Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Photocatalytic degradation of Acid Red 18 by synthesized AgCoFe2O4@Ch/AC: Recyclable, environmentally friendly, chemically stable, and cost-effective magnetic nano hybrid catalyst

Chitosan (Ch) is a linear biodegradable natural carbohydrate polymer and the most appealing biopolymer, such as low-cost biodegradability, biocompatibility, hydrophilicity, and non-toxicity. In this case, Ch was utilized to synthesize AgCoFe2O4@Ch/Activated Carbon (AC) by the modified microwave-assisted co-precipitation method. The physical and chemical structure of magnetic nanocomposites was analyzed and characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Diffuse Reflection Spectroscopy (DRS), Value stream mapping (VSM), Fourier transform spectroscopy (FTIR) and BET. The effects of various parameters on the removal of dye (Acid Red18), including catalyst dose, dye concentration, pH, and time were studied. Results showed that the highest removal efficiencies were 96.68 % and 84 % for the synthetic sample and actual wastewater, respectively, in optimal conditions (pH: 3, the initial dye concentration: 10 mgL-1, the catalyst dose: 0.14 gL-1, time: 50 min). Mineralization, according to the COD analysis, was 89.56 %. Photocatalytic degradation kinetics of Acid Red 18 followed pseudo-first order and Langmuir-Hinshelwood with constants of kc = 0.12 mg L-1 min-1 and KL-H = 0.115 Lmg-1. Synthesized photocatalytic AgCoFe2O4@Ch/AC showed high stability and after five recycling cycles was able to remove the pollutant with an efficiency of 85.6 %. So, the synthesized heterogenous magnetic nanocatalyst AgCoFe2O4@Ch/AC was easily recycled from aqueous solutions and it can be used in the removal of dyes from industries with high efficiency.

Ultrasonic treatment of dye chemicals in wastewater: A review

The existence of pollutants, such as toxic organic dye chemicals, in water and wastewater raises concerns as they are inadequately eliminated through conventional water and wastewater treatment methods, including physicochemical and biological processes. Ultrasonic treatment has emerged as an advanced treatment process that has been widely applied to the decomposition of recalcitrant organic contaminants. Ultrasonic treatment has several advantages, including easy operation, sustainability, non-secondary pollutant production, and saving energy. This review examines the elimination of dye chemicals and categorizes them into cationic and anionic dyes based on the existing literature. The objectives include (i) analyzing the primary factors (water quality and ultrasonic conditions) that influence the sonodegradation of dye chemicals and their byproducts during ultrasonication, (ii) assessing the impact of the different sonocatalysts and combined systems (with ozone and ultraviolet) on sonodegradation, and (iii) exploring the characteristics-based removal mechanisms of dyes. In addition, this review proposes areas for future research on ultrasonic treatment of dye chemicals in water and wastewater.

Effect of bismuth doping on the crystal structure and photocatalytic activity of titanium oxide

The doping of TiO2 with metals and non-metals is considered one of the most significant approaches to improve its photocatalytic efficiency. In this study, the photodegradation of methyl orange (MO) was examined in relation to the impact of Bi-doping of TiO2. The doped TiO2 with various concentrations of metal was successfully synthesized by a one-step hydrothermal method and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and UV-vis spectroscopy. The XRD results revealed that the anatase phase, with an average crystallite size of 16.2 nm, was the main phase of TiO2. According to the anatase texture results, it was found that the doping of TiO2 increased the specific surface area for Bi2O3@TiO2 without a change in the crystal structure or the crystal phase of TiO2. Also, XPS analysis confirmed the formation of Ti4+ and Ti3+ as a result of doping with Bi. The activities of both pure TiO2 and Bi-doped TiO2 were tested to study their ability to decolorize MO dye in an aqueous solution. The photocatalytic degradation of MO over Bi2O3@TiO2 reached 98.21%, which was much higher than the 42% achieved by pure TiO2. Doping TiO2 with Bi increased its visible-light absorption as Bi-doping generated a new intermediate energy level below the CB edge of the TiO2 orbitals, causing a shift in the band gap from the UV to the visible region, thus enhancing its photocatalytic efficiency. In addition, the effects of the initial pH, initial pollutant concentration, and contact time were examined and discussed.

A review of research trends on the usage of photocatalysis for wastewater treatment: bibliometric analysis

Photocatalysis is seen as a viable alternative to treating water pollution, due to its flexibility, low cost, and ability to use visible light which is a plentiful and free energy source. Hence, determining the topics of interest and widening collaboration networks will go a long way in improving research in this field. In this study, we aimed to analyze the global research trends on the usage of photocatalysis for wastewater treatment using bibliometric analysis, centered on the outputs of publications, co-authorships, countries of affiliation, and author's keyword co-occurrences. Bibliometric analysis is a review method that is well-known and more conversant to Social Science. Employing it in Physical Science, which is rarely seen, will provide an avenue and yet another method of determining common research topics as well as the potential opportunities and future research in the field. A potential hybrid review paper of great importance to future research in the area will be produced. A total of 1373 articles published within 27 years between 1993 and 2020 were extracted from the Scopus database. In the beginning, less attention was given to the said topic, because after the oldest article was published in 1993, there was no record of other publications until after 5 years (1998). However, from 2002 there was a growing interest in research in that field, with a cumulative increase every year to date, except for a few years with fewer publications. Meanwhile, the number of publications has risen significantly from 2017 to 2020, with an increase of more than 70 publications every year; this is expected to increase rapidly in the coming years. Recently researchers are focusing on developing efficient photocatalysts for contaminants of emerging concern, like pharmaceutical and refinery wastewater, however, the usage of conducting polymers to produce nanocomposite which was found to be very effective is still lagged in wastewater treatment, as such it will be a good area of future research on effective photocatalysts for wastewater treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40899-023-00868-5.

