Abstract Capacitive deionization (CDI) is an emerging desalination technology, particularly useful for removing ionic and polarizable species from water. In this context, the desalination performance of fluoride and other toxic species (lead and arsenic) present in brackish water at an industrial scale of a few kilo liters using a CDI prototype built by InnoDI Private Limited is demonstrated. The prototype is highly efficient in removing ionic contaminants from water, including toxic and heavy metal ions. It can remove fluoride ions below the World Health Organization (WHO) limit (1.5 ppm) at an initial concentration of 7 ppm in the input feed water. The fluoride removal efficiency of the electrodes (at a feed concentration of 6 ppm) deteriorates by ≈4–6% in the presence of bicarbonate and phosphate ions at concentrations of 100 ppm each. The removal efficiency depends on flow rate, initial total dissolved solids, and other co‐ions present in the feed water. Interestingly, toxic species (As3+/5+ and Pb2+) are also removed efficiently (removal efficiency > 90%) by this technology. The electrodes are characterized extensively before and after adsorption to understand the mechanism of adsorption at the electrode.

Mixed metal-oxides are an important class of materials studied for the adsorptive removal of contaminants in water. However, the lack of affordable and versatile immobilisation techniques limits its large-scale deployment in water purification. The present work describes the use of protonated chitosan as a template and reinforcing agent to fabricate FeOOH-MnxOy bimetal-oxide granules formed via complexation of metal-oxides with hydroxyl and amine groups in chitosan. The synthesis procedure also enables the modulation of nanocomposite into granules of different shapes and sizes. XRD and XPS analyses confirm the existence of MnO, Mn2O3, MnO2, and FeOOH phases in the composite. The granules showed excellent affinity to scavenge the model pollutant, Pb2+, through inner-sphere complexation with an estimated Sips isotherm capacity of 108.12 mg/g. The chemical stability analysis of the composite showed that the leaching of Fe and Mn from the composite is pH, contact time, and temperature dependent. The background ions can also affect the chemical stability of the composite. However, Fe and Mn leaching were well within the permissible limit under typical groundwater pH and temperature. There is no significant effect on Pb2+ intake by competing ions such as Cl-, NO3-, HCO3-, Ca2+, Fe2+, and Mn2+. In short, the improved adsorption capacity, the ability to form hydraulically stable granules, and ease of synthesis make the composite a practical adsorbent for removing heavy metal ions in water.

The use of renewable resources has been gaining interest due to their high economic benefits. They are attractive as a sustainable alternative to conventional resources for producing useful and valuable materials. The paper focuses on using a composite of graphene-oxide and chitosan, an aquaculture waste-derived material, as a renewable feedstock for producing a sealant for healing micro-cracks in concrete. The sealant named Eco-Nanoseal is well characterised, and its interaction with concrete is studied. A possible binding mechanism of Eco-Nanoseal with concrete is proposed. The nanofibrous film-forming composite can quickly solidify in the concrete environment without any external polymerising agent. The quick ability to form a solid plug and strong bonding with the concrete surface makes Eco-Nanoseal a potential candidate for healing micro-cracks in concrete. The novel application is demonstrated well in M25 grade concrete cube specimens. With low environmental factor (E-factor) and process mass intensity (PMI) values of 0.05 and nearly 1, respectively, the Eco-Nanoseal complies the critical parameters of materials' sustainability indices. The Eco-Nanoseal is a promising and environmentally-friendly alternative to synthetic polymer-based adhesives.

Capacitive deionization (CDI) is an emerging, cost‐effective alternative for energy‐efficient desalination technology. Efficient electrode materials based on individual reduced graphene oxide (rGO) nanosheets are produced by functionalizing them with polystyrene (rGO–PS) through an in situ polymerization process involving rGO, styrene monomer, and divinylbenzene. The rGO–PS‐integrated composite nanostructures are subsequently functionalized with sulfonate and quaternary amine functionalities to achieve positively and negatively charged electro‐adsorbent ion‐exchange resins (EAIERs), respectively. These EAIERs ‘molecular constructs’ are used to fabricate CDI electrodes, and deionization is performed to remove various ions. These molecular constructs promote faster charge transfer at the electrode–electrolyte interface and maintained the electrical conductivity of the active rGO. This leads to a high electroadsorption capacity of 15.93 mg g −1 of Cl − using NaCl solution with a conductivity of 802 µS in laboratory batch experiments, which is approximately five times higher than the adsorption capacity of rGO electrodes reported earlier (≈2–3 mg g −1 ) in comparable experimental conditions. No significant Faradaic redox reactions or chemical changes are observed on the electrode surface, which make these electrodes exhibit excellent electrochemical stability even after multiple adsorption/desorption cycles.

