The photodegradation of methylene blue in water with PVDF/GO/ZnO composite membrane

Modeling sustainable photocatalytic degradation of acidic dyes using Jordanian nano-Kaolin-TiO2 and solar energy: Synergetic mechanistic insights

The abstract highlights the global issue of environmental contamination caused by organic compounds and the exploration of various methods for its resolution. One such approach involves the utilization of titanium dioxide (TiO2) as a photocatalyst in conjunction with natural adsorption materials like kaolin. The study employed a modeling-based approach to investigate the sustainable photocatalytic degradation of acidic dyes using a Jordanian nano-kaolin-TiO2 composite material and solar energy. Mechanistic insights were gained through the identification of the dominant reactive oxygen species (ROS) involved in the degradation process, as well as the synergetic effect between adsorption and photocatalysis. The Jordanian nano-kaolin-TiO2 composite was synthesized using the sol-gel method and characterized. The nanocomposite photocatalyst exhibited particle sizes ranging from 27 to 41 nm, with the TiO2 nanoparticles well-dispersed within the kaolin matrix. The efficacy of this nanocomposite in removing Congo-red dye was investigated under various conditions, including pH, initial dye concentration, and photocatalyst amount. The optimal conditions for dye removal were found to be at pH 5, with an initial dye concentration of 20 ppm, and using 0.1 g of photocatalyst, resulting in a 95 % removal efficiency. The mechanistic insights gained from this study indicate that the hydroxyl radicals (•OH) generated during the photocatalytic process play a dominant role in the degradation of the acidic dye. Furthermore, the synergetic effect between the adsorption of the dye molecules onto the photocatalyst surface and the subsequent photocatalytic degradation by the ROS was found to enhance the overall removal efficiency. These findings contribute to the fundamental understanding of the photodegradation mechanisms and guide the development of more efficient photocatalytic systems for the treatment of acidic dye-containing wastewater. The use of solar power during the purification procedure also leads to cost reduction and strengthens sustainability efforts.

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Analysis of Ag-DP25/PET plasmonic nano-composites as a visible-light photocatalyst for wastewater treatment: Experimental/theoretical studies, and the DFT-MB degradation mechanism

The development of polymeric-composites Agx%DP25-PET (x = 0,1,2,3) may significantly boost the potential application of Agx%DP25 (x = 0,1,2,3) photocatalytic powders. Producing large-scale nano-composites with hybrid-surfaces, that are also flexible materials and easy to employ in a variety of environments. A set of photocatalytic nan-composites embedded with the polymeric binder poly (acrylonitrile-co-butadiene)-dicarboxy terminated (C7H9N) were performed and evaluated for wastewater treatment applications. The results reveal that the flexible polymeric composites (Agx%DP25-PET, x = 0,1,2,3) have photocatalytic activity in aqua media to degrade methylene blue (MB) under visible-light. The addition of C7H9N to immobilize photocatalytic powders on the PET surface reduces photo-generated electron-hole recombination. The materials were characterized by HR-TEM, SEM/EDX, XRD, FT-IR, UV-Vis DRS and PL. The Agx%DP25-PET (x = 0,1,2,3) photocatalytic reactions exhibited productive discoloration/degradation rates, in both aerobic (AE) and anaerobic (AN) environments. The superior photodegradation of Ag2%DP25-PET was attributed to a combination of two effects: LSPR (localized surface plasmon resonance) and Ag-TiO2/environment affinities. The findings of molecular dynamics (MD) simulation and Fukui Function (FF) based on density functional theory (DFT) provide significant insight into the photocatalytic requirements for MB discoloration/degradation. The experimental/theoretical analysis aimed to offer an in-depth understanding of medium/surface interactions on decorated TiO2 materials, as well as how these interactions affect overall degradation behavior.

The Hydrothermal-Assisted Approach Improves the Photocatalytic and Energy Storage Performance of Novel CuSe-TiO2-GO Composite

This study reports a novel CuSe-TiO2-GO composite, synthesized by a facile hydrothermal method at a controlled temperature, and investigates its electrochemical performance for supercapacitors (SCs) and photocatalytic behavior for degrading methylene blue (MB) dye. The compositional phase structure and chemical bond interaction were thoroughly investigated. The as-fabricated pristine, binary, and ternary composites underwent comprehensive characterization employing spectroscopic techniques and electrochemical analysis. Compared with pure and binary compounds (CuSe, TiO2, and binary CuSe-TiO2 composites), the ternary CuSe-TiO2-GO composites demonstrated a high degradation efficiency while degrading MB in less than just 80 min (240 min, 100 min, and 140 min, respectively). The photocatalytic activity of the ternary CuSe-TiO2-GO composites is enhanced due to the highly positive conduction band of CuSe, leading to the quick excitation of electrons to the conduction band of CuSe. Subsequently, graphene oxide (GO) left holes on the photocatalyst surface for MB, as GO assisted the photoexcited electron-hole pairs, resulting in enhanced photocatalytic performance. The CuSe-TiO2-GO electrode for the supercapacitor indicates a 310.6 F/g and 135.2 F/g capacitance when the discharge current upsurges from 1 to 12 A/g. The good photocatalytic and energy storage performance is due to the smaller charge transfer resistance, which promotes efficient separation of electron-hole pairs.

