Preparation of DOPA-TA coated novel membrane for multifunctional water decontamination

Developing cellulose-based hydrophobic/hydrophilic composites for efficient adsorption of oils and heavy metals from water

The oily wastewater and heavy metal ions have been increasingly discharged into water environment, posting a serious threat to ecosystems and human health. However, it remains challenging to use single separation technology to effectively remove oil and heavy metal ions in oil-water mixtures simultaneously. Herein, novel hydrophobic/hydrophilic composites (HHC) were successfully prepared by using A4 paper-derived hydrophilic cellulose as the modified matrix, modifying the polydopamine layer and in-situ growth nanoscale zero-valent iron as active adsorption materials, combined with oleic acid-modified hydrophobic magnetic hollow carbon microspheres, which were used to efficiently and rapidly adsorb heavy metals and oil in oil-water mixtures. Under the optimal adsorption conditions, the adsorption amounts of As(III), As(V), Pb(II) and Cu(II) were 289.6 mg/g, 341.9 mg/g, 241.2 mg/g and 277.5 mg/g, respectively, and the mass transfer rate of HHC to the target ions is fast. The HHC have efficient separation performance for layered oil-water mixtures and emulsified oil-water mixtures, with separation efficiency of 97 % and 92 %. At the same time, due to the abundant adsorption sites, the HHC also exhibit splendid regeneration performance for the four ions after multiple adsorption utilization. Our work designed a approach to achieving promising oil and heavy metal adsorbents with higher adsorption capacity and better regenerative properties.

Biodegradable Chitosan-Based Membranes for Highly Effective Separation of Emulsified Oil/Water

Efficient separation of oil droplets from oil/water emulsions is necessary for many energy and food industrial processes and for industrial wastewater treatment. Membrane microfiltration has been explored to address this issue because it is simple to operate and low in cost. However, filtration of oil droplets with a size around or less than 1 μm is still a major challenge. Furthermore, the fabrication process for polymeric membranes often uses hazardous organic solvents and petroleum-derived and nonbiodegradable raw materials, which pose additional environmental health and safety risk. In this study, we examined the use of chitosan-based membranes to efficiently remove oil droplets with an average diameter of ∼1 μm. The membranes were fabricated based on the rapid dissolution of chitosan in an alkaline/urea solvent system at a low temperature, thus avoiding the use of any toxic organic solvent. The chitosan membranes were further modified by dopamine and tannic acid (TA). The as-prepared membrane was characterized in terms of surface morphology, pore size distribution, and mechanical strength. The membrane performance was evaluated on a custom-designed crossflow filtration system. The results showed that the modified chitosan membrane with dopamine and TA had a water flux of 230.9 LMH at 1bar transmembrane pressure and oil droplet rejection of 99%. This water flux represented an increase of more than 10 times when compared with the original chitosan membrane without modification. The study also demonstrated excellent antifouling properties of the modified membrane that could achieve near 100% water flux recovery.

Polydopamine Induced Wettability Switching of Cellulose Nanofibers/n-Dodecanethiol Composite Aerogels

The novel wettability switchable cellulose nanofiber- (CNF-) based aerogel was conveniently prepared by polydopamine mediated composition of CNF and n-dodecanethiol. The wettability of aerogels can be controlled by adjusting the PDA and n-dodecanethiol loading content, which leads to a variation of water contact angle from 0-149°. The PDA was coated on cellulose nanofibers via hydrogen bonds and then n-dodecanethiol was anchored onto the scaffolds by Michael addition reaction, which was revealed by XPS and FTIR spectra. The composite aerogel can selectively absorb a series of oily liquids from the oil/water mixture, with the maximum absorption capacity of 68 g/g. This work presented a facile strategy to prepare wettability switchable CNF-based heterogenous aerogel and exhibited the potential of the composite aerogel for oil/water separation.

