Reductive-degradation of carcinogenic azo dyes using Anacardium occidentale testa derived silver nanoparticles

Development of Monolithic Hyper-Cross-Linked Polystyrene-Supported Ultrasmall Nano-Ag Catalysts for Enhanced NaBH4-Mediated Dye Degradation

Synthesizing catalyst supports with appropriate compositions and structures is crucial for reducing the sizes of metal nanoparticles and enhancing their catalytic activities. In this work, a series of monolithic hyper-cross-linked supports (HCP-CC) with hierarchical pores were synthesized. The monolithic structure facilitated easy operation in catalytic reactions, while the composition and structure of HCP-CC could be tailored simultaneously by utilizing the functional cross-linking agent cyanogen chloride. Furthermore, in situ loading of nano-Ag into HCP-CC resulted in the hybrid catalyst HCP-CC-Ag. The synergy of confinement and coordination effect controlled and limited the size of nano-Ag to approximately 3 nm, classifying them as ultrasmall nanoparticles, which ensured outstanding catalytic activity. This hybrid catalyst could improve the reaction rate constant to 0.423 min-1; it efficiently promoted the degradation of organic dye and exhibited great universality and recyclability, making it a potential heterogeneous catalyst for dye wastewater treatment.

Instant and efficient greenly silver nanoparticles for remediating atrazine and methylene blue from contaminated water

In an attempt to create economically feasible and sustainable wastewater treatment "green" techniques, Malva parviflora leaf water extract was used for biosynthesizing silver nanoparticles (Malva-AgNPs). Fourier transform infrared, ultraviolet-visible (UV-Vis), scanning electron microscopy, and dynamic light scattering (DLS) were used for the characterization of Malva-AgNPs. UV-Vis and DLS analysis revealed the stability of the Malva-AgNPs at a wavelength of 420 nm and an average size of 100 nm ± 1 nm. A zeta potential of - 26.4 mV provides additional support for the stability of the material. The removal studies were conducted using atrazine and methylene blue (MB) in a single or mixed liquid state. The adsorbent dose, pH, incubation time, and pollutant concentration in the adsorption process were investigated. The optimal removal for 500 mg L-1 of atrazine and MB at the adsorbent dosage of 450 mg, when incubated for 5 min, was found to be 99.5% and 82.03% for atrazine and MB, respectively. Also, Malva-AgNPs eliminated more than 95% and 50% of the atrazine and MB mixture, respectively, in 5 min. The kinetics study showed that the pseudo-second-order kinetics model was a better fit for explaining the experimental adsorption experiments for atrazine and MB. The obtained equilibrium adsorption data were examined using the Langmuir and Freundlich isotherm models, which indicate that atrazine and MB have maximum adsorption capacities of 434.78 mg g-1 and 400 mg g-1, respectively.

Sustainable synthesis of spongy-like porous carbon for supercapacitive energy storage systems towards pollution control

In this study, the fruit of Terminalia chebula, commonly known as chebulic myrobalan, is used as the precursor for carbon for its application in supercapacitors. The Terminalia chebula biomass-derived sponge-like porous carbon (TC-SPC) is synthesized using a facile and economical method of pyrolysis. TC-SPC thus obtained is subjected to XRD, FESEM, TEM, HRTEM, XPS, Raman spectroscopy, ATR-FTIR, and nitrogen adsorption-desorption analyses for their structural and chemical composition. The examination revealed that TC-SPC has a crystalline nature and a mesoporous and microporous structure accompanied by a disordered carbon framework that is doped with heteroatoms such as nitrogen and sulfur. Electrochemical studies are performed on TC-SPC using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. TC-SPC contributed a maximum specific capacitance of 145 F g-1 obtained at 1 A g-1. The cyclic stability of TC-SPC is significant with 10,000 cycles, maintaining the capacitance retention value of 96%. The results demonstrated that by turning the fruit of Terminalia chebula into an opulent product, a supercapacitor, TC-SPC generated from biomass has proven to be a potential candidate for energy storage application.

