Removal of endocrine disruptors and pharmaceuticals by graphene oxide-based membranes in water: A review.

Membrane-based water treatment has emerged as a promising solution to address global water challenges. Graphene oxide (GO) has been successfully employed in membrane filtration processes owing to its reversible properties, large-scale production potential, layer-to-layer stacking, great oxygen-based functional groups, and unique physicochemical characteristics, including the creation of nano-channels. This review evaluates the separation performance of various GO-based membranes, manufactured by coating or interfacial polymerization with different support layers such as polymer, metal, and ceramic, for endocrine-disrupting compounds (EDCs) and pharmaceutically active compounds (PhACs). In most studies, the addition of GO significantly improved the removal efficiency, flux, porosity, hydrophilicity, stability, mechanical strength, and antifouling performance compared to pristine membranes. The key mechanisms involved in contaminant removal included size exclusion, electrostatic exclusion, and adsorption. These mechanisms could be ascribed to the physicochemical properties of compounds, such as molecular size and shape, hydrophilicity, and charge state. Therefore, understanding the removal mechanisms based on compound characteristics and appropriately adjusting the operational conditions are crucial keys to membrane separation. Future research directions should explore the characteristics of the combination of GO derivatives with various support layers, by tailoring diverse operating conditions and compounds for effective removal of EDCs and PhACs. This is expected to accelerate the development of surface modification strategies for enhanced contaminant removal.

Adsorption of Ba2+ and Sr2+ on Ti3C2Tx MXene in model fracking wastewater.

Wastewater from hydraulic fracking contains both organic and inorganic pollutants; the latter include radioactive nuclides such as Ba2+ and Sr2+. We explored whether MXene (Ti3C2Tx), a novel adsorbent, could remove Ba2+ and Sr2+ from model wastewater. Zeta potential analysis showed that MXene had a high negative surface charge. MXene adsorbed Ba2+ and Sr2+ via electrostatic attraction, as confirmed by the adsorption at different solution pH values and in the presence of various concentrations of other ions (NaCl and CaCl2). MXene exhibited outstanding adsorption of Ba2+ and Sr2+, to approximately 180 and 225 mg g-1, respectively, when 1 g L-1 MXene was admixed with adsorbates at 2 g L-1. MXene exhibited very rapid adsorption kinetics, attaining equilibrium within 1 h. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed that MXene adsorbed Ba2+ and Sr2+, respectively, via ion exchange and inner-sphere complex formation. Finally, we performed MXene reusability tests; reusability was excellent over at least four cycles. Thus, MXene removed Ba2+ and Sr2+ from model fracking wastewater.

Heterogeneous sonocatalytic degradation of an anionic dye in aqueous solution using a magnetic lanthanum dioxide carbonate-doped zinc ferrite-reduced graphene oxide nanostructure.

We report herein the sonochemical synthesis of a lanthanum dioxide carbonate (La2O2CO3) and zinc ferrite (ZnFe2O4)-loaded reduced graphene oxide (LZF-rGO) nanoheterostructure for ultrasound (US)-assisted degradation of methyl orange (MO) from water. The MO was chosen as a model organic dye due to its toxicological and biodegradable-resistant properties. The LZF-rGO catalyst was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results of characterizations confirmed successful synthesis of sonocatalyst. Among different removal systems, US/LZF-rGO displayed outstanding sonodegradation performance for degradation of MO. The maximum removal efficiency of 75.9% was achieved using 0.2 g/L sonocatalyst, 20 mg/L MO, and 0.71 W/cm2 US power intensity for 65 min. MO can be partially adsorbed on LZF-rGO but mostly sonodegraded by reactive radical species. The reaction conditions were optimized by investigating the effect of key operating parameters, including the sonocatalyst dosage, initial MO concentration, US power intensity, presence of inorganic salts, and use of an enhancer, on the decolorization of MO. The degradation intermediates produced from MO during the sonocatalytic process were identified by UPLC®/MS-MS, and possible mechanism and pathway for the degradation of MO in the US/LZF-rGO system were also proposed. Reusability experiments with this sonocatalyst revealed a less than 10% drop in the degradation efficiency after four adsorption-desorption cycles.

