Highly Efficient Biodecolorization/Degradation of Congo Red and Alizarin Yellow R by Chloroperoxidase from Caldariomyces fumago: Catalytic Mechanism and Degradation Pathway

Enhanced photocatalytic degradation of organic pollutants by green-synthesized gold nanoparticles using polysaccharide for environmental remediation

The recent rise in textile dye wastewater discharge into the environment has detrimental effects on living organisms and human health. The present study reports a facile approach to green-synthesized AuNPs employing sesbania gum for catalytic and photocatalytic degradation of organic pollutants. The obtained AuNPs were characterized by various techniques such as UV-vis, FT-IR, SEM, TEM, AFM, zeta potential, LC-MS, and XPS. The XRD patterns revealed a highly crystalline and face-centered cubic structure. XPS and EDX analysis defined the chemical composition and product purity of SBG-AuNPs. Photocatalytic degradation of hazardous dyes congo red and safranin-O using SBG-AuNPs showed a rapid decomposition rate with 94.69 % under visible light irradiation. The effect of pH, dye concentration, and catalyst dose on photodegradation and recyclability was also studied. The kinetic plots were used to calculate the rate constant, showing a pseudo-first-order reaction. Scavenger trap experiments confirmed the role of h+ and superoxide(.O2-) as active species, and LCMS analysis was used to identify the degradation intermediates. The catalytic reduction of SBG-AuNPs was studied for brilliant green (BG) and methylene blue (MB) in the presence of NaBH4, resulting the degradation efficiency of 90.37 % and 84.52 %, respectively. This study presents an innovative approach for designing highly efficient photocatalysts for environmental remediation and wastewater treatment from textile dyes.

Electrochemical oxidation of azo dyes degradation by RuO2-IrO2-TiO2 electrode with biodegradation Aeromonas hydrophila AR1 and its degradation pathway: An integrated approach

Azo dyes are the most varied class of synthetic chemicals with non-degradable characteristics. They are complex compounds made up of many different parts. It was primarily utilized for various application procedures in the dyeing industry. Therefore, it's crucial to develop an economical and environmentally friendly approach to treating azo dyes. Our present investigation is an integrated approach to the electrooxidation (EO) process of azo dyes using RuO2-IrO2-TiO2 (anode) and titanium mesh (cathode) electrodes, followed by the biodegradation process (BD) of the treated EO dyes. Chemical oxygen demand (COD) removal efficiency as follows MB (55%) ≥ MR (45%) ≥ TB (38%) ≥ CR (37%) correspondingly. The fragment generated during the degradation process which was identified with high-resolution mass spectrometry (HRMS) and its degradation mechanism pathway was proposed as demethylation reaction and N-N and C-N/C-S cleavage reaction occurs during EO. In biodegradation studies by Aeromonas hydrophila AR1, the EO treated dyes were completely mineralized aerobically which was evident by the COD removal efficiency as MB (98%) ≥ MR (92.9%) ≥ TB (88%) ≥ CR (87%) respectively. The EO process of dyes produced intermediate components with lower molecular weights, which was effectively utilized by the Aeromonas hydrophila AR1 and resulted in higher degradation efficiency 98%. We reported the significance of the enhanced approach of electrochemical oxidation with biodegradation studies in the effective removal of the pollutants in dye industrial effluent contaminated water environment.

Efficient degradation of Congo red by persulfate activated with different particle sizes of zero-valent copper: performance and mechanism

In this study, Congo red (CR) was degraded by different particle sizes of zero-valent copper (ZVC) activated persulfate (PS) under mild temperature. The CR removal by 50 nm, 500 nm, 15 μm of ZVC activated PS was 97%, 72%, and 16%, respectively. The co-existence of SO₄^2- and Cl^- promoted the degradation of CR, and HCO₃^- and H₂PO₄^- were detrimental to the degradation. With the reduction of ZVC particle size, the effect of coexisting anions on degradation grew stronger. The high degradation efficiency of 50 nm and 500 nm ZVC was achieved at pH=7.0, while the high degradation of 15 μm ZVC was achieved at pH=3.0. It was more favorable to leach copper ions for activating PS to generate reactive oxygen species (ROS) with the smaller particle size of ZVC. The radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that SO₄^-•, •OH and •O₂^- existed in the reaction. The mineralization of CR reached 80% and three possible paths were suggested for the degradation. Moreover, the degradation of 50 nm ZVC can still reach 96% in the 5th cycle, indicating promising application potential in dyeing wastewater treatment.

