Toxic Water Contaminants Research Articles

Real-time SERS sensing of highly toxic seawater contaminants using plasmonic silver assembled pyramidal/nanowire heterostructures

Hierarchically oriented plasmonic nanostructures have attracted an advanced molecular sensing platform for multifaceted applications. In the present work, we have attempted to fabricate ultrasensitive and cost-effective pyramidal/nanowire hetero arrays, hosted with silver nanoparticles for the effective surface-enhanced Raman spectroscopy (SERS) assisted detection of toxic water contaminants. Three-dimensionally oriented pyramidal/nanowire hetero arrays with enhanced surface area were fabricated by combining wet etching and metal-assisted chemical etching techniques. The regulation of structural features was achieved by controlling the process parameters during fabrication. Particularly, the evolution of morphological properties of the hybrid sensor was investigated in terms of nanowire aspect ratio and further analyzed in terms of SERS properties. The hetero arrays exhibited significant enhancement in Raman signal for sensing organic pollutants. Moreover, these hetero arrays with a nanowire length of ∼1 µm exhibited the highest signal enhancement. Further, the excellent reproducibility and reusability characteristics were also demonstrated for the fabricated sensors. Different cationic and anionic organic pollutants were employed for efficacy studies which showed detection limits ranging from femtomolar to picomolar levels. Finally, the real-time sensing of organic contaminants such as aniline was also investigated from seawater with an estimated enhancement factor of 8 × 108, indicating that as-fabricated hetero arrays can perform as outstanding SERS sensors for environmental remediation applications.

Adsorption Behavior and Mechanisms of Trihalomethanes onto Virgin and Weathered Polyvinyl Chloride Microplastics.

Microplastics that adsorb various toxic contaminants in water may be transported into cells and organs, possibly posing toxicological risks in the aquatic environment. Disinfection byproducts (DBPs), which are ubiquitous in chlorinated drinking water and wastewater, may have some potential to sorb onto microplastics (MPs) through hydrophobic or electrostatic interactions. However, DBP adsorption on microplastics has not yet been closely examined. This work investigated the adsorption behavior of trihalomethanes (THMs)-a regulated and ubiquitous DBP class in chlorinated water-onto virgin and weathered polyvinyl chloride (PVC) microplastics, the most widely used plastic material in drinking water distribution and sewer systems. A comparative analysis of kinetic and isotherm test results indicated that the adsorption mechanisms mainly involved hydrophobic interactions from a combination of weak and strong physisorption behavior and possibly chemisorption. The adsorption coefficients from all the models examined suggested that the adsorption of THMs, and perhaps chemically similar DBPs, onto virgin PVC microplastics can be 10-20 µg g-1. However, the weathered PVC microplastics contained more polar functional groups, which led to a decreased hydrophobicity and reduced THM adsorption capacity by approximately 10%. These findings offer novel insights into the possible adsorption characteristics of disinfection byproducts (DBPs) onto microplastics and will assist in targeting more toxic DBPs for future investigations.

Predictive modeling of copper (II) adsorption from aqueous solutions by sawdust: a comparative analysis of adaptive neuro-fuzzy interference system (ANFIS) and artificial neural network (ANN) approaches

Heavy metal ions are considered to be the most prevalent and toxic water contaminants. The objective of thois work was to investigate the effectiveness of employing the adsorption technique in a laboratory-size reactor to remove copper (II) ions from an aqueous medium. An adaptive neuro-fuzzy inference system (ANFIS) and a feed-forward artificial neural network (ANN) were used in this study. Four operational factors were chosen to examine their influence on the adsorption study: pH, contact duration, initial Cu (II) ions concentration, and adsorbent dosage. Using sawdust from wood, prediction models of copper (II) ions adsorption were optimized, created, and developed using the ANN and ANFIS models for tests. The result indicates that the determination coefficient for copper (II) metal ions in the training dataset was 0.987. Additionally, the ANFIS model’s R 2 value for both pollutants was 0.992. The findings demonstrate that the models presented a promising predictive approach that can be applied to successfully and accurately anticipate the simultaneous elimination of copper (II) and dye from the aqueous solution.

