Novel Graphene Oxide Based Nanocomposites: Synthesis and Application Towards Adsorptive Removal of Toxic Inorganic/Organic Pollutants from Aqueous Media

In this doctoral work, we have synthesized a series of GO based composite nanoadsorbents such as MgO-MgFe2O4 decorated GO (MgO-MgFe2O4/GO), amine functionalized GO mounted with ZnO-ZnFe2O4 (NH2-GO/ZnO-ZnFe2O4), AlOOH-FeOOH nanorods functionalized GO (GO/AlOOH-FeOOH) and GO/g-C3N4 decorated with Fe3O4 (GO/g-C3N4-Fe3O4) nanomaterials by using hydrothermal method. Then the prepared GO based metal oxide nanocomposites were used as novel adsorbent for adsorption study of inorganic pollutants such as fluoride ions (F-), hexavalent chromium (Cr(VI)), arsenate (As(V)) and organic pollutants like methylene blue (MB) dye, tetracycline (TC) antibiotic from water. The formation, composition, bonding, crystalline phase, surface morphology, size, and surface area of these prepared nanocomposites were analyzed by XRD, FTIR, Raman, XPS, FESEM, HRTEM, and BET analytical techniques. Batch adsorption experiments were carried out under various conditions including pH, time, concentration, adsorbent dose and temperature. The synthesized MgO-MgFe2O4/GO magnetic nanocomposite was used as adsorbent for removal of F- ions from water. The maximum adsorption capacity for F- ions removal is found to be 34 mg/g, which is higher as comparable to MgO-Fe2O3 nanocomposite. The amine functionalized GO decorated with ZnO-ZnFe2O4 (NH2-GO/ZnO-ZnFe2O4) nanocomposite material was used for remediation of Cr (VI) from water. It was observed that introduction of NH2 groups to GO/ZnO-ZnFe2O4 nanocomposite play a very important role for remediation of hexavalent chromium with a maximum uptake capacity of 109.89 mg/g. Apart from this we have also prepared GO/AlOOH-FeOOH composite nanomaterials by one step hydrothermal method and have used for decontamination of arsenate (As(V)) ions from water. Experimental finding reveals that the prepared GO based nanocomposite material is highly efficient for remediation of As(V) ions from water. Furthermore, we have also synthesized GO/g-C3N4 (graphitic carbon nitride) 2D layered composite materials decorated with Fe3O4 nanoparticles and have used for removal of methylene blue (MB) dye and tetracycline (TC) antibiotic from aqueous media. It was found that the adsorption of TC and MB was pH dependent and maximum adsorption capacities of 120 and 220 mg/g were achieved for TC and MB respectively. All the prepared GO based nanoadsorbents were regenerated and reused up to 5 successive cycles without major loss in their sorption capacity. From the obtained experimental results, plausible adsorption mechanism has been proposed for all adsorption process

Nanostructured Metal Oxide-Based Acetone Gas Sensors: A Review.

Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors

Nanocomposites à base de g-C3N4 et ZnxCd1-xS comme photocatalyseurs pour la production d'hydrogène à partir de l'eau sous la lumière solaire