Removal of trivalent chromium ions in model contaminated groundwater using hexagonal boron nitride as an adsorbent.

The feasibility of using hexagonal boron nitride (h-BN) to treat heavy metal Cr(III) from model contaminated groundwater was evaluated in this study by adsorption experiments and characterizations. To the best of our knowledge, this study is the first attempt to conduct the adsorption of Cr(III) by h-BN under various experimental conditions such as exposure time, ratio of adsorbates and adsorbents, solution pH, background ions with different ionic strength, and the presence of humic acids (HA) in model contaminated groundwater. The optimized h-BN showed excellent maximum adsorption capacity (i.e., 177 mg ∙ g-1) when the concentrations of Cr(III) and h-BN were 10 and 10 mg ∙ L-1, respectively. Subsequently, we confirmed there was a negligible change in the adsorption performance of Cr(III) by h-BN in the presence of co-ions (i.e., K and Mg) in concentrations in a range from 50 to 1000 mg ∙ L-1. Furthermore, the adsorption performance of Cr(III) gradually improved with HA concentrations from 2.5 to 25 mg ∙ L-1. Interestingly, the maximum adsorption performance of Cr(III) by both HA and h-BN increased until 500 mg ∙ g-1 in the presence of 25 mg ∙ L-1 HA. The adsorption mechanism was clarified by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Additionally, we successfully confirmed that h-BN could be reused until five cycles. On the basis of the adsorption performance results and characterizations, h-BN can be utilized as an efficient and practical adsorbent to treat Cr(III) in groundwater treatment.

Photocatalytic boron nitride-based nanomaterials for the removal of selected organic and inorganic contaminants in aqueous solution: A review.

Boron nitride (BN) coupled with various conventional and advanced photocatalysts has been demonstrated to exhibit extraordinary activity for photocatalytic degradation because of its unique properties, including a high surface area, constant wide-bandgap semiconducting property, high thermal-oxidation resistance, good hydrogen-adsorption performance, and high chemical/mechanical stability. However, only limited reviews have discussed the application of BN or BN-based nanomaterials as innovative photocatalysts, and it does not cover the recent results and the developments on the application of BN-based nanomaterials for water purification. Herein, we present a complete review of the present findings on the photocatalytic degradation of different contaminants by various BN-based nanomaterials. This review includes the following: (i) the degradation behavior of different BN-based photocatalysts for various contaminants, such as selected dye compounds, pharmaceuticals, personal care products, pesticides, and inorganics; (ii) the stability/reusability of BN-based photocatalysts; and (iii) brief discussion for research areas/future studies on BN-based photocatalysts.

Adsorption of uranyl ion on hexagonal boron nitride for remediation of real U-contaminated soil and its interpretation using random forest.

Acid leaching has been widely applied to treat contaminated soil, however, it contains several inorganic pollutants. The decommissioning of nuclear power plants introduces radioactive and soluble U(VI), a substance posing chemical toxicity to humans. Our investigation sought to ascertain the efficacy of hexagonal boron nitride (h-BN), an highly efficient adsorbent, in treating U(VI) in wastewater. The adsorption equilibrium of U(VI) by h-BN reached saturation within a mere 2 h. The adsorption of U(VI) by h-BN appears to be facilitated through electrostatic attraction, as evidenced by the observed impact of pH variations, acidic agents (i.e., HCl or H2SO4), and the presence of background ions on the adsorption performance. A reusability test demonstrated the successful completion of five cycles of adsorption/desorption, relying on the surface characteristics of h-BN as influenced by solution pH. Based on the experimental variables of initial U(VI) concentration, exposure time, temperature, pH, and the presence of background ions/organic matter, a feature importance analysis using random forest (RF) was carried out to evaluate the correlation between performances and conditions. To the best of our knowledge, this study is the first attempt to conduct the adsorption of U(VI) generated from real contaminated soil by h-BN, followed by interpretation of the correlation between performance and conditions using RF. Lastly, a. plausible adsorption mechanism between U(VI) and h-BN was explained based on the experimental results, characterizations, and a. comparison with previous adsorption studies on the removal of heavy metals by h-BN.