Preparation and characterization of rare earth element nanoparticles for enhanced photocatalytic degradation

The present work focuses on the photocatalytic degradation of methylene blue (MB) on erbium ion (Er³⁺) doped TiO₂ under visible light. Pure TiO₂ nanoparticles and erbium (Er³⁺) doped TiO₂ nanocomposite (Er³⁺/TiO₂) NCs were synthesized using the sol-gel method. The synthesized (Er³⁺/TiO₂) NCs were characterized using Fourier transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HR-SEM), elementary dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS), specific surface area (BET), zeta potential, and particle size. Different parameters were used to study their efficiency for the photoreactor (PR) and the synthesized catalyst. These parameters include pH of the feed solution, the rate of flow, the presence of an oxidizing agent (aeration pump), different ratios of nanoparticles, the amount of catalyst, and the concentrations of pollutants. An example of an organic contaminant was the dye methylene blue (MB). The result achieved using the synthesized nanoparticles (I) under ultraviolet light pure TiO₂ was found to have degraded by 85%. For (Er³⁺/TiO₂) NCs under visible light, dye removal increased with pH to a maximum of 77% degradation at pH 5. Furthermore, photocatalytic efficiency improves to 80% at 40 rpm (3 l/h) low motor speed. The degradation efficiency decreased to 70% when the MB concentration was increased from 5 to 30 mg/L. When oxygen content was increased using an air pump, and deterioration reached 85% under visible light, it improved performance.

High efficiency and rapid treatment of naproxen sodium wastewater by dielectric barrier discharge coupled with catalysis

Pharmaceutical wastewater has the characteristics of high organic concentration and poor biodegradability, which will cause serious environmental pollution when discharged into water bodies. In this work, naproxen sodium was used to simulate pharmaceutical wastewater by dielectric barrier discharge technology. The effects of dielectric barrier discharge (DBD) and combined catalysis on the removal of naproxen sodium solution were studied. The removal effect of naproxen sodium was affected by discharge conditions, including discharge voltage, frequency, air flow rate and electrode materials. It was found that the highest removal rate of naproxen sodium solution was 98.5%, when the discharge voltage was 7000 V, the frequency was 3333 Hz, and the air flow rate was 0.3 m³/h. In addition, the effect of the initial conditions of naproxen sodium solution was studied. The removal of naproxen sodium was relatively effective at low initial concentrations as well as under the condition of weak acid or near-neutral solution. However, the initial conductivity of naproxen sodium solution had little effect on the removal rate. The removal effect of naproxen sodium solution was compared by using catalyst combined with DBD plasma and DBD plasma alone. x%La/Al₂O₃, Mn/Al₂O₃ and Co/Al₂O₃ catalysts were added. The removal rate of naproxen sodium solution reached the highest after adding 14%La/Al₂O₃ catalyst, which played the best synergistic effect. The removal rate of naproxen sodium was 18.4% higher than that without catalyst. The results showed that the combination of DBD and La/Al₂O₃ catalyst may be a promising method to remove naproxen sodium efficiently and quickly. And this method is a new attempt to treat naproxen sodium.

Solar light-based advanced oxidation processes for degradation of methylene blue dye using novel Zn-modified CeO2@biochar

Herein, a novel nanocomposite, namely, Zn-modified CeO₂@biochar (Zn/CeO₂@BC), is synthesized via facile one-step sol-precipitation to study its photocatalytic activity towards the removal of methylene blue dye. Firstly, Zn/Ce(OH)₄@biochar was precipitated by adding sodium hydroxide to cerium salt precursor; then, the composite was calcined in a muffle furnace to convert Ce(OH)₄ into CeO₂. The crystallite structure, topographical and morphological properties, chemical compositions, and specific surface area of the synthesized nanocomposite are characterized by XRD, SEM, TEM, XPS, EDS, and BET analysis. The nearly spherical Zn/CeO₂@BC nanocomposite has an average particle size of 27.05 nm and a specific surface area of 141.59 m²/g. All the tests showed the agglomeration of Zn nanoparticles over the CeO₂@biochar matrix. The synthesized nanocomposite showed remarkable photocatalytic activity towards removing methylene blue, an organic dye commonly found in industrial effluents. The kinetics and mechanism of Fenton-activated dye degradation were studied. The nanocomposite exhibited the highest degradation efficiency of 98.24% under direct solar irradiation of 90 min, at an optimum dosage of 0.2 g l^-1 catalyst and 10 ppm dye concentration, in the presence of 25% (V/V) 0.2 ml (4 µl/ml) hydrogen peroxide. The hydroxyl radical generated from H₂O₂ during the photo-Fenton reaction process was attributed to the nanocomposite's improved photodegradation performance. The degradation process followed pseudo-first-order kinetics having a rate constant (k) value of 0.0274 min^-1.

Optimization Study on Synergistic System of Photocatalytic Degradation of AR 26 and UV-LED Heat Dissipation

In this work, a novel UV-LED/TiO2 photocatalytic system, having a single layer with ten LED beads, was designed to simultaneously achieve UV-LED cooling and wastewater degradation, to deal with heat dissipation problems of high-power UV-LEDs. To gain more insight into this system, the parameters affecting both cooling and photocatalytic performance were first optimized using AR 26 as a basis. With respect to sewage, sewage with a flow rate of 80 mL/min and a temperature of 20 °C helped to keep a lower temperature of UV-LED, which benefits the long-term operation stability of LED beads. For parameters affecting the photocatalytic performance only, the experiments showed that TiO2 with moderate dosing (0.75 g/L) under strong acid conditions (pH = 2) helped to further improve photocatalytic activity when the initial concentration of AR 26 was 45 mg/L. Lastly, to illustrate the advantages of this novel system, the performance of the synergistic system was compared with a conventional photocatalytic reactor with respect to degradation performance, optical quantum efficiency, and energy consumption. The results showed that the degradation efficiency and light source utilization ratio of this coupled system were, respectively, 2.1 times and 1.5 times as much as those of a conventional reactor. As the unit power consumption of the synergistic system was only 0.18-fold more than that of a conventional reactor, our work suggests that this synergistic system with the advantage of LED lamp beads has a bright future in dealing with refractory organic pollutants of sewage.

