Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite

Removal of humic acid interference in soil enzymatic analysis using poly-γ-glutamic acid

Soil enzymes are biological indicators in environmental and agricultural monitoring. However, brownish humic acid (HA) in samples interferes significantly with various analytical methods, especially in optical-based techniques. Here, we implemented a coagulation-flocculation process to carry out continuously an enzymatic reaction without separation and transfer of a sample solution. The elimination of HA in a soil suspension using poly-γ-glutamic acid (PGA) by coagulation to minimize the HA interference in soil enzymatic analysis was investigated. As a result of the optimization of preliminary parameters, the removal efficiency of HA was > 92% in 100 mg L^-1 HA in neutral pH, using 100 mg L^-1 PGA and aluminum trivalent as a coagulant aid. However, the fluorescent intensity of the enzyme product (i.e., 4-methylumbelliferone) decreases by about 50% as HA was removed under the conditions used. A decrease in the enzymatic detection of 3,3',5,5'-tetramethylbenzidine (TMB) was not observed from treated samples even though the initial level of HA was different. The results suggested that the coagulation-flocculation approach is suitable for the reduction of HA interference, while maintaining target analyte detection. Therefore, the proposed sample treatment can be used to examine enzyme activity based on TMB product detection without regular standard addition calibration.

Superior removal of humic acid from aqueous stream using novel calf bones charcoal nanoadsorbent in a reversible process

While the potable water disinfection regimen has significantly reduced waterborne diseases, development of disinfection byproducts (DBP) during this process has brought a global threat to the environment and human health. The most notorious water pollutant, humic acid (HA), transforms into carcinogenic byproducts during the disinfection process (chlorination) of water treatment. HA removal methods are neither economic nor widely available. This study addresses the most urgent global issue of HA removal by developing an innovative and self-regenerative process based on a low-cost and self-regenerative calf bone char (CBC) that removed 92.1-100% of HA. CBC-based HA removal has not been described yet. The developed CBC, as a super adsorbent of HA, was initially characterized by a scanning electron microscope. Various parameters of adsorption/desorption and self-regeneration of CBC adsorbent were experimentally determined. Results show that prepared CBC with a 112 m²/g surface area exhibited adsorption of 38.08 mg/g (HA = 20 mg/L, pH = 4.0) which is several folds higher than the typical amount of HA present in water. The 30 m reaction time was enough to remove HA which is the shorter HA time in comparison to other similar studies. The increase of HA from 0.5 to 5 g/L, raises % HA removal (36.7-99.8%) while a pH decrease (10-4) increases adsorption (12.3-98.3%). The adsorption data fitted well with the pseudo-second-order model and the Langmuir isotherm which demonstrate that adsorption takes place by a monolayer formation. Thermodynamic constants supported the endothermic, spontaneous and reversible nature of adsorption which can attain 100% HA removal. 100% regeneration of exhausted CBC by NaOH further supports the sustainability of the process. CBC as a new adsorbent material thus provides an economical and sustainable water pre-treatment procedure. The present study provides technical guidance for building a cost-effective and scalable process capable of providing clean water.

Polycyclic Aromatic Hydrocarbon Sorption by Functionalized Humic Acids Immobilized in Micro- and Nano-Zeolites

Polycyclic aromatic hydrocarbons (PAHs) are hazardous compounds originating from anthropogenic activity. Due to their carcinogenic properties for humans, several technologies have been developed for PAH removal. Sorption with natural and organic materials is currently one of the most studied due to its low cost and its environmentally friendly nature. In this work, a hybrid sorbent involving functionalized humic acids (HAs) and nano-zeolite is proposed to entrap PAHs. The use of functionalized HAs immobilized in a porous support is designed to address the instability of HAs in solution, which has been already reported. HA functionalization was carried out to increase the non-polarity of HAs and aliphatic group formation. The HAs were functionalized by esterification/etherification with alkyl halides, and their chemical changes were verified by FTIR and NMR. The sorption isotherms of the functionalized HAs in micro- and nano-zeolites were used to assess the performance of the nano-zeolites in adsorbing these HAs. The hybrid support allowed the removal of anthracene and pyrene at percentages higher than 90%; fluoranthene, of angular molecular structure, was adsorbed at 85%. PAHs are ubiquitous in the environment, and a stable sorption of them in solid matrices will allow their removal from the environment through effective and environmentally friendly methods.

