Arsenic removal from groundwater by MnO2-modified natural clinoptilolite zeolite: effects of pH and initial feed concentration

Arsenite oxidation and adsorptive arsenic removal from contaminated water: a review

Arsenic poisoning of groundwater is one of the most critical environmental hazards on Earth. Therefore, the practical and proper treatment of arsenic in water requires more attention to ensure safe drinking water. The World Health Organization (WHO) sets guidelines for 10 μg/L of arsenic in drinking water, and direct long-term exposure to arsenic in drinking water beyond this value causes severe health hazards to individuals. Numerous studies have confirmed the adverse effects of arsenic after long-term consumption of arsenic-contaminated water. Here, technologies for the remediation of arsenic from water are highlighted for the purpose of understanding the need for a single-point solution for the treatment of As(III)-contaminated water. As(III) species are neutral at neutral pH; the solution requires transformation technology for its complete removal. In this critical review, emphasis was placed on single-step technologies with multiple functions to remediate arsenic from water.

Characterization and properties of manganese oxide film coated clinoptilolite as filter material in fixed-bed columns for removal of Mn(II) from aqueous solution

A new filter material, manganese oxide film coated clinoptilolite (MOFCC), was characterized and introduced to explore the effect in treating high concentration of manganese (1.71-2.12 mg L-1) from aqueous solution in fixed-bed column. Adsorption behavior of Mn(II) can be approximately described with the Langmuir isotherm. During the continuous 30 days filtration experiment, the removal rate of Mn(II) has maintained to be above 95.51%, the accumulated removal amount (806.42 mg) is much higher than the theoretical adsorption capacity (89.71 mg), which indicated that the removal of manganese by MOFCC includes both adsorption and auto-catalytic oxidation process, and it does not require a start-up period. SEM, EDS, XPS, XRD, ZETA potential and BET analyses were used to observe the surface properties of MOFCC. The manganese oxide film of MOFCC exhibits in clusters, apparently on occupied surface, the main component of the manganese oxide film is (Na0.7Ca0.3)Mn7O14·2.8H2O, the specific surface area of MOFCC is 38.76 m2 g-1, and the pore size is concentrated in the range of 3-40 nm, within the mesoporous range mesopores. pHpzc (point of zero charge) value is about 2.36. The characteristics of MOFCC make it an excellent manganese removal filter material for water treatment plant. Therefore, there is a long-term practical significance to develop new system for deep removal of manganese based on MOFCC.

Engineering of 3D graphene hydrogel-supported MnO2-FeOOH nanoparticles with synergistic effect of oxidation and adsorption toward highly efficient removal of arsenic

Iron-manganese-based adsorbent has been regarded as a promising candidate for arsenic purification from water, especially the inorganic As(III), due to its inherent advantage of low cost and large-scale producibility. However, the nanoparticle aggregation, metal leaching and insufficient removal efficiency remain the main challenges in the practical applications of the granular adsorbents. In this work, we develop a universal strategy for the fabrication of an active Fe(III) oxyhydroxide-Mn(IV) oxide/3D graphene oxide (GO) gel composite via a simple hydrothermal reaction. The successful immobilization of Fe-Mn oxyhydroxide/oxides on the interconnected GO gels was intuitively confirmed by the transmission electron microscopy and atomic force microscopy. The combinative characterizations of the X-ray absorption near edge structure and X-ray photoelectron spectroscopy clearly reveal the electron transfer from Fe atoms to Mn atoms. The optimized Fe-Mn/GO composites possess the superior performance with the removal efficiency of over 90% for As(III) at pH 7.0 and ∼97% for As(V) at pH 5.0 and the As(III, V) levels (100 μg l^-1) are reduced to below the WHO guideline of 10 μg l^-1. The sorption isotherm and kinetic experiments on the As removal were also carried out. The post characterizations are employed to better unveil the oxidation-adsorption mechanism. Notably, the application of Fe-Mn/GO composites in the treatment of As-simulated natural water demonstrated a stable and continuous operation for over 20 days and an effluent concentration of arsenic as low as the 10 μg l^-1 in a specially designed flow reactor.

Enhancing mechanism of arsenic(iii) adsorption by MnO2-loaded calcined MgFe layered double hydroxide

The use of MnO2/MgFe-layered double hydroxide (MnO2/MgFe-LDH) and MnO2/MgFe-layered double oxide (MnO2/MgFe-LDO400 °C) for arsenic immobilization from the aqueous medium is the subject of this research. Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to characterise MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C. Based on our developed method, MnO2 was spread on the clay composites' surfaces in the form of a chemical bond. The clay composite exhibited a good adsorption effect on arsenic. The experimental findings fit the pseudo-second-order model well, indicating that the chemisorption mechanism played a significant role in the adsorption process. Furthermore, the Freundlich model suited the adsorption isotherm data of all adsorbents well. The recycling experiment showed that MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C exhibited good stability and reusability. In summary, MnO2/MgFe-LDH and MnO2/MgFe-LDO400 °C are promising for developing processes for efficient control of the pollutant arsenic.

