Search

Synthetic dyes are known to be toxic and endocrine disruptors. Therefore, advance and fast processes based on low-cost and highly proficient nanomaterials are required for their elimination. Herein, zinc oxide coupled copper hexacyanoferrate (ZnO-CuHCF) nanocomposite was prepared using plant extract of Azadirachta indica. Nanocomposite was characterized throughspectroscopic and electron microscopic techniques. Distorted cubic nanocomposite with particle size range of 50–100 nm was obtained and appearance of stretching vibration around 483 cm−1 confirmed the bonding of O of ZnO and Cu of CuHCF to form ZnO-CuHCF. Subsequently, nanocomposite was utilized as photocatalyst for removal of selected dyes under sunlight. At moderate dosage and neutral pH, nanocomposites was found highly active for quantitative degradation (97–99%) of Eriochrome Black T (EBT) and of Rhodamine B (RB) within 3 h of sunlight exposure. Photodegradation of dyes by nanocomposite was consisting of initial Langmuir adsorption followed by first order kinetics. Comparative to natives, nanocomposite was more capable and lowered the t1/2 value of EBT (0.6 h) and RB (0.9 h) to a greater extent. The findings were attributed to higher surface area (95 m2 g−1) and particle stability (zeta potential: −40.4 mV) of nanocomposite as well as synergistic effects of parent materials. Mechanism of the photo-catalysis was investigated by using radical scavenger and understanding the steps involved in removal process. Applicability of the nanocomposite for almost ten cycles of dye removal ensures its stability and excellent catalytic efficiency. Overall, present work provides an effective and sustainable photocatalyst having worth of industrial applications.

Polycyclic aromatic hydrocarbons (PAHs) are causing environmental concerns due to their persistent nature and carcinogenicity. Hence, their removal through advanced nanomaterials with characteristics of low-cost and high efficiency is essential. In view of this, bimetallic oxides (BMOs) nanocomposites of NiO-ZnO, ZnCo2O4, MnCo2O4 and CoFe2O4 were synthesized via green route using leaf extract of Aegle marmelos. Subsequently, these BMOs were investigated for photocatalytic removal of selected PAHs like anthracene (ANTH) and phenanthrene (PHEN) from water. Nanospheres of NiO-ZnO, ZnCo2O4, and CoFe2O4 and nanosheets of MnCo2O4 with particle size range of 10–30 nm were confirmed by transmission electron microscopy. At neutral pH, nanocomposites showed excellent ability in degrading 2 mg L−1 of PAHs (ANTH: 98%; PHEN: 93%) within 12 h under the exposure of sunlight. Among the synthesized BMOs, NiO-ZnO was found best followed by ZnCo2O4, MnCo2O4 and CoFe2O4. This fact is attributed to the highest surface area (129 m2 g−1) and particles stability (zeta potential: −30 eV) of NiO-ZnO. Photodegradation of PAHs by nanocomposites followed first order kinetics and fitted in Langmuir model for adsorption. Higher degradation under sunlight and lower removal efficiency with scavenger confirmed the photodegradation activity of nanocomposites. Overall, reusable (n = 10) nanocomposites with no loss of activity have high photocatalytic potential in the removal of carcinogenic PAHs.

Aromatic amines (AAs), the major group of industrial and environmental chemicals have raised concern due to their thermodynamic stability coupled with carcinogenicity. Thus, their effective elimination was carried out by nanomaterials especially metal hexacyanoferrates (MHCFs). Iron hexacyanoferrate (FeHCF), Nickel hexacyanoferrate (NiHCF) and Cobalt hexacyanoferrate (CoHCF) were synthesized using green methodology. TEM analysis showed the formation of hexagonal nanorods (

Discharge of dyes (major industrial coloring agents ∼700,000 tonnes) in environment is of concern due to their high perseverance, toxicity and carcinogenicity. Thus, effective elimination of organic dye (methylene blue) was carried out by poly(methyl methacrylate) (PMMA) incorporated metal oxide nanocomposites. Spherical and semi crystalline Fe3O4-PMMA, ZnO-PMMA, CuO-PMMA and Ni2O3-PMMA were self-assembled via green route employing Sapindus mukkorossi (Plant extract). At optimised conditions (dye conc: 2 mg L−1; catalyst: 80 mg: neutral pH) MO-PMMA showed maximum degradation efficiency (90–99%; t1/2 = 5.1–5.6 h) than that of individual MO (74–80%; t1/2 = 5.8–6.8 h) credited to improved thermal stability and surface area via incorporation of MO into PMMA matrix. Like MO, highest degradation with ZnO-PMMA (99%; Xm = 0.135 mg/g) followed by Ni2O3-PMMA (98%), CuO-PMMA (93%) and Fe3O4-PMMA (90%) could be attributed to its high surface area (85.32 m2 g−1) and least zeta potential (-22.5 eV). Adsorption of MB over catalyst was statistically significant with Langmuir isotherms (R2: 0.99 and p value: 0.0005) and first order kinetics with greatly reduced half-life. Comparatively higher degradation in sunlight than dark, and involving hydroxylation, oxidation and ring opening clearly reinforced boosted oxidation of MB by OH. Moreover, reduction in degradation (50-40%) in presence of OH scavengers supported the photocatalytic activity of nanocomposites. MB was degraded into minor non-toxic by-products such as (Z)-hexa-3,5-dien-1-ol and (Z)-buta-1,3-dien-1-ol and benzoquinone. Overall, by virtue of greater active sites, high surface activity and semiconducting nature, the as-synthesized MO-PMMA photocatalyst is a promising, recyclable (n = 10) and eco-friendly panorama in the treatment of organic- pollutants in water and wastewater-treatment.