Le processus de photocatalyse est l'un des moyens prometteurs d'utiliser l'énergie solaire à grande échelle pour différents types d'applications tels que la production d'hydrogène comme énergie propre ou encore la purification de l'eau et l'air contre les polluants et les produits chimiques nocifs. Néanmoins, le pourcentage de l’énergie du rayonnement solaire utilisé est généralement inférieur à 1%, en raison de la faible absorption de la lumière solair, de la rapide recombinaison de charge « électron-trou paires » et de l'instabilité photochimique. La modification de la structure des semi-conducteurs et la création de photocatalyseurs nanocomposites peuvent aider à surmonter ces problèmes. Le TiO2 est le photocatalyseur le plus étudié en raison de ses propriétés physiques et chimiques imortantes dans le processus de photocatalyse. Bien que son faible coût encourage à l'utiliser à grande échelle, sa largeur de bande interdite (EG =3.2 eV) importante, qui ne peut être activée que par irradiation UV, et sa vitesse de recombinaison des charges, ont limité son utilisation dans les applications industrielles. La création d'une hétérojonction entre TiO2 et d'autres semiconducteurs actifs sous la lumière visible est l’un des moyens les plus prometteurs pour utiliser les propriétés du dioxyde de titane dans la région du visible. De plus, le nitrure de carbone graphitique (g-C3N4) a été largement étudié pour la production d'hydrogène sous irradiation lumineuse visible. Malgré le fait qu'il peut être actif dans la région du visible et réduire les protons pour générer de l'hydrogène, son efficacité est considérablement limitée en raison de son taux de recombinaison de charge élevé et de sa faible surface spécifique. Nous avons synthétisé un photocatalyseur nanocomposite de g-C3N4 et TiO2 afin d’améliorer la procédure de séparation des charges et donc de produire plus d'hydrogène. Des nanodisques de titanate uniformes (TND) avec un diamètre compris entre 12 et 35 nm ont été synthétisés à l’aide d’une méthode solvothermale. Les feuilles nanométriques de g-C3N4 ont été synthétisés par des techniques de sonication, puis ont été mélangées avec des TND. Après cela, une étape de calcination a non seulement généré des contacts intimes avec deux semi-conducteurs, mais aussi converti les TND en nanoparticules de TiO2. En raison de la position des bandes de valence et de conduction des deux semi-conducteurs, les électrons photogénérés sont en mesure de passer du g-C3N4 au TiO2. Grâce à l’ajout de Pt comme cocatalyseur ainsi que comme fournisseur de sites actifs, les électrons photoexcités sont en capacité de réduire les protons de l'eau et de générer du dihydrogène. Cette hétérojonction pourrait produire plus du double l’hydrogène que le gC3N4 pur dans les mêmes conditions. Nous avons créé une nouvelle forme de feuille nanométrique de g-C3N4 contenant des lacunes de carbone avec des trous dans tous les plans de feuille. Après la synthèse du matériau de vrac g-C3N4 à partir du dicyandiamide, le matériau obtenu a été chauffé à 650 ° C sous argon pendant 2 h. Après avoir refroidi, il a été calciné à nouveau à 500 ºC pendant 2 heures sous air. Ainsi, sa surface spécifique a été considérablement augmenté de 28 m2.g-1 de g-C3N4 à 160 m2.g-1. En outre, ces traitements par étapes ont introduit certains défauts tels que des lacunes de carbone à l'intérieur de la structure des feuilles nanométriques de g-C3N4. Ces derniers ont fourni des sites photocatalytiques hautement actifs pour l'évolution de l'hydrogène. Par conséquent, sa production d'hydrogène est dix fois supérieure à celle du g-C3N4 brut sous irradiation de la lumière visible. Il a montré une efficacité quantique très élevée de 29,2% et 21,3% à 400 nm et 420 nm, respectivement. Enfin, nous avons généré une solution solide de zinc-cadmium (ZnxCd1-xS) par synthèse solvothermale en utilisant des précurseurs de glycérates métalliques de Cd et Zn. Ensuite, le matériau a été calciné (500 ºC pendant 4 heures) et traité avec H2S à 450 ºC pendant 2 heures. Ainsi, une solution solide homogène de ZnxCd1-xS avec structure cristallographique de wurtzite hexagonale a été formée. Il convient de mentionner que le semi-conducteur obtenu peut absorber une large partie du spectre visible, de plus, sa largeur de bande interdite