Sn(IV)porphyrin-Incorporated TiO2 Nanotubes for Visible Light-Active Photocatalysis

In this study, two distinct photocatalysts, namely tin(IV)porphyrin-sensitized titanium dioxide nanotubes (SnP-TNTs) and titanium dioxide nanofibers (TNFs), were synthesized and characterized using various spectroscopic techniques. SnP-TNTs were formed through the hydrothermal reaction of NaOH with TiO2 (P-25) nanospheres in the presence of Sn(IV)porphyrin (SnP), resulting in a transformation into Sn(IV)porphyrin-imbedded nanotubes. In contrast, under similar reaction conditions but in the absence of SnP, TiO2 (P-25) nanospheres evolved into nanofibers (TNFs). Comparative analysis revealed that SnP-TNTs exhibited a remarkable enhancement in the visible light photodegradation of model pollutants compared to SnP, TiO2 (P-25), or TNFs. The superior photodegradation activity of SnP-TNTs was primarily attributed to synergistic effects between TiO2 (P-25) and SnP, leading to altered conformational frameworks, increased surface area, enhanced thermo-chemical stability, unique morphology, and outstanding visible light photodegradation of cationic methylene blue dye (MB dye). With a rapid removal rate of 95% within 100 min (rate constant = 0.0277 min-1), SnP-TNTs demonstrated excellent dye degradation capacity, high reusability, and low catalyst loading, positioning them as more efficient than conventional catalysts. This report introduces a novel direction for porphyrin-incorporated catalytic systems, holding significance for future applications in environmental remediation.

Preparation of mixed matrix self-cleaning membrane incorporated by Z-scheme heterostructure via robust engineering in terms of dimension for decreasing cake fouling in a cross-flow reactor

Reducing irreversible fouling in polymer membranes by integrating photocatalytic and membrane processes as the self-cleaning photocatalytic membrane is a promising candidate for improving membrane filtration performance. In this study, mixed matrix photocatalytic membranes were prepared from the combination of different morphologies ZnO-g-C3N4 heterostructure in the polymer matrix by the phase-separation method. To investigate the self-cleaning and performance properties of mixed matrix photocatalytic membranes prepared from different morphologies heterostructures, the photocatalytic membrane reactor with a visible-light source was applied. Nanoflower/nanosheet (NF/NS) ZnO-g-C3N4 photocatalytic membrane showed good self-cleaning performance owing to the high photocatalytic performance of NF/NS ZnO-g-C3N4 heterostructure by the reduction of irreversible membrane fouling, thus improving the antifouling and filtration performance of the membrane. Also, the morphology and the uniform distribution of the NF/NS ZnO-g-C3N4 heterostructure in the membrane matrix caused good hydrophilic properties, high porosity, and a more symmetrical structure in the (NF/NS) ZnO-g-C3N4 photocatalytic membrane (F4). For the F4 membrane, the permeability and rejection values increased from 40.35 L m-2 h-1 and 90.9% in the dark environment to 84.37 L m-2 h-1 and 97.4% under visible-light for dye pollutants. Accordingly, F4 had the best filtration and self-cleaning performance, which can be used as a promising visible-light photocatalytic membrane in wastewater treatment processes.

In situ growth of BiOBr on copper foam conductive substrate with enhanced photocatalytic performance

Photocatalysis technology based on solar-powered semiconductors is widely recognized as a promising approach for achieving eco-friendly, secure, and sustainable degradation of organic contaminants. Nevertheless, conventional photocatalysts exhibit drawbacks such as a wide bandgap, and rapid recombination of photoinduced electron/hole pairs, in addition to complicated separation and recovery procedures. In this research, we cultivated BiOBr in situ on the surface of copper foam to fabricate a functional photocatalyst (denoted as BiOBr/Cu foam), which was subsequently employed for the photodegradation of Methylene Blue. Based on photodegradation experiments, the 0.3 BiOBr/Cu foam demonstrates superior photocatalytic efficacy compared to other photocatalysts under solar light irradiation. Furthermore, its ease of separation from the solution enhances its potential for reuse. The analysis of charge transfer revealed that the copper foam functions as an effective electron scavenger within the BiOBr/Cu foam, thereby facilitating charge separation and the generation of photo-induced holes. This phenomenon contributes to a significantly enhanced production of hydroxyl radicals. This study provides a valuable perspective on the design and synthesis of photocatalysts with heightened practicality, employing a conductive substrate.

Recent advances in visible light-activated photocatalysts for degradation of dyes: A comprehensive review

The rapid development in industrialization and urbanization coupled with an ever-increasing world population has caused a tremendous increase in contamination of water resources globally. Synthetic dyes have emerged as a major contributor to environmental pollution due to their release in large quantities into the environment, especially owing to their high demand in textile, cosmetics, clothing, food, paper, rubber, printing, and plastic industries. Photocatalytic treatment technology has gained immense research attention for dye contaminated wastewater treatment due to its environment-friendliness, ability to completely degrade dye molecules using light irradiation, high efficiency, and no generation of secondary waste. Photocatalytic technology is evolving rapidly, and the foremost goal is to synthesize highly efficient photocatalysts with solar energy harvesting abilities. The current review provides a comprehensive overview of the most recent advances in highly efficient visible light-activated photocatalysts for dye degradation, including methods of synthesis, strategies for improving photocatalytic activity, regeneration and their performance in real industrial effluent. The influence of various operational parameters on photocatalytic activity are critically evaluated in this article. Finally, this review briefly discusses the current challenges and prospects of visible-light driven photocatalysts. This review serves as a convenient and comprehensive resource for comparing and studying the fundamentals and recent advancements in visible light photocatalysts and will facilitate further research in this direction.

