Enhanced Photocatalytic Degradation of Synthetic Dyes and Industrial Dye Wastewater by Hydrothermally Synthesized G–CuO–Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Hybrid Nanocomposites Under Visible Light Irradiation

To enhance the degradation of colour and chemical oxygen demand using photocatalytic activity, Graphene–CuO–Co₃O₄ hybrid nanocomposites were synthesized using an in situ surfactant free facile hydrothermal method. The photocatalytic degradation of synthetic anionic dyes, methyl orange (MO) and Congo red (CR), and industrial textile wastewater dyes under visible light irradiation was evaluated. The synthesized nanocomposite was characterized structurally and morphologically using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscope, and Fourier transform infrared spectroscopy. Evaluation of the colour indicated complete removal at 15 min of irradiation for the MO and CR dyes, with 99% degradation efficiency. The reaction time for the primary effluent wastewater dye was 60 min for 81% dye removal. In contrast, a longer reaction time was required to meet the national discharge regulation for the raw wastewater dye, 300 min for 60% dye removal. The mechanism for dye degradation using the Graphene–CuO–Co₃O₄ hybrid nanocomposite was elucidated using the Langmuir–Hinshelwood model, and the rate constant and half-life of the degradation process were calculated. The results demonstrate that photocatalytic degradation using a hybrid nanocomposite and visible light irradiation is a sustainable alternative technology for removing colour from wastewater dye.     

Straightforward Synthesis of Mn3O4/ZnO/Eu2O3-Based Ternary Heterostructure Nano-Photocatalyst and Its Application for the Photodegradation of Methyl Orange and Methylene Blue Dyes

Zinc oxide-ternary heterostructure Mn₃O₄/ZnO/Eu₂O₃ nanocomposites were successfully prepared via waste curd as fuel by a facile one-pot combustion procedure. The fabricated heterostructures were characterized utilizing XRD, UV–Visible, FT-IR, FE-SEM, HRTEM and EDX analysis. The photocatalytic degradation efficacy of the synthesized ternary nanocomposite was evaluated utilizing model organic pollutants of methylene blue (MB) and methyl orange (MO) in water as examples of cationic dyes and anionic dyes, respectively, under natural solar irradiation. The effect of various experimental factors, viz. the effect of a light source, catalyst dosage, irradiation time, pH of dye solution and dye concentration on the photodegradation activity, was systematically studied. The ternary Mn₃O₄/ZnO/Eu₂O₃ photocatalyst exhibited excellent MB and MO degradation activity of 98% and 96%, respectively, at 150 min under natural sunlight irradiation. Experiments further conclude that the fabricated nanocomposite exhibits pH-dependent photocatalytic efficacy, and for best results, concentrations of dye and catalysts have to be maintained in a specific range. The prepared photocatalysts are exemplary and could be employed for wastewater handling and several ecological applications.     

Facile synthesis of zirconia supported nanomaterials for efficient photocatalytic applications

The recent study enlightens the synthesis and characterization of zirconia (ZrO₂), Fe-doped ZrO₂ (Fe@ZrO₂), and Ni-doped ZrO₂ (Ni@ZrO₂) catalysts having new-fangled morphology with tuned band gap as photocatalysts for degradation of textile wastewater dyes methylene blue (MB), malachite green (MG), and their mixtures. SEM imaging of Fe@ZrO₂ and Ni@ZrO₂ is interestingly varied from ZrO₂ as well as doping of transition metals greatly affects the morphology of composites. The optimization study depicts that the pH, time (min) and catalyst amount (g) have a direct relation with degradation efficiency, while the dye concentration (mg/L) has an indirect relation as well. The photocatalytic studies depict that the degradation of MB and MG follows oxidation pathway via hydroxyl radicals (OH^•) and holes. Reusability of catalysts corresponds to a little decrease in degradation efficiency in the first two cycles and decreases to about ∼10% (Ni@ZrO₂) and ∼12% (Fe@ZrO₂) in next three cycles.     

