Layer-by-layer assembly of bio-inspired borate/graphene oxide membranes for dye removal

Enhanced filtration membranes with graphene oxide and tannic acid for textile industry wastewater dye removal

A novel modification technique employing a layer-by-layer (LbL) self-assembly method, integrated with a pressure-assisted filtration system, was developed for enhancing a commercial polyethersulfone (PES) microfiltration (MF) membrane. This modification involved the incorporation of tannic acid (TA) in conjunction with graphene oxide (GO) nanosheets. The effectiveness of the LbL method was confirmed through comprehensive characterization analyses, including ATR-FTIR, SEM, water contact angle (WCA), and mean pore size measurements, comparing the modified membrane with the original commercial one. Sixteen variations of PES MF membranes were superficially modified using a three-factorial design, with the deposited amount of TA and GO as key factors. The influence of these factors on the morphology and performance of the membranes was systematically investigated, focusing on parameters such as pure water permeability (PWP), blue corazol (BC) dye removal efficiency, and flux recovery rate (FRR). The membranes produced with the maximum amount of GO (0.1 mg, 0.55 wt%) and TA as the inner and outer layers demonstrated remarkable FRR and significant BC removal, exceeding 80%. Notably, there was no significant difference observed when using either 0.2 (1.11 wt%) or 0.4 mg (2.22 wt%) in the first layer, as indicated by the Tukey mean test. Furthermore, the modified membrane designated as MF/TA0.4GO0.1TA0.4 was evaluated in the filtration of a simulated dye bath wastewater, exhibiting a BC removal efficiency of 49.20% and a salt removal efficiency of 27.74%. In conclusion, the novel PES MF membrane modification proposed in this study effectively enhances the key properties of pressure-driven separation processes.

Layer-by-layer Assembly of Nanosheets with Matching Size and Shape for More Stable Membrane Structure than Nanosheet-Polymer Assembly

Layer-by-layer (LbL) assembly of oppositely charged materials has been widely used as an approach to make two-dimensional (2D) nanosheet-based membranes, which often involves 2D nanosheets being alternately deposited with polymer-based polyelectrolytes to obtain an electrostabilized nanosheet-polymer structure. In this study, we hypothesized that using 2D nanosheets with matching physical properties as both polyanions and polycations may result in a more ordered nanostructure with better stability than a nanosheet-polymer structure. To compare the differences between nanosheet-nanosheet vs nanosheet-polymer structures, we assembled negatively charged molybdenum disulfide nanosheets (MoS2) with either positively charged graphene oxide (PrGO) nanosheets or positively charged polymer (PDDA). Using combined measurements by ellipsometer and quartz crystal microbalance with dissipation, we discovered that the swelling of MoS2-PrGO in ionic solutions was 60% lower than that of MoS2-PDDA membranes. Meanwhile, the MoS2-PrGO membrane retained its permeability upon drying, whereas the permeability of MoS2-PDDA decreased by 40% due to the restacking of MoS2. Overall, the MoS2-PrGO membrane demonstrated a better filtration performance. Additionally, our X-ray photoelectron spectroscopy results and analysis on layer density revealed a clearer transition in material composition during the LbL synthesis of MoS2-PrGO membranes, and the X-ray diffraction pattern suggested its resemblance to an ordered, layer-stacked structure. In conclusion, the MoS2-PrGO membrane made with nanosheets with matching size, shape, and charge density exhibited a much more aligned stacking structure, resulting in reduced membrane swelling under high salinity solutions, controlled restacking, and improved separation performance.

Superhydrophobic modification of cellulosic paper-based materials: Fabrication, properties, and versatile applications

Cellulose is the cheapest and mostly widespread green raw material on earth. Due to the easy and versatile developed modification of cellulose, many cellulosic paper-based sustainable materials and their multifunctional applications have attained increasing interest under the background of the implementation of the "plastic ban" policy. However, intrinsic cellulose paper is hydrophilic and non-water-proof, which highly limited its application, thus becoming a bottleneck for the development of "cellulosic paper-based plastic replacement". Unquestioningly, the superhydrophobic modification of cellulosic paper-based materials and the extension of their high value-added applications are highly desired, which is the main content of this review. More importantly, we presented the comprehensive discussion of the functionalized applications of superhydrophobic cellulosic paper-based materials ranging from conventional products to high value-added functional materials such as paper straw and paper mulch film for the first time, which have great industrialization potential and value. This review would offer the valuable guidance and insightful information for the rational construction of sustainable superhydrophobic cellulosic paper for advanced functional devices.