Fabrication of Polyvinylidene Difluoride Membrane with Enhanced Pore and Filtration Properties by Using Tannic Acid as an Additive

Potential use of tannic acid (TA) as an additive for fabrication of polyvinylidene difluoride (PVDF) membrane was investigated. The TA was introduced by blending into the dope solution with varying concentrations of 0, 1, 1.5, and 2 wt%. The prepared membranes were characterized and evaluated for filtration of humic acid (HA) solution. The stability of the membrane under harsh treatment was also evaluated by one-week exposure to acid and alkaline conditions. The results show that TA loadings enhanced the resulting membrane properties. It increased the bulk porosity, water uptake, and hydrophilicity, which translated into improved clean water flux from 15.4 L/m².h for the pristine PVDF membrane up to 3.3× for the TA-modified membranes with the 2 wt% TA loading. The flux recovery ratio (FRR) of the TA-modified membranes (FRRs = 78–83%) was higher than the pristine one (FRR = 58.54%), with suitable chemical stability too. The improved antifouling property for the TA-modified membranes was attributed to their enhanced hydrophilicity thanks to improved morphology and residual TA in the membrane matric.

Tannic acid-based functional coating: surface engineering of membranes for oil-in-water emulsion separation

Recent progress in the tannic acid-based functional coating for surface engineering of membranes toward oil-in-water emulsion separation is summarized.

A Dopamine/Tannic-Acid-Based Co-Deposition Combined with Phytic Acid Modification to Enhance the Anti-Fouling Property of RO Membrane

Reverse osmosis (RO) membranes are widely used in the field of water treatment. However, there are inevitably various fouling problems during long-term use. Surface engineering of RO membranes, such as hydrophilic modification, has attracted broad attention for improving the anti-fouling performance. In this work, we constructed a green biomimetic composite modification layer on the surface of polyamide membranes using a dopamine (DA)/tannic acid (TA) co-deposited layer to bridge the polyamide surface and hydrophilic phytic acids (PhA). The DA/TA interlayer could firmly adhere to the RO membranes, reducing the aggregation of DA and providing abundant phenolic hydroxyl sites to graft PhA. Meanwhile, the anchored PhA molecule bearing six phosphate groups could effectively improve the superficial hydrophilicity. The membranes were characterized by the SEM, AFM, XPS, water contact angle test, and zeta potential test. After surface modification, the hydrophilicity, smoothness, and surface electronegativity were enhanced obviously. The flux and rejection of the virgin membrane were 76.05 L·m⁻²·h⁻¹ and 97.32%, respectively. While the modified D2/T4-PhA membrane showed decent permeability with a water flux of 57.37 L·m⁻²·h⁻¹ and a salt rejection of 98.29%. In the dynamic fouling test, the modified RO membranes demonstrated enhanced anti-fouling performance toward serum albumins (BSA), sodium alginates (SA), and dodecyl trimethyl ammonium bromides (DTAB). In addition, the modified membrane showed excellent stability in the 40 h long-term test.

Multifunctional membranes with super-wetting characteristics for oil-water separation and removal of hazardous environmental pollutants from water: A review

Over the past few years, oil-water separation techniques have been widely researched due to influences of oil pollution. The oil pollution is significantly increasing day-by-day because of ever-increasing usage of oil in daily routine of humans and industrial activities. The separation of water from oil-water emulsions/mixtures through membrane technology has provided absolute necessary qualities such as low cost, eco-friendly, easy-operation and energy efficient. To build up the filter membranes with special super-wettability properties and bearing excellent multifunctional applications is highly attractive research area in current decade. However, evolution of membrane technology suffered many deficiencies including severe fouling, short-standing against high flow speed, surface wettability disorders, non-reusable and limited application. In this review article, we outline the recent advances in membrane technology with respect to special super-wettability properties, enhanced characteristics for purpose to serve oil-water separation, and more specifically its multifunctional applications. Therefore, this study is made for membranes having other than applications, in addition to oil-water separation. Further, the wetting phenomenon of these multifunctional membranes is addressed and highlighted the brief overview of surface wetting types including Superhydrophobic-Superoleophilic membranes, Superhydrophilic-Superoleophobic membranes, and Superhydrophilic-underwater Superoleophobic membranes. Moreover, relative fabrication procedures and multifunctional applications of developed multifunctional super-wetting membranes are also discussed along with wetting behavior. Finally, the current developments and achievements for oil-water separation multifunctional super-wetting membranes are concluded. Besides, it also explores the future challenges and obstacles associated to these membranes. Hence, this article provides brief overview of advancement of oil-water separation based multifunctional super-wetting membranes and ended with new thoughts of further modification/enhancement.

