Tight Ultrafiltration Ceramic Membrane for Separation of Dyes and Mixed Salts (both NaCl/Na2SO4) in Textile Wastewater Treatment

Facile synthesis of S, N-co-doped carbon dots for bio-imaging, Fe3+ detection and DFT calculation

Turning waste into wealth, herein, two highly fluorescent N and S co-doped carbon dots (N, S-CDs-A and N, S-CDs-B) were synthesized by the hydrothermal reaction of contaminant reactive red 2 (RR2) and L-cysteine or L-methionine, respectively. The detailed morphology and structure of N, S-CDs were characterized by XRD, Raman spectrum, FTIR spectra, TEM, HRTEM, AFM and XPS. The maximum fluorescent of N, S-CDs-A and N, S-CDs-B are 565 and 615 nm under different excitation wavelengths with moderate fluorescence intensity of 14.0 % and 6.3 %, respectively. The microstructure models of N, S-CDs-A and N, S-CDs-B, which were induced by FT-IR, XPS and element analysis, had been applied in DFT calculation. The result indicated that the doping of S and N is beneficial to obtain the red-shift of fluorescent spectra. Both N, S-CDs-A and N, S-CDs-B showed highly sensitive and selective to Fe3+. N, S-CDs-A can also detect Al3+ ion with high sensitivity and selectivity. Finally, N, S-CDs-B was successfully applied in cell imaging.

Semiaromatic Polyamide-Based Membrane in Forward Osmosis: Molecular Insights

Despite the increased interest in forward osmosis (FO) in recent years, the technology's advancement in commercial and industrial applications has been hampered by the absence of suitable FO membranes and ideal draw solutes, which demands the exploration of new membranes and novel draw solutes targeted for some specific applications. In this context, we considered a semiaromatic polyamide (SAPA) for an application where monovalent salt can be permeated but has high selectivity toward divalent salt and excellent water permeability. In this regard, we constructed an atomistic model for the membrane via a heuristic approach using an equilibrated mixture of hydrolyzed trimesoyl chloride and piperazine monomers and performed nonequilibrium molecular dynamics simulations on the SAPA membrane in the FO process to understand the structural properties and performance of the membrane at the atomistic level. We used pure water as the feed and Na₂SO₄ as the draw solution. It is observed that the SAPA membrane shows excellent water permeability and no reverse draw solute flux. To further test the dynamics of salt ions inside the membranes, we performed two distinct equilibrium simulations on systems consisting of either monovalent salt, such as NaCl, or divalent salt, such as Na₂SO₄. The atomistic details of the interactions between the functional groups of the membrane and salt ions provided in this work can inspire further experiments on SAPA membranes in the context of separation of monovalent and divalent salts, which have applications in the treatment of textile industry wastewater.

High-Performance γ-Al2O3 Multichannel Tube-Type Tight Ultrafiltration Membrane Using a Modified Sol-Gel Method

We introduced a modified sol-gel method using polyvinyl alcohol (PVA) as an additive to improve the permeability of γ-Al₂O₃ membranes by minimizing the thickness of the selective layer and maximizing the porosity. First, the analysis revealed that the thickness of γ-Al₂O₃ decreased as the concentration of PVA increased in the boehmite sol. Second, the properties of the γ-Al₂O₃ mesoporous membranes were greatly influenced by the modified route (method B) compared to the conventional route (method A). The results showed that the porosity and surface area of the γ-Al₂O₃ membrane increased, and the tortuosity decreased considerably using method B. This effect was attributed to the adsorption of PVA molecules on the surface of the boehmite particles, which depended on the synthesis route. The experimentally determined pure water permeability trend and the Hagen-Poiseuille mathematical model confirmed that the modified method improved the performance of the γ-Al₂O₃ membrane. Finally, the γ-Al₂O₃ membrane fabricated via a modified sol-gel method with a pore size of 2.7 nm (MWCO = 5300 Da) exhibited a pure water permeability of over 18 LMH/bar, which is three times higher than that of the γ-Al₂O₃ membrane prepared using the conventional method.

