Developing Polycation-Clay Sorbents for Efficient Filtration of Diclofenac: Effect of Dissolved Organic Matter and Comparison to Activated Carbon

Characterization of dissolved black carbon and its binding behaviors to ceftazidime and diclofenac pharmaceuticals: Employing the molecular weight fractionation

As the ubiquitous component of the aquatic environment, dissolved organic matter (DOM) readily bind with residual pharmaceutical contaminants (PCs) and influence their environmental behaviors. However, the binding mechanisms between dissolved black carbon (DBC), a vital part of the natural DOM pool, and PCs were poorly researched. In this study, the bulk DBC was divided into four fractions in molecular weight (MW) via an ultrafiltration system, and the properties of DBC and their binding interaction with two kinds of typical PCs (ceftazidime (CAZ) and diclofenac (DCF)) were explored concretely. The results showed that low MW component was the main contributor to bulk DBC, and the aromaticity increased with the increase of MW. The categories of chemical structures and fluorescent substances in different MW DBC were similar. Multispectral techniques showed that the oxygen-enriched compounds in DBC had the higher affinity to CAZ/DCF. The -NH-, -COOH, -NH₂ groups in CAZ molecules appeared to form the hydrogen bond with DBC. Fluorescence quenching experiments were analyzed, and the binding mechanisms were specifically expounded from the thermodynamic perspective. The fluorophore of fulvic acid-like compounds (FA) were quenched by both static and dynamic quenching mechanisms, while only static quenching occurred for humic acid-like compounds (HA). For bulk DBC, the hydrogen bond and van der Waals force were the major forces in the HA-CAZ system, while the hydrophobic force made the primary contribution to the HA-DCF system, which might be ascribed to the higher hydrophobic nature of DCF. Notably, with the increase of HA MW, the main binding mode of HA-CAZ/DCF changed from hydrophobic force to hydrogen bond and van der Waals force gradually, which also directly proved that various noncovalent interactions co-driven the binding processes. Our findings are beneficial to better assess the fate of DBC and PCs and the corresponding complexes in the aquatic environment.

Advances in Amine-Surface Functionalization of Inorganic Adsorbents for Water Treatment and Antimicrobial Activities: A Review

In the last decade, adsorption has exhibited promising and effective outcomes as a treatment technique for wastewater contaminated with many types of pollutants such as heavy metals, dyes, pharmaceuticals, and bacteria. To achieve such effectiveness, a number of potential adsorbents have been synthesized and applied for water remediation and antimicrobial activities. Among these inorganic adsorbents (INAD), activated carbon, silica, metal oxide, metal nanoparticles, metal–organic fibers, and graphene oxide have been evaluated. In recent years, significant efforts have been made in the development of highly efficient adsorbent materials for gas and liquid phases. For gas capture and water decontamination, the most popular and known functionalization strategy is the chemical grafting of amine, due to its low cost, ecofriendliness, and effectiveness. In this context, various amines such as 3-aminopropyltriethoxysilane (APTES), diethanolamine (DEA), dendrimer-based polyamidoamine (PAMAM), branched polyethyleneimine (PEI), and others are employed for the surface modification of INADs to constitute a large panel of resource and low-cost materials usable as an alternative to conventional treatments aimed at removing organic and inorganic pollutants and pathogenic bacteria. Amine-grafted INAD has long been considered as a promising approach for the adsorption of both inorganic and organic pollutants. The goal of this review is to provide an overview of surface modifications through amine grafting and their adsorption behavior under diverse conditions. Amine grafting strategies are investigated in terms of the effects of the solvent, temperature, and the concentration precursor. The literature survey presented in this work provides evidence of the significant potential of amine-grafted INAD to remove not only various contaminants separately from polluted water, but also to remove pollutant mixtures and bacteria.

