Fouling Removal Research Articles

Effective and low-toxicity: A membrane cleaning method using peroxymonosulfate catalytic chlorination

In chemical membrane cleaning, the challenge is to efficiently remove irreversible fouling while minimizing the impact on membrane materials. Particularly, traditional hypochlorite cleaning will further lead to the generation of toxic halogenated by-products. To address these issues, a combined system composed of peroxymonosulfate and chloride (PMS/Cl−) was applied to clean irreversible-humic-acid-fouled polyethersulfone (PES) membranes. After fouled membranes were soaked for 1 h in a PMS/Cl− solution (10 mM/15 mM) at 25 °C under neutral conditions, 94% flux recovery and 96% resistance removal were realized. Surface properties of virgin and cleaned membranes were very similar, confirming the effectiveness of the PMS/Cl− solution in removing irreversible foulants. The stability of membrane separation performance during multiple fouling and cleaning cycles further confirmed the minimal impact on membrane materials. Rapid diminution of the peaks centered in the region of fulvic-like and humic-like components, monitored under 3D-fluorescence for the cleaning solution, was attributed to PMS-catalyzed chlorination, thereby revealing the primary foulant detachment mechanism. Crucially, the approach exhibited lower toxicity than hypochlorite, as evidenced by reduced halogenated by-products and lower acute toxicity to Photobacterium phosphoreum T3. Overall, this novel cleaning system is promising for the efficient and environmentally friendly removal of irreversible organic foulants in practical water-treatment.

Efficacies and mechanisms of different cleaning strategies for NF and RO membranes in a full-scale zero liquid discharge system

Membrane fouling conditions can be distinct for multi-step nanofiltration (NF) and reverse osmosis (RO) membrane processes in zero liquid discharge (ZLD) system. Customizing cleaning procedures according to fouling characteristics is imperative to improve the overall cleaning efficiency of the system. Herein, we performed four different “alkaline + acid” cleaning procedures, including alkaline solution (NaOH), acid solution (citric acid), metal chelating agents (Na2EDTA), and surfactants (SDS), on five fouled NF and RO membranes from a full-scale ZLD system for cold-rolling wastewater brine treatment. The“alkaline + acid” cleaning procedures were effective for organic and inorganic combined fouling removal in two-stage NF process, but failed to remove SiAl complex scaling completely for the 2nd RO process. Due to the slight membrane fouling, both performance and surface properties of 1st and 3rd pass RO membranes did not change significantly after the cleaning. The high pH-induced solubilization were the major mechanism for the removal of the SiAl complex. Na2EDTA/SDS addition caused the decrease of foulant-foulant and foulant-membrane interactions. Customizing membrane cleaning procedures based on membrane fouling characteristics can facilitate the stable operation of hybrid membrane system for the practical industrial wastewater ZLD treatment.

Adsorption and cake layer fouling in relation to Fenton cleaning of ceramic nanofiltration membranes

Catalytic ceramic nanofiltration (NF) is a promising technology for direct wastewater reclamation, given its high separation selectivity and reactive surfaces for oxidative removal of fouling. A better understanding of the relation between fouling types and oxidative cleaning efficacy under high organic loading conditions is of practical importance for realizing stable filtration/cleaning performance in long-term water reclamation operations. In this work, Fenton cleaning, using a hydrogen peroxide solution and an iron oxychloride catalyst pre-coat layer on top of commercially available ceramic NF membranes, was studied with respect to high organic loaded fouling, simulated by a concentrated sodium alginate solution in the presence of calcium. Adsorption (in the absence of a permeate flow) and constant-pressure filtration (with a permeate flow) experiments were performed to distinguish between permeance decreases as a result of either adsorptive or cake layer fouling. The results show that the flux evolution could be divided into an initial sharp flux decline, due to rapid adsorption of the foulants, and a subsequent gradual flux decrease, resulting from progressive cake build-up on the membrane. The two-stage flux decrease was enhanced during the constant-pressure filtration experiments, because they start at a high flux with a high fouling rate, while the flux gradually decreases as fouling proceeds. During multiple adsorption/cake filtration/Fenton cleaning cycles, the cake layer fouling was sufficiently removed by Fenton cleaning in contrast to the adsorptive fouling. However, the total permeate production during ceramic NF was not influenced by the remaining adsorptive fouling (after cleaning), since the adsorptive fouling always only occurs at the beginning of each cycle. The findings provide new insights into the criteria for evaluating and optimizing the efficacy of oxidative (Fenton) cleaning during ceramic NF in water treatment.

