Enhanced adsorption of arsenate onto a natural polymer-based sorbent by surface atom transfer radical polymerization

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

Cost-effective phosphorus removal from aqueous solution by a chitosan/lanthanum hydrogel bead: Material development, characterization of uptake process and investigation of mechanisms

Excessive phosphorus is one of the main reasons leading to eutrophication that causes severe ecosystem imbalance and negative human health impacts. In this study, several chitosan (CS)/lanthanum (La) hydrogel beads were first synthesized and tested for phosphorus removal. The stable cross-linked CS/La hydrogel bead prepared with the optimized conditions of 10 wt% La/CS and 1.5 mL of 5% glutaraldehyde demonstrated exceptional performance in the removal. It removed phosphate effectively from an aqueous solution in the pH range from 2 to 7. The complete phosphate uptake was achieved at contact time of 6 h under the completely mixing batch condition. The experimental maximum adsorption capacity of 107.7 mg g^-1 was observed at solution pH 4. The phosphate adsorption was well described by the Freundlich isotherm and the intraparticle surface diffusion model. Furthermore, the adsorbent was effectively regenerated and reused in a five-cycle adsorption-desorption operation. The removal of phosphate can be attributed to electrostatic attraction and ion exchange. Moreover, the bead was capable of removing heavy metals: copper, zinc and lead. This adsorbent may be served as a cost-effective material for the treatment of phosphorus-contaminated water so as to minimize the occurrence of eutrophication.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5-9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO₄^3- g^-1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

Advances in application of cotton-based adsorbents for heavy metals trapping, surface modifications and future perspectives

Cotton-based adsorbents (CBAs) are promising materials for combating the problem of heavy metal pollution of environmental waters. This is ascribed to the low cost, abundance, biodegradability and efficiency of CBAs. Herein we review the adsorption of heavy metals (HMs) onto CBAs. We found that several surface modifications were employed to improve the efficiency of the CBAs. These modifications were effected via thermal, physical and chemical means to obtain activated carbons, biochars, ionic liquids, aerogels, hydrogels, chitosans and nanoparticle-derived CBAs. The CBAs exhibited maximum HMs uptake as low as 0.002 mg/g to as high as 505.6 mg/g. Although, the cotton-derived activated carbons and biochars exhibited enhanced HM uptake from that of the unmodified CBAs, they were less efficient than CBAs modified by other methods. Recent chemical, ionic liquid, chitosan and nano-derived CBAs were the most efficient, with high uptake and fast kinetic removal. However, the nanoparticle-based adsorbents are preferred to the chemically modified forms, due to the possibility of secondary pollution and the noxious effect of the latter to the environment. Findings showed that chemical treatment produced CBAs most efficient for As(V), Pb(II) and Fe(III), while ionic liquid CBA was more efficient for Cu(II) and Ni(II). Nano-based treatment was suitable for the uptake of Co(II), Zn(II), Pb(II) and Cd(II), while the chitosan based adsorbent was viable for Hg(II). Isotherm and kinetic evaluation of CBAs mostly conformed to the Langmuir and pseudo-second order models, respectively. Spontaneous adsorption of HMs onto CBAs was deduced from thermodynamic analysis, with endothermic and exothermic characteristics. Over 88% desorption of HMs was obtained from the CBAs studied with good average reusability from 3 to 20 cycles. We also discussed the directions for future research.

