Nickel-doped magnetic carbon aerogel derived from xanthan gum: a competent catalyst for the degradation of single and binary dye-based water pollutants.

Toxic organic dyes (colorants) are one of the main causes of water pollution that releases destructive effluents in the environment. To overcome this issue, a fundamental need to produce a novel, efficient catalyst for the degradation and mineralization of dye mixtures has arisen. The objective of this research is to develop an eminent Ni-doped magnetic carbon aerogel (Ni-MCA) catalyst using graft co-polymerization method having xanthan gum as backbone doped with Ni-magnetic nanoparticles (Ni-MNPs), that do not show agglomeration and easy to separate. The examination revealed that Ni-MCA provided exceptional magnetic characteristics (Ms = 52.75 emu/g) and potent catalytic activity for the degradation of mono- as well as binary-dye solutions of Congo red (CR) and methyl green (MG) dyes. The formation was verified by various characterization techniques such as FTIR, VSM, XRD, XPS, SEM, TEM, and EDX mapping. Interestingly, Ni-MCA shows faster result on anionic dye CR up to 97% with degradation rate of 5.647 × 10-1 min-1, and MG dye shows degradation of 95.7% with the degradation rate of 2.169 × 10-1 min-1, while dye mixture is showing 90% degradation with rate of 2.159 × 10-1 min-1.

Effect of indium (III) doping on Ag3PO4 catalyst stabilization and its visible light photocatalytic activity toward toxic dyes in water.

Indium(III)-doped Ag3PO4 (In-AgP) catalysts at different weight percentages were elaborated by co-precipitation and subjected to XRD, SEM, UV-vis DRS, and FTIR characterization. The prepared catalysts were of spherical morphology and their diameters depends on doping dosage. The whole materials crystallize in a centered cubic system with a slight dissimilation in the positions of the characteristic peaks as a function of indium dosage. The photocatalytic performance of the catalysts under visible light was investigated in the photocatalytic degradation of anionic dye (methyl orange (MO)) and cationic dye (auramine O (AO)) in moderate acid, neutral, and basic pH conditions. Results showed more selectivity to MO than AO. Furthermore, indium-doped samples are more active in the acidic medium than the pure Ag3PO4 (AgP), and 10%In-AgP catalyst presents the highest activity. The degradation efficiency reached 99 % in 60 min for MO and in 180 min for AO. In addition, a high recycling stability was achieved and the catalyst retains its degradation capacity above 99 % after five cycles.

A facile two-step hydrothermal preparation of 2D/2D heterostructure of Bi2WO6/WS2 for the efficient photodegradation of methylene blue under sunlight.

A facile two-step hydrothermal method was successfully used to prepare a photocatalyst Bi2WO6/WS2 heterojunction for methyl blue (MB) photodegradation. Fabricated photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Band gap measurements were carried out by diffuse reflectance spectroscopy (DRS). Results indicated that the prepared heterostructure photocatalyst has increased visible light absorption. Photocatalytic performance was evaluated under sunlight irradiation for methylene blue (MB) degradation as a model dye. Variations in pH (4-10), amount of catalyst (0.025-0.1 g/L), and initial MB concentrations (5-20 ppm) were carried out, whereas all prepared catalysts were used to conduct the tests with a visible spectrophotometer. Degradation activity improved with the pH increase; the optimum pH was approximately 8. Catalyst concentration is directly related to degradation efficiency and reached 93.56% with 0.075 g of the catalyst. Among tested catalysts, 0.01 Bi2WO6/WS2 has exhibited the highest activity and a degradation efficiency of 99.0% in 40 min (min) for MB. MB photodegradation follows pseudo-first-order kinetics, and obtained values of kapp were 0.0482 min-1, 0.0337 min-1, 0.0205 min-1, and 0.0087 min-1 for initial concentrations of 5 ppm, 10 ppm, 15 ppm, and 20 ppm, respectively. The catalyst was reused for six cycles with a negligible decrease in the degradation activity. Heterostructure 0.01 Bi2WO6/WS2 has exhibited a photocurrent density of 16 µA cm-2, significantly higher than 2.0 and 4.5 µA cm-2 for the pristine WS2 and Bi2WO6, respectively. The findings from these investigations may serve as a crucial stepping stone towards the remediation of polluted water facilitated by implementing such highly efficient photocatalysts.

