Selective Degradation of Orange II with the Cobalt(II)–Bicarbonate–Hydrogen Peroxide System

Treatment of textile wastewater using the Co(II)/NaHCO3/H2O2 oxidation system

Textile wastewater (TWW) is one of the most hazardous wastewaters for ecosystems when it is discharged directly into water streams without adequate treatment. Some organic pollutants, such as dyes in TWW, are considered refractory compounds that are difficult to degrade using conventional chemical and biological methods. The bicarbonate-activated peroxide (BAP) system is an advanced oxidation process (AOP) based on applying H2O2, which has been demonstrated to be a clean and efficient technology for dye degradation, with the advantage of operating under slightly alkaline pH conditions. In this study, response surface methodology (RSM) based on a central composite design (CCD) was used to optimize the degradation of TWW contaminated with the azo dye Acid Black 194 using the BAP system catalyzed with cobalt ions in solution (Co2+). The analysis of variance (ANOVA) technique was applied to identify significant variables and their individual and interactive effects on the degradation of TWW. The optimum reagent concentrations for degrading TWW at 25 °C and with 45 μM Co2+ were 787.61 and 183.34 mM for H2O2 and NaHCO3, respectively. Under these conditions, complete decolorization (≥99.40), 32.20 % mineralization, and 52.02 % chemical oxygen demand removal were achieved. Additionally, the acute toxicity of textile wastewater before and after oxidation was evaluated with guppy fish (Poecilia reticulata), showing a total reduction in mortality after treatment with the Co2+-BAP system. The Co2+-BAP oxidation system is a potential method for textile wastewater treatment, which, in addition to achieving complete decolorization and partial mineralization, improves biodegradability and reduces the toxicity of the treated water.

Enhancing acid orange II degradation in ozonation processes with CaFe2O4 nanoparticles as a heterogeneous catalyst

This study used CaFe2O4 nanoparticles as a catalyst for ozonation processes to degrade Acid Orange II (AOII) in aqueous solution. The study compared heterogeneous catalytic ozonation (CaFe2O4/O3) with ozone treatment alone (O3) at different pH values (3-11), catalyst dosages (0.25-2.0 g L-1), and initial AOII concentrations (100-500 mg L-1). The O3 alone and CaFe2O4/O3 systems nearly completely removed AOII's color. In the first 5 min, O3 alone had a color removal efficiency of 75.66%, rising to 92% in 10 min, whereas the CaFe2O4/O3 system had 81.49%, 94%, and 98% after 5, 10, and 20 min, respectively. The O3 and CaFe2O4/O3 systems degrade TOC most efficiently at pH 9 and better with 1.0 g per L CaFe2O4. TOC removal effectiveness reduced from 85% to 62% when the initial AOII concentration increased from 100 to 500 mg L-1. The study of degradation kinetics reveals a pseudo-first-order reaction mechanism significantly as the solution pH increased from 3 to 9. Compared to the O3 alone system, the CaFe2O4/O3 system has higher k values. At pH 9, the k value for the CaFe2O4/O3 system is 1.83 times higher than that of the O3 alone system. Moreover, increasing AOII concentration from 100 mg L-1 to 500 mg L-1 subsequently caused a decline in the k values. The experimental data match pseudo-first-order kinetics, as shown by R2 values of 0.95-0.99. AOII degradation involves absorption, ozone activation, and reactive species production based on the existence of CaO and FeO in the CaFe2O4 nanocatalyst. This catalyst can be effectively recycled multiple times.

Novel pH-Responsive CaO2@ZIF-67-HA-ADH Coating That Efficiently Enhances the Antimicrobial, Osteogenic, and Angiogenic Properties of Titanium Implants

Titanium-based implants often lead to premature implant failure due to the lack of antimicrobial, osteogenic, and angiogenic properties. To this end, a new strategy was developed to fabricate CaO2@ZIF-67-HA-ADH coating on titanium surfaces by combining calcium peroxide (CaO2) nanoparticles, zeolite imidazolate framework-67 (ZIF-67), and the chemical coupling hyaluronic acid-adipic acid dihydrazide (HA-ADH). We characterized CaO2@ZIF-67-HA-ADH with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results demonstrated that CaO2@ZIF-67-HA-ADH was pH-sensitive and decomposed rapidly under acidic conditions, and it released inclusions slowly under neutral conditions. Antibacterial experiments showed that the CaO2@ZIF-67-HA-ADH coating had excellent antibacterial properties and effectively killed methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO-1). Cell experiments revealed that the CaO2@ZIF-67-HA-ADH coating promoted pro-osteoblast adhesion, proliferation, and differentiation and also promoted the migration and angiogenesis of human umbilical vein endothelial cells (HUVECs), exhibiting excellent osteogenic and angiogenic properties. In in vivo animal implantation experiments, the CaO2@ZIF-67-HA-ADH coating exhibited strong antimicrobial activity early after implantation and excellent osseointegration later after implantation. In conclusion, the pH-responsive CaO2@ZIF-67-HA-ADH coating conferred excellent antibacterial, osteogenic, and angiogenic properties to titanium implants, which effectively enhanced osseointegration of the implants and prevented bacterial infection; the coating shows promise for use in the treatment of bone defects.