Structural design of semiconductor nanomaterials via facile and green methodology is noteworthy to advance their photocatalytic activity for resolving the problem of energy and environment. Herein, sunlight active zinc oxide coupled with cadmium sulfide (ZnO@CdS) was synthesized by employing the leaf extract of Azadirachta indica. Subsequently, it was used for removal of chlorpyrifos (CP) and atrazine (Atz) pesticides that have shown high persistence, bioaccumulation, and toxicity in the environment. Synthesized ZnO@CdS nanocomposite was characterized by spectroscopic and microscopic techniques. The unique morphology of nanocomposite (particle size ≤ 50 nm) and appearance of stretching vibrations at 600 cm−1 for Zn-S and 679 cm−1 for Cd-O has confirmed the coupling of ZnO with CdS. The degradation conditions were optimized by varying the pesticide amounts, catalyst dose, and pH under the sunlight irradiation. At moderate dosage and neutral pH, the nanocomposite was found highly efficient for the quantitative removal of pesticides (89–91%) due to improved surface area (111 m2g−1), low band energy (1.67 eV), and semiconducting nature resulted from synergism. The degradation followed Langmuir adsorption and first order kinetics. The Effect of ionic strength was helpful to understand the interaction mechanism involved in the removal of contaminants. Being more effective than natives, ZnO@CdS has substantially suppressed the half-life of pesticides as revealed from generation of smaller and less toxic metabolites in GC–MS analysis. The charge separation was supported by photoluminescence and UV-reflectance studies. A scavenger analysis has indicated the presence of active radicals in photocatalysis. The Applicability of green or alternative photocatalyst for multiple times (n = 10) confirmed its sustainability and high efficiency for environmental and industrial purposes.

Release of colouring agents into the environment alarms the need to design a cheap, quick and safe process. Owing to environmental safety concern, synthesis of two metal hexacyanoferrates (MHCFs) based on cadmium (CdHCF) and manganese (MnHCF) was carried out using natural plant extract of Azadirachta indica and water as a solvent. Synthesized MHCFs were utilized for the removal of an acid dye (fuchsin acid, FA) and a xanthenes dye (rhodamine B, RB). The reactions were optimized at various conditions of dye concentration, catalyst dose, reaction pH, time and source of light. The MHCFs showed excellent results with both the dyes within very limited span of time (2 h). Consequently, 98% of FA and 97% of RB were degraded with 10 mg of CdHCF, at neutral pH and under sunlight. The degradation process followed the first-order reaction kinetics having t1/2 around 0.3 min. The MHCFs exhibited difference of only little percentage in degradation owing to a very slight difference between their surface areas (CdHCF: 54.1 m2 g−1; MnHCF: 49.7 m2 g−1). The synthesised nanocatalysts were stable as indicated by their higher negative zeta potential values. The adsorption of dyes was found to be maximum with CdHCF having Xm value 19.69 mg g−1 and 18.15 mg g−1 for FA and RB, respectively. Photocatalytic degradation involved the main role of hydroxyl radical as indicated by decline in activity of nanocatalyst in the presence of scavengers. All in all, this study presents highly active nanomaterials with higher surface area, stability and semiconducting properties under natural conditions.

Bimetallic metal oxide (BMO) are extremely useful heterogeneous and recoverable catalyst owing to improved semiconducting efficiency, cationic impurities and supports. Hence, their synthesis via ecofriendly green route based on biogenic sources (natural surfactant–water) is highly encouraging. Herein, three BMO nanoparticles, namely Ni-Cu oxide (NiCuO), Cu-Cr oxide (CuCr2O4) and Ni-Cr oxide (NiCrO3) were synthesized after employing Aegle marmelos leaf extract. Transmission electron microscopy analysis confirmed that highly crystalline BMO formed were below 50 nm with variable shapes, like nanorods of Ni-Cu oxide; nanospheres of Ni-Cr oxide and nanoflowers of Cu-Cr oxide. Successively, photocatalytic potential of BMO nanoparticles were evaluated for removal of various harmful phenols (phenol, 2, 4-dinitrophenol and 3-aminophenol) from simulated water. Under optimized conditions (phenol concentration: 1 × 10−4 M; catalyst dose: 15 mg; pH: ∼7.0), 3-aminophenol was supremely removed (97% Ni-Cu oxide > 95% Ni-Cr oxide > 92% Cu-Cr oxide) followed by phenol (95% Ni-Cu oxide > 92% Ni-Cr oxide > 89% Cu-Cr oxide) and 2,4-DNP (91% Ni-Cu oxide > 89% Ni-Cr oxide > 87% Cu-Cr oxide). Results seemed to appear in accordance of highest value of zeta potential, BET surface area and uniform distribution of Ni-Cu oxide. The maximum catalytic degradation of 3-aminophenol among other phenols was credited to its highest basicity. Minor and lesser-toxic metabolites like oxalic acid, benzoquinone, (Z)-hex-3-enedioic acid, (Z)-but-2-enal, (Z)-4-oxobut-2-enoic acid were identified, later undergo mineralization. Overall, green synthesized BMO nanocomposites are cheap, reusable (n = 10) with properties of greater active sites, high surface activity, low band gap with charge separation and semiconducting nature and recommended for bright future of environment.

