Reduced graphene oxide-based composite membranes for in-situ catalytic oxidation of sulfamethoxazole operated in membrane filtration

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.

Cobalt oxide functionalized ceramic membrane for 4-hydroxybenzoic acid degradation via peroxymonosulfate activation

Membrane separation and sulfate radicals-based advanced oxidation processes (SR-AOPs) can be combined as an efficient technique for the elimination of organic pollutants. The immobilization of metal oxide catalysts on ceramic membranes can enrich the membrane separation technology with catalytic oxidation avoiding recovering suspended catalysts. Herein, nanostructured Co₃O₄ ceramic catalytic membranes with different Co loadings were fabricated via a simple ball-milling and calcination process. Uniform distribution of Co₃O₄ nanoparticles in the membrane provided sufficient active sites for catalytic oxidation of 4-hydroxybenzoic acid (HBA). Mechanistic studies were conducted to determine the reactive radicals and showed that both SO₄^•- and ^•OH were present in the catalytic process while SO₄^•- plays the dominant role. The anti-fouling performance of the composite Co@Al₂O₃ membranes was also evaluated, showing that a great flux recovery was achieved with the addition of PMS for the fouling caused by humic acid (HA).

Magnesium Ortho-Vanadate/Magnesium Oxide/Graphene Oxide Embedded through Cellulose Acetate-Based Films for Wound Healing Applications

A multifunctional nano-films of cellulose acetate (CA)/magnesium ortho-vanadate (MOV)/magnesium oxide/graphene oxide wound coverage was fabricated. Through fabrication, different weights of the previously mentioned ingredients were selected to receive a certain morphological appearance. The composition was confirmed by XRD, FTIR, and EDX techniques. SEM micrograph of Mg₃(VO₄)₂/MgO/GO@CA film depicted that there was a porous surface with flattened rounded MgO grains with an average size of 0.31 µm was observed. Regarding wettability, the binary composition of Mg₃(VO₄)₂@CA occupied the lowest contact angle of 30.15 ± 0.8^o, while pure CA represents the highest one at 47.35 ± 0.4°. The cell viability % amongst the usage of 4.9 µg/mL of Mg₃(VO₄)₂/MgO/GO@CA is 95.77 ± 3.2%, while 2.4 µg/mL showed 101.54 ± 2.9%. The higher concentration of 5000 µg/mL exhibited a viability of 19.23%. According to optical results, the refractive index jumped from 1.73 for CA to 1.81 for Mg₃(VO₄)₂/MgO/GO@CA film. The thermogravimetric analysis showed three main stages of degradation. The initial temperature started from room temperature to 289 °C with a weight loss of 13%. On the other hand, the second stage started from the final temperature of the first stage and end at 375 °C with a weight loss of 52%. Finally, the last stage was from 375 to 472 °C with 19% weight loss. The obtained results, such as high hydrophilic behavior, high cell viability, surface roughness, and porosity due to the addition of nanoparticles to the CA membrane, all played a significant role in enhancing the biocompatibility and biological activity of the CA membrane. The enhancements in the CA membrane suggest that it can be utilized in drug delivery and wound healing applications.

Membranes Coated with Graphene-Based Materials: A Review

Graphene is a popular material with outstanding properties due to its single layer. Graphene and its oxide have been put to the test as nano-sized building components for separation membranes with distinctive structures and adjustable physicochemical attributes. Graphene-based membranes have exhibited excellent water and gas purification abilities, which have garnered the spotlight over the past decade. This work aims to examine the most recent science and engineering cutting-edge advances of graphene-based membranes in regard to design, production and use. Additional effort will be directed towards the breakthroughs in synthesizing graphene and its composites to create various forms of membranes, such as nanoporous layers, laminates and graphene-based compounds. Their efficiency in separating and decontaminating water via different techniques such as cross-linking, layer by layer and coating will also be explored. This review intends to offer comprehensive, up-to-date information that will be useful to scientists of multiple disciplines interested in graphene-based membranes.