Removal of Azo Dyes from Wastewater through Heterogeneous Photocatalysis and Supercritical Water Oxidation

Azo dyes are synthetic organic dyes used in the textile, leather, and paper industries. They pose environmental problems due to their toxic and persistent nature. The toxicity is due to the presence of azo groups in the dye molecule that can break down into aromatic amines, which are highly toxic to aquatic organisms and humans. Various treatment methods have been developed to remove azo dyes from wastewater. Conventional wastewater treatments have some drawbacks, such as high operating costs, long processing times, generation of sludge, and the formation of toxic by-products. For these reasons, a valid alternative is constituted by advanced oxidation processes. Good results have been obtained using heterogeneous photocatalysis and supercritical water oxidation. In the former method, a photocatalyst is in contact with wastewater, a suitable light activates the catalyst, and generated reactive oxygen species that react with pollutants through oxidative reactions to their complete mineralization; the latter involves pressurizing and heating wastewater to supercritical conditions in a reactor vessel, adding an oxidizing agent to the supercritical water, and allowing the mixture to react. In this review paper, works in the literature that deal with processing wastewater containing azo dyes through photocatalysts immobilized on macroscopic supports (structured photocatalysts) and the supercritical water oxidation technique have been critically analyzed. In particular, advancement in the formulation of structured photocatalysts for the degradation of azo dyes has been shown, underlying different important features, such as the type of support for the photoactive phase, reactor configuration, and photocatalytic efficiency in terms of dye degradation and photocatalyst stability. In the case of supercritical water oxidation, the main results regarding COD and TOC removal from wastewater containing azo dyes have been reported, taking into account the reactor type, operating pressure, and temperature, as well as the reaction time.

Aluminium doped ZnO nanostructures for efficient photodegradation of indigo carmine and azo carmine G in solar irradiation

Aluminium doped zinc oxide (AZO) nanomaterials (AlxZn1-xO) with x fraction varying as 0.02 and 0.04 were synthesized using the auto-combustion method using glycine as a fuel. The synthesized catalysts were characterized with X-ray diffraction (XRD), UV–Visible Spectroscopy (UV–Vis), Raman spectroscopy, Photoluminescence (PL) spectroscopy, and High Resolution Transmission Electron Microscopy (HR-TEM). XRD results showed that synthesized materials possessed good crystallinity, while UV–VIS was employed to find the band gaps of synthesized materials. Raman was used to determine the vibrational modes in the synthesized nanoparticles, while TEM analysis was performed to study the morphology of the samples. Industrial effluents such as indigo carmine and azo carmine G were used to test the photodegradation ability of synthesised catalysts. Parameters such as the effect of catalyst loading, dye concentration and pH were studied. The reduction in crystallite size, band gap and increased lattice strain for the 4% AZO was the primary reason for the degradation in visible irradiation, degrading 97 and 99% equimolar concentrations of indigo carmine and azo carmine G in 140 min. The Al doped ZnO was found to be effective in faster degradation of dyes as compared to pure ZnO in presence of natural sunlight.

Green and environmentally sustainable fabrication of SnS2 quantum dots/chitosan nanocomposite for enhanced photocatalytic performance: Effect of process variables, and water matrices

Concerns over the availability of clean water and the quality of treated wastewater are significant problems that call for an appropriate solution to improve the water quality. The present work emphasized the synthesis of novel SnS₂ quantum dots (QDs) deposited on chitosan via a facile green precipitation method involving neem (Azadirachta indica) leaf extract and investigating its photocatalytic performance for the degradation of Crystal violet (CV) dye under varying reaction parameters, other organic and inorganic salts and water matrices. The crystal structure, surface morphology, and elemental composition of the prepared SnS₂ (QDs)/Ch composite were evaluated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and energy dispersive X-ray analysis (EDAX) techniques. The average size of SnS₂/Chitosan nanoparticles was calculated to be 8.8 nm using XRD, with the average diameter of SnS₂ QDs to be 3.3 nm from TEM. UV-visible spectroscopy was used to investigate its optical properties. The direct band gap of SnS₂/Chitosan estimated from Tauc's plot came to be 2.5 eV. The prepared novel SnS₂/Ch composite showed outstanding photocatalytic activity for the degradation of CV through the Advanced Oxidation Process (AOP). The fabricated photocatalyst caused 98.60 ± 1.34 % degradation of CV within a short period of 70 min under optimum conditions. The photodegradation reaction followed pseudo-first-order rate kinetics with a rate constant of 0.0815 min^-1. Furthermore, the photocatalyst showed high stability and was reusable for up to four cycles. The present work fulfils the aim of designing a novel, green, and efficient visible light-active nano-photocatalyst.

