showed stable gel structure upto 80 °C in contrast to Dy-Alg or 1:2 Dy-Alg-Ch hydrogel beads showing stabilization effect of adding chitosan to Dy-Alg beads. The hybrid hydrogel beads (1:2 and 1:1) showed much better swelling compared to Dy-Alg hydrogel beads. The as-prepared beads with higher chitosan content showed significantly high adsorption of cationic dye Rhodamine B (RhB) whereas decrease in chitosan content favored the adsorption of anionic dye Fluorescein (Flu). The mechanism of adsorption process was evaluated by fitting adsorption data to kinetic models which reveals that adsorption of both the dyes involve chemisorption phenomena determined mainly by film and intraparticle diffusion in case of RhB and by multiple steps in case of Flu. The easy and fast fabrication, outstanding mechanical and stable properties indicated the hydrogel as a promising material for the wastewater treatment with cost- effective performance.

Green synthesis of novel magnetite mixed metal oxides with cationic surfactant nanocomposite: Investigation of its effective removal of Azorubine E122 food dye and antimicrobial activity

Design and assembly of novel nanocomposites with multi‐purpose activities including efficient adsorption behavior toward different pollutants and microbial growth inhibition of various active biological species is a challenging aspect. Therefore, the current study is devoted to fabricating a novel nanocomposite of mixed metal oxides (ZrO2 and SiO2) with magnetite (Fe3O4) and cationic surfactants (cetyltrimethyl ammonium bromide [CTAB] and dodecyltrimethyl ammonium bromide [DoTAB]) via a solvent free microwave methodology to yield ZrSiO4 NPs‐CTAB@Fe3O4 NPs‐DoTAB. The as‐prepared nanocomposite was characterized by SEM to confirm the existence of homogeneous particles (~32.45 nm). The chemical structure of nanocomposite was also confirmed from the energy dispersive X‐ray spectroscopy (EDX), Fourier‐transform infrared spectroscopy (FTIR), and X‐ray diffraction (XRD) analyses. The surface area of this nanocomposite was also determined by the Brunauer‐ Emmett‐ Teller (BET) method and found to correspond to 6.319 m2 g−1. Remediation of Azorubine E122 food dye was optimized in the presence of a number of controlling parameters. The maximum adsorption capacity was characterized as 66.55 mg g−1 using 50 mg nanocomposite at 20 min. Kinetics and isotherm modeling evaluations referred to the best fitting with pseudo‐second order and Freundlich model, respectively. The antibacterial activity of ZrSiO4 NPs‐CTAB@Fe3O4 NPs‐DoTAB nanocomposite was assessed against Escherichia coli ATCC® 25922™ and Staphylococcus aureus ATCC® 25923™, and the collected data proved efficient growth inhibition (p < 0.05) at considerably low concentrations of the investigated nanocomposite. Therefore, the evaluated ZrSiO4 NPs‐CTAB@Fe3O4 NPs‐DoTAB nanocomposite was concluded to afford excellent antibacterial activity and efficient magnetic removal behavior of organic dyes. Hence, it is recommended as a talented material for purification of water resources containing multi‐chemical and biological pollutants as well. Finally, this study is expected to open new prospects for manufacturing other new nanocomposites with the aim of future applications in the removal of different chemical pollutants as well as viruses and bacteria.

Adsorptive removal of anionic azo dye by Al3+-modified magnetic biochar obtained from low pyrolysis temperatures of chitosan.

Magnetic γ-Fe2O3/Al3+@chitosan-derived biochar (m-Fe2O3/Al3+@CB) was prepared by introducing magnetic maghemite (γ-Fe2O3) nanoparticles and aluminum sulfate [Al2(SO4)3] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-Fe2O3/Al3+@CB was used to remove typical anionic azo dye (Congo red, CR). Effects of initial CR concentration, contact time, initial pH value, background electrolytes, and temperature on CR adsorption by m-Fe2O3/Al3+@CB were studied. Compared with magnetic chitosan-derived biochar (m-Fe2O3@CB), m-Fe2O3/Al3+@CB exhibited excellent performance for a wider range of pH values (pH 1-7) and in the presence of background electrolyte. The introduction of Al3+ is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94mgg-1) of m-Fe2O3/Al3+@CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-Fe2O3/Al3+@CB is a potential adsorbent for effective removal of organic dyes from aqueous solution due to its high adsorption capacity and convenient magnetic recovery and stronger anti-interference ability against coexisting anions in wastewater.

Uptake of BF Dye from the Aqueous Phase by CaO-g-C3N4 Nanosorbent: Construction, Descriptions, and Recyclability

Removing organic dyes from contaminated wastewater resulting from industrial effluents with a cost-effective approach addresses a major global challenge. The adsorption technique onto carbon-based materials and metal oxide is one of the most effective dye removal procedures. The current work aimed to evaluate the application of calcium oxide-doped carbon nitride nanostructures (CaO-g-C3N4) to eliminate basic fuchsine dyes (BF) from wastewater. CaO-g-C3N4 nanosorbent were obtained via ultrasonication and characterized by scanning electron microscopy, X-ray diffraction, TEM, and BET. The TEM analysis reveals 2D nanosheet-like nanoparticle architectures with a high specific surface area (37.31 m2/g) for the as-fabricated CaO-g-C3N4 nanosorbent. The adsorption results demonstrated that the variation of the dye concentration impacted the elimination of BF by CaO-C3N4 while no effect of pH on the removal of BF was observed. Freundlich isotherm and Pseudo-First-order adsorption kinetics models best fitted BF adsorption onto CaO-g-C3N4. The highest adsorption capacity of CaO-g-C3N4 for BF was determined to be 813 mg. g−1. The adsorption mechanism of BF is related to the π-π stacking bridging and hydrogen bond, as demonstrated by the FTIR study. CaO-g-C3N4 nanostructures may be easily recovered from solution and were effectively employed for BF elimination in at least four continuous cycles. The fabricated CaO-g-C3N4 adsorbent display excellent BF adsorption capacity and can be used as a potential sorbent in wastewater purification.