Innovative progress in graphene derivative-based composite hybrid membranes for the removal of contaminants in wastewater: A review

Graphene derivatives (graphene oxide) are proved as an innovative carbon materials that are getting more attraction in membrane separation technology because of its unique properties and capability to attain layer-to-layer stacking, existence of high oxygen-based functional groups, and generation of nanochannels that successively enhance the selective pollutants removal performance. The review focused on the recent innovations in the development of graphene derivative-based composite hybrid membranes (GDHMs) for the removal of multiple contaminants from wastewater treatment. To design GDHMs, it was observed that at first GO layers undergo chemical treatments with either different polymers, plasma, or sulfonyl. After that, the chemically treated GO layers were decorated with various active functional materials (either with nanoparticles, magnetite, or nanorods, etc.). By preparing GDHMs, properties such as permeability, porosity, hydrophilicity, water flux, stability, feasibility, mechanical strength, regeneration ability, and antifouling tendency were excessively improved as compared to pristine GO membranes. Different types of novel GDHMs were able to remove toxic dyes (77-100%), heavy metals/ions (66-100%), phenols (40-100%), and pharmaceuticals (74-100%) from wastewater with high efficiency. Some of GDHMs were capable to show dual contaminant removal efficacy and antibacterial activity. In this study, it was observed that the most involved mechanisms for pollutants removal are size exclusion, transport, electrostatic interactions, adsorption, and donnan exclusion. In addition to this, interaction mechanism during membrane separation technology has also been elaborated by density functional theory. At last, in this review the discussion related to challenges, limitations, and future outlook for the applications of GDHMs has also been provided.

FeCl3-activated biochar catalyst for heterogeneous Fenton oxidation of antibiotic sulfamethoxazole in water

One-step FeCl₃-mediated pyrolysis/activation was developed for preparation of bermudagrass (BG)-derived FeCl₃-activated biochars (FA-BCs) from bermudagrass (BG) as a heterogenous Fenton catalyst for heterogeneous Fenton oxidation of sulfamethoxazole (SMX) in water. The FA-BC prepared at the FeCl₃ to BG mass ratio of 2 (FA-BC) exhibited higher adsorption and Fenton oxidation of SMX than other mass ratios of the FeCl₃ to BG. FA-BC presented the great surface area (835 m²/g) and high SMX adsorption capacity (195 mg SMX/g BC), which was higher than various BCs in the previous studies. Additionally, the surface of FA-BC was attached with Fe₂O₃, Fe⁰, and Fe₃O₄ after the FeCl₃ activation. Under the optimal conditions for Fenton reaction (SMX concentration, 100 mg/L; loading of FA-BC, 0.1 g/L; dose of H₂O₂, 200 mg/L; temperature, 20 °C; pH 3; reaction time, 12 h), SMX and COD removal efficiencies reached 99.94% and 65.19%, respectively. Increasing reaction temperature from 20 to 50 °C significantly improved the SMX oxidation rate from 0.46 to 1.04 h^-1. The HO· radicals were proved to play a major role during the Fenton oxidation of SMX. In addition, the SMX solution treated by Fenton oxidation showed much less toxicity than the initial SMX solution. Additionally, the reusability tests of FA-BC indicated that 89.58% removal efficiency for SMX was still achieved after 3 cycles of Fenton oxidation under the optimal conditions. Furthermore, FA-BC can also efficiently remove SMX from the dairy wastewater. Therefore, FA-BC showed a high potential to eliminate aqueous SMX through adsorption and heterogeneous Fenton oxidation.

Metal-free graphene-based catalytic membranes for persulfate activation toward organic pollutant removal: a review

Owing to their ultrathin two-dimensional structure and efficient catalytic ability for persulfate activation, graphene-based nanocarbons exhibit considerable application potential in fabricating carbonaceous composite membranes for in situ catalytic oxidation to remove organic pollutants. This approach offers significant advantages over conventional batch systems. However, the relationships between the physicochemical properties of carbon mats and performance of graphene-based catalytic membranes in water purification remain ambiguous. Herein, we summarize the main mechanisms of in situ catalytic oxidation and the facile fabrication strategies of carbonaceous composite membranes. Different factors influencing the performance of graphene-based catalytic membranes are comprehensively discussed. The defective level, heteroatom doping, and stacking morphology of carbon mats and operational conditions during filtration play critical roles in the oxidative degradation of target pollutants. Long-term operation leads to the deterioration of catalytic activity and transmembrane pressure, especially in the complex water matrix. Finally, the present challenges and future perspectives are presented to improve the anti-fouling performance and catalytic stability of membranes and develop scalable fabrication methods to promote the engineering applications of in situ catalytic oxidation in real water purification.