Capacitive deionization (CDI) is an emerging and promising new technology for removal of ionic as well as polarizable species from water. It is an alternative to membrane-based technologies, having low operational cost, enhanced energy efficiency, and less water rejection. The technology works on the principle of electroadsorption of ions at the surface of electrically charged electrodes, generally made of porous carbon materials. The concept of CDI date back to the 1960s but the community of CDI has grown exponentially in last two decade. The chapter deals with the history of CDI, different patents which revolutionized the technology and the theory of electroadsorption. Different advancements in the technology such as introduction of different cell architectures, parameters responsible for efficient CDI cells, development of different novel electrode materials such as carbon aerogel (CA), carbon cloth, carbon nanotubes (CNTs), graphene and its composites, carbon fibers, and mexenes, and commercialization of CDI products have been discussed in detail. The chapter also gives a brief outlook on the current status and future development of this technology.

This paper describes a labour efficient and cost-effective strategy to prepare few-layered of reduced graphene oxide like (RGOL) sheets from graphite. The self-propagated combustion route enables the bulk production of RGOL sheets. Microscopic and spectroscopic analyses confirmed the formation of few-layer graphene sheets of an average thickness of ∼3 nm and the presence of some oxygen functional groups with a C/O ratio of 8.74. A possible mechanistic pathway for the formation of RGOL sheets is proposed. The optical properties of the RGOL sample were studied in detail by means of Spectroscopic Ellipsometry (SE). The experimental abilities of SE in relating the optical properties with the number of oxygen functionalities present in the samples are explored. The data were analysed by a double-layered optical model along with the Drude-Lorentz oscillatory dispersion relation. The refractive index (n = 2.24), extinction coefficient (k = 2.03), and dielectric functions are obtained using point-by-point analysis and are also checked for Kramers-Kronig (KK) consistency.

The present study is targeted toward understanding the interaction between important and technologically relevant poly morphs of iron oxides/oxyhydroxides with arsenic species at neutral pH. The existence of various arsenic (As) species in solution was verified by Raman measurements. Their species-dependent adsorption on the affordable arsenic removal media, confined metastable 2-line ferrihydrite (CM2LF) was investigated. The results were compared with common adsorption media, hematite (alpha-Fe2O3) and magnetite (Fe3O4). X-ray photoelectron spectroscopy was used to investigate the changes in the core levels of Fe 2p and As 3d resulting from the uptake of arsenic species. Binding of various As species with CM2LF was confirmed by FTIR studies. Raman adsorption data were found to fit a pseudo-second-order model. Results of this study show the synthesized nanocomposite of CM2LF to be very effective for the removal of As(III) and As(V) species in comparison to various materials at neutral pH. A model for the adsorption of As(III) and As(V) species in water on a ferrihydrite particle was developed. This accounted for the large uptake capacity.

Extraction of silver into water occurs from its apparently inert metal surface by the simple carbohydrate glucose. Here we show that there are large synergistic effects in the extraction process, which results in ca. 45 times larger leaching with specific molecules, when used along with glucose. While glucose (1 g) alone can extract ca. 650 ppb of silver from the metal, 60 mg of it extracts ca. 30000 ppb in a combination with 200 mg of glutathione (GSH) under similar experimental conditions of 70 °C and an extraction time of 7 d, in deionized (DI) water (200 mL). This enhancement is similar when glucose is replaced with cyclodextrin (CD). This enhanced concentration of silver in solution enables the formation of the silver clusters protected with glutathione and cyclodextrin, Ag 20 (SG) 15 CD 3– , in the presence of a reducing agent. A similar extraction for copper leads to excessive leaching, and typical concentrations are even higher than the solubility limit of the copper–glutathione complex. As a result, these complexes are precipitated. This synergistic extraction is observed for zinc and stainless steel as well. Enhanced extraction is a result of the formation of complexes of metals with glutathione and the consequent leaching of the complex into solution as well as the stabilization of the complex by inclusion complexation with cyclodextrin. Enhanced leaching in the presence of glucose is mostly due to simultaneous complexation with glucose as well as glutathione. The science presented may be used for the green extraction of different metals and could be a new potential top‐down approach for metal cluster synthesis. This may also be useful for green and sustained leaching of minerals into water to regulate its quality.

