Study of parameters affecting the degradation of rhodamine-B and methyl orange dyes by Annona muricata leaf extract synthesized nanoparticles as well as their recyclability

Facile synthesis and physicochemical characterization of κ-Carrageenan-silver-bentonite based nanocatalytic platform for efficient degradation of anionic azo dyes

Water pollution due to textile industry effluents is a global concern that warrants versatile research solutions for degrading them, and for a sustainable environment. In the present work, by using the imperative role of nanotechnology, a facile one-pot synthesis has been devised to generate κ-carrageenan capped silver nanocatalyst (CSNC), and was immobilized on 2D bentonite (BT) sheets to generate nanocatalytic platform (BTCSNC) for the degradation of anionic azo dyes. The nanocomposite(s) were physicochemically characterized using UV-Vis, DLS, TEM, FESEM, PXRD, ATR-FTIR, TGA, BET and XPS etc., to obtain insights into the nanocomposite composition, structure, stability, morphology and mechanism of interaction. The obtained CNSC are monodispersed, spherical with a size of 4 ± 2 nm, and were stabilized by the functional groups (-OH, COO‾, and SO3‾) of κ-Crg. The broadening of peak corresponding to basal plane (001) of BT montmorillonite in PXRD spectra established its exfoliation upon addition of CSNC. XPS and ATR-FTIR data evidenced the absence of covalent interactions between CSNC and BT. The catalytic efficiency of CSNC and BTCSNC composites were compared for the degradation of methyl orange (MO) and congo red (CR). The reaction followed a pseudo first order kinetics, and immobilization of CSNC on BT resulted in a 3-4 fold enhancement in degradation rates. The rates achieved for the degradation kinetics are: MO degradation within 14 s (Ka 9.86 ± 2.00 min-1), and CR degradation within 120 s (Ka of 1.24 ± 0.13 min-1). Further, a degradation mechanism has been proposed by analyzing the products identified through LC-MS. The reusability studies of the BTCSNC evidenced the complete activity of the nanocatalytic platform for six cycles, and gravitational separation method for catalyst recycling. In a nutshell, the current study provided an environmentally friendly, sizable, and sustainable nano catalytic platform" for the remediation of industrial wastewater contaminated with hazardous azo dyes".

Characterization, catalytic, and recyclability studies of nano-sized spherical palladium particles synthesized using aqueous poly-extract (turmeric, neem, and tulasi)

Green synthesis of noble metal nanoparticles (NPs) has gained immense significance compared to other metal ions owing to their unique properties. Among them, palladium 'Pd' has been in the spotlight for its stable and superior catalytic activity. This work focuses on the synthesis of Pd NPs using the combined aqueous extract (poly-extract) of turmeric (rhizome), neem (leaves), and tulasi (leaves). The bio-synthesized Pd NPs were characterized to study its physicochemical and morphological features using several analytical techniques. Role of Pd NPs as nano-catalysts in the degradation of dyes (1 mg/2 mL stock solution) was evaluated in the presence of a strong reducing agent (sodium borohydride; SBH). In the presence of Pd NPs and SBH, maximum reduction of methylene blue (MB), methyl orange (MO), and rhodamine-B (Rh-B) dyes was observed under 20nullmin (96.55 ± 2.11%), 36nullmin (96.96 ± 2.24%), and 27nullmin (98.12 ± 1.33%), with degradation rate of 0.1789 ± 0.0273 min^-1, 0.0926 ± 0.0102 min^-1, and 0.1557 ± 0.0200 min^-1, respectively. In combination of dyes (MB + MO + Rh-B), maximum degradation was observed under 50nullmin (95.49 ± 2.56%) with degradation rate of 0.0694 ± 0.0087 min^-1. It was observed that degradation was following pseudo-first order reaction kinetics. Furthermore, Pd NPs showed good recyclability up to cycle 5 (72.88 ± 2.32%), cycle 9 (69.11 ± 2.19%) and cycle 6 (66.21 ± 2.72%) for MB, MO and Rh-B dyes, respectively. Whereas, up to cycle 4 (74.67 ± 0.66%) during combination of dyes. As Pd NPs showed good recyclability, they can be used for several cycles thus influencing the overall economics of the process.

Effect of size on physicochemical, antibacterial, and catalytic properties of Neolamarckia cadamba (burflower-tree) synthesized silver/silver chloride nanoparticles

Aqueous extract of Neolamarchia cadamba leaves were used in the synthesis of silver/silver chloride nanoparticles (Ag/AgCl NPs). Further they were separated based on their using step-wise centrifugation approach at 09,000, 12,000, and 15,000 rpm. Thus obtained NPs were characterized for their physicochemical features. NPs showed maximum absorbance at 455 nm, 415 nm, and 402 nm. All the NPs were found to be crystalline in nature with average crystallite size (nm) of 58.31, 23.43, and 09.56. Particle size distribution (nm) of NPs was observed to 435.43, 276.75, and 105.49, Surface charge (-mV) of NPs was observed to be 14.59, 23.90, and 32.17. Ag/AgCl NPs-rpm@15,000 showed antibacterial activity against Escherichia coli, coagulase-negative Staphylococci, and Staphylococcus aureus with zone of inhibition (mm) of 16.65, 13.69, and 14.02 at 50 µg per well, respectively. Ag/AgCl NPs-rpm@15,000 showed excellent catalytic activity in degradation of methyl red, methylene blue, rhodamine-B, and methyl orange dyes in the presence of sodium borohydride under 4, 6, 5, and 4 min with pseudo-first order rate constant (min^-1) of 0.981 (96.4%), 0.666 (97.1%), 0.905 (98.1%), and 1.032 (96.6%), respectively. Furthermore, Ag/AgCl NPs-rpm@15,000 showed good catalytic efficiency even under different dye combinations. Total combination was degraded under 18 min.