Ultrasonic treatment of endocrine disrupting compounds, pharmaceuticals, and personal care products in water: An updated review.

Pharmaceuticals, personal care products (PPCPs), and endocrine-disrupting compounds (EDCs) have seen a recent sustained increase in usage, leading to increasing discharge and accumulation in wastewater. Conventional water treatment and disinfection processes are somewhat limited in effectively addressing this micropollutant issue. Ultrasonication (US), which serves as an advanced oxidation process, is based on the principle of ultrasound irradiation, exposing water to high-frequency waves, inducing thermal decomposition of H2O while using the produced radicals to oxidize and break down dissolved contaminants. This review evaluates research over the past five years on US-based technologies for the effective degradation of EDCs and PPCPs in water and assesses various factors that can influence the removal rate: solution pH, temperature of water, presence of background common ions, natural organic matter, species that serve as promoters and scavengers, and variations in US conditions (e.g., frequency, power density, and reaction type). This review also discusses various types of carbon/non-carbon catalysts, O3 and ultraviolet processes that can further enhance the degradation efficiency of EDCs and PPCPs in combination with US processes. Furthermore, numerous types of EDCs and PPCPs and recent research trends for these organic contaminants are considered.

Ultrasonic treatment of dye chemicals in wastewater: A review.

The existence of pollutants, such as toxic organic dye chemicals, in water and wastewater raises concerns as they are inadequately eliminated through conventional water and wastewater treatment methods, including physicochemical and biological processes. Ultrasonic treatment has emerged as an advanced treatment process that has been widely applied to the decomposition of recalcitrant organic contaminants. Ultrasonic treatment has several advantages, including easy operation, sustainability, non-secondary pollutant production, and saving energy. This review examines the elimination of dye chemicals and categorizes them into cationic and anionic dyes based on the existing literature. The objectives include (i) analyzing the primary factors (water quality and ultrasonic conditions) that influence the sonodegradation of dye chemicals and their byproducts during ultrasonication, (ii) assessing the impact of the different sonocatalysts and combined systems (with ozone and ultraviolet) on sonodegradation, and (iii) exploring the characteristics-based removal mechanisms of dyes. In addition, this review proposes areas for future research on ultrasonic treatment of dye chemicals in water and wastewater.

Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review.

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

Ultrasonic degradation of selected dyes using Ti3C2Tx MXene as a sonocatalyst.

MXene, a new family of two dimensional materials, was utilized as a sonocatalyst in an ultrasonic treatment (US) process for removal of methylene blue (MB) and acid blue 80 (AB). The physico-chemical properties of MXene were characterized using scanning electron microscopy, transmission electron microscopy, porosimetry, and a zeta potential analyzer. Degradation of dyes by US was systemically investigated under several experimental conditions including: power density of US (45, 90, 135, and 180 W L-1), frequency of US (28 and 970 kHz), pH of dye solution (3.5, 7, and 10.5), solution temperature (293, 303, and 313 K), and addition of hydroxyl radical promotor (H2O2) and scavenger (t-BuOH) to concentrations of 25 mM. Based on the experimental results, the quantity of H2O2, which was used as an indicator of hydroxyl radical concentration, was an important factor in determining the degradation rate of MB and AB in this US study. Additionally, synergetic indices for removal of both dyes were higher than 1.0 in all cases, indicating the outstanding efficiency of MXene as a sonocatalyst in the US reactor for removal of both, due to an increase in both (i) the quantity of H2O2 in the US reactor and (ii) active sites for adsorbates from dispersion effects. A stability test on MXene in the US process was conducted using X-ray diffraction and five-cycle recycling performance tests. Based on our experimental data, MXene can be utilized as a sonocatalyst in the US process for a high removal rate for dyes (e.g., MB).

Ultrasound-assisted Ti3C2Tx MXene adsorption of dyes: Removal performance and mechanism analyses via dynamic light scattering.