Preparation of 1,8-dichloroanthraquinone/graphene oxide/poly (vinylidene fluoride) (1,8-AQ/GO/PVDF) mediator membrane and its application to catalyzing biodegradation of azo dyes

Anthraquinone is a redox mediator that can effectively catalyze the degradation of azo dyes by promoting the electron transfer. In this study, a mediator membrane with poly (vinylidene fluoride) (PVDF) as the membrane support and 1,8-dichloroanthraquinone (1,8-AQ) and graphene oxide (GO) as the additives was prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), atomic force microscopy (AFM) and water contact angle. The introduction of GO increases the pure water flux of the membrane to 258.56±12.93 L/(m2·h). Its catalytic performances for the biodegradation of azo dyes were evaluated. Under the optimized conditions, the 1,8-AQ/GO/PVDF composite membrane is able to improve the dye degradation efficiency 2.2 times for reactive red X-3B and 1.1 times for acid red B, as compared with PVDF membrane. In addition, the mediator membrane maintains stable and high catalytic efficiency in the cyclic test and over 90 % dye degradation efficiency is still obtained after 5 cycles of decolorization. These results suggest the great application potentials of the 1,8-AQ/GO/PVDF membrane in the dye wastewater treatment.

Facile Preparation of PVDF/CoFe2O4-ZnO Hybrid Membranes for Water Depollution

In this investigation, CoFe2O4-PVDF and CoFe2O4-ZnO-PVDF hybrid membranes were prepared using a modified phase inversion method in which a magnetic field was applied during the casting process to ensure a uniform distribution of nanomaterials on the membrane surface. Thus, better absorption of light and increased participation of nanoparticles in the photodegradation process is ensured. The influence of nanomaterials on the crystalline structure, surface morphology, and hydrophilicity properties of the PVDF membrane was investigated. The obtained results indicated that the hybrid membrane exhibited significant differences in its intrinsic properties due to the nanomaterials addition. The hydrophilicity properties of the PVDF membrane were improved by the presence of nanoparticles. The photocatalytic decomposition of aqueous Rhodamine B solution in the presence of the prepared membrane and under visible light irradiation was tested. The hybrid membrane containing CoFe2O4-ZnO on its surface exhibited a high removal rate.

Cellulose acetate/polyurethane blend as support matrix with high optical transparency and improved mechanical properties for photocatalyst CeO2 nanoparticles immobilization

Advanced manufacturing technologies for efficient catalytic materials have triggered the rational design of catalysts as well as extensive investigation into preparative methodologies. Herein, we report the preparation of new versatile cellulose acetate/polyurethane (CA/PU) blends for efficient immobilization of CeO2 nanoparticles, the appropriate composition of polymer mixture being chosen after rigorous analysis (SEM, FTIR, optical, mechanical). The band gap energy for hybrid films ranged between 3.02 eV and 2.05 eV, the lowest value being measured for the film with Co-doped CeO2 NPs (B3 film). The best results in photodegradation of methylene blue under visible-light irradiation was attained after 50 min for B3 film (rate constant k = 45.34× 10-3 min-1), while the total mineralization of MB in the same conditions as evaluated by HPLC-ESI MS and TOC analyses was achieved after 90 min. Effect of co-ions (SO42-, Cl- or NO3-) on photocatalytic performance was studied, and scavenger tests were used to identify the active species involved in the photocatalytic mechanism. Also, the photocatalytic efficiency of B3 sample was tested for rhodamine B, metronidazole and 4-nitrophenol degradation. Evaluation of the stability and integrity of hybrid film after 5 catalysis cycles reveal that the photocatalytic potential is retained with no substantial structural changes.

Theoretical and experimental studies on photocatalytic removal of methylene blue (MetB) from aqueous solution using oyster shell synthesized CaO nanoparticles (CaONP-O)

The development of technologies for the removal of dye from aqueous solution is most desirable if the end product is relatively green (i.e., environmentally friendly). Photodegradation (as one of such technology) and photolysis (without the catalyst) was applied to investigate the role of sol-gel synthesized calcium oxide nanoparticle (using the oyster shell as the precursor). The results obtained gave substantial evidence that calcium oxide nanoparticles catalyzed the degradation of the methylene blue dye up to a maximum percentage of 98 % removal. Degradation efficiency displayed a strong dependency on time, initial dye concentration, catalyst load, pH, and ionic strength. Chi-square and sum of square error analysis indicated that the photodegradation kinetics fitted the Langmuir-Hinshelwood, first order, and pseudo first-order models best. The half-life of the dye was significantly reduced from hours to minutes due to photocatalysis. Quantum chemical calculations indicated that the degradation proceeded through adsorption, deformation/degradation, and desorption through the chloride end of the molecule linked to the calcium active center of the catalyst. Results from Fukui functions and molecular descriptors analysis confirmed the mechanism of photocatalysis.

Radiation synthesis and photocatalytic performance of floated graphene oxide decorated ZnO/ alginate-based beads for methylene blue degradation under visible light irradiation

Organic dye contamination, emanating from pharmaceutical, paper, and textile industries into water resources, severely threatens marine and human life even at low concentrations. Photocatalysis is one of the most important remediation techniques that decolorize water by employing the power of light. In this work, the development of floated beads of Sodium Alginate/hydroxyethyl methacrylate (Alg-g-HEMA) encompass graphene oxide (GO) decorated Zinc oxide (ZnO) utilizing ionizing radiation was designed to function as a photocatalyst when exposed to visible light. Floatability was induced using calcium carbonate. GO was sonochemically decorated with ZnO nanoparticles and the yield was characterized using XRD, FTIR, TEM, SEM, and EDX techniques. Optical characteristics of the developed nanostructure were performed using UV-Vis spectrophotometry. The photocatalytic activity of the floated (Alg-g-HEMA)-ZnO@GO beads was assessed for the photo decolorization of methylene blue dye (MB) under visible light. The upshot of operational factors such as photocatalyst dose, pH, initial dye concentration, and irradiation time on the decolorization of MB was examined. It was observed that 1 g of the developed (Alg-g-HEMA)-ZnO@GO photocatalyst was able to decolorize 1000 ml of 20 ppm of MB within 150 min at pH 9. In terms of kinetics, photo-decolorization follows Langmuir Hinshelwood pseudo-first order.