Metal nanoparticles decorated mint-cellulose acetate composite as an efficient catalyst for the reduction of methyl orange

Water contamination caused by toxic compounds has emerged as one of the most severe challenges worldwide. Biomass-based nanocomposites offer a sustainable and renewable alternative to conventional materials. In this study, a nanocomposite of mint and cellulose acetate (Mint-CA) was prepared and employed as a supportive material for Cu nanoparticles (CuNPs) and Ag nanoparticles (AgNPs). The selectivity of CuNPs@mint-CA and AgNPs@mint-CA was assessed by comparing their performance in the reduction reaction of various dyes solutions. AgNPs@mint-CA exhibited superior catalytic performance, with a removal of 95.2 % for methyl orange (MO) compared to 68 % with CuNPs@mint-CA. The absorption spectra of MO exhibited a distinct peak at 464 nm. The reduction reaction of MO by AgNPs@mint-CA followed pseudo-first-order-kinetic with a rate constant of k = 0.0063 min-1 (R2 = 0.928). The highest removal of MO was achieved under the following conditions: a catalyst weight of 40 mg, an initial MO concentration of 0.07 mM, the addition of 0.5 mL of 0.1 M NaBH4, and a temperature of 25 °C. Furthermore, the AgNPs@mint-CA catalyst exhibited exceptional reducibility even after five use cycles, highlighting its potential for efficiently removing MO.

A comprehensive review on the boosted effects of anion vacancy in the heterogeneous photocatalytic degradation, part I: Focus on sulfur, nitrogen, carbon, and halogen vacancies

The greenest environmental remediation way is the photocatalytic degradation of organic pollutants. However, limited photocatalytic applications are due to poor sunlight absorption and photogenerated charge carriers' recombination. These limitations can be overcome by introducing anion vacancy (AV) (O, S, N, C, and Halogen) defects in semiconductors that enhance light harvesting, facilitate charge separation, modulate electronic structure, and produce reactive radicals. In continuing part A of this review, in this part, we summarized the recent AVs' research, including S, N, C, and halogen vacancies on the boosted photocatalytic features of semiconductor materials, like metal oxides/sulfides, oxyhalides, and nitrides in detail. Also, we outline the recently developed AV designs for the photocatalytic degradation of organic pollutants. The AV creating and analysis methods and the recent photocatalytic applications and mechanisms of AV-mediated photocatalysts are reviewed. AV engineering photocatalysts' challenges and development prospects are illustrated to get a promising research direction.

An overview of biogenic metallic nanoparticles for water treatment and purification: the state of the art

The environment is fundamental to human existence, and protecting it from dangerous contaminants should be a top priority for all stakeholders. Reducing garbage output has helped, but as the world's population grows, more waste will be generated. Tons of waste inadvertently and advertently received by environmental matrixes adversely affect the sustainable environment. The pollution caused by these activities affects the environment and human health. Conventional remediation processes ranging from chemical, physical, and biological procedures use macroaggregated materials and microorganisms to degrade or remove pollutants. Undesirable limitations of expensiveness, disposal challenges, maintenance, and formation of secondary contaminants abound. Additionally, multiple stages of treatments to remove different contaminants are time-consuming. The need to avoid these limitations and shift towards sustainable approaches brought up nanotechnology options. Currently, nanomaterials are being used for environmental rejuvenation that involves the total degradation of pollutants without secondary pollution. As nanoparticles are primed with vast and modifiable reactive sites for adsorption, photocatalysis, and disinfection, they are more useful in remediating pollutants. Review articles on metallic nanoparticles usually focus on chemically synthesized ones, with a particular focus on their adsorption capacity and toxicities. Therefore, this review evaluates the current status of biogenic metallic nanoparticles for water treatment and purification.

Microbial biodegradation of recalcitrant synthetic dyes from textile-enriched wastewater by Fusarium oxysporum

The present study reported the improvement of biological treatment for the removal of recalcitrant dyes including aniline blue, reactive black 5, orange II, and crystal violet in contaminated water. The biodegradation efficiency of Fusarium oxysporum was significantly enhanced by the addition of mediators and by adjusting the biomass density and nutrient composition. A supplementation of 1% glucose in culture medium improved the biodegradation efficiency of aniline blue, reactive black 5, orange II, and crystal violet by 2.24, 1.51, 4.46, and 2.1 folds, respectively. Meanwhile, the addition of mediators to culture medium significantly increased the percentages of total removal for aniline blue, reactive black 5, orange II, and crystal violet, reaching 86.07%, 68.29%, 76.35%, and 95.3%, respectively. Interestingly, the fungal culture supplemented with 1% remazol brilliant blue R boosted the biodegradation up to 97.06%, 89.86%, 91.38%, and 86.67% for aniline blue, reactive black 5, orange II, and crystal violet, respectively. Under optimal culture conditions, the fungal culture could degrade these synthetic dyes concentration up to 10⁴ mg/L. The present study demonstrated that different recalcitrant dye types can be efficiently degraded using microorganism such as F. oxysporum.