Carbonaceous composite membranes for peroxydisulfate activation to remove sulfamethoxazole in a real water matrix

In this study, we fabricated carbonaceous composite membranes by loading integrated mats of nitrogen-doped graphene, reduced graphene oxide, and carbon nanotubes (NG/rGO/CNTs) on a nylon microfiltration substrate and employed it for in-situ catalytic oxidation by activating peroxydisulfate (PDS) for the removal of sulfamethoxazole (SMX) in a real water matrix. The impact of coexisting organics on the performance of carbonaceous catalysis was investigated in the continuous filtration mode. Reusability testing and radical quenching experiments revealed that the non-radical pathways of surface-activated persulfate mainly contributed to SMX degradation. A stable SMX removal flux (r_SMX) of 22.15 mg m^-2·h^-1 was obtained in 24 h when tap water was filtered continuously under a low pressure of 1.78 bar and in a short contact time of 1.4 s, which was slightly lower than the r_SMX of 23.03 mg m^-2·h^-1 performed with deionized water as the control group. In addition, higher contents of protein-, fulvic acid-, and humic acid-like organics resulted in membrane fouling and significantly suppressed SMX removal during long-term filtration. Changes in the production of sulfate ions and the Raman spectra of carbon mats indicated that organics prevent the structural defects of the carbon matrix from participating in PDS activation. Moreover, NG/rGO/CNTs composite membranes coupled with activated persulfate oxidation exhibited good self-cleaning ability, because membrane fouling could be partly reversed by restoring filtration pressure during operation. This study provides a novel and effective oxidation strategy for efficient SMX removal in water purification, allowing the application of carbonaceous catalysis for the selective degradation of emerging contaminants.

Morphological features and mechanical properties of nanofibers scaffolds of polylactic acid modified with hydroxyapatite/CdSe for wound healing applications

Ternary nanocomposites, including graphene oxide (GO), hydroxyapatite (HAP), and cadmium selenite (CdSe) have been encapsulated into nanofibrous scaffolds of polylactic acid. These compositions were indexed as HAP@PLA (C1), CdSe@PLA (C2), HAP/CdSe@PLA (C3), HAP/GO@PLA (C4), and HAP/CdSe/GO@PLA (C5). Structural confirmation is executed by XRD and XPS techniques, while FESEM performs morphological characteristics. CdSe and GO dopants cause a significant increase in nanofiber diameter, HAP/GO@PLA (C4), showing thin surface fibers with fiber diameter up to 3.1 μm, followed by HAP/CdSe/GO@PLA (C4) composite that belongs to filament size up to 2.1 μm. On the other hand, the mechanical properties reveal that the dual dopant composites HAP/CdSe@PLA (C3) and HAP/GO@PLA (C4) hit the maximum tensile fracture values with 1.49 ± 0.3 and 0.99 ± 0.2 MPa. Further, the ternary C5 composite represents the lowest contact angle of 86.1 ± 3.7°. The antibacterial activity increased from 32.4 ± 9.7 and 28.4 ± 6.5% to be 85.3 ± 4.6 and 88.1 ± 5.6% for C1 and C5, respectively, against both E. coli and S. aureus in dark conditions. Moreover, the antibacterial potency enhanced from 75.4 ± 7.6 to be 83.5 ± 6.5 from dark to light conditions against E. coli for the composition of PLA containing the binary composition of HAP/CdSe.