Improved water purification by PVDF ultrafiltration membrane modified with GO-PVA-NaAlg hydrogel

This work presents a modified polyvinylidene fluoride (PVDF) ultrafiltration membrane blended with graphene oxide-polyvinyl alcohol-sodium alginate (GO-PVA-NaAlg) hydrogel (HG) and polyvinylpyrrolidone (PVP) prepared by the immersion precipitation induced phase inversion approach. Characteristics of the membranes with different HG and PVP concentrations were analyzed by field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), contact angle measurement (CA), and Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The FESEM images showed an asymmetric structure of the fabricated membranes, and possessing a thin dense layer over the top and a layer finger-like. With increasing HG content, membrane surface roughness increases so that highest surface roughness for the membrane containing 1wt% HG is with a Ra value of 281.4 nm. Also, the contact angle of the membrane reaches from 82.5° in bare PVDF membrane to 65.1° in the membrane containing 1wt% HG. The influences of adding HG and PVP to the casting solution on pure water flux (PWF), hydrophilicity, anti-fouling ability, and dye rejection efficiency were evaluated. The highest water flux reached 103.2 L/m² h at 3 bar for the modified PVDF membranes containing 0.3 wt% HG and 1.0wt% PVP. This membrane exhibited a rejection efficiency of higher than 92%, 95%, and 98% for Methyl Orange (MO), Conge Red (CR), and Bovine Serum Albumin (BSA), respectively. All nanocomposite membranes possessed a flux recovery ratio (FRR) higher than bare PVDF membranes, and the best anti-fouling performance of 90.1% was relevant to the membrane containing 0.3 wt% HG. The improved filtration performance of the HG-modified membranes was due to the enhanced hydrophilicity, porosity, mean pore size, and surface roughness after introducing HG.

Modified poly(vinylidene fluoride) nanomembranes for dye removal from water - A review

Water contamination due to soluble synthetic dyes has serious concerns. Membrane-based wastewater treatments are emerging as a preferred choice for removing dyes from water. Poly(vinylidene fluoride) (PVDF)-based nanomembranes have gained much popularity due to their favorable features. This review explores the application of PVDF-based nanomembranes in synthetic dye removal through various treatments. Different fabrication methods to obtain high performance PVDF-based nanomembranes were discussed under surface coating and blending methods. Studies related to use of PVDF-based nanomembranes in adsorption, filtration, catalysis (oxidant activation, ozonation, Fenton process and photocatalysis) and membrane distillation have been elaborately discussed. Nanomaterials including metal compounds, metals, (synthetic/bio)polymers, metal organic frameworks, carbon materials and their composites were incorporated in PVDF membrane to enhance its performance. The advantages and limitations of incorporating nanomaterials in PVDF-based membranes have been highlighted. The influence of nanomaterials on the surface features, mechanical strength, hydrophilicity, crystallinity and catalytic ability of PVDF membrane was discussed. The conclusion of this literature review was given along with future research.

Photo-Oxidation of Organic Dye by Fe2O3 Nanoparticles: Catalyst, Electron Acceptor, and Polyurethane Membrane (PU-Fe2O3) Effects

The textile industry’s discharges have long been regarded as severe water pollution. The photocatalytic degradation of dyes using semiconductors is one of the crucial methods. The present study efficiently used the mechanical method to synthesize Iron oxide Nanoparticles. XRD, FT-IR, UV-Vis DRS, and Raman analyses were performed to analyze the structural and optical. From the data provided by XRD and Raman data, we believed that the as-synthesized Iron oxide was pure hematite (α-Fe2O3) with a hexagonal structure. Additionally, the EDS results show that the synthesized material is pure. By adjusting specific parameters, including the dye concentration, the catalyst dosage, the pH, and the oxidizing agent such as H2O2 and K2S2O8, the degradation of eosin yellowish using Fe2O3 as a photocatalyst has been discussed. Additionally, the kinetics of eosin yellowish degradation has been studied. A study was also conducted using Fe2O3 nanoparticles attached to polyurethane polymer (PU) to investigate its photocatalytic activity on methylene blue, methyl orange, and indigo carmine. In 30 minutes, nearly 90% of the dyes had degraded. The total organic carbon (TOC) analysis confirmed this result.

Piezo-, photo- and piezophotocatalytic activity of electrospun fibrous PVDF/CTAB membrane

A composite material based on polyvinylidene fluoride (PVDF) nanofibers modified with cetyltrimethylammonium bromide (CTAB) was synthesized by coaxial electrospinning. The morphology and structure of the material were studied by SEM, FTIR spectroscopy, X-ray diffraction analysis, XPS, and the piezo-photo- and piezo-photocatalytic activity during the decomposition of the organic dye Methylene blue (MB) was studied. It is shown that the addition of CTAB promotes additional polarization of the PVDF structure due to ion-dipole interaction. It has been shown for the first time that the addition of CTAB promotes the photosensitivity of the wide-gap dielectric polymer PVDF (the band gap is more than 6 eV). It was demonstrated that the photocatalytic decomposition efficiency was 91% in 60 minutes. The material exhibits piezocatalytic activity – 73% in 60 minutes. Experiments on trapping active oxidizing forms have established that OH hydroxyl radicals play the main role in the photocatalytic process.