Mass Transport of Dye Solutions through Porous Membrane Containing Tannic Acid/Fe3+ Selective Layer

Tannic acid (TA)-Fe³⁺ membranes have received recent attention due to their sustainable method of fabrication, high water flux and organic solutes rejection performance. In this paper, we present a description of the transport of aqueous solutions of dyes through these membranes using the transport parameters of the Spiegler-Kedem-Katchalsky (SKK) model. The reflection coefficient (σ) and solute permeability (PS) of the considered TA-Fe³⁺ membranes were estimated from the non-linear model equations to predict the retention of solutes. The coefficients σ and PS depended on the porous medium and dye molecular size as well as the charge. The simulated rejections were in good agreement with the experimental findings. The model was further validated at low permeate fluxes as well as at various feed concentrations. Discrepancies between the observed and simulated data were observed at low fluxes and diluted feed solutions due to limitations of the SKK model. This work provides insights into the mass transport mechanism of dye solutions and allows the prediction of dye rejection by the TFC membranes containing a TA-Fe³⁺ selective layer using an SKK model.

Silicon carbide catalytic ceramic membranes with nano-wire structure for enhanced anti-fouling performance

Membrane fouling is a critical challenge for current ceramic membranes, which suffer from low flux and insufficient removal. Development of self-cleaning catalytic ceramic membranes is promising to address this challenge. Herein, we design heterogeneous silicon carbide ceramic membranes featuring a novel structure of g-C₃N₄-decorated β-SiC nano-wire catalytic functional layer, which enables enhanced anti-fouling self-cleaning performance. At chemical harsh (alkaline or especially acidic) conditions, the nano-wire membrane exhibits catalysis-enhanced removal performance for organic contaminants. Unlike conventional particle-packing membrane structure, such a nano-wire network membrane structure has not only high porosity (56.1%), but exceptional water permeance (110 L·m^-2·h^-1·bar^-1) and removal (100%) of organic substance under simulated sunlight, outperforming state-of-the-art organic membranes and ceramic membranes. Superoxide radical (∙O₂^-) was experimentally confirmed to be major reactive species responsible for self-cleaning function. We also propose a catalytic mechanism model with radical formation pathway, enabled by the as-formed g-C₃N₄@β-SiC heterojunction structure with reduced electron-hole recombination. This work would provide new insights into not only rational design of next-generation ceramic membranes with self-cleaning function but also more applications of efficient treatment of refractory wastewaters containing degradable organic substances by using such membranes.

Recovery of dyes and salts from highly concentrated (dye and salt) mixed water using nano-filtration ceramic membranes

In this study, a higher concentration of (reactive dyestuff and salt) mixed water was used to verify the feasibility of separation by membrane techniques. The commercial nano filtration ceramic membrane (MWCO 200 Da) has been used in cross flow mode for separation of dyes and salts from highly concentrated mixed water solution. NF ceramic membrane presents good permeability (pure water flux 54.15 Lm⁻² h⁻¹, TMP 8 bar), 8% dye rejection and reduced salt rejection of NaCl (<8%) and Na₂SO₄ (<25%). Consequently, the operation parameters (TMP, temperature) and solution environment (solution pH, salt concentration and dye concentration) have been intensively evaluated for separation efficiency in the NF ceramic membrane process. Significantly, the NF ceramic membrane has performed less rejection to chloride ions than sulphate ions due to the Donnan effect. Solution pH, concentration of salt and dye concentration have shown significant effects on ceramic membrane separation performance. In addition, pollutant removals were achieved with noteworthy values for the chemical oxygen demand for permeate solution also color difference between concentrate and permeate. In conclusion, the strong rejection of dyes by the NF ceramic membranes proves that it can be suitable alternatives for textile wastewater treatment process.

Efficiency of iron modified Pyrus pyrifolia peels biochar as a novel adsorbent for methylene blue dye abatement from aqueous phase: equilibrium and kinetic studies

Herein, a magnetic biochar adsorbent based on Pyrus pyrifolia discarded peels impregnated with precursor FeCl_3·6H₂O was fabricated and probed as a low-cost adsorbent for toxic cationic dye methylene blue (MB). The textural characterization of Pyrus pyrifolia magnetic biochar (PMBC) obtained from BET analysis exhibited its mesoporous nature with S_BET of 133.960 m²/g. The physicochemical characteristics of PMBC were elucidated using XRD, FTIR, SEM-EDX and TEM techniques. The impregnation of FeCl₃ has a significant impact on the microstructure of Pyrus pyrifolia based biochar which resulted in enhancement in adsorption efficiency of PMBC. The sorption parameters adsorbent dosage, time, initial MB concentration, and pH were thoroughly elucidated using a batch methodology which were found to be 0.8 g/L, 40 min, 90 mg/L and 6, respectively. Temkin and pseudo-second-order rate equation respectively appropriated the equilibrium data than the rest of the models. The maximum adsorption capacity determined by the Langmuir model was found to be 967.80 mg/g. The adsorbent exhibited better regeneration up to 3 cycles validating its practical usage. The facile synthesis, economic, and environmentally benign characteristic of Pyrus pyrifolia magnetic biochar corroborated it as a highly efficient adsorbent to sequester MB from an aqueous phase.