Eco-Friendly Synthesis of Functionalized Carbon Nanodots from Cashew Nut Skin Waste for Bioimaging

In this study, Anacardium occidentale (A. occidentale) nut skin waste (cashew nut skin waste) was used as a raw material to synthesize functionalized carbon nanodots (F-CNDs). A. occidentale biomass-derived F-CNDs were synthesized at a low temperature (200 °C) using a facile, economical hydrothermal method and subjected to XRD, FESEM, TEM, HRTEM, XPS, Raman Spectroscopy, ATR-FTIR, and Ultraviolet-visible (UV–vis) absorption and fluorescence spectroscopy to determine their structures, chemical compositions, and optical properties. The analysis revealed that dispersed, hydrophilic F-CNDs had a mean diameter of 2.5 nm. XPS and ATR-FTIR showed F-CNDs had a crystalline core and an amorphous surface decorated with –NH2, –COOH, and C=O. In addition, F-CNDs had a quantum yield of 15.5% and exhibited fluorescence with maximum emission at 406 nm when excited at 340 nm. Human colon cancer (HCT-116) cell assays showed that F-CNDs readily penetrated into the cells, had outstanding biocompatibility, high photostability, and minimal toxicity. An MTT assay showed that the viability of HCT-116 cells incubated for 24 h in the presence of F-CNDs (200 μg mL–1) exceeded 95%. Furthermore, when stimulated by filters of three different wavelengths (405, 488, and 555 nm) under a laser scanning confocal microscope, HCT-116 cells containing F-CNDs emitted blue, red, and green, respectively, which suggests F-CNDs might be useful in the biomedical field. Thus, we describe the production of a fluorescent nanoprobe from cashew nut waste potentially suitable for bioimaging applications.

Cationic Polystyrene-Based Hydrogels as Efficient Adsorbents to Remove Methyl Orange and Fluorescein Dye Pollutants from Industrial Wastewater

Water pollution from dyes is harmful to the environment, plants, animals, and humans and is one of the most widespread problems afflicting people throughout the world. Adsorption is a widely used method to remove contaminants derived from the textile industry, food colorants, printing, and cosmetic manufacturing from water. Here, aiming to develop new low-cost and up-scalable adsorbent materials for anionic dye remediation and water decontamination by electrostatic interactions, two cationic resins (R1 and R2) were prepared. In particular, they were obtained by copolymerizing 4-ammonium methyl and ethyl styrene monomers (M1 and M2) with dimethylacrylamide (DMAA), using N-(2-acryloylamino-ethyl)-acrylamide (AAEA) as cross-linker. Once characterized by several analytical techniques, upon their dispersion in an excess of water, R1 and R2 provided the R1- and R2-based hydrogels (namely R1HG and R2HG) with equilibrium degrees of swelling (EDS) of 900% and 1000% and equilibrium water contents (EWC) of 90 and 91%, respectively. By applying Cross' rheology equation to the data of R1HG and R2HG's viscosity vs. shear rate, it was established that both hydrogels are shear thinning fluids with pseudoplastic/Bingham plastic behavior depending on share rate. The equivalents of -NH₃⁺ groups, essential for the electrostatic-based absorbent activity, were estimated by the method of Gaur and Gupta on R1 and R2 and by potentiometric titrations on R1HG and R2HG. In absorption experiments in bulk, R1HG and R2HG showed high removal efficiency (97-100%) towards methyl orange (MO) azo dye, fluorescein (F), and their mixture (MOF). Using F or MO solutions (pH = 7.5, room temperature), the maximum absorption was 47.8 mg/g in 90' (F) and 47.7 mg/g in 120' (MO) for R1, while that of R2 was 49.0 mg/g in 20' (F) and 48.5 mg/g in 30' (MO). Additionally, R1HG and R2HG-based columns, mimicking decontamination systems by filtration, were capable of removing MO, F, and MOF from water with a 100% removal efficiency, in different conditions of use. R1HG and R2HG represent low-cost and up-scalable column packing materials that are promising for application in industrial wastewater treatment.