Uptake of noble metals by cereal plants is not reported in literature. Our study of 505 native rice landraces showed that nine of them accumulate silver at a high concentration when grown in the same soil. Among these, a medicinal rice landrace from West Bengal, Garib-sal was found to accumulate silver at an especially high concentration in the grains. Cultivation of Garib-sal rice in three successive years in Basudha farm in the rice growing period of June-October confirmed that for the same concentration of silver in the soil (similar to 0.15 mg/kg), Garib-sal accumulates it in the grains to the extent of similar to 15 mg/kg. Laboratory experiments also demonstrated that silver uptake by Garib-sal is significantly greater than for other varieties grown on the same soil, and that the metal accumulates mostly in the grain. To detect the location of deposition of silver in the grains, secondary ion mass spectrometry was performed. The images reveal that the silver is concentrated in the aleuronic layer of the rice bran. Its concentration decreases in the subaleurone and becomes negligible in the endosperm. Accumulation of silver does not alter the grain morphology and chemical characteristics. The metal may be extracted from the bran after milling of the rice, thereby causing no loss of the foodstuff.

This paper explores the reduction of water dispersed graphene oxide (GO) by sunlight as an environmentally friendly alternative to conventional methods of reduction of GO. The possible mechanism of the reduction process is delineated. The electrical and thermal conductivity, the degree of reduction and structural defects of sunlight reduced GO (sRGO) are studied thoroughly and compared with RGO samples produced through hydrazine (hRGO) and hydrothermal (hyRGO) reduction routes. The study reveals that the production of sRGO is feasible and its electronic properties are on a par with those of hRGO. Interestingly, sRGO showed the least structural defects, good dispersibility and higher conductivity vis-avis its counterparts. This cost effective and environmentally friendly method of reducing GO to RGO with enhanced electronic properties may find applications in bio-sensing and electrochemical energy storage devices.

Cyclodextrin-polymer composite electrospun nanofibers were developed for micropollutant (MP) removal from water. The fibers were fabricated by electrospinning of mixed poly(ether sulfone) (PES) and beta-cyclodextrin (CD) solutions under optimal conditions. The composite fibers were compared with bare PES nanofibers prepared by the same method. Scanning electron microscopy revealed that CD did not alter the fiber morphology, while the fiber capacity for MP uptake was enhanced by CD through the formation of inclusion complexes. The availability of CD on the fibers was confirmed by the emergence of visible luminescence due to the inclusion of a quantum cluster, Au25SBB18 (SBB = 4-(tertbutyl)benzylmercaptan in thiolate form), in the cavities of CD exposed on fiber surfaces. The steroid hormone estradiol (E2) (100 ng/L) and pesticide chlorpyrifos (CP) (5 mg/L) were used as model pollutants in batch experiments designed to measure uptake potential. The nanofibers interact strongly with the model pollutants because of their high surface area and surface affinity. Increases of 20% in E2 uptake and 80% in CP uptake compared with bare PES nanofibers were observed. This behavior indicates promising applications of CD-containing materials for MP removal in water treatment and membrane technology.