Construction of a highly stable g-C3N4/NH2-MIL-88B(Fe)/CD@graphene oxide self-cleaning membrane for dye wastewater separation and degradation

A g-C3N4/NH2-MIL-88B(Fe)/CD@GO membrane (M2) was prepared by a simple vacuum filtration method.

Tailored design of nanofiltration membranes for water treatment based on synthesis-property-performance relationships

Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Recent developments in porous ceramic membranes for wastewater treatment and desalination: A review

The development of membrane technology has proved vital in providing a sustainable and affordable supply of clean water to address the ever-increasing demand. Though liquid separation applications have been still dominated by polymeric membranes, porous ceramic membranes have gained a commercial foothold in microfiltration (MF) and ultrafiltration (UF) applications due to their hydrophilic nature, lower fouling, ease of cleaning, reliable performance, robust performance with harsh feeds, relative insensitivity to temperature and pH, and stable long-term flux. The enrichment of research and development on porous ceramic membranes extends its focus into advanced membrane separation technologies. The latest emerging nanofiltration (NF) and membrane distillation (MD) applications have witnessed special interests in constructing porous membrane with hydrophilic/functional/hydrophobic properties. However, NF and MD are relatively new, and many shortcomings must be addressed to compete with their polymeric counterparts. For the last three years (2018-2020), state-of-the-art literature on porous ceramic membranes has been collected and critically reviewed. This review highlights the efficiency (permeability, selectivity, and antifouling) of hydrophilic porous ceramic membranes in a wide variety of wastewater treatment applications and hydrophobic porous ceramic membranes in membrane distillation-based desalination applications. A significant focus on pores characteristics, pore sieving phenomenon, nano functionalization, and synergic effect on fouling, the hydrophilic porous ceramic membrane has been discussed. In another part of this review, the role of surface hydrophobicity, water contact angle, liquid entry pressure (LEP), thermal properties, surface micro-roughness, etc., has been discussed for different types of hydrophobic porous ceramic membranes -(a) metal-based, (b) silica-based, (c) other ceramics. Also, this review highlights the potential benefits, drawbacks, and limitations of the porous membrane in applications. Moreover, the prospects are emphasized to overcome the challenges in the field.

Green Electrospun Membranes Based on Chitosan/Amino-Functionalized Nanoclay Composite Fibers for Cationic Dye Removal: Synthesis and Kinetic Studies

Chitosan/poly(vinyl alcohol)/amino-functionalized montmorillonite nanocomposite electrospun membranes with enhanced adsorption capacity and thermomechanical properties were fabricated and utilized for the removal of a model cationic dye (Basic Blue 41). Effects of nanofiller concentrations (up to 3.0 wt %) on the morphology and size of the nanofibers as well as the porosity and thermomechanical properties of the nanocomposite membranes are studied. It is shown that the incorporation of the nanoclay particles with ∼10 nm lateral sizes into the polymer increases the size of the pores by about 80%. To demonstrate the efficiency of the adsorbents, the dye removal rate is investigated as a function of pH, adsorbent dosage, dye concentration, and nanofiller loading. The highest and fastest dye removal occurs for the nanofibrous membranes containing 2 wt % nanofiller, where about 80% of the cationic dye is removed after 15 min. This performance is at least 20% better than the pristine chitosan/poly(vinyl alcohol) membrane. The thermal stability and compression resistance of the nanocomposite membranes are found to be higher than those of the pristine membrane. In addition, reusability studies show that the dye removal performance of this nanocomposite membrane reduces by only about 5% over four cycles. The adsorption kinetics is explained by the Langmuir isotherm model and is expressed by a pseudo-second-order kinetic mechanism that determines a spontaneous chemisorption process. The results of this study provide a valuable perspective on the fabrication of high-performance, reusable, and efficient electrospun fibrous nanocomposite adsorbents.