Efficient Degradation of Congo Red in Water by UV-Vis Driven CoMoO4/PDS Photo-Fenton System

In order to improve the catalytic activity of cobalt molybdate (CoMoO₄), a PDS-activated and UV-vis assisted system was constructed. CoMoO₄ was prepared by coprecipitation and calcination, and characterized by XRD, FTIR, Raman, SEM, TEM, XPS, TGA Zeta potential, BET, and UV-Vis DRS. The results showed that the morphology of the CoMoO₄ nanolumps consisted of stacked nanosheets. XRD indicated the monoclinic structures with C2/m (C³_2h, #12) space group, which belong to α-CoMoO₄, and both Co²⁺ and Mo⁶⁺ ions occupy distorted octahedral sites. The pH of the isoelectric point (pHIEP) of CMO-8 at pH = 4.88 and the band gap of CoMoO₄ was 1.92 eV. The catalytic activity of CoMoO₄ was evaluated by photo-Fenton degradation of Congo red (CR). The catalytic performance was affected by calcination temperature, catalyst dosage, PDS dosage, and pH. Under the best conditions (0.8 g/L CMO-8, PDS 1 mL), the degradation efficiency of CR was 96.972%. The excellent catalytic activity of CoMoO₄ was attributed to the synergistic effect of photo catalysis and CoMoO₄-activated PDS degradation. The capture experiments and the ESR showed that superoxide radical (·O₂^-), singlet oxygen (¹O₂), hole (h⁺), sulfate (SO₄^-·), and hydroxyl (·OH^-) were the main free radicals leading to the degradation of CR. The results can provide valuable information and support for the design and application of high-efficiency transition metal oxide catalysts.

Gentle one-step co-precipitation to synthesize bimetallic CoCu-MOF immobilized laccase for boosting enzyme stability and Congo red removal

Laccase has received extensive attention in pollutant degradation due to its high efficiency and environmental friendliness, but free laccase has poor stability, easy inactivation, and difficulty in recycling, which limited its application. It was a smart strategy to construct a synergistic system for the efficient adsorption and degradation of pollutants by enzyme immobilization to improve the stability and recyclability of the enzyme. In this study, the materials were synthesized by a one-step co-precipitation method. With Cu-MOF as the main body, Co²⁺ was introduced to construct bimetallic CoCu-MOF as the protective carrier of the enzyme. The enzyme-carrying capacity and enzyme activity of Lac@CoCu-MOF were 2-fold and 3.5-fold higher than those of Lac@Cu-MOF, respectively. Lac@MOF composites had a good protective effect on enzyme in various interfering environments. At pH = 7, free laccase was completely inactivated and Lac@CoCu-MOF maintained 51.76% enzyme activity. In addition, the removal rate of Congo red by Lac@CoCu-MOF reached 90 % in 1 h at pH = 4 % and 95 % in 5 h at pH = 7, and the final TOC mineralization rate reached 86.05 %. After six cycles, the degradation rate of Lac@CoCu-MOF remained above 75 %. Therefore, Lac@CoCu-MOF was constructed with the advantages of enzyme immobilization (enhanced stability and easy operation), material adsorption, and biocatalysis (fast diffusion and high activity), which has great guiding significance for the industrial application of enzyme.