Simultaneous reduction in cadmium and arsenic accumulation in rice (Oryza sativa L.) by iron/iron-manganese modified sepiolite

It is challenging to reduce the cadmium (Cd) and arsenic (As) contents of brown rice simultaneously due to their converse chemical behaviors in the paddy soil. Clay minerals, such as sepiolite (SEP), have significant advantages in remediating Cd-contaminated soil. Moreover, iron or manganese oxide loaded SEP can improve the As adsorption efficiency. Herein, ferric nitrate modified sepiolite (NIMS) and iron‑manganese modified sepiolite (FMS) were prepared to study their effects on Cd and As accumulation in rice using pot experiments. The results showed that NIMS and FMS had a larger specific surface area than SEP. The application of SEP only decreased Cd content (by 45%), while NIMS and FMS treatments reduced both Cd (by 57% and 87%) and As (by 30% and 25%) contents in brown rice compared with the control. The X-ray photoelectron spectroscopy (XPS) analysis results indicated that MnO₂ and MnOOH^⁎ in FMS enhanced the adsorption and co-precipitation of Cd as well as the oxidation of As(III) to As(V). The NIMS, as well as the FMS application, increased soil pH, decreased the exchangeable Cd and non-specifically and specifically adsorbed As fractions in soil, and reduced the level of Cd in the pore water. Moreover, NIMS and FMS addition limited the transfer of As from the soil to the roots by enhancing its sequestration in the iron plaque. On the other hand, FMS treatment significantly promoted the uptake of Mn by rice (P < 0.05). The results suggested that both NIMS and FMS were promising materials for simultaneous reduction of Cd and As accumulation in rice. Notably, FMS had better performance in reducing the Cd content in rice than that of NIMS.

Zirconium hydroxide nanoparticle encapsulated magnetic biochar composite derived from rice residue: Application for As(III) and As(V) polluted water purification

Finding a low-cost and suitable adsorbent is still in urgent need for efficient decontamination of As(III) and As(V) elements from the polluted waters. A novel zirconium hydroxide nanoparticle encapsulated magnetic biochar composite (ZBC) derived from rice residue was synthesized for the adsorptive capture of As(III) and As(V) from aqueous solutions. The results revealed that ZBC showed an acceptable magnet separation ability and its surface was encapsulated with lots of hydrous zirconium oxide nanoparticles. Compared to As(III), the adsorption of As(V) onto ZBC was mainly dependent on the pH of the solution. The intraparticle diffusion model described the adsorption process. ZBC showed satisfactory adsorption performances to As(III) and As(V) with the highest adsorption quantity of 107.6 mg/g and 40.8 mg/g at pH 6.5 and 8.5, respectively. The adsorption of As(III) and As(V) on ZBC was almost impervious with the ionic strength while the presence of coexisting ions, especially phosphate, significantly affected the adsorption process. The processes of complexation reaction and electrostatic attraction contributed to the adsorption of As(III) and As(V) onto ZBC. ZBC prepared from kitchen rice residue was found to be a low cost environmentally friendly promising adsorbent with high removal capacity for As(III) and As(V) and could be recycled easily from contaminated waters.

Robust Al3+ MOF with Selective As(V) Sorption and Efficient Luminescence Sensing Properties toward Cr(VI)

Herein, we report the synthesis and characterization of a new robust Al³⁺ metal-organic framework MOF, [Al(OH)(PATP)]·solvent (Al-MOF-1, with PATP^2- = 2-((pyridin-2-ylmethyl)amino)terephthalate). Al-MOF-1 exhibits excellent stability from highly acidic (pH = 2) to basic (pH = 12) aqueous solutions or in the presence of oxoanionic species [As(V) and Cr(VI)]. On the contrary, the related MIL-53(Al) MOF (Al(OH) (BDC), with BDC^2- = terephthalate) shows a partial structure collapse under these conditions, signifying the superior chemical robustness of Al-MOF-1. Al-MOF-1 was proved to be an effective sorbent toward As(V) with efficient sorption capacity (71.9 ± 3.8 mg As/g), rapid sorption kinetics (equilibrium time ≤1 min), and high selectivity in the presence of various competing anions. Furthermore, Al-MOF-1 revealed high sorption capacities for Cr(VI) species in both neutral (124.5 ± 8.6 mg Cr/g) and acidic (63 ± 2 mg Cr/g) aqueous media, combining fast kinetics and relatively good selectivity. The limited porosity (BET = 38 m²/g) and small pores (2-3 Å) of the material indicate that the sorption process occurs exclusively on the external surface of Al-MOF-1 particles. The driving force for the capture of oxoanions by Al-MOF-1 is the strong electrostatic interactions between the oxoanionic species and the positively charged surface of MOF particles. Aiming at a practical wastewater treatment, we have also immobilized Al-MOF-1 on a cotton substrate, coated with polydopamine. The fabric sorbent exhibited highly effective removal of the toxic oxoanionic species from aqueous media under either batch or dynamic (continuous flow) conditions. In addition, Al-MOF-1 was found to be a promising luminescence sensor for detecting trace amounts of Cr(VI) in real water samples, with Cr(VI) being successfully detected at concentrations well below the acceptable limits (<50 ppb). Moreover, Al-MOF-1 was demonstrated to be a sufficient water sensor in organic solvents (LOD ≤0.25% v/v). All the above indicate that Al-MOF-1 represents a multifunctional material with a multitude of potential applications, such as environmental remediation, industrial wastewater treatment, chemical analysis, and water determination in biofuels.