Mitigation of arsenic and fluoride from water via porous polymeric network knitted with zirconium moiety in three-dimensional shape: Experimental and mathematical modeling investigation

The presence of toxic contaminants in water seriously threatens human health. Thus, in order to address the water pollution through toxic contaminants, a new type of cross-linked porous polymeric microsphere namely; poly(Zirconyl dimethacrylate) (pZrDMA), was successfully prepared by a single-step facile approach. The pZrDMA comprises an acrylate chain of zirconium moiety, which is a proficient adsorbent for arsenic and fluoride remediation. A series of pZrDMA were prepared by varying the relative amounts of reactants to get an appropriate composition. The pZrDMA having, a high surface area (SA: 392.12 m2 g−1) and porosity (Pore size: 0.93–2.36 µm), has exhibited maximum adsorption capacities (qe) of 4.26 mg g−1, 4.22 mg g−1 and 198.5 mg g−1 As(V), As(III) and F− respectively. The pZrDMA displayed high removal efficiency (>97 %) for all the ions over a wide pH range (2.0 ± 0.2 to 10 ± 0.2). The adsorption kinetic and isotherms are well described by the pseudo-second-order model (PSO), and Langmuir isotherm model for both toxic ions arsenic and fluoride. The multicomponent adsorption isotherm with arsenic and fluoride has also studied. The experimental data analysis using the ANN model provides a high accuracy of the model with larger correlation coefficient values (R > 0.99). The pore diffusion modeling predicted the breakthrough time of 174 h, 1542 h, and 1466 h for F−, As(V), and As (III), respectively.

Effective photocatalytic degradation of methylene blue (MB) and reactive red 120 (RR120) using Al substituted ZnO nanoparticles

The discharge of dyes into the environment from industries can have an adverse impact on human and aquatic health, even at low concentrations. Therefore, this work aims to eliminate the toxic dyes using aluminium (Al) substituted ZnO nanoparticles (NPs) before they mix into the water bodies. The substitution of Al modifies its crystal structure and extends its optical absorption, that improves the photocatalytic activity of ZnO NPs. The X-ray diffraction of the prepared NPs exhibited a well-defined wurtzite phase of ZnO. The crystallite size of ZnO nanoparticles decreases with an increase in Al concentration. The scanning electron microscopic images of Al substituted ZnO NPs revealed vertically aligned rod-like particles. The size of synthesized particles decreased by rising the concentration of Al, and this impact was due to the inhibition of particle growth. The band gap of the Al substituted ZnO decreased compared to pure ZnO. The 20 mg of Al (5%) substituted ZnO catalysts degrade 99.7% of methylene blue (MB) and 99.6% of reactive red 120 (RR120) with rate constants of 0.01701 min−1 and 0.0680 min−1. The 5% Al substituted ZnO NPs were found to be an efficient catalyst for the removal of toxic contaminants in water.

A single functionalized graphene nanocomposite in cross flow module for removal of multiple toxic anionic contaminants from drinking water.

Polyether sulfone (PES)-based thin-film nanofiltration (TFN) membranes embedded with ferric hydroxide (FeIII(OH)x) functionalized graphene oxide (GO) nanoparticles were fabricated through interfacial polymerization for a generalized application in removal of a plethora of anionic and toxic water contaminants. Following the most relevant characterization, the newly synthesized membranes were fitted in a novel flat sheet cross-flow module, for experimental investigation on purification of live contaminated groundwater collected from different affected areas. The separation performances of the membranes in the flat sheet cross-flow module demonstrated that GOF membranes had higher selectivity for monovalent and divalent salt rejections than pristine GO membranes. Furthermore, both membranes were tested for simultaneously removing widely occurring hazardous ions of heavy metals and metalloids in groundwater, such as arsenic, selenium, chromium, and fluoride. Compared to the pristine GO and the reported membranes in the literature, the GOF membrane exhibited remarkable performance in terms of rejection efficiency (Cr (VI): 97.2%, Se (IV): 96.6%, As(V): 96.3%, F- 88.4%) and sustained flux of 184 LMH (Lm-2h-1) at an optimum transmembrane pressure of 16bar. The investigated membrane module equipped with the GOF membrane proved to be a low-cost system with higher anionic rejection and sustained high flux at a comprehensive pH range, as evident over long hours of study vis-à-vis reported systems.