est fortement affecté par le rapport Zn / Cd et varie entre 2,35 et 3,4 eV (0≤x≤1). Les meilleurs résultats pour l'évolution de l'hydrogène ont été obtenus à partir de l'échantillon Zn30Cd70S avec dépôt de MoS2 comme cocatalyseur. Il peut générer de l'hydrogène dans des longueurs d'onde les plus longues de la région de la lumière visible et ses rendements quantiques sont : 46,6% à 400 nm à 23,4% à 500 nm ainsi que 11,3% à 550 nm.Photocatalysis process is one of the promising ways to use solar energy in large scale for various kind of application including producing hydrogen as clean energy and purify water and air from harmful pollutants and chemicals. Nevertheless, the solar conversion efficiency of photocatalysts are usually below 1% because of weak sunlight absorption, high charge recombination and high photochemical instability. Modifying semiconductor structure and creating nanocomposite photocatalyst can help to overcome these issues. TiO2 is the most well-known photocatalysts because of its physical and chemical properties in photocatalysis process. Although its low cost encourages people to utilize it in large scale, its large band gap, which can only be activated under UV irradiation, and high rate of charge recombination, limited its usage in industrial applications. Creating an heterojunction between TiO2 and others visible light active semiconductor, is one of the best way to take advantage of TiO2 in visible region. Furthermore, graphitic carbon nitride (g-C3N4) has been widely investigated for its potential in hydrogen production under visible light irradiation. Despite the fact that it can activated in visible light region and reduce protons to generate hydrogen, its efficiency is considerably limited because of its high rate of charge recombination and low specific surface area. We synthesized a nanocomposite photocatalyst of g-C3N4 and TiO2 in order to increase charge separation procedure and so it can produce more hydrogen. Uniform titanate nanodisks (TNDs) with diameter between 12 and 35 nm were synthesized with a solvothermal method. Nanosheets of g-C3N4 were synthesized via sonication techniques and then were mixed with TNDs. After that, a calcination step not only made intimate contacts with two semiconductors, but also converted TNDs into TiO2 nanoparticles. Due to the position of conduction band edges of two semiconductors, photogenerated electrons could transfer from g-C3N4 to TiO2. There with a help of Pt as a cocatalyst and active sites provider, photoexcited electrons reduced protons from water and generated hydrogen. This heterojunction could produce more than double hydrogen as pristine g-C3N4 under the same conditions. We created a novel g-C3N4 nanosheets with carbon vacancies and nanoholes throughout nanosheet planes. After synthesis g-C3N4 bulk material from dicyandiamide, the obtained material was heated to 650 ºC under argon flow for 2 hr. After it cooled down, it was calcined again at 500 ºC for 2 hr. As a result, its specific surface area increased significantly from 28 m2 g-1 of bulk g-C3N4 to 160 m2 g-1. Moreover, these stepwise treatments introduced some defects as carbon vacancies inside the structure of g-C3N4 nanosheets. They provided highly active photocatalytic sites for hydrogen evolution. Therefore, its hydrogen production was ten times higher than bulk material of g-C3N4 under visible light irradiation. It showed very high quantum efficiencies of 29.2% and 21.3% at 400 nm and 420 nm, respectively. Finally, we generated zinc cadmium solid solution (ZnxCd1-xS) with synthesizing metal-glycerate of Cd and Zn via solvothermal method. Then, the material was calcined (500 ºC for 4 hr) and treated with H2S at 450 ºC for 2hr. Thus, an homogeneous solid solution of ZnxCd1-xS with hexagonal wurtzite crystal structure was formed. It should be mentioned that the obtained semiconductor could absorb a wide range of visible light energy and its band gap is strongly affected by Zn/Cd ratio and varies between 2.35 and 3.4 eV (0≤x≤1). The best results for hydrogen evolution was gained from Zn30Cd70S sample with depositing MoS2 as a cocatalyst. It could generate hydrogen in longer wavelengths of visible light region and its quantum efficiencies were: 46.6 % at 400 nm to 23.4% at 500 nm as well as 11.3% at 550 nm