Chrysene is a high molecular weight polycyclic aromatic hydrocarbon and priority pollutant due to its persistent nature and toxicity. Ecological concern of this emerging contaminant calls for low-cost and efficient removal practices. Recently, doped or coupled nanomaterials with advanced characteristics are fascinating. Therefore, we have synthesized crystalline nanocubes (∼100 nm) of Fe2O3@ZnHCF nanocomposite using plant extract of Azadirachta indica and subsequently used it for degradation of chrysene. Under sunlight, a rapid initial exponential decrease in concentration of chrysene over time revealed high photo-activity of doped Fe2O3@ZnHCF because of remarkably improved surface area (343.436 m2 g−1) and band gap energy (2.18 eV). At optimum catalyst dose (25 mg) and neutral pH photodegradation of chrysene (2 mg L−1) up to 92% followed first order kinetics and Langmuir isotherms. Comparing with constituents, doped nanocubes (Xm = 45.45 mg g−1) were more effective for degradation as revealed by three to six times greater adsorption of chrysene than ZnHCF (Xm = 16.22 mg g−1) and Fe2O3 (Xm = 7.348 mg g−1). Moreover, it reduced the t1/2 value of chrysene (0.54 h) manifolds than that of Fe2O3 (t1/2 = 23.41 h) and ZnHCF (t1/2 = 8.66 h) nanoparticles. GC–MS results revealed the presence of smaller and safer by-products like malealdehyde, propionic acid and but-2-ene-1,2,4-triol that are formed by oxidation of chrysene by OH radical. Catalysts were also found reusable for ten cycles without significant loss in activity. Overall, Fe2O3@ZnHCF nanocubes might be believed to be a promising photocatalyst for environmental protection by virtue of greater active sites, high surface activity, low band gap with charge separation and semiconducting nature.

The low-cost and highly efficient pesticides are largely used in residential, agricultural, and commercial applications. Their prevalent occurrence, bioaccumulation, and chronic toxicity to living beings have raised environmental concern and call for their whole eradication, especially from water. By virtue of semiconducting nature and high surface area, nanomaterials have become efficient adsorbent and photocatalyst in removal of toxins. To confirm this, the potential of highly crystalline metal hexacyanoferrates (MHCFs) of Zn, Cu, Co, and Ni was evaluated in deprivation of selected hazardous pesticides, viz., chlorpyrifos (CP), thiamethoxam (TH), and tebuconazole (TEB). Sharp nanocubes of ZnHCF (~ 100 nm), distorted nanocubes of CuHCF (~ 100 nm), and nanospheres of CoHCF and NiHCF (

Organophosphorus pesticides are most popular and broadly used owing to high-efficiency and organochlorines have longer persistence and irregular use in developing countries. The potential of bioaccumulation and persistence coupled with their toxicity call for development of effective low-cost elimination methods Prussian blue (Iron hexacyanoferrate; FeHCF) and its analogues have been widely employed in several applications due to outstanding characteristics (high surface area and photo-induced properties). Hence, highly crystalline and sharp hexagonal nanorods ( OH) based oxidation of pesticides. Besides, FeHCF catalyst (with low band gap) can be easily photo-activated. Overall, greater active sites, high surface activity, low band gap and semiconducting nature of FeHCF make it promising photocatalyst for waste-water-treatment.

Aromatic amines (AA) are a group of industrial and environmental pollutants with high thermodynamic stability and carcinogenicity. Their toxicity has raised concern worldwide and calls for the development of effective elimination methods based on nanomaterials. Recently, the high adsorbing and photocatalytic efficiency of widely used metal hexacyanoferrates was observed. To confirm this, potential of potassium zinc hexacyanoferrate (ZnHCF) and potassium copper hexacyanoferrate (CuHCF) were evaluated in remediation of simulated water containing selected hazardous AAs. Highly crystralline and sharp nanocubes of ZnHCF (∼50 nm) and distorted nanocubes of CuHCF (∼100 nm) were synthesized via green route using sapindus mukorossi (raw ritha) as a biosurfactant. Under optimized conditions—concentration of amine(1.0 × 10 −4 M), catalyst (25 mg) and neutral pH, ZnHCF was found better with maximum degradation efficiency (90% of p-anisidine, 76% of p-toluidine, 71% of aniline and 70% of p-chloroaniline) followed by CuHCF (88%, 72%, 69% and 64%, respectively). This might be because of its higher zeta potential and BET surface area of ZnHCF. The highest adsorption (%) of p-anisidine on acidic surface of catalysts is probably due to its highest basicity. Statistical treatment of data fitted to various adsorption isotherms indicated the monolayer adsorption of AAs over surface of catalyst i.e., Langmuir with highest regression coefficient values (R 2 more than 0.98 for all AAs). GC–MS analysis confirmed the formation of small, non-toxic by-products such as benzoquinone, hydroquinone, but-2-enal, 4-oxobut-2-enoic acid and malealdehyde. The potential of MHCF nanoparticles can be explored more effectively in removal of organic pollutants for solving the water pollution problems.

