Adsorption of As(V) on surfactant-modified natural zeolites

Removal of perfluoroalkyl acids from aqueous media by surfactant-modified clinoptilolites

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are environmentally persistent, bioaccumulating, and toxic compounds that have attracted global attention. It is challenging to reduce the residual concentrations of these compounds to safe discharge limits. In this study, batch experiments were performed to evaluate natural clinoptilolite and clinoptilolites modified (MC) with cetylpyridinium chloride (CPC-MC), didodecyldimethylammonium bromide (DDAB-MC), hexadecyltrimethylammonium bromide (HDTMA-MC), and tetramethylammonium chloride (TMA-MC) as cost-effective aqueous PFAS adsorbents. The removal capacities of the adsorbents for the majority of the PFASs decreased in the following order: DDAB-MC > CPC-MC ≫ modified natural clinoptilolite with hexadecyltrimethyl ammonium bromide (HDTMA-MC) ≫ modified natural clinoptilolite with tetramethylammonium chloride (TMA-MC) ≈ natural clinoptilolite modified with NaCl (NC). In particular, CPC-MC and DDAB-MC reduced PFASs concentration in 50 μg/L by up to 98% for perfluorooctane sulphonate. Within 30 min, CPC-MC (30.5 μg/L) and DDAB-MC (32.1 μg/L) met the PFOS water quality criterion of 36 μg/L in inland surface waters. Both adsorbents met this criterion at the highest solution volume (40 mL) and 0.125 g/L (solid-to-liquid ratio of 1:8). PFASs with short hydrocarbon chains competed more for adsorption. PFASs with sulphonate functional groups were also adsorbed more than carboxyl groups in single- and multi-PFAS solutions. The modified surfaces of clinoptilolites controlled PFAS adsorption through hydrophobic and electrostatic interactions. PFAS removal with surfactant-modified clinoptilolites is cost-effective and protects aquatic environments by using surplus natural materials.

Modification of natural zeolites and their applications for heavy metal removal from polluted environments: Challenges, recent advances, and perspectives

In recent decades, environmental pollution has become a significant problem for human health and environmental impact. The high accumulation of heavy metals in waters and soils from different sources was conducted by finding efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites have found wide-ranging applications in environmental remediation and protection, considering various treatment and modification methods designed to enhance the natural zeolites' adsorptive or ion-exchange capabilities for increased efficiency. This paper briefly consolidates the recent scientific literature related to the main characteristics of natural and modified zeolites, the advantages and limitations of their environmental remediation application, and summarizes the methodologies applied to natural zeolites in order to improve their properties. Their application for removing heavy metals from water systems and soils is also comprehensively discussed. This review highlights the excellent potential of natural zeolites to be used after specific treatment or modification as a sustainable and green material to solve numerous environmental pollution issues.

Facile and innovative application of surfactant-modified-zeolite from Austrian fly ash for glyphosate removal from water solution

This study highlights a pioneering approach in the development of an efficient, affordable, and economically feasible adsorbent specifically tailored for the removal of glyphosate (Gly) from contaminated water. To accomplish this objective, a low-cost and pure NaA Zeolite (NaAZ) was synthesized with 93% crystallinity from Austrian fly ash (AFA) as a precursor for the first-time. Taguchi design was employed to optimize critical parameters such as the SiO2/Al2O3 ratio, alkalinity concentration, time, and temperature. The cation exchange capacity (CEC) and external cation exchange capacity (ECEC) are determined as critical factors for the modification process. Subsequently, the pure NaAZ was modified with hexadecyl trimethyl ammonium chloride (HDTMAC), a cationic surfactant. The utilization of surfactant-modified zeolite (SMZ) for Gly removal demonstrates its innovative application in this field, highlighting its enhanced adsorption capacity and optimized surface properties. The AFA, NaAZ, and SMZ were characterized using analytical techniques including XRD, XRF, FTIR-ATR, SEM, TGA, BET, CHNSO analyzer and ICP-OES. The adsorbent exhibited effective Gly removal through its pH-dependent charge properties (pH 2-10), with an optimized pH 6 facilitating a significant electrostatic interaction between the adsorbent and Gly. SMZ demonstrated remarkable adsorption capacity and removal efficacy, surpassing most reported adsorbents with values of 769.23 mg/g and 98.92% respectively. Our study demonstrates the significant advantage of the SMZ, with a low leaching concentration of only 6 ppm after 60 days, ensuring environmental safety, long-term stability, and public health considerations. The kinetics of the adsorption process was well described by the pseudo-second order and the Freundlich isotherm. Pore diffusion and H-bonding were postulated to be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption. Consequently, SMZ provides a practical significance, broad applicability and promising solution for Gly removal, facilitating sustainable water treatment.

