Metal-Ion-Induced Luminescence <i>Enhancement</i> in Protein Protected Gold Clusters

We probed the interaction between Au38@BSA and various heavy metal ions using luminescence spectroscopy. Interestingly, Au38@BSA showed luminescence enhancement upon interaction with Cd2+ and Pb2+ at concentrations higher than 1 ppm, due to the formation of cluster aggregates. Such aggregates were detected by dynamic light scattering (DLS) and high resolution electron microscopy (HRTEM) studies. Luminescence enhancement of Au38@BSA in the presence of Cd2+ was due to the interaction of Cd2+ with the cluster core, while Pb2+-induced luminescence enhancement was due to BSA-Pb2+ interaction. Observations were further supported by X-ray photoelectron spectroscopy (XPS) studies. This kind of phenomenon has been observed in protein protected clusters for the first time. We believe that such metal-ion-induced luminescence enhancement can be used to synthesize cluster systems with enhanced optical properties and different ion–cluster interactions can be used to develop metal ion sensors using Au38@BSA

Sparingly Soluble Constant Carbonate Releasing Inert Monolith for Enhancement of Antimicrobial Silver Action and Sustainable Utilization

Silver, a metal with phenomenal commercial importance has been exploited in its ionic form in the field of water purification, with the objective of delivering microbially safe drinking water. Silver released at such concentrations is unrecoverable and has to be reduced to ensure sustainable utilization of the metal. We have shown that small concentrations of carbonate can effectively bring down the amount of silver ion used for microbial disinfection by half. Implementation of this finding requires constant carbonate releasing materials in natural water for an extended period. In this work, we describe a hybrid material with intrinsically high stability in water that is prepared using naturally abundant ingredients which releases carbonate constantly and in a controlled fashion. This composition in conjunction with reduced silver ion concentration delivers mircobially safe water, tested with <i>E. coli</i> and MS2 phage. Use of constant carbonate releasing material for antimicrobial applications can reduce the unrecoverable silver released into the environment by ∼1300 tons/year. We also show that the composition can be modified to release cations of choice without disturbing the CO₃^2– release from the same. A sustained release of selective cations along with carbonate can supplement drinking water with the minerals of interest

Sparingly Soluble Constant Carbonate Releasing Inert Monolith for Enhancement of Antimicrobial Silver Action and Sustainable Utilization

Silver, a metal with phenomenal commercial importance has been exploited in its ionic form in the field of water purification, with the objective of delivering microbially safe drinking water. Silver released at such concentrations is unrecoverable and has to be reduced to ensure sustainable utilization of the metal. We have shown that small concentrations of carbonate can effectively bring down the amount of silver ion used for microbial disinfection by half. Implementation of this finding requires constant carbonate releasing materials in natural water for an extended period. In this work, we describe a hybrid material with intrinsically high stability in water that is prepared using naturally abundant ingredients which releases carbonate constantly and in a controlled fashion. This composition in conjunction with reduced silver ion concentration delivers mircobially safe water, tested with <i>E. coli</i> and MS2 phage. Use of constant carbonate releasing material for antimicrobial applications can reduce the unrecoverable silver released into the environment by ∼1300 tons/year. We also show that the composition can be modified to release cations of choice without disturbing the CO₃^2– release from the same. A sustained release of selective cations along with carbonate can supplement drinking water with the minerals of interest

Species-Specific Uptake of Arsenic on Confined Metastable 2‑Line Ferrihydrite: A Combined Raman-X-Ray Photoelectron Spectroscopy Investigation of the Adsorption Mechanism

The present study is targeted toward understanding the interaction between important and technologically relevant polymorphs 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 (α-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

Interference of Phosphate in Adsorption of Arsenate and Arsenite over Confined Metastable Two-Line Ferrihydrite and Magnetite

Contamination of groundwater by arsenic (As­(III/V)) is a serious global issue, and phosphate (P­(V)) is known to be the biggest interference in adsorption-based remediation methods. The present study is focused on understanding the interaction between phosphate and iron oxides/oxy-hydroxides with two well-known classes of potential adsorbents in the important pH range of 5–9 and the effect of such interactions on the uptake of arsenite and arsenate. Spectroscopic studies such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were used to understand the binding of various oxyanions of phosphorous and arsenic with the iron oxides/oxy-hydroxides, exploring the core levels of P 2p and Fe 2p. Materials used for adsorption experiments were magnetite (MAG) and a nanocomposite, confined metastable two-line ferrihydrite (CM2LF); CM2LF is used for arsenic remediation in the affected states in India. Further, we studied the interference of P­(V) in As­(III/V) adsorption. The kinetics of adsorption was quantified using ion chromatography (IC), where P­(V) alone followed a pseudo-second-order model. In the case of mixed solutions, namely, APmix1 (P­(V) + As­(III)) and APmix2 (P­(V) + As­(V)), kinetics data suggested that P­(V) or As­(III/V) oxyanions partially follow the pseudo-second-order model. Results also confirmed that CM2LF performed better than magnetite (MAG) for As­(III/V) uptake in the presence of P­(V). As­(III) and As­(V) species are more competitive than P­(V) at neutral pH. A model for the adsorption of P­(V) species in water on ferrihydrite particles was developed using density functional theory (DFT). This accounted for phosphate complexation at various pH values. The study is highly useful in developing an affordable solution for sustainable arsenic remediation. Various aspects of sustainability are discussed