Expanded polystyrene (EPS) is a major component of marine debris globally. Recently, hazardous hexabromocyclododecanes (HBCDDs) were detected in EPS buoys used for aquaculture farming. Subsequently, enrichment of HBCDDs was found in nearby marine sediments and mussels growing on EPS buoys. It was suspected that EPS buoys and their debris might be sources of HBCDDs. To confirm this, the release of HBCDDs from EPS spherules detached from a buoy to seawater was investigated under field (open sea surface and closed outdoor chambers with sun exposure and in the dark) and laboratory (particle-size) conditions. In all exposure groups, initial rapid leaching of HBCDDs was followed by slow desorption over time. Abundant release of HBCDDs was observed from EPS spherules exposed to the open sea surface (natural) and on exposure to sunlight irradiation or in the dark in controlled saline water. Water leaching and UV-light/temperature along with possibly biodegradation were responsible for about 37% and 12% of HBCDDs flux, respectively. Crumbled EPS particles (≤1 mm) in samples deployed on the sea surface for 6 months showed a high degree of weathering. This implies that surface erosion and further fragmentation of EPS via environmental weathering could enhance the leaching of HBCDDs from the surface of EPS. Overall, in the marine environment, HBCDDs could be released to a great extent from EPS products and their debris due to the cumulative effects of the movement of large volumes of water (dilution), biodegradation, UV-light/temperature, wave action (shaking), salinity and further fragmentation of EPS spherules.

Rapid industrialization and extensive use of pesticides in agriculture practices have contributed to the leaking of pesticide residues into water. Among them, organochlorines are highly toxic with half-lives of many years followed by organophosphates (OPs). Being banned in many countries, most of the pesticides are still persisting in the environment. Due to high perseverance, toxicity and potential to bioaccumulation, their removal is imperative. In this direction, conventional adsorbents such as commercial activated carbon, agricultural and natural waste were highly employed. In modern era, nanomaterials (including nanocomposites and nanobiocomposite) with high surface area come out as most economic, rapid and effective catalyst. TiO2 (photocatalyst) and Fe0 by itself or with oxidizing agents are playing a promising role in elimination of pesticide pollution and open the opportunities for exploring other nanoparticles as well. Further, their modified, doped or composites form showed enhanced characteristics due to introduction of new energy levels or increase in surface area. In contrast to TiO2 and Fe0, various nanostructured metal oxides found to degrade OP pesticides by rapid reactive adsorption followed by cleavage of P–O bond via SN2 mechanism. The present review focuses on the present status of pesticide removal using nanoparticles through adsorption together with photocatalytic or redox or reactive degradation. Herein, detailed information on several pesticides, problems related to pesticide, their metabolites, environmental concentration and need for degradation has been presented. In addition, importance of green synthesized nanoparticles along with limitation and potential health risk of nanomaterials in degradation of various organic pollutants has been highlighted.

The green synthesis of nanomaterials has gained great attention in the recent times. These methods are not only ecofriendly but also efficient and safer. Iron hexacyanoferrates (FeHCF) are widely used in various applications because of several properties such as ion-exchanging, photomagnetic, electrochromic etc. Hence, their large-scale-synthesis via green routes is the need of present time. Herein we have reported green synthesis of using sapindus-mukorossi as natural surfactant and water as solvent. TEM analysis revealed the formation of FeHCFs nanoparticles (size range:10–60 nm) of hexagonal, rod and spherical shape. Finally, the potential of synthesized FeHCF nanoparticles were investigated for photo-catalytic degradation of hazardous PAHs (anthracene, phenanthrene, chrysene, fluorene, and benzo (a) pyrene) in water as well as soil. Under optimized conditions (PAHs: 50 mg L−1, catalyst dose: 25 mg, neutral pH and solar irradiation), almost all treated PAHs were transformed to smaller non-toxic byproducts. The formation of small and non-toxic metabolites has been confirmed by GC–MS analysis. Anthracene and its isomer named phenanthrene, were degraded to maximum extent of 80 to 90% in both water and soil whereas, the degradation of fluorene, chrysene and benzo (a) pyrene were ∼70-80%. Overall, FeHCFs nanoparticles found as excellent adsorbents and photocatalysts for the degradation of persistent organic pollutants. The advantage of present work lies in its quick approach for green synthesis of low-cost and efficient catalyst along with ability to fabricate almost uniformly distributed nanoparticles and their application in making our environment green.

There is about 700,000 tonnes of dyes, of more than 10,000 types, that are used as coloring agents in industries, mainly for textile. The release of dyes in natural media is of concern due to their high persistence, toxicity and potential to the bioaccumulate in living organisms. In particular, the most commercialized and carcinogenic azo dyes, that pocess a benzidine function, needs urgent attention. Here, we review the current status of cationic and anionic dyes. We present dye removal techniques using nanoparticles through adsorption and degradation. Among dye removal techniques, adsorption was found the most efficient and cheap. For that, conventional adsorbents such as commercial activated carbon, chitosan and natural waste are often employed. We discuss the use of ZnO, TiO2 and Fe0 to remove dye pollution.

Recently, nanoparticle-based immobilization of biocatalytic systems is getting interested in bioremediation efficiency. Therefore, green synthesized ZnO (

This study reports the distribution of Cr, Ni, Cu and Pb in waters, sediments, macrophytes and fish of the Yamuna River’s patch in Delhi (India). This is one of the most polluted stretches of rivers in the world. Water from this river is used fosr irrigation, industrial and domestic purposes, including drinking water. The effects of season and anthropogenic practices were identified. Almost zero dissolved oxygen and high levels of lead and phosphate indicate the polluted state of the aquatic system. The enrichment factors in sediments (with respect to reference site) vary in the range of 0.60–82.9% (Cr), 1.40–90.5% (Ni), 1.00–85.3% (Cu) and 3.80–86.6% (Pb). The toxic effects due to Ni and Pb could frequently be visible in aquatic life as their values fall above the probable effect level (36 mg Kg−1 for Ni and 91.3 mg Kg−1 for Pb). The metal contents in the macrophyte (Eichhornia crassipes) and the fish (Oreochromis niloticus) generally increase in the summer season. Cu and Pb accumulate preferenti...