Adsorption of heavy metals on natural zeolites: A review

Water pollution has jeopardized human health, and a safe supply of drinking water has been recognized as a worldwide issue. The increase in the accumulation of heavy metals in water from different sources has led to the search for efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites are promising materials for removing heavy metals from different sources contaminating the water. It is important to know the structure, chemistry, and performance of the removal of heavy metals from water, of the natural zeolites to design water treatment processes. This review focuses on critical analyses of the application of distinct natural zeolites for the adsorption of heavy metals from water, specifically, arsenic (As(III), As(V)), cadmium (Cd(II)), chromium (Cr(III), Cr(VI)), lead (Pb(II)), mercury(Hg(II)) and nickel (Ni(II)). The reported results of heavy-metal removal by natural zeolites are summarized, and the chemical modification of natural zeolites by acid/base/salt reagent, surfactants, and metallic reagents has been analyzed, compared, and described. Furthermore, the adsorption/desorption capacity, systems, operating parameters, isotherms, and kinetics for natural zeolites were described and compared. According to the analysis, clinoptilolite is the most applied natural zeolite to remove heavy metals. It is effective in removing As, Cd, Cr, Pb, Hg, and Ni. Additionally, an interesting fact is a variation between the natural zeolites from different geological origins regarding the sorption properties and capacities for heavy metals suggesting that natural zeolites from different regions of the world are unique.

Zeolite Nanoparticles Loaded with 2-Methoxystradiol as a Novel Drug Delivery System for the Prostate Cancer Therapy

The estrogen metabolite 2-methoxyestradiol (2ME) is a promissory anticancer drug mainly because of its pro-apoptotic properties in cancer cells. However, the therapeutic use of 2ME has been hampered due to its low solubility and bioavailability. Thus, it is necessary to find new ways of administration for 2ME. Zeolites are inorganic aluminosilicates with a porous structure and are considered good adsorbents and sieves in the pharmaceutical field. Here, mordenite-type zeolite nanoparticles were loaded with 2ME to assess its efficiency as a delivery system for prostate cancer treatment. The 2ME-loaded zeolite nanoparticles showed an irregular morphology with a mean hydrodynamic diameter of 250.9 ± 11.4 nm, polydispersity index of 0.36 ± 0.04, and a net negative surface charge of -34 ± 1.73 meV. Spectroscopy with UV-vis and Attenuated Total Reflectance Infrared Fourier-Transform was used to elucidate the interaction between the 2ME molecules and the zeolite framework showing the formation of a 2ME-zeolite conjugate in the nanocomposite. The studies of adsorption and liberation determined that zeolite nanoparticles incorporated 40% of 2ME while the liberation of 2ME reached 90% at pH 7.4 after 7 days. The 2ME-loaded zeolite nanoparticles also decreased the viability and increased the mRNA of the 2ME-target gene F-spondin, encoded by SPON1, in the human prostate cancer cell line LNCaP. Finally, the 2ME-loaded nanoparticles also decreased the viability of primary cultures from mouse prostate cancer. These results show the development of 2ME-loaded zeolite nanoparticles with physicochemical and biological properties compatible with anticancer activity on the human prostate and highlight that zeolite nanoparticles can be a good carrier system for 2ME.

Applications of Nano-Zeolite in Wastewater Treatment: An Overview

Nano-zeolite is an innovative class of materials that received recognition for its potential use in water and tertiary wastewater treatment. These applications include ion-exchange/sorption, photo-degradation, and membrane separation. The aim of this work is to summarize and analyze the current knowledge about the utilization of nano-zeolite in these applications, identify the gaps in this field, and highlight the challenges that face the wide scale applications of these materials. Within this context, an introduction to water quality, water and wastewater treatment, utilization of zeolite in contaminant removal from water was addressed and linked to its structure and the advances in zeolite preparation techniques were overviewed. To have insights into the trends of the scientific interest in this field, an in-depth analysis of the variation in annual research distribution over the last decade was performed for each application. This analysis covered the research that addressed the potential use of both zeolites and nano-zeolites. For each application, the characterization, experimental testing schemes, and theoretical analysis methodologies were overviewed. The results of the most advanced research were collected, summarized, and analyzed to allow an easy visualization and comparison of these research results. Finally, the gaps and challenges that face these applications are concluded.