Peanut Leaf-Inspired Hybrid Metal-Organic Framework with Humidity-Responsive Wettability: toward Controllable Separation of Diverse Emulsions

Damage to the responsive superwetting material by external stimuli during the responsive process has been a ticklish question in recent years. We overcome this barrier by imitating a peanut leaf and designing a humidity-responsive MIL-100 (Fe)/octadecylamine-coated stainless steel mesh (HR-MOS). Such a material shows superhydrophilicity when ambient humidity is higher than saturated humidity, while it shows superhydrophobicity and high adhesion to water when ambient humidity is lower than saturated humidity. The peanut leaf-like two-level nanostructure of MIL-100 (Fe) is speculated as the principal factor to bring about the binary synergy wettability of the material. Accordingly, the material can realize humidity-controlled separation of at least 12 types of emulsions along with satisfactory durability. The responsive condition of the material is mild and green, which does lower damage to the material and environment. This strategy is the first to realize humidity-responsive wettability transition and provides a novel approach for manually controlled environmental protection.

Encapsulated green magnetic nanoparticles for the removal of toxic Pb2+ and Cd2+ from water: Development, characterization and application

Current research is based on an innovative approach of the fabrication of encapsulated sustainable, green, phytogenic magnetic nanoparticles (PMNPs), to inhibit the generation of secondary pollutants (Iron/Fe^o) during water treatment applications. These novel bio-magnetic membrane capsules (BMMCs) were prepared using two-step titration gel crosslink method, with polyvinyl alcohol and sodium alginate matrix as the model encapsulating materials to eliminate potentially toxic metals (Pb²⁺ and Cd²⁺) from water. The development of BMMCs was characterized by FTIR, XRD, XPS, SEM, VSM, TGA and EDX techniques. The effects of various operating parameters, adsorbent dose, contact time, solution pH, temperature, initial concentration of metals cations and co-existing ions were studied. The hysteresis loops have illustrated an excellent super-paramagnetic nature, demonstrating the smooth encapsulation of PMNPs without losing their magnetic properties. The maximum monolayer adsorptive capacities estimated at pH 6.5 by the Langmuir isotherm model were 548 and 610.67 mg/g for Pb²⁺ and Cd²⁺, respectively. The novel BMMCs did not only control oxidation of PMNPs but also sustained the adsorptive removal over a wide range of pH (3-8), and the electrostatic interaction and ion-exchange were the core adsorption mechanisms. The BMMCs could easily be regenerated using 25% HNO₃ as an eluent for successful usage in seven repeated cycles. Therefore, the BMMCs as a material can be used as an excellent sorbent or composite material to remove toxic metals Pb²⁺ and Cd²⁺, showing strong potential for improving water and wastewater treatment technologies.

Polyphenols at interfaces

Polyphenols are important molecules in living organisms, particularly in plants, where they serve as protectants against predators. They are also of fundamental importance in pharmacology for their antioxidant and antibacterial activities. Since a few years polyphenols are also used in surface functionalization mimicking the tannin deposition observed when tea or red wine are in contact with the surface of cups or glasses respectively. The interaction of polyphenols with proteins to yield colloids and of polyphenol with surfaces will be reviewed in this article to provide an overview of such particles and surface functionalization methods in modern surface science. Particular emphasis will be given to biological applications of polyphenols at interfaces.