Classification of Nanomaterials and the Effect of Graphene Oxide (GO) and Recently Developed Nanoparticles on the Ultrafiltration Membrane and Their Applications: A Review

The emergence of mixed matrix membranes (MMMs) or nanocomposite membranes embedded with inorganic nanoparticles (NPs) has opened up a possibility for developing different polymeric membranes with improved physicochemical properties, mechanical properties and performance for resolving environmental and energy-effective water purification. This paper presents an overview of the effects of different hydrophilic nanomaterials, including mineral nanomaterials (e.g., silicon dioxide (SiO2) and zeolite), metals oxide (e.g., copper oxide (CuO), zirconium dioxide (ZrO2), zinc oxide (ZnO), antimony tin oxide (ATO), iron (III) oxide (Fe2O3) and tungsten oxide (WOX)), two-dimensional transition (e.g., MXene), metal-organic framework (MOFs), covalent organic frameworks (COFs) and carbon-based nanomaterials (such as carbon nanotubes and graphene oxide (GO)). The influence of these nanoparticles on the surface and structural changes in the membrane is thoroughly discussed, in addition to the performance efficiency and antifouling resistance of the developed membranes. Recently, GO has shown a considerable capacity in wastewater treatment. This is due to its nanometer-sized holes, ultrathin layer and light and sturdy nature. Therefore, we discuss the effect of the addition of hydrophilic GO in neat form or hyper with other nanoparticles on the properties of different polymeric membranes. A hybrid composite of various NPs has a distinctive style and high-quality products can be designed to allow membrane technology to grow and develop. Hybrid composite NPs could be used on a large scale in the future due to their superior mechanical qualities. A summary and future prospects are offered based on the current discoveries in the field of mixed matrix membranes. This review presents the current progress of mixed matrix membranes, the challenges that affect membrane performance and recent applications for wastewater treatment systems.

Synthesis and characterization of a novel composite of rice husk-derived graphene oxide with titania microspheres (GO-RH/TiO2) for effective treatment of cationic dye methylene blue in aqueous solutions

Graphene oxide (GO) was synthesized utilizing rice husk (RH) as the starting raw material via a modified Hummers' method. Ground pencil leads were used as a control powder of the starting raw material to monitor the consistency of the synthesis method. TiO₂ microspheres were synthesized via a precipitated method using the pluronic F127 solution as the pore template. GO derived from RH (GO-RH) was composited with TiO₂ microspheres as GO-RH/TiO₂ composites by an impregnation method with weight ratios of 3:1, 2:2, and 1:3. Characterized results revealed GO-RH formed a ternary phase material of graphene oxide, graphite oxide, and silica. A typical microstructure of the calcined TiO₂ microspheres was found as the agglomerated anatase nanoparticles. Furthermore, the composites belong to large surface areas and numerous oxygen-containing functionalities on their surfaces. Removal efficiencies of cationic dye methylene blue (MB) from aqueous solutions by the composites, GO-RH and TiO₂, were studied under UV illumination for 180 min. Due to the effective combination of adsorption and photodegradation for the MB removal, the composites provided the higher efficiencies (99-100%) faster than those of GO-RH and TiO₂ and could be reused at least 4 times. Finally, a mechanism of the MB removal by the composites was proposed.

Investigation on the feasibility of recycled polyvinylidene difluoride polymer from used membranes for removal of methylene blue: experimental and DFT studies

This study reports the feasibility of recycled polyvinylidene difluoride (PVDF) beads to decolourize methylene blue (MB) from aqueous streams. The beads were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR) for its morphological and structural analysis. The effect of various process parameters such as adsorbent dose, initial concentration, contact time, and pH was studied. The first principle density functional theory (DFT) calculations were performed to investigate the underlying mechanism behind the adsorption process. The MB dye adsorption on recycled PVDF beads followed the pseudo-second-order kinetics and Langmuir isotherm, indicating the adsorption was chemical and monolayer. The maximum adsorption capacity obtained was 27.86 mg g^-1. The adsorption energy of MB-PVDF predicted from the DFT study was -64.7 kJ mol^-1. The HOMO-LUMO energy gap of PVDF decreased from 9.42 eV to 0.50 eV upon interaction with MB dye due to the mixing of molecular orbitals. The DFT simulations showed that the interaction of the MB dye molecule was from the electronegative N atom of the MB dye molecule, implying that electrostatic interactions occurred between the recycled PVDF beads and the positively charged quaternary ammonium groups in MB dye. The present study demonstrates the potential of recycled PVDF beads for a low-cost dye removal technique from textile wastewater.

High-performance photocatalytic membranes for water purification in relation to environmental and operational parameters

Growing technologies, increasing population and environmental pollution lead to severe contamination of water and require advanced water treatment technologies. These aspects lead to the need to purify water with advanced smart materials. This paper reviews the recent advances (during the last 5 years) in photocatalytic composite membranes used for water treatment. For this purpose, the authors have reviewed the main materials used in the development of (photocatalytic membranes) PMs, environmental and operational factors affecting the performance of photocatalytic membranes, and the latest developments and applications of PMs in water purifications. The composite photocatalytic membranes show good performance in the removal and degradation of pollutants from water.

Efficient Removal of Methylene Blue Using Living Biomass of the Microalga Chlamydomonas moewusii: Kinetics and Equilibrium Studies

The efficiency of the living biomass of the microalga Chlamydomonas moewusii in removing methylene blue dye is determined. The kinetics, equilibrium isotherms, and the effects on this process of the pH, contact time, and initial concentration of the dye are studied. Fourier transform infrared spectrometry and point of zero charge are used to characterize the biomass and explore the process. The maximum removal capacity derived from the Langmuir isotherm is 212.41 ± 4.55 mg/g after 7 h of contact time at pH 7. The removal process is rapid because kinetic studies revealed that the best fit of the data is with pseudo-third-order kinetics. The removal efficiency is dependent on the pH; as the pH increased, the efficiency is higher. These results show that the living biomass of this microalga is a very efficient biosorbent and therefore very suitable for the removal of methylene blue from aqueous solutions.