Laboratory investigation of arsenic removal from the aquatic environment using nano adsorbents extracted from native zeolite

The presence of arsenic in water is a major problem in communities due to its toxicity and hazard. The aim of this study was to evaluate the removal efficiency of arsenic by CTAB-modified clinoptilolite zeolite from aqueous solution. The effect of contact time, pH, ionic strength, zeolite dose and CTAB concentration on arsenic removal were investigated. Structural analysis of XRD showed that the adsorbent used in this study was composed of clinoptilolite due to three strong peaks in 9.8, 22 and 27 degrees with intervals of 8.9, 3.9 and 3.1. Optimum condition for effective adsorption were obtained at pH = 3, zeolite dose of 5 g L–1, CTAB concentration of 5 mM, ionic strength of 0.1 M sodium chloride and contact time of 10 minutes. This study suggested that, the CTAB modified zeolite can be used as an effective and inexpensive adsorbent to remove arsenic from aqueous solutions, since it is a low-cost, abundant and locally available.

Evidences on As(III) and As(V) interaction with iron(III) oxides: Hematite and goethite

Arsenic, which is ubiquitous in nature, was found associated with iron oxides in soils and sediments. Our interest was to utilize the same mechanism for the sorptive removal of arsenic from groundwater. The iron(III) oxides: hematite, goethite, were synthesized, characterized and sorption studies of arsenic [As(III) and As(V)] were carried out in batch mode. For studying the evidence of the interaction between arsenic and iron oxide during the process of sorption, a new electrochemical method was developed. Differential pulse voltammetry (DPV) study indicated that the sorbed arsenic species is redox active on the surface of the sorbent. X-ray photoelectron spectroscopy (XPS) measurement was performed for confirmation of the changes occurring to the oxidation states of iron as well as arsenic after the sorption. XPS studies confirmed that the behavior of arsenic species on hematite/goethite was similar and occurs via a partial redox reaction. During sorption of As(III), a partial oxidation occurs resulting in As(V) species, simultaneously the Fe(III) present in the iron oxide gets reduced to Fe(II). However, during the sorption of As(V), there occurs a Fe(II) oxidation followed by As(V) reduction. Based on the results, a mechanistic scheme for sorption of arsenic on iron(III) oxides as sorbents was proposed.

Testing of Chemically Activated Cellulose Fibers as Adsorbents for Treatment of Arsenic Contaminated Water

Exposure to different arsenic concentrations (higher than 10 μg/L), either due to the direct consumption of contaminated drinking water or indirectly by using contaminated food is harmful for human health. Therefore, it is important to remove arsenic from aqueous solutions. Among many arsenic removal technologies, adsorption offers a promising solution with a good efficiency, however the material used as adsorbent play a very vital role. The present investigation evaluated the behavior of two cellulose-based adsorbent materials, i.e., viscose fibers (V) and its TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) derivative, obtained by using the well-established TEMPO-mediated protocol (VF). Due to the known arsenic affinity for Fe ions the two materials were later doped with it. This was done after a preliminary functionalization with di-2-ethylhexyl phosphoric acid (DEHPA), to obtain two materials: V-DEHPA-Fe and VF-DEHPA-Fe. Arsenic adsorption is known to be pH dependent (between 6 and 8); therefore, the optimal pH range for As(V) adsorption has been established. In order to evaluate the adsorption mechanism for both the synthesized materials, the influence of contact time, temperature and initial concentration was evaluated. Langmuir, Freundlich and Sips equilibrium isotherm models were used in order to determine the ability of the model to describe As(V) adsorption process. The maximum adsorption capacity of the material V-DEHPA-Fe was 247.5 µg As(V)/g with an As(V) initial concentration of 5 mg/L and for the material VF-DEHPA-Fe it was 171.2 µg As(V)/g with initial concentration of 5 mg/L.

Simultaneous immobilization of As and Cd in a mining site soil using HDTMA-modified zeolite

Arsenic (As) and cadmium (Cd) co-contamination has been a typical problem in Chinese agricultural land adjacent to historical metal mining and smelting activities. Remediation of As and Cd in soil has encountered many difficulties owing to the distinct nature of the two metal(loid)s. In this study, we developed a remediation scheme by adding a hexadecyltrimethylammonium (HDTMA)-modified zeolite to a mining site soil and evaluated the immobilization effect. The result of the increased surface zeta potential indicates that the HDTMA modification conferred the zeolite with adsorbability towards As through the cationic surfactant head. The addition of the highest dosage of HDTMA-modified zeolite (10%) to the contaminated soil greatly improved soil organic matter by 1.4 times, partly due to the elevated C loading on the zeolite from HDTMA. Sequential extraction results show that the addition of HDTMA-modified zeolite not only increased the residual fraction of As (by 2.7-5.9%) but also reduced the toxicity-related fraction (by 2.3-2.7%) when compared to the unmodified zeolite and blank treatments. The oxidizable fractions of Cd in the modified zeolite treatment were significantly higher than that in the blank soil. Besides, the exchangeable fractions of Cd were all significantly reduced in the zeolite treatments. Enzyme activity assays show that the HDTMA-modified zeolite treatment could greatly improve soil microbial environment. The physiologically based extraction test (PBET) also proved that the bioavailability of As and Cd was reduced after the modified zeolite treatment.