From urea to melamine cyanurate: Study of a class of thermal condensation routes for the preparation of graphitic carbon nitride

Producción CientíficaThis work presents a survey of the intermediates in the well-known thermal synthesis of graphitic carbon nitride from urea. The analysis of the crystalline phases depicts a successive transformation of the precursor into different substances previously used as starting reactants, whereby melamine cyanurate arises as the ultimate precursor of a class of thermal condensation routes to obtain graphitic carbon nitride. The study of the optical properties of the synthesized materials evidences the simultaneous production of an amorphous phase with a significant presence of melon oligomers. These results are also supported by the further characterization of the materials performed using THz-TDS, FT-IR, HRTEM, and XPS techniques, and by theoretical studies conducted using semi-empirical quantum chemistry methods.Junta de Castilla y León (grant VA296P18)Ministerio de Ciencia, Innovación y Universidades (grant PID2020-320 119418GB-I00

Novel Metal Oxide Nanostructures for Adsorption and Photocatalytic Degradation of Organic Dyes from Aqueous Stream

Recent research focused on the applications of nanomaterials in environmental remediation especially the treatment of natural waters, industrial and domestic waste water and the polluted underground water. Providing clean water and a clean environment for the world growing population is a challenging task. The present thesis represents an extensive view of the use of nanomaterials in environmental remediation such as water purification using single and composite metal oxide nanomaterials by sorption and photocatalysis of toxic organic dyes. In the present study, we have synthesized 1D iron oxide nanomaterials and iron oxide based nanocomposites such as Fe2O3-SnO2, Fe2O3-CuO, Fe2O3/ZnFe2O4/ZnO, and MgFe2O4-Fe2O3 of different morphology using precipitation, hydrothermal and reflux methods. Apart from this we have also synthesized MgO nanomaterials and iron oxide impregnated mesoporous MCM-41 by wet chemical impregnation method. The obtained metal oxide nanomaterials and their nanocomposites were characterized using XRD, SEM, TEM, EDAX, XPS, Raman, FTIR, UV-Vis-DRS and BET surface area analytical techniques and were used as adsorbents and photocatalysts for decontamination of organic dyes from aqueous solutions. We have synthesized ferrous oxalate, hematite and maghemite nanorods by precipitation method. The XRD patterns indicate the formation of different crystalline phases of ferrous oxalate (FeC2O4.2H2O), hematite (α-Fe2O3) and maghemite (γ-Fe2O3). The SEM and TEM images confirm the formation of rod shaped morphology with diameter in the range of 100-200 nm and length up to micrometers. The prepared nanorods were used as adsorbents for removal of carcinogenic Congo red dye from aqueous solution. After the batch adsorption study, the maximum adsorption capacities of the adsorbents were found to be 103, 232 and 78 mg/g for FeC2O4.2H2O, γ-Fe2O3 and α-Fe2O3 nanorods, respectively. We have also prepared Fe2O3-SnO2 composite nanorods by using same precipitation method. XRD study revealed the presence of magnetic γ-Fe2O3 phase along with SnO2 in Fe2O3–SnO2 composite. The Fe2O3–SnO2 composite nanorods were used as adsorbents for removal of Congo red dye from aqueous solution. Among different compositions, Fe2O3–SnO2 (Fe:Sn=8:2) composite nanorod showed highest percentage adsorption with sorption capacity of 182 mg/g. Mesoporous MCM-41 and MCM-41 impregnated with iron oxide nanomaterials (Fe-MCM-41) were prepared by a facile surfactant based wet chemical method. The experimental results indicate the formation of porous nanostructure with high surface area (>800 m2/g) and particle size in the range of 200-400 nm. The mesoporous materials were used as adsorbents for the removal of Methylene blue from aqueous media. The maximum adsorption capacity of Fe-MCM-41 was found to be 194 mg/g and was higher than that of MCM-41. MgO nanomaterials with different morphologies such as: nanorods, hierarchical nanostructures and nanoflakes were synthesized by precipitation, reflux and hydrothermal methods, respectively. The prepared nanomaterials were used as adsorbents to remove as Malachite green and Congo red from aqueous media. The hierarchical MgO nanostructure exhibited excellent adsorption performance for removal of Malachite green and Congo red with maximum sorption capacities of 1205 and 1051 mg/g, respectively. Using same synthesis methods we have used iron salt precursor along magnesium to prepare MgFe2O4 and MgFe2O4-Fe2O3 composite nanostructures. The MgFe2O4-Fe2O3 nanocomposite prepared by precipitation method was regarded as a superb photocatalyst for 99.9 % methylene blue degradation. We have also synthesized Fe2O3-CuO composite nanorod by same precipitation method. From FESEM and TEM analysis it was observed that the spherical CuO nanoparticles are decorated uniformly onto the α-Fe2O3 nanorod surface forming a one-dimensional heteronanostructure. The obtained 1D Fe2O3-CuO nanocomposite exhibited higher photocatalytic activity than individual α-Fe2O3 nanorods and CuO nanoparticles for degradation of Methyl orange from aqueous media under solar light irradiation. Furthermore, we have synthesized α-Fe2O3 nanoparticle and Fe2O3/ZnFe2O4, Fe2O3/ZnFe2O4/ZnO and ZnFe2O4/ZnO mixed oxide nanocomposites by varying different molar ratio of Fe and Zn using hydrothermal method. The nanocomposite with Fe:Zn=70:30 and 60:40 contains ternary Fe2O3/ZnFe2O4/ZnO phase. The nanomaterials have been used for photocatalytic degradation of Malachite green from aqueous media using solar light irradiation. The ternary Fe2O3/ZnFe2O4/ZnO (Fe:Zn=70:30) nanocomposite exhibits highest photocatalytic activity among all the prepared nanomaterials. The enhanced activity could be attributed to the cascade electron transfer from ZnFe2O4 to ZnO to Fe2O3through the interfacial potential gradient in the ternary nanostructur