Highly hydrophilic and antifouling poly(vinylidene fluoride) hybrid ultrafiltration membranes incorporated with silver‐loaded iron‐based metal–organic frameworks

AbstractSilver‐loaded iron‐based metal–organic frameworks (Ag@FeBTC) are synthesized and incorporated with poly (vinylidene fluoride) (PVDF) to make hybrid ultrafiltration (UF) membranes and are efficiently utilized to treat water containing macromolecular pollutants. The chemical functionality and semi‐amorphous nature of the Ag@FeBTC are validated by FT‐IR and XRD, respectively. The morphology and elemental composition of PVDF/Ag@FeBTC membranes are probed by SEM and EDX mapping. The creation of pores is visibly seen in cross‐sectional SEM images and the improvement in roughness is noticed in AFM images. Because of the improved hydrophilicity of Ag@FeBTC on the PVDF membrane matrix, the contact angle is reduced to 33.9°. The excellent dispersion of Ag@FeBTC on the PVDF membrane matrix is observed through elemental mapping. The PVDF/Ag@FeBTC hybrid membranes exhibited higher pure water flux (160 L m−2 h−1) and greater than 90% rejection as well as flux recovery ratio for foulant removal (BSA and HA). The antimicrobial property of PVDF/Ag@FeBTC hybrid membranes is probed using a zone of inhibition test against E. coli and S. aureus, and the results revealed that the hybrid membranes possess superior antibacterial behavior. The long‐term stability of MOF in hybrid membranes is confirmed by AAS. Overall characterization and performance results of the hybrid PVDF/Ag@FeBTC UF membrane clearly demonstrated its potential use for water treatment applications.

Enhanced hydroxyl radical generation for micropollutant degradation in the In2O3/Vis-LED process through the addition of periodate

Periodate (PI) as an oxidant has been extensively studied for organic foulants removal in advanced oxidation processes. Here PI was introduced into In2O3/Vis-LED process to enhance the formation of ·OH for promoting the degradation of organic foulants. Results showed that the addition of PI would significantly promote the removal of sulfamethoxazole (SMX) in the In2O3/Vis-LED process (from 9.26% to 100%), and ·OH was proved to be the dominant species in the system. Besides, the process exhibited non-selectivity in the removal of different organic foulants. Comparatively, various oxidants (e.g., peroxymonosulfate, peroxydisulfate, and hydrogen peroxide) did not markedly promote the removal of SMX in the In2O3/Vis-LED process. Electrochemical analyses demonstrated that PI could effectively receive photoelectrons, thus inhibiting the recombination of photogenerated electron-hole (e−/h+) pairs. The holes then oxidized the adsorbed H2O to generate ·OH, and the PI converted to iodate at the same time. Additionally, the removal rate of SMX reduced from 100% to 17.2% as Vis-LED wavelengths increased from 440 to 560 nm, because of the low energy of photons produced at longer wavelengths. Notably, the species of PI do not affect its ability to accept electrons, resulting in the degradation efficiency of SMX irrespective of pH (4.0–10.0). The coexistence of inorganic cations and anions (such as Cl−, CO32−/HCO3−, SO42−, Ca2+, and Mg2+) also had an insignificant effect on SMX degradation. Furthermore, the process also showed excellent degradation potential in real water. The proposed strategy provides a new insight for visible light-catalyzed activation of PI and guidance to explore green catalytic processes for high-efficiency removal of various organic foulants.