LaCoxFe1-XO3 (0≤x≤1) spherical nanostructures prepared via ultrasonic approach as photocatalysts

To harvest the photon energy, a sequenceof perovskite-type oxides of LaCoxFe1-xO3 (0 ≤x≤1) nanostructures with distinct 'Cobalt' doping at the position of B-site are successfully prepared via a simple ultrasonic approach as photocatalyst. The crystallinity, phase identification, microstructure, and morphology of perovskite nanocomposites were analyzed to better understand their physicochemical properties. The catalytic efficiency was assessedusing Congo Red (CR) dye by visible light irradiation for 30 min. Applying terephthalic acid as a probe molecule, the formation of hydroxyl radicals during the processes was investigated. The photocatalytic efficacy was measured by varying different Co/Fe stoichiometric molar ratios and noticed the order of sequence is 0.2 > 0.6 > 0.4 > 0.8 > 0.5 > 0 > 1 after 30 min of reaction time. Finally using LaCo0.2Fe0.8O3 nanostructures, cycling studies (n = 3) were performed to determine its photostability and reusability. The photocatalytic methodology proposed in this study was discussed extensively.

A novel electrocatalytic filtration system with carbon nanotube supported nanoscale zerovalent copper toward ultrafast oxidation of organic pollutants

In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0-7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu²⁺/Cu⁺ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and ¹O₂via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu²⁺-O-O-SO₃^-), and then ¹O₂ will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.

Microwave photo-oxidation with diverse oxidants for Congo red degradation: effect of oxidants, degradation pathway and economic analysis

The present study investigated the efficacy of microwave photo-oxidation (MWPO) process with two oxidants i.e. persulphate (PS) and hydrogen peroxide (H₂O₂) for degradation of Congo red (CR). The result indicated a CR degradation efficiency of 98% and 96.8% with PS and H₂O₂, respectively, in 30 min of reaction with corresponding PS dosage of 50 mg/L and H₂O₂ dosage of 180 mg/L. The COD removal efficiency with the two oxidants were 97.7% and 94.9%, respectively. Higher dosages of oxidant and CR reduced the efficiency of the process in both the cases due to self-quenching. Effect of pH and initial CR concentration on CR removal efficiency also has been studied. Degradation of CR followed pseudo-first-order kinetics with a removal rate constant of 0.12/min and 0.09/min, respectively, with PS and H₂O₂. The main mechanism of CR degradation was cleavage of the benzene-benzene bond, cleavage of benzene-N bond and hydroxylation. Economic analysis of the MWPO process indicated an energy consumption of 18.3 kWh/g of CR removal and 18.4 kWh/g of COD removal. The process was effective in the rapid degradation and mineralization of high concentration of CR within 30 min.

Photoelectrocatalytic Degradation of Congo Red Dye with Activated Hydrotalcites and Copper Anode

Photoelectrocatalysis is a novel technique that combines heterogeneous photocatalysis with the application of an electric field to the system through electrodes for the degradation of organic contaminants in aqueous systems, mainly of toxic dyes. The efficiency of these combined processes depends on the semiconductor properties of the catalysts, as well as on the anodic capacity of the electrode. In this study, we propose the use of active hydrotalcites in the degradation of Congo red dye through processes assisted by ultraviolet (UV) irradiation and electric current. Our research focused on evaluating the degradation capacity of Congo red by means of photolysis, catalysis, photocatalysis, electrocatalysis, and photoelectrocatalysis, as well as identifying the effect of the properties of the active hydrotalcites in these processes. The results show that a maximum degradation was reached with the photoelectrocatalysis process with active hydrotalcites and a copper anode at 6 h with 95% in a half-life of 0.36 h. The degradation is favored by the attack of the OH• radicals under double bonds in the diazo groups where the electrode produces Cu2+ ions, and with the photogenerated electrons, the recombination speed of the electron–hole in the hydrotalcite catalyst is reduced until the complete degradation.