Solar-driven photocatalytic chlorine activation for the simultaneous degradation of pharmaceuticals and personal care products and the inactivation of Escherichia coli in drinking water

Removal of pharmaceuticals and personal care products (PPCPs) is often inefficient during conventional water treatment, posing threats to human health. Herein, we have developed a novel solar/TiO2/chlorine system upgraded from chlorine disinfection for the simultaneous degradation of PPCPs and the inactivation of Escherichia coli from drinking water. The addition of 100 μM of chlorine to the photocatalytic process considerably enhanced the degradation efficiency of PPCPs and demonstrated excellent disinfecting abilities, as confirmed by a 4.7 × increase in the carbamazepine degradation rate constant coupled with a 3.2-log (99.94%) reduction of E. coli cells within 1 min. Photoinduced charge pairs (hVB+ and eCB-) were identified for reactive species generation, and HO• and ClO• were the primary contributors to PPCPs degradation. The process exhibited satisfactory carbamazepine degradation efficiency in different water matrices and the cycling tests showed the TiO2 photocatalyst to be highly stable and reusable. Overall, our solar/TiO2/chlorine system is a potentially effective alternative to conventional drinking water treatment using chlorination.

Insights into Photothermally Enhanced Photocatalytic U(VI) Extraction by a Step-Scheme Heterojunction

In this work, a CdS/BiVO₄ step-scheme (S-scheme) heterojunction with self-photothermally enhanced photocatalytic effect was synthesized and applied for efficient U(VI) photoextraction. Characterizations such as transient absorption spectroscopy and Tafel test together confirmed the formation of S-scheme heterojunctions, which allows CdS/BiVO₄ to avoid photocorrosion while retaining the strong reducing capacity of CdS and the oxidizing capacity of BiVO₄. Experimental results such as radical quenching experiments and electron spin resonance show that U(VI) is rapidly oxidized by photoholes/^•OH to insoluble UO₂(OH)₂ after being reduced to U(IV) by photoelectrons/^•O₂⁻, which precisely avoids the depletion of electron sacrificial agents. The rapid recombination of electron-hole pairs triggered by the S-scheme heterojunction is found to release large amounts of heat and accelerate the photocatalysis. This work offers a new enhanced strategy for photocatalytic uranium extraction and presents a direction for the design and development of new photocatalysts.

Performance of a solar photocatalysis reactor as pretreatment for wastewater via UV, UV/TiO2, and UV/H2O2 to control membrane fouling

The performance of a solar photocatalysis reactor as pretreatment for the removal of total organic carbon (TOC) and turbidity from municipal wastewater was achieved by implementing an integrated system as tertiary treatment. The process consisted of ultraviolet (UV) sunlight, UV sunlight/H₂O₂, and UV sunlight/TiO₂ nanocatalysts as pretreatment steps to prevent ultrafiltration (UF) membrane fouling. The characterization of TiO₂ was conducted with X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy , and Brunauer–Emmett–Teller surface area analysis. This study investigated the effect of time and solar radiation using UV, UV/H₂O₂, and UV/TiO₂ to remove TOC and turbidity. The transmembrane pressure improvement was studied using a UF membrane system to pretreat wastewater with different UV doses of sunlight for 5 h and UV/H₂O₂ and UV/TiO₂. The results showed that the highest removal efficiency of the turbidity and TOC reached 95% and 31%, respectively. The highest removal efficiency of the turbidity reached 40, 75, and 95% using UV, UV/H₂O₂, and UV/TiO₂, respectively, while the optimal removal efficiency of TOC reached 20%, 30%, and 50%, respectively.

Effective photocatalytic degradation of amoxicillin using MIL-53(Al)/ZnO composite

A promising hierarchical nanocomposite of MIL-53(Al)/ZnO was synthesized as a visible-light-driven photocatalyst to investigate the degradation of amoxicillin (AMX). MIL-53(Al)/ZnO ultrafine nanoparticles were obtained by preparing Zn-free MIL-53Al and employing it as a reactive template under hydrothermal and chemical conditions. The synthesized nanocomposite (MIL-53(Al)/ZnO) has a low content of Al > 1.5% with significantly different characterizations of the parent compounds elucidated by various analyses such as SEM, TEM, XRD, EDX, and UV-Vis. The effect of operational parameters (catalyst dose (0.2-1.0 g/L), solution pH (3-11), and initial AMX concentration (10-90 mg/L)) on the AMX removal efficiency was studied and optimized by the response surface methodology. A reasonable goodness-of-fit between the expected and experimental values was confirmed with correlation coefficient (R²) equal to 0.96. Under the optimal values, i.e., initial AMX concentration = 10 mg/L, solution pH ~ 4.5, and catalyst dose = 1.0 g/L, 100% AMX removal was achieved after reaction time = 60 min. The degradation mechanism and oxidation pathway were vigorously examined. The AMX degradation ratios slightly decreased after five consecutive cycles (from 78.19 to 62.05%), revealing the high reusability of MIL-53(Al)/ZnO. The AMX removal ratio was improved with enhancers in order ([Formula: see text]> H₂O₂ > S₂O₈^-2). The results proved that 94.12 and 98.23% reduction of COD were obtained after 60 and 75 min, respectively. The amortization and operating costs were estimated at 3.3 $/m³ for a large-scale photocatalytic system.

Strainer-Separable TiO2 on Halloysite Nanocomposite-Embedded Alginate Capsules with Enhanced Photocatalytic Activity for Degradation of Organic Dyes

Photocatalysis driven by natural sunlight is an attractive approach to removing pollutants from wastewater. Although TiO₂–based photocatalysts using various support nano-materials with high catalytic activity and reusability have been developed for purifying wastewater, the centrifugal separation methods used for the nanocatalysts limit their use for treating large amounts of water. Here, we prepared a TiO₂ nano-catalyst supported on a halloysite nanotube (HNT)-encapsulated alginate capsule (TiO₂@HNT/Alcap) to recapture the catalysts rapidly without centrifugation. The structure of TiO₂@HNT/Alcap was characterized by X-ray diffraction, SEM, and TGA. In our system, the combination of HNTs and alginate capsules (Alcaps) improved the efficiency of adsorption of organic pollutants to TiO₂, and their milli = meter scale structure allowed ultra-fast filtering using a strainer. The TiO₂@HNT/Alcaps showed ~1.7 times higher adsorption of rhodamine B compared to empty alginate capsules and also showed ~10 and ~6 times higher degradation rate compared to the HNT/Alcaps and TiO₂/Alcaps, respectively.