Chromium (VI) is a major water pollutant and suspected carcinogen with high persistence. Therefore, advance and fast processes based on low-cost and highly proficient nanomaterials are required for its elimination. Herein, nickel oxide-decorated zinc hexacyanocobaltate framework (NiO@ZnHCC) was synthesized by green method and subsequently, evaluated as photocatalyst for removal of Cr (VI) from synthetic wastewater. Various parameters were optimized in simulated water consisting of variable amounts of Cr(VI) (50–250 mg L−1) and catalyst dose (5–25 mg) at different pH (4–9)under sunlight exposure for 5 h. Highly crystalline nanocomposite (particle size range: 50–100 nm) consisting of NiO wrapped ZnHCC cubes piled together was confirmed by spectroscopic and microscopic analysis. At optimum catalytic dose (15 mg) and neutral pH, sharp decline in 50 mg L−1of Cr (VI) to Cr (III)was visually confirmed by colour change from orange to green. Highest removal (92%) of Cr (VI) by NiO@ZnHCCnanocomposite (Langmuir Xm= 39 mg g−1) followed first order kinetics and indicated its greater efficiency as compared to individuals (NiO: 79% and ZnHCC: 86%). This might be due to improved surface area (78.9 m2 g−1), low band energy (2.1 eV) and semiconducting nature resulted from synergism of NiO (32.4 m2 g−1; 3.6 eV) and ZnHCC (38.9 m2 g−1; 2.3 eV). Moreover, NiO@ZnHCC reduced the half-life of Cr(VI) up to 1.1 h than that with ZnHCC (2.3 h) and NiO (3 h). Photo-catalytic reduction was probed using radical-scavenger analysis. Charge separation mechanism was supported by photoluminescence and UV reflectance studies. Overall, due to greater surface activity, stability, reusability up to ten-cycles and charge separation (e-+h+ pairs) led to promotion of huge free radicals, NiO@ZnHCC might be supposed as promising photocatalyst for industrial applications with bright future.

Nonylphenol (NP) and 2,4-dinitrophenol (2,4-DNP) are causing serious environmental concerns owing to their toxic, carcinogenic, persistentancy and bio-accumulating properties. It has been found that their concentrations are abundant near to industries and in many water bodies due to untreated release. Therefore, their complete removals using low-cost, efficient and environmental friendly techniques from water are required. Sunlight active metal hexacyanocobaltates nanoparticles have been reported beneficial heterogeneous and recoverable catalysts. Therefore, a green route based on utilization of natural material (Azadirachta indica leaf extract) and water was developed for the synthesis of cadmium hexacynocobaltate (CdHCC) and manganese hexacyanocobaltate (MnHCC) nanoparticles. Electron microscopic analysis revealed nanometer range (∼100 nm) for CdHCC and MnHCC particles. Synthesized nanomaterials were employed for the degradation of substituted phenols under direct Sunlight to follow the natural scenario. Maximum degradation of selected phenols (CdHCC- NP: 70 %; 2,4-DNP: 77 %, MnHCC- NP: 90 %; 2,4-DNP: 97 %) required 25 mg of catalyst per 50 mg L−1 of phenols at neutral pH under Sunlight irradiation. This excellent photocatalytic activity of the MnHCC might be due to high surface activity (surface areas of CdHCC and MnHCC were 95 m2 g-1 and 448 m2 g-1, respectively) and particles stability (as observed from zeta potential, CdHCF: -13.5 mV; MnHCF: -19.2 mV). The degradations followed first-order kinetics. Adsorption plots were best fitted with Langmuir isotherm. GC–MS analysis of the final reaction mixtures showed the formation of low molecular weight and safer compounds, which were finally mineralized. Degradation mechanism of NP and 2,4-DNP involved OH radicals based oxidation, hydroxylation, and ring-opening. These materials were found reusable up to ten times revealing sustainability. Overall, these Sunlight responsive novel metal hexacyanocobaltate nanomaterials might be promising and sustainable materials for remediation of environmental contaminants.

Transition metal oxides (TMO) constitute a most amazing class of materials with a wide range of properties and applications; therefore, their synthesis using a green approach is a necessity. As such, sunlight irradiation was employed to synthesize various TMO nanostructures (ZnO, CuO, Co3O4, NiO and Cr2O3) using water as a solvent. Nanoparticles obtained with distinct morphologies, such as nanotubes (ZnO; 86.86% (CuO) > 85.89% (NiO) > 80.35% (Co3O4), depending on the sizes of the respective TMO nanoparticles. This is also supported by the finding of small and non-toxic by-products such as but-2-enal, sulfur trioxide and benzoquinone. With high potential observed in the removal of dyes, TMO nanoparticles have a bright future with respect to their use as important adsorbents in waste water treatment. The advantage of the present work lies in the green synthesis of nanoparticles and their application in helping to make our environment green.