Surface modification of commercial reverse osmosis membranes using both hydrophilic polymer and graphene oxide to improve desalination efficiency

Various methods have been applied to modify the surface of reverse osmosis (RO) membranes to modify the membrane performance to enhance the flux, rejection, and resistance to various factors of fouling. Hence, the main objective of the current study is to modify the surface of commercial RO membranes using the synergistic effect of the hydrophilic polymer and graphene oxide (GO). GO nanosheets were firstly synthesized by the modified hummer method, then characterized by FTIR, XRD, and SEM analyses. Then, the polyacrylic acid (PAA) was grafted on the membrane surface for membrane fabrication. Furthermore, effective factors of grafting such as monomer concentration, time, and temperature of polymerization were optimized. After that, different amounts of GO nanosheets were loaded in PAA optimized layer. Then, the effect of GO loading on the RO membrane structure and performance was investigated. The outcomes of membrane characterization demonstrated that modified RO membranes had a smoother surface, more negative surface charge, a little better hydrophilicity, and more thickness. Moreover, the results of PAA and GO optimization were shown that grafting 1.5 mM of PAA and loading 0.1 wt% of GO nanosheets give the best membrane performance. This membrane (GO 0.1@1.5M PAA/RO) between all modified membranes has the most water flux (37.1 L/m²h), the highest NaCl rejection (98%), and the best antifouling efficiency. Ultimately, it was concluded that the grafting of GO@PAA on the surface of a commercial RO membrane is an efficient approach for the enhancement of desalination and antifouling performance of this kind of membrane.

Waste eggshell-supported CuO used as heterogeneous catalyst for reactive blue 19 degradation through peroxymonosulfate activation (CuO/eggshell catalysts activate PMS to degrade reactive blue 19)

Advanced oxidation processes play an important role in the removal of organic pollutants from wastewater, in which it is essential to develop an eco-friendly, effective, stable, and inexpensive catalyst. Herein, waste eggshell-supported copper oxide (CuO/eggshell) was synthesized via a facile method and employed as peroxymonosulfate (PMS) activator for the elimination of reactive blue 19 (RB19). CuO/eggshell exhibited high degradation efficiency of RB19 (approximately 100%) by activation of PMS under the optimum conditions of 20 mg/L RB19, 0.2 g/L CuO/eggshell, 0.36 mM PMS, and initial pH 7.12 within 20 min. In addition, the effects of catalyst dosage, PMS concentration, initial pH, inorganic ions, and humic acid on RB19 degradation were investigated. Scavenging experiments and electron paramagnetic resonance revealed that multiple reactive oxygen species, including sulfate radicals (SO₄^·-), hydroxyl radicals (^·OH), superoxide radicals (O₂^·-), and singlet oxygen (¹O₂), contributed to RB19 degradation, and ¹O₂ played a dominant role. Finally, a possible PMS activation mechanism was proposed. This study suggests that loading catalytically active components onto waste eggshell is eco-friendly and effective for enhancing the degradation of dyes from wastewater.

D-spacing controllable GO membrane intercalated by sodium tetraborate pentahydrate for dye contamination wastewater treatment

Sodium tetraborate pentahydrate (STB) was intercalated into graphene oxide (GO) nanosheets to form a nanocomposite (STB@GO). Subsequently, it was self-assembled on a substrate membrane to prepare STB@GO nanofiltration membrane. The properties of the STB@GO powder samples and the nanofiltration membrane were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), contact angle (CA), and zeta potential. When the STB concentration was 1.0 g/L in the cross-linking reaction, the membrane was described as the STB₂@GO membrane and exhibited a large interlayer space (d-spacing = 1.347 nm), high hydrophilicity (CA = 22.2°), and high negative potential (zeta = -18.0 mV). Meanwhile, the pure water flux of the membrane was significantly increased by 56.60% than that of the GO membrane. In addition, the STB₂@GO membrane exhibited a favorable capability for dye rejection,98.52% for Evans blue (EB), 99.26% for Victoria blue B (VB), 91.94% for Alizarin yellow (AY), and 93.21% for Neutral red (NR). Furthermore, the STB₂@GO membrane performed better in dye separation under various types and concentrations of dye, pH values, and ions in solution. Thus, this study provides a promising method for preparing laminated GO nanofiltration membranes for dye wastewater treatment.

Advanced graphene oxide-based membranes as a potential alternative for dyes removal: A review

Graphene oxide (GO) is one of the most well-known graphene derivatives which, due to its outstanding chemical, electrical and optical properties as well as its high oxygen content, has been recently applied in several fields such as in the construction of sensors, as antimicrobial agent for biomedical applications, as well as nanofiller material for membranes applied in wastewater treatment. In this last-mentioned field, the synthesis and functionalization of membranes with GO has proven to improve the performance of membranes applied in the treatment of wastewater containing dyes, regarding antifouling behavior, selectivity and flux. In this review, an overview of water pollution caused by effluents containing synthetic dyes, the advantages and limitations of GO-based membranes and the latest research advances on the use of GO-based membranes for dyes removal, including its impact on membrane performance, are discussed in detail. The future panorama of the applicability of GO-based membranes for the treatment of water contaminated by dyes is also provided.