Graphene-based TiO2 composites for photocatalysis & environmental remediation: synthesis and progress

Photoactive nanomaterials constitute an emerging field in nanotechnology, finding an extensive array of applications spanning diverse areas, including electronics and photovoltaic devices, solar fuel cells, wastewater treatment, etc. Titanium dioxide (TiO₂), in its thin-film form, has been exhaustively surveyed as potential photocatalysts for environmental remediation owing to its innocuousness, stability, and photocatalytic characteristics when subjected to ultraviolet (UV) irradiation. However, TiO₂ has some shortcomings associated with a large bandgap value of around 3.2 eV, making it less efficient in the visible spectral range. TiO₂ is often consolidated with various carbon nanomaterials to overcome this limitation and enhance its efficiency. Graphene, a 2-dimensional allotrope of carbon with a bandgap tuned between 0 and 0.25 eV, exhibits unique properties, making it an attractive candidate to augment the photoactivity of semiconductor (SC) oxides. Encapsulating graphene oxide onto TiO₂ nanospheres demonstrates intensified photocatalytic properties and exceptional recyclability for the degeneration of certain dyes, including Rhodamine B. This review encompasses various techniques to synthesize graphene-based TiO₂ photoactive composites, emphasizing graphene capsulized hollow titania nanospheres, nanofibers, core/shell, and reduced graphene oxide-TiO₂-based nanocomposites. It also consolidates the application of the aforestated nanocomposites for the disintegration of various synthetic dyes, proving efficacious for water decontamination and degradation of chemicals and pharmaceuticals. Furthermore, graphene-based TiO₂ nanocomposites used as lithium (Li)-ion batteries manifesting substantial electrochemical performance and solar fuel cells for energy production are discussed here.

Fabrication and Photocatalytic Properties of Zinc Tin Oxide Nanowires Decorated with Silver Nanoparticles

With the continuous advancement of high-tech industries, how to properly handle pollutants has become urgent. Photocatalysis is a solution that may effectively degrade pollutants into harmless molecules. In this study, we synthesized single crystalline Zn2SnO4 (ZTO) nanowires through chemical vapor deposition and selective etching. The chemical bath redox method was used to modify the ZTO nanowires with Ag nanoparticles to explore the photocatalytic properties of the nanoheterostructures. The combination of the materials here is rare. Optical measurements by photoluminescence (PL) and UV-Vis show that the PL spectrum of ZTO nanowires was mainly in the visible light region and attributed to oxygen vacancies. The luminescence intensity of the nanowires was significantly reduced after modification, demonstrating that the heterojunction could effectively reduce the electron-hole pair recombination. The reduction increased with the increase in Ag decoration. The conversion from the UV-Vis absorption spectrum to the Tauc Plot shows that the band gap of the nanowire was 4.05 eV. With 10 ppm methylene blue (MB) as the degradation solution, ZTO nanowires exhibit excellent photodegradation efficiency. Reusability and stability in photodegradation of the nanowires were demonstrated. Photocatalytic efficiency increases with the number of Ag nanoparticles. The main reaction mechanism was confirmed by photocatalytic inhibitors. This study enriches our understanding of ZTO-based nanostructures and facilitates their applications in water splitting, sewage treatment and air purification.

Comparison of TiO2 catalysis and Fenton's treatment for rapid degradation of Remazol Red Dye in textile industry effluent

The contamination of water bodies by toxic industrial effluents is a serious threat to environment and the exposed organisms. The treatment of carcinogenic azo dyes in wastewater of grossly polluting textile industry is a major challenge considering the persistent nature of chemical dyes against biological treatment. The present study explores efficacy of advanced oxidation processes—photocatalysis and photo-Fenton, towards degradation of Remazol Red dye in the textile industry effluent. It was observed that both processes can completely remove the colour and approximately 85% mineralization of the dye within reaction time of 60 min and 8 min, respectively. The economic analysis placed photo-Fenton as a cost-effective method with treatment cost of approx. 0.0090 US $/litre of wastewater containing Remazol Red dye. Although, Photocatalysis was relatively slow, it is substantially effective in removal/degradation of colour from textile effluent against the biological treatment. The study concludes that photo-Fenton and Photocatalysis are cost-effective and substantial treatment options for removal of toxicity arising from coloured textile effluents.

Sunlight-promoted photodegradation of Congo red by cadmium-sulfide decorated graphene aerogel

Herein, a simpler-viable methodology for the surface decoration of pear fruit derived graphene aerogel (GA) via cadmium sulfide (CdS) has been presented. GA can be easily synthesized from bio-mass, which provide an economic advantage. Surface decoration via CdS imparts photocatalytic activities in functionalized graphene aerogels (f-GA). CdS-f-GA is being explored here as a photocatalyst for the degradation of a toxic azo dye named Congo red in the presence of sunlight. The rate and mechanism associated with photodegradation were analyzed by performing kinetics and radical trap-based quenching experiments. Nuclear magnetic resonance and fourier transform infrared spectroscopy analyses of the control and photodegraded products were performed to ensure the degradation of the organic framework of Congo red. Additionally, the real-life applicability of CdS-f-GA was also analyzed by degrading the dye in different types of industrial samples (via the method of external spiking), which can advance its practical relevance.