Aromatic phenols, found in various industrial effluents, are categorized as priority pollutants and seeking attention owing to their life threatening effects. In present study, nanocomposite of zinc oxide coupled with prussian blue (ZnO@FeHCF) was synthesized by green method using Azadirachta indica leaf extract. Nanocomposite was characterized by relevant techniques and found crystalline as well as nanosized. Fabricated nanocomposite was employed for the eradication of various phenols under Sunlight. Photocatalytic degradation of phenol, 3-aminophenol (3-AP) and 2,4-dinitrophenol (2,4-DNP) was performed at different parameters of pollutant-concentration, catalyst-amount, pH, contact-time and exposure of Sunlight. Obtained results showed the maximum removal of 3-AP (97%) followed by phenol (95%) and 2,4-DNP (93%) that is attributed to their basicity differences. Compared to ZnO and FeHCF, the nanocomposite was found more effective in degrading the phenols and lowered the t1/2 value of 3-AP (4.04 h), phenol (4.405 h) and 2,4-DNP (4.68 h) to a greater-extent. Effect of different foreign-anions was also studied to verify nanocomposite’s efficiency under natural conditions. Better photocatalytic activity of the nanocomposite as compared to ZnO and FeHCF might be due to longer-life-span of charge-carriers as revealed by photoluminescence study. Mechanism of the photocatalysis was investigated by using radical-scavenger to understand the steps involved in removal process. It was found that OH was the main species promoting the degradation of phenols. Sunlight active nanocomposite found to show excellent catalytic reusability up to 10 cycles. Overall, green synthesized nanocomposite is cheap, reusable, high-surface-activity, low band gap with charge separation recommended for bright future of environment.

Bisphenol-A (BPA) is an alleged endocrine-disrupter and carcinogen compound. Due to this, complete removal of BPA from environment is highly imperative to protect living organisms. Metallic ferrites have been proven with excellent properties and efficiency in various commercial applications. Therefore, crystalline nanoparticles of size less than 50 nm, of cobalt (CoFe2O4) and zinc (ZnFe2O4) ferrites were fabricated employing leaf-extract of Azarachita indica and water. Both ferrites (20 mg) were found effective in Sunlight assisted photocatalytic removal of 50 mg L−1 of toxic BPA from water at neutral pH. Nanoparticles of ZnFe2O4 showed highest efficiency (92%) followed by CoFe2O4 (89%) than bared ones like Fe2O3 (70%), ZnO (68%) and Co3O4 (54%). Results obtained were in good agreement with uppermost BET surface-area and Zeta-potential value, of uniformly distributed nanoparticles of two ferrites. Calculated band gap energies of ZnFe2O 4 and CoFe2O 4 were, 2.14 eV and 2.42 eV, respectively. GC–MS analysis of reaction mixture revealed the formation of minor and non-toxic metabolites (mass below 100) that finally undergo mineralization. Proposed degradation pathways revealed the role of hydroxyl radical that led to subsequent oxidation and hydrolysis of the BPA. Total organic carbons and scavenger analysis indicated the 58% mineralization after 5 h and involvement of free radical mechanism under direct sunlight. Overall, green synthesized ferrites were found remarkable photocatalysts and reusable (n = 10) with significant retain of activity. Furthermore, such ferrites nanoparticles may be recommended for further treatment of noxious contaminants in view of their large surface area, high charge separation capacity.

Polycyclic-aromatic-hydrocarbons (PAHs) have been categorized as priority-pollutants due to their mutagenic, persistence and proven carcinogenicity. Owing to omnipresence and toxicity of PAHs and derivatives, their complete removal is highly-imperative. Therefore, iron-oxide based chitosan-nanocomposites mediated photo-oxidative degradation of toxic prototype PAHs such as anthracene (ANTH) and phenanthrene (PHEN) was explored. Such nanocomposites of distinct morphologies were synthesized via green route employing Azadirachta-indica as natural surfactant in aqueous medium. Synthesized materials showed excellent photocatalytic efficiency in exponential decay of ANTH and PHEN with time (12 h) under direct sunlight. At neutral pH, photodegradation of PAHs (2 mgL−1) by nanocomposites (20 mg) followed Ist order kinetics and Langmuir model (R2: 0.99; p value OH, h+ and ˙O2- active species in the oxidation of selected PAHs. Overall, present study provides an alternative insight on preparing effective, green, reusable (n = 10), stable nanocomposites for the removal of carcinogenic PAHs.

Bisphenol-A (BPA) is suspected of been endocrine-disrupter and carcinogen. Hence, removal of extensively used BPA by low-cost and efficient coupled-nanomaterials is viewed as vital to environmental protection. Herein, nanocomposite of ZnO doped with zinc-hexacyanoferrate (ZnO@ZnHCF) was employed for photodegradation of BPA. Green synthesized nanocomposite consisted of ZnO wrapped ZnHCF distorted nanocubes piled together. Under daylight, prompt early exponential decline in concentration over time revealed elevated photo-activity of nanocomposite. Improvement in surface-area (113.491 m2g−1) and band-gap (2.2 eV) of catalyst was resulted from synergism of semiconducting and intercalative feature of ZnO and ZnHCF. At optimum catalyst-dose (25 mg) and neutral pH, photodegradation of BPA (97% of 2 mgL−1) followed first-order-kinetics involving initial Langmuir adsorption isotherms (R2 ≥ 0.996; p ≤ 0.05). Nanocomposites were more effective for greater adsorption of BPA (Xm = 18.0 mg g−1) than the ZnHCF (10.8 mg g−1) and ZnO (3.9 mg g−1). Moreover, doped ZnO@ZnHCF reduced the half-life of BPA upto 2.8 h than that with bared ZnHCF (8 h) and ZnO (17.4 h). GC–MS revealed presence of smaller and safer byproducts clearly supported electron excitement from wrapped-nanocomposite followed by oxidation of BPA with countless OH. Degradation pathways were constructed to track-ways leading to mineralization. Overall, due to greater surface-activity, reusability upto ten-cycles and charge separation (e−+h+ pairs) led to promotion of huge free radicals, ZnO@ZnHCF might be supposed a promising photocatalyst.