Synthesis of molecularly imprinted polymer for removal of Congo red

Congo red (CR) is an anionic azo dye widely used in many industries including pharmaceutical, textile, food and paint industries. The disposal of huge amount of CR into the various streams of water has posed a great threat to both human and aquatic life. Therefore, it has become an important aspect of industries to remove CR from different water sources. Molecular imprinting technology is a very slective method to remove various target pollutant from environment. In this study a precipitation polymerization was employed for the effective and selective removal of CR from contaminated aqueous media. A series of congo red molecularly imprinted polymers (CR-MIPs) of uniform size and shape was developed by changing the mole ratio of the components. The optimum ratio (0.1:4: 20, template, functional monomer and cross-linking monomer respectively) for CR1-MIP from synthesized polymers was able to rebind about 99.63% of CR at the optimum conditions of adsorption parameters (contact time 210 min, polymer dosage 0.5 g, concentration 20 ppm and pH 7). The synthesized polymers were characterized by various techniques such as Fourier Infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), Thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), and Brumauer-Emmett-Teller (BET). The polymer particles have successfully removed CR from different aqueous media with an efficiency of about ~ 90%.

Ti/PbO2-Sm2O3 composite based electrode for highly efficient electrocatalytic degradation of alizarin yellow R

In this work, a novel Ti/PbO₂-Sm₂O₃ composite electrode with high electrocatalytic activity is successfully fabricated via simple electrodeposition method and further investigated for electrochemical degradation of alizarin yellow R (AYR) wastewater. The test results of X-ray diffraction, field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy confirm that Sm₂O₃ is successfully composited with PbO₂. The coating of Ti/PbO₂-Sm₂O₃ composite electrode stacked by typical pyramid-like micro-particles exhibits smooth and compact surface morphology which is conducive to enhancing the corrosion resistance of electrode. Furthermore, electrochemical performance tests indicate that Ti/PbO₂-Sm₂O₃ composite electrode has advantages of higher oxygen evolution potential, lower charge transfer resistance and longer lifetime over Ti/PbO₂ electrode. Electrolyte concentration, plate space, initial pH and cell voltage are assessed to optimize the degradation condition of AYR. The results show that COD removal efficiency and degradation efficiency of AYR on Ti/PbO₂-Sm₂O₃ composite electrode reach up to 79.90% and 80.00% under the optimal conditions (Na₂SO₄ electrolyte concentration 9.0 g L^-1, plate space 3.0 cm, initial pH 5, cell voltage 3.0 V and electrolysis time 150 min), respectively. The degradation of AYR follows pseudo-first-order reaction kinetics, and a plausible mineralization pathway of AYR is proposed on the basis of the identification of major intermediate products. These results suggest that Ti/PbO₂-Sm₂O₃ composite electrode is a promising candidate for electrocatalytic degradation of AYR wastewater.

Improved Biodegradation of Synthetic Azo Dye by Anionic Cross-Linking of Chloroperoxidase on ZnO/SiO2 Nanocomposite Support

A novel ZnO nanowire/macroporous SiO₂ composite was used as a support to immobilize chloroperoxidase (CPO) by in situ cross-linking method. An anionic bi-epoxy compound was synthesized and used as a long-chained anionic cross-linker, and it was adsorbed on the surface of ZnO nanowires through static interaction before reaction with CPO, creating a new approach to change the structure, property, and catalytic performance of the produced cross-linking enzyme aggregates (CLEAs) of CPO. The immobilized CPO showed high activity in the decolorization of three azo dyes. The effect of various conditions such as the loading amount of CPO, solution pH, temperature, and dye concentration was optimized on the decolorization. Under optimized conditions, the decolorization percentage of Acid Blue 113, Direct Black 38, and Acid Black 10 BX reached as high as 95.4, 92.3, and 89.1%, respectively. The immobilized CPO exhibited much better thermostability and resistance to pH inactivation than free CPO. The storage stability and reusability were greatly improved through the immobilization. It was found from the decolorization of Acid Blue 113 that 83.6% of initial activity retained after incubation at 4 °C for 60 days and that 80.9% of decolorization efficiency retained after 12 cycles of reuses.