Nanometer effect promoting arsenic removal on α-MnO2 nano-surface in aqueous solution: DFT+U research

The nanometer effect in the process of arsenic ions removal on α-MnO₂ nano-surface is studied by the first-principle method through microfacet models. Several parameters, such as adhesion energy, electrostatic potential, and Mulliken population were calculated to illuminate the internal mechanism. The results show that the adsorption energies of As(OH)₃ molecules on MnO₂[(100×110)] nanostructure are smaller than that on the bulk surface with the same concentration, which means the nanometer effect is beneficial to enhance the adsorption ability of MnO₂ nano-surface. In an aqueous solution, there exist two possible removal ways of As ions. One is the direct reaction of As(OH)₃→As(OH)₆^-, which occurs both in bulk surface and nano-surface. However, to nanomaterials, there exists another removal way of As(OH)₃→As(OH)₄→As(OH)₆^- through an intermediate As(OH)₄ molecule produced by nanometer effect. Furthermore the smaller electrostatic potential of As ions on [(100×110)] nano-surface is beneficial to enhance the removal capability of As ions. Then the reason why MnO₂ nanomaterials have better catalytic activity than the bulk materials is originated from its much less adhesion energy, much more removal ways, and much smaller electrostatic potential. So this research provides a detailed understanding of the removal capability of toxic ions influenced by a nanometer effect.

An Experimental Study of Fluoride Removal from Wastewater by Mn-Ti Modified Zeolite

The emerging interest in fluoride-removal from wastewater has attracted attention to zeolite since it has been considered as a natural adsorbent. However, the fluoride-removal efficiency of natural zeolite is generally low. As part of the effort to improve the zeolite adsorption efficiency, we have produced and tested the Mn-Ti modified zeolite. In the current work, the material preparation is discussed, and prepared materials were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy, and Fourier transform infrared (FTIR) spectra. Both static and dynamic experiments were conducted to examine the effects of independent variables. In the static adsorption section, sensitivity analysis experiments were conducted for independent variables, such as adsorbent dosage, pH, temperature, and competitive ions. The maximum adsorption capacity is 2.175 mg/g, which was obtained at PH = 7, temperature = 25 °C, and initial fluoride concentration = 10 mg/L. For adsorption kinetics, both Lagergren and Pseudo-second order models predict the experiments very well, which probably demonstrates that the current process is a combination of physical sorption and chemisorption. For adsorption isotherms, the Freundlich model performs better than the Langmuir model since it is usually applied to illustrate adsorption on inhomogeneous surfaces. In the dynamic adsorption section, sensitivity analysis experiments were also conducted for independent variables, such as adsorbent thickness, flow velocity, initial fluoride concentration, and PH. Additionally, the adsorption mechanism is also discussed. The main reason is the hydrated metal fluoride precipitate formation. As we know, the current work provides the first quantified comparison of the natural zeolite and the Mn-Ti modified zeolite regarding fluoride-removal efficiency.

Adsorption properties and mechanism of uranium by three biomass materials

Wood fibers, bamboo fibers and rice husk were applied to the adsorption of uranium from aqueous solution to understand the uranium adsorption behavior and mechanism by these natural sorbents. The effects of time, adsorbent particle size, pH, adsorbent dosage, temperature and initial concentration were studied using batch technique. The adsorption mechanism was discussed by isothermal adsorption models, adsorption kinetic models. The results suggested that the three biomass adsorbents showed great efficiency of adsorption for uranium. The adsorption capacity of biosorbents of comparatively small particle size and large dosage is quite high. Uranium adsorption achieved a maximum adsorption amount at around pH 3 for wood fibers and bamboo fibers, and around pH 5 for rice husk. All isotherms fitted well to the Langmuir Freundlich and D-R equation, indicating that the adsorption process is favorable and dominated by ion exchange. Rice husk had a highest adsorption capacity, followed by bamboo fibers, while wood fibers had little uranium adsorption under the studied conditions, and the adsorption capacity was 12.22, 11.27 and 11.04 mg/g, respectively. The equilibrium data was well represented by the pseudo-second-order kinetics, indicating that the adsorption rate was controlled by chemical adsorption. Ion exchange was the main adsorption mechanism, and the exchange ions were mainly Na+ and K+.