New insight into adsorption and co-adsorption of arsenic and tetracycline using a Y-immobilized graphene oxide-alginate hydrogel: Adsorption behaviours and mechanisms

Heavy metals (e.g., arsenic (As)) and tetracycline (TC) usually coexist in wastewater from livestock farm, whereas the co-adsorption behaviours and mechanisms of As(V) and TC were not well-known. This study investigated the adsorption and co-adsorption of As(V) and TC by a novel yttrium-immobilized-graphene oxide-alginate hydrogel (Y-GO-SA) to explore the adsorption behaviours and mechanisms. The adsorption of As(V) and TC was pH-dependent. The maximum adsorption capacities under the studied concentrations were 273.39 mg/g for As(V), and 477.9 mg/g for TC, respectively, which are much higher than many other reported adsorbents. Furthermore, As(V) adsorption was due to ion exchange between hydroxyl groups and H₂AsO₄^2- groups and H-bonds formed with O-containing groups on Y-GO-SA, and the adsorption of TC by Y-GO-SA was mainly ascribed to electrostatic interaction, H-bonds, π - π EDA interaction, n-π EDA interaction, and cation-bonding bridge effects. The co-adsorption of As(V) and TC in binary system indicated that the presence of TC obviously suppressed the adsorption of As(V) due to the competition for active sites, whereas the effect of presence of As(V) on adsorption of TC can be negligible due to the balance contributions from its contrary effects, i.e. enhancement (anion-π interaction) and reduction (competition for Y ions) in TC adsorption. Finally, the hydrogels performed well in the treatment of livestock farm waste water. It can be anticipated that the prepared 3D hydrogel can be used as a powerful adsorbent in the practical application of waste water treatment, owing to its easy separation, high adsorption and good reusability.

Development and characterization of yttrium-ferric binary composite for treatment of highly concentrated arsenate wastewater

Highly concentrated arsenic generated from industrial operation processes has posted a great thrust to humans. In this study, yttrium-ferric binary composite prepared through a simple co-precipitation method and applied for removing highly concentrated arsenic from the simulated arsenic-containing water. An optimal molar ratio of Y/Fe was determined as 8:1, which had a point of zero charge of around 7.0. The yttrium-ferric binary composite was aggregated by the nano-sized particles. The chemical state of yttrium and iron in the adsorbent was + III. The maximum adsorption capacities of the adsorbent towards arsenate (As(V)) were 401.8 mg-As/g at pH 4 and 288.7 mg-As/g at pH 7, respectively. A contact time of 8 h was sufficient to achieve 80% of the ultimate removal, faster than many reported/commercial water treatment materials. The existence of fluoride and phosphate ions significantly retarded the uptake of arsenic, indicating that likely the adsorbent was capable of adsorbing both contaminants. The mechanism study with several tools such as X-ray photoelectron spectroscopy (XPS) indicated that such functional groups as hydroxyl and carbonate groups participated in the As(V) adsorption process via ligand exchange followed by the inner-sphere complexation.

Novel cotton fabric adsorbent for efficient As(V) adsorption

A novel amine functionalized nonwoven cotton fabric (EDA-GMA-g-NCF) adsorbent material for As(V) adsorption was prepared by using plasma-initiated graft polymerization of glycidyl methacrylate (GMA) onto nonwoven cotton fabric (NCF) and then its modification with ethylenediamine (EDA). The resultant nonwoven cotton fabric adsorbent was examined by using FT-IR, SEM, and XPS techniques. As(V) adsorption experiments were performed in batch mode as a function of pH, contact time, initial concentration, coexisting ions, ionic strength, and tap water applications. Ethylenediamine carrying nonwoven cotton fabric-based functional adsorbent showed efficient, rapid As(V) removal with high adsorption capacity. The experimental data shows that adsorption mechanism fits to the Langmuir isotherm, and adsorption kinetic follows a pseudo-second-order model. Between pH 2-8 range, nonwoven cotton fabric adsorbent is effective at pH 3 for As(V) adsorption. The maximum adsorption capacity of the nonwoven cotton fabric for As(V) was 217.39 mg/g. The adsorbent could be easily regenerated at least ten cycles with 3% HNO₃ solution. EDA-GMA-g-NCF was also efficient for tap water applications with high percent As(V) removal. Thermodynamic parameters show that the As(V) adsorption process was spontaneous and exothermic. Graphical abstract Preparation of cotton fabric adsorbent and As(V) treatment process.