Efficient solar light-driven degradation of Congo red with novel Cu-loaded Fe3O4@TiO2 nanoparticles

In this work, Cu-loaded Fe₃O₄@TiO₂ core shell nanoparticles were prepared in a single pot by coating of TiO₂ on Fe₃O₄ nanoparticles followed by Cu loading. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), thermogravimetric analysis (TGA), Brunauer-Emmett- Teller (BET), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), and valence band X-ray photoelectron spectroscopy (VB XPS) techniques were used for characterization of as prepared nanoparticles. Synergism between copper and titania was evaluated by studying the solar light-driven photodegradation of Congo red dye solution in the presence of Fe₃O₄@TiO₂ nanoparticles on one side and Cu-loaded Fe₃O₄@TiO₂ nanoparticles on the other side. The latter performed better than the former catalyst, indicating the enhanced activity of copper-loaded catalyst. Further photodegradation was studied by three means, i.e., under ultraviolet (UV), refluxing, and solar radiations. Cu-loaded Fe₃O₄@TiO₂ enhanced the degradation efficiency of Congo red dye. Thus, Cu act possibly by reducing the band gap of TiO₂ and widening the optical response of semiconductor, as a result of which solar light could be used to carry out photocatalysis. Graphical abstract Photodegradation of congo red over Cu-loaded Fe₃O₄@TiO₂ nanoparticles.

Rapid degradation of Congo red by molecularly imprinted polypyrrole-coated magnetic TiO2 nanoparticles in dark at ambient conditions

A novel molecularly imprinted polymer (MIP)-coated magnetic TiO2 nanocomposite was prepared, using methyl orange (MO) as the dummy template and pyrrole as functional monomer, for degradation of Congo red (CR). The nanocomposite was characterized by Fourier transform infrared spectroscopy, thermo-gravimetric analysis, X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The imprinting efficiency of the imprinted nanoparticles was investigated by static binding test, and their degradation ability toward CR was also studied. Moreover, the effects of pH, temperature, dissolved oxygen and oscillation rate on degradation rate of CR were investigated. Results showed that the imprinted nanocomposite had higher adsorption ability for MO compared with the non-imprinted one. Moreover, it could degrade CR rapidly in dark at room temperature and atmospheric pressure and could be recycled easily by a magnet with a good reusability. A degradation mechanism was proposed according to LC-MS analysis of degradation products of CR. The new imprinted nanoparticles showed high catalytic activity at ambient conditions without light illumination and additional chemicals, and therefore, it can be potentially applied to the rapid, "green" and low-cost degradation of CR in industrial printing and dyeing wastewater.

Detoxification and color removal of Congo red by a novel Dietzia sp. (DTS26) - a microcosm approach

The present study deals with the decolorization and detoxification of Congo red (CR) by a novel marine bacterium Dietzia sp. (DTS26) isolated from Divar Island, Goa, India. The maximum decolorization of 94.5% (100 mg L(-1)) was observed under static condition within 30 h at pH 8 and temperature 32±2°C. Bacterially treated samples could enhance the light intensity by 38% and the primary production levels 5 times higher than the untreated. The strain was also able to reduce COD by 86.4% within 30 h at 100 mg L(-1) of CR dye. The degraded metabolites of CR dye were analyzed by FTIR, HPLC, GC-MS and the end product closely matches with 4-amino-3-naphthol-1-sulfonate which is comparatively less toxic than CR. Bioassay experiments conducted in treated samples for Artemia franciscana showed better survival rates (after 72 h) at higher concentration of CR (500 mg L(-1)). This work suggests the potential application of DTS26 in bioremediation of dye wastes and its safe disposal into coastal environment.

Evaluation of cobalt oxide, copper oxide and their solid solutions as heterogeneous catalysts for Fenton-degradation of dye pollutants

Co_0.5Cu_0.5O nanoparticles were synthesized via the calcination of corresponding oxalates and showed outstanding catalytic performance for the Fenton-degradation of Congo red.