Development of a new near-infrared, spectrophotometric, and colorimetric probe based on phthalocyanine containing mercaptoquinoline unit for discriminative and highly sensitive detection of Ag+, Cu2+, and Hg2+ ions

A new near-infrared, spectrophotometric, and colorimetric probe based on a phthalocyanine-containing mercaptoquinoline unit (MQZnPc) has been constructed and utilized for discriminative and highly selective/sensitive detection of Ag+, Cu2+, and Hg2+ ions by using proper masking agents like EDTA, KI, and NaCl. The probe only responds to Ag+, Cu2+, and Hg2+ among the tested ions without any interference. The probe performs quite well (the limit of detection: 160 ppb, 148 ppb, and 276 ppb of Ag+, Cu2+, and Hg2+ions for UV–Vis, and 15 ppb, 37 ppb, and 467 ppb of Ag+, Cu2+, and Hg2+ ions for fluorescence, respectively), and has a fast response time (150 sec, 90 sec, and 90 sec of Ag+, Cu2+, and Hg2+ions for UV–Vis, and 300 sec, 240 sec, and 90 sec Ag+, Cu2+, and Hg2+ions for fluorescence, respectively). The probe also displays a colorimetric feature for UV–Vis and smartphone applications. Based on a single probe, Ag+, Cu2+, and Hg2+ ions which are the main toxic water contaminants could be recognized very quickly and colorimetrically with high recovery values in tap water samples. This study stands out with its unique properties compared to the related studies in the literature.

Silver-platinum bimetallic nanoparticles as heterogeneous persulfate activator for the oxidation of malachite green

Fabrication of noble metal nanoparticles by using green chemical method with plant extract as reducing agent to the in situ oxidation toxic water contaminants have been the subject of various investigators due to their enhanced catalytic efficiencies. This paper describes the extraction of caffeic acid from Artemisia herba-alba aqueous extract, and preparation of silver (Ag), platinum (Pt), and silver-platinum (Ag-Pt) nanoparticles with caffeic acid as a reducing and capping agent. The as-prepared Ag-Pt NPs was used as a heterogeneous activator of persulphate (K2S2O8) for the in situ chemical oxidation of malachite green (MG). The Ag-Pt NPs shows no surface Plasmon resonance absorption band. The malachite green dye was completely decolorized in presence of Ag-Pt/K2S2O8 system. SO4-• and HO• radicals generated by the cleavage of S2O82- peroxide activation with Ag-Pt were responsible for the MG decolorization as well as mineralization. The Ag-Pt NPs acted as a sacrificial electron donor. The Ag-Pt NPs were characterized by using conventional techniques such as, UV–visible, FTIR, SEM, TEM, EDX, XPS, and XRD spectroscopic methods.

Recycled Smelter Slags for In Situ and Ex Situ Water and Wastewater Treatment—Current Knowledge and Opportunities

Slags from the ferrous and nonferrous metallurgical industries have been used to treat toxic contaminants in water and wastewater. Using slag as a recycling or renewable resource rather than a waste product has environmental and economic benefits. Recycled smelter slags can be used in both in situ and ex situ treatment. However, their application has some limitations. One of the challenges is how to handle spent slag adsorbents, as they contain the accumulation of solid waste loaded with high concentrations of toxic contaminants. These challenges can be overcome by regeneration, recycling, reuse, and immobilization treatment of spent slag adsorbents. The present paper explored the scientific and technical information about the composition, reaction mechanisms, adsorption capacity, and opportunities of recycled slags while adsorbing toxic compounds from contaminated water. It comprehensively reviewed the current state of the art for using smelting slags as sustainable adsorbents for water and wastewater. The study revealed that ferrous slags are more effective in removing a wide range of toxic chemicals than nonferrous smelter slags. It investigated the necessary improved approach through the 5Rs (i.e., reduce, reuse, recycle, remove, and recover) using smelter slags as reactive materials in ex situ and in situ treatment.

Elevated Adsorption of Lead and Arsenic over Silver Nanoparticles Deposited on Poly(amidoamine) Grafted Carbon Nanotubes.