Photocatalytic Filtration of Zinc Oxide-Based Membrane with Enhanced Visible Light Responsiveness for Ibuprofen Removal

The growing interest in mixed matrix membranes (MMMs) for developing photocatalytic membranes has provided a new direction in the search for efficient methods to concurrently separate and degrade contaminants. In this study, a visible light-responsive photocatalyst was blended into a polyvinylidene fluoride (PVDF) membrane casting solution to prepare PVDF-ZnO/Ag2CO3/Ag2O MMMs using the wet phase inversion method. The potential of ZnO/Ag2CO3/Ag2O as a photocatalytic component that is incorporated into the membrane was explored in detail under various loadings (0.5–2.91 wt%). The membranes were tested under ibuprofen (IBF) aqueous solution to analyze the membrane behavior in the synergistic combination of membrane filtration and photodegradation. The resulting PVDF-ZnO/Ag2CO3/Ag2O membrane with a rougher membrane surface area and excellent light harvesting capability showed higher photocatalytic filtration activity in removing IBF under visible light irradiations. The MMM fluxes demonstrated higher IBF fluxes than their initial fluxes at certain durations. This indicates that the membrane actively responds to light irradiation. The increase in the positive flux could be attributed to the photoinduced hydrophilicity generated by the ZnO/Ag2CO3/Ag2O photocatalyst, resulting in easier water layer formation and rapid transport through membranes. The highest IBF removal was demonstrated by the PVDF‑ZAA2 membrane (1.96 wt% loading), with 49.96% of IBF removal within 180 min upon visible light irradiation. The reason for this lower IBF removal is that the UF membrane pores exceed the size of IBF molecules, thereby preventing the size exclusion mechanism. Thus, charge repulsion, hydrophobic adsorption, and photocatalytic activity were considered along with the IBF removal of the photocatalytic membranes. However, the recyclability of the PVDF‑ZAA2 photocatalytic membrane showed a great improvement, with 99.01% of IBF removal recovery after three cycles. These results highlight the potential of such hybrid membranes in mitigating membrane fouling by providing a platform for photocatalysts to continuously degrade pollutants present in such wastewaters. Therefore, the hybridization of a photocatalyst and membrane provides insight that could be utilized to improve and retrofit current water effluent treatment methods.

A review of graphene-TiO2 and graphene-ZnO nanocomposite photocatalysts for wastewater treatment

Technologies for wastewater remediation have been growing ever since the environmental and health concern is realized. Development of nanomaterials has enabled mankind to have different methods to treat the various kinds of inorganic and organic pollutants present in wastewater from many resources. Among the many materials, semiconductor materials have found many environmental applications due to their outstanding photocatalytic activities. TiO₂ and ZnO are more effectively used as photocatalyst or adsorbents in the withdrawal of inorganic as well as organic wastes from the wastewater. On the other hand, graphene is tremendously being investigated for applications in environmental remediation in view of the superior physical, optical, thermal, and electronic properties of graphene nanocomposites. In this work, graphene-TiO₂ and graphene-ZnO nanocomposites have been reviewed for photocatalytic wastewater treatment. The various preparation techniques of these nanocomposites have been discussed. Also, different design strategies for graphene-based photocatalyst have been revealed. These nanocomposites exhibit promising applications in most of the water purification processes which are reviewed in this work. Along with this, the development of these nanocomposites using biomass-derived graphene has also been introduced. PRACTITIONER POINTS: Graphene-TiO₂ and graphene-ZnO nanocomposites are effective for wastewater treatment through photocatalysis. These nanocomposite photocatalysts have been used in the form of membrane as well as antibacterial agents. Synthetic strategies and design considerations of graphene-based photocatalyst play a major role. Biomass-derived graphene-TiO₂ and graphene-ZnO nanocomposites have also found application in wastewater treatment.

Visible Light-Driven GO/TiO2-CA Nano-Photocatalytic Membranes: Assessment of Photocatalytic Response, Antifouling Character and Self-Cleaning Ability

Photocatalysis and membrane technology in a single unit is an ideal strategy for the development of wastewater treatment systems. In this work, novel GO (x wt%)/TiO2-CA hybrid membranes have been synthesized via a facile non-solvent induced phase inversion technique. The strategy aimed to address the following dilemmas: (1) Effective utilization of visible light and minimize e-/h+ recombination; (2) Enhanced separation capability and superior anti-fouling and self-cleaning ability. The experimental results reveal that the integration of nano-composite (GO/TiO2) boosts the membrane properties when compared to pristine CA and single photocatalyst employed membrane (GO-CA and TiO2-CA). The effect of GO content on the properties of the photocatalytic membrane has been determined by utilizing three different ratios of GO, viz. 0.5 wt%, 1 wt%, and 2 wt% designated as NC(1)-CA, NC(2)-CA, and NC(3)-CA, respectively. Amongst them, NC(3)-CA membrane showed state-of-the-art performance with an elevated photocatalytic response (four times higher than pristine CA membrane) toward methyl orange. Moreover, the water flux of NC(3)-CA membrane is 613 L/m2h, approximately three times higher than bare CA membrane (297 L/m2h), while keeping the MO rejection high (96.6%). Besides, fouling experiments presented the lowest total and fouling resistance ratios and a higher flux recovery ratio (91.78%) for the NC(3)-CA membrane, which endows the membrane with higher anti-fouling and self-cleaning properties. Thus, NC(3)-CA membrane outperforms the other as synthesized membranes in terms of separation efficiency, visible light photo-degradation of pollutant, anti-fouling and self-cleaning ability. Therefore, NC(3)-CA membrane is considered as the next generation membrane for exhibiting great potential for the wastewater treatment applications.