Alloying effect of PdCu-TiO2 in photocatalytic membrane reactor for efficient removal of humic acid foulant

Photocatalytic membrane reactor (PMR), coupling photocatalysis and membrane separation, has shown a considerable potential in foulant removal. However, the serious membrane fouling and fragile membrane stability still limit the application of current PMR systems. Here, we report a strategy that PdCu alloy deposited on TiO2, which is incorporated with polyvinylidene fluoride membrane, achieves high humic acid (HA) rejection efficiency (100%) with enhanced membrane permeation and anti-fouling performance. Detailed characterizations demonstrate that alloying effect of PdCu-TiO2 plays multiple roles in improving PMR performance: (1) providing the paired Pd-Cu sites for enhancing HA adsorption and transferring electrons from Pd-Cu sites to HA to improve photocatalytic HA removal; (2) inducing the photothermal effect due to the carrier damping, which directly enhances membrane permeation. The remarkable properties of PdCu-TiO2 membrane in PMR confirm the significance of alloying effect for treating aqueous organic pollutants.

Removal of Membrane Fouling and Control of Halogenated By-Products by a Combined Cleaning Process with Peroxides and Sodium Hypochlorite

Sodium hypochlorite (NaClO) solution is wildly used to remove membrane fouling-derived organic materials and restore membrane flux, which can result in the formation of halogenated by-products. To reduce the halogenated by-products, a combined cleaning process with NaClO and peroxides including hydrogen peroxide (H2O2), peroxydisulfate (PDS), and peroxymonosulfate (PMS) were applied in offline mode to remove the organic fouling. It was found that all the combined cleaning processes could effectively restore the membrane flux. Compared with the process of NaClO cleaning followed by peroxide cleaning (NaClO–peroxide), fewer halogenated by-products were generated in the NaClO post-combined cleaning process (peroxide–NaClO), and the PDS–NaClO cleaning process exhibited the best performance in controlling by-products. Overall, most by-product generation showed a positive correlation with reaction time and temperature.

The peroxidase-like cleaning strategy for organic fouling of water treatment membranes based on MoS2 functional layers

Efficient cleaning strategies play a key role in implementing sustainable and economic membrane operations during water treatments and purification. We proposed in this paper to construct the functional layers on the surface of PES substate using MoS2 nanosheets synthesized by a hydrothermal method, namely MoS2/PES membrane. The membrane structure and properties were characterized by SEM, XRD, EDS and FTIR. This is then followed by an evaluation of the membrane fouling of the functional layers, and in turn exploring the membrane cleaning strategy. The specific catalytic effects between MoS2 nanosheets with peroxidase-like activity, and the cleaning agent (H2O2) was subtly combined to endow MoS2 functional layers with specific catalysis. Humic acid (HA, as a representative organic foulant) having the filtration efficiency (~91 %) of MoS2/PES membrane was ~6 % higher than that of the pristine PES membrane. The flux recovery rate of MoS2/PES membrane (~75 %) was significantly larger than the PES membrane (~16 %) under optimized conditions. Results of 7 cycles of consecutive membrane fouling and cleaning demonstrated MoS2 functional layers not only relieved membrane fouling but also exhibited higher water flux. The outstanding performance of MoS2 functional layers could be explained by their stacked honeycomb pore-like structure and the catalytic characteristics of MoS2-like peroxidases. H2O2 was used to trigger the in-situ catalytic function of MoS2 layers, generating strong ROS and oxygen for the enhanced removal of organic foulants. This study provides new insights into devising a novel membrane cleaning strategy using advanced functional nanomaterials.