Permanganate release from silica-based hollow mesoporous coagulant combined with UV for spatiotemporal enrichment and degradation of diclofenac sodium

In this work, the novel hollow mesoporous coagulant was prepared by chitosan-polydopamine coating and permanganate loading into silica nanoparticles for investigating the simultaneous enrichment and degradation of diclofenac sodium (DCFS) combined with ultraviolet irradiation. The enrichment kinetic of DCFS was explained well with pseudo-second-order model, indicating the exist of hydrogen bonding. Based on the correlation coefficients, the enriched isotherms were fitted by models which accorded with the BET > Freundlich > Langmuir sequence. The result showed that, in addition to the coagulant and DCFS, there were aromatic stackings among DCFS molecules. Due to both effects of which, the DCFS enrichment could be realized significantly in the range of pH 4.0-9.0. It was degraded at the copresence of ultraviolet and permanganate released from coagulant in acidic aqueous medium. The release mechanism was simulated through Korsmayer-Peppas model, implying case-II transport and Fickian diffusion. Additionally, Mn (V) and •OH radicals were vital in the DCFS degradation process. The coagulant could be reloaded at least ten times and that from each cycle was used directly for DCFS removal for six times without rinse process, which provided a potential application in environmental remediation.

Chemico-nanotreatment methods for the removal of persistent organic pollutants and xenobiotics in water - A review

While the technologies available today can generate high-quality water from wastewater, the majority of the wastewater treatment plants are not intended to eliminate emerging xenobiotic pollutants, pharmaceutical and personal care items. Most endocrine disrupting compounds (EDCs) and personal care products (PPCPs) are more arctic than most regulated pollutants, and several of them have acid or critical functional groups. Together with the trace occurrence, EDCs and PPCPs create specific challenges for removal and subsequent improvements of wastewater treatment plants. Various technologies have been investigated extensively because they are highly persistent which leads to bioaccumulation. Researchers are increasingly addressing the human health hazards of xenobiotics and their removal. The emphasis of this review was on the promising methods available, especially nanotechnology, for the treatment of xenobiotic compounds that are accidentally released into the setting. In terms of xenobiotic elimination, nanotechnology provides better treatment than chemical treatments and their degradation mechanisms are addressed.

Designing clay-polymer nanocomposite sorbents for water treatment: A review and meta-analysis of the past decade

Clay-polymer nanocomposites (CPNs) have been studied for two decades as sorbents for water pollutants, but their applicability remains limited. Our aim in this review is to present the latest progress in CPN research using a meta-analysis approach and identify key steps necessary to bridge the gap between basic research and CPN application. Based on results extracted from 99 research articles on CPNs and 8 review articles on other widely studies sorbents, CPNs had higher adsorption capacities for several inorganic and organic pollutant classes (including heavy metals, oxyanions, and dyes, n = 308 observations). We applied principal component analysis, analysis of variance, and multiple linear regressions to test how CPN and pollutant properties correlated with Langmuir adsorption model coefficients. While adsorption was, surprisingly, not influenced by mineral properties, it was influenced by CPN fabrication method, polymer functional groups, and pollutant properties. For example, among the pollutant classes, heavy metals had the highest adsorption capacity but the lowest adsorption affinity. On the other hand, dyes had high adsorption affinities, as reflected by the linear correlation between adsorption affinity and pollutant molecular weight. Scaling from 'basic research' to 'technological application' requires testing CPN performance in real water, application in columns, comparison to commercial sorbents, regeneration, and cost evaluation. However, our survey indicates that of the 158 observations, only 20 compared the CPN's performance to that of a commercial sorbent. We anticipate that this review will promote the design of smart and functional CPNs, which can then evolve into an effective water treatment technology.

A critical review of contaminant removal by conventional and emerging media for urban stormwater treatment in the United States

Stormwater is a major component of the urban water cycle contributing to street flooding and high runoff volumes in urban areas, and elevated contaminant concentrations in receiving waters from contact with impervious surfaces. Engineers and city planners are investing in best management practices to reduce runoff volume and to potentially capture and use urban stormwater. However, these current approaches result in moderate to low contaminant removal efficiencies for certain classes of contaminants (e.g., particles, nutrients, and some metals). This review describes options and opportunities to augment existing stormwater infrastructure with conventional and emerging reactive media to improve contaminant removal. This critical analysis characterizes media physicochemical properties and mechanisms contributing to contaminant removal, describes possible candidates for new engineered media, highlights lab and field studies investigating stormwater media contaminant removal, and identifies possible limitations and knowledge gaps in media implementation. Following this analysis, information is provided regarding factors that may contribute to or adversely impact urban stormwater treatment by media. The review closes with insights into additional research directions and important information necessary for safe and effective urban stormwater treatment using media.