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.

Removal of polycyclic aromatic hydrocarbons from aqueous media using modified clinoptilolite

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) are widespread in the environment. In this study, the removal of PAHs from aqueous media was assessed using samples of clinoptilolite, a natural zeolite, pre-treated with 1 mol/L of NaCl, (Na pre-treated clinoptilolite, NC). Samples (10 g) of NC were separately modified with 5, 2, 2, and 20-mmol/L solutions of cetylpyridinium chloride (CPC), didodecyldimethyl ammonium bromide (DDAB), hexadecyltrimethylammonium bromide (HDTMA), and tetramethyl ammonium chloride (TMA) surfactants as potential cost-effective adsorbents. The kinetics, optimal sorbent dosage, and competitive effects were evaluated through batch adsorption tests using deionised water spiked with five PAHs (anthracene (50 μg/L), fluoranthene (100 μg/L), fluorene (100 μg/L), phenanthrene (100 μg/L), and pyrene (100 μg/L)). The surfactant non-modified (NC) and TMA-MC (modified clinoptilolite) exhibited PAH removal of <66% from the spiked concentration in aqueous solution, while CPC-MC, DDAB-MC, and HDTMA-MC achieved removal rates of >93% for the five PAHs after 24 h at a solid:liquid ratio of 1:100. The remaining concentrations of anthracene and fluoranthene were below 3 μg/L, and that of fluorene was <6 μg/L, lower than the water quality criteria of British Columbia, Canada, for protecting aquatic life. However, HDTMA-MC retained >83% of the fluorene. Over 80% of all PAHs were absorbed within 15 min for the CPC-MC and DDAB-MC, and the maximum adsorption was reached in <2 h. Three kinetic models were applied assuming pseudo-first-order, pseudo-second-order, and intra-particle equations, and the results were well-represented by the pseudo-second-order equation. The PAH sorption results indicated that the adsorption mechanism is based on PAH hydrophobicity, and π-π electron-donor-acceptor interaction with surfactant. CPC and DDAB with two long chain hydrocarbons had more PAH adsorption than HDTMA with one, and TMA with no long chain hydrocarbons (DDAB-MC > CPC-MC > HDTMA-MC ≫ TMA-MC > NC). With a solid:liquid ratio of 1:200, over 90%, 80%, and 70% of the anthracene, fluoranthene, and pyrene were adsorbed by the CPC-MC, DDAB-MC, and HDTMA-MC, respectively.

Modulation of cytotoxicity by consecutive adsorption of tannic acid and pesticides on surfactant functionalized zeolites

This study investigated the environmental application of FAU type zeolites modified with cationic surfactants (cetylpyridinium chloride, tetrapropylammonium chloride and benzalkonium chloride). Adsorbent characterization was conducted using Fourier-transform infrared and Raman spectroscopy, thermogravimetry and differential thermal analysis, atomic force microscopy and X-ray powder diffraction. The efficiency for tannic acid adsorption from aqueous solution on the surface of prepared composites is studied and the adsorption process was modelled with different isotherm equations. Surfactant modifications of zeolites led to improved adsorption properties compared to FAU zeolites alone. The proposed mechanism controlling the adsorption of tannic acid onto surfactant modified zeolites mainly relies on π-π and hydrophobic interactions. The investigated materials are promising adsorbents for tannic acid and similar phenolics and may be important for environmental and dietary aspects of polyphenol persistence and usage. Further on, functionalized zeolites were studied for insecticide acetamiprid removal, prior to and after tannic acid retention. Promising findings of insecticide co-adsorption with tannic acid led to cytotoxicity evaluation. The cytotoxicity modulation effect of zeolites and tannic acid on acetamiprid points to the essential role of both components in insecticide toxicity reduction.