Simple sonochemical synthesis, characterization of TmVO4 nanostructure in the presence of Schiff-base ligands and investigation of its potential in the removal of toxic dyes.

Thulium vanadate (TmVO4) nanorods were successfully prepared by a simple sonochemical approach using Schiff-base ligands. Additionally, TmVO4 nanorods were employed as a photocatalyst. The most optimal crystal structure and morphology of TmVO4 have been determined and optimized by varying Schiff-base ligands, the molar ratio of H2Salen, the sonication time and power, and the calcination time. A Eriochrome Black T (EBT) analysis revealed that the specific surface area was 24.91 m2/g. A bandgap of 2.3 eV was determined by diffuse reflectance spectroscopy (DRS) spectroscopy, which makes this compound suitable for visible photocatalytic applications. In order to assess the photocatalytic performance under visible light, two anionic dyes (EBT) and cationic dyes (Methyl Violet (MV)) were used as models. A variety of factors have been studied in order to improve the efficiency of the photocatalytic reaction, including dye type, pH, dye concentration, and catalyst loading. Under visible light, the highest efficiency was achieved (97.7%) when 45 mg TmVO4 nanocatalysts were present in 10 ppm Eriochorome Black T at pH = 10.

A critical review on pineapple (Ananas comosus) wastes for water treatment, challenges and future prospects towards circular economy.

Each year, nearly 30 million tons of pineapple fruit are harvested for food and drinking industries, along with the release of a huge amount of pineapple wastes. Without the proper treatment, pineapple wastes can cause adverse impacts on the environment, calling for new technologies to convert them into valuable products. Here, we review the production and application of adsorbents derived from pineapple wastes. The thermal processing or chemical modification improved the surface chemistry and porosity of these adsorbents. The specific surface areas of the pineapple wastes-based adsorbents were in range from 4.2 to at 522.9 m2·g-1. Almost adsorption systems followed the pseudo second order kinetic model, and Langmuir isotherm model. The adsorption mechanism was found with the major role of electrostatic attraction, complexation, chelation, and ion exchange. The pineapple wastes based adsorbents could be easily regenerated. We suggest the potential of the pineapple wastes towards circular economy.

Role of interfacial contact between 2D materials and preselected nanostructures in the degradation of toxic dyes: Multifunctional facets of graphene.

Designing intimate interfacial contact between nanostructures and two-dimensional (2D) materials is highly desirable to influence the movement of generated charge carriers. Nanostructured zinc oxide (ZnO) is a fascinating material with unique optical and electrical properties. 2D reduced graphene oxide (rGO) exhibits semiconductor behaviour with tunable catalytic activity and excellent biocompatibility. Hence, we have designed a hybrid material by selecting nanostructures of an oxide semiconductor (ZnO) with reduced graphene oxide (rGO) using a hard integration technique followed by a low-temperature hydrothermal route. The good encapsulation of rGO over the ZnO nanorods was confirmed by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The photocatalytic activities of ZnO, rGO, and ZnO/rGO were studied under visible-light irradiation using three different toxic dyes, methylene blue (MB), methyl orange (MO), and Congo red (CR). The composite materials exhibited excellent efficiencies of 100, 95, and 90% for the degradation of MB, MO, and CR, respectively. Moreover, the degradation of the dye was found to follow first-order kinetics. The enhanced efficiencies are attributed to the adsorption and efficient charge transfer from rGO to the conduction band of ZnO. The role of the multifunctional facets of graphene was presented to elucidate the visible-light activity of the composite materials for enhanced efficiency. The main reactive species (e-) of the reduction reaction were confirmed through a radical trapping experiment, which showed the generation of highly reactive •OH radicals that decompose the toxic dye. The results provide a perspective for developing graphene-based composite materials with desired preselected nanostructures for solar energy utilisation.