Performance of synthesized cast and electrospun PVA/chitosan/ZnO-NH2 nano-adsorbents in single and simultaneous adsorption of cadmium and nickel ions from wastewater

The performance of synthesized cast and electrospun polyvinyl alcohol/chitosan/zinc oxide/aminopropyltriethoxylsilane (PVA/chitosan/ZnO-APTES) nano-adsorbents were compared in removal of Cd(II) and Ni(II) ions from wastewater. The adsorbents were characterized by SEM, BET, FTIR and TGA analyses. Furthermore, the swelling investigations were carried out to study the adsorbent stability in aqueous solution. The effect of several parameters such as contents of ZnO-NH₂, contact time, initial Cd(II) and Ni(II) concentration and temperature on the adsorption capacity was investigated in a batch mode. In comparison with cast adsorbent, nanofiber adsorbent indicated the better adsorption performance. The experimental data well fitted the double-exponential kinetic model. In single metal ion system, the maximum adsorption capacity of nanofiber for Cd(II) and Ni(II) ions is estimated to be 1.239 and 0.851 mmol/g, respectively, much higher than q_m of cast adsorbent for Cd(II) (0.625 mmol/g) and Ni(II) (0.474 mmol/g) ions. Thermodynamic parameters were investigated to identify the nature of adsorption process. In binary system of Cd(II)-Ni(II) ions, the inhibitory effect of competitive Cd(II) ion on the Ni(II) adsorption was greater than the inhibitory effect of competitive on the Cd(II) adsorption. The selectivity adsorption of both nanofiber and cast adsorbents was in order of Cd(II) > Ni(II).

Screening of physicochemical treatment processes for reducing toxicity of hair care products wastewaters

Toxicity reduction in wastewaters from small hair care products manufacturing companies using coagulation/flocculation/sedimentation or flotation, membrane separation and powdered activated charcoal adsorption was evaluated. Raw wastewater composition varied widely within and especially between companies, but all exhibited high acute toxicity to Daphnia similis (EC(I)50; 48 h < 0.02-0.33%). Coagulation with aluminum sulfate and polyaluminum chloride aided by cationic or anionic polymers, as well as filtration on ultra (UF) and nanofiltration (NF) membranes efficiently removed turbidity (>99%) and oil and grease (>99%) and all treated samples exhibited similar dissolved organic matter contents. However, elimination of acute toxicity was only achieved after UF on submerged hollow fiber membrane, while other membrane modules (tubular UF and NF) produced filtrates with residual toxicities equal to or higher than the wastewater samples treated by coagulation processes. Adsorption removed up to 90% of the soluble COD remaining after coagulation or membrane processes, but did not eliminate acute toxicity, possibly because of the presence of activated charcoal or substances leached from it in the treated samples. The results indicate the need for further studies to develop treatment strategies that can guarantee non-toxic effluents at costs compatible with those of the simple manufacturing processes used at small-scale cosmetics manufacturing plants.

Effective treatment of emulsified oil wastewater by the coagulation–flotation process

Ship emulsified oil wastewater was used as the research object in this study. The highly efficient coagulant demulsification degreasing mechanism and microbubble flotation technology were combined and the effects of coagulant type and dosage amount on the demulsification of emulsified oil wastewater were evaluated. The influence of the mixed coagulation effect of pH values, temperature, and hydraulic condition parameters were determined and water intake, air intake, and oil content were regulated. The coagulant for the demulsification of emulsified oil wastewater was screened; the dosage was 500 mg L⁻¹, and the removal capacity of the coagulant was in the following order: polyaluminum ferric chloride (PAFC) > polyaluminum chloride (PAC) > polysilicate aluminum ferric sulfate (PSAFS) > alum > Al₂(SO₄)₃ > polyferric sulfate > FeCl₃. Polyacrylamide (PAM) with added water was used to further reduce the oil content. The PAFC, PAC, and PSAFS were selected as coagulation–air flotation dynamic test alternative agents. The investment quantities of PAFC, PSAFS and PAM were 300 mg L⁻¹, 300 mg L⁻¹ and 30 mg L⁻¹, respectively. The stirring time was 5 min, the pH value was 6.5–6.9, the flow rate was 0.25 m³ h⁻¹, the oil content of the emulsified oil wastewater was 3000–5000 mg L⁻¹ and the effluent oil was stable below 15 ppm. The microbubble generation device using air flotation effluent was used in the two air flotation treatments to enhance the device efficiency. The air flotation device adopted the structural design of the upper part of the water inlet and the lower part of the micro-air bubble, which can increase the collision probability of the microbubble and improve the efficiency of oil removal.

Ship emulsified oil wastewater was used as the research object in this study.