Zeolite-Rich Composite Materials for Environmental Remediation: Arsenic Removal from Water

Natural zeolites are used as adsorbents in purification processes due to their cation-exchange ability and molecular sieve properties. Surface modified natural zeolites (SMNZs), produced by attaching cationic organic surfactants to the external surface, can simultaneously act as ionic exchangers and organic molecule adsorbents. In this paper, SMNZs were produced and investigated as adsorbents for As(V) removal from wastewater: two natural zeolites, clinoptilolite and phillipsite, were modified using HDTMA-Br and HDTMA-Cl as surfactants. The obtained samples were then characterized under static and dynamic conditions. Results showed that As(V) removal follows a pseudo-second order kinetic, with fast adsorption rates: every sample reached 100 % removal in 2 h, while equilibrium data showed a Langmuir-like behavior, with a greater anion uptake by the HDTMA-Br modified SMNZs due to the formation of a compact and complete micellar structure. Finally, fixed-bed tests were performed to characterize the samples under dynamic conditions assessing the effect of severe operating parameters on the dynamic exchange capacity, selectivity and efficiency of the process. The obtained results demonstrate a good ability of the tested materials to adsorb As(V) from wastewater, confirming the effectiveness of the proposed surface modification technique in expanding the possibility of using natural zeolites in these processes.

Synergistic control of internal phosphorus loading from eutrophic lake sediment using MMF coupled with submerged macrophytes

Sediment phosphorus (P) is the main source of endogenous P for lake eutrophication. An in-situ combined technology for determination the removal effect of sediment P in all fractions was first developed using the novel modified maifanite (MMF) and submerged macrophytes in this study. MMF was synthesized using an acidification process (2.5 mol/L H₂SO₄) and then a calcination (400 °C) method. The morphology and structure of MMF were characterized by XRD, SEM, XPS, and BET. We tested the removal effects of sediment P by MMF and submerged macrophytes in combination and separately. The results demonstrated that the synergistic removal capacity of sediment P using MMF coupled with submerged macrophytes was higher than the sum of them applied separately. MMF could promote the submerged macrophytes growth and enhance the adsorption of extra P on MMF through root oxygenation and nutrient allocation. The microcosm experiment results showed that sediment from fMMF+V. spiralis exhibited the most microbial diversity and abundance among the sediment. The combination of MMF and submerged macrophytes increased the Firmicutes abundance and decreased the Bacteroidetes. These results indicated that adsorption-biological technology can be regarded as a novel and competitive technology to the endogenous pollution control in eutrophic shallow lakes.

Performance evaluation of surfactant modified kaolin clay in As(III) and As(V) adsorption from groundwater: adsorption kinetics, isotherms and thermodynamics

In this paper surfactant modified kaolin clay for As(III) and As(V) was prepared by intercalating hexadecyltrimethylamonium bromide (HDTMA-Br) cationic surfactant onto the clay interlayers. Batch experiments were used to evaluate the effectiveness of surfactant modified kaolin clay towards As(III) and As(V) removal. The results revealed that adsorption of As(III) and As(V) is optimum at pH range 4–8. The maximum As(III) and As(V) adsorption capacities were found 2.33 and 2.88 mg/g, respectively after 60 min contact time. The data for adsorption of As(III) showed a better fit too pseudo first order model of reaction kinetics while the data for As(V) fitted better to pseudo second order model. The adsorption isotherm data for As(III) and As(V) fitted well to Langmuir model indicating that adsorption of both species occurred on a mono-layered surface. Adsorption thermodynamics model revealed that adsorption of As(III) and As(V) was spontaneous and exothermic. The presence of Mg²⁺ and Ca²⁺ increased As(III) and As(V) adsorption efficiency. The regeneration study showed that synthesized adsorbent can be used for up to 5 times with maximum As(III) and As(V) percentage removal of 54.2% and 62.33%, respectively achieved after 5^th cycle. Surfactant modified kaolin clay mineral showed higher adsorption capacity towards As(III) and As(V) as compared to unmodified kaolin clay mineral and competitive with other adsorbent in the literature. The results obtained from this study revealed that surfactant modified kaolin mineral is a candidate material for arsenic remediation from groundwater.

Characterizations and mechanisms for synthesis of chitosan-coated Na-X zeolite from fly ash and As(V) adsorption study

Solid waste fly ash with low aluminum of Yunnan Province in China was used as pristine material to prepared chitosan-coated Na-X zeolite, and the obtained composite material was employed as As(V) adsorbent. Then, the prepared materials were characterized by XRD, FT-IR, and XPS. And the results suggested that the low aluminum fly ash was successfully convert into Na-X zeolite, and the mineralization between Si-OH of the obtained Na-X zeolite and C-OH of chitosan was the dominated mechanism for coated chitosan over the surface of Na-X zeolite. From the batch experiments of As(V) removal, it has been found that the coated chitosan could significantly improve As(V) performance of Na-X zeolite. The optimal working pH for removal As(V) by chitosan-coated Na-X zeolite was attained at pH 2.1 ± 0.1, and the maximum adsorption capacity was 63.23 mg/g. And the adsorption data at different interval time was excellent fitted by pseudo-second-order kinetic model. From the analyze of XPS, the results suggested that As(V) uptake over adsorbent by the bond of As-N and As-O and the surface hydroxyl group of Al-OH and -NH₂ were involved in uptake As(V) from acid wastewater.