Tamisolve® NxG as an Alternative Non-Toxic Solvent for the Preparation of Porous Poly (Vinylidene Fluoride) Membranes

Tamisolve^® NxG, a well-known non-toxic solvent, was used for poly(vinylidene fluoride) (PVDF) membranes preparation via a non-solvent-induced phase separation (NIPS) procedure with water as a coagulation bath. Preliminary investigations, related to the study of the physical/chemical properties of the solvent, the solubility parameters, the gel transition temperature and the viscosity of the polymer-solvent system, confirmed the power of the solvent to solubilize PVDF polymer for membranes preparation. The role of polyvinylpyrrolidone (PVP) and/or poly(ethylene glycol) (PEG), as pore former agents in the dope solution, was studied along with different polymer concentrations (10 wt%, 15 wt% and 18 wt%). The produced membranes were then characterized in terms of morphology, thickness, porosity, contact angle, atomic force microscopy (AFM) and infrared spectroscopy (ATR-FTIR). Pore size measurements, pore size distribution and water permeability (PWP) tests placed the developed membranes in the ultrafiltration (UF) and microfiltration (MF) range. Finally, PVDF membrane performances were investigated in terms of rejection (%) and permeability recovery ratio (PRR) using methylene blue (MB) in water solution to assess their potential application in separation and purification processes.

UV Photochromism in Transition Metal Oxides and Hybrid Materials

Limited levels of UV exposure can be beneficial to the human body. However, the UV radiation present in the atmosphere can be damaging if levels of exposure exceed safe limits which depend on the individual the skin color. Hence, UV photochromic materials that respond to UV light by changing their color are powerful tools to sense radiation safety limits. Photochromic materials comprise either organic materials, inorganic transition metal oxides, or a hybrid combination of both. The photochromic behavior largely relies on charge transfer mechanisms and electronic band structures. These factors can be influenced by the structure and morphology, fabrication, composition, hybridization, and preparation of the photochromic materials, among others. Significant challenges are involved in realizing rapid photochromic change, which is repeatable, reversible with low fatigue, and behaving according to the desired application requirements. These challenges also relate to finding the right synergy between the photochromic materials used, the environment it is being used for, and the objectives that need to be achieved. In this review, the principles and applications of photochromic processes for transition metal oxides and hybrid materials, photocatalytic applications, and the outlook in the context of commercialized sensors in this field are presented.

Photocatalytic self-cleaning properties of m-phenylene isophthalamide membranes enhanced by immobilization of GO-ZnO-Ag for dye wastewater disposal

Drawing self-cleaning technology into polymer membranes offers an extensive solution to overcome the membrane fouling obstacle. Herein, the GO-ZnO-Ag nano-hybrid particles with photocatalytic activity prepared via the microwave hydrothermal method were immobilized in poly(m-phenylene isophthalamide) (PMIA) membranes. Not only was the thorny issue in catalyst recovery avoided, but also the satisfactory photocatalytic self-cleaning performance of the polymer membrane was awarded. GO and noble metal silver nanoparticles (AgNPs) acted as a conductive electron transfer carrier and an electron host, respectively, which hindered the recombination rate of excited electrons and holes on ZnO under UV light. The UV-driven PMIA membrane photodegradation rates of MB and Cr(VI) were up to 97.2% and 94.3%, respectively, at 150 min on photodegradation kinetics. Also, MB was completely degraded at 180 min. For MB and Cr(VI) mix solutions, their degradation efficiencies were 78.1% and 71%, respectively. The BSA rejection rate of the modified polymer membrane was 93.8%, and the water flux was 408.8 (L·m−2·h−1). Permeability was maintained at a high level after repeated use. Therefore, the newly designed PMIA/GO-ZnO-Ag series membranes could expand the application of polymers in wastewater disposal industry.

Integrated photocatalysis-adsorption-membrane separation in rotating reactor for synergistic removal of RhB

A synergistic system of integrated photocatalysis-adsorption-membrane separation in a rotating reactor was designed. The composite membrane was prepared via filtration process under vacuum, and it was composed of graphene oxide (GO) acted as the separation membrane, activated carbon (AC) as the adsorbent and Ag@BiOBr as the photocatalyst, respectively. In this Ag@BiOBr/AC/GO membrane system, rotation of the membrane could avoid the light-shielding effect from organic color pollutants to achieve the complete removal of pollutants. More importantly, the synergistic effect among photocatalysis, adsorption and membrane separation in rotating reactor was significant for the efficient removal of rhodamine B (RhB). In the Ag@BiOBr/AC/GO composite membrane, GO membrane layer could reject the organic molecular by the assistance of AC layer with efficient adsorption capacity, and Ag@BiOBr at outer layer could photodegrade the organics under visible light irradiation. The photocatalysis process could solve the problem of membrane fouling and adsorption could assist GO membrane for stopping the permeation of pollutants. Meanwhile, GO membrane was not only beneficial for catalyst recovery, but also could concentrate the pollutants via the membrane separation to accelerate the photocatalytic degradation. At the same time, both the photocatalysis degradation and membrane separation could promote the adsorption ability of AC. This synergistic system showed the significant potential for the practical application in the future.

The photocatalytic activity of the SnO2/TiO2/PVDF composite membrane in rhodamine B degradation

The immobilization of photocatalysts is considered an effective approach to solve the problem of the difficult recycling of powdered nanocatalysts after photocatalytic degradation.