Nanocellulose-Reinforced Organo-Inorganic Nanocomposite for Synergistic and Affordable Defluoridation of Water and an Evaluation of Its Sustainability Metrics

Fluoride (F–) is one of the common naturally occurring anions present in groundwater worldwide that may be beneficial or detrimental depending on the total amount ingested and the duration of exposure. Among all the remediation techniques, adsorption using nanomaterials shows superior efficiency and the process can be eco-friendly and economical. We report cellulose nanofiber-polyaniline (PANI)-templated ferrihydrite nanocomposite synthesized by a green one-pot process where the iron precursor not only acts as an oxidant for the polymerization of aniline to give emaraldine base–emaraldine salt (EB–ES) form of PANI but also forms 2-line ferrihydrite (FeOOH) nanoparticles in situ. These nanoparticles get embedded into the cellulose–PANI blend to give a granular nanocomposite having double action sites for adsorption and robustness which also prevent nanoparticle leaching. Doped PANI and FeOOH act as synergistic adsorption sites for F– removal which results in an enhanced uptake capacity. The materials’ adsorption mechanism and removal performance have been evaluated by diverse analytical techniques. The investigations led to the conclusion that the material is suitable to be used as adsorption media in the form of simple cartridges for gravity-fed water purification. In addition, the impact of such materials on the environment has been assessed by evaluating the relevant sustainability metrics and socio-economic parameters

Sustainable and Affordable Composites Built Using Microstructures Performing Better than Nanostructures for Arsenic Removal

Arsenicosis was recognized over 104 years ago. Elevated arsenic (As) concentrations in water is faced by about 200 million people worldwide and has become one of the biggest challenges in the context of water purification. Providing sustainable and affordable solutions to tackle this menace is a need of the hour. Adsorption on advanced materials is increasingly being recognized as a potential solution. Here, we report various functionalized microcellulose-reinforced 2-line ferrihydrite composites which show outstanding As­(III) and As­(V) adsorption capacities. Green synthesis of the composite yields granular media with high mechanical strength which show faster adsorption kinetics in a wide pH range, irrespective of the presence of other interfering ions in water. The composites and their interaction with As­(III) and As­(V) were studied by XRD, HRTEM, SEM, XPS, Raman, TG, and IR spectroscopy. Performance of the media in the form of cartridge reaffirms its utility for point-of-use water purification. We show that cellulose microstructures are more efficient than corresponding nanostructures for the purpose of arsenic remediation. We have also performed an evaluation of several sustainability metrics to understand the “greenness” of the composite and its manufacturing process

Highly Sensitive As³⁺ Detection Using Electrodeposited Nanostructured MnO<i>_x</i> and Phase Evolution of the Active Material during Sensing

A simple, one-step electrodeposition approach has been used to fabricate MnOx on an indium-doped tin oxide substrate for highly sensitive As3+ detection. We report an experimental limit of detection of 1 ppb through anodic stripping voltammetry with selectivity to As3+ in the presence of 10 times higher concentrations of several metal ions. Additionally, we report the simultaneous phase evolution of active material occurring through multiple stripping cycles, wherein MnO/Mn2O3 eventually converts to Mn3O4 as a result of change in the oxidation states of manganese. This occurs with concomitant changes in morphology. Change in the electronic property (increased charge transfer resistance) of the material due to sensing results in an eventual decrease in sensitivity after multiple stripping cycles. In a nutshell, this paper reports stripping-voltammetry-induced change in morphology and phase of as-prepared Mn-based electrodes during As sensing

Cellulosic Ternary Nanocomposite for Affordable and Sustainable Fluoride Removal

Adsorption is shown to be an extremely affordable and sustainable way of producing clean water, particularly in resource-limited settings. In this paper, we sought to synthesize an effective cellulose-based composite adsorbent from eco-friendly, earth-abundant, and consequently affordable ingredients at room temperature for fluoride removal from drinking water. We utilized the synergistic effect of various renewable materials and active sites of metal oxyhydroxides in developing an effective adsorbent, which is physically stable under the conditions of use. Nanoscale oxyhydroxides of aluminum and iron were scaffolded into a matrix of carboxymethyl cellulose (CMC) to form a nanocomposite adsorbent, which was prepared in water, eventually making a water-stable porous solid. This was used in batch and cartridge adsorption experiments for fluoride removal. The adsorbent surface before (in situ) and after fluoride uptake was characterized using various analytical techniques. The in situ composite exhibited a surface area of 134.3 m2/g with an amorphous solid structure with Al and Fe uniformly distributed in the cellulose matrix. From the batch adsorption experiments, we observed 80% fluoride removal within the first 3 min of contact, with a maximum uptake capacity of 75.2 mg/g as modeled by the Langmuir adsorption isotherm, better than most reported materials. The adsorbent effectively reduced F– levels in field water from 10 to 0.3 mg/L, less than 1.5 mg/L the World Health Organization upper limit for drinking water. Optimum F– removal was achieved between the pH of 4–9; however, the effectiveness of the adsorbent was reduced in the presence of competing ions in the order PO43– > SiO32– > CO32– > HCO3– > SO42–. A cartridge experiment demonstrated the applicability of the adsorbent in a domestic point-of-use water purifier for defluoridation. Sustainability metrics of the material were evaluated. Defluoridation using the material is estimated to cost $3.3 per 1000 L of treated water at the scale of community implementation projects