An efficient adsorbent, CNTs-PAMAM-Ag, was prepared by grafting fourth-generation aromatic poly(amidoamine) (PAMAM) to carbon nanotubes (CNTs) and successive deposition of Ag nanoparticles. The FT-IR, XRD, TEM and XPS results confirmed the successful grafting of PAMAM onto CNTs and deposition of Ag nanoparticles. The absorption efficiency of CNTs-PAMAM-Ag was evaluated by estimating the adsorption of two toxic contaminants in water, viz., Pb(II) and As(III). Using CNTs-PAMAM-Ag, about 99 and 76% of Pb(II) and As(III) adsorption, respectively, were attained within 15 min. The controlling mechanisms for Pb(II) and As(III) adsorption dynamics were revealed by applying pseudo-first and second-order kinetic models. The pseudo-second-order kinetic model followed the adsorption of Pb(II) and As(III). Therefore, the incidence of chemisorption through sharing or exchanging electrons between Pb(II) or As(III) ions and CNTs-PAMAM-Ag could be the rate-controlling step in the adsorption process. Further, the Weber-Morris intraparticle pore diffusion model was employed to find the reaction pathways and the rate-controlling step in the adsorption. It revealed that intraparticle diffusion was not a rate-controlling step in the adsorption of Pb(II) and As(III); instead, it was controlled by both intraparticle diffusion and the boundary layer effect. The adsorption equilibrium was evaluated using the Langmuir, Freundlich, and Temkin isotherm models. The kinetic data of Pb(II) and As(III) adsorption was adequately fitted to the Langmuir isotherm model compared to the Freundlich and Temkin models.

Eco-friendly synthesis of durable aerogel composites from chitosan and pineapple leaf-based cellulose for Cr(VI) removal

Chromium (VI) oxyanion is one of the most toxic contaminants in water which causes cancer and genetic mutations in humans. In this work, the bio-based aerogels are successfully synthesized from pineapple leaves (PLs) and chitosan (CS) by an effective and eco-friendly method (including homogenizing, mixing, and freeze-drying) that is feasible for mass production to manage Cr(VI) pollution. The influences of different freezing approaches (refrigerator, isotropic and anisotropic freezing), solid concentrations, and weight ratios of cellulose to chitosan on the morphology, physical parameters, and Cr(VI) adsorption of the aerogels are comprehensively investigated. The fabricated aerogels are ultra-lightweight (20–30 mg/cm3), highly porous (above 97.5%), durable (Young’s modulus of 1.8–11.7 kPa), and strongly acid resistant (below 12% of weight loss at pH 3). The difference in pore size among freezing techniques is clarified by scanning electron microscopy, suggesting that anisotropic freezing is ineffective for non-nanoprecursors. The findings show the strong influence of chitosan content and pH of the medium on Cr(VI) adsorption of the PL/CS aerogels due to the electrostatic attraction between Cr(VI) oxyanions and protonated amine groups. The theoretical Langmuir maximum Cr(VI) uptake is up to 210.6–211.4 mg/g, which is generally comparable to carbon-based and costly metal-organic framework materials. The adsorption isotherm and kinetics of the samples are appropriate to the Langmuir model and the pseudo-second-order model, respectively. Furthermore, the Cr-absorption capacity retention rates of prepared aerogel are above 75% after 6 absorbing cycles by NaOH solution. Based on the results, the product cellulose/chitosan aerogel can be considered a potential adsorbent for Cr(VI) removal.

Optimizing Fe0/Ni0/alginate beads as a stable and recoverable catalyst for removing highly toxic water contaminants: full-factorial design

Pollution by highly toxic contaminants poses a great threat to the aquatic environment and human life. Bimetallic materials have been proven to be efficient for the removal of such contaminants. In this study, the bimetallic Fe0/Ni0/alginate beads have been prepared using solvothermal technique followed by polymerization of alginate. Full-factorial design has been utilized to optimize the preparation conditions including the weight ratios of Fe and Ni, and time of the solvothermal process. The bimetal made from equal weights of Ni and Fe metals along with alginate has shown the best efficiency for the removal of 2,4,6-trichlorophenol (2,4,6-TCP, ~ 70%) as a model organic pollutant under acidic conditions (pH = 2) with minor contribution of alginate component in the removal process. Adsorption followed by reduction has been defined as the removal mechanism using GC/MS/MS chromatography in the case of 2,4,6-TCP. A mathematical model was established to describe the 2,4,6-TCP removal by the optimally prepared material. Differently, Pb2+ ions were removed predominantly by the alginate with minor effect of the bimetal (max. removal = 96.91% at pH 5 and after 2 h contact time). Accordingly, it was difficult to describe this process by a mathematical model. However, in both cases, the optimally prepared material has exhibited superior stability and reusability rather than the neat Fe0/Ni0 bimetal under the same experimental conditions. To sum up, the designed bimetallic Fe0/Ni0/alginate beads can be considered as an efficient catalyst for the removal of highly toxic pollutants from aqueous media.