Assembly of SPS/MgSi assisted by dopamine with excellent removal performance for ciprofloxacin

In this work, magnesium silicate-based sulfonated polystyrene sphere composites (SPS/MgSi) were synthesized by one-step (SMD1) and two-step (SMD2) methods. For SMD1, MgSi particles were densely assembled on the surface of SPS, assisted by complexation between Fe³⁺ and hydroxyl phenol. For SMD2, SPS/SiO₂ was firstly obtained by the same method as SMD1, and then SPS/SiO₂ was transformed directly to SPS/MgSi under hydrothermal conditions. Therefore, MgSi obtained by the two-step method had an interwoven structure. Compared to SPS, MgSi and SMD1, SMD2 presented a larger specific surface area and more negative surface charges. Therefore, SMD2 showed superior adsorption performance toward CIP with concentrations of 5, 10 and 50 mg/L, and for 50 mg/L, the equilibrium adsorption capacity could reach 329.7 mg/g. The adsorption process is fast and can be described by the pseudo-second-order kinetic model. The relationship between pH value and Zeta potential demonstrated that electrostatic interaction dominated the adsorption process. In addition, competitive adsorption showed that the effect of Na⁺ was negligible but the effect of Ca²⁺ was dependent on its concentration. Humid acid (HA) could slightly promote the absorption of CIP by SMD2. After five rounds of adsorption-desorption, the equilibrium adsorption capacity of SMD2 still remained at 288.6 mg/L for 50 mg/L CIP. Notably, SMD2 presented likewise superior adsorption capacity for CIP with concentrations of 10 and 50 mg/L in Minjiang source water. All the results indicated that this synthesis method is universal and that SMD2 has potential as an adsorbent for CIP removal from aquatic environments.

Bi2MoO6 nanofilms on the stainless steel mesh by PS-PED method: Photocatalytic degradation of diclofenac sodium as a pharmaceutical pollutant

For the first time, Bi₂MoO₆ nanofilms were successfully synthesized by simultaneous pulse sonication-pulse electrodeposition (PS-PED) on the stainless steel mesh surface. Bismuth molybdate films were formed under various combinations of electrodeposition and sonication (sono-electrodeposition) in continuous and pulse modes. Porous Bi₂MoO₆ films synthesized by PS-PED method and showed the highest efficiency in photocatalytic degradation in comparison with other films. Bi₂MoO₆ film obtained from PS-PED had a thickness of 13.78 nm while, the thickness for the electrodeposition method was 39.52 nm. The high photocatalytic efficiency is attributed to the high surface roughness and low thickness of film synthesized by PS-PED method. Indeed, ultrasound played a key role in the synthesis of films with high surface roughness. On the other hand, shock waves and micro-jets could be dissolved diffusion problems and reduced the dendrite like structures in deposition process. Simultaneous application of pulse modes for both combined methods led to more growth of crystallographic planes. This is due to reaction of ions on the surface in interval relaxation times and produce more nuclei for growth. In order to obtain a high efficiency, response surface methodology was used for optimization of effective variable parameters (t_on, t_off and sonication amplitude) in film preparation.

Application of surfactant modified montmorillonite with different conformation for photo-treatment of perfluorooctanoic acid by hydrated electrons

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a class of highly persistent contaminants with high bioaccumulation and toxicity. Our previous studies showed that perfluorooctanoic acid (PFOA) can be completely defluorinated under UV irradiation in organo-montmorillonite/indole acetic acid (IAA) system. However, there is still lack of information for the degradation mechanism and the test for wastewater treatment. Here, we systematically investigated the defluorination reaction in the presence of different organo-montmorillonites and found that the degradation process was apparently controlled by the configuration of surfactants. In hexadecyltrimethyl ammonium (HDTMA)-modified montmorillonite, HDTMA exists as a tilt conformation and isolated clay interlayer from the aqueous solution, protecting hydrated electrons generated by photo-irradiation of IAA from quenching by oxygen. Defluorination hydrogenation process was the dominant degradation pathway. While in poly-4-vinylpyridine-co-styrene (PVPcoS)-modified montmorillonite, due to the multiple charges of PVPcoS, a flat conformation parallel to clay surface was expected. Hydroxyl radicals, which were generated by the reaction of hydrated electrons with oxygen molecules diffused into clay interlayer, are also involved in the degradation process. Our results further demonstrate that mixture modified montmorillonite could combine the advantages of both modifications, thus showing superior reactivity even for actual industrial wastewater without any pretreatment. This technique would have great potential for treatment of actual wastewater.