The in situ catalytic oxidation of sulfamethoxazole via peroxydisufate activation operated in a NG/rGO/CNTs composite membrane filtration

Metal-free carbonaceous composite membranes have been proven to effectively drive novel in situ catalytic oxidation for the degradation of organic pollutants via persulfates activation. In this study, nitrogen-doped graphene (NG) was employed as a modifier to enhance the catalytic activity of the carbon mats by assembly with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) on the top of a nylon supporter. The morphology and performance of the NG/rGO/CNTs composite membrane were compared to those obtained without the addition of NG (rGO/CNTs). Owing to the larger nanochannels for water delivery and stronger hydrophobicity on the surface, the NG/rGO/CNTs composite membrane shows a superior low-pressure filtration performance in favor of energy-saving operation. For the in situ catalytic oxidation of the NG/rGO/CNTs composite membrane through the activation of peroxydisufate (PDS), the average removal rate of sulfamethoxazole (SMX), one of frequently detected sulfonamide antibiotics in water, can reach 21.7 mg·m^-2·h^-1 under continuous filtration mode, which was 17% more rapid than that of the rGO/CNTs, resulting in significant detoxifying of the oxidation intermediates. Owing to the addition of NG into the carbon mats, the reactive nitrogen-doped sites identified by X-Ray photoelectron spectroscopy (XPS), such as pyridinic and graphitic N, played important roles in PDS activation, while both the radical and non-radical pathways were involved in in situ catalytic oxidation. According to the experimental evidence of the effects that solution environment has on the SMX removal and transmembrane pressure, the NG/rGO/CNTs composite membrane shows a relatively high resistance to changes in the solution pH, chloride ion inhibition, and background organics fouling. These results suggest a new approach to the application of activated persulfate oxidation in water treatment, such that improvements to the reaction stability warrant further investigation.

Nanofibers of cellulose acetate containing ZnO nanoparticles/graphene oxide for wound healing applications

A combination of nanostructured zinc oxide (ZnO) or graphene oxide or both of them with cellulose acetate (CA) enhances a new functionality of nanofibers aiming to improve bio-composite materials for wound healing application. The obtained nanofibers have been investigated using XRD, FTIR, and FESEM. It was observed that the maximum height of the roughness increased from 253 to 651.9 nm for both GO and ZnO/GO in the powdered phase, while it plunged from 613 to 482 nm and developed to 801 nm for ZnO@CA, GO@CA, and ZnO/GO@CA, receptively. Further, the mechanical properties of the obtained scaffolds have been tested and displayed a tremendous variation of tensile strength from 5.44 ± 0.81 to 12.87 ± 0.93 and 8.82 ± 1.2 MPa, while the toughness increased from 23.29 ± 1.4 to 68.95 ± 4.5 and 57.75 ± 3.6 MJ/m³ for ZnO@CA, GO@CA and ZnO/GO@CA, receptively. Moreover, the cell viability was investigated and showed a progression of 97.38 ± 3.9% for ZnO/GO@CA. Furthermore, the adhesion of human fibroblasts cell line towards the obtained nanofibrous scaffolds were examined and displayed that cells were proliferated and spread considerably through the scaffolds, whereas their filopodia have followed the morphology of the fibers.

Bibliometric approach to the perspectives and challenges of membrane separation processes to remove emerging contaminants from water

The presence of contaminants in water is concerning due to the potential impacts on human health and the environment, and ingested contaminants cause harm in various ways. The conventional water treatment systems are not efficient to remove these contaminants. Therefore, novel techniques and materials for the removal of contaminants are increasingly being developed. The separation process using modified membranes can remove these micropollutants; therefore, they have attracted significant research attention. Among the materials used for manufacturing of these membranes, composites based on graphene oxide and reduced graphene oxide are preferred owing to their promising properties, such as mechanical resistance, thermal and chemical stability, antifouling capacity, water permeability, high thermal and electrical conductivity, high optical transmittance and high surface area. Membrane separation processes (MSP) can be used as secondary or tertiary treatment during the supply of wastewater. However, the efficient and accessible applications of these technologies are challenging. This study aims to demonstrate the main concepts of membrane separation processes and their application in the removal of emerging contaminants. This study reports bibliometric mapping, relevant data on studies using membranes as water treatment processes, and their viability in industrial applications. The main challenges and perspectives of these technologies are discussed in detail as well.

Ag nanoparticle-decorated carbon nanotube sponges for removal of methylene blue from aqueous solution

Fabrication of AgNP-Pdop-CNTS for MB adsorption and regeneration.