Efficient Catalytic Degradation of Selected Toxic Dyes by Green Biosynthesized Silver Nanoparticles Using Aqueous Leaf Extract of Cestrum nocturnum L

In the present study, the catalytic degradation of selected toxic dyes (methylene blue, 4-nitrophenol, 4-nitroaniline, and congo red) using biosynthesized green silver nanoparticles (AgNPs) of Cestrum nocturnum L. was successfully performed. These AgNPs are efficiently synthesized when a reaction mixture containing 5 mL of aqueous extract (3%) and 100 mL of silver nitrate (1 mM) is exposed under sunlight for 5 min. The synthesis of AgNPs was confirmed based on the change in the color of the reaction mixture from pale yellow to dark brown, with maximum absorbance at 455 nm. Obtained NPs were characterized by different techniques, i.e., FTIR, XRD, HR-TEM, HR-SEM, SAED, XRD, EDX, AFM, and DLS. Green synthesized AgNPs were nearly mono-dispersed, smooth, spherical, and crystalline in nature. The average size of the maximum number of AgNPs was 77.28 ± 2.801 nm. The reduction of dyes using a good reducing agent (NaBH4) was tested. A fast catalytic degradation of dyes took place within a short period of time when AgNPs were added in the reaction mixture in the presence of NaBH4. As a final recommendation, Cestrum nocturnum aqueous leaf extract-mediated AgNPs could be effectively implemented for environmental rehabilitation because of their exceptional performance. This can be utilized in the treatment of industrial wastewater through the breakdown of hazardous dyes.

Bacterial-driven upcycling spent Ag into high-performance catalyst for toxic organics reduction

Achieving up-cycling and reusing of silver from the waste X-rays films is currently a huge challenge. Here, we designed a facile method that upcycles Ag⁺ extract efficiently from waste film into highly dispersed value-added biological Ag/AgO-AgCl nanoparticles (bio-Ag/AgO-AgCl NPs) using Bacillus thuringiensis-secreted extracellular polymeric substance without additional reductants and electron donors. The recovery efficiency of silver exceeded 99.8%. Surprisingly, the bio-Ag/AgO-AgCl NPs can well solve the bottleneck problem of slow Ag catalytic kinetics. When the amount of catalyst was 1.9 mg, the reduction efficiency and reduction rate of 10 ppm methyl orange were 97.9% and 7 min, and that of 30 ppm Congo red were 95.3% and 5 min respectively, which is superior to other chemically synthesized silver-base catalysts. This bioremediation methodology provides an effective and practical technical approach for precious metal remediation and sustainable energy development.

Green-Routed Carbon Dot-Adorned Silver Nanoparticles for the Catalytic Degradation of Organic Dyes

Herein, a simple, cost-effective, and in-situ environmentally friendly approach was adopted to synthesize carbon dot-adorned silver nanoparticles (CDs@AgNPs) from yellow myrobalan (Terminalia chebula) fruit using a hydrothermal treatment without any additional reducing and or stabilizing agents. The as-synthesized CDs@AgNP composite was systematically characterized using multiple analytical techniques: FESEM, TEM, XRD, Raman, ATR-FTIR, XPS, and UV-vis spectroscopy. All the results of the characterization techniques strongly support the idea that the CDs were successfully made to adorn the AgNPs. This effectively synthesized CDs@AgNP composite was applied as a catalyst for the degradation of organic dyes, including methylene blue (MB) and methyl orange (MO). The degradation results revealed that CDs@AgNPs exhibit a superior catalytic activity in the degradation of MB and MO in the presence of NaBH4 (SB) under ambient temperatures. In total, 99.5 and 99.0% rates of degradation of MB and MO were observed using CDs@AgNP composite with SB, respectively. A plausible mechanism for the reductive degradation of MB and MO is discussed in detail. Moreover, the CDs@AgNP composite has great potential for wastewater treatment applications.

A comprehensive review on sustainable greener nanoparticles for efficient dye degradation

The effluents released from textile industries mainly consist of dyes, metals and other pollutants. Dyes often are discharged in wastewater streams causing adverse effect on the environment. To eliminate these harmful dyes, various techniques are emerging out of which nanotechnology is the most reliable and safer. Nanotechnology offers convincing applications in case of environmental and economic concerns. The bio-synthesis of nanoparticles has several advantages over conventional methods and approach towards environment concern as well. Biological method of nanoparticles synthesis is concluded to be the most promising and efficient in action. Bio-synthesised nanoparticles could be used for treatment and decolourisation of dyes in an efficient manner. This review comprises the study of number of bio-synthesised nanoparticles utilised for degradation of various dyes present as pollutants in wastewater. Bio-synthesised nanoparticles such as gold, silver, iron, cobalt, zinc, titanium and molybdenum used for degradation of various dyes have been discussed in this review.