Multivariate analysis and multiple linear regression as a tool to estimate the behavior of hexazinone in Brazilian soils

Weed control efficiency and the environmental contamination potential of herbicides depend on soil sorption and desorption. Among the indexes that evaluate the soil adsorption processes, the coefficients sorption (Kf_s) and desorption (Kf_d) obtained by Freundlich isotherms can provide accurate information about the behavior of an herbicide in the soil. The values of Kf_s and Kf_d of an herbicide vary according to the physicochemical characteristics of the soil, so it is possible to estimate these coefficients with high precision if good predictive mathematical models are constructed. Therefore, our objective aimed to evaluate the use of multiple regression models (MLR) associated with multivariate techniques to estimate the coefficient Kf_s and Kf_d for the hexazinone based on the chemical and physical attributes of soils. The correlation analyses, principal components, and clustering analysis allowed the multiple linear regression technique to generate models with higher adjustment coefficient (R²) for Kf_s (0.73 to 0.99) and Kf_d (0.94 to 0.99), and lower root mean squared error (RMSE) for Kf_s (0.003 to 0.065) and Kf_d (0.018 to 0.120). Regression models created from groups of soils showed greater prediction performance for Kf_s and Kf_d. The organic matter followed by the cation exchange capacity was the most important attributes of soils in sorption and desorption processes of hexazinone.

Ag3PO4 Deposited on CuBi2O4 to Construct Z-Scheme Photocatalyst with Excellent Visible-Light Catalytic Performance Toward the Degradation of Diclofenac Sodium

CuBi₂O₄/Ag₃PO₄ was synthesized through a combination of hydrothermal synthesis and an in situ deposition method with sodium stearate as additives, and their textures were characterized with XRD, XPS, SEM/HRTEM, EDS, UV-Vis, and PL. Then, the photodegradation performance of CuBi₂O₄/Ag₃PO₄ toward the degradation of diclofenac sodium (DS) was investigated, and the results indicate that the degradation rate of DS in a CuBi₂O₄/Ag₃PO₄ (1:1) system is 0.0143 min⁻¹, which is 3.6 times that in the blank irradiation system. Finally, the photocatalytic mechanism of CuBi₂O₄/Ag₃PO₄ was discussed, which follows the Z-Scheme theory, and the performance enhancement of CuBi₂O₄/Ag₃PO₄ was attributed to the improved separation efficiency of photogenerated electron–hole pairs.

Polymer-clay composite geomedia for sorptive removal of trace organic compounds and metals in urban stormwater

Functionalized polymer-clay composites were developed and characterized as engineered geomedia for trace contaminant removal during infiltration of urban runoff. Montmorillonite clays were functionalized with either poly(diallyldimethylammonium) chloride (PDADMAC) or poly(4-vinylpyridine-co-styrene) (PVPcoS) to enhance organic compound sorption using a simple, scalable synthesis method. Seven representative trace organic compounds and six trace metals were employed to assess the performance of the polymer-clay composites relative to biochar (i.e., an adsorbent proposed for similar purposes) in batch sorption and column studies under simulated stormwater conditions. Contaminant and geomedia electrostatic and hydrophobic interactions, and the presence of natural organic matter (NOM) affected sorption. In batch studies, polymer-clay composites exhibited similar performance to biochar for perfluoroalkyl substance removal, but had lower affinity for polar pesticides and tris(2-chloroethyl) phosphate. Oxyanion removal was greatest for positively-charged PDADMAC-clay composites (particularly Cr[VI]), while PVPcoS-clay composites removed over 95% of Ni, Cd, and Cu. NOM decreased removal of all organic compounds, but increased trace metal removal on clay composites due to sorption of NOM-complexed metals. Polymer-clay composite-amended columns best removed oxyanions, while biochar-amended columns exhibited superior removal for all trace organics. At 3 wt% geomedia-sand loading, clay composites exhibited significantly higher saturated hydraulic conductivity than biochar, which is advantageous when clogging is a concern or when rapid infiltration is needed. Under typical urban stormwater conditions, the clay composites will remove contaminants for at least 20-30 years before regeneration or replacement is needed.