Colloidal metal nanocatalysts to advance orange II hydrogenolysis tracked by a microplate reader

The thermal reduction method was applied to synthesize metal nanoparticles using poly(1-vinyl-2-pyrrolidone) as an organic stabilizer to control metal nanoparticle agglomeration. Colloidal metal nanoparticles, gold, palladium, and gold–palladium nanoparticles were synthesized, and UV–visible spectrophotometry and high-resolution transmission electron microscopy analyses were conducted to characterize them. The metal nanoparticle micrographs showed well-dispersed particles with an average size of 9.6 nm (Au), 15.4 nm (Pd), and 10.6 nm (AuPd). All the colloidal metal nanoparticles served as nanocatalysts to advance a reductive degradation of orange II in presence of borohydride ions. For a prompt screening of catalytic activity, the microplate reader system was considered at a fixed maximum absorbance wavelength of λ 489 nm respected by orange II. Excess borohydride ions were used to construct pseudo-first kinetic conditions. The Langmuir–Hinshelwood model allowed the finding of kinetic activity on the surface of metal nanoparticles. AuPd nanocatalyst interface exhibited low activation energy (5.38 kJ mol−1) compared to the one on Au (8.19 kJ mol−1) and Pd (7.23 kJ mol−1).

Graphical Abstract

Minute Cu2+ coupling with HCO3- for efficient degradation of acetaminophen via H2O2 activation

Homogeneous Cu²⁺-mediated activation of H₂O₂ has been widely applied for the removal of organic contaminants, but fairly high dosage of Cu²⁺ is generally required and may cause secondary pollution. In the present study, minute Cu²⁺ (2.5 μM) catalyzed H₂O₂ exhibited excellent efficiency in degradation of organic pollutants with the assistant of naturally occurring level HCO₃^- (1 mM). In a typical case, acetaminophen (ACE) was completely eliminated within 10 min which followed the pseudo-first-order kinetics. Singlet oxygen and superoxide radical rather than traditionally identified hydroxyl radical were the predominant reactive oxygen species (ROS) responsible for ACE degradation. Meanwhile, Cu³⁺ was deduced through Cu⁺ and p-hydroxybenzoic acid formation analysis. CuCO₃(aq) was the main complex with high reactivity for the activation of H₂O₂ to form ROS and Cu³⁺. The removal efficiency of ACE depended on the operating parameters, such as Cu²⁺, HCO₃^- and H₂O₂ dosage, solution initial pH. The presence of Cl^-, HPO₄^2-, humic acid were found to retard ACE removal while other anions such as SO₄^2- and NO₃^- had no obvious effect. ACE exhibited lower degradation efficiency in real water matrices than that in ultra-pure water. Nevertheless, 58-100% of ACE was removed from domestic wastewater, lake water and tap water within 60 min. Moreover, eight intermediate products were identified and the possible degradation pathways of ACE were proposed. Additionally, other typical organic pollutants including bisphenol A, norfloxacin, lomefloxacin hydrochloride and sulfadiazine, exhibited great removal efficiency in the Cu²⁺/H₂O₂/HCO₃^- system.

Application of percarbonate and peroxymonocarbonate in decontamination technologies

Sodium percarbonate (SPC) and peroxymonocarbonate (PMC) have been widely used in modified Fenton reactions because of their multiple superior features, such as a wide pH range and environmental friendliness. This broad review is intended to provide the fundamental information, status and progress of SPC and PMC based decontamination technologies according to the peer-reviewed papers in the last two decades. Both SPC and PMC can directly decompose various pollutants. The degradation efficiency will be enhanced and the target contaminants will be expanded after the activation of SPC and PMC. The most commonly used catalysts for SPC activation are iron compounds while cobalt compositions are applied to activate PMC in homogenous and heterogeneous catalytical systems. The generation and participation of hydroxyl, superoxide and/or carbonate radicals are involved in the activated SPC and PMC system. The reductive radicals, such as carbon dioxide and hydroxyethyl radicals, can be generated when formic acid or methanol is added in the Fe(II)/SPC system, which can reduce target contaminants. SPC can also be activated by energy, tetraacetylethylenediamine, ozone and buffered alkaline to generate different reactive radicals for pollutant decomposition. The SPC and activated SPC have been assessed for application in-situ chemical oxidation and sludge dewatering treatment. The challenges and prospects of SPC and PMC based decontamination technologies are also addressed in the last section.