Functional GO-based membranes for water treatment and desalination: Fabrication methods, performance and advantages. A review

Graphene oxide (GO) and GO-based materials have gained a significant interest in the membrane synthesis and functionalization sector in the recent years. Inspired by their unique and tuneable properties, several GO-based nanomaterials have been investigated and utilized as effective nanofillers for various membranes in the water treatment, purification and desalination sectors. This paper comprehensively reviews the recent advances of GO utilization in pressure, concentration and thermal-driven membrane processes. A brief overview on GO particles, properties, synthesis and functionalization methods was provided. The conventional and the state-of-art fabrication methods of GO-based membranes were summarized and discussed, and consequently the GO-based membranes were classified into different categories. The applications, types, and the performance in terms of flux and rejection were summarized and reviewed. The advantages of GO-based membranes in terms of antifouling properties, bactericidal effects, mechanical strength and stability have been reviewed, too. The review gives insights on the future perspectives of GO functional materials and their potential use in the various membrane processes discussed herein.

The removal of anionic and cationic dyes from an aqueous solution using biomass-based activated carbon

In this study, two biomass-based adsorbents were used as new precursors for optimizing synthesis conditions of a cost-effective powdered activated carbon (PAC). The PAC removed dyes from an aqueous solution using carbonization and activation by KOH, NaOH, and H₂SO₄. The optimum synthesis, activation temperature, time and impregnation ratio, removal rate, and uptake capacity were determined. The optimum PAC was analyzed and characterized using Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), Zeta potential, and Raman spectroscopy. Morphological studies showed single-layered planes with highly porous surfaces, especially PAC activated by NaOH and H₂SO₄. The results showed that the experimental data were well-fitted with a pseudo-second-order model. Based on Langmuir isotherm, the maximum adsorption capacity for removing methylene blue (MB) was 769.23 mg g⁻¹ and 458.43 mg g⁻¹ for congo red (CR). Based on the isotherm models, more than one mechanism was involved in the adsorption process, monolayer for the anionic dye and multilayer for the cationic dye. Elovich and intraparticle diffusion kinetic models showed that rubber seed shells (RSS) has higher α values with a greater tendency to adsorb dyes compared to rubber seed (RS). A thermodynamic study showed that both dyes’ adsorption process was spontaneous and exothermic due to the negative values of the enthalpy (ΔH) and Gibbs free energy (ΔG). The change in removal efficiency of adsorbent for regeneration study was observed in the seventh cycles, with a 3% decline in the CR and 2% decline in MB removal performance. This study showed that the presence of functional groups and active sites on the produced adsorbent (hydroxyl, alkoxy, carboxyl, and π − π) contributed to its considerable affinity for adsorption in dye removal. Therefore, the optimum PAC can serve as efficient and cost-effective adsorbents to remove dyes from industrial wastewater.

A nanocomposite paper comprising calcium silicate hydrate nanosheets and cellulose nanofibers for high-performance water purification

Removal of soluble organic and inorganic contaminants from wastewater to produce clean water has received much attention recently. However, the simultaneous enhancement of water permeability and removal efficiency is still a challenge for filtration membranes. Here, we present a new kind of nanocomposite paper (CSH/CNF) consisting of calcium silicate hydrate (CSH) nanosheets and cellulose nanofibers (CNFs), and demonstrate the rapid water filtration and highly efficient contaminant (e.g., dyes, proteins, and metal ions) adsorption properties. The CNFs can serve as the bridging material to connect the CSH nanosheets to form a porous network structure and vital channels in the CSH/CNF paper for rapid water transportation. The weight ratio of CSH nanosheets in the paper is up to 75–85%. The weight ratio of CSH nanosheets has a significant effect on the water permeability and removal efficiency. The water permeability of the CSH/CNF paper with 82.5 wt% CSH nanosheets reaches as high as 312.7 L m⁻² h⁻¹ bar⁻¹, which is about 14.7 times that of the CSH/CNF paper with 75 wt% CSH nanosheets. Because of the high specific surface area and abundant adsorption sites of CSH nanosheets, the CSH/CNF paper with 82.5 wt% CSH nanosheets exhibits high adsorption capacities and removal efficiencies for methyl blue (242.6 mg g⁻¹, 97.3%), bovine serum albumin (289.2 mg g⁻¹, 98.5%) and Pb²⁺ ions (366.2 mg g⁻¹, 98.2%). The CSH/CNF nanocomposite paper holds great potential for application in environmental wastewater purification.

A nanocomposite paper with high water permeability and removal efficiency was prepared for the removal of organic and inorganic contaminants by filtration.