Numerical investigation about the unsteady behavior of a free submerged cavitation jet using the SBES approach

Submerged cavitation jet has emerged as an efficient method for the removal of ship fouling. Due to the complicated revolution of cavitation cloud, it has attracted great research interest. Ascertaining the internal flow dynamics of cavitating jets is always a challenge. Thus, this paper investigates the unsteady behavior of a free submerged cavitating jet numerically in three dimensions. The turbulent cavitation flow is simulated utilizing the Stress-Blended Eddy Simulation (SBES) turbulent model combined with the Schnerr-Sauer cavitation model. The results are compared with the data from a famous experiment, and they exhibit good agreement in both time-averaged and unsteady characteristics. The cavitation life stages, i.e., the cavitation growth, shedding, contraction, and collapse are explored. In results, cavitation cloud forms around the jet core. Cavitation cloud shedding involves complex factors, including shear layer instability, complex pressure gradients, and re-entrant motion, and it may also be related to the potential core and jet core instability. Additionally, cavitation cloud development is closely related to the jet core and exhibits synchronous behavior. After the cavitation cloud collapse, a local high pressure is observed and then cavity rebound is generated, where the collapse can be either mild or intensive.

Responsive polymer thin films

Responsive polymer thin films

Base-activated persulfate strategy for ceramic membrane cleaning after treatment of natural surface water

The natural organic matters (NOM) have been proved to form the hydraulically irreversible membrane fouling, which limit the application of the membrane in water treatment processes. To solve the membrane fouling caused by NOM, a novel one-step chemical cleaning method for the ceramic membrane derived from the base-activated persulfate oxidation process was developed in this study. When the SiC ceramic membranes was used to filtrate practical river water, the permeate flux dropped 65% as ΔTMP reached 30 kPa. After 2 h immersion of the fouled membrane in the cleaning solution (2 mM PMS and 8 mM NaOH), the flux recovery rate nearly reached 100%. Direct backwash of the membrane by the above cleaning solution further reduced the cleaning time to 25 mins, while achieving similar cleaning effect. Then the cleaned membranes were immersed in NaClO solution to release all the residual foulants, but the fluorescence excitation-emission matrix spectra (EEM) and total organic carbon (TOC) of the solution were found insignificant, which demonstrated the base-activated persulfate strategy had effectively removed the irreversible membrane fouling. Free radical quenching experiments were carried out and·O2- was identified as the dominant ROS responsible for the removal of the membrane foulants. The permeate flux and filtration efficiency of the SiC membrane were stable after 5 consecutive fouling-cleaning cycles, and the membrane structure was not damaged. In summary, the base-activated persulfate strategy is an efficient and cleaner method for SiC membrane cleaning, which is potential to be applied in practical membrane water treatment process.

Characterization of asphaltene removal mechanisms from well columns using surface energy

The deposition of asphaltene in well columns would compromise flow assurance and possible occurrence of under deposit corrosion. The formed deposit is the net difference between deposition and removal of asphaltene fouling. While there has been a body of research on deposition, the subjects of removal and its dominant mechanisms have received less attention. The present study therefore examines the most important removal mechanisms of shear force, rolling, and rebound under field operating conditions. To achieve this, the removal critical velocity was examined as a function of oil properties of density (870–1000 kg/m3) and viscosity (1.5–3.0 cP), casing diameter (4.5–7 in), and casing substrate (two grades of carbon steel). Experiments were used to determine the preliminary surface energy/tension characteristics of the investigated casing surfaces, crude oil sample, and crude oil-extracted asphaltene particles. The findings revealed that the casing substrate would profoundly influence the removal of asphaltene from the surface whereas the impact of oil properties and casing diameter would be meagre. Furthermore, the larger the asphaltene particles, the greater the possibility for asphaltene removal. For similar thermodynamic, hydrodynamic, and geometrical conditions, the rebound is the major mechanism for removal of asphaltene deposits, according to the predicted critical removal velocities. Finally, to calculate the proportion of precipitated asphaltene particles that would ultimately attach to the surface of the casing, the sticking probability is examined.