An Integrative Approach to Study Bacterial Enzymatic Degradation of Toxic Dyes.

Synthetic dyes pose a large threat to the environment and consequently to human health. Various dyes are used in textile, cosmetics, and pharmaceutical industries, and are released into the environment without any treatment, thus adversely affecting both the environment and neighboring human populations. Several existing physical and chemical methods for dye degradation are effective but have many drawbacks. Biological methods over the years have gained importance in the decolorization and degradation of dye and have also overcome the disadvantages of physiochemical methods. Furthermore, biological methods are eco-friendly and lead to complete decolorization. The mechanism of decolorization and degradation by several bacterial enzymes are discussed in detail. For the identification of ecologically sustainable strains and their application at the field level, we have focused on bioaugmentation aspects. Furthermore, in silico studies such as molecular docking of bacterial enzymes with dyes can give a new insight into biological studies and provide an easy way to understand the interaction at the molecular level. This review mainly focuses on an integrative approach and its importance for the effective treatment and decolorization of dyes.

Hybrid Materials Based on Silica Matrices Impregnated with Pt-Porphyrin or PtNPs Destined for CO2 Gas Detection or for Wastewaters Color Removal.

Multifunctional hybrid materials with applications in gas sensing or dye removal from wastewaters were obtained by incorporation into silica matrices of either Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl)-porphyrin (PtTAOPP) or platinum nanoparticles (PtNPs) alone or accompanied by 5,10,15,20-tetra-(4-allyloxy-phenyl)-porphyrin (TAOPP). The tetraethylorthosilicate (TEOS)-based silica matrices were obtained by using the sol-gel method performed in two step acid-base catalysis. Optical, structural and morphological properties of the hybrid materials were determined and compared by UV-vis, fluorescence and FT-IR spectroscopy techniques, by atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) and by Brunauer-Emmett-Teller (BET) analysis. PtTAOPP-silica hybrid was the most efficient material both for CO2 adsorption (0.025 mol/g) and for methylene blue adsorption (7.26 mg/g) from wastewaters. These results were expected due to both the ink-bottle mesopores having large necks that exist in this hybrid material and to the presence of the porphyrin moiety that facilitates chemical interactions with either CO2 gas or the dye molecule. Kinetic studies concerning the mechanism of dye adsorption demonstrated a second order kinetic model, thus it might be attributed to both physical and chemical processes.

Synthesis of AgNPs coated with secondary metabolites of Acacia nilotica: An efficient antimicrobial and detoxification agent for environmental toxic organic pollutants.

This study concentrates on biosynthesis of Silver Nanoparticles (AgNPs) from stem extract of Acacia nilotica (A. nilotica). The reaction was completed at a temperature ~40-45 °C and time duration of 5 h. AgNPs were thoroughly investigated via advanced characterization techniques such as UV-Vis spectrophotometry (UV-Vis), Fourier Transform Infrared spectroscopy (FTIR), X-ray Diffractometry (XRD), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), Thermo Gravimetric Analysis (TGA), Diffuse Reflectance Spectroscopy (DRS), Brunner-Emmett-Teller (BET), Dynamic Light Scattering (DLS), and Zeta potential analysis. AgNPs with average size below 50 nm were revealed by all the measuring techniques. Maximum surface area ~5.69 m2/g was reported for the as synthesized NPs with total pore volume ~0.0191 mL/g and average pore size ~1.13 nm. Physical properties such as size and shape have changed the surface plasmon resonance peak in UV-visible spectrum. Antimicrobial activity was reported due to denaturation of microbial ribosome's sulphur and phosphorus bond by silver ions against bacterium Methicillin Resistant Staphylococcus aureus (MRSA) and fungus Candida Albican (CA). Furthermore, AgNPs degraded toxic pollutants such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP) and various hazardous dyes such as Congo Red (CR), Methylene Blue (MB) and Methyl Orange (MO) up to 95%. The present work provided low cost, green and an effective way for synthesis of AgNPs which were utilized as potential antimicrobial agents as well as effective catalyst for detoxification of various pollutants and dyes.