Nano Ag@bioactive microspheres from marine sponge Clathria frondifera: Fabrication, fortification, characterization, anticancer and antibacterial potential evaluation

Bioresources are attaining much importance in the discovery of drugs and delivering agents. In particular, marine sponges are of great interest due to their metabolites production for the survival in risky environment. The incorporation of silver nanoparticles with marine sponge derived metabolites was reported for the first time. In this work, a facile material has been generated of great efficacy in solving environmental and health issues, as a recipe of silver and marine sponge Clathria frondifera, named as Ag Fortified Sponge spheres (AFS). AFS spheres were successfully synthesized after method optimization, using the various extracts of marine sponge Clathria frondifera as effective reducing agent in Ag (I) to Ag (0) reduction. Bioactive material from marine sponge and AgNP from the reduction of AgNO₃ solution stablishing one another and thus AFS spheres were attaining long lifetime along with enhanced antimicrobial activity. The characterization of synthesized AFS and other AgNPs (1-4) has done using FT-IR, PXRD, FESEM, TEM, and UV-vis data. The presence of functional groups such as, Ag-O, and Ag-C stretching bonds in the AFS compounds indicated that it is composed of silver oxides and organo-silver, respectively. The synthesized Ag NPs were found to be spherical like structure with an average size of ∼20 nm. The cytotoxic response of AFS was assessed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and morphological changes. AFS are exact spherical, micro sized and effective in inhibiting the growth of both gram positive and gram-negative bacteria. Anticancer studies were also carried out and ensued with excellent activity in the HELA cells with potential application in the medical industry.

Nanostructured TiO2 Sensitized with MoS2 Nanoflowers for Enhanced Photodegradation Efficiency toward Methyl Orange

Nanostructured titanium dioxide (TiO₂) has a potential platform for the removal of organic contaminants, but it has some limitations. To overcome these limitations, we devised a promising strategy in the present work, the heterostructures of TiO₂ sensitized by molybdenum disulfide (MoS₂) nanoflowers synthesized by the mechanochemical route and utilized as an efficient photocatalyst for methyl orange (MO) degradation. The surface of TiO₂ sensitized by MoS₂ was comprehensively characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence spectroscopy (PL), Brunauer-Emmett-Teller (BET) surface area, and thermogravimetric analysis (TGA). From XRD results, the optimized MoS₂-TiO₂ (5.0 wt %) nanocomposite showcases the lowest crystallite size of 14.79 nm than pristine TiO₂ (20 nm). The FT-IR and XPS analyses of the MoS₂-TiO₂ nanocomposite exhibit the strong interaction between MoS₂ and TiO₂. The photocatalytic results show that sensitization of TiO₂ by MoS₂ drastically enhanced the photocatalytic activity of pristine TiO₂. According to the obtained results, the optimal amount of MoS₂ loading was assumed to be 5.0 wt %, which exhibited a 21% increment of MO photodegradation efficiency compared to pristine TiO₂ under UV-vis light. The outline of the overall study describes the superior photocatalytic performance of 5.0 wt % MoS₂-TiO₂ nanocomposite which is ascribed to the delayed recombination by efficient charge transfer, high surface area, and elevated surface oxygen vacancies. The context of the obtained results designates that the sensitization of TiO₂ with MoS₂ is a very efficient nanomaterial for photocatalytic applications.

Equilibrium and Kinetic Study of Anionic and Cationic Pollutants Remediation by Limestone-Chitosan-Alginate Nanocomposite from Aqueous Solution

In this work, low-cost and readily available limestone was converted into nanolimestone chitosan and mixed with alginate powder and precipitate to form a triple nanocomposite, namely limestone—chitosan–alginate (NLS/Cs/Alg.), which was used as an adsorbent for the removal of brilliant green (BG) and Congo red (CR) dyes in aqueous solutions. The adsorption studies were conducted under varying parameters, including contact time, temperature, concentration, and pH. The NLS/Cs/Alg. was characterized by SEM, FTIR, BET, and TEM techniques. The SEM images revealed that the NLS/Cs/Alg. surface structure had interconnected pores, which could easily trap the pollutants. The BET analysis established the surface area to be 20.45 m²/g. The recorded maximum experimental adsorption capacities were 2250 and 2020 mg/g for CR and BG, respectively. The adsorption processes had a good fit to the kinetic pseudo second order, which suggests that the removal mechanism was controlled by physical adsorption. The CR and BG equilibrium data had a good fit for the Freundlich isotherm, suggesting that adsorption processes occurred on the heterogeneous surface with a multilayer formation on the NLS/Cs/Alg. at equilibrium. The enthalpy change (ΔH⁰) was 37.7 KJ mol⁻¹ for CR and 8.71 KJ mol⁻¹ for BG, while the entropy change (ΔS⁰) was 89.1 J K⁻¹ mol⁻¹ for CR and 79.1 J K⁻¹ mol⁻¹ BG, indicating that the adsorption process was endothermic and spontaneous in nature.