Effect of temperature, wall shear stress, and NaOH concentration on cleaning effectiveness.

The objective of this research was to evaluate the effect of various operational parameters and their interaction on cleaning rate of NaOH. The parameters include wall shear stress, temperatures, and NaOH concentrations of cleaning fluid. The higher cleaning effectiveness for proteinaceous deposits was achieved at higher wall shear stress. The wall shear stress of 2.42Pa removed over 90% of foulant after 10min of operation, which was significantly higher than the removal of lower wall shear stress (0.84 and 0.39Pa). Similarly, the cleaning rate increased with increase in temperature and concentration of cleaning solution. The use of cleaning solution (0.05% NaOH) at 65°C provided significantly higher cleaning rate than 25°C. A cleaning solution concentration of 0.5% NaOH provided significantly higher removal of foulant than 0% or 0.05% concentrations. However, analysis on the interaction between temperature and the wall shear stress suggested that the temperature above 45°C and wall shear stress above 0.65Pa did not provide significant improvement in cleaning efficacy. When a cleaning solution temperature was maintained at 45°C, higher wall shear stress provided more rapid removal of the foulant when the cleaning agent concentration was 0.05% or 0.5%. In water rinse conducted without chemical agents, no much improvements in foulant removal were observed with increase in wall shear stress. The change of activation energy (Ea ) indicates that water rinse was sensitive to temperature change at higher wall shear stress. However, cleaning with cleaning agents was less sensitive to temperature variation compared to the water rinse. PRACTICAL APPLICATION: Considering the intense use of water and chemical compounds during cleaning operation, finding operating condition to ensure acceptable cleanness with minimized input is desired. Temperature, cleaning agent concentration, and wall shear stress are the major components to influence the cleaning efficacy. The result of the study demonstrates the potential for optimization of in-place cleaning by appropriate adjustments of the CIP operating parameters.

Novel high-throughput screening platform identifies enzymes to tackle biofouling on reverse osmosis membranes

Biofouling is a ubiquitous problem in many industrial systems including reverse osmosis (RO) desalination units where the biofilm impedes the water flow. It is essential to develop novel cleaning methods that are non-damaging and environmentally friendly. The most promising cleaning agents are enzymes, which can selectively cleave the components that stabilize the biofilm. However, biofilm-degrading enzymes are often difficult to identify due to the unknown matrix composition and lack of effective screening methods. To overcome this, a flexible screening platform was developed to evaluate enzyme treatment on fouling removal directly on RO membranes. The developed platform was used to identify enzymes that could degrade biofilms on fouled RO membranes. The membrane biofilms were destabilized by a range of enzyme groups, most effectively by proteases, lipases, DNase, cellulolytic enzymes, and pectin-degrading enzymes. The most effective enzyme formulations could clean the membranes more effectively than conventional chemical cleaning agents, removing 45 % of the biofilm compared with 0 %–19 % for the chemicals (p ≤ 0.001), indicating that enzymes have the potential to replace or complement chemical cleaning. The screening platform thus proved a potent tool for systematically studying biofilms and could be applied to combat biofilms in many other applications.

Application of Nanozymes in Environmental Monitoring, Management, and Protection

Nanozymes are nanomaterials with enzyme-like activity, possessing the unique properties of nanomaterials and natural enzyme-like catalytic functions. Nanozymes are catalytically active, stable, tunable, recyclable, and versatile. Therefore, increasing attention has been paid in the fields of environmental science and life sciences. In this review, we focused on the most recent applications of nanozymes for environmental monitoring, environmental management, and environmental protection. We firstly introduce the tuning catalytic activity of nanozymes according to some crucial factors such as size and shape, composition and doping, and surface coating. Then, the application of nanozymes in environmental fields are introduced in detail. Nanozymes can not only be used to detect inorganic ions, molecules, organics, and foodborne pathogenic bacteria but are also involved in the degradation of phenolic compounds, dyes, and antibiotics. The capability of nanozymes was also reported for assisting air purification, constructing biofuel cells, and application in marine antibacterial fouling removal. Finally, the current challenges and future trends of nanozymes toward environmental fields are proposed and discussed.