Dipole-Orientation-Dependent Förster Resonance Energy Transfer from Aromatic Head Groups to MnBr42- Blocks in Organic-Inorganic Hybrids

The understanding and visualization of dipole-dipole interaction on molecular scale are scientifically fundamental and extremely of interest. Herein, two new zero-dimensional (0D) Mn hybrids with aromatic head groups and alkyl tails as organic spacers are selected as models. It was found that the dipole interaction between head groups and Mn blocks could have a huge impact on their crystalline structures as well as the luminescent properties. The parallel-oriented dipoles of the head groups and MnBr₄^2- blocks contribute to an efficient Förster Resonance Energy Transfer (FRET) in cetylpyridinium manganese bromide ([C16Py]₂MnBr₄), while the process is absent in 1-methyl-3-hexadecylimidazolium manganese bromide ([C16mim]₂MnBr₄) with perpendicular-oriented dipoles. This work gives insight into the influence of organic spacers on the geometry and the dipole interaction of Mn polyhedron in the hybrids, which could be of great interest in the future optical regulations and structural design.

Organic contaminants removal from industrial wastewater by CTAB treated synthetic zeolite Y

Due to environmental issues, wastewater treatment is a main concern for most industries and providing access to clean and affordable water is one of the big challenges. Besides, industrial wastewater contains many pollutants, one of the most toxic contaminants is organics. Currently, zeolites are widely used as an adsorbent to remove such pollutants. This study examines a surfactant modified zeolite Y (SMZY), as an applicable solution, to get over this problem. Here, zeolite Y, synthesized from bentonite, is used as an adsorbent basis. Then, it is characterized by XRD, FTIR, BET, SEM, and TGA. Next, it is modified by hexadecyltrimethyl ammonium bromide (CTAB) surfactant in different concentrations. These SMZYs are used to adsorb organic contaminants of an olefin plant wastewater. Based on adsorption capacity evaluated by several isotherms, such as Langmuir, Freundlich, Sips and Dubinin-Radushkevich, total organic carbon (TOC) content of wastewater reduced up to 89%. The optimum modification method and possible mechanism for obtaining this result is presented in the current research. Furthermore, to understand the nature of adsorption process, Van der Waals, hydrophobic, and electrostatic interactions are determined. The results indicate that adsorption process depends on both hydrophobic and electrostatic interactions.

Removal of aromatic and hydrophobic fractions of natural organic matter (NOM) using surfactant modified magnetic nanoadsorbents (MNPs)

The present study investigated the potential of surfactant modified magnetic nanoadsorbents (MNPs) for the removal of aromatic and hydrophobic fractions of natural organic matter (NOM), leading to the formation of trihalomethanes (THMs) in chlorinated drinking water. Co-precipitation method was used for the synthesis of MNPs. However, MNPs have a tendency to form an agglomeration. Therefore, polyethylene glycol (PEG) was used as a surface modifier to reduce the agglomeration. The PEG-coated MNPs were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), BET surface area, X-ray diffraction (XRD), Fourier transform spectrometer (FTIR), and zeta (ζ) potential. FESEM observation indicates that PEG-coated MNPs were spherical in shape and 25 nm in size. Zeta potential values (- 58.35 to - 74.9 mV) indicated excellent stability of PEG-MNPs. FTIR spectra indicated the presence of a -CH₂ group, responsible for the chemical interaction between aromatic and humic content. Batch experiments were conducted by studying the effect of pH, contact time, and adsorbent dosage on NOM removal. Excellent removal of DOC (94.49%) and UV₂₅₄ (89.32%) was observed at the optimum dose of adsorbent (0.75 g/L) and at pH 7.0. Adsorption kinetics followed pseudo-second-order reaction (R², 0.973) and occurs by multilayer chemisorption which is due to the chemical interaction between aromatic and humic compounds of NOM with MNPs. Thus, MNPs showed great potential as a novel adsorbent for the removal of aromatic and hydrophobic compounds of NOM and can significantly be used to curtail the problem of THMs in drinking water supplies.

Performance of a zeolite modified withN,N-dimethyl dehydroabietylamine oxide (DAAO) for adsorption of humic acid assessed in batch and fixed bed columns

Factors that affect adsorption of a synthetic humic acid (HA) on a zeolite modified with the surfactantN,N-dimethyl dehydroabietylamine oxide (DAAO) (SMZ) were investigated in batch and fixed bed column experiments.