Variation and comparison of biotoxicity during typical biological treatment of dyeing wastewater

In present study, dyeing wastewater samples were collected from three typical dyeing wastewater treatment plants in Wujiang, Shengze and Shanghai, China. Physicochemical properties and biotoxicity indicators (luminescent bacteria acute toxicity and umu genotoxicity) were tested and the relationships among them were analyzed. The results revealed that two biotoxicity indicators varied significantly among different treatment units of three plants. After treatment by plant A, luminescent bacteria acute toxicity of dyeing wastewater reduced effectively, while umu genotoxicity increased significantly. Two biotoxicity indicators exhibited decrease and increase trends during the treatment processes of plant B and plant C, respectively. Correlation analysis indicated that there was little correlation among biotoxicity indicators and physicochemical properties, meanwhile two kinds of biotoxicity indicators were relatively independent. Therefore, it was recommended that comprehensive evaluation of dyeing wastewater toxicity needs the combination of various biotoxicity indicators, and the relationship among biotoxicity indicators and physicochemical properties of dyeing wastewater should be established individually. The results of this study would offer a general understanding and evaluation of biotoxicity during actual dyeing wastewater treatment processes and provide database for toxicity reduction and management of dyeing wastewater.

Solvothermal synthesis of facet-dependent BiVO4 photocatalyst with enhanced visible-light-driven photocatalytic degradation of organic pollutant: assessment of toxicity by zebrafish embryo

The BiVO₄ photocatalyst plays a very important role in photocatalytic reactions attributed to its unique crystalline structure, size, morphology and surface area. Herein, we report a facet-dependent monoclinic scheelite BiVO₄ (m-BiVO₄) photocatalyst with uniform truncated square (18 sided) hexagonal bipyramidal shape synthesized by a template-free and surfactant-free solvothermal method using ethylene glycol solvent under cost-effective and mild reactions. The structural, morphological and optical properties of the m-BiVO₄ photocatalyst are widely characterized. The photocatalytic activity of the m-BiVO₄ photocatalyst is tested towards 20 ppm methylene blue (MB) dye aqueous solution as a pollutant model under visible light irradiation. Enhanced visible-light driven photoactivity with dye degradation efficiency of approx. 91% at a rate of 0.388 × 10⁻² min⁻¹ is obtained, presumably due to the presence of high-active (040) facets. Zebrafish embryo toxicity test of treated MB dye solution reveals the degradation and toxicity reduction of the MB dye. Moreover, the recycling experiment validates that the m-BiVO₄ photocatalyst has a great structural stability with reliable performance. This work may provide a lucid and expedient strategy to synthesize highly crystalline (040) facet-dependent semiconductor photocatalyst toward dye degradation and obviously industrial wastewater remediation.

Synthesis and characterization of L-asparagine stabilised gold nanoparticles: Catalyst for degradation of organic dyes

L-asparagine functionalized gold nanoparticles (Asp-AuNPs), have been synthesized by reducing HAuCl₄ in presence of L-asparagine at 70 °C for 8 h. Asp-AuNPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS); the nanoparticles formed were spherical in shape with average size of 13.5 ± 3.7 nm. Synthesized Asp-AuNPs were found to exhibit excellent catalytic properties for the degradation of different organic dyes viz. Rhodamine B (RB), methyl orange (MO), acid red 27 (amaranth) and xylenol orange (XO) in the presence of sodium borohydride (NaBH₄). Asp-AuNPs acts as electron relay system and serve as effective catalyst for complete degradation of all the tested dyes. Rate kinetic investigations suggested that catalysed degradation reactions follow pseudo-first order reaction kinetics with rate constant of 0.904 min^-1, 0.314 min^-1, 0.228 min^-1 and 0.1 min^-1 for RB, MO, amaranth and XO respectively.

Antimicrobial activity of a silver-microfibrillated cellulose biocomposite against susceptible and resistant bacteria

Antibiotic Microbial Resistance (AMR) is a major global challenge as it constitutes a severe threat to global public health if not addressed. To fight against AMR bacteria, new antimicrobial agents are continually needed, and their efficacy must be tested. Historically, many transition metals have been employed, but their cytotoxicity is an issue and hence must be reduced, typically by combination with organic polymers. Cellulose of natural origin, especially those derived from unavoidable residues in the food supply chain, appears to be a good capping agent for the green synthesis of silver nanoparticles. Herein, we describe a green synthesis method to produce a novel biocomposite, using ascorbic acid as reducing agent and microfibrillated cellulose as a capping agent and demonstrate this material to be an efficient antimicrobial agent. Silver nanoparticles were obtained in the cellulose matrix with an average size of 140 nm and with antimicrobial activity against both sensitive and resistant Gram positive (using 1500 ppm) as well as sensitive and resistant Gram negative (using 125 ppm) bacteria. Also, an inverted disk-diffusion methodology was applied to overcome the low-solubility of cellulose compounds. This novel silver nanoparticle-cellulose biocomposite synthesized by a green methodology shows the potential to be applied in the future development of biomedical instruments and therapeutics.