Transition metal incorporated,modified bismuth oxide (Bi2O3) nano photo catalyst for deterioration of rosaniline hydrochloride dye as resource for environmental rehabilitation

The work presented here deals with the fabrication of bare Bi₂O₃ and modified Bi₂O₃ photocatalyst. The Bi₂O₃ material was modified with selected transition metals Co²⁺, Ni²⁺ with the 1% and 3% atomic weight percent insitu doping method via co-precipitation strategy. These three catalysts were successfully utilized for the waste water purification via photocatalytic degradation route. These all fabricated materials were precisely characterized by characterization techniques such as XRD, SEM, TEM, BET, IR and UV-DRS. The characterization techniques reveal the successful synthesis of material and effective modification of bismuth oxide lattice. Since, surface area for modified Bi₂O₃ was found to be enhanced in comparison to the bare Bi₂O_3, as well as declined band gap energy for modified Bi₂O₃ clearly indicates the successful doping of Co²⁺, Ni²⁺ metals. The bare Bi₂O₃ and modified Bi₂O₃ catalyst were employed for photocatalytic degradation of cationic dye R-HCl dye. The modified Bi₂O₃ found to be excellent over degradation efficiency of R-HCl with almost 97% of dye degradation in comparison to the bare Bi₂O_3. Reactive oxygen species experiment demonstrate that the addition of isopropyl alcohol (IPA), benzoquinone (BQ) and EDTA found to be successful to quench ^.OH, O₂^.- and h⁺ in photocatalysis mechanism. Additionally, the modified Bi₂O₃ was employed for phenol molecule degradation to investigate the possible excitation of this molecule under visible light irradiation.     

Construction of a novel ZnCo2O4/Bi2O3 heterojunction photocatalyst with enhanced visible light photocatalytic activity

A novel ZnCo₂O₄/Bi₂O₃ heterojunction photocatalyst was prepared via balling method. The enhanced photocatalytic activity is mainly attributed to the broad photoabsorption and low recombination rate of photogenerated electron-hole pairs, which is driven by the photogenerated potential difference formed at the ZnCo₂O₄/Bi₂O₃ heterojunction interface.     

Highly dispersed Mn2O3−Co3O4 nanostructures on carbon matrix as heterogeneous Fenton-like catalyst

This work reports the synthesis of various carbon (Vulcan XC-72 R) supported metal oxide nanostructures, such as Mn₂O₃, Co₃O₄ and Mn₂O₃−Co₃O₄ as heterogeneous Fenton-like catalysts for the degradation of organic dye pollutants, namely Rhodamine B (RB) and Congo Red (CR) in wastewater. The activity results showed that the bimetallic Mn₂O₃−Co₃O₄/C catalyst exhibits much higher activity than the monometallic Mn₂O₃/C and Co₃O₄/C catalysts for the degradation of both RB and CR pollutants, due to the synergistic properties induced by the Mn−Co and/or Mn (Co)−support interactions. The degradation efficiency of RB and CR was considerably increased with an increase of reaction temperature from 25 to 45°C. Importantly, the bimetallic Mn₂O₃−Co₃O₄/C catalyst could maintain its catalytic activity up to five successive cycles, revealing its catalytic durability for wastewater purification. The structure–activity correlations demonstrated a probable mechanism for the degradation of organic dye pollutants in wastewater, involving •OH radical as well as Mn²⁺/Mn³⁺ or Co²⁺/Co³⁺ redox couple of the Mn₂O₃−Co₃O₄/C catalyst.     

