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The application of green synthesized nanocomposites for the prevention of environmental pollution is increasing nowadays. Here, a green composite has been synthesized by embedding MnO2 on Rauvolfia tetraphylla leaves using its leaf extract hereinafter termed as MnO2@RTL, and demonstrated for crystal violet (CV) dye removal from simulated and real wastewater. The surface properties of the material were determined by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDX), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), and Brunauer-Emmet-Teller (BET) surface area, pHZPC, and zeta potential. The material exhibits a remarkable adsorption capacity of 61.162 mg/g at 328 K and pH 7. The adsorption was best fitted with Pseudo-second-order kinetic (R2 = 0.998) and a combination of Langmuir and Freundlich isotherm model (R2 = 0.994–0.999). The thermodynamic study revealed spontaneous (ΔG values = − 2.988 to − 4.978 kJ/mol) and endothermic (ΔH values = 6.830 to 11.018 kJ/mol) adsorption. After adsorption, 80% regeneration occurred with 50% methanol, and recycled up to five times. Advantageously, the material was able to remove CV dye in the presence of coexistent ions and from industrial wastewater, confirming field applicability. The adsorption capacity of the material is superior to previously reported materials. The standard deviation and relative standard deviations have been evaluated to be 0.000422–0.000667 and 0.473–0.749%, which suggests the reliability of the experiments. The exhausted material, after recycling, was pyrolyzed to overcome the disposal problem. It was established as a secondary adsorbent with 73% efficiency which makes the material win–win. The material showed antibacterial properties with Staphylococcus aureus bacteria with a zone of inhibition 5 mm. [ABSTRACT FROM AUTHOR]

Herein, we are reporting the carbon nano onions (CNO)-based sulphonated poly(ethersulfone) (SPES) composite membranes by varying CNO content in SPES matrix for water desalination applications. CNOs were cost-effectively synthesized using flaxseed oil as a carbon source in an energy efficient flame pyrolysis process. The physico- and electrochemical properties of nanocomposite membranes were evaluated and compared to pristine SPES. Moreover, the chemical characterisation of composite membranes and CNOs were illustrated using techniques such as nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), thermogravimetric analysis (TGA) and universal tensile machine (UTM). In the series of nanocomposite membranes, SPES-0.25 composite membrane displayed the highest water uptake (WU), ion exchange membrane (IEC) and ionic conductivity (IC) values that were enhanced by 9.25%, ~ 44.78% and ~ 6.10%, respectively, compared to pristine SPES membrane. The electrodialytic performance can be achieved maximum when membranes possess low power consumption (PC) and high energy efficiency (Ee). Therefore, the value of Ee and Pc for SPES-0.25 membrane has been determined to be 99.01 ± 0.97% and 0.92 ± 0.01 kWh kg−1, which are 1.12 and 1.11 times higher than the pristine SPES membrane. Hence, integrating CNO nanoparticles into the SPES matrix enhanced the ion-conducting channels. [ABSTRACT FROM AUTHOR]

The perception of spatio-temporal variability of winter precipitation covering dominant water resources and environment over Kashmir Himalaya is a pre-eminent perspective under current social interests. The main objectives of the study are, firstly, to unriddle the whole (1980–2020) and post-2000 trend in the winter season precipitation (WP), frequency of low-pressure systems (Lp-S), and western disturbances (WDs) to understand the footprints of climate change over the region; secondly, to evaluate the spatio-temporal variability of winter precipitation under the dominance of global teleconnection indices, using both station and reanalysis datasets. Modified Mann-Kendell test and a linear regression model were utilized to extract the trend and significance in WP, Lp-S, and WDs. The results reveal that WP shows an insignificant decreasing trend (1980–2020), with an increasing trend post-2000, while a decreasing trend is seen during post-2000 in the frequency of Lp-S and WDs. The contribution of WP to annual precipitation shows decadal variability with a decreasing trend post-2000. The anatomy of winter extreme precipitation days has shown a decreasing trend (1980–2020), with a robust coupled increasing trend with WP post-2000. The dynamics of ten severe WD-based extreme precipitation events show that a cyclonic circulation and trough connects the Arabian Sea and the Himalayas, bringing additional moisture to the study region and resulting in extreme precipitation. The cogency of global teleconnections on the variability of WP shows that a pattern with positive phase of NAO, ENSO, and a negative phase in Siberian high intensifies the WD-based precipitation. The study discovers its applicability for the regional forecast system in predicting the winters. [ABSTRACT FROM AUTHOR]