Graphene oxide nanocomposite magnetic microbeads for the remediation of positively charged aromatic compounds

Integrating graphene as an inorganic nanostructure within a hydrogel matrix enables the creation of a unique hybrid composite combining the peculiar chemical and physical properties of graphene with the high porosity and stability of hydrogels as for example agarose gel. As a consequence, the resulting material forms a double-network system providing advantages deriving from both the components. In this study, we present the synthesis of novel magnetic porous agarose-based graphene oxide microbeads for the adsorption and separation of positively charged aromatic molecules. The hydrogel-based graphene oxide beads revealed an ultrafast adsorption kinetics for positively charged aromatic dyes. We tested this material for the purification of fluorescent-tagged biomolecules. In addition, reduced graphene oxide microbeads were decorated with palladium nanoparticles, showing a high catalytic activity towards the reduction of dyes by sodium borohydride. Our results show that magnetic agarose based graphene microbeads with enhanced physical-chemical properties can be used for several biochemical applications.

Silver nanoparticles in dye effluent treatment: A review on synthesis, treatment methods, mechanisms, photocatalytic degradation, toxic effects and mitigation of toxicity

The current scenario of water resources shows the dominance of pollution caused by the draining of industrial effluents. The polluted waters have resulted in severe health and environmental hazards urging for a suitable alternative to resolve the implications. Various physical and chemical treatment steps currently in use for dye effluent treatment are more time consuming, cost-intensive, and less effective. Alternatively, nanoparticles due to their excellent surface properties and chemical reactivity have emerged as a better solution for dye removal and degradation. In this regard, the potential of silver nanoparticles in dye effluent treatment was greatly explored. Efforts were taken to unravel the kinetics and statistical optimization of the treatment conditions for the efficient removal of dyes. In addition, the role of silver nanocomposites has also experimented with colossal success. On the contrary, studies have also recognized the mechanisms of silver nanoparticle-mediated toxicity even at deficient concentrations and their deleterious biological effects when present in treated water. Hence, the fate of the silver nanoparticles released into the treated water and sludge, contaminating the soil, aquatic environment, and underground water is of significant concern. This review summarizes the current state of knowledge regarding the use of silver nanoparticles and silver-based nanocomposites in effluent treatment and comprehends the recent research on mitigation of silver nanoparticle-induced toxicity.

Improved charge separation through H2O2 assisted copper tungstate for enhanced photocatalytic efficiency for the degradation of organic dyes under simulated sun light

In the recent years, copper tungstate (CuWO₄) has been widely researched for its photocatalytic properties as it responds in the visible light range to augment the utilization of solar energy. In the present report, CuWO₄ was synthesized through a facile and cost-effective solvothermal method, followed by annealing process at 700^∘C. The structural, morphological, compositional and optical property of the synthesized powders were examined by X-ray diffraction, scanning electron microscope, UV-visible, Raman and photoluminescence studies. The photocatalytic activity of the nanostructured CuWO₄ was evaluated by the degradation of methylene blue (MB) and methyl orange (MO) in aqueous solution under one sun light irradiation. The degradation efficiency of MB was found to be about 70% while that of MO was only 57% at 240 min in the same irradiation time. Surprisingly, the degradation process was accelerated by the addition of electron capturing agent H₂O₂ and thus MB dye was completely degraded within the time interval of 30 min while MO degraded in 75 min. These results prove that CuWO₄ nanoparticles possess significant photocatalytic activity towards MO and MB dyes, thus indicating the feasibility of using CuWO₄ for the active treatment of organic contaminants in the industrial effluents.