Oxygen doped graphitic carbon nitride nanosheets for the degradation of organic pollutants by activating hydrogen peroxide in the presence of bicarbonate in the dark

The development of novel wastewater treatment processes that use heterogeneous catalysts to activate hydrogen peroxide (H2O2) with bicarbonate (HCO3 -) has been a subject of great interest in recent years; however, significant challenges remain, despite research into numerous metal-based catalysts. The work presented herein employed oxygen-doped graphitic carbon nitride (O/g-C3N4) as a non-metal catalyst for activating H2O2 in the presence of HCO3 -, and this method represented the first system capable of removing organic pollutants in the dark, to our knowledge. The catalysts were characterized using several microscopic imaging, spectroscopic, electrochemical, and crystallographic techniques, as well as N2-physorption procedures. Analysis of the results revealed that the O/g-C3N4 catalyst possessed a high specific surface area and many defect sites. Various operational parameters, including the relative amounts of HCO3 -, H2O2, and O/g-C3N4, were systemically investigated. A clear performance enhancement was observed in the degradation of organic contaminants when subjected to the HCO3 --H2O2-O/g-C3N4 system, and this result was ascribed to the synchronous adsorption and chemical oxidation processes. The novel system presented herein represented a new water treatment technology that was effective for removing organic contaminants.

Experimental data of a catalytic decolorization of Ponceau 4R dye using the cobalt (II)/NaHCO3/H2O2 system in aqueous solution

The treatment by Advanced Oxidation Processes (AOPs) of wastewater polluted with dyes is of particular interest in the field of environmental engineering, especially for the removal azo-dyes, representing over 50% of the global annual production of dyes. Unfortunately, most azo-dyes are non-biodegradable and can be toxic to aquatic organisms. This is the first data article that applies the methodology of response surface for the optimization of decolorization of an azo-compound using cobalt in a homogeneous medium as the catalyst of a bicarbonate activated hydrogen peroxide (BAP) system which, in turn, is an emerging technology for wastewater treatment. The Response Surface Methodology (RSM) based on a Central Composite Design (CCD) was used to evaluate and optimize the influence of three experimental variables (stoichiometric dosage of H₂O₂, molar ratio H₂O₂/NaHCO₃ and cobalt concentration) on the decolorization of Ponceau 4R. Reactions were performed at 25 °C, pH 8.3 with a reaction time of 2 h. Analysis of variance (ANOVA) showed values of R² and adjusted-R² of 0.9815 and 0.9648, and experimental data were fit to a second-order regression model. The optimal conditions to achieve a maximum decolorization (96.31%) of a Ponceau 4R aqueous solution of 20 mg/l were: 4.73 times stoichiometric dosage of H₂O₂, molar ratio H₂O₂/NaHCO₃ of 1.70 and cobalt concentration of 11.16 µM. Under the optimal reaction conditions, the influence of temperature (20, 25, 30 and 35 °C) on decolorization was evaluated and data were adjusted to second order kinetics. To verify the efficiency of the BAP system on the decolorization of Ponceau 4R, under the optimal conditions of reaction, UV–Vis spectra, at different reaction times, were measured. Additionally, blank experiments in order to evaluate the effect of individual factors in the Ponceau 4R decolorization, using BAP system, were carried out. Data showed that the Co(II)-NaHCO₃-H₂O₂ system is a suitable technology for the decolorization of azo-dyes aqueous solutions.