One step forward: How can functionalization enhance the adsorptive properties of graphene towards metallic ions and dyes?

Functionalized graphene and its derivatives have been subject of many recent studies investigating their use as scavenger of various industrial pollutants. Adsorption is a feasible treatment, which can employ a wide variety of materials as adsorbents. Additionally, graphene has been distinguished for its remarkable properties, such as mechanical resistance, flexibility and electric conductivity. A relevant aspect of functionalized graphene is related to its selectivity, resulting in increased removal rates of specific pollutants. Hence, the functionalization process of graphene nanosheets is the cutting edge of the materials and environmental sciences, promoting the development of innovative and highly capable sorbents. The purpose of this review is to assemble the available information about functionalized graphene nanomaterials used for the removal of water pollutants and to explore its wide potential. In addition, various optimal experimental conditions (solution pH, equilibrium time, adsorbent dosage) are discussed. In each topic, aspects of environmental protection of adsorption process were evaluated, as well as the most recent works, available from high impact journals in the field, have been explored. Additionally, the employment of natural compounds to functionalize, reduce and support graphene, was evaluated as green alternatives to chemicals.

Adsorptive performance of MOF nanocomposite for methylene blue and malachite green dyes: Kinetics, isotherm and mechanism.

In the present study, Fe3O4@AMCA-MIL-53(Al) nanocomposite was utilized for the adsorptive removal of highly toxic MB and MG dyes from aqueous environment. The batch adsorption tests were performed at different contact time, pH, Fe3O4@AMCA-MIL-53(Al) dose, initial concentration of dyes and temperature. The maximum adsorption capacity of MB and MG dyes onto of Fe3O4@AMCA-MIL-53(Al) using Langmuir equation was 1.02 and 0.90 m mol/g, respectively. The isotherm and kinetic studies revealed that adsorption data were well fitted to Langmuir isotherm and pseudo-first-order kinetics models. Various thermodynamic parameters were also calculated and interpreted. The positive and negative values of ΔH° and ΔG° indicated that the adsorption was endothermic and spontaneous, respectively. The adsorptive binding of MB and MG on Fe3O4@AMCA-MIL53(Al) nanocomposite was directed by carboxylate and amide groups through electrostatic interaction, π-π interaction and hydrogen bonding. The desorption of both dyes from Fe3O4@AMCA-MIL-53(Al) was also performed using mixed solution of 0.01 M HCl/ethanol. Thus, we conclude that the Fe3O4@AMCA-MIL-53(Al) was an outstanding material for the removal of dyes from aqueous environment.

Bismuth oxide decorated graphene oxide nanocomposites synthesized via sonochemical assisted hydrothermal method for adsorption of cationic organic dyes.

Bismuth oxide decorated graphene oxide (Bi2O3@GO) nanocomposites were successfully synthesized by sonochemical method followed by hydrothermal treatment. The structural, morphology/microstructure and functional groups were investigated through X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared (FTIR) spectroscopy, respectively. In the FESEM and TEM studies, well dispersed Bi2O3 nanoparticles of size 3-5nm were found uniformly distributed throughout the surface and edges of GO sheets. The HRTEM measurements on the Bi2O3 nanoparticle decorated graphene oxide shows imaged lattice spacing of 3.2Å corresponding to (111) plane of Bi2O3 which confirms the successful synthesis of bismuth oxide decorated graphene oxide (Bi2O3@GO) nanocomposite. The synthesized nanocomposite was employed for adsorption and removal of cationic organic dyes like RhB from industrial wastewater. The effect of various parameters, viz., contact time, temperature, pH and amount of adsorbent on the adsorption capability as well as dye removal capacity of the adsorbent was studied in detail. Under optimized conditions, like, contact time (65min), amount of adsorbent (5mg), temperature (35°) and pH (4), the adsorption capacity of GO and Bi2O3@GO were recorded and the percentage of removal was found to be 64% and 80.7% for GO and Bi2O3@GO, respectively. The Bi2O3@GO nanocomposite shows higher adsorption capacity (320mg/g) as compare to only GO (224mg/g). The adsorption isotherm follows both the Temkin as well as Langmuir isotherm having heat of sorption 65.88 with Langmuir constant of 13.13 corresponding to the complete monolayer coverage of 387.44mg/g. The adsorption kinetics also follow, both pseudo first order and intraparticle diffusion model with adsorption capacity of 84.91mg/g and intra particle diffusion rate constant of 10.53mg/g min1/2 for Bi2O3@GO nanocomposites. Our results suggest that the prepared Bi2O3@GO nanocomposites possess potential application as high-performance renewable adsorbent for removal of toxic dyes from wastewater.