Insights into Photothermally Enhanced Photocatalytic U(VI) Extraction by a Step-Scheme Heterojunction

In this work, a CdS/BiVO 4 step-scheme (S-scheme) heterojunction with self-photothermally enhanced photocatalytic effect was synthesized and applied for efficient U(VI) photoextraction. Characterizations such as transient absorption spectroscopy and Tafel test together confirmed the formation of S-scheme heterojunctions, which allows CdS/BiVO 4 to avoid photocorrosion while retaining the strong reducing capacity of CdS and the oxidizing capacity of BiVO 4 . Experimental results such as radical quenching experiments and electron spin resonance show that U(VI) is rapidly oxidized by photoholes/ • OH to insoluble UO 2 (OH) 2 after being reduced to U(IV) by photoelectrons/ • O 2 - , which precisely avoids the depletion of electron sacrificial agents. The rapid recombination of electron-hole pairs triggered by the S-scheme heterojunction is found to release large amounts of heat and accelerate the photocatalysis. This work offers a new enhanced strategy for photocatalytic uranium extraction and presents a direction for the design and development of new photocatalysts.

Fast photodegradation of antibiotics and dyes by anionic surfactant-aided CdS/ZnO nanodispersion

Photocatalytic technology has broad applications in energy and environmental science. In this study, we synthesized a type II heterojunction CdS/ZnO nanodispersion by means of one-pot precipitation. Different from previous studies,...

Novel ultralong and photoactive Bi2Ti4O11/TiO2 heterojunction nanofibers toward efficient textile wastewater treatment

The elimination of dyes from textile wastewater with a lower carbon footprint is highly contingent on the design of green catalysts. Here, we innovatively developed ultralong one-dimensional Bi₂Ti₄O₁₁/TiO₂ heterojunction nanofibers via electrospinning so as to photocatalytically degrade dyes efficiently and sustainably through the utilisation of renewable solar irradiation. The heterostructured Bi₂Ti₄O₁₁/TiO₂ nanofibers exhibited desirable activity in the visible light region through the slight shift of the absorption edge to a longer wavelength. The Bi₂Ti₄O₁₁/TiO₂ nanofibers calcined at 550 °C had a lower optical band gap (3.08 eV) than that of the pure TiO₂ (3.32 eV), as evidenced by their higher photocatalytic degradation kinetics of a model dye (Acid Orange 7) (2.5 times greater than those of pure TiO₂). The enhanced visible light photocatalytic performance arose from the formation of both the Bi₂Ti₄O₁₁/TiO₂ heterojunction and the effective separation of photogenerated holes and electrons. The employment of ultralong Bi₂Ti₄O₁₁/TiO₂ heterojunction nanofibers for dye removal/decolourisation under visible light is an efficient, cost effective and sustainable solution, which will provide significant insights for practical textile wastewater treatment in view of practical engineering applications.

The elimination of dyes from textile wastewater with a lower carbon footprint is highly contingent on the design of green catalysts.

Supported TiO2 in Ceramic Materials for the Photocatalytic Degradation of Contaminants of Emerging Concern in Liquid Effluents: A Review

The application of TiO₂ as a slurry catalyst for the degradation of contaminants of emerging concern (CEC) in liquid effluents has some drawbacks due to the difficulties in the catalyst reutilization. Thus, sophisticated and expensive separation methods are required after the reaction step. Alternatively, several types of materials have been used to support powder catalysts, so that fixed or fluidized bed reactors may be used. In this context, the objective of this work is to systematize and analyze the results of research inherent to the application of ceramic materials as support of TiO₂ in the photocatalytic CEC removal from liquid effluents. Firstly, an overview is given about the treatment processes able to degrade CEC. In particular, the photocatalysts supported in ceramic materials are analyzed, namely the immobilization techniques applied to support TiO₂ in these materials. Finally, a critical review of the literature dedicated to photocatalysis with supported TiO₂ is presented, where the performance of the catalyst is considered as well as the main drivers and barriers for implementing this process. A focal point in the future is to investigate the possibility of depurating effluents and promote water reuse in safe conditions, and the supported TiO₂ in ceramic materials may play a role in this scope.

Photocatalytic degradation of MB by TiO2: studies on recycle and reuse of photocatalyst and treated water for seed germination

Photocatalysis is an effective way for treatment of wastewater and degradation of dyes. It is important to assess the reusability of photocatalyst and treated water after the treatment process. In this study, the photocatalytic activity of TiO₂ (titanium dioxide) and TiO₂-TMAOH (titanium dioxide-tetramethylammonium hydroxide) was analyzed for degradation of methylene blue dye. Enhanced degradation of methylene blue is observed while treated with TiO₂-TMAOH with photodegradation efficiency (PDE) 80% within 20 min. A further study shows the reusability of TiO₂ for degradation of dye for six cycles with a decrease in photodegradation efficiency from 90% (cycle-1) to 50% (cycle-2). Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV) analysis were carried out to identify the functional groups in treated water, traces of titanium, and TMAOH, respectively. Seed germination of Vigna radiata using TiO₂- and TiO₂-TMAOH-treated water shows equivalent and consistent growth. Water quality analysis of treated water shows improved biochemical oxygen demand (BOD) level (1.5 mg L^-1), which is suitable for reusability of water for many applications. The outcomes suggest treated water can be used for irrigation and plantation purposes.