Aromatic substituted phenols and their by-products discharged from numerous industries are of environmental concern due to their toxic, carcinogenic, recalcitrant, and bioaccumulating properties. Therefore, their complete removal from waters by low-cost, efficient, environmentally friendly nanomaterial-based treatment techniques is desirable. Double metal cyanide complexes (DMCC) are the extremely useful heterogeneous and recoverable catalyst. Hence, green route has been developed for several DMCC and their photocatalytic efficiency was evaluated for degradation of toxic phenols. Herein, nanocubes for hexacyanocobaltate of iron (FeHCC ~ 200 nm), nickel (NiHCC 94% FeHCC > 93% NiHCC) > phenol (94% ZnHCC > 92% FeHCC > 91% NiHCC) > 2,4-DNP (92% ZnHCC > 91% FeHCC > 90% NiHCC). This is attributed to highest basicity of 3-aminophenol containing excess of free electrons. Highest catalytic potential of ZnHCC (Xm = 0.54–0.43 mg/g) is because of its highest surface area and negative zeta potential along with sharp morphology and crystallinity. Adsorption of phenols over catalyst was statistically significant with Langmuir isotherms (R2 ≥ 0.96; p value ≤ 0.05). Small and non-toxic by-products like oxalic acid, benzoquinone, (Z)-hex-3-enedioic acid, (Z)-but-2-enal, and (Z)-4-oxobut-2-enoic acid were identified in GC-MS. Degradation modes involving hydroxylation, oxidative skeletal rearrangement, and ring opening clearly supported enhanced oxidation of phenols by •OH. Overall, due to greater active sites, high surface activity, low band gap, and semiconducting nature, DMCC revealed promising potential for solar photocatalytic remediation of wastewater.

Polycyclic aromatic hydrocarbons (PAHs) the ubiquitous, persistent and carcinogenic environmental contaminants have raised concern worldwide. Recently, their removal methodologies are advanced after exploring nanomaterials. Therefore, degradation of selected toxic PAHs (3–5 rings) using potassium zinc hexacyanoferrate (KZnHCF) nanocubes was studied. Highly crystalline and sharp KZnHCF nanocubes (∼100 nm) were obtained by green route using sapindus mukorossi. In both water and soil, anthracene and phenanthrene were degraded to maximum extent (80–93%), whereas, the degradation of fluorene, chrysene and benzo (a) pyrene were ∼70–80%.Because of small size (lower molecular weight), large number of anthracene and phenanthrene molecules were adsorbed on catalyst as compared to other PAHs. Higher degradation of PAHs in water than in the soil is attributed to the easy absorption of PAHs on catalyst in water and slow diffusion of PAHs on organic content of soil. PAHs were degraded at the concentration of 50 mg/L, 25 mg catalyst dose, neutral pH and solar irradiation. Higher proficiency of the catalyst was revealed by degradation of PAHs into small and non-toxic by-products such as malealdehyde, 4-oxobut-2-enoic acid and o-xylene. Overall, the potential KZnHCF nanostructures open future scope for eradication of other pollutants from the environment.

The role of marine plastic debris and microplastics as a carrier of hazardous chemicals in the marine environment is an emerging issue. This study investigated expanded polystyrene (EPS, commonly known as styrofoam) debris, which is a common marine debris item worldwide, and its additive chemical, hexabromocyclododecane (HBCD). To obtain a better understanding of chemical dispersion via EPS pollution in the marine environment, intensive monitoring of HBCD levels in EPS debris and microplastics was conducted in South Korea, where EPS is the predominant marine debris originate mainly from fishing and aquaculture buoys. At the same time, EPS debris were collected from 12 other countries in the Asia-Pacific region, and HBCD concentrations were measured. HBCD was detected extensively in EPS buoy debris and EPS microplastics stranded along the Korean coasts, which might be related to the detection of a quantity of HBCD in non-flame-retardant EPS bead (raw material). The wide detection of the flame retardant in sea-floating buoys, and the recycling of high-HBCD-containing EPS waste inside large buoys highlight the need for proper guidelines for the production and use of EPS raw materials, and the recycling of EPS waste. HBCD was also abundantly detected in EPS debris collected from the Asia-Pacific coastal region, indicating that HBCD contamination via EPS debris is a common environmental issue worldwide. Suspected tsunami debris from Alaskan beaches indicated that EPS debris has the potential for long-range transport in the ocean, accompanying the movement of hazardous chemicals. The results of this study indicate that EPS debris can be a source of HBCD in marine environments and marine food web.

Polycyclic aromatic hydrocarbons (PAHs), pervasive and precedence pollutants have potential to decimate the bionetwork and human health. Therefore, photocatalytic degradation of toxic three membered PAHs, namely acenaphthene (ACN), phenanthrene (PHN) and fluorene (FLU) was explored in water and soil. Titanium dioxide based zinc hexacyanoferrate framework (TiO2@ZnHCF) nanocomposite was synthesized via a two step A. indica mediated co-precipitation method. Under sunlight, fall in concentration of PAHs (Water- 93%–96%, soil- 82%–86% and river sediment- 81.63%–85.43%) with time revealed superior activity of nanocomposite (TiO2@ZnHCF) as compared to the bared one. Slower degradation in soil and sediment could be attributed to the reduced diffusion caused by the interaction between the organic content of soil/sediment with PAHs. Doping caused an increase in surface area (118.15 m2g-1) with decrease in band gap energy (1.65 eV) and photoluminescence intensity. PAHs removal (Xm = 9.48 mg g−1 of ACN, 9.35 mg g−1 of PHN and 8.96 mg g−1 of FLU) involved role of “cation- π” interaction with nanocomposite. Besides, it reduced t1/2 values of ACN (1.88 h), PHN (2.09 h) and FLU (2.86 h) and resulted into smaller by-products. Smaller by-products like (Z)-prop-1-ene-1,2,3-triol (m/z = 91) and (E)-3-hydroxyacrylaldehyde (m/z = 71) identified in GC–MS, evidently braced e− excitement from encapsulated nanocatalyst followed by OH (active species) based oxidation of PAHs. Lower photoluminescence intensity indicates the least charge carrier recombination with highest photocatalytic activity of nanocomposites. Inclusive of the present study provides promising photocatalyst with greater surface activity, low quantum yield with charge separation, reusable up to ten cycles deprived of substantial loss of its action and suppressing the cost of process.