The rapid growth of carbon dioxide (CO2) emissions raises concern about the possible consequences of atmospheric CO2 increase, such as global warming and greenhouse effect. Photocatalytic CO2 conversion has attracted researchers' interests to find a sustainable route for its elimination. In the present study, a direct Z-scheme TiO2/g-C3N4 composite (T-GCN) was fabricated via a facile hydrothermal route for the photocatalytic reduction of CO2 into methane (CH4) and methanol (CH3OH), under visible light irradiation without an electron mediator. The microstructure of the as-obtained TiO2/g-C3N4 nanocomposites was fully characterized for its physicochemical, structural, charge separation, electronic, and photo-excited carrier separation properties. The effect of CO2 and H2O partial pressure was studied to find the best operational conditions for obtaining maximum photocatalytic efficiency; the PCO2 and PH2O were 75.8 and 15.5 kPa, respectively, whereas, by increasing the light intensity from 20 to 80 mW/cm2, a remarkable improvement in the reduction rate takes place (from 11.04 to 32.49 μmol.gcat−1.h−1 methane production, respectively). Finally, under the most favorable light, PCO2 and PH2O conditions, high methanol and methane rates were obtained from the CO2 photocatalytic reduction through T-GCN (1.44 μmol.gcat.−1.h−1 and 32.49 μmol.gcat.−1.h−1, respectively) and an integrated proposition for the Z-scheme mechanism of photocatalytic reduction was proposed. This study offers a promising strategy to synthesize a Z-scheme T-GCN heterojunction with high photocatalytic performance for effective CO2 conversion. [ABSTRACT FROM AUTHOR]

Dyes and phenols are extensively used chemicals in petrochemicals, pharmaceuticals, textile, and paints industries. Due to high persistence, bioaccumulation, and toxicity, their removal from the environment is highly imperative by advanced techniques. Single metal oxide nanomaterials are generally associated with limitations of large bandgap (> 3eV) and charge recombination. Therefore, heterometallic oxides (HMOs) as CuFe2O4, CuMn2O4, and MnZn2O4 have been synthesized via green route by employing leaf extract of Azadirachta indica. XRD revealed the crystalline nature of HMOs nanospheres with particle size less than 100 nm. Subsequently, HMOs nanocatalysts were used as photocatalyst for removal of 3-amino phenols (3-AP) and eriochrome black T (EBT) from water under sunlight. Reaction parameters namely pollutant concentration (50–130 mgL-1), catalyst dose (20–100 mg), and pH (3–11) were optimized in order to get best results. Substantial degradation (80–95%) of pollutants (50 mgL-1) by HMOs (80 mg) was achieved at neutral pH under sunlight exposure. Highest removal by CuFe2O4 might be due to its high surface area (35.7 m2g-1), low band gap (2.4 eV), larger particle stability (Zeta potential: -22.0 mV), and lower photoluminescence intensity. Sharp declines in curves were visually confirmed by color change and indicated for first-order kinetics of degradation with initial Langmuir adsorption. Spectrophotometric analysis revealed that half-life (t1/2) of 3-AP (0.9-1.7 h) and EBT (0.6-0.8 h) were significantly reduced. Faster degradation of EBT than 3-AP was because of less electronegative N-atom at the diazo group. Scavenger analysis indicated the presence of active radicals in photo-catalytic degradation of 3-AP and EBT. All HMOs have shown high reusability (n=8) which ensures their stability, sustainability, and efficiency. Overall, green synthesized HMOs nanoparticles with prominent surface characteristics offer a viable alternative photocatalyst for industrial applications. [ABSTRACT FROM AUTHOR]