Self-Supply of O2 and H2O2 by a Nanocatalytic Medicine to Enhance Combined Chemo/Chemodynamic Therapy

Combined chemo/chemodynamic therapy is a promising strategy to achieve an improved anticancer effect. However, the hypoxic microenvironment and limited amount of H2O2 in most solid tumors severely restrict the efficacy of this treatment. Herein, the construction of a nanocatalytic medicine, CaO2@DOX@ZIF-67, via a bottom-up approach is described. CaO2@DOX@ZIF-67 simultaneously supplies O2 and H2O2 to achieve improved chemo/chemodynamic therapy. In the weakly acidic environment within tumors, CaO2@DOX@ZIF-67 is broken down to rapidly release the Fenton-like catalyst Co2+ and the chemotherapy drug doxorubicin (DOX). The unprotected CaO2 reacts with H2O to generate both O2 and H2O2. The generated O2 relieves the hypoxia in the tumor and further improve the efficacy of DOX. Meanwhile, the generated H2O2 reacts with Co2+ ions to produce highly toxic •OH through a Fenton-like reaction, resulting in improved chemodynamic therapy.

Multi-wavelength spectrophotometric determination of hydrogen peroxide in water by oxidative coloration of ABTS via Fenton reaction

In this study, a sensitive and low-cost multi-wavelength spectrophotometric method for the determination of hydrogen peroxide (H₂O₂) in water was established. The method was based on the oxidative coloration of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) via Fenton reaction, which resulted in the formation of green radical (ABTS^•+) with absorbance at four different wavelengths (i.e., 415 nm, 650 nm, 732 nm, and 820 nm). Under the optimized conditions (C_ABTS = 2.0 mM, C_Fe²⁺ = 1.0 mM, pH = 2.60 ± 0.02, and reaction time (t) = 1 min), the absorbance of the generated ABTS^•+ at 415 nm, 650 nm, 732 nm, and 820 nm were well linear with H₂O₂ concentrations in the range of 0-40 μM (R² > 0.999) and the sensitivities of the proposed Fenton-ABTS method were calculated as 4.19 × 10⁴ M^-1 cm^-1,1.73 × 10⁴ M^-1 cm^-1, 2.18 × 10⁴ M^-1 cm^-1, and 1.96 × 10⁴ M^-1 cm^-1, respectively. Meanwhile, the detection limits of the Fenton-ABTS method at 415 nm, 650 nm, 732 nm, and 820 nm were respectively calculated to be 0.18 μM, 0.12 μM, 0.10 μM, and 0.11 μM. The absorbance of the generated ABTS^•+ in ultrapure water, underground water, and reservoir water was quite stable within 30 min. Moreover, the proposed Fenton-ABTS method could be used for monitoring the variations of H₂O₂ concentration during the oxidative decolorization of RhB in alkali-activated H₂O₂ system.

Effective degradation of Orange G and Rhodamine B by alkali-activated hydrogen peroxide: roles of HO2- and O2·

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. The process of alkali-activated hydrogen peroxide (H₂O₂) was superior for the treatment of alkaline dye wastewater because no additional reagents were required except H₂O₂. However, an important and interesting phenomenon had been observed that the primary reactive species were found different for degrading organic pollutants with the process of alkali-activated H₂O₂. Azo dye of Orange G (OG) and triphenylmethane dye of Rhodamine B (RhB) were chosen as the target organic pollutants. The influences of various parameters on OG and RhB degradation by alkali-activated H₂O₂ were evaluated. Furthermore, different scavengers, including ascorbic acid, methanol, t-butanol, isopropyl alcohol, furfuryl alcohol, and nitro blue tetrazolium, have been tested to identify the active species involved in dye degradation, and it was found that O₂^·- was mainly responsible for degrading OG, while HO₂^- anion was the primary oxidant for degrading RhB.

Carbonate-activated hydrogen peroxide oxidation process for azo dye decolorization: Process, kinetics, and mechanisms

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. This study is the first time to investigate the potential of carbonate-activated hydrogen peroxide (CAP) oxidation process for the removal of organic pollutant from highly alkaline wastewaters. Azo dye acid orange 7 (AO7) was selected as a model pollutant. The influences of various parameters on AO7 decolorization by the CAP oxidation were evaluated. Furthermore, the active species involved in AO7 degradation were explored using scavenger experiments and electron spin resonance analysis. Additionally, AO7 degradation products by the CAP oxidation were identified to elucidate possible transformation pathways. Results showed that the CAP oxidation had better AO7 decolorization performance compared to bicarbonate-activated hydrogen peroxide method. The AO7 decolorization efficiency augmented from 3.70 ± 0.76% to 54.27 ± 2.65% when carbonate concentration was increased from 0 to 50 mM at pH 13.0, and then changed slightly with further increasing carbonate concentration to 70 mM. It increased almost linearly from 5.95 ± 0.32% to 94.03 ± 0.39% as H₂O₂ concentration was increased from 5 to 50 mM. Moreover, trace amount of Co(II) could facilitate AO7 decolorization by the CAP reaction. Superoxide and carbonate radicals might be the main reactive oxygen species involved in the CAP process. Finally, a possible degradation pathway of AO7 by the CAP oxidation was proposed based on the identified products.