Polycyclic aromatic hydrocarbons (PAHs), pervasive plus priority emerging pollutants have the potential to destruct the bionetwork. Therefore, photocatalytic decay of toxic 4- and 5-ring membered PAHs, namely benz[a]anthracene (BaA) and benzo[a]pyrene (BaP), was explored in water. The nanocomposite of zinc hexacyanoferrate encapsulated with zinc oxide (ZnHCF@ZnO) was synthesized by Azadirachta indica mediated co-precipitation under normal conditions. Sunlight exposure caused a quick downfall in the concentration of PAH with composite exposing its eminent photo-activity. Encapsulation resulted in enhanced surface area (113 m2 g−1) and lesser band gap energy (2.2 eV) of nanocomposite owing to the synergism of semiconducting stuff of zinc oxide and intercalative properties of ZnHCF. At neutral pH, photo-degradation of PAHs (2 mg L−1) by optimum dose of catalyst followed first order kinetics and Langmuir isotherms (R2≥0.98; p ≤ 0.05). Slightly lower elimination of BaP (90%) than BaA (93%) might be due to its higher molecular weight and conjugation. Mechanism exploration revealed the involvement of “cation- π” interaction effectively between nanocomposite and PAHs (Xm =25.6 mg/g of BaA and 21.7 mg/g of BaP) than bared (ZnO and ZnHCF). Besides, it compacts the t1/2 value of BaA(0.35 h) and BaP (0.49 h) up to manifolds than its constituents (13–26 h). Smaller by-products like prop-2-en-1-ol, propionic acid and acrylic acid identified in GC MS, clearly supported electron excitement from encapsulated nanocomposite followed by OH (active species)based oxidation of PAHs. Particularly, the mineralization evaluation of PAHs through TOC analysis confirmed its conversion into H2O and CO2. Inclusive of the present study provides promising photo-catalyst with greater surface activity, low quantum yield with charge separation and reusable for ten cycles deprived of substantial loss of its action. Similar studies can be promoted to build up methods that can accurately predict the acceleration in the environment clean up strategies.

Endocrine phenols (EPs), cytotoxic, genotoxic and persistent pollutants have been found in most environmental monitoring. Therefore, photodegradation of these EPs, namely bisphenol a (BPA) and nonylphenol (NP) was explored in water. Nanocomposite of iron hexacyanoferrate encapsulated with zinc oxide (ZnO@FeHCF) was synthesized by natural plant extract A. indica mediated co-precipitation method. The nanocomposite (100 nm) had thin flakes like morphology with irregular surface comprising ZnO nanoflowers over it. The sharp peaks obtained in the PXRD ensure its higher crystallinity and purity. Fall in concentration of EPs followed exponential decay with time revealing superior activity of nanocomposite. Coupling caused an increase in surface area (80 m2 g−1) along with lesser band gap energy (1.1 eV) of nanocomposite. Photodegradation of EPs (2 mg L−1) by optimum dosage of catalyst followed first order kinetics and langmuir isotherms at neutral pH. Slightly lower elimination of NP (91%) than BPA (94%) might be due to its complex structure. Comparative to bare nanoparticles, ZnO@FeHCF were found more effective in EPs adsorption and degradation (Xm = 7.61 mg g−1 of BPA and 7.05 mg g−1 of NP) involving “cation- π” interaction between nanocomposite and EPs. Further, half life was reduced to BPA (2.47 h) and NP (2.60 h) better than its constituents. Lower photoluminescence intensity indicates the least charge carrier recombination in nanocomposite. The properties of nanocomposite include large surface area, higher surface activity, and lower band gap energy having least charges recombination tendency make it a highly efficient nanocatalyst for further treatment of hazardous pollutants.

Organochlorines (OCs) are the most hazardous class of pesticides, therefore, banned or restricted in several countries. The major sources of OCs include food industries, agriculture and sewage wastes. Their effluents discharged into the water bodies contain extremely high concentration of OCs which ultimately causes environmental concern. Because of their high persistence, toxicity and potential to bioaccumulation, their removal from wastewater is imperative. The degradation techniques are now advanced using nanomaterials of various kinds. During the last few years, nanoparticles such as TiO2 and Fe are found to be excellent adsorbents and efficient photocatalysts for degrading more or less whole OCs as well as their toxic metabolites, which opens the opportunities for exploring various other nanoparticles as well. It is noteworthy that such methodologies are economic, fast and very efficient. In this review, the detailed information on different types of OC pesticides, their metabolites, environmental concern and present status on degradation methods using nanoparticles have been reviewed. An attempt has also been made to highlight the research gaps prevailing in the current research area.