Preparation of PVDF/CdS/Bi2WO6/ZnO hybrid membrane with enhanced visible-light photocatalytic activity for degrading nitrite in water

In this work, a visible light-driven ternary heterojunction photocatalyst, CdS/Bi₂WO₆/ZnO, was synthesized using hydrothermal, ultrasonic dispersion, and deposition precipitation methods. The results show that photocatalysts with flower-like heterostructures were obtained, which could efficiently separate electron-hole pairs, and the photocatalytic activity was thereby significantly enhanced. Furthermore, CdS/Bi₂WO₆/ZnO and polyvinylidene fluoride (PVDF) were used to fabricate hybrid membranes via a phase-conversion method. The samples were characterized using SEM, TEM, EDX, XRD, DRS, XPS, PL, and N₂ adsorption-desorption isotherms, and the transient photocurrent response. The photocatalytic activity of the hybrid membrane was evaluated, and 92.58% of the nitrite was converted into non-toxic substances within 4 h under simulated sunlight irradiation. This result indicated that the photocatalyst exhibited a good photocatalytic activity after immobilization. The possible mechanism was elucidated by studying the product during the photocatalytic degradation, and the effects of different pH values, electron scavengers, and hole scavengers on the photocatalytic performance were further investigated.

Engineering and Characterization of Antibacterial Coaxial Nanofiber Membranes for Oil/Water Separation

In the present study, a coaxial nanofiber membrane was developed using the electrospinning technique. The developed membranes were fabricated from hydrophilic cellulose acetate (CA) polymer and hydrophobic polysulfone (PSf) polymer as a core and shell in an alternative way with addition of 0.1 wt.% of ZnO nanoparticles (NPs). The membranes were treated with a 2M NaOH solution to enhance hydrophilicity and thus increase water separation flux. Chemical and physical characterizations were performed, such as Fourier transform infrared (FTIR) spectroscopy, and surface wettability was measured by means of water contact angle (WCA), mechanical properties, surface morphology via field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and microscopy energy dispersive (EDS) mapping and point analysis. The results show higher mechanical properties for the coaxial nanofiber membranes which reached a tensile strength of 7.58 MPa, a Young's modulus of 0.2 MPa, and 23.4 M J.m-3 of toughness. However, treated mebranes show lower mechanical properties (tensile strength of 0.25 MPa, Young's modulus of 0.01 MPa, and 0.4 M J.m-3 of toughness). In addition, the core and shell nanofiber membranes showed a uniform distribution of coaxial nanofibers. Membranes with ZnO NPs showed a porous structure and elimination of nanofibers after treatment due to the formation of nanosheets. Interestingly, membranes changed from hydrophobic to hydrophilic (the WCA changed from 90 ± 8° to 14 ± 2°). Besides that, composite nanofiber membranes with ZnO NPs showed antibacterial activity against Escherichia coli. Furthermore, the water flux for the modified membranes was improved by 1.6 times compared to the untreated membranes.

Enhanced antifouling performance of PVDF ultrafiltration membrane by blending zinc oxide with support of graphene oxide nanoparticle

This paper reports a novel nanocomposite additive for a polyvinylidene fluoride (PVDF) membrane with high hydrophilicity through the association of graphene oxide (GO) and ZnO. The influence of the hydrophilicity of GO-ZnO on the PVDF membrane was examined on different GO-ZnO loadings. The porosity and wettability (or hydrophilicity) of the membrane were improved significantly by blending GO-ZnO nanocomposite. In addition, the water flux of the GO-ZnO/PVDF membrane was 48% higher than that of bare PVDF, and the anti-fouling properties of this modified membrane were also improved. The irreversible fouling ratio (Rir) of bovine serum albumin (BSA) was reduced substantially with increasing the loading of GO-ZnO nanocomposite. The lowest irreversible fouling ratio (7.21%) was obtained for the membrane containing 0.2 wt % GO-ZnO of the nanocomposite (M6). GO-ZnO modification PVDF membranes were assumed to reduce the affinity between membrane and BSA foulant, which improved the anti-fouling properties PVDF membrane. In the activated sludge flux test, the membrane containing GO-ZnO in the polymer matrix had a higher flux than that of the bare PVDF membrane. The effluent quality after the composite membrane (0.6 NTU) was stable, indicating that the composite membrane can be used for practical applications Overall, the properties of the PVDF membrane were improved after modification due to hydrogen bonding or the hydrophilicity of the GO-ZnO nanocomposite.

Effects of ultrasonication duration and graphene oxide and nano-zinc oxide contents on the properties of polyvinyl alcohol nanocomposites

Nanofibrous composite membranes consisting of polyvinyl alcohol (PVA), graphene oxide (GO), and zinc oxide nanoparticles (ZnO NPs) were prepared by and ultrasonic processing, and electrospinning. The performance of the membranes containing different GO-to-ZnO NP mass ratios was comprehensively investigated in terms of density, mechanical properties, water vapor permeability, optical property, biodegradability and antimicrobial properties. The results showed that an appropriate sonication time (30 min) improved the membrane performance; the composite nanofibrous membrane with a GO-to-ZnO NP mass ratio of 3:7 and 30 min sonication exhibited the best performance with a water vapor permeability of (0.62 ± 0.01) × 10^-2 g·h^-1 m^-2 pa^-1, and strain and stress values of 307.84 ± 2.96% and 12.82 ± 0.56 MPa, respectively. Particularly, the UV barrier property of the composite nanofibrous membrane was enhanced. Furthermore, the membrane exhibited strong antibacterial activity against foodborne pathogenic and spoilage bacteria. Thu, it can thus be used as an active food packaging material to ensure the safety of food products and to extend their shelf-life.