Herein, ultrasonication (US)-assisted novel nanomaterial Ti3C2Tx MXene was utilized as a selective adsorbent for treatment of synthetic dyes in model wastewater. Two types of US frequencies, 28 and 580 kHz, were applied to disperse MXene to evaluate the feasibility of US-assisted MXene for wastewater treatment. The physico-chemical properties of MXene after US were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential. According to FTIR and XPS, 28 kHz US-assisted MXene had a greater amount of oxygenated functional groups and dispersion compared to 580 kHz US-assisted and pristine MXene. Subsequently, US-assisted MXene was utilized as an adsorbent for the removal of positively charged methylene blue (MB) and negatively charged methyl orange. Both 28 and 580 kHz US-assisted MXene showed better adsorption performance for only MB compared to stirring-assisted MXene based on kinetics, isotherms, and several water chemistry factors including solution pH, temperature, ionic strength, and humic acid. Advantages of US-assisted MXene for water treatment are its fast kinetics at low dose and high selectivity for positively charged target compounds (i.e., MB). The main adsorption mechanism between MXene and MB was electrostatic interaction (attraction); however, physical properties (i.e., aggregation kinetics and hydrodynamic diameter), measured via dynamic light scattering, were also found to be critical factors in controlling the adsorption performance of the system. Lastly, US-assisted MXene exhibited a high regeneration property, based on 4th adsorption-desorption cycles.

Novel Z-scheme Ag3PO4/Fe3O4-activated biochar photocatalyst with enhanced visible-light catalytic performance toward degradation of bisphenol A.

A novel solid-state Z-scheme heterostructure, Ag3PO4/Fe3O4 co-doped bamboo-derived activated biochar (Ag-Fe@BAB), was synthesized as an efficient photocatalyst via a co-precipitation method. Ag-Fe@BAB was used as a magnetically recoverable photocatalyst to generate free radical species with peroxydisulfate (PDS) activation under visible-LED-light illumination. The successful synthesis of Ag-Fe@BAB was confirmed by various characterization techniques. Bisphenol A (BPA) was used as a model pollutant to evaluate the photocatalytic activities of the Vis/Ag-Fe@BAB/PDS system. To confirm the photocatalytic performance of the Vis/Ag-Fe@BAB/PDS system, the effects of significant operating parameters such as the contact time, concentration of oxidant, photocatalyst dosage, and solution pH on the degradation of BPA were evaluated. We confirmed that 95.6% BPA was degraded within 60 min in the Vis/Ag-Fe@BAB/PDS system under 1.0 g/L photocatalyst, pH 6.5, and 0.5 mM PDS. The degradation mechanism of BPA in the Vis/Ag-Fe@BAB/PDS system was mainly attributed to O2‾ owing to its photocatalytic performances in the presence of p-benzoquinone as a scavenger. Furthermore, the radical species produced in the Vis/Ag-Fe@BAB/PDS system were identified by electron spin resonance. Finally, we demonstrated the recyclability of the Ag-Fe@BAB photocatalyst through its excellent magnetic property.

A review on MXene-based nanomaterials as adsorbents in aqueous solution.

Environmental pollution has intensified and accelerated due to a steady increase in the number of industries, and finding methods to remove hazardous contaminants, which can be typically divided into inorganic and organic compounds, have become inevitable. One of the widely used water treatment technologies is adsorption and various kinds of adsorbents for the removal of inorganic and organic contaminants from water have been discovered. Recently, MXene, as an emerging nanomaterial, has gained rapid attention owing to its unique characteristics and various applicability. Particularly, in the area of adsorptive application, MXene and MXene-based adsorbents have shown great potential in a large number of studies. In this regard, a comprehensive understanding of the adsorptive behavior of MXene-based nanomaterials is necessary in order to explain how they remove inorganic and organic contaminants in water. Adsorption by MXene-based adsorbents tends to be highly influenced by not only the physicochemical properties of these adsorbents but also water quality, such as pH value, temperature, background ion, and natural organic matter. Therefore, in this review paper, the effect of various water quality on the adsorption of inorganic and organic contaminants by various types of MXene and MXene-based adsorbents is explored. Furthermore, this review also covers general trends in the synthesis of MXene and regeneration of MXene-based adsorbents in order to assess their stability.