Experimental and theoretical investigations on a CVD grown thin film of polymeric carbon nitride and its structure

A polymeric carbon nitride thin film has been grown using chemical vapor deposition. The characterization of the material shows that it has the same molecular composition as a formerly synthesized graphitic carbon nitride powder but both substances differ widely in their structural organization. In particular, our analyses reveal a paradoxical character in which the thin film sample exhibits simultaneously a high degree of organization in the stacking of the polymer sheets with strong inter-layer interactions, as expected from the growth technique, and a complete lack of crystallinity. A comprehensive theoretical study based on massive semi-empirical quantum chemistry computations has permitted to explain the properties of the material and to elucidate fundamental issues regarding the structural conformation of graphitic carbon nitride

Towards Green, Enhanced Photocatalysts for Hydrogen Evolution

This book gathers selected research on the preparation, characterization and application of new organic/inorganic composites endowed with photo(electro)catalytic properties for the photocatalytic production of H2. In these pilot studies, the photoactive materials were tested under either UV-visible or, even more conveniently, under visible light for H2 evolution in “sacrificial water splitting” or “photoreforming” systems. In addition, a review article on the use of 2D materials and composites as potential photocatalysts for water splitting is included

Carbon-Based Nanomaterials for (Bio)Sensors Development

Carbon-based nanomaterials have been increasingly used in sensors and biosensors design due to their advantageous intrinsic properties, which include, but are not limited to, high electrical and thermal conductivity, chemical stability, optical properties, large specific surface, biocompatibility, and easy functionalization. The most commonly applied carbonaceous nanomaterials are carbon nanotubes (single- or multi-walled nanotubes) and graphene, but promising data have been also reported for (bio)sensors based on carbon quantum dots and nanocomposites, among others. The incorporation of carbon-based nanomaterials, independent of the detection scheme and developed platform type (optical, chemical, and biological, etc.), has a major beneficial effect on the (bio)sensor sensitivity, specificity, and overall performance. As a consequence, carbon-based nanomaterials have been promoting a revolution in the field of (bio)sensors with the development of increasingly sensitive devices. This Special Issue presents original research data and review articles that focus on (experimental or theoretical) advances, challenges, and outlooks concerning the preparation, characterization, and application of carbon-based nanomaterials for (bio)sensor development

Layered Double Hydroxides

Very few materials have attracted so much attention in recent years, both from researchers and industry, as layered double hydroxides (LDHs) have. LDHs, which are also referred to as anionic clays or hydrotalcites, are a wide class of inorganic ionic lamellar clay materials consisting of alternately stacked positively charged metal hydroxide layers with intercalated charge-balancing anions in hydrated interlayer regions. Their unique properties, such as their extremely high versatility in chemical composition and intercalation ability, extraordinary tuneability in composition as well as morphology, good biocompatibility and high anion exchangeability, have triggered immense interdisciplinary interest for their use in many different fields of chemistry, biology, medicine, and physics. Indeed, the applications of LDHs are constantly growing: LDHs, in the form of aggregated lamellar clusters, exfoliated single-layer nanosheets, or hierarchical films of interconnected nanoplatelets, can be effectively used as nanoscale vehicles in drug delivery, heterogeneous catalysts and supports for molecular catalysts, ion exchangers and adsorbents, solid electrolytes or fillers in electrochemistry, for the fabrication of superhydrophobic surfaces, water treatment and purification, and the synthesis of functional thin films. This book gathers the contributions to the Special Issue “Layered Double Hydroxides” of Crystals, which includes two review articles and seven research papers