Chemical hazard of robotic hull in-water cleaning discharge on coastal embryonic fish

In-water cleaning (IWC) involves the removal of biofilms and foulants from the hull of a ship using brush or water jet. During IWC, several factors associated with the harmful chemical contaminants release to the marine environment, which can create “hotspots” of chemical contamination in coastal areas. To elucidate the potential toxic effects of IWC discharge, we investigated developmental toxicity in embryonic flounder, which are sensitive life stage to chemical exposure. Zinc and copper were the dominant metals, while zinc pyrithione was the most abundant biocide associated with IWC discharge in two remotely operated IWC. Discharge from IWC carried by both remotely operated vehicles (ROVs) produced developmental malformations including pericardial edema, spinal curvature, and tail-fin defects. In an analyses of differential gene expression profiles (fold-change of genes with a cutoff < 0.05) as assessed by high-throughput RNA sequencing, genes associated with muscle development were commonly and significantly changed. The gene ontology (GO) of embryos exposed to IWC discharge from ROV A activities highly enriched muscle and heart development, while cell signaling and transport were evident in embryos exposed to IWC discharge of ROV B. We analyzed the gene network by significant GO terms. In the network, TTN, MYOM1, CASP3, and CDH2 genes appeared to be key regulators of the toxic effects on muscle development. In embryos exposed to ROV B discharge, HSPG2, VEGFA, and TNF genes related to the nervous system pathway were affected. These results shed light on the potential impacts of muscle and nervous system development in non-target coastal organisms exposed to contaminants found in IWC discharge.

CaO2-based tablet for effective and green membrane cleaning without additional catalysts

Natural organic matter humic acid (HA) coupled with the inorganic metal oxides FeOx + MnOx will cause severe irreversible membrane fouling. Chemical cleaning is indispensable for the removal of irreversible membrane foulants and sustainable membrane filtration, while conventional cleaning methods have limitations with low cleaning efficiency, high reagents consumption and potential membrane damage. For the first time, calcium peroxide (CaO2), a solid alternative for liquid hydrogen peroxide (H2O2), is proposed for the membrane cleaning. For membranes fouled by HA, it is noteworthy that 40 mg/32.15 cm2 CaO2 tablet without any other catalyst can restore the terminal membrane flux dramatically from 51% to 82% in only 5 min, which is far more than 3 wt% H2O2 alone (only from 51% to 59%). Moreover, Fenton-like reaction induced by in-situ membrane foulants FeOx + MnOx further enhances the membrane flux from 53% to 97%. Based on HA oxidation tests and reactive species identification in CaO2 tablets cleaning process for the case of HA-fouled membranes and HA + FeOx + MnOx-fouled membranes, singlet oxygen (O21) in CaO2 system dominated the strong oxidation of electron-rich compounds HA, which plays a key role in membrane flux recovery. With involvement of FeOx + MnOx, signal intensities of free radicals such as hydroxyl radicals (OH•) are enhanced greatly, which further achieves more outstanding membrane cleaning performance. These results underline that the novel CaO2 system provides a promising candidate for more portable and cost-effective membrane cleaning method in a nonradical pathway.

Fouling management in oceanic carbon capture via in-situ electrochemical bipolar membrane electrodialysis