Manganese-based advanced nanoparticles for biomedical applications: future opportunity and challenges

Nanotechnology is the most promising technology to evolve in the last decade. Recent research has shown that transition metal nanoparticles especially manganese (Mn)-based nanoparticles have great potential for various biomedical applications due to their unique fundamental properties. Therefore, globally, scientists are concentrating on the development of various new manganese-based nanoparticles (size and shape dependent) due to their indispensable utilities. Although numerous reports are available regarding the use of manganese nanoparticles, there is no comprehensive review highlighting the recent development of manganese-based nanomaterials and their potential applications in the area of biomedical sciences. The present review article provides an overall survey on the recent advancement of manganese nanomaterials in biomedical nanotechnology and other fields. Further, the future perspectives and challenges are also discussed to explore the wider application of manganese nanoparticles in the near future. Overall, this review presents a fundamental understanding and the role of manganese in various fields, which will attract a wider spectrum of the scientific community.

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.

Adsorption of U(VI) from aqueous solution by using KMnO4-modified hazelnut shell activated carbon: characterisation and artificial neural network modelling

This study is based on U(VI) removal from wastewater by KMnO₄-modified hazelnut shell activated carbon (KM-HSAC) using adsorption technology. A characterisation study of KM-HSAC was conducted through scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS) analysis. The rough surface of KM-HSAC contains many irregular microspores. The EDS pattern confirmed the U(VI) adsorption on the KM-HSAC. A batch study experiment gave optimum results for U(VI) at pH 6, contact time of 160 min, initial U(VI) concentration of 155.56 mg/L and KM-HSAC dosage of 4 g/L, with a maximum adsorption capacity of 22.27 mg/g. The prediction performance of artificial neural network models was validated through the low values of statistical error (2.708 and 8.241 for RMSE of training and testing data, respectively) and the high determination coefficient value (0.987 and 0.906 for training and testing data, respectively). Experimental results suggest that KM-HSAC has a high potential for the removal of U(VI) from wastewater.

Removal of decidedly lethal metal arsenic from water using metal organic frameworks: a critical review

Water contamination is worldwide issue, undermining whole biosphere, influencing life of a large number of individuals all over the world. Water contamination is one of the chief worldwide danger issues for death, sickness, and constant decrease of accessible drinkable water around the world. Among the others, presence of arsenic, is considered as the most widely recognized lethal contaminant in water bodies and poses a serious threat not exclusively to humans but also towards aquatic lives. Hence, steps must be taken to decrease quantity of arsenic in water to permissible limits. Recently, metal-organic frameworks (MOFs) with outstanding stability, sorption capacities, and ecofriendly performance have empowered enormous improvements in capturing substantial metal particles. MOFs have been affirmed as good performance adsorbents for arsenic removal having extended surface area and displayed remarkable results as reported in literature. In this review we look at MOFs which have been recently produced and considered for potential applications in arsenic metal expulsion. We have delivered a summary of up-to-date abilities as well as significant characteristics of MOFs used for this removal. In this review conventional and advanced materials applied to treat water by adsorptive method are also discussed briefly.

Synthesis of Fe Doped Poly p-Phenylenediamine Composite: Co-Adsorption Application on Toxic Metal Ions (F- and As3+) and Microbial Disinfection in Aqueous Solution

Water is regarded as an important natural resource to sustain life, and its purification is an important criterion that determines its quality and usefulness. In this study, the incorporation of Fe³⁺ oxide onto a phenylenediamine (pPD) polymer matrix through chemical co-polymerization was prepared, and its arsenite and fluoride removal potentials at optimal conditions from aqueous solution were evaluated. The morphology and structural analysis of the synthesized Fe-doped pPD (Fe-pPD) were comparatively evaluated using the FT-IR, SEM, EDS, and XRD techniques. Fe was successfully incorporated onto pPD matrix as confirmed by different morphological characterizations. The rate of adsorption of F⁻ and As³⁺ onto the Fe-pPD composite best followed the pseudo-second-order kinetic model. The experimental data for both As³⁺ and F⁻ onto the Fe-pPD composite better fit the Freundlich isotherm model at different operating temperatures. Overall, the synthesized composite exhibited a strong affinity towards fluoride uptake (96.6%) than arsenite uptake (71.14%) with a maximum capacity of 6.79 (F⁻) and 1.86 (As³⁺) mg/g. Additionally, the synthesized adsorbent showed some level of antimicrobial activity against common water-borne bacterial. Therefore, the Fe-doped pPD composite has the potential ability for inorganic metal species pollutants remediation and bacterial disinfection in community-level water purification processes.

Graphene oxide-iron modified clinoptilolite based composites for adsorption of arsenate and optimization using response surface methodology

In this study, graphene oxide and composites of graphene oxide-iron modified clinoptilolite were synthesized and used for arsenate removal from aqueous solution. All adsorbents were characterized using X-ray diffraction and specific surface area analysis. The specific surface areas of composites were found to be less than the iron modified clinoptilolite. The time required to reach equilibrium was determined as 3 hours for all adsorbents. The Box-Behnken statistical experiment design method was used to determine the effects of initial arsenate concentration, pH and the amount of adsorbent on the percent arsenate removal. Graphene oxide was not as effective as composites for arsenate adsorption from water. Arsenate adsorption on composites was showed good compatibility with the Freundlich isotherm. The maximum arsenate uptake was realized at pH 4 for graphene oxide and at pH 7 for composites. The maximum adsorption capacities obtained at the optimum points determined by using the Box-Behnken design method were calculated as 39.49, 117.98 and 124.64 µg.g^-1 for graphene oxide and composites, respectively.