Magnetic nanomaterials: Greener and sustainable alternatives for the adsorption of hazardous environmental contaminants

The global water resources have been considerably damaged by organic and inorganic pollutants generated as a result of fast urbanization and industrialization. Toxic contaminants in water pose a serious health threat to both humans and aquatic life. In terms of cost and performance, current remediation technologies are inadequate for eliminating low-concentration contaminants. Nanomaterials have unique advantages in this regard, including precisely adjustable surface areas, durability, and biocompatibility. Also, the surface functionalization of the nanoparticles can facilely be carried out to increase their selectivity and specificity towards a variety of pollutants. Among various nanomaterials the magnetic nanoparticles (MNPs) are promising class of nanomaterials due to their biocompatible, target-specific, easily regenerable, and reusable characters. They also feature simple separation techniques, high surface-to-volume ratios, and high adsorption rates. Based on these features their implication in wastewater treatment has dragged an enhanced amount of attention for the researchers. Therefore, MNPs provide a simple, low-maintenance alternative to traditional adsorbents for extracting contaminants from wastewater. Magnetic separation can reduce the environmental impact of MNPs in final effluents by managing the concentration of nanoadsorbents. MNPs are now in the development stage, however they are a promising treatment alternative for large-scale water treatment plants. The main objective of the present review is to focus on the efforts being carried out in the application of MNPs for the remediation of hazardous pollutants including organics, heavy metal ions, pharmaceutics, dyes, radioactive elements, and pathogens. Furthermore, the review present critical assessment and overview of a variety of magnetic nanomaterials and their applications to water and wastewater treatment. Finally, the feasibility of structure-property relationships, adsorption mechanisms, modeling for the removal of water pollutants, legality and toxicity, economic assessments, and future research directions for the complete utilization of MNPs are also discussed in detail.

Recyclable luminescence sensor for Cu2+, Cr2O72− and CrO42− in water and acid/base vapor response based on water-stable bipyridyl-based Ln-MOFs

Detecting toxic contaminants in water, such as heavy metal ions and chromate ions, is important for public health and the environment. In the context, luminescence lanthanide-organic frameworks have been the competitive means to recognize such contaminants. Herein, two Ln-MOFs, [Ln3(L)2(HCOO)(H2O)5]·14H2O (H4L ​= ​2,6-di(2,4-dicarboxyphenyl)-4-(pyridine-4-yl)pyridine) (Ln ​= ​Eu, 1-Eu and Ln ​= ​Tb, 1-Tb), have been synthesized solvothermally by using the selection of the bipyridyl-tetracarboxylic ligand (H4L). Single-crystal X-ray diffraction indicates that this two Ln-MOFs are isostructural and contain uncoordinated pyridyl nitrogen atoms and water molecules, which provides the Lewis-base sites for detecting various small molecules. Moreover, both 1-Eu and 1-Tb exhibit excellent chemical stability in aqueous solution with the pH ranging from 2 to 13. Thanks to such characteristics, 1-Eu can be served as a multi-responsive luminescence sensor for Cu2+, Cr2O72− and CrO42− in deionized water, tap water and river water via luminescent quenching. Notably, the sensing processes toward Cu2+, Cr2O72− and CrO42− exhibit high selectivity and sensitivity, and good recyclability. The luminescence sensing mechanism was carefully studied by PXRD, XPS, and UV spectroscopy. In addition, 1-Eu also displays luminescence turn-off/on when alternately exposed to HCl and NH3 gases, which can mainly be attributed to the protonation/deprotonation process by the free bipyridyl N sites. The work illustrates 1-Eu could shed light on the exploration of MOF-based sensors for analytical applications.