Applications of MXene-based membranes in water purification: A review.

Since MXenes (a new family of two-dimensional materials) were first produced in 2011, they have become very attractive nanomaterials due to their unique properties and the range of potential industrial applications. Numerous recent studies have discussed the environmental applications of different MXenes in adsorption, catalysis, and membranes. Only a limited number of MXene-based membrane studies have been published to date, and most have discussed only specific MXenes (i.e., Ti3C2Tx), a small number of solutes (e.g., dyes and inorganic salts), and laboratory-scale short-term experiments under limited water-quality and operational conditions. In addition, to our knowledge, there has been no review of MXene-membrane studies. It is therefore essential to assess the current status of understanding of the performance of these membranes in liquid separation and water purification. Here, a comprehensive literature review is conducted to summarize the current preparation techniques for MXene-based membranes and their applications, particularly in terms of environmental and industrial applications (e.g., water treatment and organic solvent filtration), and to direct future research by identifying gaps in our present understanding. In particular, this review focuses on several key factors, including the effects of preparation techniques on membrane properties, operational conditions, and compound properties that influence liquid separation during MXene-based membrane filtration.

Comprehensive evaluation of the removal mechanism of carbamazepine and ibuprofen by metal organic framework.

Pharmaceutical products (PhACs) in water sources are considered to be a severe environmental issue. To mitigate this issue, we used a metal-organic framework (MOF) as an adsorbent to remove selected PhACs (i.e., carbamazepine (CBM) and ibuprofen (IBP)). This work was carried out to characterize the MOF, then confirm its feasibility for removing the selected PhACs. In particular, based on practical considerations, we investigated the effects of various water quality conditions, such as solution temperature, pH, ionic strength/background ions, and humic acid. MOF exhibited better removal rates than commercial powder activated carbon (PAC), considering pseudo-second order kinetic model. We clarified the competitive PhACs adsorption mechanisms based on the results obtained under various water quality conditions and found that hydrophobic interactions were the most important factors for both adsorbates. To confirm the practicality of MOF adsorption, we carried out regeneration tests with four adsorption and desorption cycles using acetone as a cleaning solution. Furthermore, to support the results of our regeneration tests, we characterized the MOF samples before and after adsorbate exposure using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Overall, MOF can be used in practical applications as efficient adsorbents to remove PhACs from water sources.

Removal of heavy metals from water sources in the developing world using low-cost materials: A review.

Heavy metal contamination is a growing concern in the developing world. Inadequate water and wastewater treatment, coupled with increased industrial activity, have led to increased heavy metal contamination in rivers, lakes, and other water sources in developing countries. However, common methods for removing heavy metals from water sources, including membrane filtration, activated carbon adsorption, and electrocoagulation, are not feasible for developing countries. As a result, a significant amount of research has been conducted on low-cost adsorbents to evaluate their ability to remove heavy metals. In this review article, we summarize the current state of research on the removal of heavy metals with an emphasis on low-cost adsorbents that are feasible in the context of the developing world. This review evaluates the use of adsorbents from four major categories: agricultural waste; naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass; and other locally-available waste materials. Along with a summary of the use of these adsorbents in the removal of heavy metals, this article provides a summary of the influence of various water-quality parameters on heavy metals and these adsorbents. The proposed adsorption mechanisms for heavy metal removal are also discussed.

Enhanced sonocatalytic degradation of carbamazepine and salicylic acid using a metal-organic framework.