Removal of natural organic matter (NOM) and its constituents from water by adsorption - A review

Natural organic matter (NOM) is produced through metabolic reactions in water supply in drinking water sources and has been reported to cause several problems including objectionable taste and color of water, formation of disinfection by-products (DBPs) and reducing the amount of dissolved oxygen in water. The removal of NOM and its constituents from water is a challenging issue worldwide. Many technologies have been examined for this purpose. The properties and amount of NOM, however, can significantly affect the process efficiency. In the present work, an overview of the recent research studies dealing with adsorption method for the removal of NOM and related compounds from water is presented. A wide variety of conventional and non-conventional adsorbents have been reviewed for their potential in NOM removal from water. As revealed from the literature reviewed, modified adsorbents, composite materials and few nanomaterials have shown promising results for NOM removal from water. The main findings obtained for the removal of NOM using different adsorbents have been discussed in this review.

An innovative zinc oxide-coated zeolite adsorbent for removal of humic acid

Zinc oxide (ZnO)-coated zeolite adsorbents were developed by both nitric acid modification and Zn(NO3)2·6H2O functionalization of zeolite 4A. The developed adsorbents were used for the removal of humic acid (HA) from aqueous solutions. The synthesized materials were characterized by porosimetry analysis, scanning electron microscopy, X-Ray diffraction analysis, and high resolution transmission electron microscopy. The maximum adsorption capacity of the adsorbents at 21±1°C was about 60mgCg(-1). The results showed that the positive charge density of ZnO-coated zeolite adsorbents was proportional to the amount of ZnO coated on zeolite and thus, ZnO-coated zeolite adsorbents exhibited a greater affinity for negatively charged ions. Furthermore, the adsorption capacity of ZnO-coated zeolite adsorbents increased markedly after acid modification. Adsorption experiments demonstrated ZnO-coated zeolite adsorbents possessed high adsorption capacity to remove HA from aqueous solutions mainly due to strong electrostatic interactions between negative functional groups of HA and the positive charges of ZnO-coated zeolite adsorbents.

A core–shell structure of polyaniline coated protonic titanate nanobelt composites for both Cr(vi) and humic acid removal

The current methods for chromium and natural organic matter decontamination from wastewater present limitations, such as high cost, poor reproducibility, and detrimental environmental effects as well as by secondary waste.

The coagulation characteristics of humic acid by using acid-soluble chitosan, water-soluble chitosan, and chitosan coagulant mixtures

Chitosan is a potential substitute for traditional aluminium salts in water treatment systems. This study compared the characteristics of humic acid (HA) removal by using acid-soluble chitosan, water-soluble chitosan, and coagulant mixtures of chitosan with aluminium sulphate (alum) or polyaluminium chloride (PACl). In addition, we evaluated their respective coagulation efficiencies at various coagulant concentrations, pH values, turbidities, and hardness levels. Furthermore, we determined the size and settling velocity of flocs formed by these coagulants to identify the major factors affecting HA coagulation. The coagulation efficiency of acid- and water-soluble chitosan for 15 mg/l of HA was 74.4% and 87.5%, respectively. The optimal coagulation range of water-soluble chitosan (9-20 mg/l) was broader than that of acid-soluble chitosan (4-8 mg/l). Notably, acid-soluble chitosan/PACl and water-soluble chitosan/alum coagulant mixtures exhibited a higher coagulation efficiency for HA than for PACl or alum alone. Furthermore, these coagulant mixtures yielded an acceptable floc settling velocity and savings in both installation and operational expenses. Based on these results, we confidently assert that coagulant mixtures with a 1:1 mass ratio of acid-soluble chitosan/PACl and water-soluble chitosan/alum provide a substantially more cost-effective alternative to using chitosan alone for removing HA from water.

Removal of natural organic matter (NOM) from an aqueous solution by NaCl and surfactant-modified clinoptilolite

Zeolitic tuffs are found in different parts of the world. Iranian zeolite is a low-cost material that can be frequently found in nature. Surfactant-modified zeolite (SMZ) can be used for the adsorption of natural organic matter (NOM) from aqueous solutions. The adsorption study was conducted to evaluate the adsorption capacity of SMZ; furthermore, the effects of contact time, initial pH, and the initial adsorbent dose on the adsorption process were investigated in a batch system. The kinetic studies showed that the adsorption of NOM on SMZ was a gradual process. The optimum initial pH values for the adsorption of NOM on SMZ were in the acidic ranges. The batch kinetic experiments showed that the adsorption followed the pseudo-second-order kinetic model with good correlation coefficients. The equilibrium data were well described by the Langmuir isotherm model. The results show that the natural zeolite being modified with NaCl and hexadecyltrimethylammonium bromide as a cationic surfactant was an appropriate adsorbent for the removal of NOM.