A Study on removal of Methylene Blue dye by photo catalysis integrated with nanofiltration using statistical and experimental approaches

In this work, the removal of Methylene Blue dye from the synthetic textile effluent has been investigated using a hybrid system (photocatalysis and nanofiltration). The Commercial ZnO powder was used as a catalyst in the photocatalytic operation. Response surface methodology (RSM) was employed to optimize the various operating parameters such as pH, catalyst loading and time duration and this optimization has enhanced the decolorization efficiencies. The results were compared and contrasted with the individual as well as the combined systems at optimized conditions. The results indicate that the photocatalysis process alone has resulted in 33% of dye decolorization and 26.5% of total organic carbon (TOC) removal, while the individual ceramic nanoflitration system has yielded 43% of decolorization and 35.03% TOC removal. About 94% of the dye was decolorized, and 70% of TOC was removed in 94.23 minutes of operation by the hybrid system at optimized initial operating conditions.

Experimental studies on water matrix and influence of textile effluents on photocatalytic degradation of organic wastewater using Fe-TiO2 nanotubes: Towards commercial application

The application of photocatalysis for the effective removal of textile dyes is dependent on various parameters related with both water quality and different chemicals discharge during the dying process. Because the oxidation rates of the particular mixtures mainly influenced by the elements of the water matrix. These elements comprised of organic, inorganic salts, heavy metals, and ions. The impact of water matrices (Tap water, DI water, seawater, surface water, and ultra-pure water) on the Congo red decolorization, total organic carbon, and chemical oxygen demand removal efficacy has been assessed using Fe-TiO₂ nanotubes as a photocatalyst. The photocatalytic degradation rate decreased in unclean water due to the interferences of dissolved organics and minerals. However, all the environmental water matrices depict the significant decrease in turbidity and conductivity after treating with photocatalytic process. The photoactivity and capacity for decantation are the two crucial elements that have an impact on the "practical efficiency" of photocatalysts. Moreover, the textile wastewater contains a large quantity of dyes mixed with number of detrimental chemicals and other effluents discharged into the water which consequently pollute ecosystem and cause serious risks to human health. For environmental applications, we investigated individually the impact of various harmful chemicals commonly discharged from each step of textile wet processing which can have inhibiting or promoting effect on the azo dye photocatalytic degradation.

Remediation of textile industry organic dye waste by photocatalysis using eggshell impregnated ZnO/CuO nanocomposite

Heterogeneous photocatalysis using nanocomposites is of great research interest in the treatment of industrial wastewater. The impregnated photocatalyst was produced by liquid state reaction of ZnO/CuO nanocomposite with extracted eggshells. The structure, functional group, metal composition, bandgap, and photocatalytic activity of the nanocomposites were characterized by using X-ray diffraction, Fourier-transform infrared spectroscopy, atomic absorption spectrometry, and UV-Vis spectroscopy, respectively, in the absence and presence of eggshells. Photocatalytic degradation activities of the nanocomposites under UV light irradiation have been tested for a real sewage sample taken from Debre Berhan Textile Industry. From the results, the optimized degradation efficiency of the dye was 97.95% with 0.4 g dose of the photocatalyst, 120 min irradiation time, 120 °C temperature, and pH of 6.7. The results revealed that eggshell impregnated nanocomposite had better catalytic activity than the naked nanocomposite. This is due to the highly porous structure of eggshell biomasses and their sorption characteristics. In conclusion, when nanocomposites are supported by eggshell biomasses, they are excellent photocatalysts and can minimize the contamination of organic dyes from textile effluents.

Activation of peroxymonosulfate by phosphite: Kinetics and mechanism for the removal of organic pollutants

In this study, phosphite (HPO₃^2-) was used as a novel activator to activate peroxymonosulfate (PMS) for acid orange 7 (AO7) removal. Under the optimized conditions, the decolorization efficiency of AO7 was 82.1% within 60 min with rate constant values (k_obs) of 0.0301 min^-1. Besides, effects of the solution pH and the co-existing inorganic anions including Cl^-, HCO₃^-, HPO₄^2- and SO₄^2- on AO7 removal were also investigated. Except for SO₄^2-, other examined co-existing inorganic anions displayed favorable effects on the removal of AO7. Furthermore, the mechanism for PMS activation by the HPO₃^2- was deeply elucidated by radical scavenger including ethanol (EtOH), tert-butanol (TBA), l-histidine and tiron, and electron spin resonance (ESR) studies. It was proposed that singlet oxygen (¹O₂) would be the dominant reactive oxygen species (ROS) in the HPO₃^2-/PMS system for contamination degradation at neutral pH condition. The findings of this study provided useful information for the application of the substances in industrial wastewaters to activate PMS for organic contaminants degradation and in particular for HPO₃^2--rich electroplating wastewater treatment.

Development of photochemical integrated submerged membrane bioreactor for textile dyeing wastewater treatment

A pilot-scale photocatalytic membrane bioreactor (PMBR) was developed for the treatment of textile dyeing wastewater. The PMBR is made of mild steel rectangular reactor of photocatalytic unit and polyethersulphone submerged hollow fibre membrane bioreactor unit with the working volume of about 20 L. For easy recovery, the tungsten oxide (WO₃) and WO₃/1% graphene oxide (GO)-powdered photocatalyst were made into bead and immersed in photocatalytic reactor. Graphene oxide incorporation has shown better results in decolourisation and degradation when compared with WO₃ alginate alone. The incorporation of GO into WO₃ minimises the recombination of photogenerated electron-hole pairs. The operating conditions such as 3 h of contact time for photocatalysis reaction (WO₃/1% GO), 10 h hydraulic retention time for MBR and 100 kPa of transmembrane pressure were optimised. Chemical oxygen demand removal efficiency of 48% was attained with photocatalysis, and the removal efficiency was further increased up to 76% when integrated with MBR. The colour removal efficiency after photocatalysis was 25% further increased up to 70% with MBR. Complete total suspended solid removal has been achieved with this hybrid system.