Review: Efficiently performing periodic elements with modern adsorption technologies for arsenic removal

Arsenic (As) toxicity is a global phenomenon, and it is continuously threatening human life. Arsenic remains in the Earth's crust in the forms of rocks and minerals, which can be released into water. In addition, anthropogenic activity also contributes to increase of As concentration in water. Arsenic-contaminated water is used as a raw water for drinking water treatment plants in many parts of the world especially Bangladesh and India. Based on extensive literature study, adsorption is the superior method of arsenic removal from water and Fe is the most researched periodic element in different adsorbent. Oxides and hydroxides of Fe-based adsorbents have been reported to have excellent adsorptive capacity to reduce As concentration to below recommended level. In addition, Fe-based adsorbents were found less expensive and not to have any toxicity after treatment. Most of the available commercial adsorbents were also found to be Fe based. Nanoparticles of Fe-, Ti-, Cu-, and Zr-based adsorbents have been found superior As removal capacity. Mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.) removed As efficiently from water. Oxidation of AsO₃^3- to AsO₄^3-and adsorption of oxidized As on the mixed element-based adsorbent occurred by different adsorbents. Metal organic frameworks have also been confirmed as good performance adsorbents for As but had a limited application due to nano-crystallinity. However, using porous materials having extended surface area as carrier for nano-sized adsorbents could alleviate the separation problem of the used adsorbent after treatment and displayed outstanding removal performances.

Characterization of Fe(III) Adsorption onto Zeolite and Bentonite

In this study, the adsorption of Fe(III) from aqueous solution on zeolite and bentonite was investigated by combining batch adsorption technique, Atomic adsorption spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. Although iron is commonly found in water and is an essential bioelement, many industrial processes require efficient removal of iron from water. Two types of zeolite and two types of bentonite were used. The results showed that the maximum adsorption capacities for removal of Fe (III) by Zeolite Micro 20, Zeolite Micro 50, blue bentonite, and brown bentonite were 10.19, 9.73, 11.64, and 16.65 mg.g⁻¹, respectively. Based on the X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) analyses of the raw samples and the solid residues after sorption at low and high initial Fe concentrations, the Fe content is different in the surface layer and in the bulk of the material. In the case of lower initial Fe concentration (200 mg.dm⁻³), more than 95% of Fe is adsorbed in the surface layer. In the case of higher initial Fe concentration (4000 mg.dm⁻³), only about 45% and 61% of Fe is adsorbent in the surface layer of zeolite and bentonite, respectively; the rest is adsorbed in deeper layers.

Fabrication of an (α-Mn2O3:Co)-decorated CNT highly sensitive screen printed electrode for the optimization and electrochemical determination of cyclobenzaprine hydrochloride using response surface methodology

A new chemically optimized screen-printed electrode modified with a cobalt-doped α-Mn2O3 nanostructure on carbon nanotube paste (α-Mn2O3:Co@CNTs) has been constructed for the recognition of cyclobenzaprine hydrochloride. The prepared paste is based on the incorporation of oxide ion conductors, such as the α-Mn2O3 nanostructure with cobalt and ion pairs (tetraphenyl borate coupled with the drug), as electroactive species in the screen-printed electrode to increase the sensor surface area and decrease electrical resistance. The central composite design is a useful methodology for the estimation and modeling of the exact optimum parameters specifically designed for this process. This is a good way to graphically clarify the relationship between various experimental variables and the slope response. The proposed sensor, α-Mn2O3:Co@CNTs, possesses very good sensitivity and the ability to recognize the drug over the concentration range of 1 × 10-6 to 1 × 10-2 mol L-1 at 25 ± °C with a detection limit of 2.84 × 10-7 mol L-1. It exhibits a reproducible potential and stable linear response for six months at a Nernstian slope of 58.96 ± 0.76 mV per decade. The proposed electrode approach has been successfully applied in the direct determination of the drug in its pure and dosage forms.

Adsorption behavior and mechanism of arsenic on mesoporous silica modified by iron-manganese binary oxide (FeMnOx/SBA-15) from aqueous systems

Iron-manganese binary oxides (FeMnO_x) can remove contaminants from aqueous solutions with high efficiency, and mesoporous silica (SBA-15) is widely used as a supporting material due to its large specific surface area and good stability. In this study, SBA-15 was used to support FeMnO_x in the synthesis of a novel arsenic (As) adsorbent (FeMnO_x/SBA-15), and its characteristics under different reaction conditions, such as pH, temperature, presence of competing ions, and humic acid, were tested. The results showed that the contaminant adsorption efficiency of the novel adsorbent was better than that of bare FeMnO_x, as the addition of SBA-15 decreased the agglomeration effect of FeMnO_x. Additionally, FeMnO_x/SBA-15 underwent calcination to further enhance its performance. The state of iron and manganese in FeMnO_x/SBA-15 and the corresponding arsenic removal efficiency were improved by calcination at 350 °C with an FeMnO_x/SBA-15 mass fraction of approximately 45%. Almost 90% of As (50 mL, 5.0 mg L^-1) could be removed by 0.2 g L^-1 of FeMnO_x/SBA-15 (mass ratio of 45% and calcination temperature of 350 °C). The FeMnO_x/SBA-15 could regenerate and still be used after four consecutive cycles. The high As sorption capacity, ability to regenerate, and reusability of FeMnO_x/SBA-15 confirmed that this adsorbent is promising for treating As-contaminated drinking water.