Carbonate and carbonate anion radicals in aqueous solutions exist as CO3(H2O)62− and CO3(H2O)6˙− respectively: the crucial role of the inner hydration sphere of anions in explaining their properties

An effort to reproduce the physical properties of CO₃²⁻ and CO₃˙⁻ in water proves that one has to include an inner hydration sphere of six water molecules for both anions.

Dioxygen-mediated oxidation of hydroquinone with cobalt ions in a bicarbonate aqueous solution for the production of active radicals

Cobalt(ii) ions exhibit high efficiency for hydroquinone oxidation in HCO₃⁻ solution with O₂ to produce hydroxyl radicals.

Catalytic degradation of Acid Orange 7 with hydrogen peroxide using CoxOy-N/GAC catalysts in a bicarbonate aqueous solution

The cobalt-based catalysts CoxOy-N/GAC were prepared by pyrolysis of a cobalt–phenanthroline complex on granular active carbon in nitrogen atmosphere, and tested for the degradation of Acid Orange 7 with H₂O₂ in a bicarbonate aqueous solution.

Co2+-loaded periodic mesoporous aluminum phosphonates for efficient modified Fenton catalysis

Periodic mesoporous aluminum phosphonates exhibit high uptake capability for Co²⁺ and thus oxidizing ability in organic contaminant decomposition.

Hollow cobalt phosphonate spherical hybrid as high-efficiency Fenton catalyst

Organic-inorganic hybrid of cobalt phosphonate hollow nanostructured spheres were prepared in a water-ethanol system through a mild hydrothermal process in the absence of any templates using diethylenetriamine penta(methylene phosphonic acid) as bridging molecule. SEM, TEM and N2 sorption characterization confirmed a hollow spherical micromorphology with well-defined porosity. The structure and chemical states of the hybrid materials were investigated by FT-IR, XPS and thermogravimetric analysis, revealing the homogeneous integrity of inorganic and organic units inside the network. As a heterogeneous catalyst, hollow cobalt phosphonate material exhibited considerable catalytic oxidizing decomposition of methylene blue with sulfate radicals as compared to cobalt phosphonate nanoparticles synthesized in single water system, which could be attributed to enhanced mass transfer and high surface area for the hollow material. Some operational parameters, including pH and reaction temperature, were found to influence the oxidation process. The present results suggest that cobalt phosphonate material can perform as an efficient heterogeneous catalyst for the degradation of organic contaminants, providing insights into the rational design and development of alternative catalysts for wastewater treatment.

Facile synthesis of magnetic ZnFe2O4-reduced graphene oxide hybrid and its photo-Fenton-like behavior under visible iradiation

A magnetic ZnFe2O4-reduced graphene oxide (rGO) hybrid was successfully developed as a heterogeneous catalyst for photo-Fenton-like decolorization of various dyes using peroxymonosulfate (PMS) as an oxidant under visible light irradiation. Through an in situ chemical deposition and reduction, ZnFe2O4 nanoparticles (NPs) with an average size of 23.7 nm were anchored uniformly on rGO sheets to form a ZnFe2O4-rGO hybrid. The catalytic activities in oxidative decomposition of organic dyes were evaluated. The reaction kinetics, effect of ion species and strength, catalytic stability, degradation mechanism, as well as the roles of ZnFe2O4 and graphene were also studied. ZnFe2O4-rGO showed to be a promising photocatalyst with magnetism for the oxidative degradation of aqueous organic pollutants and simple separation. The combination of ZnFe2O4 NPs with graphene sheets leads to a much higher catalytic activity than pure ZnFe2O4. Graphene acted as not only a support and stabilizer for ZnFe2O4 to prevent them from aggregation, largely improving the charge separation in the hybrid material, but also a catalyst for activating PMS to produce sulfate radicals at the same time. The ZnFe2O4-rGO hybrid exhibited stable performance without losing activity after five successive runs.

The role of carbonate as a catalyst of Fenton-like reactions in AOP processes: CO3˙− as the active intermediate

The reaction Co(H₂O)₆²⁺ + H₂O₂ proceeds via a transient that decomposes into Co^II(H₂O)(OOH)(OH)₂ + CO₃˙⁻. Plausible biological implications are pointed out.