The impact of alkaline earth oxides on Bi2O3 and their catalytic activities in photodegradation of Bisphenol A

The BPA into wastewater has posed a threat to environment and human health. Hence, we aimed to eliminate BPA in a short time and with a rapid degradation rate from food wastewater. Herein, the effects of different alkaline-earth oxide doped with Bi₂O₃ nanoparticles on the photocatalytic degradation of bisphenol A were investigated. SrO-Bi₂O₃, CaO-Bi₂O₃, and MgO-Bi₂O₃ binary oxides were prepared by wet-impregnation method. The structural and optical features of catalysts were clarified BET, XRD, DRS, FT-IR, PL, and SEM techniques. The photocatalytic activities of catalysts were compared for different light sources. Considering that the characterization analysis and experimental results, the highly improved photocatalytic activity was mainly attributed to the effective structure of the SrO-Bi₂O₃ binary oxide and the strong alkali properties in the nanocomposite. Obviously, 5wt% SrO-Bi₂O₃ photocatalyst showed more excellent degradation performance and highest degradation reaction rate (0.21 mg l^–1 min^–1) within 30 min. It was observed that the photocatalytic activity improved by the additive of alkaline oxide on Bi₂O₃.     

Large-scale preparation of fernwort-like single-crystalline superstructures of CuSe as Fenton-like catalysts for dye decolorization

A simple green hydrothermal template-free method was developed to prepare single-crystalline superstructures of fern-wort-like copper selenide (CuSe) in large-scale by using polyvinylpyrrolidone (PVP) as both reductant and surfactant for the first time. Time-dependent morphologic evolution was made in order to explore the formation mechanism of the as-prepared product. The copper selenides with different morphologies, phases and structural forms could be prepared by varying the synthesis parameters, such as precursor molar ratios, precursor combinations, and the molecular weight of PVP. The fernwort-like superstructures of CuSe show excellent Fenton-like catalytic activities in degrading malachite green (MG) and rhodamine B (RhB). These catalysts play an important role in the degradation process of MG and RhB solution with the aid of H₂O₂ which can yield highly reactive hydroxyl radicals (HO·). Besides, the as-prepared CuSe catalyst is stable and reusable, thus it could be applied to the treatment of the dye contaminated waste water.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

Catalytic effect of lucunary heteropolyanion containing molybdenum and tungsten atoms on decolorization of direct blue 71

In this research,a lucunary Keggin structure,[PMo₂W₉O₃₉]^7- was selected as an efficient homogenous catalyst for degradation of an azo dye（direct blue 71） and a simple method was developed for degradation of DB71.The method is based on the oxidation of azo dye in the presence of a lucunary Keggin form of polyoxometalates,K₇[PMo₂W₉O₃₉]? 19H₂O,as a homogenous catalyst at room temperature.The reaction is monitored spectrophotometrically by measuring the absorbance of dye atλ=585 nm.Some parameters including concentration of catalyst,concentration of H₂O₂,pH and reaction time were investigated and optimized. Results show that K₇[PMo₂W₉O₃₉]? 19H₂O is more efficient in the presence of hydrogen peroxide.Degradation of dye in the presence of the catalyst and H₂O₂ could lead to the disappearance approximately 65%of dye after 60 min.But degradation for the same experiment performed in the absence of catalyst or in the absence of H₂O₂ was 22%or 5%respectively.Approximately 87% azo dyes has been eliminated after 90 min in the presence of catalyst,H₂O₂ and optimize conditions(0.6 g/L of K₇[PMo_2- W₉O₃₉H₉H₂O,0.08 mol/L hydrogen peroxide and room temperature).     

Enhanced photocatalytic degradation of azo dyes using nano Fe3O4

Nanosized magnetic Fe₃O₄ synthesized via sonochemical route was used as a photocatalyst for the degradation of azo dyes, methyl red and congo red. The novelty of the photo catalyst is its easy recovery by magnetic force and its recycling ability due to its long-term stability, in addition to its cost effectiveness, non-toxicity and non-carcinogenicity. A detailed feasibility study has been carried out on the photocatalytic degradation of the azo dyes at various pH and at various concentrations of photocatalyst, dye and H₂O₂. The presence of photocatalyst is found to significantly accelerate the degradation of azo dyes and the optimal dosage is found to be 0.075 and 0.2?g/l for methyl red and congo red, respectively. Langmuir?CHinshelwood kinetic analysis revealed pseudo-first-order kinetics for the photocatalytic degradation of the dyes and the degradation products were identified using spectral analysis. The degradation study revealed the following order of reactivity: Photo-Fe₃O₄?>?Photo-H₂O₂?>?Fe₃O₄?>?H₂O₂.     