Fast one-pot laser-based fabrication of ZnO/TiO2-reduced graphene oxide nanocomposite for photocatalytic applications

Laser synthesis is rapidly emerging to be an efficient and unique method for the synthesis of a wide spectrum of nanomaterials owing to its ease of setup, simplicity, and generation of high-purity nanomaterials. This study explores a pulse laser ablation protocol in the synthesis of ZnO-TiO2 (ZT) and ZnO-TiO2-reduced graphene oxide (ZT-rGO) nanocomposites. The effect of rGO loading (5 %, 10 %, and 20 %) was investigated on the nature of the crystalline nanostructures formed, the increased thermal stability achieved, and the effective removal of methylene blue dye. Following fabrication, the nanocatalyst materials were characterized by TEM, PXRD, SEM/EDX, AFM, UV–Vis, TGA, and FTIR. Using UV illumination, the as-synthesized photocatalysts were evaluated in the photodegradation of methylene blue (MB) as a model dye pollutant. Among the nanocomposites, the ZT-rGO 5 % shows the best photocatalytic activity by having a preferential rate constant of 0.149 min−1. The nanocomposites were prepared in 30 min, providing 98.5 % MB removal within just 30 min, using 10 mg/L of MB and 20 mg/L of the catalyst. During the photodegradation process, the rGO component serves as an electron trap, thus enhancing the formation of holes which are the mainstay of any photocatalytic process. As demonstrated by the work reported, the laser ablation technique shows great promise in the fabrication of ZT-rGO nanocomposites and similar analogs relevant to the efficient decolorization of wastewater.

Facile Surface Treatment of 3D-Printed PLA Filter for Enhanced Graphene Oxide Doping and Effective Removal of Cationic Dyes

The structured adsorption filter material is one of the ways to enhance the practical applicability of powdered adsorbents, which have limitations in the real water treatment process due to difficulty in the separation process. In this study, three-dimensional (3D) printing technology was applied to prepare filter materials for water treatment processes. A 3D-printed graphene-oxide (GO)-based adsorbent is prepared on a polylactic acid (PLA) scaffold. The surface of the PLA scaffold was modified by subjecting it to strong alkaline or organic solvent treatment to enhance GO doping for realizing effective adsorption of cationic dye solutions. When subjected to 95% acetone treatment, the structural properties of PLA changed, and particularly, two main hydrophilic functional groups (carboxylic acids and hydroxyls) were newly formed on the PLA through cleavage of the ester bond of the aliphatic polyester. Owing to these changes, the roughness of the PLA surface increased, and its tensile strength decreased. Meanwhile, its surface was doped mainly with GO, resulting in approximately 75% methylene blue (MB) adsorption on the 3D-printed GO-based PLA filter. Based on the established optimal pretreatment conditions, a kinetic MB sorption study and an isotherm study were conducted to evaluate the 3D-printed GO-based PLA filter. The pseudo-second-order model yielded the best fit, and the MB adsorption was better fitted to the Langmuir isotherm. These results suggested that chemical adsorption was the main driver of the reaction, and monolayer sorption occurred on the adsorbent surface. The results of this study highlight the importance of PLA surface modification in enhancing GO doping and achieving effective MB adsorption in aqueous solutions. Ultimately, this study highlights the potential of using 3D printing technology to fabricate the components required for implementing water treatment processes.

In vitro hyperspectral analysis of tattoo dyes.

There is no method that can guarantee effective, quick, and noninvasive removal of tattoo dyes. Laser methods are considered to be the method of choice. In this study, an attempt was made to determine the in vitro spectral characteristics of selected dyes used in permanent makeup and tattoos and to analyze the obtained parameters in terms of laser treatments optimization. Hyperspectral analysis was performed to determine the spectral characteristics of the dye on the entire surface of the slide. Seven dyes used in permanent makeup and tattoos were analyzed in vitro. The maximum reflectance and the wavelength for a given dye were determined for the maximum reflectance in the studied wavelength range: 400-1000nm. The optical properties of the dyes were determined based on visible light imaging using camera. The maximum radiation reflectance ranges from 634 to 732nm for the tested dyes. Visually very similar colors may differ significantly in the wavelength for which the maximum absorption of the radiation occurs. White and yellow dyes are characterized by the highest reflectance value. The black dye is characterized by the lowest reflectance coefficient. Low reflectance of black dye results in more safe and effective removal treatments. The homogeneity of radiation absorption can be identified using methods of analysis and processing of images in visible light. Optimization of the wavelength of which the maximum absorption/reflectance of radiation occurs may allow us to increase the effectiveness of laser treatments for removing permanent makeup and tattoos.

Porous polydopamine nanospheres with yolk shell-like structure to effectively remove methylene blue, bisphenol A, and tetracycline from wastewaters

A porous PDA nanoadsorbents with yolk shell-like structures was developed for effective removal of cationic dyes, EDCs, and antibiotics from water.

Effective removal of Congo red dye from aqueous solution using activated MgO-nanoparticles

Effective removal of Congo red dye from aqueous solution using activated MgO-nanoparticles

Enhanced catalytic activity of ZnO–CuO–Co3O4 composites achieved using a mechanochemical method for effective Fenton-like dye removal: the generation and catalytic mechanism of various superficial active sites

Mechanochemical treatment for ZnO–Co3O4–CuO composites boosted their catalysis in the Fenton-like degradation of organic wastewater through exposing active oxygen vacancies and Cu/Co–O dangling bonds.