Chiral poly(amide-imide)/ZnS nanocomposite as a new adsorbent for simultaneous removal of cationic dyes from aqueous solution

A new adsorbent, poly(amide-imide)/zinc sulfide nanocomposite (PAI/ZnS NC), was fabricated and identified by Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission-scanning electron microscopy, and transmission electron microscopy. Then, the obtained NC was applied for the simultaneous removal of auramine O (AO) and rhodamine B (RB) dyes from aqueous solution via the interactions of hydrogen bonding, π– π stacking, and Lewis acid–base interaction. The effects of operational variables including pH, PAI/ZnS NC mass, AO and RB concentration, and sonication time on removal efficiency were examined and optimized values were found to be 8.0, 16 mg, 11 mg L−1, and 6 min, respectively. The adsorption capacities of PAI/ZnS NC for the removal of AO and RB dyes were found to be 70.92 and 91.74 mg g−1, respectively. Ultraviolet–visible spectrophotometer was used to determine the amount of residual dye in solution. Fitting the experimental equilibrium data to isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich reveals the suitability of the Langmuir model with high correlation coefficients ( R2 = 0.998 for AO and R2 = 0.999 for RB). Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models applicability was tested and the pseudo-second-order equation controls the kinetics of the adsorption process. Furthermore, this study establishes that PAI/ZnS NC can be successfully applied as a low-cost adsorbent and conserve its high efficiency after nine cycles for the removal of AO and RB dyes.

Polysulfone-Polyvinyl Pyrrolidone Blend Polymer Composite Membranes for Batik Industrial Wastewater Treatment

Batik wastewater, in general, is colored and has high concentrations of BOD (biological oxygen demand), COD (chemical oxygen demand), and dissolved and suspended solids. Polysulfone (PSf)-based membranes with the addition of polyvinyl pyrrolidone (PVP) were prepared to treat batik industrial wastewater. PSf/PVP membranes were prepared using the phase inversion method with N-methyl-2 pyrrolidone (NMP) as the solvent. Based on the membrane characterization through FESEM, water contact angle, porosity, and mechanical tests showed a phenomenon where the addition of PVP provided thermodynamic and kinetic effects on membrane formation, thereby affecting porosity, thickness, and hydrophilicity of the membranes. The study aims to observe the effect of adding PVP on polysulfone membrane permeability and antifouling performance on a laboratory scale through the ultrafiltration (UF) process. With the addition of PVP, the operational pressure of the polysulfone membrane was reduced compared to that without PVP. Based on the membrane filtration results, the highest removal efficiencies of COD, TDS (total dissolved solid), and conductivity achieved in the study were 80.4, 84.6, and 83.6%, respectively, on the PSf/PVP 0.35 membrane operated at 4 bar. Moreover, the highest color removal efficiency was 85.73% on the PSf/PVP 0.25 operated at 5 bar. The antifouling performance was identified by calculating the value of total, reversible, and irreversible membrane fouling, wherein in this study, the membrane with the best antifouling performance was PSf/PVP 0.25.

High efficient dye removal with hydrolyzed ethanolamine-Polyacrylonitrile UF membrane: Rejection of anionic dye and selective adsorption of cationic dye

The dye-water treatment using UF membrane is still a challenge. In the present study, the optimized PAN-ETA ultrafiltration membrane was hydrolyzed and subsequently characterized by SEM, IR, CA, XPS, NMR, mechanic measurement, etc. The obtained membrane (H-PAN-ETA) was used for dye removal and it showed both an excellent anti-dye fouling and a good rejection property for anionic dyes. I.e. 96% rejection for methyl blue (MB), 99% for congo red (CR), 94% for acid fuchsin (AF) with no sign of contamination by dye. The flux of H-PAN-ETA membrane maintained at 50-53 L m^-2⋅ h^-1 during a 10-h filtration, which is higher than that of tight UF membranes reported. Meanwhile, H-PAN-ETA membrane was able to selectively remove cationic dyes, such as methylene blue (MEB), rhodamine B (RB) and, crystal violet (CV), or the mixture of anionic dye/cationic dye by adsorption process. Its adsorption capacity remained unchanged after 20 cycles. Finally, the immobile electrical double layer (EDL) theory combined with electrostatic force was introduced to explain the separation mechanism of charged UF membrane, which is helpful to instruct the preparation of UF membrane for dye removal.