Built-in piezoelectric field improved photocatalytic performance of nanoflower-like Bi2WO6 using low-power white LEDs

Photocatalysis technology has been proved to be a potential strategy for removal of organic dyes, however high-power light sources are generally necessary to initiate photocatalytic reaction. In this work, we employed an excellent photocatalyst of Bi₂WO₆ with visible light harvest and meanwhile an intrinsic ferroelectricity, which realized the efficient degradation of organic dye via the synergetic photopiezocatalysis. Through coupling the illumination by a low-power (9 W) LED and the ultrasonic vibration (120 W) by an ultrasonic cleaner, the nanoflower-like Bi₂WO₆ composed of ultrathin nanosheets showed a much more enhanced photopiezocatalysis performance for purification of organic dye than the individual photocatalysis and piezocatalysis. Furthermore, the high mineralization efficiency and the good durability of the Bi₂WO₆ catalyst were demonstrated. The possible mechanism of photopiezocatalysis was finally proposed, where the ultrasound-induced piezoelectric field in Bi₂WO₆ drove photo-generated electrons and holes to diffuse along opposite directions, consequently promoting the separation efficiency of charge carriers. This work indicates that the synergetic photopiezocatalysis by coupling irradiation and ultrasonic vibration is a promising strategy to purify organic pollutants in wastewater.     

一种生态友好粉煤灰基地质聚合物的合成及光催化性能

以乌洛托品为孔形成剂,制备出孔结构可调控的粉煤灰基地质聚合物;通过半导体耦合设计,合成出In_2O_3和NiO双负载粉煤灰基地质聚合物催化剂;采用XRF、TGA/DSC、FESEM、XRD、FT-IR、UV-Vis等对催化剂的组成、结构及性能进行表征,考查了该催化剂体系对模拟印染废水的光催化降解活性、降解机理及反应动力学。结果表明:孔形成剂的掺入能够显著地改善地质聚合物的孔结构,调变BET比表面积及介孔体积;双负载5%In_2O_3及1%NiO的粉煤灰基地质聚合物催化剂对碱性品绿染料的最高降解率(95.65%),归因于In_2O_3与NiO形成的p-n结半导体耦合体系以及In_2O_3与PAFAG载体之间产生强相互作用,改善了光生电子-空穴对的分离效率,从而提高了光催化染料降解活性。     

Heterogeneous Fenton-like reactions with a novel hybrid Cu–Mn–O catalyst for the degradation of benzophenone-3 in aqueous media

This study focuses on the heterogeneous Fenton-like reaction performed over a novel hybrid Cu–Mn–O catalyst for the degradation of a model compound benzophenone-3 (BP-3) in aqueous media. The hybrid Cu–Mn–O catalysts with different Cu/Mn molar ratios were synthesized using co-precipitation and hydrothermal methods, and their composition and morphology were characterized using XRD and SEM analyses. Key parameters including the Cu/Mn ratio in the synthesis, pH and titration of H₂O₂ were shown to significantly influence the degradation of BP-3. A hybrid catalyst with a chemical composition of Cu_1.4Mn_1.6O₄, Mn₃O₄, and Mn₂O₃ exhibiting a morphology of nanofibers and nanoparticles demonstrated the highest catalytic activity in the degradation of BP-3. After 240 min of degradation, 81.5% of BP-3 was removed, which could be mostly related to the presence of hydroxyl radicals (˙OH). Unlike the conventional Fenton reaction that performs well under highly acidic conditions, BP-3 can be degraded in a wider pH range (2.6–7.1) in the Fenton-like reaction presented herein. Considering the mild conditions used for this Fenton-like system, this novel hybrid catalyst remains promising for wastewater treatment.     