Simultaneous capturing of mixed contaminants from wastewater using novel one-pot chitosan functionalized with EDTA and graphene oxide adsorbent

The emergence of inorganic and organic contaminants has raised great concerns owing to their adverse impact on human health and ecological security. Herein, first time one-pot process was applied for chitosan (CS) functionalization using graphene oxide (GO) and ethylenediaminetetraacetic acid (EDTA) for simultaneous capturing of toxic inorganic (lead (Pb2+) and cadmium (Cd2+)) and organic (ciprofloxacin (CIP) and sildenafil (SDF)) contaminants from wastewater. In this approach, we believe that CS would work as a backbone, GO would capture both inorganic and organic contaminants via electrostatic interactions, while EDTA would make complexation with heavy metals. Various parameters including pH, reaction time, concentration, reusability etc. were evaluated to achieve the best experimental result in monocomponent system. The prepared adsorbent displayed an excellent monolayer adsorption capacity of 351.20 and 264.10 mg g−1 for Pb2+ and Cd2+, respectively, while a heterogeneous sorption capacity of 75.40 and 40.90 mg g−1 for CIP and SDF, respectively. The kinetics data fitted well to Pseudo-second order (PSO) kinetics model for both types of contaminants and gave faster interaction towards metal ions (higher k2) than organic contaminants. Experimental results showed excellent adsorption efficiencies at environmental levels in the capturing of both inorganic and organic contaminants at the same time from polluted water. The capturing mechanism of both types of contaminants was explained by elemental mapping, EDS, and FT−IR spectra. Overall, easy synthesis, excellent capturing capacity, and reusability imply that the prepared adsorbent has a sufficient potential for the treatment of co-existing toxic contaminants in water.

In-situ fabrication of novel flower like MoS2/CoTiO3 nanorod heterostructures for the recyclable degradation of ciprofloxacin and bisphenol A under sunlight

Effectual degradation of toxic water contaminants is a crucial step in water purification and designing an efficient semiconductor based hybrid structure photocatalyst is a good approach to achieve this. Benefiting from the combination of semiconductors, a series of novel visible-light active flower-like MoS2/CoTiO3 nanorod heterostructures with excellent morphological contact interface were prepared through a facile in-situ hydrothermal process. These heterostructures were well characterized and demonstrated high photocatalytic performance for ciprofloxacin (CIP) and bisphenol A (BPA) under sunlight irradiation. Compared to pristine CoTiO3 and MoS2, the optimal catalyst (5 wt% MoS2/CoTiO3) presented 39.97 and 22.32 times higher activity for CIP degradation and 26.85 and 15.66 times higher activity for BPA degradation, respectively. This improved activity can be accounted for the effective interfacial contact which promotes the efficient charge carriers separation and reduce its recombination. The catalyst exhibited decent stability and was potentially reused for five cycles without significant loss in activity. Furthermore, based on active species scavenging experiments the plausible photodegradation mechanism is discussed in detail.

Electrical, Photocatalytic, and Humidity Sensing Applications of Mixed Metal Oxide Nanocomposites.

Mixed metal oxide nanocomposites (NCs) comprising Cu–Sr (CS), Sr–Cd (SC), and Cd–Cu (CC) were fabricated via a sol–gel method. Structural investigations of fabricated samples were carried out via X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The Maxwell–Wagner model, attributing to poor conducting layers around the conducting grains, was indicated to be followed by all of the NCs while investigating the dielectric properties. The Space-charge polarization and hoping mechanism contributed to low AC conductivity at lower frequencies and high AC conductivity at higher frequencies. The as-synthesized NCs effectively degraded two toxic water contaminants, such as crystal violet (CV) and Congo red (CR). Furthermore, the NCs were also evaluated for humidity sensing measurements. All of the NCs indicated efficient response/recovery time with better stability. The extensive investigation suggested the synthesized NCs, well suited for various optical and microelectronic applications.

Effective decontamination of As(V), Hg(II), and U(VI) toxic ions from water using novel muscovite/zeolite aluminosilicate composite: adsorption behavior and mechanism.