Adsorptive removal of resorcinol on a novel ordered mesoporous carbon (OMC) employing COK-19 silica scaffold: Kinetics and equilibrium study

Phenolic compounds and their derivatives have been found in industrial wastewater, which pose threats to the natural environment. Ordered mesoporous carbon (OMC) has been identified as an ideal adsorbent possessing high specific surface area and large pore volume to alleviate these pollutants. A novel ordered mesoporous carbon was prepared using COK-19 template with the cubic Fm3m structure for the first time. Ordered mesoporous silica COK-19 was synthesized and reported in 2015. Sucrose as the carbon precursor was impregnated into the mesopores of silica and converted to carbon through carbonization process using sulfuric acid as a catalyst. Ordered mesoporous carbon was obtained after the removal of silica framework using hydrofluoric acid. Boric acid was employed for the preparation of OMCs with tunable pore sizes in the range of 6.9-16.6 nm. Several characterization techniques such as nitrogen adsorption-desorption isotherms, transmission electron microscope (TEM), Fourier transform infrared spectroscopy, Boehm titration and elemental analysis were employed to characterize the OMCs. The pore size analysis and TEM images confirmed that OMC has replicated the mesostructure of the COK-19. Results obtained from adsorption kinetics and isotherms suggest that the Pseudo-second-order model and Langmuir isotherm well described the experimental data.

Investigation on the adsorption of phosphorus in all fractions from sediment by modified maifanite

Sediment phosphorus (P) removal is crucial for the control of eutrophication, and the in-situ adsorption is an essential technique. In this study, modified maifanite (MMF) prepared by acidification, alkalization, salinization, calcination and combined modifications, respectively, were first applied to treat sediment P. The morphology and microstructure of MMF samples were characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET). Various adsorption parameters were tested, such as dosage of maifanite, time, operation pH and temperature. The adsorption mechanisms were also investigated and discussed. Results showed that CMMF-H2.5-400 (2.5 mol/L H₂SO₄ and calcined at 400 °C) exhibited the highest P adsorption capacity. Thus, it was selected as the in-situ adsorbent material to control the internal P loading. Under the optimal conditions of dynamic experiments, the adsorption rates of TP, IP, OP, Fe/Al-P and Ca-P by CMMF-H2.5-400 were 37.22%, 44.41%, 25.54%, 26.09% and 60.34%, respectively. The adsorption mechanisms analysis revealed that the adsorption of P onto CMMF-H2.5-400 mainly by ligand exchange. Results of this work indicated that the modification treatment could improve the adsorption capacity of maifanite, and CMMF-H2.5-400 could be further applied to eutrophication treatment.

Preparation and application of modified zeolites as adsorbents in wastewater treatment

Natural zeolite has been recognized as a useful adsorbent for wastewater treatment for removing cations. Natural zeolite is a kind of porous material with large specific surface area but limited adsorption capacity. In recent years, emphasis has been given to prepare the surface modified zeolite using various procedures to enhance the potential of zeolite for pollutants. Modification treatment for zeolite can greatly change surface chemistry and pore structure. The article describes various modification methods of zeolite, and introduces the removal mechanisms of common pollutants such as ammonium, phosphorus and heavy metals. In addition, this review paper intends to present feasibility of applying modified zeolite to constructed wetlands which will be beneficial to achieve higher removal effect.

Synthetic Iron Oxides for Adsorptive Removal of Arsenic

Removal of arsenic from water reservoirs is the issue of great concern in many places around the globe. As adsorption is one of the most efficient techniques for treatment of As-containing media, thus the present study concerns application of iron oxides-hydroxides (akaganeite) as adsorbents for removal of this harmful metal from aqueous solution. Two types of akaganeite were tested: synthetic one (A) and the same modified using hexadecyltrimethylammonium bromide (A_M). Removal of As was tested in batch studies in function of pH, adsorbent dosage, contact time, and initial arsenic concentration. The adsorption isotherms obey Langmuir mathematical model. Adsorption kinetics complies with pseudo-second-order kinetic model, and the constant rates were defined as 2.07 × 10^-3and 0.92 × 10^-3 g mg^-1 min^-1 for the samples (A) and (A_M), respectively. The difference was caused by significant decrease in adsorption rate in initial state of the process carried out for the sample A_M. The maximum adsorption capacity achieved for (A) and (A_M) akaganeite taken from Langmuir isotherm was 148.7 and 170.9 mg g^-1, respectively. The results suggest that iron oxides-hydroxides can be used for As removal from aqueous solutions.