一种生态友好粉煤灰基地质聚合物的合成及光催化性能

以乌洛托品为孔形成剂,制备出孔结构可调控的粉煤灰基地质聚合物;通过半导体耦合设计,合成出In₂O₃和NiO双负载粉煤灰基地质聚合物催化剂;采用XRF、TGA/DSC、FESEM、XRD、FT-IR、UV-Vis等对催化剂的组成、结构及性能进行表征,考查了该催化剂体系对模拟印染废水的光催化降解活性、降解机理及反应动力学。结果表明：孔形成剂的掺入能够显著地改善地质聚合物的孔结构,调变BET比表面积及介孔体积;双负载5% In₂O₃及1% NiO的粉煤灰基地质聚合物催化剂对碱性品绿染料的最高降解率（95.65%）,归因于In₂O₃与NiO形成的p-n结半导体耦合体系以及In₂O₃与PAFAG载体之间产生强相互作用,改善了光生电子-空穴对的分离效率,从而提高了光催化染料降解活性。     

Preparation and visible light photocatalytic activity of Bi2O3/Bi2WO6 heterojunction photocatalysts

The Bi₂O₃/Bi₂WO₆ heterojunction photocatalysts were prepared by a two-step solvothermal process using Bi(NO₃)₃-ethylene glycol solution as Bi source. The catalysts were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflection spectroscopy. The heterostructure catalysts are composed of Bi₂O₃ nanoparticles as modifier and 3D Bi₂WO₆ microspheres as substrate. Bi₂O₃ nanoparticles with diameters of about 10-15 nm are tightly grown on the lateral surface of the Bi₂WO₆ microspheres. The hierarchical Bi₂O₃/Bi₂WO₆ microspheres exhibit higher photocatalytic activity than the single phase Bi₂WO₆ or Bi₂O₃ for the degradation of rhodamine B under visible light illumination (λ>420 nm). The enhancement of the photocatalytic activity of the Bi₂O₃/Bi₂WO₆ heterojunction catalysts can be ascribed to their improved light absorption property and the reduced recombination of the photoexcited electrons and holes during the photocatalytic reaction. The effect of loading amount of Bi₂O₃ on the catalytic performance of the heterojunction catalysts was also investigated and the optimal content of Bi₂O₃ is 3 wt%. The Bi₂O₃/Bi₂WO₆ heterojunction photocatalysts are essentially stable during the photocatalytic process.     

Efficient and reusable Cu (II)-metalated silica-based inorganic-organic hybrid catalyst for dye degradation

An efficient silica-based inorganic-organic hybrid was synthesized by using 3-(2-aminoethylamino)propyltrimethoxylsilane as linker and 2-Quinolinecarboxaldehyde for Schiff's base formation which was further coordinated by Cu (II) chloride. The hybrid was characterized by relevant techniques, i.e., FT-IR, DRUV-Vis, SEM, EDX, ICP-AES, TGA and EPR technique which support its formation. The synthesized hybrid material was successfully used as heterogeneous catalyst for degrading Reactive Black-5 (RB-5), a non-biodegradable diazo dye. The degradation mechanism follows advanced oxidation technique utilizing hydrogen peroxide as an environmentally amiable green oxidant; where the hybrid catalyst decomposes H₂O₂ to generate ·OH free radicals. Effects of dye concentration, H₂O₂ concentration and temperature variation on dye degradation process were studied and best reaction conditions for maximum degradation of RB-5 were also worked out. The catalyst showed 87% dye degradation in 130 ?min at best reaction conditions. Easy separation, reusability and efficient dye degradation ability of the catalyst are the motivating factors for the development of such hybrid material for solving critical environmental issues.     