Muscovite/phillipsitic zeolite was introduced as a novel inorganic composite of stunning adsorption properties. The composite was investigated in the uptake reactions of Hg(II), As(V), and U(VI) as highly toxic water contaminants considering different adsorption factors. The adsorption properties of muscovite/phillipsitic zeolite are highly dependent on the pH values and the best decontamination percentages can be obtained at pH4, pH5, and pH5 for Hg(II), As(V), and U(VI), respectively. The kinetic studies demonstrated adsorption equilibrium for Hg(II), As(V), and U(VI) after 360min, 300min, and 360min, respectively. The equilibrium modeling suggested monolayer uptake for all the metals and represented mainly by the Langmuir model considering both the values of determination coefficient and chi-squared (χ2). The estimated maximum capacities are 117mg/g (Hg(II)), 122.5mg/g (As(V)), and 138.5mg/g (U(VI)) which are higher values than several studied adsorbents. The Dubinin-Radushkevich adsorption energies of Hg(II) (19.4kJ/mol), As(V) (25.6kJ/mol), and U(VI) (26.47kJ/mol) signify chemical adsorption mechanisms and close to the obtained values for the ion-exchange process. Additionally, the composite is of high reusability properties and was applied effectively for five decontamination cycles. Graphical abstract.

Heterojunction C3N4/MoO3 microcomposite for highly efficient photocatalytic oxidation of Rhodamine B

The photocatalysis has been well recognized in the photodegradation of toxic contaminants in water. The heterojunction of various semiconductors is widely used to improve photocatalytic properties compared to the single-component system. In this work, we prepared a heterojunction based photocatalyst using a wet-chemical technique consisting of pyrolysed porous C3N4 and hydrothermally synthesized MoO3 nanobelt like structure for enhanced photocatalytic oxidation of rhodamine B under visible light irradiation. The developed microcomposite was well characterized for its structural and morphological analysis to understand the crystal structure and surface properties. The increase in catalytic activity with C3N4/MoO3 microcomposite is attributed to the efficient photogeneration of electron-hole pairs, and charge transfer due to favorable band positions of C3N4/MoO3, which is not possible with individual materials. Radical trapping experiments were conducted with the microcomposite to confirm the major participating species in the photochemical reaction and the cyclic experiments were also carried out for stability of the designed composite for the photochemical process. This work also emphasizes the development of heterojunction microcomposite for environmental remediation.

Catalytic Converters for Water Treatment.

Fresh water demand is driven by human consumption, agricultural irrigation, and industrial usage and continues to increase along with the global population. Improved methods to inexpensively and sustainably clean water unfit for human consumption are desired, particularly at remote or rural locations. Heterogeneous catalysts offer the opportunity to directly convert toxic molecules in water to nontoxic products. Heterogeneous catalytic reaction processes may bring to mind large-scale industrial production of chemicals, but they can also be used at the small scale, like catalytic converters used in cars to break down gaseous pollutants from fuel combustion. Catalytic processes may be a competitive alternative to conventional water treatment technologies. They have much faster kinetics and are less operationally sensitive than current bioremediation-based methods. Unlike other conventional water treatment technologies (i.e., ion exchange, reverse osmosis, activated carbon filtration), they do not transfer contaminants into separate, more concentrated waste streams. In this Account, we review our efforts on the development of heterogeneous catalysts as advanced reduction technologies to treat toxic water contaminants such as chlorinated organics and nitrates. Fundamental understanding of the underlying chemistry of catalytic materials can inform the design of superior catalytic materials. We discuss the impact of the catalytic structure (i.e., the arrangement of metal atoms on the catalyst surface) on the catalyst activity and selectivity for these aqueous reactions. To explore these aspects, we used model metal-on-metal nanoparticle catalysts along with state-of-the-art in situ spectroscopic techniques and density functional theory calculations to deduce the catalyst surface structure and how it affects the reaction pathways and hence the activity and selectivity. We also discuss recent developments in photocatalysis and electrocatalysis for the treatment of nitrates, touching on fundamentals and surface reaction mechanisms. Finally, we note that despite over 20 years of growing research into heterogeneous catalytic systems for water contaminants, only a few pilot-scale studies have been conducted, with no large-scale implementation to date. We conceive of modular, on- or off-grid catalytic units that treat drinking water at the household tap, at a community well, or for larger-scale reuse of agricultural runoff. We discuss how these may be enhanced by combination with photocatalytic or electrocatalytic processes and how these reductive catalytic modules (catalytic converters for water) can be coupled with other modules for the removal of potential water contaminants.