To assist reaching net-zero emissions, the dissolved carbon in the ocean can be extracted to enable an indirect air capture. An electrochemical bipolar membrane electrodialysis (BPMED) is a sustainable method for such capture. The BPMED enables a pH-swing that manipulates the oceanic carbonate-equilibrium using electricity. However, at alkaline-pH, an in-situ process suffers from inorganic fouling within the stack, increasing the cost of capture. In the current work, we investigate fouling management strategies including fouling control (i.e., membrane- configuration and current-flow rate optimization) and fouling removal methods. Fouling removal methods including air and CO2(g) sparging, dissolved CO2 (aq) cleaning, back-pressure, flow rate increase, and acid-wash are investigated under accelerated fouling conditions. The stack configuration containing the BPM-AEM pairs shows 4 × lower fouling than the BPM-CEM stack, while the carbonate-extraction and faradaic efficiency are similar for both configurations. From the scaling removal methods, only the acid wash combined with the back-pressure removed all the inorganic fouling, recovering both the cell voltage and pressure drop to their initial values. Upon the air sparging, the total cell voltage and pressure drop increased even more due to the trapped gas inside the netted spacers. Cleaning via dissolved and gaseous CO2 decreases the cell pH, dissolving hydroxide/carbonate-based fouling, but decreases the carbonate-removal significantly which is not preferred. Applying the back-pressure and higher flow rates decelerated the scaling buildup but was not enough to remove the fouling. Using BPM-AEM stacks in combination with periodic acid cleaning has potential as resilient oceanic carbon removal via BPMED.

Application of a membrane photobioreactor combined with microalgae for shrimp culture wastewater treatment

Shrimp farming has emerged as a multi-billion-dollar industry in our country, creating numerous economic benefits. However, this sector has several negative environmental impacts. Recent studies on the utilization of microalgae for wastewater treatment are of current interest due to their environmental remediation ability, as well as their potential to generate economic value from the biomass produced after treatment. This study aimed to evaluate the wastewater treatment efficiency of Chlorella Vulgaris using a PMBR membrane photobiological model in shrimp aquaculture. The evaluation process included an acclimatization phase and a treatment effectiveness evaluation phase, which lasted a total of 101 days. Algae biomass, the removal efficiency of COD, N-NO -, N-NO -, N-NH +, and P-PO 3-, and membrane fouling behavior were analyzed. The initial results demonstrated that the algae were well-adapted to shrimp aquaculture wastewater. The removal efficiency of N-NO -, N-NO -, N-NH +, and P-PO 3- and COD was 88.55%, 76.15%, 84.58%, 78.07%, and 81.33%, respectively. The algae biomass steadily increased from 91.3 mg/L to 327.69 mg/L, reaching an average level of about 208 mg/L. Additionally, the transmembrane pressure (TMP) evaluation indicated that the necessary time for membrane fouling removal was approximately 25-26 days.

Fouling Resistance and Release Properties of Poly(sulfobetaine) Brushes with Varying Alkyl Chain Spacer Lengths and Molecular Weights

We examined the effects of alkyl carbon spacer length (CSL) and molecular weight on fouling resistance and release properties of zwitterionic poly(sulfobetaine methacrylate) brushes. Using surface-initiated atom transfer radical polymerization, we synthesized two series of brushes with CSL = 3 and 4 and molecular weight from 19 to 1500 kg ·mol-1, corresponding to dry brush thickness from around 6 to 180 nm. The brush with CSL = 3 was nearly completely wet with water (independent of molecular weight), whereas the brush with CSL = 4 exhibited a strong increase in water contact angle with molecular weight. Though the two-brush series had distinct wetting properties, both series of brushes exhibited similarly great resistance against fouling by Staphylococcus epidermidis bacteria and Aspergillus niger fungi spores when submerged in water, indicating that neither molecular weight nor CSL strongly affected the antifouling behavior. We also compared the efficacy of brushes against fouling by fungi and silicon oil in air. Brushes grafted to filter paper were strongly fouled by fungi and silicon oil in air. Grafting the polymers to the filter paper, however, greatly enhanced removal of the foulant upon rinsing. The removal of fungi and silicon oil when rinsed with a salt solution was enhanced by 219 and 175%, respectively, as compared to a blank filter paper control. Thus, our results indicate that these zwitterionic brushes can promote foulant removal for dry applications in addition to their well-known fouling resistance in submerged conditions.