Fe3O4-CuO-activated carbon composite as an efficient adsorbent for bromophenol blue dye removal from aqueous solutions

Dye wastewater from industries is posing tremendous health hazards. The lethal dyes can be eliminated using nanomaterials and scientific approach like adsorption which is facile, cheap, safe as well as ecofriendly. Fe₃O₄-CuO-AC composite was prepared by a hydrothermal method and used for the removal of dyes in wastewater. The composite material was characterized by various techniques such as XRD, SEM, EDS, TEM and FT-IR. The Fe₃O₄-CuO-AC composite was used to treat five types of dyes in water. Fe₃O₄-CuO-AC composite showed the highest adsorption capability for bromophenol blue (BPB) dye. The effects of initial concentration, pH, the amount of adsorbent and temperature were also studied. The optimum conditions were found to be 20 ppm dye concentration, pH 9, an adsorbent dose of 0.06 gL^─1 at 65 °C. A removal efficiency of 97% was obtained for BPB dye during 120 min of adsorption. Kinetic studies indicated that a pseudo-second order is the most suitable model for the adsorption process. The Fe₃O₄-CuO-AC composite showed better adsorption capacity as compare to Fe₃O₄-AC except for the Methyl green dye. The maximum adsorption capacity was found to be 88.60 mg/g for BPB. Additionally, the thermodynamic parameters (ΔS°, ΔH° and ΔG°) showed that the process was spontaneous and exothermic. All the above results revealed that the Fe₃O₄-CuO-AC compositecan be an effective adsorbent for removing dyes from wastewater.     

Preparation of Al2O3-supported nano-Cu2O catalysts for the oxidative treatment of industrial wastewater

Cuprous oxide (Cu₂O) nanoparticles supported on Al₂O₃ prepared using two different methods (hereafter referred to as catalyst I and II, respectively) were characterized by XRD and TEM. The catalytic activities of catalyst I and II during the treatment of industrial wastewater were then investigated. Specifically, the progress of the catalytic oxidation of industrial wastewater was observed by monitoring the time-dependent change in the chemical oxygen demand (COD) of industrial wastewater when the catalysts were applied. The results indicated that the catalytic activity of catalyst II was greater than that of catalyst I. Furthermore, under optimal conditions the COD removal efficiency was 94.59%. Finally, the mechanism by which the oxidative degradation of the industrial wastewater occurred could be explained based on a hydroxyl radical mechanism.     

Binary α-Fe2O3–Co3O4 nanostructures for advanced oxidation process: Role of synergy for enhanced catalysis

Iron and its binary oxides are meticulously exploited for environmental remediations. However, only limited studies have been carried out on the degradation of industrial organics by advanced oxidation process. In this study, iron oxide, cobalt oxide, and iron–cobalt binary oxides were synthesized by a modified hydrothermal method as heterogeneous Fenton-like catalysts for the removal of methylene blue (MB) from wastewaters. The oxide nanostructures were characterized by different analytical techniques. Studying the effects of various parameters such as catalyst dose, MB concentration, and H₂O₂ concentration, the reaction conditions were optimized to enhance the removal of MB dye. The results revealed that α-Fe₂O₃–Co₃O₄ shows much higher activity than both Co₃O₄ and α-Fe₂O₃ for the degradation of MB at room temperature and beyond. The binary α-Fe₂O₃–Co₃O₄ shows degradation efficiency of 96.4% at 65 °C within 60 min. Furthermore, the binary α-Fe₂O₃–Co₃O₄ catalyst retains its activity for up to four successive cycles. A probable mechanism is also proposed, involving the generation of ‧OH radical as well as Fe²⁺/Fe³⁺ or Co²⁺/Co³⁺ redox couple of the binary α-Fe₂O₃–Co₃O₄ catalyst.