Removing arsenic from water with an original and modified natural manganese oxide ore: batch kinetic and equilibrium adsorption studies

Arsenic contamination of drinking water is a serious water quality problem in many parts of the world. In this study, a low-cost manganese oxide ore from Vietnam (Vietnamese manganese oxide (VMO)) was firstly evaluated for its performance in arsenate (As(V)) removal from water. This material contains both Mn (25.6%) and Fe (16.1%) mainly in the form of cryptomelane and goethite minerals. At the initial As(V) concentration of 0.5 mg/L, the adsorption capacity of original VMO determined using the Langmuir model was 0.11 mg/g. The modified VMOs produced by coating VMO with iron oxide (Fe^a-VMO) and zirconium oxide (Zr^a-VMO) at 110 °C and 550 °C achieved the highest As(V) adsorption capacity when compared to three other methods of VMO modifications. Langmuir maximum adsorption capacities of Fe^a-VMO and Zr^a-VMO at pH 7.0 were 2.19 mg/g and 1.94 mg/g, respectively, nearly twenty times higher than that of the original VMO. Batch equilibrium adsorption data fitted well to the Langmuir, Freundlich, and Temkin models and batch kinetics adsorption data to pseudo-first order, pseudo-second order, and Elovich models. The increase of pH progressively from 3 to 10 reduced As(V) adsorption with a maximum reduction of 50-60% at pH 10 for both original and modified VMOs. The co-existing oxyanions considerably weakened the As(V) removal efficiency because they competed with As(V) anions. The competition order was PO₄^3- > SiO₃^2- > CO₃^2- > SO₄^2-. The characteristics of the original and modified VMOs evaluated using SEM, FTIR, XRD, XRF, surface area, and zeta potential explained the As(V) adsorption behaviour.

Use of (modified) natural adsorbents for arsenic remediation: A review

Arsenic (As) is a ubiquitous element found in the atmosphere, soils and rocks, natural waters and organisms. It is one of the most toxic elements and has been classified as a human carcinogen (group I). Arsenic contamination in the groundwater has been observed in >70 countries, like Bangladesh, India, West Bengal, Myanmar, Pakistan, Vietnam, Nepal, Cambodia, United States and China. About 200 million people are being exposed to excessive As through consumption of contaminated drinking water. Therefore, developing affordable and efficient techniques to remove As from drinking water is critical to protect human health. The currently available technologies include coagulation-flocculation, adsorption, ion exchange, electrochemical conversion and membrane technologies. However, most of the aforementioned treatment techniques require high initial and maintenance costs, and skilled manpower on top of that. Nowadays, adsorption has been accepted as a suitable removal technology, particularly for developing regions, because of its simple operation, potential for regeneration, and little toxic sludge generation. Processes based on the use of natural, locally available adsorbents are considered to be more accessible for developing countries, have a lower investment cost and a lower environmental impact (CO₂ emission). To increase their performance, these materials may be chemically modified. Hence, this review paper presents progress of adsorption technologies for remediation of As contaminated water using chemically modified natural materials.

Synthesis of fly ash based zeolite-reduced graphene oxide composite and its evaluation as an adsorbent for arsenic removal

A zeolite-reduced graphene oxide (ZrGO) based composite was synthesized to remove arsenic from water. To make a low-cost adsorbent, zeolite was synthesized using an inexpensive waste material; fly ash, which was further used to produce the ZrGO composite. Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and Raman spectra were used to characterize the morphology and surface composition of the synthesized materials. Synthesized materials: zeolite, rGO and ZrGO were evaluated as an adsorbent to remove arsenic from water. The results indicated that all three were able to adsorb arsenic from water but the removal efficiency of ZrGO was the best as it was able to bring down the arsenic concentration within the WHO permissible limits. The maximum adsorption capacity for 100 μg/L of initial arsenic concentration was found to be 49.23 μg/g. Results indicate that pseudo second order kinetics describes the arsenic adsorption on ZrGO. Adsorption isotherm study for ZrGO shows best fit for Redlich-Peterson model of adsorption.