Fouling and Retention Mechanisms of Selected Cationic and Anionic Dyes in a Ti3C2Tx MXene-Ultrafiltration Hybrid System

Ti₃C₂T_x MXenes, a very new family of nanostructured material, were applied in combination with an ultrafiltration (UF) membrane (MXene-UF) for removal of the selected dyes including methylene blue (MB) and methyl orange (MO) as the first attempt. The normalized flux of the MXene-UF (0.90 for MB and 0.92 for MO) indicated better performance than a single UF (0.86 for MB and 0.90 for MO) and a powdered activated carbon (PAC)-UF (0.72 for MB and 0.75 for MO) for both dyes. The addition of an adsorbent decreased the irreversible fouling of the hybrid system compared to single UF, due to adsorption of dyes. The observed dominant fouling mechanism was cake layer fouling, evaluated using a resistance-in-series model, permeate flux modeling, and four conceptual blocking law models. PAC in particular acted as a foulant, leading to a severe flux decline. The average retention rate was found to be on the order of PAC-UF (57.7 and 47.9%) > MXene-UF (51.7 and 34.9%) > single UF (45.0 and 34.7%) for MB and MO, respectively. The results showed that although PAC exhibits relatively strong adsorption performance, MXene-UF also exhibited high selectivity due to electrostatic interaction between the MXene and dyes. In addition, humic acid (HA) adsorption on the membrane led to a reduction in the effective membrane area, resulting in a higher retention and lower flux for MXene-UF in the presence of HA. Furthermore, higher retention was observed for MXene-UF at pH 10.5 compared to pH 3.5 and 7, because MXene has more negative terminations at higher pH, leading to greater MB adsorption. Additionally, because of the bridging effect between the membrane and the MXene and competition between MB and cation ions for adsorption on the MXene, lower retention and flux were observed in MXene-UF with background ions.

Preparation and Photocatalytic Properties of a Bagasse Cellulose-Supported Nano-TiO2 Photocatalytic-Coupled Microbial Carrier

Intimate coupling of photocatalysis and biodegradation (ICPB) has shown promise in removing unwanted organic compounds from water. In this study, bagasse cellulose titanium dioxide composite carrier (SBC-TiO₂) was prepared by low-temperature foaming methods. The optimum preparation conditions, material characterization and photocatalytic performance of the composite carrier were then explored. By conducting a single factor test, we found that bagasse cellulose with a mass fraction of 4%, a polyvinyl alcohol solution (PVA) with a mass fraction of 5% and 20 g of a pore-forming agent were optimum conditions for the composite carrier. Under these conditions, good wet density, porosity, water absorption and retention could be realized. Scanning electron microscopy (SEM) results showed that the composite carrier exhibited good biologic adhesion. X-ray spectroscopy (EDS) results confirmed the successful incorporation of nano-TiO₂ dioxide into the composite carrier. When the mass concentration of methylene blue (MB) was 10 mg L⁻¹ at 200 mL, 2 g of the composite carrier was added and the initial pH value of the reaction was maintained at 6, the catalytic effect was best under these conditions and the degradation rate reached 78.91% after 6 h. The method of preparing the composite carrier can aid in the degradation of hard-to-degrade organic compounds via ICPB. These results provide a solid platform for technical research and development in the field of wastewater treatment.

Hydrophilic SiC hollow fiber membranes for low fouling separation of oil-in-water emulsions with high flux

The dry-wetting spinning technique involving immersion-induced phase inversion and dry-sintering was applied to prepare two types of SiC and Al₂O₃ hollow fiber membranes.

Polymeric graphitic carbon nitride (g-C3N4)-based semiconducting nanostructured materials: Synthesis methods, properties and photocatalytic applications

In recent years, various facile and low-cost methods have been developed for the synthesis of advanced nanostructured photocatalytic materials. These catalysts are required to mitigate the energy crisis, environmental deterioration, including water and air pollution. Among the various semiconductors explored, recently novel classes of polymeric graphitic carbon nitride (g-C₃N₄)-based heterogeneous photocatalysts have established much greater importance because of their unique physiochemical properties, large surface area, low price, and long service life, ease of synthesis, product scalability, controllable band gap properties, low toxicity, and high photocatalytic activity. The present comprehensive review focuses on recent achievements in a number of facile chemical synthesis methods for semiconducting polymeric carbon nitrides and their heterogeneous nanohybrids with various dopants, nanostructured metals, metal oxides, and nanocarbons, as well as the parameters influencing their physiochemical properties and photocatalytic efficiency, which are discussed with reference to various catalytic applications such as air (NO_x) purification, wastewater treatment, hydrogen generation, CO₂ reduction, and chemical transformation. The mechanisms for the superior photocatalytic activity of polymeric g-C₃N₄-based heterogeneous photocatalysts are also discussed. Finally, the challenges, prospects, and future directions for photocatalytic polymeric g-C₃N₄-based semiconducting materials are described.