A metal-organic framework (MOF) was used as a sonocatalyst for ultrasonic (US) processes, to improve the degradation of two selected pharmaceutical active compounds (PhACs); carbamazepine (CBM) and salicylic acid (SA). The intrinsic characteristics of the MOF were characterized using a porosimeter (N2-BET) and scanning electron microscope (SEM). Various experiments were carried out under conditions with different US frequencies (28 and 1000 kHz), US power densities (45-180 W L-1), pH conditions (3.5, 7, and 10.5), and temperatures (293, 303, and 313 K) to investigate the degradation rates of the selected PhACs. Improved removal rates of PhACs were demonstrated within 60 min at 28 kHz (46% for SA; 47% for CBM) and 1000 kHz (60% for SA; 99% for CBM) with an MOF concentration of 45 mg L-1 in the US/MOF system, in comparison to 28 kHz (20% for SA; 25% for CBM) and 1000 kHz (37% for SA; 97% for CBM) under the 'US only' process. The removal of CBM was greater than that of SA under all experimental conditions due to the intrinsic properties of the PhACs. The degradation rates of PhACs are related to the quantity of H2O2; degradation is thus mostly affected by OH oxidation, which is generated by the dissociation of water molecules. The advantages of the 'US/MOF system' are as follows: (i) dispersion of MOF by US can improve sites and reactivity with respect to adsorption between the adsorbate (PhACs) and the adsorbent (MOF), and (ii) dispersed MOF acted as additional nuclei for water molecule pyrolysis, leading to the production of more OH. Therefore, based on the synergy indices, which were calculated using the removal rate constants [k1 (min-1)] of the pseudo-first order kinetic model, the 'US/MOF system' can potentially be used to treat organic pollutants (e.g., PhACs).

Comprehensive evaluation on removal of lead by graphene oxide and metal organic framework.

Graphene oxide (GO) and metal-organic framework (MOF) as adsorbents were applied to removal of Pb(II) with comprehensive characterizations and various experimental conditions. Various characterizations were conducted to clarify the physico-chemical properties of adsorbents. The analyses of adsorption experiments included (i) dosage amounts, (ii) isotherm and kinetic studies, and (iii) several factors related to water chemistry (i.e., solution pH, background ions, and humic acid). The maximum equilibrium adsorption capacity (qe) for Pb(II) using the GO and MOF was 555 and 108 mg g-1, respectively, as determined in the optimum dosage experiments. Although the surface area of the MOF (629 m2 g-1) was much larger than that of the GO (19.8 m2 g-1), the adsorption capacity of the MOF was five times lower due to electrical repulsion. Thus, the MOF was utilized as the control group for comparison with the GO to evaluate the adsorption mechanisms in the experiments related to surface charge (i.e., under various pH and humic acid conditions). The adsorption isotherms and kinetics model determined using GO followed the Langmuir model (R2 > 0.99) and pseudo-second-order model (R2 > 0.99), respectively. Additionally, three adsorption-desorption cycles were conducted with the GO adsorbent to evaluate the maintenance of the removal ratio after regeneration and the equilibrium adsorption capacity was determined. Finally, the adsorption of other heavy metals (i.e., Cu(II), Cd(II), and Zn(II)), separately and in mixtures, was also evaluated to determine the selectivity of the adsorbents.

Effect of chlorination condition and permeability of chlorine species on the chlorination of a polyamide membrane.

Most studies on membrane chlorination have been investigated in an unpressurized chlorination mode, even if the polyamide membrane was continuously exposed to chlorine under high operating pressure in real water/wastewater treatment plants. In this study, performance changes due to polyamide membrane chlorination were investigated in both pressurized and unpressurized chlorination modes. Chlorination in an unpressurized mode showed a flux increase at high pH and a flux decline at low pH due to the compaction and swelling of the polyamide chains, respectively. On the other hand, chlorination performed in a pressurized mode decreased the water flux in both acidic and alkaline conditions, showing that compaction is overwhelming compared to swelling. The permeability of HOCl, a dominant species at low pH, through the polyamide membrane was pH independent and almost similar to the system recovery, but the permeability of OCl(-), which is dominant at high pH, was maxima at a neutral pH. The different performance behaviors of membranes chlorinated at various pH conditions in the presence or absence of applied pressure could be explained by the permeability of chlorine species and compaction/swelling of polymer chains after chlorination. The effect of membrane chlorination on the chemical property changes at the two different modes was confirmed using attenuated total reflection Fourier transform infrared analysis, and a conceptual model of performance change was proposed to explain the performance discrepancy between the two chlorination modes.