In this experimental study, the effects of 2D reduced graphene oxide (rGO) sheets on the properties of Portland cement paste in comparison to popularly reviewed nanomaterials like aluminium oxide nanopowder (n-Al2O3) and colloidal silicon dioxide nanoparticles (n-SiO2) were investigated. The addition of 0.02% rGO sheets by weight of cement increased the 7 and 28 days flexural strength up to 70% and 23% respectively when compared to control paste. Moreover, its incorporation substantially decreased the sizes of pores/voids in the paste, even compared to the other nanomaterials, as characterized by Mercury Intrusion Porosimetry (MIP) and 3D X-ray Computed Tomography (CT) aided with image analysis technique. The assessment of Portlandite content by Thermo-gravimetric Analysis did not indicate major differences between the pastes, with the exception of the paste incorporating nano-silica. Microstructural analysis by Fourier Transform Infrared Spectroscopy, X-ray diffraction and Scanning Electron Microscopy did not reveal any major differences between the control paste and the pastes incorporating nanomaterials. The overall results suggest that the performance of rGO was better in comparison to other two nanomaterials, despite the significantly lower amounts that were used in the paste.

This paper reports dehalogenation of various organohalides, especially aliphatic halocarbons and pesticides at reduced graphene oxide-silver nanocomposite (RGO@Ag). Several pesticides as well as chlorinated and fluorinated alkyl halides were chosen for this purpose. The composite and the products of degradation were characterized thoroughly by means of various microscopic and spectroscopic techniques. A sequential two-step mechanism involving dehalogenation of the target pollutants by silver nanoparticles followed by adsorption of the degraded compounds onto RGO was revealed. The composite showed unusual adsorption capacity, as high as 1534 mg/g, which facilitated the complete removal of the pollutants. Irrespective of the pollutants tested, a pseudo-second-order rate equation best described the adsorption kinetics. The affinity of the composite manifested chemical differences. The high adsorption capacity and re-usability makes the composite an excellent substrate for purification of water. (C) 2016 Elsevier B.V. All rights reserved.

Uptake of metal ions into rice occurs while it is being cooked in metal vessels, leading to corrosion of the utensils. This study deals with silver, copper, and aluminum uptake during cooking in respective vessels, with a special emphasis on silver. The metal uptake is routed through solution, enhanced in the presence of specific anions like carbonate, and attenuated when the rice is polished. The concentration of silver in rice increases with the time of cooking with a concomitant decrease in the concentrations of Fe and Zn, suggesting a substitution mechanism for metal ion uptake. The results for some common rice varieties of use across the Indian subcontinent are presented. Similar behavior was observed for cooking in copper and aluminum vessels. Among the three metals studied, aluminum showed reduced uptake. Studies have been done to probe the interaction of metal ions with glucose and sucrose, and efficient complex formation was detected with all these ions, implying that starch can also form complexes with them. The cooking practices used in this study are reminiscent of local customs and practices that were chosen deliberately to relate to the true implications of these results.

We report the preparation of a carbon aerogel (CA) material utilizing the simultaneous co-assembly of organic and inorganic precursors, having a high Brunauer-Emmet-Teller surface area of 2600 m(2)/g, through a one-step sol-gel process. This CA was characterized using different spectroscopic and microscopic techniques. The as-synthesized CA with its tunable porosity, high mechanical strength, transport property and electrical conductivity was found to be a suitable candidate for water desalination via capacitive deionization (CDI). The optimum working potential for CDI was in the range of 1.2-1.4 V. The material was tested for the removal of different ions of varying charges and the experiment was performed for multiple cycles. The result showed high adsorption capacity of 10.54 mg/g for Cl- in laboratory batch experiments compared to 3-4 mg/g reported for most of the CDI materials. The materials were also characterized after adsorption/desorption cycles. Adsorption was physical in nature and the ions desorbed completely after reversing the polarity. The result showed that the material can be used for multiple cycles without any change in its spectroscopic and adsorption properties. (C) 2015 Elsevier Ltd. All rights reserved.

Unprecedented silver ion leaching, in the range of 0.7 ppm was seen when metallic silver was heated in water at 70 °C in presence of simple carbohydrates, such as glucose, making it a green method of silver extraction. Extraction was facilitated by the presence of anions, such as carbonate and phosphate. Studies confirm a two-step mechanism of silver release, first forming silver ions at the metal surface and later complexation of ionic silver with glucose; such complexes have been detected by mass spectrometry. Extraction leads to microscopic roughening of the surface making it Raman active with an enhancement factor of 5×10(8) .