Soursop (Annona muricata) Properties and Perspectives for Integral Valorization

The increased international interest in the properties of soursop (Annona muricata) alerts us to the sustainability of productive chain by-products, which are rich in phytochemicals and other properties justifying their industrial application in addition to reducing the environmental impact and generating income. Chemical characteristics of soursop by-products are widely known in the scientific community; this fruit has several therapeutic effects, especially its leaves, enabling it to be used by the pharmaceutical industry. Damaged and non-standard fruits (due to falling and crushing) (30-50%), seeds (3-8.5%), peels (7-20%), and leaves, although they constitute discarded waste, can be considered as by-products. There are other less cited parts of the plant that also have phytochemical components, such as the columella and the epidermis of the stem and root. Tropical countries are examples of producers where soursop is marketed as fresh fruit or frozen pulp, and the valorization of all parts of the fruit could represent important environmental and economic perspectives. Based on the chemical composition of the fruit as well as its by-products and leaves, this work discusses proposals for the valorization of these materials. Soursop powder, bioactive compounds, oil, biochar, biodiesel, bio-oil, and other products based on published studies are presented in this work, offering new ideas for opportunities for the regions and consumers that produce soursop.

Photocatalytic Performance Improvement by Doping Ag on ZnO/MWCNTs Nanocomposite Prepared with Pulsed Laser Ablation Method Based Photocatalysts Degrading Rhodamine B Organic Pollutant Dye

ZnO/MWCNTs nanocomposite has significant potential in photocatalytic and environmental treatment. Unfortunately, its photocatalytic efficacy is not high enough due to its poor light absorbance and quick recombination of photo-generated carriers, which might be improved by incorporation with noble metal nanoparticles. Herein, Ag-doped ZnO/MWCNTs nanocomposite was prepared using a pulsed laser ablation approach in the liquid media and examined as a degradable catalyst for Rhodamine B. (RhB). Different techniques were used to confirm the formation of the nanostructured materials (ZnO and Ag) and the complete interaction between them and MWCNTs. X-ray diffraction pattern revealed the hexagonal wurtzite crystal structure of ZnO and Ag. Additionally, UV-visible absorption spectrum was used to study the change throughout the shift in the transition energies, which affected the photocatalytic degradation. Furthermore, the morphological investigation by a scanning electron microscope showed the successful embedding and decoration of ZnO and Ag on the outer surface of CNTs. Moreover, the oxidation state of the formed final nanocomposite was investigated via an X-ray photoelectron spectrometer. After that, the photocatalytic degradations of RhB were tested using the prepared catalysts. The results showed that utilizing Ag significantly impacted the photo degradation of RhB by lowering the charge carrier recombination, leading to 95% photocatalytic degradation after 12 min. The enhanced photocatalytic performance of the produced nanocomposite was attributed to the role of the Ag dopant in generating more active oxygen species. Moreover, the impacts of the catalyst amount, pH level, and contact time were discussed.

Biogenic synthesis of novel platinum-palladium bimetallic nanoparticles from aqueous Annona muricata leaf extract for catalytic activity

This work reports the fast and effective bio-fabrication of novel platinum-palladium bimetallic nanoparticles (Pt-Pd BNPs) along with their counterparts Pt and Pd monometallic NPs (MNPs) through aqueous Annona muricata leaf extract. The bio-fabrication of the NPs was achieved within 2 h at 100 °C and pH 7 which was established by the occurrence of dark brown color for Pt MNPs and black color for Pd MNPs and Pt-Pd BNPs. NPs were evaluated for their catalytic activity in the reduction of methyl orange (MO), rhodamine-B (rh-B), and methylene blue (MB) textile dyes in presence of sodium borohydride as a reducing agent. Pt-Pd (1:3) BNPs showed higher MO dye degradation (96.84 ± 2.05% in 50 min) followed by Pd MNPs (97.07 ± 1.46% in 60 min), Pt-Pd (3:1) BNPs (97.34 ± 1.17% in 70 min) and Pt-Pd (1:1) BNPs (98.12 ± 1.04% in 80 min). Pd MNPs showed significant catalytic activity in the reduction of rh-B dye by 97.27 ± 1.14% in 12 min followed by Pt-Pd (3:1) BNPs (96.76 ± 2.17% in 18 min), Pt-Pd (1:3) BNPs (96.53 ± 1.97% in 33 min) and Pt-Pd (1:1) BNPs (97.11 ± 2.09% in 39 min). Pt-Pd (1:3) BNPs also showed higher MB dye degradation (96.95 ± 1.57% in 40 min) followed by Pd MNPs (96.22 ± 2.36% in 55 min), Pt-Pd (3:1) BNPs (97.29 ± 1.22% in 75 min) and Pt-Pd (1:1) BNPs (96.45 ± 2.19% in 105 min). However, Pt MNPs showed no catalytic activity. Standard disc diffusion method was used to evaluate the NPs toxicity towards Escherichia coli and Staphylococcus aureus, which showed no inhibitory zones. NPs showed less toxicity compared to potassium dichromate (control) against Artemia nauplii. Among the NPs studied, Pt-Pd (1:1) BNPs showed less toxicity with 100% mortality only at 100 µg/mL concentration followed by Pt MNPs (≥ 80 µg/mL), Pt-Pd (1:3) BNPs (≥ 60 µg/mL), Pt-Pd (3:1) BNPs (≥ 60 µg/mL) and Pd MNPs (≥ 40 µg/mL) after 72 h exposure. These evaluations support the application of bio-fabricated Pt-Pd BNPs as nano-catalysts in textile dyes degradation.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02935-0.