Synergistic removal effect of P in sediment of all fractions by combining the modified bentonite granules and submerged macrophyte

The removal efficiency of sediment phosphorus (P) with the in-situ synergistic effect of modified bentonite granules (MBG) and Vallisneria spiralis (V. spiralis) in West Lake, Hangzhou, China was investigated for the first time in the study. CMBG-Na10-450 (nitrification (10% Na₂CO₃)-calcination (450 °C) combined modification) was prepared and characterized, and the removal effects of sediment P of all fractions with CMBG-Na10-450 and V. spiralis in combination and separately were evaluated in batch experiments. Results showed that CMBG-Na10-450 could promote the growth of V. spiralis, and the residual P of the sediment not adsorbed on CMBG-Na10-450 was changed through root oxygenation and nutrition allocation, and then enhanced the extra P adsorption on CMBG-Na10-450. The combination of MBG and V. spiralis exhibited a synergistic removal effect higher than the summation of MBG and V. spiralis applied separately. The results of microcosm experiments showed that the combination of CMBG-Na10-450 and V. spiralis enhanced the function of P metabolism by increasing the special genus that belongs to the family Erysipelotrichaceae.

Removal of arsenic III and V from laboratory solutions and contaminated groundwater by metallurgical slag through anion-induced precipitation

Metallurgical slag was used for the simultaneous removal of high concentrations of arsenite and arsenate from laboratory solutions and severely contaminated groundwater. Apart from demonstrating the high efficiency of arsenic removal in presence of competing species, the work aims to explore the physicochemical mechanisms of the process by means of microscopy observation and a detailed statistical analysis of existing kinetic and isotherm equations. Fitting was performed by non-linear least squares using weighted residuals; ANOVA and bootstrap methods were used to compare the models. Literature suggests that the metal oxides in the slag are efficient adsorbents of As(III) and (V). However, the low surface area of the slag precludes adsorption; SEM observation provide evidence of a mechanism of co-precipitation of lixiviated cations with contaminant anions. The reaction kinetics provide essential information on the interaction between the contaminants, particularly on the common ion effect in groundwater. The Fritz-Schlünder isotherm allows modelling the saturation effect at low slag doses. The efficiency of the process is demonstrated by an arsenic removal of 99% in groundwater using 4-g slag/L, resulting in an effluent with 0.01 mg As/L, which is below Mexican and international standards for drinking water.

Adsorpsi Alkil Benzena Sulfonat Menggunakan Zeolit Termodifikasi Cetyltrimethylammonium

Dalam penelitian ini dilakukan modifikasi zeolit alam teraktivasi NH4Cl (H-Zeolit) dengan surfaktan CTAB (Cetyltrimethylammonium Bromide) berbagai konsentrasi yaitu sebesar 0,25 mM (ZMS-1), 1 mM (ZMS-2), dan 100 mM (ZMS-3) sebagai adsorben senyawa ABS (Alkil Benzena Sulfonat). Karakterisasi dilakukan terhadap H-Zeolit dan ZMS menggunakan spektrofotometer FTIR. Parameter utama dalam penelitian ini adalah variasi konsentrasi ABS (50, 75, dan 100 ppm) dan waktu kontak (15, 30, 45, 60, 75, dan 90 menit). Konsentrasi ABS yang teradsorpsi dianalisis dengan spektrofotometer UV-Vis menggunakan metode MBAS (Methylene Blue Active Substance). Hasil spektra FTIR zeolit alam termodifikasi surfaktan (ZMS) menunjukkan puncak pada bilangan gelombang 2931,80 cm-1; 2854,65 cm-1 dan 1404,18 cm-1  yang mengindikasikan keberadaan gugus CTAB pada zeolit. Konsentrasi maksimum dan waktu optimum ABS yang dapat dijerap oleh per 0,1 gram ZMS adalah 50 ppm dalam 25 mL pada waktu 60 menit dengan persen adsorpsi sebesar 84,04% untuk H-Zeolit ; 96,42% untuk ZMS-1; 96,48% untuk ZMS-2; dan 97,29% untuk ZMS-3. Performa ZMS cenderung meningkat dengan konsentrasi CTAB pada zeolit.