Research on the removal mechanism of antimony on α-MnO2 nanorod in aqueous solution: DFT + U method

Although previous papers have reported the desorption process of antimony (Sb) ions adsorbed on α-MnO₂ nanomaterials, some trace Sb(OH)₄^- molecular observed in experiments have not been understood clearly. Using two models as popular bulk surface and new microfacet, several parameters, such as adsorption energy, bond length, total density of state (TDOS) and activation energy, were calculated to research and analyze the catalytic reaction of Sb oxides on α-MnO₂. The results show that the bulk surface model has the "mirror effect" in revealing the catalytic property of α-MnO₂ nanorods. Using MnO₂[(100 × 110)] microfacet model, a new molecular Sb(OH)₄- molecular appears in the reaction process of Sb(OH)₃ + H₂O → Sb(OH)₄^- + H⁺. Further comparing the geometric morphology and TDOS of Sb(OH)₄- with Sb(OH)₆^- molecular, it is found that their bonding length, dihedral and energy orbital of bonding peaks are too close to set the Sb(OH)₄- as the precursor product of Sb(OH)₆^- molecular. Then the desorption process of Sb ions on α-MnO₂ nanorods is virtually transformed into Sb(OH)₃ → Sb(OH)₄^-  → Sb(OH)₆^- way in aqueous solution. Thus, our findings open an avenue for detailed and comprehensive theoretical studies of catalytic reaction by nanomaterials.

As(V) removal capacity of FeCu bimetallic nanoparticles in aqueous solutions: The influence of Cu content and morphologic changes in bimetallic nanoparticles

In this study, bimetallic nanoparticles (BMNPs) with different mass ratios of Cu and Fe were evaluated. The influence of the morphology on the removal of pollutants was explored through theoretical and experimental studies, which revealed the best structure for removing arsenate (As(V)) in aqueous systems. To evidence the surface characteristics and differences among BMNPs with different mass proportions of Fe and Cu, several characterization techniques were used. Microscopy techniques and molecular dynamics simulations were applied to determine the differences in morphology and structure. In addition, X-ray diffraction (XRD) was used to determine the presence of various oxides. Finally, the magnetization response was evaluated, revealing differences among the materials. Our cumulative data show that BMNPs with low amounts of Cu (Fe_0.9Cu_0.1) had a non-uniform core-shell structure with agglomerate-type chains of magnetite, whereas a Janus-like structure was observed in BMNPs with high amounts of Cu (Fe_0.5Cu_0.5). However, a non-uniform core-shell structure (Fe_0.9Cu_0.1) facilitated electron transfer among Fe, Cu and As, which increased the adsorption rate (k), capacity (q_e) and intensity (n). The mechanism of As removal was also explored in a comparative study of the phase and morphology of BMNPs pre- and post-sorption.

A Comparative Study on Removal of Hazardous Anions from Water by Adsorption: A Review

This paper presents a comparative review of arsenite (As(III)), arsenate (As(V)), and fluoride (F−) for a better understanding of the conditions and factors during their adsorption with focus on (i) the isotherm adsorption models, (ii) effects of pH, (iii) effects of ionic strength, and (iv) effects of coexisting substances such as anions, cations, and natural organics matter. It provides an in-depth analysis of various methods of arsenite (As(III)), arsenate (As(V)), and fluoride (F-) removal by adsorption and the anions’ characteristics during the adsorption process. The surface area of the adsorbents does not contribute to the adsorption capacity of these anions but rather a combination of other physical and chemical properties. The adsorption capacity for the anions depends on the combination of all the factors: pH, ionic strength, coexisting substances, pore volume and particles size, surface modification, pretreatment of the adsorbents, and so forth. Extreme higher adsorption capacity can be obtained by the modification of the adsorbents. In general, pH has a greater influence on adsorption capacity at large, since it affects the ionic strength, coexisting anions such as bicarbonate, sulfate, and silica, the surface charges of the adsorbents, and the ionic species which can be present in the solution.

Engineering metal (hydr)oxide sorbents for removal of arsenate and similar weak-acid oxyanion contaminants: A critical review with emphasis on factors governing sorption processes

To create an integrative foundation for engineering of the next generation inexpensive sorbent systems, this critical review addresses the existing knowledge gap in factor/performance relationships between weak-acid oxyanion contaminants and metal (hydr)oxide sorbents. In-depth understanding of fundamental thermodynamics and kinetics mechanisms, material fabrication, and analytical and characterization techniques, is necessary to engineer sorbent that exhibit high capacity, selectivity, stability, durability and mass transport of contaminants under a wide range of operating and water matrix conditions requirements. From the perspective of thermodynamics and kinetics, this critical review examines the factors affecting sorbent performances and analyzes the existing research to elucidate future directions aimed at developing novel sorbents for removal of weak-acid oxyanion contaminants from water. Only sorbents that allow construction of simple and inexpensive water treatment systems adapted to overcome fiscal and technological barriers burdening small communities could pave the road for providing inexpensive potable water to millions of people. Novel sorbents, which exhibit (1) poor performances in realistic operating and water matrix conditions and/or (2) do not comply with the purely driven economics factors of production scalability or cost expectations, are predestined to never be commercialized.