Benzene carboxylic acid derivatized graphene oxide nanosheets on natural zeolites as effective adsorbents for cationic dye removal

Graphene oxide (GO) nanosheets were grafted to acid-treated natural clinoptilolite-rich zeolite powders followed by a coupling reaction with a diazonium salt (4-carboxybenzenediazoniumtetrafluoroborate) to the GO surface. Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) revealed successful grafting of GO nanosheets onto the zeolite surface. The application of the adsorbents for the adsorption of rhodamine B from aqueous solutions was then demonstrated. After reaching adsorption equilibrium the maximum adsorption capacities were shown to be 50.25, 55.56 and 67.56 mg g(-1) for pristine natural zeolite, GO grafted zeolite (GO-zeolite) and benzene carboxylic acid derivatized GO-zeolite powders, respectively. The adsorption behavior was fitted to a Langmuir isotherm and shown to follow a pseudo-second-order reaction model. Further, a relationship between surface functional groups, pH and adsorption efficiency was established. Results indicate that benzene carboxylic acid derivatized GO-zeolite powders are environmentally favorable adsorbents for the removal of cationic dyes from aqueous solutions.

Influence of film stability and aging of plasma polymerized allylamine coated quartz particles on humic acid removal

Plasma polymerized allylamine (ppAA) films have been successfully deposited on to the surface of quartz particles via a rotating barrel plasma reactor for humic acid removal. The films were deposited at a power of 25 W, allylamine flow rate of 4.4 sccm and polymerization times of 5 to 60 min. X-ray photoelectron spectroscopy was used to investigate the influence of short-term stirring in water and film age on surface chemistry. Stirring results in a reduction in the nitrogen concentration, which was greatest for shorter polymerization times. Film aging of up to 52 weeks appeared to result in a reduction in the concentration of C-N species. The influence of batch, recycling, and film age on humic acid removal was investigated. Humic acid removal appeared to be reproducible across three separate batches for polymerization times of 20 min or more, which was attributed to film thickness. Recycling of the ppAA films was most successful at pH 11 for up to 4 humic acid removal/regeneration cycles. Successful regeneration at pH 11 was attributed to electrostatic repulsion of the adsorbed humic acid molecules. Decreasing the pH of the regeneration solution reduced the number of successful regeneration cycles due to greater retention of adsorbed humic acid via electrostatic attraction. Film age appears to have minimal effect on humic acid removal where freshly deposited and 52-week-old films removed similar masses of humic acid. Successful production and development of ppAA coated quartz particles has resulted in a functional material that can be incorporated into a water treatment system to improve water quality.

Coexistence of adsorption and coagulation processes of both arsenate and NOM from contaminated groundwater by nanocrystallined Mg/Al layered double hydroxides

In this study, nanocrystallined Mg/Al layered double hydroxides (LDH-CO3) and chloridion intercalated nanocrystallined Mg/Al LDHs (LDH-Cl) were synthesized and used for simultaneous removal of arsenic and natural organic matter (NOM) from contaminated groundwater. Humic acid (HA) was selected as a model compound of NOM. The maximum adsorption capacities of arsenate (As(V)) on LDH-CO3 and LDH-Cl are 44.66 and 88.30 mg/g, respectively, and those of HA on LDH-CO3 and LDH-Cl are 53.16 and 269.24 mg/g, respectively. It was found that more than 98% of arsenic and 94% of NOM were eliminated by LDH-Cl from both arsenic and NOM-rich groundwater, which is used as drinking water in Togtoh County, Inner Mongolia, China. The arsenic concentration declined from 231 to 4 μg/L, which meets the drinking water standard. The adsorption mechanisms were determined by using X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and extended X-ray absorption fine structure spectroscopy techniques (EXAFS). The results showed that the removal of HA was mainly via surface complexation as well as coagulation at the surface of LDHs, while the adsorption of As(V) was mainly via ion-exchange process. The presence of HA exhibited little inhibiting effect on As(V) adsorption by occupying partial binding sites on LDH surfaces. Nevertheless, it could not affect the ion-exchange process of As(V) with the interlayer anions of LDHs. The removal of As(V) and HA can be carried out independently due to the different adsorption mechanisms. By integrating the experimental results, it is clear that LDH-Cl can be potentially used as a cost-effective material for the purification of both arsenic and NOM contaminated groundwater.