To provide safe water to the suffering community, a porous, and three-dimensional architecture (ZrLMA) is presented for the removal of fluoride from contaminated water. The structural moiety of ZrLMA contains zirconium dimethacrylate (ZrDMA) and lauryl methacrylate (LMA). Various experimental factors, i.e., the effect of adsorbent's dose, feed concentration of fluoride, pH, pHpzc, and interfering ions, are investigated to evaluate its performance. The binding energy between ZrLMA and F− ions is investigated by density functional theory and found to be − 271.3 kJ mol−1, which indicates a high level of interaction between ZrLMA and F− ions at atomic and molecular levels. Freundlich and Langmuir adsorption isotherm models are best fitted with the obtained experimental data with the maximum adsorption capacity for fluoride as 19.8 mg g−1 (pH 7.0 ± 0.2, initial F− concentration: 10 mg l−1 and dose: 0.5 g l−1). The kinetics and thermodynamic parameters (ΔG, ΔH, and ΔS) are also investigated. The uniqueness of the adsorbent is due to its covalently co-ordinated metallic-polymeric moiety, which provides stable architecture during the sorption process irrespective of the nature of the surrounding medium. Due to its absolute structural integrity, the adsorbent does not leach out any trace elements (Zr, F−) in the treated water during the adsorption process while maintaining original characterstics of the water from field water samples as well. An attempt has been made to recover fluoride at the end of the process. Hence, the approach is environment friendly for the remediation and recovery of pollutants due to its excellent reusability with effluent treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The preparation of carbons in virgin and Ti-modified forms under controlled conditions at low temperature from plantain pseudo-stem (Musa paradisiaca) was achieved. These prepared carbons were characterized for instrumental studies such as BET, FTIR, XRD, SEM with EDS and TGA to understand the chemistry and modification. The determination of IEP and pHZPC established the presence of positive surface sites on the virgin (VMPC) and Ti-modified (TiMPC) carbons to facilitate the sorption of fluoride. The fluoride removal efficiency as a function of time, pH, dose, initial fluoride concentration, temperature, and co-ion intervention was studied. The maximum fluoride removal of about 81.2 and 97.7% was achievable with VMPC and TiMPC, respectively, after 20 min at the pH of 2.04 and continued for the equilibrium of 60 min. Temperature was found to be influential both by way of initial increase followed by a decrease in the fluoride uptake of MPCs. Regeneration was very consistent up to 7 cycles with the residual fluoride concentration below the WHO guide line of 1.5 mg L−1. Highest intervention due to hydrogen carbonate ions was observed during the fluoride removal process. Kinetic (pseudo-first-order, pseudo-second-order, and intra-particle diffusion) and isotherm models (Langmuir, Freundlich, and DKR) were checked for their compliance with the present sorption system. These low temperature synthesized MPCs are found to be effective candidates in the process of fluoride abatement in water. [ABSTRACT FROM AUTHOR]

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 < 10 nm), and zinc (ZnHCC ~ 500 nm) were synthesized after employing Aegle marmelos. Subsequently, at neutral pH and sunlight irradiation, 15 mg of catalysts were able to degrade the maximum extent of phenols (1 × 10−4 M) in the order: 3-aminophenol (96% ZnHCC > 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. [ABSTRACT FROM AUTHOR]

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 (< 10 nm) were synthesized via green route using Sapindus mukorossi (raw ritha). At 50 mg L−1 of pesticide, 15 mg of MHCF photocatalyst, neutral pH and sunlight irradiation, selected agrochemicals were degraded to maximum extent (91-98%) by ZnHCF followed by CuHCF (85-91%), NiHCF (73-85%), and CoHCF (70-83%). This might be because of highest zeta potential and BET surface area of ZnHCF. The highest adsorption of CP (83-98%) followed by TH (76-95%) and TEB (70-91%) on acidic surface of catalysts might be related to access of free electrons in their structures. On treatment with MHCF photocatalyst, targets underwent mineralization along with formation of some minor and non-toxic by-products such as (Z) but-2-enal, 3-aminopropanoic acid, and pyridin-3-ol, identified after mass spectrometric analysis of reaction mixture. Based on them, degradation pathways have been proposed to reveal the potential of MHCF for solar photocatalytic removal of organic pollutants in environment. [ABSTRACT FROM AUTHOR]