Accumulation of 152+154Eu(III) by Aspergillus sydowii and Trichoderma harzianum

Radionuclides-resistant filamentous fungi were isolated from radionuclides' contaminated soils. Effects of contact time, mycelia dosage, pH, ionic strength and thiol compounds on ^152+154Eu(III) accumulation on two kinds of filamentous fungi (Aspergillus sydowii and Trichoderma harzianum, denoted as A. sydowii and T. harzianum, respectively) were investigated by batch techniques. The maximum tolerance to Eu(III) concentration of A. sydowii and T. harzianum reached 3000 mg/L and 3500 mg/L, and the Eu(III) accumulation on A. sydowii and T. harzianum can be fitted better with the pseudo-second-order kinetic model, respectively. Filamentous fungi were characterized by FT-IR and acid base titrations, and morphological structures of mycelia changed obviously under Eu(III) stress by SEM and TEM analysis. The results suggested that filamentous fungi could play an important role in the migration and transformation of radionuclides in the environment.

Photocatalytic degradation of metronidazole and methylene blue by PVA-assisted Bi2WO6–CdS nanocomposite film under visible light irradiation

The enhanced photocatalytic performance of nanocomposite is synthesized via the hydrothermal method and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) and photoluminescence spectroscopy (PL). Under visible light irradiation, PVA assisted Bi2WO6–CdS nanocomposite film displayed enhanced photocatalytic efficiency and inhibition of photocorrosion as compared with pure CdS, pure Bi2WO6 and Bi2WO6–CdS composite. The PVA assisted Bi2WO6–CdS composite film catalyst showed stable catalytic performance until seven successive runs with 92% of methylene blue(MB) degradation, and easy to recover after degradation of organic pollutant. PVA assisted Bi2WO6–CdS nanocomposite film has optimal band edge position for superior photocatalytic degradation. Furthermore, the trapping experiment was carried out using different scavenger for active species. Among the active species, OH· are the most responsive species which play a vital role in the degradation of metronidazole and MB.

Functionalized chitosan electrospun nanofiber for effective removal of trace arsenate from water

An environment-friendly iron functionalized chitosan elctrospun nanofiber (ICS-ENF) was synthesized for trace arsenate removal from water. The ICS-ENF was fabricated by electrospinning a mixture of chitosan, PEO and Fe(3+) followed by crosslinking with ammonia vapor. The physicochemical properties of ICS-ENF were characterized by FESEM, TEM-EDX and XRD. The ICS-ENF was found to be highly effective for As(V) adsorption at neutral pH. The As(V) adsorption occurred rapidly and achieved equilibrium within 100 min, which was well fitted by pseudo-second-order kinetics model. The As(V) adsorption decreased with increased ionic strength, suggesting an outer-sphere complexation of As(V) on ICS-ENF. Freundlich model well described the adsorption isotherm, and the maximum adsorption capacity was up to 11.2 mg/g at pH 7.2. Coexisting anions of chloride and sulfate showed negligible influence on As(V) removal, but phosphate and silicate significantly reduced As(V) adsorption by competing for adsorption sites. FTIR and XPS analysis demonstrated -NH, -OH and C-O were responsible for As(V) uptake. ICS-ENF was easily regenerated using 0.003 M NaOH, and the removal rate remained above 98% after ten successively adsorption-desorption recycles. This study extends the potential applicability of electrospun nanofibers for water purification and provides a promising approach for As(V) removal from water.

Fabrication and testing of zirconium-based nanoparticle-doped activated carbon fiber for enhanced arsenic removal in water

A Zr-nanoparticle-doped ACF from this study shows a great potential for removal of arsenic from contaminated groundwater.

Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal

Chronic contamination of groundwaters by both arsenic (As) and fluoride (F) is frequently observed around the world, which has severely affected millions of people. Fluoride and As are introduced into groundwaters by several sources such as water-rock interactions, anthropogenic activities, and groundwater recharge. Coexistence of these pollutants can have adverse effects due to synergistic and/or antagonistic mechanisms leading to uncertain and complicated health effects, including cancer. Many developing countries are beset with the problem of F and As laden waters, with no affordable technologies to provide clean water supply. The technologies available for the simultaneous removal are akin to chemical treatment, adsorption and membrane processes. However, the presence of competing ions such as phosphate, silicate, nitrate, chloride, carbonate, and sulfate affect the removal efficiency. Highly efficient, low-cost and sustainable technology which could be used by rural populations is of utmost importance for simultaneous removal of both pollutants. This can be realized by using readily available low cost materials coupled with proper disposal units. Synthesis of inexpensive and highly selective nanoadsorbents or nanofunctionalized membranes is required along with encapsulation units to isolate the toxicant loaded materials to avoid their re-entry in aquifers. A vast number of reviews have been published periodically on removal of As or F alone. However, there is a dearth of literature on the simultaneous removal of both. This review critically analyzes this important issue and considers strategies for their removal and safe disposal.

Arsenate resistant Penicillium coffeae: a potential fungus for soil bioremediation

Bioremediation is an effective method for the treatment of major metal contaminated sites. Fungi were isolated from soil samples collected from different arsenate contaminated areas across India. An isolate, Penicillium coffeae, exhibited resistance to arsenate up to 500 mM. Results indicated that pretreatment of biomass with alkali (NaOH) enhanced the percentage of adsorption to 66.8% as compared to that of live and untreated dead biomass whose adsorption was 22.9% and 60.2% respectively. The physiological parameters evaluated in this study may help pilot studies aimed at bioremediation of arsenate contaminated effluents using arsenate resistant fungus P. coffeae.

Use of chitosan and chitosan-derivatives to remove arsenic from aqueous solutions--a mini review

Arsenic removal has become a relevant concern due to the final confirmation of its behaviour as chronic human carcinogen, corresponding to an ever-increasing contamination of water, soil and crops in many parts of the world. Developing easily accessible removal strategies is therefore a primary environmental matter. Chitosan and chitosan derivatives show good adsorption performances against arsenic removal and are considered low cost products, easily obtainable. This review provides a summary of recent advances of the application of these compounds in the area of sorption sciences for arsenate and arsenite removal from water, focusing on equilibrium and kinetic mechanisms.

Arsenic accumulation and distribution in relation to young seedling growth in Atriplex atacamensis Phil

Even at trace levels, arsenic is of environmental and health concern due to its high toxicity. The xerohalophyte plant species Atriplex atacamensis grows on an arsenic-contaminated mining area in North Chile. Young seedlings that were grown from seeds collected from these plants were grown in a nutrient solution under controlled environmental conditions and were exposed for 14 and 28 days to 0, 100 or 1000 μM arsenate. More than 75% of the plants that were exposed to the highest As dose survived until the end of the treatment. The seedling growth was reduced (100 μM As) or inhibited (1000 μM As) in the stress conditions, but the plants were able to efficiently close their stomata and perform osmotic adjustments to avoid secondary water stress. Arsenic accumulated up to 400 μg g(-1) DW in the shoots and 3500 μg g(-1) DW in the roots. Arsenate drastically impaired the P content and increased glycinebetaine content, although no arsenobetaine was found in the tissues. With the exception of arsenite and arsenate, no As-containing organic compound was detected. Arsenic was not excreted by the trichomes that were present at the leaf surface. Although an increase in the total level of non-protein thiols suggested that arsenite fixation on the sulfhydryl groups could occur in the stressed tissues, the majority of the soluble arsenic remained in its oxidized state As(V). Arsenate induced an increase in the free soluble polyamine concentrations in all of the organs, and it increased the proportion of spermidine and spermine and decreased the proportion of putrescine in the polyamine pool. Therefore, it is likely that these polycationic molecules may assist in arsenate sequestration in the stressed tissues, and A. atacamensis may represent a promising plant species that can be tested in field trials for its phytomanagement of As-contaminated sites in desert areas.