Polycyclodextrin-Clay Composites: Regenerable Dual-Site Sorbents for Bisphenol A Removal from Treated Wastewater

The greatest challenge of wastewater treatment is the removal of trace concentrations of persistent micropollutants in the presence of the high concentration of effluent organic matter (EfOM). Micropollutant removal by sorbents is a common practice, but sorbent employment is often limited because of fouling induced by EfOM and challenging sorbent regeneration. We directly addressed these two issues by designing regenerable dual-site composite sorbents based on polymerized β-cyclodextrin, modified with a cationic group (pCD⁺) and adsorbed to montmorillonite (pCD⁺-MMT). This dual-site composite was tailored to simultaneously target an emerging micropollutant, bisphenol A (BPA), through inclusion in β-cyclodextrin cavities and target anionic EfOM compounds, through electrostatic interactions. The removal of BPA from treated wastewater by the composite was not compromised despite the high removal of EfOM. The composites outperformed many recently reported sorbents. Differences in composite performance was discussed in terms of their structures, as characterized with TGA, XRD, BET and SEM. The simultaneous filtration of BPA and EfOM from wastewater by pCD⁺-MMT columns was demonstrated. Furthermore, successful in-column regeneration was obtained by selectively eluting EfOM and BPA, with brine and alkaline solutions, respectively. Finally, the composites removed trace concentrations of numerous high priority micropollutants from treated wastewater more efficiently than commercial activated carbon. This study highlights the potential to design novel dual-site composites as selective and regenerable sorbents for advanced wastewater treatment.

Designing a regenerable stimuli-responsive grafted polymer-clay sorbent for filtration of water pollutants

A novel, stimuli-responsive composite, based on poly(4-vinylpyridine) (PVP) brushes, end-grafted to montmorillonite clay (GPC), was designed as a regenerable sorbent for efficient removal of pollutants from water. We characterized the novel composite sorbent and its response to pH, employing Fourier transform infrared, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry analysis and zeta potential measurements. In comparison with conventional, electrostatically adsorbed PVP composites (APC), the GPC presented superior characteristics: higher polymer loading without polymer release, higher zeta potential and lower pH/charge dependency. These superior characteristics explained the significantly higher removal of organic and inorganic anionic pollutants by this composite, in comparison with the removal by APC and by many reported sorbents. For example, the filtration (20 pore volumes) of selenate by GPC, APC and a commercial resin column was complete (100%), negligible (0%) and reached 90% removal, respectively. At low-moderate pH, the grafted polymer undergoes protonation, promoting pollutant adsorption, whereas at high pH, the polymer deprotonates, promoting pollutant desorption. Indeed, 'in-column' regeneration of the GPC sorbents was achieved by increasing pH, and upon a second filtration cycle, no reduction in filter capacity was observed. These findings suggest the possible applicability of this stimuli-responsive sorbent for water treatment.

Investigation of the Adsorption of Amphipathic macroRAFT Agents onto Montmorillonite Clay