Green Synthesis of Biogenic Silver Nanoparticles for Efficient Catalytic Removal of Harmful Organic Dyes

The present article reports an environmentally benign method for synthesizing silver nanoparticles using the fruit extract of Viburnum opulus L. as a source of bioactive compounds, which can act as reducing agents of the silver ions and also as stabilizing agents of the obtained nanoparticles. The catalytic ability of the synthesized silver nanoparticles (AgNPs) to remove toxic organic dyes was also evaluated. The biosynthesis of silver nanoparticles was firstly confirmed by UV-Vis spectral analysis, which revealed the presence of the characteristic absorption peak at 415 nm corresponding to the surface plasmon vibration of colloidal silver. Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) studies were conducted to confirm the presence of bioactive phytocompounds, especially phenolics, as capping and stabilizing agents of the AgNPs. The size, morphology and crystalline nature of the synthesized AgNPs were investigated by transmission electron microscopy and X-ray diffraction techniques revealing that the obtained nanoparticles were spherical shaped, with an average diameter of 16 nm, monodispersed, face centered cubic nanoparticles. Further, the catalytic ability in the degradation of tartrazine, carmoisine and brilliant blue FCF dyes by NaBH4 was evaluated. The results demonstrated an efficient activity against all the investigated dyes being an outstanding catalyst for the degradation of brilliant blue FCF. This eco-friendly synthetic approach can generate new tools useful in environmental pollution control.

Ecofriendly Synthesis of Fluorescent Nitrogen-Doped Carbon Dots from Coccinia grandis and its Efficient Catalytic Application in the Reduction of Methyl Orange

Facile and fast hydrothermal process for the synthesis of nitrogen doped carbon dots (N-CDs) from Coccinia grandis (C. grandis) extract is discussed here. The morphology of prepared N-CDs was characterized by high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) method. The optical properties of the prepared N-CDs were revealed by Ultraviolet-Visible (UV-Vis) and photoluminescence spectroscopy. X-ray diffraction (XRD) and Raman spectroscopic techniques were employed to examine the crystallinity and graphitization of prepared N-CDs. The nitrogen doping was confirmed by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The prepared nitrogen doped carbon dots released blue fluorescence at 405 nm beneath the excitation of 310 nm. The prepared N-CDs influenced the catalytic performance of NaBH₄ in the reduction of methyl orange. The rate constant for the reduction of organic dye (methyl orange) by NaBH₄ in the presence of the prepared green catalyst was also determined.

Sustainable synthesis of silver nanoparticles using exposed X-ray sheets and forest-industrial waste biomass: Assessment of kinetic and catalytic properties for degradation of toxic dyes mixture

Silver being the precious metal, its recovery from the waste and utilization is a worthy attempt. The present study represents a very promising sustainable approach for the synthesis of silver nanoparticles (AgNPs), where prime raw materials are waste products (silver metal extracted from waste X-ray sheets and Sal deoiled seed cake (DOC), a plant-based waste as reducing-capping agent). Upon reaction of silver nitrate extracted from waste X-ray sheets and Sal DOC extract at room temperature, the characteristic yellowish-brown color appeared within 30 min. Peak at 485-495 in UV-visible spectrophotometer confirmed the synthesis of AgNPs. X-ray waste synthesized (XRWS) AgNPs were polycrystalline in nature and have face centered cubic (fcc) lattice. Majority of them were polygonal in shape (size range 30-150 nm) with some flower like aggregates as revealed by Transmission Electron Microscope. The XRWS-AgNPs were stabilized by organic groups adhered to their surface and had good stability with a zeta potential of -27.60 mV. These XRWS-AgNPs could work as an efficient catalyst for the reduction of five selected azo dyes individually as well as mixture of these dyes. The degraded products of the individual dyes were identified using Gas Chromatography Mass Spectroscopy. Experimental values obtained for dye degradation study were fitted with first and second order linear kinetic model to know about rate of the reaction.

Phyto-Nanocatalysts: Green Synthesis, Characterization, and Applications

Catalysis represents the cornerstone of chemistry, since catalytic processes are ubiquitous in almost all chemical processes developed for obtaining consumer goods. Nanocatalysis represents nowadays an innovative approach to obtain better properties for the catalysts: stable activity, good selectivity, easy to recover, and the possibility to be reused. Over the last few years, for the obtaining of new catalysts, classical methods—based on potential hazardous reagents—have been replaced with new methods emerged by replacing those reagents with plant extracts obtained in different conditions. Due to being diversified in morphology and chemical composition, these materials have different properties and applications, representing a promising area of research. In this context, the present review focuses on the metallic nanocatalysts’ importance, different methods of synthesis with emphasis to the natural compounds used as support, characterization techniques, parameters involved in tailoring the composition, size and shape of nanoparticles and applications in catalysis. This review presents some examples of green nanocatalysts, grouped considering their nature (mono- and bi-metallic nanoparticles, metallic oxides, sulfides, chlorides, and other complex catalysts).