Mechanism and performance for adsorption of 2-chlorophenol onto zeolite with surfactant by one-step process from aqueous phase

To decrease the power, material, and time consumption in wastewater treatment, a one-step process was performed to remove 2-chlorophenol (2-CP) from aqueous phase using zeolite and cetyltrimethylammonium bromide (CTAB). Compared with the traditional two-step process, the one-step process used in this study achieved almost eight times higher 2-CP adsorption capacity within a shorter time and maintained high removal efficiencies (around 65%) in reuse tests, thus becoming an efficient and economically acceptable alternative process. For the one-step process, the kinetic data fitted well with a nonlinear pseudo-second-order model, and the isotherm data fitted well with the Dubinin-Astakhov (DA) model. The uptake of 2-CP was highly dependent on pH, increasing in the pH range of 3-6. The enhanced 2-CP removal in a one-step adsorption process can be explained by the larger amount of surfactant loading (≥0.056mmol/g), as determined from the total organic carbon (TOC) and zeta potential. Due to the formation of a loose CTAB bilayer, the hydrophobic partition and the interaction with the positively charged "head" of CTAB bilayers were decisive for the enhancement of pollutant adsorption. Therefore, organic pollutants could be removed from water alongside the synthesis of hydrophobic zeolite in a one-step process, which is a promising technology for the in-situ treatment of organic wastewater.

Biosorption and retention of orthophosphate onto Ca(OH)2-pretreated biomass of Phragmites sp

The biosorption of phosphorus in the form of orthophosphate (Po) from wastewater using biomass as the sorbent is of potential importance because the Po-loaded biomass could be applied in the agricultural sector as fertilizer and soil conditioner. However, biomass generally displays a very low affinity for Po sorption and therefore biomass surface modification is required. In the present study, the biomass (as model grinded leaves of Phragmites sp. were used) was pretreated with Ca(OH)2 to enhance Po biosorption capacity (qe). The results indicate that the alkaline pretreatment resulted in a modification of surface functional groups. It was concluded that the main sorption mechanisms were ligand exchange and electrostatic attraction. A series of experiments were conducted to investigate the performance of the pretreated biomass for Po uptake under various conditions. Isotherm and thermodynamic studies were also applied and analyzed. The biosorption process was best described by the pseudo-second order kinetic model and Langmuir isotherm, which gave a qmax of 12.27mgP/g at 25°C and pH7. The Ca(OH)2 treated Phragmites biomass applied in this study for Po recovery may present some potential advantages in terms of costs and environmental impact.

Sorption mechanism(s) of orthophosphate onto Ca(OH)2pretreated bentonite

Bentonite was chemically pretreated with Ca(OH)₂to enhance orthophosphate phosphorus (OPP) sorption capacity (q_e).

Pretreatment effects on the sorption of Cr(VI) onto surfactant-modified zeolite: Mechanism analysis

Adsorption of Cr(VI) onto different pretreated zeolites modified with cetylpyridinium chloride (CPC) is investigated using batch studies, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM). The results indicate that acidification after alkalization is the most effective pretreatment method, and only alkalization would significantly reduce the sorption capability. This behavior is due to the precipitates, such as CaCO3 and MgCO3, generated after alkalization on zeolite surface interfere the formation of the CPC bilayer, which provides active sites for sorbing Cr(VI). The schematic of the adsorption mechanism is presented. The results indicate that developing a better understanding of the influence of different pretreatments is quite helpful and suggest that the content of Ca/Mg/Fe could be a good indication of the effectiveness of preprocessing.

Arsenic and antimony in water and wastewater: overview of removal techniques with special reference to latest advances in adsorption

Arsenic and antimony are metalloids, naturally present in the environment but also introduced by human activities. Both elements are toxic and carcinogenic, and their removal from water is of unquestionable importance. The present article begins with an overview of As and Sb chemistry, distribution and toxicity, which are relevant aspects to understand and develop remediation techniques. A brief review of the recent results in analytical methods for speciation and quantification was also provided. The most common As and Sb removal techniques (coagulation/flocculation, oxidation, membrane processes, electrochemical methods and phyto and bioremediation) are presented with discussion of their advantages, drawbacks and the main recent achievements. Literature review on adsorption and biosorption were focused in detail. Considering especially the case of developing countries or rural communities, but also the finite energy resources that over the world are still dependent, recent research have focused especially readily available low-cost adsorbents, as minerals, wastes and biosorbents. Many of these alternative sorbents have been presenting promising results and can be even superior when compared to the commercial ones. Sorption capacities were accurately compiled for As(III,V) and Sb(III,V) species in order to provide to the reader an easy but detailed comparison. Some aspects related to experimental conditions, comparison criteria, lack of research studies, economic aspects and adsorption mechanisms were critically discussed.