Recently, there has been significant interest in the use of the reversible addition-fragmentation chain-transfer (RAFT) technique to generate a variety of organic/inorganic colloidal composite particles in aqueous dispersed media using the so-called macroRAFT-assisted encapsulating emulsion polymerization (REEP) strategy. In this process, special attention should be paid to the adsorption of the macromolecular RAFT (macroRAFT) agent onto the inorganic particles, as it determines the final particle morphology and can also influence latex stability. In this work, different amphipathic macroRAFT agents were synthesized by RAFT, and their adsorption onto commercial Montmorillonite clay Cloisite Na⁺ (MMT) was studied by means of adsorption isotherms. Three types of macroRAFT agents were considered: a nonionic one based on poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA), anionic ones, including a block copolymer and random copolymers, based on acrylic acid (AA), BA and PEGA, and cationic ones based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), BA and PEGA. Six adsorption isotherm models (Langmuir, Freundlich, Tempkin, Redlich-Peterson, Sips, and Brunauer-Emmett-Teller) were adjusted to the experimental isotherms. The nonionic macroRAFT agent formed a monolayer on the clay surface with a maximum adsorption capacity of 400 mg g^-1 at pH 8, as determined from the Sips adsorption model. Adsorption of the AA-based macroRAFT agents onto MMT was moderate at alkaline pH due to electrostatic repulsions, but increased with decreasing pH. The DMAEMA-based macroRAFT agents displayed a much stronger interaction with the oppositely charged MMT surface at acidic pH due to electrostatic interactions, and the concentration of adsorbed macroRAFT agent reached values as high as 800 mg g^-1. The BET model fitted the experimental data relatively well indicating multilayer adsorption promoted by the presence of the hydrophobic BA units. In addition, the cationic macroRAFT agents afforded stable MMT/macroRAFT agent complexes as evaluated by dynamic light scattering and zeta potential analyses.

Catalytic polymer-clay composite for enhanced removal and degradation of diazinon

It is well established that organophosphate pesticides, such as diazinon, pose environmental and health risks. Diazinon is prone to rapid acidic hydrolysis, forming the less toxic compound 2-isopropyl-6-methyl-4-pyrimidinol (IMP). In this study, diazinon surface catalyzed hydrolysis was achieved by its adsorption to a composite, based on protonated poly (4-vinyl-pyridine-co-styrene) (HPVPcoS) and montmorillonite (MMT) clay. The adsorption affinity and kinetics of diazinon to HPVPcoS-MMT were significantly higher than those obtained to the deprotonated PVPcoS-MMT, emphasizing the importance of hydrogen bonding. Correspondingly, diazinon filtration by HPVPcoS-MMT columns was highly efficient (100% for 100 pore volumes), while filtration by columns of PVPcoS-MMT or granular activated carbon (GAC) reached only 55% and 85%, respectively. Regeneration of HPVPcoS-MMT by pH increase was demonstrated and sorbent reuse was successful, whereas regeneration and reuse of GAC and PVPcoS-MMT were inefficient. Proton transfer from HPVPcos-MMT to diazinon, investigated by FTIR analysis, supports the suggested mechanism of surface catalyzed hydrolysis. These findings demonstrate the applicability of such bi-functional sorbents, to adsorb and degrade pollutants, for efficient water treatment.

Phosphorus adsorption by a modified polyampholyte-diatomaceous earth material containing imidazole and carboxylic acid moieties: batch and dynamic studies

Phosphorus removal in water was achieved by using a polyampholyte supported on diatomaceous earth.

Efficient Filtration of Effluent Organic Matter by Polycation-Clay Composite Sorbents: Effect of Polycation Configuration on Pharmaceutical Removal

Hybrid polycation-clay composites, based on methylated poly vinylpyridinium, were optimized as sorbents for secondary effluent organic matter (EfOM) including emerging micropollutants. Composite structure was tuned by solution ionic strength and characterized by zeta potential, FTIR, X-ray diffraction, and thermal gravimetric analyses. An increase in ionic strength induced a transition from a train to a loops and tails configuration, accompanied by greater polycation adsorption. Composite charge reversal (zeta potential -18 to 45 mV) increased the adsorption of EfOM and humic acid (HA), moderately and sharply, respectively, suggesting electrostatic and also nonspecific interactions with EfOM. Filtration of EfOM by columns of positively charged composites was superior to that of granular activated carbon (GAC). The overall removal of EfOM was most efficient by the composite with a train configuration. Whereas a composite with a loops and tails configuration was beneficial for the removal of the anionic micropollutants diclofenac, gemfibrozil and ibuprofen from EfOM. These new findings suggest that the loops and tails may offer unique binding sites for small micropollutants which are overseen by the bulk EfOM. Furthermore, they may explain our previous observations that in the presence of dissolved organic matter, micropollutant filtration by GAC columns was reduced, while their filtration by composite columns remained high.