Photocatalytic and Biological Oxidation Treatment of Real Textile Wastewater

With rapidly growing urbanization and industrialization in developing countries, a large volume of wastewater is produced from industries that contain chemicals generating high environmental risks, which could affect health and socio-economic activities if not treated properly. In this study, the discoloration of wastewater containing azo dyes by chemical oxidation process combined with a biological treatment was evaluated and applied on real textile wastewater generated from one Ethiopian industrial site. The use of TiO2 as a photocatalyst and the effect of the addition of H2O2 on color removal were investigated. Photocatalysis was followed by aerobic biological treatment and their combination resulted in 93.3 and 90.4% removal of color and chemical oxygen demand (COD), respectively. These results revealed that the combination of photocatalytic and biological treatment approach shows a promising potential for the removal of color from real textile wastewater.

Photocatalytic Degradation of Alizarin Red S, Amaranth, Congo Red, and Rhodamine B Dyes Using UV Light Modified Reactor and ZnO, TiO2, and SnO2 as Catalyst

The photocatalytic degradation of dyes (alizarin red S, amaranth, congo red, and rhodamine B) present in wastewater was performed with UV lamp. The catalysts employed for this investigation were ZnO, TiO2, and SnO2. The kinetic studies of dyes degradation followed first order reaction. ZnO was found to be most efficient photo-catalyst for degrading these dyes. The optimal result for alizarin red S was k = 0.2118 min−1, t1/2 = 3.27 min, and R2 = 0.7998, for amaranth was k = 0.146 min−1, t1/2 = 4.74 min, and R2 = 0.8348, for congo red was k = 0.2452 min−1, t1/2 = 2.8 min, and R2 = 0.8382, and for rhodamine B was k = 0.1915 min−1, t1/2 = 3.6 min, and R2 = 0.76.

A review of smart electrospun fibers toward textiles

Electrospinning as a versatile technology has attracted a large amount of attention in the past few decades due to the facile way to produce micro- and nano-scale fibers featuring flexibility, large specific surface area and high porosity. Stimuli-responsive polymers are a class of smart materials that are capable of sensing surround environment and interacting with them. Therefore, the combination of electrospinning and smart materials could have a great deal of benefits over the development of smart fibers. In this review, it offers a comprehensive understanding of smart electrospun fibers toward textile applications. Firstly, the definition of smart fibers and the differences between interactive fibers and passive interactive fibers are briefly introduced. Then some interactive fibers made from temperature-, pH-, light-, electric field/electricity-, magnetic field-, multi-responsive polymers, as well as some polymers featuring piezoelectric and triboelectric effect which are suitable flexible electrics, are emphasized with their applications in the form of electrospun fibers. Afterwards, some passive and hybrid smart electrospun fibers are introduced. Finally, associated challenges and perspectives are summarized and discussed.

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Understanding of passive smart electrospun fibers and interactive smart electrospun fibers.

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The recent progress in flexible electronics from electrospun fibers.

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The recent progress in stimuli-responsive polymers applied in interactive smart electrospun fibers.

Application of a Photocatalyst as an Inactivator of Bovine Coronavirus

Bovine coronavirus (BCoV), a major causative pathogen of bovine enteric and respiratory diseases and a zoonotic pathogen transmissible between animals and humans, has led to severe economic losses in numerous countries. BCoV belongs to the genus Betacoronavirus, which is a model of a pathogen that is threatening human health and includes severe acute respiratory syndrome coronavirus (SARS-CoV), SARS-CoV-2, and Middle East respiratory syndrome coronavirus. This study aimed to determine whether photocatalytic material effectively reduces CoVs in the environment. Using the film adhesion method of photocatalytic materials, we assessed its antiviral activity and the effect of visible light irradiation according to methods defined by the International Organization for Standardization. Consequently, photocatalytic material was found to have antiviral activity, reducing the viral loads by 2.7 log TCID₅₀ (tissue culture infective dose 50)/0.1 mL (500 lux), 2.8 log TCID₅₀/0.1 mL (1000 lux), and 2.4 log TCID₅₀/0.1 mL (3000 lux). Hence, this photocatalytic material might be applicable not only to reducing CoVs in the cattle breeding environment but also perhaps in other indoor spaces, such as offices and hospital rooms. To our knowledge, this study is the first to evaluate the antiviral activity of a photocatalytic material against CoV.

Spectroscopic Measurements of Dissolved O3, H2O2 and OH Radicals in Double Cylindrical Dielectric Barrier Discharge Technology: Treatment of Methylene Blue Dye Simulated Wastewater

Advanced oxidation technologies (AOTs) focusing on nonthermal plasma induced by dielectric barrier discharge are adequate sources of diverse reactive oxygen species (ROS) beneficial for water and wastewater treatment. In this study, indigo, peroxytitanyl sulphate and terephthalic acid methods were used to approximate the concentrations of O3, H2O2 and OH produced in a double cylindrical dielectric barrier discharge (DCDBD) plasma configuration. The effect of pH and scavengers as well as the amount of chemical probes on the generation of oxidants was investigated. The efficiency of the DCDBD reactor was further evaluated using methylene blue (MB) as model pollutant. The results demonstrated that the formation of oxidants O3, H2O2 and OH in the DCDBD reactor was pH-dependent. Furthermore, the presence of scavengers such as phosphates, bicarbonates and carbonates in the solution diminished the amount of OH in the system and hence could impact upon the degree of detoxification of targeted pollutants during water and wastewater treatment. The MB simulated dye was totally decomposed into H2O, dissolved CO2 and simpler aqueous entities. Herein the DCDBD design is an adequate AOT that can be used worldwide for effective decontamination of water and wastewater.