Synthesis and Modification of Clinoptilolite

Clinoptilolite is a natural mineral with exceptional physical characteristics resulting from its special crystal structure, mainstreamed into a large zeolite group called heulandites. An overall view of the research related to the synthesis, modification and application of synthetic clinoptilolite is presented. A single phase of clinoptilolite can be hydrothermally synthesized for 1–10 days in an autoclave from various silica, alumina, and alkali sources with initial Si/Al ratio from 3.0 to 5.0 at a temperature range from 120 to 195 °C. Crystallization rate and crystallinity of clinoptilolite can be improved by seeding. The modification of clinoptilolite has received noticeable attention from the research community, since modified forms have specific properties and therefore their area of application has been broadening. This paper provides a review of the use of organic compounds such as quarter alkyl ammonium, polymer, amine and inorganic species used in the modification process, discusses the processes and mechanisms of clinoptilolite modification, and identifies research gaps and new perspectives.

Use of PVA/α-MnO2-stearic acid nanocomposite films prepared by sonochemical method as a potential sorbent for adsorption of Cd (II) ion from aqueous solution

Alpha manganese dioxide (α-MnO₂) nanorods have been covalently functionalized with stearic acid by solvothermal method. The α-MnO₂-stearic acid nanorods were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. The amount of stearic acid grafted onto α-MnO₂ surface was determined about 41wt% by thermogravimetric analysis. The α-MnO₂-stearic acid nanorods was used as nanofiller for the preparation of poly(vinyl alcohol) (PVA) nanocomposites (NCs). The NCs with 1, 3, and 5wt% of nanofiller were prepared through ultrasound assisted technique as an economical, fast, eco-friendly, and effective method. The PVA/α-MnO₂-stearic acid NCs were characterized by different techniques. The results showed that with increasing the α-MnO₂-stearic acid content, the thermal stability and tensile properties were improved. Besides, the NC 5wt% was used as adsorbent for sorption of Cd (II) ion. The adsorption efficiency of NC 5wt% in different initial concentrations of Cd (II) ion (20-100mgL^-1) was 58-95%. All the isotherm data were well fitted by both Langmuir and Freundlich equations. The adsorption kinetics study demonstrated that pseudo-second-order model was the best fit with the experimental data. The results indicated that prepared NCs are promising adsorbents for the removal of Cd (II) ion from the aqueous solution.

Amorphous nanosized Al–Ti–Mn trimetal hydrous oxides: synthesis, characterization and enhanced performance in arsenic removal

Arsenite oxidation and arsenate adsorption on surface of amorphous nanosized Al–Ti–Mn trimetal hydrous oxides.

Covalent surface modification of α-MnO2 nanorods with l-valine amino acid by solvothermal strategy, preparation of PVA/α-MnO2-l-valine nanocomposite films and study of their morphology, thermal, mechanical, Pb(ii) and Cd(ii) adsorption properties

The surface of α-manganese dioxide (α-MnO₂) nanorods was modified chemically with l-valine amino acid by a solvothermal strategy.

Sorption behaviour of Pu4+ and PuO22+ on amido amine-functionalized carbon nanotubes: experimental and computational study

Amido amine-functionalized multi-walled carbon nanotubes (MWCNT-AA) were used for efficient and selective solid phase separation of plutonium(iv) and plutonium(vi).

Tailored zeolites for the removal of metal oxyanions: overcoming intrinsic limitations of zeolites

This review aims to present a global view of the efforts conducted to convert zeolites into efficient supports for the removal of heavy metal oxyanions. Despite lacking affinity for these species, due to inherent charge repulsion between zeolite framework and anionic species, zeolites have still received considerable attention from the scientific community, since their versatility allowed tailoring them to answer specific requirements. Different processes for the removal and recovery of toxic metals based on zeolites have been presented. These processes resort to modification of the zeolite surface to allow direct adsorption of oxyanions, or by combination with reducing agents for oxyanions that allow ion-exchange with the converted species by the zeolite itself. In order to testify zeolite versatility, as well as covering the wide array of physicochemical constraints that oxyanions offer, chromium and arsenic oxyanions were selected as model compounds for a review of treatment/remediation strategies, based on zeolite modification.

Comparison of treated laterite as arsenic adsorbent from different locations and performance of best filter under field conditions

Arsenic pollution in groundwater is a worldwide concern due to its chronic effects on human health. Numerous studies have been carried out to obtain cost-effective arsenic removal method. Adsorption using natural materials or its treated forms is found to be cost-effective technology. Raw laterite (RL) or its treated form (TL) is studied recently as arsenic adsorbent for aqueous system. Laterite composition varies with geographical location and extent of lateritization. The study on effects of arsenic adsorption with varying composition of laterite is not explored yet. Four laterite samples with different compositions are examined to remove arsenic from water. These laterite samples are activated using an optimized acid followed by base treatment method in order to determine the effects of RL composition on arsenic adsorption behavior of TL. Higher iron and aluminum containing RL samples show higher arsenic adsorption behavior. Similarly, TL obtained from higher iron and aluminum containing RL sample shows the higher specific surface area (130-180 m(2) g(-1)) and pore volume (0.28-0.35 mL g(-1)). Two household filters using TL are deployed in arsenic affected area of Barasat, 24 Parganas (N), West Bengal, India and their performance is monitored for about a year.