Preparation and characterization of surfactant-modified hydroxyapatite/zeolite composite and its adsorption behavior toward humic acid and copper(II)

A novel composite material, i.e., surfactant-modified hydroxyapatite/zeolite composite, was used as an adsorbent to remove humic acid (HA) and copper(II) from aqueous solution. Hydroxyapatite/zeolite composite (HZC) and surfactant-modified HZC (SMHZC) were prepared and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscope. The adsorption of HA and copper(II) on SMHZC was investigated. For comparison purposes, HA adsorption onto HZC was also investigated. SMHZC exhibited much higher HA adsorption capacity than HZC. The HA adsorption capacity for SMHZC decreased slightly with increasing pH from 3 to 8 but decreased significantly with increasing pH from 8 to 12. The copper(II) adsorption capacity for SMHZC increased with increasing pH from 3 to 6.5. The adsorption kinetic data of HA and copper(II) on SMHZC obeyed a pseudo-second-order kinetic model. The adsorption of HA and copper(II) on SMHZC took place in three different stages: fast external surface adsorption, gradual adsorption controlled by both film and intra-particle diffusions, and final equilibrium stage. The equilibrium adsorption data of HA on SMHZC better fitted to the Langmuir isotherm model than the Freundlich isotherm model. The equilibrium adsorption data of copper(II) on SMHZC could be described by the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The presence of copper(II) in solution enhanced HA adsorption onto SMHZC. The presence of HA in solution enhanced copper(II) adsorption onto SMHZC. The mechanisms for the adsorption of HA on SMHZC at pH 7 may include electrostatic attraction, organic partitioning, hydrogen bonding, and Lewis acid-base interaction. The mechanisms for the adsorption of copper(II) on SMHZC at pH 6 may include surface complexation, ion exchange, and dissolution-precipitation. The obtained results indicate that SMHZC can be used as an effective adsorbent to simultaneously remove HA and copper(II) from water.

Adsorption-desorption behavior of 2,4-D on NCP-modified bentonite and zeolite: implications for slow-release herbicide formulations

Clay minerals have obtained considerable attention for slow-release formulation of herbicides to increase weed control efficacy and reduce leaching potential and environmental pollution. This study deals with preparing, characterizing and examining the potentials of modified bentonite and zeoilite in adsorption and release of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide. 2,4-D sorption of the N-cetylpyridinium (NCP)-modified bentonites and zeolites were much higher than those of unmodified substrates. The 2,4-D adsorption capacity of the organo-minerals increased with increasing surfactant loading. Desorption isotherms of 2,4-D did not coincide their corresponding sorption isotherms showing hysteresis. The proportion of 2,4-D released from the organo-minerals after seven desorption cycles varied between 29% and 50% of the total retained herbicide. The sorbed 2,4-D on the adsorbents showed gradual release pattern with time. The release pattern of 2,4-D from NCP-modified bentonite and zeolite, make these synthetic organo-minerals suitable candidate for slow release formulation of 2,4-D.

Synthesis and surfactant modification of clinoptilolite and montmorillonite for the removal of nitrate and preparation of slow release nitrogen fertilizer

This article introduces the synthesis of clinoptilolite and montmorillonite, and their surfactant modification by using solutions of hexadecyltrimethylammonium bromide (CH(3)(CH(2))(15)N(Br)(CH(3))(3), HDTMAB) and dioctadecyldimethylammonium bromide ((CH(3)(CH(2))(17))(2)N(Br)(CH(3))(2), DODMAB). The feasibility of using surfactant modified silicates (SMSs) as a potential adsorbent for nitrate and for slow release of nutrient has been investigated. Adsorption isotherms of NO(3)(-) on SMSs have been measured at aqueous concentration of 160-280 mg L(-1). The SMSs show much higher adsorption capacity than the unmodified materials as determined by Langmuir adsorption isotherm. The surfactant modification and increased surfactant loading concentration enhance the nitrate anion retaining capacity of silicates (montmorillonite (16.05 mg g(-1))<clinoptilolite (30.58 mg g(-1))<DODMAB loaded clinoptilolite (75.19 mg g(-1))<DODMAB loaded montmorillonite (76.92 mg g(-1))<HDTMAB loaded montmorillonite (80.65 mg g(-1))<HDTMAB loaded clinoptilolite (125.00 mg g(-1))). The adsorption data fitted well with the Langmuir and Freundlich isotherms. The slow nutrient release studies have been performed by thin layers-funnel analytical test and soil column percolating system. The obtained results indicate that SMSs are very good adsorbent for NO(3)(-) and a slow release of nitrogen is achievable as it releases NO(3)(-) still after 15-20 days of leaching study.