Fabrication of RuO2-Ag3PO4 heterostructure nanocomposites: Investigations of band alignment on the enhanced visible light photocatalytic activity.

The RuO2-Ag3PO4 heterostructured nanocomposite was successfully synthesized by facile in situ deposition of porous ruthenium oxide (RuO2) nanoparticles on the surface of the silver phosphate (Ag3PO4). Under visible light irradiation, the 0.5wt.% RuO2-Ag3PO4 heterostructure photocatalyst exhibits enhanced photocatalytic efficiency compared to other composites of RuO2-Ag3PO4 and Ag3PO4. The optimized 0.5wt.% RuO2-Ag3PO4 nanocomposites exhibited 1.5 times enhanced photocatalytic activity towards the degradation of methylene blue (MB) than Ag3PO4. Moreover, the degradation rate of 0.5wt.% RuO2-Ag3PO4 nanocomposite towards the cationic dyes MB and rhodamine B (RhB) was nearly 6.6 times and 4.7 times higher than that towards the anionic dye methyl orange (MO). The formed heterojunction electric field of 310mV at the interface between RuO2 and Ag3PO4 heterostructure induces downward band bending of Ag3PO4. Also, this electric field increases the separation efficiency of electrons-holes resulting higher degradation efficiency. The quenching effect of scavengers test confirms that holes are reactive species and the RuO2-Ag3PO4 nanocomposite is highly stable, exhibited 88% of MB degradation after 4 recycles. The RuO2-Ag3PO4 nanocomposites inhibit self oxidation of Ag3PO4 resulting improved efficiency and stability.

A versatile bio-based material for efficiently removing toxic dyes, heavy metal ions and emulsified oil droplets from water simultaneously.

Developing versatile materials for effective water purification is significant for environment and water source protection. Herein, a versatile bio-based material (CH-PAA-T) was reported by simple thermal cross-linking chitosan and polyacrylic acid which exhibits excellent performances for removing insoluble oil, soluble toxic dyes and heavy metal ions from water, simultaneously. The adsorption capacities are 990.1mgg-1 for methylene blue (MB) and 135.9mgg-1 for Cu2+, which are higher than most of present advanced absorbents. The adsorption towards organic dyes possesses high selectivity which makes CH-PAA-T be able to efficiently separate dye mixtures. The stable superoleophobicity under water endows CH-PAA-T good performance to separate toluene-in-water emulsion stabilized by Tween 80. Moreover, CH-PAA-T can be recycled for 10 times with negligible reduction of efficiency. Such versatile bio-based material is a potential candidate for water purification.

Efficient photocatalytic degradation of toxic dyes from aqueous environment using gelatin-Zr(IV) phosphate nanocomposite and its antimicrobial activity.

In the present study, gelatin-Zr(IV) phosphate nanocomposite (GT/ZPNC) was synthesized by sol-gel method by mixing the gelatin gel into the inorganic part Zr (IV) phosphate (ZP). The GT/ZPNC was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy (SEM), transmission electron micron scope (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The photodegradation activity of GT/ZPNC was explored for the removal of methylene blue (MB) and fast green (FG) dyes from aqueous solution. It was found that 87.81% MB and 89.91% FG were degraded within five hours. Also, the kinetics of photocatalytic degradation for MB and FG was investigated via pseudo first-order kinetic model with higher regression coefficient values (R2). The antimicrobial efficiency of GT/ZPNC was investigated against E. coli.